Lv Motors Protection

...................................................................................

Cahier technique no. 211

The protection of LV motors

G. BaurandV. Moliton

Collection Technique

Building a New Electric World

"Cahiers Techniques" is a collection of documents intended for engineers and technicians, people in the industry who are looking for more in-depth information in order to complement that given in product catalogues.

Furthermore, these "Cahiers Techniques" are often considered as helpful "tools" for training courses.They provide knowledge on new technical and technological developments in the electrotechnical field and electronics. They also provide better understanding of various phenomena observed in electrical installations, systems and equipments. Each "Cahier Technique" provides an in-depth study of a precise subject in the fields of electrical networks, protection devices, monitoring and control and industrial automation systems.

This constantly updated collection can be downloaded from:http://www.technical-publications.schneider-electric.com

Please contact your Schneider Electric representative if you want either a"Cahier Technique" or the list of available titles.

The "Cahiers Techniques" collection is part of the Schneider Electric’s "Collection technique".

Foreword

The author disclaims all responsibility subsequent to incorrect use of information or diagrams reproduced in this document, and cannot be held responsible for any errors or oversights, or for the consequences of using information and diagrams contained in this document.Reproduction of all or part of a "Cahier Technique" is authorised with the compulsory mention:"Extracted from Schneider Electric "Cahier Technique" no. ..." (please specify).

no. 211The protection of LV motors

ECT 211 first issue, January 2007

Vivien MOLITON

He graduated from the Ecole Nationale Supérieure d’Ingénieurs of Limoges (ENSIL) in 2002, specializing in “Mechatronics”. In the same year, he set up the Mechatronics R&D Laboratory at Schneider Electric. In the Measurement and Protection department, he participated in the development of a new range of motor circuit-breakers and the Tesys U starter-controller under the Telemecanique brand.

Gilles BAURAND

Graduate in Electromechanical Engineering, ENSICAEN (Ecole Nationale Supérieure d’Ingénieurs de Caen) in 1977.He joined Telemecanique in 1978 as a technical manager for the development of control and electronic protection relays, holding this post until 1985.He managed the laboratory of the Motor Protection Contactor and Relay Department from 1986 to 1991, and was then responsible for the advance development of this department from 1992 to 2004.He has been responsible for the advance development of the PPC (Power Protection & Control) field at Schneider Electric since early in 2005.

Cahier Technique Schneider Electric no. 211 / p.2

Cahier Technique Schneider Electric no. 211 / p.

The protection of LV motors

Contents 1 Introduction p. 4

2 Brief guide to electric motors 2.1 The various types of motor p. 5

2.2 The applications of low-voltage motors p. 6

3 Causes of faults and their consequences .1 Internal faults in the motor: p. 7 Damage to the stator or rotor winding

.2 Faults external to the motor: p. 8 Phenomena related to the motor power supply

. Faults external to the motor: p. 11 Phenomena related to the use of the motor

.4 Summary p. 12

4 Protection functions 4.1 Short-circuit protection p. 13

4.2 Overload protection p. 14

4. Selection table for protection relays p. 19

4.4 “Motor circuit-breakers” (thermal-magnetic circuit-breakers) p. 20

5 Motor starters 5.1 Background p. 21

5.2 The basic functions of motor starters p. 21

5. The special case of electronic starters and variable speed drives p. 2

5.4 A complementary function: communication p. 2

5.5 Motor starters and coordination p. 24

5.6 Control and protective switching devices (CPS) p. 26

5.7 Discrimination p. 27

5.8 Example p. 27

6 Conclusion p. 29

Appendix 1: Modular system of the Tesys U starter-controller p. 30

Appendix 2: The main starting modes p. 31

Appendix 3 : Bibliography p. 35

All electric motors must be designed to meet the requirements of specified operating conditions, and cannot operate outside these without the risk of immediate or long-term damage to the motor itself and/or to its environment.

In order to eliminate this risk, or at least reduce it considerably, machine designers and installers provide protection devices selected from manufacturers’ catalogs.

But which of all these existing devices should be provided, given that they must “interact” (operate) with isolation and control equipment? How do we choose? And, above all, how can we be sure that the chosen equipment will be fully compatible?

This “Cahier Technique” is designed to answer these questions, by describing all the factors to be taken into account and then detailing the various solutions offered by manufacturers, including complete units known as “motor starters”.


1 Introduction

All electric motors have operating limits. Exceeding these limits will result, sooner or later, in the destruction of the motor and also of the machines driven by it, causing immediate stoppages and lost production.

This form of load, which converts electrical energy to mechanical energy, can be the site of mishaps due to electrical or mechanical factors.

Electricalovervoltage, voltage drop, unbalance, or phase

loss, causing variations in the current drawn;short circuits where the current can reach

destructive levels for the load;

MechanicalRotor stall, momentary or prolonged overload leading to an increase in the current drawn by the motor and consequently a dangerous heating of its windings.

The cost of these mishaps can be high. It includes lost production, the loss of raw materials, the repair of the production equipment, the loss of production quality, and delays in delivery. The economic imperative of increasing competitiveness for businesses implies the reduction of costs related to the loss of service continuity and low quality.

These mishaps can also have dramatic consequences for the safety of personnel coming into direct or indirect contact with the motor.

bv

v

b

To avoid these mishaps, or at least limit their consequences and prevent them from causing damage to equipment and disturbances in the line supply, protective systems must be used. They can isolate equipment to be protected from the line, by tripping breaking devices in response to the detection and measurement of variations in electrical values (voltage, current, etc.).

Each motor starter must therefore incorporate:short circuit protection, to detect and cut off, as

quickly as possible, abnormal currents which are generally more than 10 times the nominal current (In)

overvoltage protection, to detect current increases up to approximately 10 In and cut off the starter before the heating of the motor and the conductors damages the insulation

This protection is provided by specific devices such as fuses, circuit-breakers, overload relays or combination devices offering several types of protection.

Note: Protection against “ground faults”, which includes protection of personnel and fire-proofing, is not covered in this document, since it is usually provided as part of the power distribution system for a piece of equipment, a workshop or a whole building.

b

b


2 Brief guide to electric motors

2.1 The various types of motor

There are three main categories of electric motor:

asynchronous motorssynchronous motorsDC motors

Each of these consists of a fixed part, the stator or field coil, and a moving part, the rotor or armature.

Asynchronous motors

The stators of these motors have windings supplied with alternating current and positioned so as to create a rotating magnetic field (rotating flux) at the synchronous speed W. For a three-phase power supply, the most common configuration has three windings (which may include several coils) connected in a delta or star arrangement. The rotors usually consist of conductive bars short-circuited at their ends, as in “squirrel cage” motors (for low power applications), or, less commonly, windings, as in asynchronous motors with wound rotors (for high power applications). The rotating flux generated by the stator induces a current in the rotor and causes it to rotate (see Laplace’s law). Its speed W’ is less than the synchronous speed W of the rotating flux; this difference is called the “slip” (s), corresponding to the relative loss of speed:

,

demonstrating the concept of asynchronism.

Asynchronous motors are suitable for low and medium power applications, especially those in which the starting torque has to increase with the speed. These are the most widely used motors, because of their low cost, robustness and ease of installation and maintenance. Under local control, they have the disadvantage of having high starting currents, up to 8 times the nominal current (see Fig. 1 ).

Synchronous motors

Like asynchronous motors, these have a stator consisting of windings supplied with alternating current. The characteristic feature of these motors is the synchronization between the rotation speed of the rotor and that of the rotating field created by the stator. This feature is present because the rotor of a synchronous motor consists of permanent magnets or a winding supplied with direct current, establishing a fixed magnetic field. This characteristic makes their construction more complex and is reflected in their higher cost.

bbb

s =Ω−Ω'

Ωs =

Ω−Ω'Ω

Synchronous motors are mainly used for very high power applications (> MW), requiring a constant speed regardless of the load, but they can be difficult to start, and for this reason they are often combined with variable speed drives.

DC motorsIn these motors, the stator and the rotor both consists of windings through which direct current is passed. The current is taken to the armature by means of a commutator with brushes. The stator creates a fixed magnetic field which makes the conductors in the rotor move, according to Laplace’s law.

Direct current motors are mainly used for applications requiring precise, rapid speed control, and can withstand high overloads. They have the disadvantage of having commutators whose brushes and rings require regular maintenance. Precautions must also be taken when starting and stopping these motors, and it is especially important to avoid cutting off the excitation if the armature is live: stopping in this way will cause the rotor to race.

For further information on the different types of motors and their operation, see Schneider Electric “Cahier Technique” no. 207.

Fig. 1 : Graph of I = f(t) for an asynchronous motor.

Starting peak (magnetizing peak)

Ip = 10 to 13 În: Magnetizing currentId = 4 to 8 In: Starting currentIn: Nominal rms current

Motor startingphase

Normal motor operation

20 to 30 ms 1 to 10 s t

Ip

Id

In


2.2 The applications of low-voltage motors

There are two types of low-voltage (LV) motors:

single-phase

three-phase

They are supplied at voltages ranging from 220 to 90 V. Most low-voltage electric motors have a power of less than 100 kW. As the power increases, the current becomes greater (P = UI.cosj), and the components involved (motors, equipment, wiring and protection) must be given suitable dimensions.

For economic reasons, medium-voltage (MV) motors are used above the 100 kW level (see Fig. 2 ).

b

b

Fig. 2 : Applications of electric motors according to their power and supply voltage.

13.8

2.20

0.69

0.22

100 1500 P (kW)

Voltage (kV)

LV

MV


3 Causes of faults and their consequences

In an installation including electric motors, we can distinguish two types of fault: faults originating internally in the motor, and faults originating externally.

Internal faults: short-circuit between phase and groundshort-circuit between phasesshort-circuit between coilsoverheating of the windingsbreaking of a bar in squirrel cage motorsproblems relating to the bearingsetc.

External faults:The origins of these faults lie outside the electric motor, but their consequences can cause damage to the motor.

bvvvvvvv

b

These malfunctions can arise from:the power source:

- power cuts- phase reversal or unbalance- brownout- overvoltage- etc.

the operating mode of the motor:- overload operation- the number of starts and the starting operations- the load inertia- etc.

the installation of the motor:- misalignment- unbalance- excessive stresses on the shaft- etc.

v

v

v

3.1 Internal faults in the motor: Damage to the stator or rotor winding

The stator winding of an electric motor consists of copper conductors insulated with varnish. Breaks in this insulation can cause a permanent short circuit between a phase and ground, between two or even three phases, or between the coils of a single phase (see Fig. 3 ).

It can be caused by phenomena which may be electrical (surface discharge, overvoltage), thermal (overheating) or even mechanical (vibration,

Fig. 3 : The windings of motors are the parts which are most vulnerable to electrical faults and operating mishaps.

electrodynamic stresses on the conductors).Insulation faults can also occur in the rotor winding, with the same result: the motor becomes unserviceable.

The most common cause of damage to the windings of a motor is an excessive rise in their temperature. This rise is often caused by an overload which leads to an increase in the current flowing in these windings.

Statorwindings


The graph in Figure 4, supplied by most electric motor manufacturers, shows the change in insulation resistance as a function of temperature: as the temperature rises, the insulation resistance decreases. The service life of the windings, and therefore of the motor, is greatly reduced as a result.

The graph in Figure 5 shows how a % increase in the current, equivalent to a temperature rise of approximately +10°, cuts the service life of the windings by half. Overload protection is therefore essential to prevent overheating and reduce the risks of internal damage to the motor due to the breakdown of insulation in the windings.

100

10

1

0.10 80604020

°C

Insulationresistance (MΩ)

100

75

50

25

0InT

1.05xInT+10

1.1xInT+20

1.15xInT+30

Current°C

Service life (%)

Fig. 4 : Change in the insulation resistance of motor windings as a function of their temperature

Fig. 5 : Service life of motors as a function of their operating temperature or current consumption

3.2 Faults external to the motor: Phenomena related to the motor power supply

OvervoltageAny voltage applied to equipment where the peak value exceeds the limits of a range defined by a standard or a specification is an overvoltage (see Schneider Electric “Cahiers Techniques” nos. 11 and 179).

Temporary or permanent overvoltages (see Fig. 6 ) can have different origins, namely:

atmospheric (lightning strikes)electrostatic dischargesoperation of equipment connected to the same

networketc.

Their principal characteristics are shown in the table in Figure 7 hereafter.

These disturbances, which are superimposed on the line voltage, can act in two ways:

in common mode, between the active conductors and the ground

in differential mode, between the different active conductors

bbb

b

b

b

t

V

Fig. 6 : Example of overvoltage.

In most cases, the effect of an overvoltage is a dielectric breakdown in the motor windings, which destroys the motor.


Phase unbalanceA three-phase system is unbalanced when the three voltages are not equal in amplitude and/or are not at angles of 120° to each other.

The unbalance (see Fig. 8 ) can be caused by the disconnection of a phase (asymmetry fault), by the presence of single-phase loads in the immediate environment of the motor, or by the power source itself.

Fig. 7 : Characteristics of different types of overvoltage.

Type of overvoltage Duration Edge steepness - frequency

Damping

Atmospheric Very short (1 to 10 µs) Very high (1000 kV/µs) High

Electrostatic discharge Very short (ns) High (10 MHz) Very high

Operational Short (1 ms) Average (1 to 200 kHz) Average

At ????? frequency Long (> 1 s) Line supply frequency Zero

which generates high rotor currents, causing a very considerable overheating of the rotor and leading to the overheating of the motor (see Fig. 9 ).

t

VVmax

Vmin

Fig. 8 : Voltage readings from an unbalanced three-phase system.

The following equation can be used to approach the calculation of the unbalance:

U = 100 MAXVmax − Vmean

Vmean,Vmean− Vmin

Vmean

where:U is the unbalance (%)Vmax is the highest voltageVmin is the lowest voltage

Vmean =V1+ V2 + V3( )

3The consequences of an unbalance of the voltages applied to a motor are a decrease in the useful torque and an increase in losses; the unbalances give rise to an inverse component

Amount of unbalance (%)

0 2 3,

Staotr current (A) In 1.01 In 1.0 In 1.07 In

Increased losses (%)

0 12. 2

Heating (%) 100 10 11 128

Fig. 9 : Effect of voltage unbalance on the operating characteristics of a motor.

IEC standard 003-2 provides a derating rule based on the voltage unbalance (see Fig. 10 ) which is recommended for use when this phenomenon is known or predictable in the power line supplying the motor. This derating factor can be used either to increase the motor dimensions to allow for the unbalance, or to decrease the operating current of a motor with respect to its nominal current.

1

0.9

0.8

0.70 4 5321

Voltageunbalance(%)

Derating factor

Fig. 10 : Derating of a motor as a function of the voltage unbalance in its power supply.


Brownouts and power cutsA brownout (see Fig. 11 ) is an abrupt voltage drop at one point of an electrical power network, to a value which is conventionally taken to be from 90% to 1% of the nominal voltage of the LV network (IEC 1000-2-1). Power cuts are a special case of brownout where the drop exceeds 99% (IEC). They are characterized by a single parameter: their duration. Short power cuts have a duration of less than 1 minute (IEC), while long power cuts have a longer duration. The term “micro-cut” is used for durations of about one millisecond.

If precautions are not taken, the fast reconnection (~ 10 ms) of a decelerating asynchronous motor runs the risk of reclosing in phase opposition between the source and the residual voltage maintained by the asynchronous motor. In this case, the first current peak can be as much as three times the starting current (1 to 20 In) (see Schneider Electric “Cahier Technique” no. 11).

These overcurrents and the consequent voltage drops have a number of effects on the motor:

additional heating and electrodynamic forces in the coils which may cause breaks in the insulation

shocks with abnormal mechanical stresses on the couplings, leading to premature wear or even breakage

They can also affect other equipment such as contactors (causing wear on the contacts or even welding them together), or cause the tripping of the master protection devices of the installation and thus stop a production line or a workshop.

The consequences for a synchronous motorThe consequences are practically the same as those for asynchronous motors. However, synchronous motors can withstand larger brownouts (about 0% greater) without stalling, because their inertia is generally greater and the voltage has less effect on the torque. If stalling occurs, the motor stops, and the whole starting procedure, which may be complex, has to be recommenced.

Effects on variable speed machinesThe problems posed by brownouts affecting variable speed drives are as follows:

the impossibility of supplying sufficient voltage to the motor (loss of torque, deceleration)

malfunction of the control circuits supplied directly from the line

overcurrent when the voltage is restored (recharging of the filter capacitors of the variable speed drives)

overcurrent and current unbalance in the line if a brownout occurs in one phase only

Variable speed drives generally fail if a voltage drop of more than 1% occurs.

Presence of harmonicsAny periodic function (of frequency f) can be broken down into a sum of sine waves with a frequency of h x f (where h is an integer)

y(t) = Y0 + Yhsin(h=1

∞

∑ hωt + ϕh)

whereY0 is the continuous componenth is the order of the harmonicw is the pulsation (2pf)Yh is the amplitude of the harmonic of order hY1 is the fundamental component

v

v

b

b

v

v

v

v

-1

1

0.

V

-0.

0t

Fig. 11 : Example of a brownout and a brief power cut.

These voltage variations may be due either to a random phenomenon outside the application (a fault in the mains network or an accidental short circuit) or a phenomenon caused by the installation itself (connection of high loads such as motors, transformers, etc.). These variations can have drastic effects on the motor.

The consequences for an asynchronous motorWhen a brownout occurs, the torque of an asynchronous motor (proportional to the square of voltage) decreases abruptly and causes deceleration. This deceleration is a function of the amplitude and duration of the brownout, the inertia of the rotating frames and the torque-speed characteristic of the driven load. If the torque developed by the motor becomes less than the resistive torque, the motor stops (stalls). After a power cut, the return of the power generates a demand for reacceleration current which is similar to the starting current and with a duration dependent on the duration of the power cut.

When the installation has numerous motors, their simultaneous reacceleration can cause a voltage drop in the upstream impedances in the network. The duration of the brownout is then prolonged and can make reacceleration difficult (requiring long restarts with overheading) or even impossible (where the motor torque is less than the resistive torque).

b


The harmonic distortion rate (or THD, “Total Harmonic Distortion”) provides a measure of the deformation of the signal:

THD(%)= 100xYh

Y1

2

h=2

∞

∑

The harmonic currents and voltages are created by non-linear loads connected to the line supply. Harmonic distortion (see Fig. 12 ) is a form of pollution of the line supply which can give rise to problems at a rate of more than %.

The electronic power devices (variable speed drives, inverters, etc.) are the principal sources which inject harmonics into the line. Since the motor is not perfect, it can also create 3rd order harmonics; in a delta connection, flux rebalancing can then occur, generating a current in its windings.

The presence of harmonics causes an increase in eddy current losses, leading to additional heating. They can also generate pulsating torques (causing vibration and mechanical fatigue) and noise nuisance, and limit the use of motors at full load (see Schneider Electric “Cahier Technique” no. 199).

t

V

h1h5h total (h1+h5)

Fig. 12 : Sinusoidal voltage reading, including 5th order harmonics.

3.3 Faults external to the motor: Phenomena related to the use of the motor

Motor starting: excessively long and/or frequent startingThe starting phase of a motor is the period required for it to reach its nominal rotation speed. The starting time (tS) depends on the resistive torque (Tr) and the motor torque (Tm). An increase in the resistive torque, due to the load to be driven, together with a decrease in the motor torque, due to a line voltage drop (20 to 30% of Un), causes an increase in the motor starting time as follows:

tS(s) =π30

JN

Tm − TrwhereJ is the global moment of inertia of the moving frames N(r.p.s.) is the rotation speed of the rotor.Because of its intrinsic characteristics, each motor can only withstand a limited number of starts, generally specified by its manufacturer (as the number of starts per hour). Similarly, each motor has a maximum starting time which is a function of its starting current (see Fig. 13 ).

t (s)

20

15

109876

5

4

3

3 4 5 7 10 15

IS

IN

Fig. 13 : Permissible start times of motors as a function of the ratio between starting current and nominal current.


Rotor lockingThe locking of a motor due to mechanical factors creates an overcurrent approximately equal to the starting current. However, the heating which it causes is much greater, since the losses in the rotor are kept at their maximum level throughout the locking and ventilation is prevented if it is dependent on the rotation of the rotor. The rotor temperatures can become very high (30 °C).

Fig. 14 : Summary of the faults which can affect a motor, with their causes, effects and consequences.

3.4. Summary

This summary, shown in table form in Figure 14, shows the possible causes, the probable effects and the established consequences of each type of fault.

In all cases, two forms of protection are always required for motors:

short-circuit protectionoverload (overheating) protection

bb

Fault Cause Effects Consequences for the motor

Short circuit b Contact between more than one phase, between one phase and neutral, or between several coils of a single phase

b Current peakb Electrodynamic forces on the conductors

Destruction of the windings

Overvoltage b Lightningb Electrostatic dischargeb Operation

b Dielectric breakdown in the windings

Destruction of the windings due to loss of insulation

Voltage unbalance

b Disconnection of a phaseb Single phase load upstream of the motor

b Decreased useful torqueb Increased losses

Overheating(1)

Brownouts b Instability of the line supply voltageb Connection of large loads


Overheating(1)

Harmonics b Pollution of the line supply by variable speed drives, inverters, etc.


Overheating(1)

Excessive starting time

b Excessively high resistive torqueb Brownouts

Increased starting time Overheating(1)

Locking b Mechanical problem Overcurrent Overheating(1)

Overload b Increased resistive torqueb Brownouts

Increase in current drawn Overheating(1)

(1) Followed by short-circuiting and destruction of the windings after a period which depends on the importance and/or frequency of the fault.

Overload (deceleration or overspeed)The overload of a motor is caused by an increase in the resistive torque or by a drop in the supply line voltage (> 10% Un). The increase in the current drawn by the motor causes heating which reduces its service life and can be fatal in the longer or shorter term.


4 Protection functions

4.1 Short-circuit protection

BackgroundA short circuit is a direct connection between two points having different electrical potentials; the types of short circuit are:

alternating current: A connection between phases, between a phase and neutral, between a phase and a conductive frame, or between the coils of a single phase

direct current: A connection between the two polarities or between a conductive frame and the polarity insulated from it

There are various possible causes: Deterioration of the insulating varnish on the conductors, loosening, breakage or stripping of wires or cables, presence of metallic foreign bodies, conductive deposits (dust, moisture, etc.), penetration of water or other conductive liquids, deterioration of the load, and errors in wiring at start-up or during servicing.

A short circuit is indicated by an abrupt increase in the current, which may become several hundred times greater than the operating current in just a few milliseconds. A short circuit can have devastating effects and cause major damage to equipment. It is characterized by two phenomena:

A thermal phenomenon which corresponds to the amount of energy released in the electrical circuit through which the short-circuit current I flows for a time t, according to the formula I2t, expressed in A2s. This thermal effect can cause:

melting of the contacts of the contactordestruction of the thermal elements of a

bimetallic relay, in the case of type I coordination (see the “Coordination” section)

generation of electric arcsburning of insulating materialsfire in the equipment.

An electrodynamic phenomenon between the conductors gives rise to strong mechanical forces, caused by the flow of current, with the following effects:

deformation of the conductors forming the motor windings

breakage of the insulating supports of the conductors

repulsion of the contacts (inside contactors) which may lead to their melting and welding

b

b

b

vv

vvv

b

v

v

v

Such effects are dangerous to both property and personnel. It is therefore essential to use short-circuit protection devices designed to detect faults, and to break the circuit very quickly, if possible before the current reaches its maximum level. Two protection devices are commonly used for this purpose:

fuses (circuit breakers) which break the circuit by blowing, and must be replaced subsequently

magnetic trip circuit-breakers, often simply called “magnetic circuit-breakers” which automatically break the circuit when their poles are opened, and which only require a resetting operation to bring them back into service.

Short-circuit protection can also be incorporated into multi-function devices such as motor circuit-breakers and contactor/circuit-breakers.

Definitions and characteristicsThe main characteristics of short-circuit protection devices are:

the breaking capacity: i.e. the highest presumed short-circuit current which a protection device can interrupt at a given voltage

the making capacity: i.e. the highest current which the protective device can pass at its nominal voltage in specified conditions. The making capacity is equal to k times the breaking capacity, according to the table in Figure 15 .

FusesFuses provide protection for one phase at a time (single-phase protection), with a high breaking capacity in a small volume. They limit the level of I2t and the electrodynamic stresses (Ipeak).

v

v

b

b

Fig. 15 : Breaking and making capacity as specified by IEC Standard 60947-2 for circuit-breakers.

Breaking capacity (BC)

Cos j Making capacity (MC)

. kA < BC < kA 0.7 1. BC

kA < BC < 10 kA 0. 1.7 BC

10 kA < BC < 20 kA 0.3 2 BC

20 kA < BC < 0 kA 0.2 2.1 BC

0 kA < BC 0.2 2.2 BC


They are fitted as follows:either to special supports called fuseholdersor in isolators, where they replace sockets or

terminal strips (see Fig. 16 ).

bb

currents, circuit-breakers operate more quickly than fuses.

This protection conforms to IEC Standard 097-2.

Effective interruption of a short-circuit current requires three essential functions:

very fast detection of the fault currentvery fast separation of the contactsinterruption of the short-circuit current

Most magnetic circuit-breakers for motor protection are current limiters, and therefore also contribute to the coordination (see Fig. 18 ). Their particularly short breaking time enables them to interrupt the short-circuit current before it reaches its maximum amplitude. The thermal and electrodynamic effects are therefore also limited, thus providing better protection of cables and equipment.

bbbL1 L3L2

a b

Fig. 16 : Fused 32 A and 125 A isolators (Telemecanique LS1-D32 [a] and GS1-K4 [b]).

Note that fuse cartridges with strikers can be combined with an all-pole breaking device (often the motor control contactor) to prevent single-phase operation after they have blown.Type aM fuses are used for motor protection. They have the characteristic of allowing excess magnetizing currents to pass when motors are switched on. Therefore, they are unsuitable for overload protection (unlike gG fuses). For this reason, an overload relay has to be added to the motor supply circuit.As a general rule, their rating must be immediately above the full load current of the motor to be protected.

Magnetic circuit-breakersSubject to their breaking capacity, these circuit-breakers can protect installations against short circuits by means of their magnetic trip releases (one per phase) (see Fig. 17 ). Magnetic circuit-breakers are intrinsically all-pole breaking devices: the tripping of a single magnetic trip release causes the simultaneous opening of all the poles. For low short-circuit

I > I > I >

L1 L3L2

Fig. 17 : Telemecanique GV2-L magnetic circuit-breaker and its graphic symbol.

IId

t

Non-limitingLimiter

Limiting zone

Fig. 18 : Tripping curves of magnetic circuit-breakers.

4.2 Overload protection

Background

Overloading is the most common motor fault. It causes an increase in the current drawn by the motor, as well as thermal effects. The insulation class determines the normal heating of a motor at an ambient temperature of 0 °C. If the maximum operating temperature is exceeded, this reduces the service life as a result of the premature ageing of the insulation.

However, it should be noted that an overload leading to heating above the normal level does not have immediate negative consequences if it is limited in time and infrequent. Thus it does not necessarily mean that the motor must be

stopped, but normal operating conditions must be resumed as soon as possible.The importance of proper overload protection is obvious, because:

it protects the service life of motors by preventing them from operating in abnormal heating conditions

it ensures continuity of operation, by:avoiding untimely stoppage of motorsenabling restarting to be carried out in the best

safety conditions for personnel and equipment, after tripping.The actual operating conditions (ambient temperature, altitude of use and standard service) must be known in order to determine the

b

bvv


operating levels of the motor (in terms of power and current) and in order to choose effective overload protection (see Fig. 19 ). These operating levels are supplied by the motor manufacturer.

According to the desired level of protection, overload protection can be provided in the form of relays of the following types:

overload, thermal (bimetallic) or electronic, which will at least protect the motors in the following two cases:

overload, by controlling the current drawn in each phase

phase unbalance or failure, by means of their differential devices

PTC (Positive Temperature Coefficient) thermistor probe

excess torquemulti-function

Reminder: A protection relay does not have a circuit-breaking function. It is designed to open a circuit-breaking device, generally a contactor, which must have the requisite breaking capacity for the fault current to be interrupted.

b

v

v

b

bb

Fig. 19 : Derating factors of motors according to their operating conditions.

For this purpose, a protection relay has a fault contact (NC) which is to be connected in series with the power supply to the contactor coil.

Overload relays (thermal or electronic)

BackgroundThese relays protect motors against overloads, but they must allow the temporary overload caused by starting, and must not trip unless the starting time is abnormally long.

Depending on the application, the motor starting time can vary from a few seconds (for no-load starting, low resistive torque, etc.) to several tens of seconds (for a high resistive torque, high inertia of the driven load, etc.). It is therefore necessary to fit relays appropriate to the starting time. To meet this requirement, IEC Standard 097--1 defines several classes of overload relays, each characterized by their trip time (see Fig. 20 ).

The relay rating is to be chosen according to the nominal motor current and the calculated starting time.

b

Altitude Ambient temperaturem 30 °C 35 °C 40 °C 45 °C 50 °C 55 °C 60 °C

1000 1.07 1.0 1.00 0.9 0.92 0.87 0.82

100 1.0 1.01 0.97 0.93 0.89 0.8 0.79

2000 1.01 0.98 0.9 0.90 0.8 0.82 0.77

200 0.97 0.9 0.91 0.87 0.8 0.79 0.7

3000 0.93 0.91 0.87 0.8 0.80 0.7 0.71

300 0.89 0.8 0.83 0.80 0.7 0.72 0.8

000 0.83 0.81 0.78 0.7 0.72 0.8 0.

The values in the table above are provided for guidance only. In reality, the derating of a motor depends on it size, its insulation class, its type of construction (self-cooled or forced-cooled, IP 23 or IP degree of protection, etc.), and varies according to the manufacturer

Note: The nominal power which is generally shown on a motor plate is specified by the manufacturer for a continuous service S1 (operation at constant speed and for a long enough time to reach thermal equilibrium).There are other standard services, such as temporary service S2, or periodic intermittent services S3, S and S for which the motor manufacturer specifies an operating power, different from the nominal power, for each case.

Fig. 20 : Main tripping classes of overload relays according to IEC 60947-4-1.

Trip time from the following states:

Coldat 1.05 x Ir

Hotat 1.2 x Ir

Hotat 1.5 x Ir

Coldat 7.2 x Ir Narrower tolerances (band E)

Class

10 A > 2 hrs < 2 hrs < 2 mins 2 s < tp < 10 s -

10 > 2 hrs < 2 hrs < mins s < tp < 10 s s < tp < 10 s

20 > 2 hrs < 2 hrs < 8 mins s < tp < 20 s 10 s < tp < 20 s

30(1) > 2 hrs < 2 hrs < 12 mins 9 s < tp < 30 s 20 s < tp < 30 s

(1) class used infrequently in Europe, but used widely in the United StatesCold state: Initial state without previous loadHot state: Thermal equilibrium reached at Ir Ir: Setting current of the overload relay


The limits of use are also characterized by graphs (see Fig. 21 ) showing time as a function of the adjustment current (expressed as multiples of Ir).

These relays have a thermal memory (except for some electronic overload relays, as indicated by their manufacturers) and can be connected as follows:

in series with the loador, for high power, to current transformers in

series with the load

Bimetallic thermal relays (see Fig. 22 )

These are combined with contactors to protect motors, lines and equipment from small prolonged overloads. They are therefore designed to allow the normal starting of motors without tripping. However, they must be protected from large overloads by a circuit-breaker, or by fuses (see “Short-circuit protection”).

The operating principle of a thermal overload relay is based on the deformation of its bimetallic strips when heated by the current flowing through them (see Fig. 23 ).

The bimetallic strips are deformed when the current flows, and, depending on their adjustment, can cause the sudden opening of the relay contacts.

Resetting is only possible when the bimetallic strips have cooled down sufficiently.

Thermal overload relays can be used for both alternating and direct current, and are generally:

three-polecompensated, i.e. non-sensitive to variations in

ambient temperature (identical trip curve from 0 to 0 °C over a standard range (see Fig. 24 hereafter)

vv

b

vv

30

20

10

1.05 1.20

1.50 7.2 I/Ir

t (s)

Class 30

Class 20

Class 10

Fig. 21 : Tripping curves of overload relays.

Fig. 22 : Telemecanique LRD bimetallic overload relay and its graphic symbol.

Current conductorBlade with high coefficient of expansion

Blade with zero coefficient of expansion Bimetallic strip after heating

Support forming fixed point

Current input

Trip release system

Trip capacity setting Current output

Bimetallic strip with resistor

Fig. 23 : View of the inside of a thermal overload relay and detail of one of its bimetallic strips.


manually or automatically resetgraduated in “motor amperes”: the current

shown on the motor name plate is displayed directly on the relay

They can also be sensitive to a phase failure: this is the “differential” concept. This function prevents the single-phase operation of the motor, and meets the conditions of IEC 097--1 and 097--2 (see Fig. 25).

vv

Fig. 24 : Tripping zone for compensated thermal overload relays according to ambient air temperature (source: IEC 60947-4-2 and 6-2).

Fig. 25 : Operating limit of a differential thermal overload relay (sensitive to a phase failure).

Fig. 26 : Electronic overload relay (Telemecanique LR9F)

0.8 Ir

0.9 Ir

1 Ir

1.1 Ir

1.2 Ir

1.3 Ir

1.4 Ir

-10 30 40 5020100°C

Ambiant air temperature

Lower limitUpper limitTripping zone

Trip time Multiple of the setting current

> 2 hrs 2 poles : 1.0 Ir

1 pole : 0.9 Ir

< 2 hrs 2 poles : 1.1 Ir

1 pole : 0

basis of a model which reconstitutes the thermal time constants of the motor, the electronic system calculates the motor temperature constantly as a function of the current flowing through it and the operating time. The protection thus gives a better approximation of the actual conditions and can prevent incorrect tripping. Electronic overload relays are less sensitive to the thermal environment of the location where they are installed.

In addition to the conventional functions of overload relays (protection of motors from overloads and phase unbalance and failure), electronic overload relays can be supplemented with options such as:

PTC probe temperature monitoringprotection against locking and excess torqueprotection against phase inversionsprotection against insulation faultsprotection against no-load operationetc.

PTC thermistor probe relaysThese protection relays monitor the actual temperature of the motor to be protected. They offer extremely precise temperature measurement: the small volume of the probes gives them a very low thermal inertia and therefore a very short response time.Allowing direct monitoring of the stator winding temperature, they can be used to protect motors against overload, rises in ambient temperature, ventilation circuit faults, excessive starting frequency, jerky running, etc.

They comprise:One or more Positive Temperature Coefficient

(PTC) thermistor probes placed within the windings of the motors or in any area subject to heating (bearings, etc.). They are static components whose resistance increases sharply when the temperature reaches a threshold called the Nominal Operating Temperature (NOT), as shown in Figure 27 next page.

An electronic device, supplied with alternating or direct current, which constantly measures the resistance of the probes combined with it. When the NOT is reached, the threshold circuit detects the sharp resistance increase of the probe and then causes the output contacts to change state. Depending on the probes chosen, this protection method can be used as follows:

either to provide an alarm without stopping the machine (where the NOT is lower than the maximum temperature specified for the component to be protected)

or to stop the machine (where the NOT is equal to the maximum specified temperature). (see Fig. 28 next page)

The use of this protection method must be specified in advance, because the probes have to be incorporated in the windings during the manufacture of the motor, or during any rewinding operation after an mishap.

vvvvvv

b

b

v

b

Widely used, this relay offers excellent reliability, and is inexpensive. It is particularly recommended if there is a risk of the rotor locking.

However, it has the disadvantage of not taking into account in a very precise way the thermal state of the motor to be protected, and of being sensitive to the thermal environment of the location where it is installed (cabinet ventilation, etc.).

Electronic overload relays (see Fig. 26 )These relays benefit from the advantages of electronics which enables a more detailed thermal image of the motor to be created. On the

b


The choice of the PTC probes to be incorporated depends on the insulation class and structure of the motor. This choice is normally made by motor manufacturers or rewinders who are the only ones who have the necessary skill.

Because of these two constraints, the choice of PTC probe protection is generally reserved for top-range equipment with expensive motors.

Excess torque relays: a supplementary form of protection (see Fig. 29 )

As a supplement to thermal protection by relay or PTC probe, these protect the drive chain in case of rotor locking, seizing or mechanical shock.

Fig. 28 : Electronic device (Telemecanique LT3) to be combined with three thermistor probes to stop a motor when the maximum temperature is exceeded. Fig. 29 : The excess torque relay (Telemecanique

LR97D) is a supplementary form of protection in case of rotor locking, seizing or mechanical shock.

Fig. 30 : Multi-function relay (Telemecanique LT6).

Unlike most overload relays, these relays do not have a thermal memory. They have a operating characteristic for a specified time (with adjustable threshold current and delay).

The excess torque relay can be used as overload protection for motors where starting is lengthy or very frequent (e.g. those used for hoists).

Multi-function relays (see Fig. 30 )

These relays can protect motors from the main causes of heating. Moreover, the electronic technology provides these relays with capacity for communication with PLCs and supervisors via fieldbuses.

This link with a PLC facilitates the set-up and maintenance.

It makes it possible to set parameters and activate the necessary protection, to configure and operate the motor driver, and to monitor the states of starting, alarms and tripping. It can be used for exchanging data, measurement information (currents, heating, etc.) with the higher PLC level (controlling PLC), and for monitoring the thermal state of the motor. This facilitates diagnostics and the implementation of preventive measures.

These relays are used for the isolated protection of “sensitive” motors, i.e. those for which an incorrect stop would have serious effects on personal protection, safety, production losses, etc.

The diagram below shows the possibilities of a multi-function relay connected to a supervising PLC (see Fig. 31 opposite page).

4000

1330

550

250

20

NOT -20-20 0NOT -5

NOT+5NOT+15

TNF

T (°C)

High markersLow markers

R (Ω)(Logarithmic scale)

Fig. 27 : Markers or “operating points” of PTC thermistor probes.


4.3. Selection table for protection relays

M3 a

M3 a

M3 a

Modbus network

PTC probes

PLC

Multi-functionprotection relay

Computer

I > I > I >

Fig. 31 : Example of a communications network based on a multi-function relay (source: Telemecanique).

Type of relay Overload relay (thermal or electronic)

PTC probe relay Overload relay Multi-function relay

Causes of heating:

Overload

Rotor locking

Phase failure

Ventilation fault With PTC probe

Shaft bearing seizing With PTC probe

Excessive starting time Class 20 or 30

Demanding service With PTC probe

Torque shocks With PTC probe

Some Telemecanique references

LR2K, LRD, LR9D, LR9F

LT3 LR97D & LT7 LT

Tesys U : Standard or expandable CU*

Multi-function CU*

(*) CU: Control Unit Entirely suitable Possible solution Unsuitable (no protection)


4.4 “Motor circuit-breakers” (thermal-magnetic circuit-breakers)

BackgroundA “motor circuit-breaker” is a thermal-magnetic circuit-breaker which provides protection against both short circuits and overloads, by rapidly opening the faulty circuit. It is a combination of a magnetic circuit-breaker (see “Short-circuit protection”) and an overload relay (see “Overload protection”). It conforms to IEC 097-2 and 097--1 (see Fig. 32 ).

In these circuit-breakers, the magnetic devices (short-circuit protection) have a non-adjustable trip threshold, generally about 10 times the maximum setting current of thermal trips.

Their thermal elements (overload protection) are compensated against variations in ambient temperature. The thermal protection threshold can be adjusted on the front panel of the circuit-breaker. Its value must match the nominal current of the motor to be protected.

In all these circuit-breakers, coordination (type II) between the thermal elements and the short-circuit protection is provided by the design.

Additionally, in the open position, most of these devices have a sufficient clearance distance (between their contacts) to provide an isolation function. They also incorporate a padlocking device required for logging.

Tripping curvesA motor circuit-breaker is characterized by its tripping curve, which represents the trip time of the circuit-breaker as a function of the current (multiple of Ir).

This curve has four zones (see Fig. 33 ):

Fig. 32 : Motor circuit-breaker (Telemecanique GV7) and its graphic symbol.

I > I > I >

L1 L3L2

the normal operation zone 1 . Since I < Ir, there is no tripping.

the thermal overload zone 2 . The thermal element trips; the trip time decreases as the overload increases. This tripping mode is therefore called “inverse time” in standards.

The high current zone 3 , monitored by the “instantaneous magnetic element” or “short-circuit element” whose operation is instantaneous (less than ms).

And, in some circuit-breakers (electronic circuit-breakers), an intermediate zone 4 monitored by a “time-delayed magnetic element” whose operation is delayed (by 0 to 300 ms). This tripping mode is called “independent delay mode” in standards. It can be used to avoid incorrect tripping when peak magnetizing current of motors is present at switch-on.

Their limits are:Ir: setting current of the overload protection; this must match the nominal current (In) of the motor to be protected.Im: trip current of the time-delayed magnetic protection.Iinst: trip current of the instantaneous magnetic protection. This can vary from 3 to 17 times Ir, but is generally close to 10 Ir.Ics: rated breaking capacity in short circuitIcu: ultimate (maximum) breaking capacity in short circuit

b

b

b

b

I(A)Im IinstIr

t(s)

IcuIcs

Overloadzone

Short-circuitzone

1.0 Ir 1.20 Ir

1 2

3

4

Fig. 33 : Operating zones of a thermal-magnetic circuit-breaker.


5 Motor starters

5.1 Background

A motor starter has four basic functions:IsolationShort-circuit protectionOverload protectionControl (on - off).

Each motor starter can be enhanced with additional functionality according to the application requirements. These relate to:

bbbb

Power: speed adjustment, progressive starting, phase inversion, etc.

Control: auxiliary contacts, time delay, communication, etc.

In the design of a motor starter, the functions are distributed in different ways, as shown schematically in Figure 34 .

b

b

M

Thermal-magneticcircuit-breaker:b short-circuit protection,b overload protectionb isolation for maintenance.

Contactor :b on-off

MotorM

Magnetic circuit-breaker:b short-circuit protection,b isolation for maintenance.

Contactor :b on-offb disconnection in case of fault.

Variable speed drive:b progressive starting,b variable speed control,b motor protection,b overload protection.

MotorM

Isolator-fuse:b short-circuitprotection,b isolation for maintenance.

Contactor:b on-off

Overload relay:b overloadprotection

Motor

Fig. 34 : The various functions and their combinations forming a motor starter.

5.2 The basic functions of motor starters

Isolation

The isolation function is essential, and must form the basis of any circuit (see installation standards NF C1-100, IEC 03--3); it is not stipulated but is recommended for all motor starters. It serves to isolate the circuits from their power source (power supply line) in a secure way in order to protect property and personnel during maintenance, repair or modification work carried out on the downstream electrical circuits.

This isolation must be designed according to the specifications, which require:

simultaneous all-pole breakingconformity with specified clearances according

to the supply voltageinterlocking visible, or fully apparent, circuit-breaking:

bb

bb

“visible breaking” signifies that the opening of the poles can be viewed directly by an operator

apparent breaking is identified either by the position of the actuator, or by a position indicator which, according to the standard, must not indicate the “off” position unless the contacts are actually separated by a sufficient distance specified in the standards. Manufacturers offer numerous devices to perform this function. The isolation and short-circuit protection functions are often combined in a single device (e.g. fused isolator). For this purpose, some basic devices have to be supplemented with an additional device, such as a plug-in support.

Reminder: An isolator is intended to isolate a circuit; it has no breaking or making capacity. It is therefore always operated in no-load conditions.

v

v


Short-circuit protectionThis function requires the detection of overcurrents following short circuits (generally more than 10 times the nominal current) and the opening of the faulty circuit. It is provided by fuses or magnetic circuit-breakers.

Overload protectionThis function requires the detection of excess currents following overloads (Ir < Ioverloads < Im) and the opening of the faulty circuit. It is provided by electromechanical or electronic devices (overload relays) combined with a breaking device (circuit-breaker or contactor) or incorporated in electronic starters or variable speed drives. It also protects the motor line against thermal overloads.

Control“Control” signifies the closing (making) and opening (breaking) of an electrical circuit under load. The control function is provided by switches or possibly by motor circuit-breakers, starters or variable speed drives. However, the contactor is the product most commonly used for this function, since it allows remote control. For motors, this control device must permit a large number of operations (electrical durability) and must conform to IEC 097--1. According to these standards, manufacturers must specify the following characteristics for this equipment:

Control circuitthe nature of the control current, and its

frequency in the case of alternating currentthe rated voltage of the control circuits (Uc) or

the control supply voltage (Us)

Power circuitthe rated operating voltage (Uo): this is

generally expressed as the voltage between phases. It determines the operation of the

bv

v

bv

circuits to which the making and breaking capacity relates, the type of application and the starting characteristics

the rated operating current (Io) or rated operating power : this characteristic is defined by the manufacturer according to the specified conditions of use and takes into account, in particular, the rated operating voltage and the conventional thermal current (Ith corresponds to the maximum value of the test current: Ith u Ie). In the case of equipment for the direct control of a single motor, the indication of a rated operating current can be replaced or supplemented by that of the rated maximum available power.

In some cases, this information is supplemented with:

the duty rating, with details of the intermittent duty class, if applicable. The classes define different operating cycles

the rated making and/or breaking capacity. These are maximum currents, specified by the manufacturer, which a piece of equipment can establish (making) or interrupt (breaking) in a satisfactory way in specified conditions. The rated making and breaking capacities are not necessarily specified by the manufacturer, but the standard requires minimum values for each category of operation.

The standards of the IEC 097 series define operating categories according to the applications for which the control devices are intended (see Fig. 35 ). Each category is characterized by one or more operating conditions such as:

currentsvoltagesthe power factor or time constantand other operating conditions if necessary.

v

v

v

b

vvvv

Fig. 35 : The different operating categories of contactors according to their intended applications, as shown in IEC 60947-1.

Type of current Operating categories Typical applications

Alternating current

AC-1 Non-inductive or low-inductance loads, resistance furnaces. Power distribution (lighting, generator sets, etc.)

AC-2 Slip-ring motors: starting, disconnection. Equipment for intensive use (lifting, handling, grinding machines, rolling mill trains, etc.)

AC-3 Squirrel cage motors: starting, disconnection of started motors(1). Motor control (pumps, compressors, fans, machine tools, conveyors, presses, etc.)

AC- Squirrel cage motors: starting, reversing, inching. Equipment for intensive use (lifting, handling, grinding machines, rolling mill trains, etc.)

Direct current DC-1 Non-inductive or low-inductance loads, resistance furnaces.

DC-3 Shunt motors: starting, reversing, inching. Dynamic disconnection of motors for direct current.

DC- Series motors: starting, reversing, inching. Dynamic disconnection of motors for direct current.

(1) The AC-3 category can be used for inching or reversing for occasional operations of limited duration, such as the assembly of a machine; the number of these operations during these limited periods does not normally exceed five operations per minute or ten in a period of 10 minutes.


Thus the following characteristics are taken into account, for example:

the making and breaking conditions the nature of the controlled load (squirrel cage

motor, slip-ring motor, resistor)conditions in which making and breaking takes

place (motor running, motor stalled, during starting, counter-current braking, etc.).

Choosing a contactor:

The operating categories defined in the standard can be used for an initial selection of equipment capable of meeting the requirements of the motor’s intended application. However, other constraints must be taken into account, and not

vv

v

b

all of these are defined by the standard. Thus there are factors external to the application, such as the climatic conditions (temperature, humidity), the geographical location (altitude, coast).

In some situations, the reliability of the equipment can also be a critical factor, particularly when maintenance is difficult. The electrical life (durability of the contacts) of the equipment (the contactor) is also an important characteristic.

It is therefore essential to consult comprehensive, detailed catalogues, in order to ensure that the chosen equipment meets all these requirements.

5.3 The special case of electronic starters and variable speed drives

Starting asynchronous motors by direct connection to the line supply is the solution which is most common, most economical and most suitable for a wide range of machines. However, this may entail constraints (such as the inrush current on starting, mechanical shocks on starting, the impossibility of controlling acceleration and deceleration and the impossibility of varying the speed) which may be troublesome for some applications, or even incompatible with the desired operation of the machine. Electronic starters and variable speed drives (see Fig. 36 ) can overcome these problems, but the conventional protection described above is ineffective with equipment which modulates the electrical energy supplied to the motor.

Electronic variable speed drives and starters therefore have integrated protection. Modern variable speed drives generally provide overload protection for motors and self-protection. On the basis of the current measurement and data on the speed, a microprocessor calculates the motor temperature increase and sends an alarm or trip signal if the heating is excessive. Variable speed drives, and in particular frequency inverters, are also often fitted with protection against:

short-circuits between phases and between phase and ground

overvoltages and voltage dropsphase unbalancesingle-phase operation

Additionally, data produced by the thermal protection incorporated in the variable speed drive can be exchanged with a PLC or a supervisor via the communications link provided in the more advanced variable speed drives and starters.

For further information about electronic starters and variable speed drives, see Schneider-Electric “Cahier Technique” no. 208.

b

bbb

Fig. 36 : Variable speed drive (Telemecanique ATV58H).

5.4 A complementary function: communication

Communication is a function that has become almost indispensable in industrial production processes and systems. It provides a remote method of monitoring the machines of a production system, interrogating different devices, and controlling the machines.

Industrial network communication can be broken down into five levels, represented by a triangle, according to the CIM (Computer Integrated Manufacturing) concept (see Fig. 37 next page).

For this form of communication, which can also be global, between all elements of a production system, communicating components or modules (see Fig. 38 next page) are integrated into many devices, including protection devices such as multi-function relays or motor starters.

With communication modules such as AS-i, Modbus, Profibus, etc., it is possible, for example, to control a motor (remote on-off control of the motor starter), and also to remotely monitor the motor load (current measurement)


and/or existing faults (overcurrent overload, etc.) or earlier faults (log).

Communication systems are not only useful for integrating protection into automatic industrial processes, but also enable any breakdown to be anticipated (pre-alarm conditions, etc.), thus reducing downtime and ensuring continuity of operation. It therefore helps to improve equipment management, with positive effects on the economic outcome.

Entreprise level Production management

Factory level Scheduling

Workshop level Supervision

Cell level Automated systems

Machine level Sensors - Actuators

Fig. 37 : The five levels of industrial communication.

5.5. Motor starters and coordination

Fig. 38 : A starter-controller with the Modbus communication module (Telemecanique Tesys U).

Motor starter solutions

As explained at the start of this chapter, the main functions required from a motor starter (isolation, control and protection against short circuits and overloads) can be provided by different devices.

There are three possible combinations of devices (see Fig. 39 ) which enable a motor starter to provide all these functions correctly, but they require compatibility between the characteristics of each of the combined devices.

The “all in one” solution: The three functions are combined in a single device; its overall performance is guaranteed by the manufacturer. For the user, this is the simplest solution, from the design phase through to installation: it is easy to install (less wiring) and can be chosen immediately (no special research needed).

The “two device” solutionThermal-magnetic circuit-breaker + contactorCompatibility between the characteristics of the two devices must be checked by the user.

The “three device” solution Magnetic circuit-breaker + contactor + overload relayThis can cover a wide power range. This combination requires a compatibility study for the selection of the devices and an installation study for their mounting on a chassis or in an enclosure.

b

b

b

Fig. 39 : The three possible combinations of devices for a motor starter.

Solution "1 product"

Solution "2 products"

Solution "3 products"

GVE LE LC1 K LRKMagnetic + contactor + overloadcircuit-breaker relay

GV2 M LC1 KThermal-magnetic + contactorcircuit-breaker

LUmotor starter


This nature of this operation (compatibility, choice and installation) is not always obvious to users, since it is necessary to combine the characteristics of the different devices and have the skill to compare them. For this reason, manufacturers investigate the combinations of devices and then offer them in their catalogues. As part of this operation, they attempt to find optimal combinations of protection devices: this is the “coordination” concept.

Coordination between protection and control

This coordination is the optimal combination of different protection devices (for short circuits and overloads) and the control device (contactor) which make up a motor starter. Designed for a given power rating, it provides the best protection for the equipment controlled by the motor starter (see Fig. 40 ).

It has the double advantage of reducing equipment and maintenance costs, since the different protection devices are matched with each other as precisely as possible, without unnecessary redundancy.

There are different types of coordination.Two types of coordination (type 1 and type 2) are defined by IEC 097--1.

Type 1 coordination: this is the standard solution and is most commonly used. It requires that, in short-circuit conditions, the contactor or starter must not create any risk to personnel or installations. It allows the necessary repair or replacement of components before the restoration of service.

b

v

Type 2 coordination: this is the high-performance version; it requires that the contactor or starter must not create any risk for personnel or installations, and must be capable of operating afterwards. The risk of contact welding is accepted; if this occurs, the manufacturer must state the action to be taken for the maintenance of the equipment.

There is a very high performance version, provided in CPS (control and protective switching devices) and offered by some manufacturers, called “Total Coordination”.

This type of coordination requires that, in short-circuit conditions, the contactor or starter must not create any risk for personnel or installations, and must be capable of operating afterwards. The risk of contact welding is not acceptable; the motor starter must be capable of being restarted immediately.

What type of coordination should be chosen?The choice of the type of coordination depends on the operating parameters.It must meet the user’s requirements at an optimal installation cost.

Type 1Acceptable when continuity of service is not required and service can be restored after the replacement of the faulty elements.In this case, the maintenance service must be effective (available and competent). The advantage is a lower equipment cost.

Type 2To be chosen when continuity of service is required.It requires less maintenance.

v

v

b

v

v

I(A)0.7Ic 1.2Ic

In

t(s)

Ic

Tripping curves: overload relay magnetic trip release fuse

Thermal withstand limits:- contactorcircuit-breaker- overload relay

Overloadzone

Impedance-earthedshort-circuit

Short-circuitzone

1

1

2

2

3

3

To enable a motor starter to operate correctly, the coordination between all the devices must meet all the following requirements:

the overload relay must protect the magnetic circuit-breaker in the overload zone : its curve “1” must pass below that of the thermal withstand of the circuit-breaker;

and, conversely, in the short-circuit zones, in order to protect the thermal relay, the short-circuit trip curve must pass below that of the thermal withstand of the relay;

finally, in order to protect the contactor, its thermal withstand limit must be above the curves of the two trip releases (thermal, “1”, and magnetic, “3”) (or the fuse, “2”).

Note that the standard specifies the limit test currents:

up to 0.7 Ic only the thermal protection must operate;

above 1.2 Ic only the short-circuit protection must operate.

b

b

b

b

b

Fig. 40 : The principles of coordination.


When immediate restarting of the motor is essential, “Total Coordination” must be chosen. No maintenance is required.

v The types of coordination offered in manufacturers’ catalogues simplify the user’s choices and provide assurance that the motor starter conforms to the standard.

5.6 Control and protective switching devices (CPS)

CPS or “starter-controllers” are designed to perform the functions of control and protection (against overload and short circuit) simultaneously; they are also designed to enable control to be provided in short-circuit conditions.

They can also provide complementary functions such as isolation, enabling them to perform all the functions of a “motor starter”. They conform to IEC 097--2, which in particular defines the rated values and the operating categories of CPS, and to the principles of IEC 097-1 and 097--1.

The various functions of a CPS are combined and coordinated to provide continuity of service for all currents up to the rated breaking capacity for short-circuit operation, Ics, of the device. The system may or may not incorporate a single device, but its characteristics are always rated as if for a single device. Additionally, the guarantee of “total” coordination between all the functions gives the user a simple choice of an optimal protection device which is easy to use.

Even if it takes the form of a single device, a CPS can provide a degree of modularity equal to, or even greater than, that of a “three product” motor starter. This is true of the Telemecanique Tesys U starter-controller (see Fig. 41 ). This allows a control unit integrating the protection and control functions for motors from 0.1 A to 32 A to be added, or changed at any time, on a

general-purpose “power base unit” or “sub-base” rated at 32 A (see Fig. 42 ).

Additional functionality can also be installed, for the following aspects:

power: inverter unit, limitercontrol: function modules: alarms, motor load,

automatic reset, etc.communication modules: AS-i, Modbus,

Profibus, CAN-Open, etc.auxiliary contact modules, additional contacts.

bbv

v

v

Fig. 42 : Example of optional functions available with a modular system (Telemecanique Tesys U starter-controller).

1/L1

1/L3

1/L2

2/T1

6/T3

4/T2

Control unit

Power base unit

Control units

Fig. 41 : Example of a modular CPS (Telemecanique Tesys U starter-controller).

Possible functions Control units:

Standard Expandable Multi-function

Starter states (ready, operating, faulty)

Alarms (overcurrent, etc.)

Thermal alarm

Remote reset via the bus

Indication of the motor load

Fault differentiation

Parameter setting and protection functions look-up

“Log” function

“Supervision” function

Start and stop commands

Information carried on the bus (Modbus) and functions provided


5.7 Discrimination

“total discrimination”, which covers all fault current levels up to the maximum available in the installation, or “partial discrimination” which does not cover the whole range.

Discrimination methodsThere are several types of discrimination:

current-based, using a difference between the trip thresholds of the circuit-breakers connected in series

time-based, where the tripping of the upstream circuit-breaker is delayed by a few tens or hundreds of milliseconds, or use is made of the ordinary operating characteristics related to the ratings of the devices. Thus discrimination can be provided between two overload relays by meeting the condition Ir1 > 1. Ir2 (where r1 is upstream of r2).

“SELLIM” or “energy-based”, in the electricity supply field: here a limiting circuit-breaker is connected upstream, and opens for the time required for the operation of the downstream circuit-breaker, and then recloses.

logic, in which one circuit-breaker informs the other that the threshold has been exceeded, leaving the more downstream circuit-breaker the choice of whether to open.

For further information on discrimination, see Schneider Electric Cahiers Techniques no. 17.

Discrimination in processesFor process control equipment (production lines, chemical production units, etc.), the discrimination methods most commonly used between motor starters and the electrical line supply to these processes are generally current-based and time-based. In most cases, discrimination is provided by the limiting or ultra-limiting capacity of the motor starters.

b

b

b

b

In an electrical installation, the loads are connected to the generators via a sequence of isolation, protection and control devices.

Unless there is a carefully implemented discrimination plan, an electric fault may affect several protection devices. Thus a single fault can result in a larger or smaller part of the installation being switched off. This causes an additional loss of availability of electrical energy in correctly operating feeders.

To prevent this loss, in a radial feeder layout (see Fig. 43 ) the aim of discrimination is to disconnect only the faulty feeder or motor from the line supply, while keeping the largest possible part of the installation live. Thus discrimination makes it possible to combine safety and continuity of service. It also facilitates fault location.

To provide maximum continuity of service, protection devices which are coordinated with each other must be used. For this purpose, different methods are used to achieve either

D1

D2D3

Fig. 43 : Discrimination between two circuit-breakers D1 and D2 connected in series, where the same fault current is flowing through both, requires that only the circuit-breaker D2 downstream of D1 should open

5.8 Example

The aim is to select a motor starter for protecting and controlling a lifting pump where continuity of service is essential.

Technical characteristics of the motor to be protected

Three-phase asynchronous motor

Power: kW at 00 V, 0 Hz, and nominal current In ≈ 8.1 A

Operating category AC-3

Normal start (no specific starting time)

b

b

b

b

Short-circuit current of the installation calculated in relation to the equipment: Isc = 3 kA

Control voltage: 230 V.

Essential limit characteristicsThe operating conditions lead to the following choice:

for short-circuit protection, and in order to provide the requisite continuity of service, a magnetic circuit-breaker must be provided, with a breaking capacity in excess of Isc, calculated as 3 kA in this case.

b

b

b


To allow the continuous passage of the nominal current, the operating current of the magnetic circuit-breaker must be more than In = 8.1 A.

for overload protection, given normal starting, the relay must be of class 10 or 10 A, with a setting current Is of 8.1 A or slightly more.

a contactor having an operating current of more than 8.1 A. Its control coil must be supplied at 230 V a.c.

Since continuity of service is essential, type II coordination or total coordination of the protection devices is required.

b

b

Fig. 44 : Two solutions in which good coordination between the different functions of a motor starter is guaranteed (source: Telemecanique).

The hardware solutionsThe selection of equipment having all these characteristics can be difficult, especially if devices made by different manufacturers have to be combined. However, most manufacturers’ catalogues show ranges of motor starters together with tables of tested combinations, facilitating the selection process. (see Fig. 44 ).

Standard power ratings of 0/0 Hz three-phase motors in Category AC-3

Circuit-breaker Contactor Thermal overload relay

00/1 V 0 V 00 V Ref. Rating FLAm (1)

Ref.(2) Ref. Setting rangeP Ie Iq P Ie Iq P Ie Iq

kW A kA kW A kA kW A kA A A A0.08 0.22 130 0.0 0.19 130 - - - GV2 L03

or LE030. LC1 D09 LRD 02 0.1…0.2

0.09-

0.3-

130-

0.090.12

0.280.37

130130

--

--

--

GV2 L03 or LE03

0. LC1 D09 LRD 03 0.2…0.0

0.120.18

0.20.

130130

-0.18

-0.

-130

GV2 L04 or LE04

0.3 8 LC1 D09 LRD 04 0.…0.3

… … … 3 . 130 - - - - - - GV2 L14

or LE1410 10 LC1 D09 LRD 12 .…8

- - - - - - . 10 GV2 LE14 10 138 LC1 D12 LRD 12 .…8- - - - - - . 0 GV2 L14 LC1 D12 LRD 12 .…8 8. 130 GV2 L14

or LE1410 138 LC1 D09 LRD 14 7…10

Solution: GV2 L14 + LC1 D09 + LRD 14

D.O.L. starters with circuit-breaker and thermal overload relay – “3-product” solution, type 2 coordination

TeSys U starter-controllers – “1 product” solution, total coordination

- Power baseRated short-circuit breaking capacity (Isc)Volts 230 0 00 90kA 0 0 10

Note: For higher values, use limiters. At 90 V, use phase barrier LU9 SP0.

Connection Rating Ref.Power Control y 0 V 00 V 90 V

A A AScrew clamp Screw clamp 12 12 9 LUB 12

32 23 21 LUB 32

- Control unitsMaximum standard power ratings of 0/0 Hz single-/three-phase motors

Setting range

Clip on power base rating

Ref. to be completed with code indicating voltage

00/1 V 00 V 90 VkW kW kW A A

Advanced control – Pressing the Test button on the front panel simulates tripping on thermal overload.

Class 10 for three-phase motors0.09 - - 0.1…0. 12 and 32 LUCB X6pp0.2 - - 0.3…1. 12 and 32 LUCB 1Xpp1. 2.2 3 1.2… 12 and 32 LUCB 05pp. . 9 3…12 12 and 32 LUCB 12pp7. 9 1 .…18 32 LUCB 18pp1 1 18. 8…32 32 LUCB 32pp

Existing control circuit voltagesVolts 2 8…72 110…20c BLa Bc or a - ES FU

Solution: LUB12 + LUCB 12 FU

GV2 L

LC1 D

LR D

LUB 12


6 Conclusion

In any installation including electric motors, different kinds of faults can occur. But, whether they originate in the motors (short circuits between phases, etc.) or are related to the operation of the motor (rotor locking, prolonged starting, etc.) or to the power supply (overvoltage, unbalance, etc.), their effects on the motors can include short circuits and/or overheating of the windings, which may destroy them.

Accordingly, in order to avoid these mishaps or limit their effects, every motor should be protected from:

short circuits: by fuses, magnetic circuit-breakers, etc.

and overloads: by thermal or electronic overload relays, multi-function relays, etc.

In a motor starter, these protection elements are combined with an isolation device and a control device. To ensure that they perform their functions correctly, their coordination must be ensured. This is an operation which is often difficult for the designer of the installation or machine, since he has to take into account not only the type of motor, but also its mode of operation and the characteristics of the installation.

To facilitate the selection process, all major manufacturers of motor starters publish combination tables for their equipment in their catalogues. Only a few manufacturers, such as Schneider Electric, have produced devices which incorporate all the necessary elements to guarantee the correct operation of a whole installation. Thus the requisite motor protection devices can be rapidly specified and installed without the risk of random occurrences.

b

b


Appendix 1: Modular system of the Tesys U starter-controller

The Tesys U CPS, or starter-controller (made by Telemecanique) is a direct motor starter for protecting and controlling single-phase or three-phase motors. Its functions are integrated simply by plugging control units and modules into a power base unit (see Fig. 45 ). With this technology, the CPS can be adapted up to the last minute, and other plug-in elements are available to simplify or even eliminate the wiring in it.

Power base unit [1]Independent of the control voltage and the

motor power

Integrates the circuit-breaker function with a breaking power of 0 kA at 00 V, total coordination (continuity of service), and the switch function

Control units [2]Standard control unitProtection against overloads and short circuitsProtection against phase failure and unbalanceProtection against isolation faults (equipment

protection only)Manual reset

Expandable control unitIncludes the functionality of the standard

control unit (see above)When combined with a function or

communication module:- fault differentiation with manual reset- fault differentiation with remote or automatic reset- thermal pre-alarmindication of the motor load.

Multi-function control unitIncludes the functionality of the standard

control unit (see above)Reset parameters can be modified in manual

or automatic modeProtection system alarmDisplay on front panel or on remote terminal,

using Modbus RS 8 port“Log” function“Monitoring” function, displaying the main

motor parameters on the front panel of the control unit or on a remote terminal

Fault differentiation (short circuit, overload, etc.)Protection against excess torque and no-load

operation

b

b

bvvv

v

bv

v

bv

v

vv

vv

vv

Modules [3-4]Auxiliary contacts

FunctionFault differentiation (with manual reset or

remote or automatic reset)Thermal pre-alarmIndication of the motor load

CommunicationParallel busSerial bus: AS-Interface, Modbus, Profibus, etc.

Inverter unit [5]

Limiter-isolator unit [6]

b

bv

vv

bvv

6

5

1

2

3

4

Fig. 45 : Tesys U modular starter-controller.


Appendix 2: the main starting modes

DOL starting (see Fig. 46 )

This is the simplest and most economical starting mode, but, owing to its electromechanical

Fig. 47 : Electrical diagram of a star-triangle starter.

In the power networkStarting current Large overcurrent ( to 10 In)Brownout ConsiderableHarmonic disturbance Considerable during startingPower factor Low during startingIn the motorNumber of successive starts Limited (thermal withstand)Available torque Low during starting (see graph)Temperature stress Very considerable (rotor)In the mechanismStress on couplings Very considerableSuitable load types Low-inertia load

N

C

Resistive torque

Accelerationtorque

I

N

Id / In

Cd

CnCr

Cmax

NnN1 NnN1

If (Cr)In

characteristics, it cannot be used unless:the load allows a large starting torqueand the line supply allows a starting current

which may be up to 10 times the nominal current.

bb

Fig. 46 : Graphs and summary of the induced effects of the DOL starting mode.

Star-triangle startingThe principle of this mode is that the motor is started by coupling the windings in star configuration under the line voltage (see Fig. 47 ), which is equivalent to dividing the nominal voltage of the motor in star configuration by 3.The peak starting current is then divided by 3, i.e. Is = 1. to 3 In.This is a simple and economical starting mode which reduces the current peak on starting (see Fig. 48 next page).It can only be used if:

the starting load is zero, or has a low torque not exceeding 1/3 of the nominal torque

and the line can withstand the excess current during the coupling changeover.

Rheostatic stator startingThe principle is to start the motor at a reduced voltage by connecting resistors in series with the windings (see Fig. 49 next page). When the speed is stabilized, the resistors are short-circuited and the motor is coupled directly to the line supply. This operation is generally controlled by a timer.

b

b

KM2

Q1

KM3

F2

KM1

M 3

(U) (V) (W)

2 4 6

2 4 6

1 3 5

1 3 5

1 3 5 1 3 5

2 4 6

1 3 5

2 4 6

2 4 6

(X) (Y) (Z)

U1 V1 W1

U2 V2 W2

U V W

X Y Z

L1 L3L2

U V W

X Y Z


Fig. 48 : Graphs and summary of the effects of the star-triangle starting mode.

Fig. 49 : Electrical diagram and sequence of a rheostatic stator starter.

Fig. 50 : Current and torque graphs for a rheostatic stator starter.

This starting mode avoids power cuts during the starting phase; it can greatly reduce the magnetizing current peaks (transients).

However, the starting current remains high, at about . In. This starting mode causes a considerable loss of torque and power (see Fig. 50 ).

2

NResistive torque

In

2

4

II in ∆

I in Y

N

Id / In

C in ∆

C in Y

1Cr

Cmax

NnN1 NnN1

C / Cn

If (Cr)

KM1

Q1

F2

KM1

M 3

U V W

2 4 6

2 4 6

1 3 5

1 3 5

1 3 5

1 3 5

2 4 6

2

R1 R3 R5

R2 R4 R6

4 6

L1 L3L2

6

5

4

3

2

1

10050

Ic

N

Id

I (stage 2)without resistance

I (stage 1) with resistances

Cm (stage 2)

Cm (stage 1)

I∆ (direct)

1.5

1

0.5

10050

Torque

NCresistive

C∆ (direct)

In the power networkStarting current Low overcurrent (1. to 3 In)Brownout Considerable on change of couplingHarmonic disturbance Considerable during startingPower factor Degraded during startingIn the motorNumber of successive starts 2 to 3 times greater than in direct connectionAvailable torque Reduced during starting (1/3 Cn)Temperature stress Lower than in direct connectionIn the mechanismStress on couplings Lower than in direct connectionSuitable load types Low-inertia

Autotransformer startingThe motor is supplied at reduced voltage by means of an autotransformer which is switched out of the circuit after starting.


Starting takes place in three stages (see Fig. 51 ).This starting mode is used mostly in LV applications for power ratings of more than 10 kW and for mechanisms having low inertia

where the torque characteristics can withstand the decrease in motor torque in a ratio varying from 0. to 0.8 with respect to the starting torque of the motor (see Fig. 52 ).

Fig. 52 : Current and torque graphs for an autotransformer starter.

Fig. 53 : Progressive starting and deceleration unit (Telemecanique Altistart 01).

Stage 1L1 L3L2

M 3

U V W

Stage 2L1 L3L2

M 3

U V W

Stage 3L1 L3L2

M 3

U V W

K3 K2

M 3

U V WU2 V2 W2

U1 V1 W1

I > I > I >

L1 L3L2

K1

U3

V3

W3

Fig. 51 : Electrical diagram and sequence of autotransformer starting.

Electronic starting (soft starter)

When the motor is switched on, it is supplied with a progressively increasing voltage. This is produced by means of a power controller whose output voltage can be controlled by an acceleration ramp which is determined by the value of the limit current, or the torque, or is related to these two parameters (see Fig. 53 ).

This is a high-performance starting mode which allows soft starting and stopping.

In current limiting control, a maximum current (3 to In) is fixed during the starting phase, although this decreases the torque performance. This form of starting is particularly suitable for “turbine machines” such as centrifugal pumps and fans.

6

5

4

3

2

1

10050

Ic

N

Id

I (3e temps)

I (1er temps)

Cm (2e tps) Cm (3e tps)

Cm (1er tps)

I∆ (direct)

1,5

1

0,5

10050

Couple

NCrésistant

C∆ (direct)


In torque regulation control, the torque performance is optimized on starting, but with negative effects on the current drawn from the line supply.

Frequency converter startingThis operates on a principle similar to that of PWM (Pulse Width Modulation) according to a PWM sinus law. This method provides regular and shock-free rotation of the machines, even at low speed, because the output current waveform is very close to a sine wave.

This is a high-performance starting mode, used when the speed must be controlled.

Suitable for all types of machine, it can be used for the following purposes, among others:

starting high-inertia loadsstarting large loads in a network with a low

short-circuit capacityoptimizing electricity consumption in

accordance with the speed of turbine machines.

bb

b


Appendix 3: Bibliography

Standards

IEC 003-2: Rotating electrical machines.

Part 2: Effects of unbalanced voltages on the performance of three-phase induction motors.

IEC 03, NF C 1-100: Low-voltage electrical installations.

IEC 097-1: Low-voltage switchgear and controlgear - Part 1 : General rules.

IEC 097-2: Low-voltage switchgear and controlgear - Part 2 : Circuit-breakers.

IEC 097--1: Low-voltage switchgear and controlgear - Part -1: Contactors and motor-starters - Electromechanical contactors and motor-starters.

IEC 097--2: Low-voltage switchgear and controlgear - Part -2: Multiple function equipment - Control and protective switching devices (or equipment) (CPS).

IEC 097-8: Low-voltage switchgear and controlgear - Part 8 : Control units for built-in thermal protection (PTC) for rotating electrical machines.

IEC 1000-2-1: Electromagnetic compatibility (EMC) - Part 2: Environment - Section 1: Description of the environment - Electromagnetic environment for low-frequency conducted disturbances and signalling in public power supply systems.

Schneider Electric Cahiers Techniques

Overvoltages and insulation coordination in MV and HV Cahier Technique no. 11- Didier FULCHIRON

Energy-based discrimination for LV protective devices Cahier Technique no. 17 - Marc SERPINET and Robert MOREL

LV surges and surge arresters - LV insulation coordination Cahier Technique no. 179 - Christophe SéRAUDIE

Discrimination with LV power circuit-breakers Cahier Technique no. 201 - Jean-Pierre NEREAU

LV protection devices and variable speed drives (frequency converters) Cahier Technique no. 20 - Jacques SCHONEK and Yves NEBON

Electric motors ... and how to improve their control and protection Cahier Technique no. 207 - Etienne GAUCHERON

Electronic starters and variable speed drives Cahier Technique no. 208 - Daniel CLENET

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

Miscellaneous

Schémathèque Technologies du contrôle industriel, Edition CITEF - Collection Technique Telemecanique 199

Utilisation industrielle des moteurs à courant alternatif, TEC & DOC, Schneider-Electric 2001 - Jean BONAL

Protections électriques des alternateurs et moteurs, Techniques de l’Ingénieur no. D 377 - Bernard GUIGUES

Protections électriques des alternateurs et moteurs, Techniques de l’Ingénieur no. D 820 - Jacques VERSCHOORE

Guide d’installation et de maintenance des Moteurs asynchrones triphasés fermés à cage ou à bagues, Leroy Somer Document

b

b

b

b

b

Schneider Electric Schneider Electric Industries SASHead Office89, bd Franklin Roosevelt92506 Rueil-Malmaison CedexFRANCE

DTP: AXESS Valence. Transl.: Lloyd International - Tarpoley - Cheshire - GBEditor: Schneider Electric

© 2

007

Sch

neid

er E

lect

ric

01-07

Documents

Lv Motors Protection