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Power Generation Customer Training

Chapter 8

Generator Prote

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Generator / Transformer Protection

Siemens AGIndustry Sector, I IS IN ICS2 KHCP.O.Box 3240D-91050 Erlangen

E-Mail: [email protected] GP - 2

Index

1 General .............................................................................................................................31.1 What is the purpose of the generator /transformer protection? ................................3

1.2 Which requirements must meet the generator / transformer protection? .................31.3 Which fault types are there? Which damages and endangering for the plant andstaff resulting from it? ...........................................................................................................31.4 How is a generator / transformer protection built up, in principle and how does itwork? 4

2 Digital generator protection from Siemens: Siprotec V4 ...................................................43 Operation Software DIGSI...............................................................................................5

3.1 Overview...................................................................................................................5 3.2 Communication.........................................................................................................5 3.3 DIGSI Manager.........................................................................................................63.4 DIGSI Operating Tree .............................................................................................7

3.4.1 Device Configuration ............................................................................................7

3.4.2 Settings Group A ..................................................................................................83.5 Masking I/O - Device Matrix......................................................................................83.6 Continuous Function Chart CFC.............................................................................103.7 Commissioning Tool ...............................................................................................113.8 SIGRA: Visualisation and Analysis of Fault Records..............................................11

4 Single Line Diagram (Example) ...................................................................................... 124.1 Current transformer CT...........................................................................................134.2 Voltage/Potential Transformer VT / PT...................................................................13

5 Tripmatrix (Example).......................................................................................................146 Protective Functions........................................................................................................15

6.1 Rotor Earth Fault Protection (R/E/F) ANSI 64R......................................................156.2 Rotor Earth Fault Protection (R/E/F) with 1-3 Hz ANSI 64R 1-3Hz........................166.3 90% Stator Earth Fault Protection (S/E/F) ANSI 64G.............................................176.4 100% Stator Earth Fault Protection (S/E/F) ANSI 64G-100% ................................186.5 Differential Protection ANSI 87G / 87T...................................................................196.6 Overcurrent protection with voltage seal-in ANSI 50/51V.......................................206.7 Thermal (Stator) Overload ANSI 49........................................................................206.8 Unbalanced Load Protection ANSI 46....................................................................206.9 Impedance protection ANSI 21...............................................................................226.10 Out of Step Protection ANSI 78..............................................................................236.11 Reverse power protection ANSI 32R......................................................................256.12 Frequency protection ANSI 81................................................................................256.13 Overexcitation protection ANSI 24..........................................................................26

6.14

Underexcitation protection ANSI 40........................................................................26

6.15 Overvoltage protection ANSI 59 .............................................................................276.16 Undervoltage protection ANSI 27 ...........................................................................276.17 Inadvertent energizing protection ANSI 50 / 27......................................................276.18 Breaker failure protection ANSI 50BF.....................................................................276.19 DC Voltage / DC Current Protection ANSI 59NDC / 51NDC..................................286.20 Fuse Failure Monitoring FFM..................................................................................286.21 Trip Circuit Supervision...........................................................................................29

6.21.1 Trip Circuit Supervision with two binary inputs ...............................................306.21.2 Trip Circuit Supervision with one binary contact.............................................31

6.22 External trip coupling..............................................................................................32

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1 General

Generators are high-quality machines for securing the best possible continuity of powersupply. In addition to a Suitable technical design and responsible mode of operation,

automatic protection facilities have to be provided. This protection must ensure a fast andselective detection of any faults in order to minimize their dangerous effects.The protective equipment must be designed so, that any serious fault will result in animmediate disconnection, de-excitation of the generator and in serious case turbine trip.

Faults which do not cause any direct damage must be brought to the attention of theoperating staff, enabling them to operate the unit outside the critical range or to takeprecautionary measures for shutdown.

1.1 What is the purpose of the generator /transformer protection?

The identification of electrical faults and inadmissible operating states which

endangering persons or high property damages and can lead to the shut down theTG

The stepping of the fault by selective end solving commands to the operating suppliesconcerned.

The report and documentation of the appeared fault.

1.2 Which requirements must meet the generator / transformer protection?

Reliability: Faults must for certain be recognized and switched off before it can getfrom damages to endangering persons and system parts or to avoidable expansions.

Selectivity: Fault type and location have to be recognized obviously and only theactual affected plant parts have to be switched off by the protection.

Plant availability: is influenced by the two aforementioned demands Interruption andrepair times of the plant must be avoided as well as missing triggering. Redundancy: For the most important protection functions (equipment technically

independent) reserve functions shall be available (e.g. unit differential protection asreserve to the generator and block transformer differential protection).

1.3 Which fault types are there? Which damages and endangering for theplant and staff resulting from it?

Inner faults, e.g. stator ground fault, shortened winding in the generator: Requiring animmediate switching off of the operating supplies concerned since there is a damagefor which an expansion has to be feared. Examination of the damage and repair of

the operating supplies are in general necessary. Outer faults, e.g. net short circuit, unbalanced load, over load. Faults out side the

power station which endangering it. The Endangering can be eliminated by de-coupling from the grid and running on island mode. After elimination of the fault causeon the net side, an immediate re-synchronization to the grid is possible

Faults on the side of the turbine, e.g. reverse power, over/under-frequency in islandoperation: Requiring an electrical and on the steam side a protection switching off ofthe turbo set. Otherwise the turbine is endangered mechanically itself. The auxiliarypower supply from the grid is maintained.

fault in the excitation system, e.g. breakdown of power supply, fault in the thyristorbridge or controller

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1.4 How is a generator / transformer protection built up, in principle and howdoes it work?

Measuring of current and voltage at the operating supplies with transformers.Measuring of the ground fault displacement voltage with an open-delta-voltage-

transformer. Arithmetical evaluation of the measurand within the protection relay At detection of an error, tripping of marshaled command relays. Alarm report and

disturbing value storage. Measuring/error inquiry from measurand/tripping given toelectrical operating supplies and turbine.

2 Digital generator protection from Siemens: Siprotec V4

is based on a uniform basic device in a mounting rack. Are multifunction relays which covers the complete spectrum of the generator

protection, with an easily comprehensible type program

Are manual programmable about a frontal membrane keyboard or with the DIGSIsoftware about a PC Offers the possibility to read out operational measurements as well as the disturbing

value storage. Execute a constant monitoring of the measurement quantities, as well as continuous self-

diagnostics covering hardware and software of the device.

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DIGSI

DeviceConfiguration

Control &Monitoring(incl. ComtradeViewer)

Test &Control

Additional(Help, Online-Docum., Password prot. in device, Installation)

Options packages for DIGSI

SIMATIC CFC(Interlocking, Logicfunctions)

Display Editor(Mimic displaycreation)

DIGRA(Fault Evaluation,Measured value

processing)

DIGSI Remote(Remote-interrogationvia Modem)

Graphic Tools(Representation ofzones &

characteristics)

DIGSI Manager(Administration of EVS products)

Expert Package includes:

Logic Functions Remote Operation

Mimic Display Disturbance Recording

Basic Package includes:

Configuration Indication Commissioning Tools Control

3 Operation Software DIGSI3.1 Overview

3.2 Communication

or

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3.3 DIGSI ManagerThe DIGSI 4 Manager manages SIPROTEC devices including their data andcommunication connections. It can be used:

To create a project, To structure the project (definition of the plant topology), To insert objects into a project structure and structure them hierarchically, To edit project structures by duplicating, moving and deleting objects, Archive, reorganize or delete projects.

Double click on the relay (Office 7SJ621 V4.0) opens the connection faceplate

If you computer is connected to the SIPROTEC device, choose Direct, COM1 and Front.If you is not connected to the device, choose Offline, no additional changes has to be made.

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3.4 DIGSIOperating Tree

After all the data have been read in, the DIGSI 4 operating tree is builtup and the devicewindow is displayed.

These objects can be used to carry out the following actions:

Parameterizing Displaying process data

Performing operator actions Executing test functions

3.4.1 Device Configuration

The device configurationis to enable, disable and to specify protection functions

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3.4.2 Settings Group A

When a protection function is enabled, the values has to be set in Settings Group A, e.g.Unbalanced Load

3.5 Masking I/O - Device Matrix

The device matrix is a versatile tool for configuring and editing the information of aSIPROTEC 4 device. The term "information" includes the quantities used for the DIGSI 4CFC logic functions in addition to the measured values, metered values, indications andcommands of the SIPROTEC device.The device matrix is only processed with DIGSI 4. You can have the configurationdisplayed, but not change it, at the display of the device.

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The source designates the origin of an information which the device receives for furtherprocessing.Sourcesare:

Binary input BI - Optocoupler input for entering binary process indications. The numberof binary inputs is device-specific.Analog input - Transducer input for detecting analog process signals for voltage and

current. The number of voltage and current values is device-specific.Function key - For linking the operation of a function key at the operator control panel

of the SIPROTEC 4 device to the issuing of an input indication, forexample the initiation of a switching operation.

CFC - Result of a user-defined DIGSI 4 CFC (Continuous Function Chart)logic function.

System interface - Information from a control center via the system interface.

The destinationspecifies to which component an information is forwarded.

Destinationsare:

Binary output - Relay for outputting a binary signal. The number of binary outputs isdevice specific.

LED - Destination of various indication types. The number of LED's is device-specific.

System interface - Information to a control center via the system interface.CFC - Input information for further processing by DIGSI 4 CFC.Buffer - Indications which are to be saved in the SIPROTEC 4 device in the

operational indication buffer, ground fault indication buffer, networkfault buffer or warning buffer.

Configuring a Single Point Indication:

Select one of the following options:

H - (active with voltage) The indication is created if a signal is applied tothe binary input.

L - (active without voltage) The indication is created when no signal isapplied to the binary input.

_ - (not configured) The indication is not linked with the binary input.

Configuring Double Point Indications:

Select one of the following options:

X - (configured) The indication is created if a signal is applied to the binaryinput.

_ - (not configured) The indication is not linked with the binary input.

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3.6 Continuous Function Chart CFC

The DIGSI 4 CFC program is used to create logic operations ingraphical form, such asinterlock conditions or limit monitoring of measured values.Device-specific CFC functions are in part implemented in the basic parameter settings at thefactory.Generic logic blocks (AND, OR, NAND, etc.) and the analog blocks created specially for therequirements of process control engineering (for example UPPER_SETPOINT,LOWER_SETPOINT, etc.) can be used to create your own logic operations.The blocks are interconnected to CFC programs which, for example,

Perform plant-specific checks, Generate indications when measured values approach a critical

range or Form group messages for transfer to higher-level control centers.

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Binary- in and -outputs can beactivated

Danger: the related protectionfunctions are activated !

3.7 Commissioning Tool

The commissioning tool is only active in online mode.

3.8 SIGRA: Visualisation and Analysis of Fault Records

Analog Wave Forms Measuring Tools Circle Diagrams Zoom Functions Harmonic Components Display of Binary I/Os

Synchronized Views

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4.1 Current transformer CT

- ratio 11000/1 A- maximum burden 30VA- for Protection circuits- 20(5) times overcurrent will result ina 5(0,2) % deviation

!!! always short-out a CT !!!

4.2 Voltage/Potential Transformer VT / PT

- ratio 20000/110- minimum burden 45(100)VA- Class 0.2% deviation- P for Protection circuits- can withstand 3 times overvoltage

!!! never short-out a VT !!!

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5 Tripmatrix (Example)

Binary Outputs: BO 6/7 GeneratorCB Binary Inputs: BI 1 Trip from Exc..BO 8 De Excitation BI 2 Trip from Trasf.BO 11/12 Turbine Trip BI 3 eg. Cooling leakagePDP Profibus DP

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6 Protective Functions

6.1 Rotor Earth Fault Protection (R/E/F) ANSI 64R

protection for the entire excitation circuit of the generator rotor;

symmetrical capacitive coupling of a system frequency AC voltage (50Hz) into theexcitation circuit;

Calculation of the fault resistance from the impedance; Alarm stage directly adjustable in Ohms (rotor-earth resistance); Measurement circuit supervision (minimum capacitive loading current) with alarm output

Setting: eg. RREF 20 k - Alarm; RREF 5 k - Trip

Connection example

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6.2 Rotor Earth Fault Protection (R/E/F) with 1-3 Hz ANSI 64R 1-3Hz

the rotor earth fault protection works with a direct voltage of approx. 50 V, the polarityof which is reversed between 1 and 4 times per second, depending on the setting.

This voltage is symmetrically coupled to the excitation circuit via high-resistance

resistors, and at the same time connected to the earthing brush. Every time the polarity of the direct voltage Ug is reversed, a charging current Ig is

driven across the resistor unit into the rotor-earth capacitors of the excitation circuit.

In the presence of a rotor earth fault, a continuous earth current flows whose intensityis determined by the fault resistance.

The use of a low-frequency square-wave voltage eliminates the influence of the rotor-earth capacitors and ensures at the same time a sufficient margin againstinterference signals from the interference frequencies of the excitation system.

A drop of the charging current allows to detect defects in the measurement circuitsuch as wire breaks, poor brush contact etc.

Setting: eg. RREF 20 k - Alarm; RREF 5 k - Trip

Connection example

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6.3 90% Stator Earth Fault Protection (S/E/F) ANSI 64G

Measurement of phase- to-earth voltage and calculation of zero sequence voltage with aopen delta voltage transformer or a neutral grounding transformer

This principle results in a protected zone of 90%to 95%of the stator winding.

Setting: e.g. V0 = 10% of Unsec; 0.1 x 110V = 11V

Voltage distribution at the stator coils

Connecting principle: open delta voltage transformer

Open delta transformer

Connecting principle: neutral grounding transformer

UE IE = 3UE

ZE

UEZE

90%

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6.5 Differential Protection ANSI 87G / 87T

Tripping characteristic with current restraint; High degree of sensitivity; Insensitivity to DC components and current transformer saturation;

High degree of stability even with different degrees of CT saturation; Restraint feature against high inrush currents with 2nd harmonics; Restraint feature against transient and steady-state fault currents with 3rd or 5th

harmonics;

Measuring principle

differential current: Idiff = |I1 + I2|stabilization or restraining current: Istab = |I1| + |I2|

healthy generator:

Idiff = |I1 + I2| = |I1 I1| = 0Istab= |I1|+ |I2| = |I1| + |I1| = 2 |I1|

Internal fault:

Idiff = |I1+ I2| = |I1 + I1| = 2 |I1|

Istab =|I1|+ |I2| = |I1| + |I1| = 2 |I1|

Tripping characteristic

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Thermal characteristic:

Tripping characteristic: unbalanced load

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6.9 Impedance protection ANSI 21

Phase selective overcurrent fault detection with undervoltage seal-in; Calculated from measured generator voltage and generator current 1 impedance zone Z1, 1 overreach zone for zone extension Z1B (controlled via signal

Generator C.B. is ON), Polygonal tripping characteristics

Tripping characteristic impedance protection

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tot

j

G

N

)m(

NG

Nj

)N()N(

j

)G()G()tot()G()m(

)tot(

)N()G()m(

)m(

)m()m(

Zm

eU

U1

1Z

;eUU;eUU);IZm(UU

Z

UUII

I

UZ

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=

====

==

=

6.10 Out of Step Protection ANSI 78

In extensive high-voltage networks, short-circuits which are not disconnected quickly enough,or disconnection of coupling links which may result in an increasing of the couplingreactance, may lead to system swings. These consist of power swings which endanger the

stability of the power transmission. Stability problems result in particular from active powerswings which can lead to pole-slipping and thus to overloading of the synchronous machines.

Power swing detection Is based on the impedance measurement The trajectory of the complex impedance vector is evaluated. Trip decision is made dependent of the rate of change of the impedance vector and

on the location of the electrical centre of the power swing.

Equivalent of power swing

With :

where is the displacement angle between the generator voltage and the networkequivalent voltage. Under normal conditions, this angle depends on the load situation and isnearly constant. It fluctuates during power swings and can vary, in case of an out-of-stepcondition, between 0 and 360.

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Polygonal Out-of-Step Characteristic and Typical Power Swing Occurrences

An out-of-step condition requires, additionally, that the impedance vector enters a powerswing characteristic at one side and leaves it at the other side (loss of synchronism, cases and ). This is characterized in that the real component of the impedance (or its componentrectangular to the symmetrical axis P has changed its sign while passing through thecharacteristic. It is also possible for the impedance vector to enter and leave the power swingpolygon at the same side. In this case, power swing tends to be stabilized (cases and )

The resonance frequency for power swing is around 1.3Hz for most power grids.

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6.13 Overexcitation protection ANSI 24

increase of induction leads to saturation and eddy losses core heats up Calculation of the ratio U/f; Adjustable warming an tripping stage;

Characteristic selectable for calculation of the thermal stress by 8 value pairs

f

U

f

f

U

U

B

B

f

U~B

N

NMach

NMach

=

6.14 Underexcitation protection ANSI 40

maloperation of excitation system / step up transformer may result in a reduction ofthe excitation required to ensure system stability below a predetermined minimumvalue

Conductance measurement from positive sequence components; Multi step characteristic for steady state and dynamic stability limits

Admittance diagramm of a Turbo Generator (please compare with reactive capability ofgenerator)

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6.15 Overvoltage protection ANSI 59

serves to protect the electrical machine from the effects of impermissible voltageincreases

caused by incorrect manual operation of the excitation system, faulty operation of the

automatic voltage regulator, (full) load shedding of a generator Two-stage overvoltage measurement, evaluation of the highest of the three phase-to-

phase voltages

Setting: e.g. U> 115% UN / 4secU>> 140% UN / 1sec

6.16 Undervoltage protection ANSI 27

The undervoltage element measures the positive sequence voltage. Faults could be related to system stability problems It is used to ensure an open generator breaker in case of a total blackout, too. Setting: e.g. U> 70% UN / 4sec

6.17 Inadvertent energizing protection ANSI 50 / 27

Limit damages by accidental connection of the standing or already started, but not yetsynchronized generator by a fast actuation of the mains breaker.

Fault evaluation with voltage U< and current I>>

a) Trip after inadvertent energizing b) Unit connection

6.18 Breaker failure protection ANSI 50BF

monitors the reaction of a circuit breaker to a trip signal. To determine if the circuitbreaker has properly opened in response to a trip signal, one of the followingmethods is used to ascertain the status of the circuit breaker:

Checking whether the current in all three phases drops below a set thresholdfollowing a trip command,

Evaluating the position of a circuit breaker auxiliary contact. Opens a higher-level circuit breaker after a programmable time delay (breaker

failure),

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6.21.1 Trip Circuit Supervision with two binary inputs

Connection principle

No. Trip Contact CircuitBreaker

AuxCont 1 AuxCont 2 BI 1 BI 2

1 Open CLOSED Closed Open H L

2 Open OPEN Open Closed H H

3 Closed CLOSED Closed Open L L

4 Closed OPEN Open Closed L H

Condition table for binary inputs

Logic Diagram for Trip Circuit Monitoring with Two Binary Inputs

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Siemens AG

6.22 External trip coupling

up to four signals from external protection or supervision units can be incorporatedinto the processing of 7UM62 for recording and processing of external trips;

applied for trip by excitation system and for example from transformer Buchholz

protection and transformer temperature

Example:

Documents

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