Power quality and proactive network monitoring...Content of the presentation • 1. Power quality in general (EMC) • Consequences of poor Power Quality • Economical impacts •

Marko Pikkarainen29.3.2012

Power quality and proactive network monitoring

Marko PikkarainenTampere University of Technology

The Department of Electrical Energy [email protected]

SET-1520 New Applications in Electrical Energy Engineering27.3.2012


Content of the presentation

• 1. Power quality in general (EMC)• Consequences of poor Power Quality• Economical impacts• Standard (EN 50160)

Power quality quantities

• 2. Some recent changes in the field of power quality• Flicker

• 3. Proactive power quality monitoring

Power quality in general

• Power Quality: The characteristics of the electricity at a given point on in electrical system, evaluated against a set of reference technical parameters (IEC 61000-4-30)

• Electromagnetic compatibility (EMC): The ability of an electrical equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment

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Consequences of poor PQ

•Poor power quality can have different effects. The range reaches from disturbing effect on human beings (flicker) up to consequences on operation of equipment. •There are long term and momentary effects. Harmonics and unbalance cause increased losses in the utilities equipment and reduce life time of components.•Momentary effects are a sudden malfunction or damage of a device. They commonly appear with the quality parameters such as: voltage interruption, voltage dips and transient overvoltage. •The most commonly reported symptoms of power quality phenomena are light flickering, circuit breakers tripping and computers locking up or restarting. Also some damages are reported due to voltage quality problems

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Economical impacts of power quality

The importance of power quality problems can be reviewed by its economic impacts.

•In the USA economical losses due to interruptions are estimated to be between 104-164*109 dollar annually. •Other power quality problems are estimated to have 15-24*109 dollar economic loss impact annually.• Gross domestic product of USA was 14 526*109 dollar (2010)

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Regulation and standardisation

There are several regulations, standards and laws that regulate the distribution utilities actions and design and use of electrical equipments• national laws and regulations• directives and standards• general guidelines by field of business

EMC standard• IEC 61000 series

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61000-1-x General

61000-2-x Environment •Description of the environment •Classification of the environment •Compatibility levels

61000-3-x Limits •Emission limits•Immunity limits

61000-4-x Testing and measurement techniques

•Measurement techniques •Testing techniques

61000-5-x Installation and mitigation guidelines

•Installation guidelines •Mitigation methods and devices

61000-6-x Generic standards

61000-9-x Miscellaneous All the rest

EN 50160

• Standard EN 50160 defines, describes and specifies the maincharacteristics of the voltage at a network user's supply terminals inpublic low, medium and high voltage AC electricity distribution networksunder normal operating conditions. (EN 50160)

Some problems :• Covers only normal operation and even for that case only during 95% of time

obligatory• For some power quality parameters only indicative values are given• EN 50160 is not EMC standard, compliance with EN 50160 standard doesn‘t

guarantee undisturbed operation of all devices• Describes maximum values or variations of the voltage characteristics under

normal operating conditions which can be expected by the customer at any place of the network

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Voltage fluctuations and flicker

• Flicker (PST, PLT) is the subjective impression of luminance variations of lightning as a result of voltage fluctuations. • Flicker is more a physiological than a physical value. • The flicker effect depends on: the amplitude of the relative voltage fluctuation and the repetition rate of the appearance of the voltage fluctuation. With the same frequency of the voltage fluctuation the flicker effect is directly proportionally to the amplitude of the voltage variation.• Flicker causes normally no damage of devices or an interference of their function. • PST and PLT occurs without dimension (pu). • The borderline was established laboratory tests with individuals. (for incandescent lamps)

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t

u (t)

regu larsinuso ida l

vo ltage fluctua tion

U

U

regu larrectangular

voltage fluctua tion

arb itra ryrectangu lar

vo ltage fluctua tion

U2

U

0.1

1

10

0.1

0.001

1

0.01

10

0.1

100

1

1000

10

10000 changes/min

100 Hz flickerfrequency

P =1st

[%]UU


Very common reason for customer complaints (it is easy to observe)

Origins for flicker:

• starting currents of induction motors, fluctuating torque of load (stone crusher), welding machines, electro heat devices with thermostat, Electric arc furnacesRemedial measures:• Increase short circuit capacity of the network• Starting current limitation• Smoothing of load torque• Avoidance of sharp load changes • Automatic welding machines, 3-phase instead of 1-phase welding machine• For EAFs: use of DC EAF, power-factor correction, use of dynamic compensation unitsLimits in EN 50160Under normal operating conditions, in any period of one week the long term flicker severity caused by voltage fluctuation should be Plt 1 for 95 % of the time.

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Under normal operating conditions excluding the periods with interruptions, supply voltage variations should not exceed ±10 % of the nominal voltage Un.In cases of electricity supplies in networks not interconnected with transmission systems or for special remote network users, voltage variations should not exceed +10 % / - 15 % of Un. Network users should be informed of the conditions.

Under normal operating conditions:• during each period of one week 95 % of the 10 min mean r.m.s. values of the

supply voltage shall be within the range of Un ± 10 %; and• all 10 min mean r.m.s. values of the supply voltage shall be within the range of

Un + 10 % / - 15 %.

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Voltage unbalance

In EN 50160 voltage unbalance is defined as a ratio of the negative sequence voltage and positive sequence voltage

Consequences of unbalance:• Increase of the losses in the grid components• Increase losses and vibration moments in electrical machines• Could increase non-characteristical harmonic currents of rectifier and

inverter

Sources for unbalance:• Non three phase loads (most of the loads in LV level / customer end)• Railways• Electric Arc Furnaces

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1

2

UU

k u1

2

II

I u

Voltage unbalance

Remedial measures•Increase short circuit capacity of the network (network strengthening)•Distribute single phase loads evenly between phases, use three phase loads•Disconnection via converter sets of a three-phase motor and a single-phasealternator•Use inverters to change three phase system to single or two phase system•Balancing using Steinmetz principle

Limits in EN 50160•during each period of one week, 95 % of the 10 min mean r.m.s. values of the negative phase sequence component (fundamental) of the supply voltage shall be within the range 0 % to 2 % of the positive phase sequence component (fundamental). In some areas with partly single phase or two phase connected network users' installations, unbalances up to about 3 % at three-phase supply terminals occur.

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Harmonics

When the waveform of voltage or current is not pure sine wave those can be modelled using Fourier transform method (in real life it rarely is)• Fundamental: Signal component that occurs with the line frequency • Harmonics: Signal components which frequencies are multiple integer of the fundamental• Interharmonics: Signal components which frequencies are not multiple integer of thefundamental (no limits in EN 50160)• Subharmonics: Signal components which frequencies are below the mains frequency (nolimits in EN 50160)• The classical harmonics-theory deals with frequencies from 0 Hz to about 2500 Hz (50 thharmonic, Bashir tell you more about higher frequencies)

Consequences of harmonics:• increase thermal and mechanical stress of the components and devices, increases gridlosses, might produce influence for ripple-control devices, might produce flicker byinterharmonics.

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Harmonics

Sources for harmonics:• Power electronics• Transformers, iron core inductor (in normal mode

effect negligible)• Electric arc furnacesRemedial measures:• Power factor correction (passive, active)• Central filter systems (also distributed)• Changing of the mains circuits switching state, in

order to avoid resonances• Increase short circuit capacityLimits in EN 50160• during each period of one week, 95 % of the 10 min

mean r.m.s. values of each individual harmonic voltage shall be less than or equal to the value given in table

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Odd harmonics Even harmonics

Not multiples of 3 Multiples of 3Order h

Relative amplitude uh

Order h Relative amplitude uh

Order h Relative amplitude uh

5 6,00 % 3 5,00 % 2 2,00 %7 5,00 % 9 1,50 % 4 1,00 %

11 3,50 % 15 0,50 % 6..24 0,50 %13 3,00 % 21 0,50 %

17 2,00 %

19 1,50 %

23 1,50 %

25 1,50 %

NOTE: No va lues are given for harmonics of order higher than 25, as they a re usually small, but largely unpredictable due to resonance effects.

Frequency

The mains frequency is global quantity in interconnected networks. The change in frequency is result of change between power production and consumption. In interconnected networks with controlled reserves, the frequency shows only low fluctuation.• Frequency rise (more production than consumption)• Frequency falls (more consumption than production)

Consequences of abnormal frequency:• clocks that run synchronously to the line frequency may face some problems• Produce mechanical stresses in turbines• Affects to uncontrolled synchronous- and asynchronous drives

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Frequency

Remedial measures• Use of reserve power plants• Load shedding

Limits in EN 50160Interconnected 49,5 Hz - 50,5 Hz during 99,5% of a yearnetworks 47 Hz - 52 Hz during 100 % of the time

Islanded 49 Hz - 51 Hz during 95% of a weeknetworks 42,5 Hz – 57,5 Hz during 100 % of the time

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Voltage dips and swells short voltage interuptions

Temporary reduction of the r.m.s. voltage at a point in the electrical supply system when the voltage falls below 90 % of the reference voltage

• voltage dip duration (from 10 ms up to including 1 min)• voltage dip residual voltage (minimum voltage)• swells are same as dips but voltage rises above 110 % of the reference

voltage

Consequences of voltage dips• Problems with programmable logic controllers• Problems with electronic devices (restarts of computers)• Problems with asynchronous motors (halt, antiphase)

Produces costs: shut down costs, standstill costs, restart costs, additional costs

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Voltage dips and swells

Sources for voltage dips• Faults• Motor starting• Transformer switching• Swells switching operations and load disconnectionsRemedial measures• Use of dynamic voltage restorer• Change of networks switching state• Improve grid reliability• Increase short circuit capacity of the networkLimits in EN 50160• The vast majority of voltage dips has a duration less than 1 s and a

residual voltage above 40 %. However, voltage dips with a smaller residual voltage and longer duration can occur infrequently. In some areas, voltage dips with a residual voltage between 90 % and 85 % of Uc can occur very frequently as a result of the switching of loads in network users‘ installations

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~ ~= =

~

fast thyri storswitch

PQ

grid load

rectifier

energystorage

inverte r

Interruptions

Definition• condition in which the voltage at the supply terminals is lower than 5 % of the

reference voltage (EN 50160)• prearranged, when network users are informed in advance; or• accidental, caused by permanent or transient faults, mostly related to

external events, equipment failures or interference. An accidental interruption is classified as:

• a long interruption (longer than 3 min);• a short interruption (up to and including 3 min)

Consequences of interruptions• Produces costs: shut down costs, standstill costs, restart costs, additional costsSources for interruptions• Normally, interruptions are caused by the operation of switches or protective

devices. (faults)• Maintenance of components

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Interruptions

Remedial measures• Decrease fault occurrence (overhead lines -> underground cables)• Install remote controlled components to grid (switch, isolator)• Build backup connection or backup power generation units for sensitive

customers

Limits in EN 50160• Under normal operating conditions, the annual frequency of voltage

interruptions longer than three minutes varies substantially between areas. This is due to, among other things, differences in system layout (e.g. cable systems versus overhead line systems), environmental and climatic conditions.

• The duration of most of the short interruptions may be less than some seconds. Indicative values, intended to provide readers with information on the range of magnitude which can be expected, can be found in IEC/TR 61000-2-8

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High frequency signals / Mains signalling voltages

Signal superimposed on the supply voltage for the purpose of transmission of information in the public supply network and to network users' premises. Three types of signals in the public supply network can be classified:• ripple control signals: superimposed sinusoidal voltage signals in the frequency

range 110 Hz to 3 000 Hz;• power-line-carrier signals: superimposed sinusoidal voltage signals in the

frequency range 3 kHz to 148,5 kHz (for PLC purposes, in some networks also frequencies above 148,5 kHz are used.);

• mains marking signals: superimposed short time alterations (transients) at selected points of the voltage waveform

Consequences of signalling voltages• EMC problems might occur: the operation of touch dimmer lamps might be

disturbed by PLC (power line communication)

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Transient over voltages

Short duration overvoltage usually with a duration of a few milliseconds or less

Consequences of transient over voltages• Breakage of devices and components

Sources for transient over voltages• lightning, switching or operation of fuses

Remedial measures• surge protective devices (For withstanding transient overvoltages in the

vast majority of cases, LV Installations and end users’ appliances are designed according to EN 60664-1.)

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Some changes in field of power quality

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Marko Pikkarainen 29.3.2012

Flicker sensitivity of compact florescent lamps

• Flicker is the subjective impression of luminance variations of lightning as a result of voltage fluctuations. Flicker is more a physiological than a physical value. The tests to produce the borderline of flicker were established in laboratory with individuals. This borderline is valid for incandescent lamps.• The result of the European Commission Regulation number 244/2009 is that incandescent bulbs will be gradually phased out from the market• Compact fluorescent lamps have different flicker response because the working principle is different • Flickermeter is able to detect voltage changes with appearing frequency from 0.05 Hz to 35 Hz.

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25



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Flicker measurement in future

• Same measurement method but new limit • Valid for traditional voltage changes• Interharmonics are not affecting to result

• New measurement method with modified lamp characteristic and old limit (1 pu)• Interharmonics could be taken into consideration

• Replace flicker with rapid voltage changes

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u(t)

variable gainT = 1 min demodulation

PP

stlt

weightingfilterlampe -eye

H(s)squaring and

smoothingstatistical

evaluation

8.8 Hz 0.53 Hz0.05Hz 35 Hz

UU (t) U

U (t) weighted

% % %²

momentaryflickerlevell P f

Proactive power quality monitoring

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Traditional power quality monitoring

• Power quality measurements are based on centralized measurements from MV level

• Outages, frequency problems and voltage levels in MV level have been spotted from centralized measurements

• From LV side power quality is usually monitored with case specific measurements

• customer complaints and clarification requests• There has not been available comprehensive and continuous power

quality information over entire distribution network • The novel AMR technology and distribution substation automation has

increased the power quality awareness• Of some power quality quantities:

• Interruptions, voltage levels, harmonics...

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Power quality monitoring in the future

•Power quality monitoring will need information from voltage from each customer connection point

• AMI is obvious system to produce the needed data•In addition of voltage measurement a proper current measurement could provide critical information to power quality monitoring application

•AMI could short the clarification time of power quality disturbances and make it more efficient

•If the clarification time decreases also it could speed up decisions and acts of how to decrease the effect of disturbance

•Savings•Also customer satisfaction level could increase

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Proactive power quality monitoring

Goal:• To detect power quality and reliability problems automatically• To detect the most probable reason for power quality problems

automatically• To predict the behaviour of different power quality quantities in the

future • Short term prediction (operations)• Long term prediction (planning)

• To improve power quality, to operate network optimally

Methods:• efficient utilization of static and dynamic information• optimization of network monitoring processes and information

management

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New model of proactive network monitoring32


Network Information

Customer Information

Measurements(AMR, condition

monitoring, PQ, weather,

relay data, etc.)

Future scenarios

Standards,recommendations

•Analysis•Detection of potential problems

•Priorisation

Immediate actions

Proactiveactions

Operation

Maintenance

Planning

Example of proactive network monitoring, Flicker

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Network Information

Customer Information

Future scenariosMeasurements

(AMR, condition monitoring,

PQ, weather, relay data, etc.)

Standards,recommendations

•Analysis•Simulation•Detection of potential problems

•PriorisationPlanning

REFERENCES

H. Renner, M. Sakulin, Power quality, Textbook to lecture “Power quality and supply reliability“

H. Renner, “Power quality and supply reliability“, Lecture notes

M. Pikkarainen, B. A. Siddiqui, P. Pakonen, P. Verho, S. Vehviläinen, 2011, “Vision of Power Quality Monitoring and Management in Future Distribution Networks”, Conference paper, CIRED 2011.

M. Pikkarainen, P. Nevalainen, P. Pakonen, P. Verho, 2010, "Practical Case Study: Measurement of Power Quality Problems Caused by Common New Loads “, Conference paper, NORDAC

“The Cost of Power Disturbances to Industrial & Digital Economy Companies”, 2001, Consortium for Electric Infrastructure to Support a Digital Society.

European Commission Regulation, 2009, implementing Directive 2005/32/EC of the European Parliament and of the Council with regard to ecodesign requirements for non-directional household lamps, No 244/2009.

Rong Cai, 2009, “Flicker Interaction Studies and Flickermeter Improvement”, Dissertation, Eindhoven University of Technology, Netherland

EN 50160, 2007, “Voltage characteristics of electricity supplied by public distribution networks”, Standard

L. P. Frater, N. R. Watson, “Light Flicker Sensitivity of High Efficiency Compact Fluorescent Lamps”, Power Engineering Conference, 2007. AUPEC 2007. Australasian Universities

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Thank you for your attention

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Documents

Power quality and proactive network monitoring...Content of the presentation • 1. Power quality in general (EMC) • Consequences of poor Power Quality • Economical impacts •