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21, rue dArtois, F-75008 PARIS C2-211 CIGRE 2006 http : //www.cigre.org

IPS/UPS WIDE AREA MEASURING SYSTEM

B.AYUEV, P.EROKHINE, Y.KULIKOV *

SOCDO for UESRussia

SUMMARY

This paper aims to outline the purpose of the Wide Area Measuring System (WAMS) for the integratedand unified power systems (IPS/UPS) of the Commonwealth of Independent States (CIS) and Balticcountries.The WAMS provides information needed for on electric power system (EPS) behavior in both transientsand steady state condition estimation.This paper defines technical requirements for phasor measurement units (PMU) that allow to quantify,compute, and archive phasor quantities of both emergency and pre-fault conditions. The PMU consists of a multifunctional measuring transducer and a communication server installed at the substations to providefor frequency, voltage, voltage phase-angle and power flow capacity measuring in any number of substation connections to the EPS.The WAMS has the following three-ties control structure: the first level - multifunctional measuringtransducers and communication server installed at the EPS substations, the second level automated work stations (AWS) allocated in the Interconnected Dispatch Office (IDO) of the Unified Electric Systems(UES) of Russia and dispatch centers of CIS and Baltic countries, the third (the highest) level AWS of System Operator Central Dispatch Office (SO-CDO) of UES.The paper outlines the principles of measuring and computing basic operating parameters: active andreactive power, frequency, voltage phase-angles in the power system nodes , which are recorded andtransmitted to the higher control levels. The operating parameter measurement accuracy indexes arespecified. The most important of them are: frequency 0.001 Hz, voltage phase-angle one degree and

power 0,5%.The approaches to determining the expedient locations of the PMUs in EPS are presented as well. Thesynchronized measurements should cover the entire territory of CIS and Baltic countries. The PMU shall

be installed in major load nodes, power stations and substations, to make it possible to verify and adjustthe calculating model of IPS/UPS. The installed PMUs have to make it possible to measure intersystem

power flows for estimating various control area behavior and for controlling secondary frequencyregulators performance.This paper defines study trends on monitoring results usage for better quality of IPS/UPS conditions

control. Monitoring of electric power system dynamics provides an additional opportunity to estimatestatic and dynamic stability, allows to validate calculating models, enhances state estimation, facilitatesaccident analysis and simulation exercises.

KEYWORDSPhasor measurement unit, Transients, Dynamic performance, Synchronized measurement, Low frequencyoscillation.

* E-mail: kulikov.y@so-cdu.ru

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1. INTRODUCTION

An essential progress has been there in the development and application of the so-called Wide AreaMeasuring Systems (WAMS), meant for measuring regime parameters in major electric power systems(EPS). These WAMS are widely used for both to verify calculating models and to solve issues pertaining

to information support of EPS operation control. Their appearance allowed to eliminate shortages of information regarding electromechanical transients. This information is essential for an adequate analysisof EPS dynamic performance.In spite of the fact that duration of transients determined by speed-torque characteristics of electricalmachines is measured, as a rule, in seconds, these transients qualitatively define further system

performance transition to a new steady condition or to emergency state. More accurate modeling of transients will make it possible to specify transmission capacity limits regarding lines and sections andadjusting the conditions areas.

Accuracy of electromechanical transients modeling depends on how accurately the calculating modeldescribes:

generator excitation regulators, turbine speed governors, load dynamic characteristics, protection and automation means.

Correctness of the models can be checked most effectively by comparing transients parameters measured by WAMS with similar calculating parameters under the same disturbance. Important here is tosynchronize the measured parameters using high precision signals transmitted once in a second from thesatellite positioning system. Then creating WAMS any emergency state in EPS plays the role of passiveexperiment. Studying the succession of such experiments will continuously bring new information ondynamic performance of the system. It will help to improve the calculating models, to solve the other tasksin order to make condition controlling more effective.

2. WAMS AIM AND TASKS

The purpose of WAMS is to absorb the new technology of transients parameter measurement, whichcomplements the remote measurement system existing in IPS/UPS.The technology makes it possible to improve condition control quality of the EPS dynamic performancestudy.

An in-depth experimental study of electromechanical transient phenomena, that form transient condition,makes it possible to attack the following new tasks regarding conditions quality improvement.

1. IPS/UPS calculating Model VerificationAny model need to be verified, especially one designed for the analysis of electromechanical transients.

Model verification involves a comparison of transient parameters (frequency, power flows) measuredsynchronously in various pour system nodes and branches with the parameters computed on its basis for the same disturbance.

Verification objectives: models of automatic control units; load models for specifying their static response and dynamic characteristics;

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IPS/UPS digital model as a whole.

2. Low Frequency Oscillations Verification and Analysis.

After frequency fluctuation detection it may be possibly to monitor low frequency oscillations (if occur)for 15 minutes. Analyzing oscillations amplitude and mode of its propagation allows to define the sourceof oscillation and to recommend damping measures.

3. Voltage Monitoring in Grid Nodes Load stability control and voltage collapse preventing; Defying actions to control adjustable reactive power sources; System voltage levels imaging.

4. Accident Analysis

Developing analysis methodology for system and regional level accidents; developing standard accidentanalysis procedures.

5. Electric power system state estimation.

Using voltage phasors of the grid nodes, where PMUs are installed, makes it possible to create the gridframing, to lessen the problem of convergence and to shorten the state estimation time. It is particularlyimportant for IPS/UPS in view of lengthy transmission lines.

6. Voltage Phase-Angles Monitoring at Grid Nodes

It becomes possible to specify transmission capacity limits regarding certain lines and sections bycomparing on-line calculated and measured voltage angles. Specifying the limits downward will make it

possible to lessen interruptible customers capacity if power shortage in the system occurs.Quick identification of asynchronous condition becomes possible, too.

In the course of WAMS operation and development, a number of other new tasks may appear. Their solution will become possible as a result of in-depth study of power system dynamics on the basis of transients parameters detailed analysis.

3. WAMS ARRANGEMENT

WAMS diagram is shown on figure 1. This diagram presents three levels of WAMS.

On the first level currents and voltages are measured with the help of the Power Measurement Unit(PMU).The received information on normal condition currents and voltages is transmitted to thecommunication server (CS), whose architecture is shown on figure 2, is synchronized with the help of

exact time markers and is archived. Communication server controls the current condition according to theconfiguration file settings, which define the signs of coming emergency.

Those signs are: Rate of frequency change. Configuration file setting can be defined in the interval of

(0.05 2) Hz/s with a step of 0.05 Hz/s. Voltage level, which can be significant in the interval of (0 120)%.

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Fig. 1. WAMS diagram

In case emergency condition is identified, its parameters are recorded in emergency archive. Emergencycondition record contains parameters of 100 seconds of pre-fault condition, and parameters of 1000

seconds of emergency condition.

The second WAMS level is in the regional WAMS control centers allocated in the IPS Dispatch Offices(IPS DO) of UES of Russia. The regional automated work stations (AWS WAMS) are allocated on thislevel.At each AWS WAMS software (SW WAMS) is used with the following functions:

Configuration files composition for CS. With the help of standard Windows interface a user can preset the following parameters for each PMU);

Ensuring authorized access to the archive data and configuration files on CS via dial-upconnection;

Computing of the following parameters on the basis of received archive data: Transforming data storage server format into Comtrade or Csv (comma separated values) formats.

Emergencyidentification;GPSsynchronization;

Parametersmeasurement

Configurationfile Emergencyarchive

Cyclicarchive

Level 1Power system

plants or substations

PMU 1 PMU 2 PMU N

-

-

Level 2RegionalControlcenters

-

AWS of CDOfor UES

Control center

CDO for UESControl Center Archive LANCDO for UES

Communicationchannel

AWS of RegionalControl centers Archive

Communication server

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GPS antenna

Fig. 2. Communication server architecture

Emergency state parameter information that was received from communication server is: processed and transmitted to IPS DO for further use; transmitted to the third level for integration and procession.

The third WAMS level, the Control Centre, is allocated at SO-CDO. AWS WAMS of the highest level isnested in it. Each emergency state parameters coming from regional WAMS control centers are integratedhere. Information on each accident is analyzed and is used to solve the above mentioned tasks. Controlcentre distributes information on each registered accident to IPS DO of UES of Russia and to dispatchcenters of CIS and Baltic countries.

4. PHASOR MEASUREMENT UNIT

Phasor measurement unit (PMU) is the key element of WAMS. The unit consists of one or severalmultifunctional measuring transducers (MMT), of communication server and exact time signal equipmenton the basis of GPS receiver.

The PMUs are devices meant for currents and voltages instantaneous value signals receiving, for measuring, computing, recording and subsequent transmitting the recorded information to the controlcentre. The unit records:

frequency (for each phase, with reliability information); angle between grid voltage sine wave and 50 Hz sine wave, referenced to exact time signals; active power in each phase and total power of three phases; reactive power in each phase and total power of three phases; total power in each phase and total power of three phases; phase voltages; time.

PMU is installed in power plant or substation, the information is recorded and transmitted off-line in theform of archives to users via switched phone lines. The possibility of separate channel on-line datatransmission is provided, too.

GPSconnector

Modem

Server

Ethernet 100 Mbit/sec

RS 232

RS 232

To PMURS 485

To PMU

Fiber optic line

Dial-u line

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PMU architecture is shown on the figure 3.

U A U B U C U 0 I A I B I C I 0

Voltage inputs Current inputs

Digital signal processor

Fig. 3. PMU architecture

Phase and neutral voltages from voltage transformers as well as phase and neutral currents from the testcoils of current transformers are applied to PMU input. Signal levels are conditioned in the incomingcircuits of the channels with input range of analog-to-digital converters (ADC) using resistance divider (for voltage signals) and current transformers (for current signals). ADC digital codes via optical isolationenter digital signal processor (DSP).

There are circular buffers of instantaneous signal values in DSP random-access memory. At one signalcycle 128 samples of instantaneous signal values are taken. Thus, if grid nominal frequency is 50 Hz,sampling frequency amounts to 6400 Hz.

In order to compute currents, voltages and powers at each master frequency, fast Fourier transform of 128- point ADC codes array is done as well as fundamental harmonic parameters are computed.

In order to compute frequency the appropriate voltage signal is digitized with frequency of 12800 Hz, isfiltered by digital low frequency filter and then voltage zero-crossing points are defined using zero arealinear approximation and signal cycle and frequency in Hz is computed. Such an approach ensuresfrequency determination accuracy of 0.001 Hz and power determination accuracy of 0.5%.

On the basis of current and voltage codes arrays the following parameters are computed:

1. Frequency is defined as value inverse to the time interval between the two nearest one directionzero-crossings of the signal.

2. RMS phase voltage and current are defined as rms values of main components, voltage andcurrent signals.

3. Voltage between X and Y phases is calculated using the following equation cos222 Y X Y X XY U U U U U += ,

where: U X, U Y are A, B, phase voltages, and is phase shift between them.

4. Active and reactive phase power are calculated by the following equations cos X X X I U P = , in I U Q X X X s= ,

Fiber opticline

ETHERNET PPS

Transducer Converter

From GPSconnector

to CS

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where: U X is voltage, I X is current, =U I is phase shift between voltage and current maincomponent.

5. Active grid power and reactive grid power are calculated as sums of A, B and C phase active andreactive power.

6. Voltage phase-angle is calculated by the following equation

= 36050)( 1ct t PPS Z X ,

where: t Z is a positive direction voltage zero-crossing point,

tPPS is zero-crossing point of the sine wave defined by second pulse. Angle calculationaccuracy amounts to 1.

5. PHASOR MEASUREMENT UNITS ALLOCATION IN IPS/UPS GRID.

In order to resolve issues faced by the WAMS, it is essental to allocate phasor measurement units inconsideration of the following requirements:

1. It is necessary to allocate the units in major generation centers at power stations andsubstations, to make it possible to verify and adjust digital models of IPS/UPS.

2. While allocating the units IPS/UPS stretched structure should be taken into consideration.Energy facilities equipped with phasor measurement units should be distributed from the East tothe West and from the South to the North of IPS/UPS. It will allow low frequency interzonaloscillations controlling and damping measures defying.

3. Recorders allocation scheme should make it possible to measure inter-area flows for estimatingvarious control areas performance.

4. It makes sense to install recorders at secondary frequency control power stations in order toestimate effectivness of this control.

In accordance with the above principles the locations for PMU installation shown on Fig. 4 were chosen.RUSSIA

1 LENINGRADSKAYA SS

2 Y UZ HNA YA SS3 KOL SKAYA NPP4 KALININSKAYA NPP5 SS KONOSHA6 SMOLENSKAYA NPP7 KOSTROMSKAYA TPP8 KURSKAYA NPP9 RYAZ ANSKAYA TPP

10 VOLGODONSKAYA NPP11 SS CENTRALNAYA12 STAVROPOLSKAYA TPP13 BALAKOVSKAYA NPP14 VOLGOGRADSKAYA TPP15 SS CHIRYURT16 Z AINS KAYA TPP17 ZHIGULEVSKAYA HPP18 SS BEKETOVO19 TROITSKAYA TPP

0 REFTINSKAYA TPP21 SURGUTSKAYA TPP-2

2 NAZAROVSKAYA TPP3 SS A LTA Y

24 SSS BRATSKIY5 SAYANO-SHUSHENSKAYA HPP6 KHARANOVSKAYA TPP

27 ZAGORSKAYA PSP8 TPP - 26 MOSENERGO

29 KASHIRSKAYA TPP

30 S S SALASPILS

31 LITOVSKAYA TPP

32 LUKOMLSKAYA TPP

33 SS MUKACHEVO

34 SS ZAP.UKRAINSKAYA

35 KHMELNICKAYA NPP

36 SS YUZH.-UKRAINSKAYA

37 SS DONBASSKAYA

38 SS EKIBASTUZSKAYA

39 UYZH.-KAZAKHSTANSKAYA T

BALTIYA

BELORUSSIA

UKRAINE

KAZAKHSTAN

UZBEKISTAN

KYRGYZSTAN

TADJIKISTAN

40 TASHKENTSKAYA TPP

41 TOKTOGULSKAYA HPP

42 NUREKSKAYA HPP

Fig. 4. Scheme of phasor measurement units allocation in IPS/UPS

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At the present time two POWERLOG recording devices operate in IPS/UPS WAMS. They wereinstalled and put into service at the end of April 2005 at Leningradskaya and Yuzhnaya substations (IPSDO of Ural). One of the examples of frequency recording made with the help of these devices is given onthe figure 5.

-60

-50

-40

-30

-20

-10

0

10

20

-200 0 200 400 600 800 1000 1200 1400 1600

,

/

30/11/05 11:29:19 . 4 (812 )

11:29:1511:29:1911:29:2311:29:2711:29:3111:29:3511:29:3911:29:4311:29:4711:29:5

F r e u e n c

c u

t - o

f f ,

H z

1 0 - 3

Fig. 5. Example of frequency recording made with the help of POWERLOG devices

Frequency meter with 1 secondsampling int.

Leningradskaya SS

Yuzhnaya SS

0,034 Hz

50 Hz cycles

The figure presents frequency registrograms recorded at Leningradskaya and Yuzhnaya substations on November 30, 2005, 11:29:19, in the time of Surgutskaya TPP-2 Unit No. 4 outage with load of 812MW.

As the figure shows, frequency meter measuring frequency with 1 second sampling interval does notreflect transients behavior, but it shows frequecy transition from one steady-state condition to another.

The presented registrograms allow to define experimentally overall network power-frequencycharacteristic:

Hz W f P

/23882034,0

812==

.

The registrograms also allow to estimate frequency oscillation cycles, frequency changes speed in thefirst time of swing, they allow to make a conclusion that there are no low frequency oscillations and tostart IPS/UPS calculating models verification.

BIBLIOGRAPHY

[1]. A.G. Phadke, Synchronized phasor measurements a historical perspective, ( Proc. IEEE PES Transmission and Distribution Conference and Exhibition 2002: Asia Pacific , October 2002, pp. 6-11.

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