2017 International Conference on Energy, Power and Environmental Engineering (ICEPEE 2017)

ISBN: 978-1-60595-456-1

Designing of PMU Tester in Smart Substation Based on Test Method

Li HE, Yu-fei TENG, Shi-lin FENG, Zhen-chao JIANG and Ming-zhong LIU

State Grid Sichuan Electric Power Research Institute

Keywords: PMU; Smart substation; Distribution characteristics; Test method; PMU tester.

Abstract. It lacks the effective ways to test the PMU in smart substation at present. The testing

method based on distribution characteristics of acquisition unit and concentration unit of PMU in

smart substations, is proposed to solve the situation of PMU of smart substation. Therefore, the

PMU tester belonging to smart substation is designed based on the fundamental requirements of

tester according to the methods proposed, and the vital points of designing are introduced and

emphasized to tackle the reliability of PMU. The method and technology raised and the PMU tester

designed in smart substation, in practical, could complete the test of accuracy of PMU, abbreviate

the procedure of complicated data disposal and test report composing. It ensures to ameliorate the

testing efficiency and validity on PMU of smart substation.

Introduction

PMU, based on the same time scale among the substations, could be used to measure the

amplitude and phase angle of voltages and currents, active powers and reactive powers. It is widely

applied in the area of WAMS application, state estimation, relay protection, area stability control,

system analysis and estimation, etc. [1-2]

. Thus, it is an essential device for security and stability of

power systems [3-4]

.

PMU uses highly precise clock synchronization to monitor, protect and control the power

systems based on the platform of dispatching and controlling by methods of transferring data to

dispatching and controlling center [5-6]

. However, traditional ways have already failed to meet the

needs of PMU testing in smart substation as the rapid evolution of smart substation is putting

forward [7-10]

. Therefore, it is necessary to raise modifications, and to develop new devices to test

the relative function of PMU [11]

. The precision testing of PMU, among these testing items, is the

most important [12-13]

. In practice, lots of verbose and unmanageable tests concern about precisions

of static and dynamic responses, which demand laborious work without guarantees of minimized

errors and maximum correctness [14]

.

According to reference [14] proposed recently, focusing on the installation characteristics of

PMU in smart substation, a new approach has been raised to test PMU. A new PMU tester in smart

substation according to this new approach has also been developed. The tester, which integrates

optional items of testing, could play a key role of close testing loop. The close loop could

implement the testing of static and dynamic response precision of PMU quickly. Eventually, the

tester automatically generates the testing report according the testing process.

Test Method of PMU

While acquisition unit of PMU is distant from concentration unit of the device, it is not achievable

to exert a PC client receiving the data from concentration unit of PMU by using only one network

cable. Thus, two PC clients should be applied to test the PMU, among one of which sends data to

acquisition unit of PMU, the other receives data from concentration unit of PMU. From there, each

PC clients could generate the data documents labeled time. Finally, the data documents are imported

to tester software for processing and testing reports would be generated automatically. Figure 1

shows the detail principle of connections on PMU testing.

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PC client 1

PMU testerAcquisition

unit of PMU

Concentration

unit of PMU

Time

synchronic

device

Network cable

Optical fiber

Optical fiber

Opical fiber

Optical fiber

Optical fiber

PC client 2

Optical fiberNetwork cable

Figure 1. Test schematic of PMU.

Derived from figure 1, the close loop testing method is suitable for special condition of

installation of PMU. The testing method could be implemented by 2 PC clients, one sends PMU

data to acquisition unit and the other receives data from concentration unit of PMU.

Design of PMU tester

Analysis of Function on PMU Tester

As mentioned above, the effects of PMU tester are functioned with three aspects: to send data to

acquisition unit of PMU, to receive data from concentration unit of PMU, and to deal with data and

automatically generates report. In this section we shall elaborate analysis of function needs about

PMU tester incorporate with the test methods.

The PMU tester should be set up with data sending module, which simulates merge unit to send

time labeled data to acquisition unit of PMU by optical port.

Data receiving module, which accepts the time labeled data from concentration unit of PMU by

cable, should be set up within the PMU tester. The tester software should simultaneously analyze

the data and implement the job of comparison.

GPS module should receive the accurate time label correctly, as well as synchronize between the

PMU acquisition unit and concentration unit.

The software of PMU tester should work on comparison between sending data and receiving data

then generates the report. The sending data and receiving data are generated by PC client

respectively, so they should be imported in software to be processed. The test report is further

generated based on the results of calculation.

Hardware Structure of PMU Tester

Major components of the PMU tester: ARM, DSP, DSP and synchronic circuits. The hardware

structure is shown by figure 2.

PC client ARM & DSP

FPGA

Unit of data

processing

distribution & fiber

port distribution

8 fiber port

6 FT3 fiber ports

acquisition unit of

PMU

Synchronic circuit

concentration unit

of PMU

PMU tester

switch value

Figure 2. Hardware structure of PMU tester on smart substation.

Shown in figure 2, ARM plays a role in communication with PC clients in order to receive the

commands from the PMU tester and to send the sample value and GOOSE. Order received from

ARM is transferred to DSP, which produces the typical digital signal of power systems. The FPGA

receives data and orders from DSP through address bus, data bus and controlling signal. The data,

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which obeys IEC61850-9-2 protocol with accurate time labeling, is sent to acquisition unit of

pending PMU through the optical fiber.

The data received from PMU tester is transformed into the format of PMU2.0 [15]

and return back

to PMU tester after the packing and gathering processes in concentration unit of PMU. The

comparison and analysis of loopback data between sending data marked with time label are drawn

by software calculation.

Software Structure of PMU Tester

The Windows XP platform is embedded as interface of the PMU tester. The interface of PMU tester,

which administrates the whole function of tester, has advantages of facility and user friendliness.

The user of PMU tester could integrate the items of PMU testing in the software of PMU tester and

setup the standard of testing tolerances.

The PMU tester is designed and developed by the idea presented in figure 3 according to actual

condition of smart substation and close loop of testing principle on PMU in previous sections.

configurate the PMU

tester in PC client

In span of t1+△t，PC client 1

sends IEC61850-9-2 data

PC client 2 analyze the

absolute time and testing

phasor

Store the data as the

phasor format of

△t→V(I)

both files are imported in

PC client, calculate the

error according to the time

mark and value

generate the report based

on the test and

calculation.

start

end

PC client 2 receive data

from concentration unit of

PMU

Test complete?

Generate the sending file in PC client 1,

while generate the receiving file in PC

client 2. both files are produced with

time mark.

Force t1=t1+△t

yes

no

Figure 3. Flow chart of PMU tester on smart substation.

Starting test with initializing t1, the PMU tester is due to send data with IEC61850-9-2 style to

acquisition unit of PMU after one cycle of △tn (n=1,2…). Then data sent will be transformed into

the format of Ethernet protocol by PMU. It would be added with △tn to continue the test unless the

test is stopped manually. The data results file would be generated if the test ends. Due to differences

between data sent and data received for PMU tester, it is crucial to analyze the data with different

styles. The charts of process on PMU data with different style analyses is demonstrated by figure 4.

Sychronic frameThe number of

frame

ID of concentration

unit of PMUsecond

Quality of time

scaledata

16 bit check of

CRC

△t1△t2

Absolute

time t1

Absolute

time t2

Absolute

time t3

The format of

IEC61850-9-2 data

The format of

concentration unit of

PMU

include frequency, amplitude,

angle and variation of

frequency and so on

start point of test Point of first cycle

…

2 byte 2 byte 8 byte 4 byte 4 byte 14 byte 2 byte

Figure 4. Comparison of message analysis on PMU of substation.

In the circumstance of distant connection between acquisition unit of PMU and concentration

unit of PMU, 2 PC clients should be applied to send data and receive data respectively with files in

format of data sent and data received. After the test, the files should be imported in software of

PMU tester, which analyzes the time, header, tail and valid data to work out the errors.

According to reference [14], the errors of voltages and currents is defined by

1

100%N

mi si

i d

xm

X X

XE

N

(1)

Among equation (1), Exm is total error measurement; Xmi is the value of ith measurement；Xsi is the

actual value of ith measurement; Xd is basic value. The basic value of voltage is fixed to 70V. The

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basic value of currents is 1.2A while the rated value of secondary side of current transformer is 1A.

Similarly, the basic value of currents is 6A while the rated value of secondary side of current

transformer is 5A. The basic value of power is defined as 3 times of multiplication of basic value of

voltage and basic value of current.

The definition of angle, frequency and change rate of frequency is demonstrated by

1

N

mi si

im

Y Y

EN

(2)

Exm is error of measurement; Ymi is ith value of measurement; Ysi is ith actual value of measurement;

N means times of measurement.

The test report is obtained by test and calculation with Word 2007, which includes basic

information of PMU, environment of test and results of test.

In conclusion, based on the method and PMU tester developed, the test steps of PMU in smart

substation are listed below:

Step 1: implement the close loop connection according to the test principle of chart.

Step 2: import the SCD file of smart substation to the PMU tester.

Step 3: set up the input/output configuration and component message based on SCD file of smart

substation.

Step 4: connect the PMU and PMU tester, complete the items of PMU tester.

Step 5: click the start button to test the PMU automatically and finish the process, then generate

the test report automatically.

Analysis of Test Case

Background of Test

The PMU tester has been applied to a 500kV smart substation of 2/3 style. There are 2 transformers

and 4 line outlets in the smart substation.

Test on Part 500kV of Smart Substation

Take an example of a 500kV line to elaborate the static and dynamic response error of voltage and

current. According to section 1.2, 2 PC clients are used in data sending and receiving.

Set up the standard of measurements on static and dynamic test as Un is rated voltage, In is rated

current. The test results as sub values demonstrated here below are only listed in the form of typical

currents and voltage (static test) and amplitude modulation (dynamic test).

Table 1. Test results of static current and voltage on 500kV line of smart substation.

Items sub-items standards results errors

Ua (V)

10%Un 10%In 5.7735 5.7723 0.0017

50%Un 50%In 28.8675 28.8667 0.0011

100%Un 100%In 57.7350 57.7334 0.0023

Angle of Ua (°)

10%Un 10%In 0.0000 -0.0286 0.0286

50%Un 50%In 0.0000 -0.0286 0.0286

100%Un 100%In 0.0000 -0.0286 0.0286

Ia (A)

10%Un 10%In 0.1000 0.0999 0.0056

50%Un 50%In 0.5000 0.4998 0.0168

100%Un 100%In 1.0000 0.9996 0.0297

Angle of Ia (°)

10%Un 10%In 0.0000 -0.0286 0.0286

50%Un 50%In 0.0000 -0.0286 0.0286

100%Un 100%In 0.0000 -0.0286 0.0286

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Table 2. Test results of 0.1 amplitudes modulation on 500kV line of smart substation.

items standards results errors

Ua (V) 52.3152 52.3052 0.0145

Ub (V) 63.4630 63.4722 0.0133

Uc (V) 52.7471 52.7365 0.0153

Angle of Ua (°) 0.0000 -0.1776 0.1776

Angle of Ub (°) -120.0000 -120.1722 0.1722

Angle of Uc (°) 120.0000 119.8341 0.1659

fundamental frequency (Hz) 50.0000 50.0000 0.0000

Rate of change on

frequency(Hz/s) 0.0000 -0.0010 0.0010

The test items are passed according to the test results. In fact, the displays of acquisition unit of

PMU about measurement are corresponding to dispatch and control center. In conclusion, the PMU

tests results of smart substation based on the method and the PMU tester are valid and reliable.

Comparison of Test

With same tests items performed in section 3.2, the PMU tester is applied to PMU which is made by

2 manufactures with the same standards mentioned in section 3.2. The test results are given by

Tab.3.

Table 3. The comparison of test results between two PMUs produced by different manufactures.

items standards results of

man.1

results of

man.2

Errors of

man.1 (%)

Errors of

man.2 (%)

Ua (V) 57.7350 57.7334 57.7321 0.0023 0.0041

Angle of Ua (°) 0.0000 -0.0286 0.0308 0.0286 0.0308

Ia (A) 1.0000 0.9996 0.9994 0.0297 0.0500

Angle of Ia (°) 0.0000 -0.0286 0.0290 0.0286 0.0290

0.1Hzmodulation (Ua) (V) 52.3152 52.3052 52.3192 0.0145 0.0057

0.1Hzmodulation (angle of Ua) (°) 0.0000 -0.1776 0.1344 0.1776 0.1344

From the table, the items tested of both manufactures are qualified. The static test accuracy of

manufacture 1 is better than that of manufacture 2 while the dynamic test accuracy of manufacture 2

is better than that of manufacture 1.

By examining test span, data dealing time and report generation, prominent advantages of the

tests based on the method and PMU tester on smart substation are seen. Authentic automation and

intelligence of the test have been achieved from a principal level.

Summary

The essay raises the method that suits for PMU of smart substation according to the characteristics

of PMU. Based on method and function needs, the PMU tester of smart substation is developed and

researched. Introduction of crucial steps in the development have been emphasized. The tests of

voltage and current accurate about the static and dynamic tests could be implemented fast and

correctly. It surely decreases the amount of works on data processing and report writing, and

improves the effectiveness and correctness on the tests of PMU in smart substation.

According to the field tests of PMU on a new 500kV smart substation, the PMU tester is a

powerful, flexible, user-friendly device, which would guarantee reliable operations of smart

substation. The application of PMU tester developed would greatly improve the quality of domestic

wide area measurements, and ensure the security of smart power systems.

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