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Development of Digital Protective Relay Tester under IEC61850CHEN Hui，CHEN Jiong-cong，LIANG Xiao-bing，YU Nan-hua

Electric Power Research Institute of Guangdong Power Grid Corporation，

Guangzhou 510080，P.R. China

E-MAIL:[email protected]

Abstract：The novel tester of digital protective relay based on

IEC61850 is proposed in this paper. The tester’s system

architecture is based on multi-CPU(CPU+DSP) high speed

hardware platform and real time operation system, it can

receive and sample the analog test data on time, which is then

converted into digital test data according to IEC61850 protocol.This tester also has the GOOSE trip signal which receive, the

analysis digital protection device sends out，and the circuit

breaker position contact signal encoding, the group frame,

transmits GOOSE the switch status to give the digitized relay

protection installment and so on. The transient simulation

testing platform is established, which can construct the electric

quantity of each test cycle in the period of protection’s operation

for sending under IEC61850. Due to the special recursive

algorithm and detecting the action of protection，the tester can

complete the closed loop experiment of tripping-reclose-tripping

forever. With the help of man machine interface, it ’s very

convenient to performance dynamic simulation test、 static

simulation test and transient simulation test. This tester also get

the fine results in the check of transient simulation test.

Keywords： IEC61850； digital protection ； digital relay

protection tester；closed loop experiment；real time operation

system

0. Introduction

In recent years, with the rapid development of integratedsubstation automation technology and communication technology,all kinds of unconventional optic-electronic measurement system

gradually replaced electromagnetic mutual-inductance measurementsystems. As the release of IEC61850 substation automation

communication protocol, the realizing digitization in substationhas become the future direction of substation automation technology

development[1]~[4].The use of digital protection will inevitable bring changes in

corresponding test, testing equipment and testing methods. After adopting new digital protection devices, because of getting

information and transmitting control commands in accord with the

transmission IEC61850 statute of communication network, it’sdifferent from traditional relay protection in test methods [5]~[8]. Inorder to ensure the safe and stable operation of digital substation, we

need to research on test methods, means and standard, on this basis,and develop new protective relay tester.

In the IEC61850 framework, the optic-electronic transformer

of process level will transmit digital sample value which is

converted internal by the optical fiber transmission to merge unit

(MU), the merge unit do synchronous processing after the secondaryside data collection from each optic-electronic transformer, group

frame according to IEC61850-9, and transmit to new digital protective relay device through the optical fiber [9]~[11].

This tester will simulate all the operation from optic-electronic

transformer to merge unit and from relay protection to intelligentswitch, it includes the functions and characters as follows:1.It canreceive multichannel analog signals(voltage and current), and group

frame one by one according to IEC61850-9 which is transmitted to

relay protection internal in real time[12]~[13].2.It has several digitalinput port and digital output port, the action signal from relay protection is transmitted to this tester in the form of GOOSE signal

or digital output, then the tester transmits the signal to switch devicein dynamic simulation laboratory or digital input in protection tester by its own digital output.3.With the internal simulation test platform,

it can finish the closed loop experiment according to the chosen

simulation fault module or fault situation[14]. This test system is baseon the existing power system dynamic simulation experiment whichconsists of mature and widely used technology, relay protection

static test and electro-magnetic transient simulation test, it makestraditional test methods play an important role in the new digital protection test, experiments and simulation analysis experiments.

1. Hardware design

This tester ’s global design of hardware framework is shown infigure 1-1.

dual-

port

RAM

DSP

Management

CPU

AD

sampling

module

Optical

fiber interface 1

Optical

fiber

interface 2

GPS

module

Optic-electronic

isola

tion

8 pairs

of digitalinput

terminal

Optic-electronic

isolation

8 pairs

of digital

output

terminal

Human-

machine

interface

Current and

voltage

converter

Dynamic

simulation

experiment

transformer

interface

Protection device

samples valuesinput interface

Protection device

GOOSE information

output interface

External

switch

interface

Protection

device trip

junction

Fig.1-1 The structure of tester hardware

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1.1 Processor

Due to the high requirement of test system for real-time data

processing, in order to realize the function of many complex tasks

for a test device, the selection of the core processor hardware iscrucial. This tester chooses the real-time system with combinationof low-power CPU and DSP, CPU is mainly responsible for the

management, man-machine interface and communication with

DSP，and DSP has the strong data processing ability and high speed,

which is mainly responsible for data acquisition, encoding frame,

sending and receiving GOOSE signals and communication with

CPU. The data communication between CPU and DSP is mainlyfinished through dual-port RAM on DSP.

1.2 A/D sampling and control

Considering the need of common unilateral and bilateral line protection, and double ring, three ring transformer protection test,it’s composed of 27 analog channels. This tester has to transmit the

input analog signals to conventional small electrical signals through

internal current and voltage convertor, then the signals go into 16 bitA/D sampling module which is controlled by FPGA on DSP board.

1.3 Digital input and digital output

Some digital protection trip signals are still generated by

traditional hard trip logic circuit, in order to detect open and closedhard junction state in the test procedure, 8 digital input channels areestablished, and every channel has corresponding anti-jammingmeasures.

According to IEC61850 protocol, the protection sends open

and closed digital signals to on-site intelligent switch to control the breaker by Ethernet network, so this digital protective relay tester must imitate some intelligent switch functions, namely, it will outputhard logic junction, and trip simulation test device or dynamic

simulation test system switches when it receives trip data frames,

this tester establishes 8 digital output channels in all.

1.4 Network communication

This digital protective relay tester is mainly communicatedwith protection by Ethernet network, which includes samplingtransmitting signals from tester to protection and logic signals from

protection to tester, such as tripping breaker signals, blockingsignals and warning signals.

2 Design thinking

This digital protective relay tester mainly consists of twoimportant functions: analog experiment and simulation experiment,it also includes management and analysis modules of experiment

data. There functions depend on the realization of IEC61850

protocol in sampling value transmission model and GOOSEinformation model transmission. According to the demand function,this tester is determined specific software and hardwareconfigurations after its function division. The management CPU

runs on the Windows2000 operation system which is famous with

stability, using Microsoft Visual c + + development environment,the human-machine interface management software is developedwhich embeds simulation experiment function and communicationfunction with DSP, and realizes data management and analysis in the

experiment or after the experiment. The DSP runs on the small

famous real time operation system-µC/OS, due to the different priorities in task and the real-time dispatch in management CPU, itcan finish all the tasks consequence in proper sequence. The

management CPU and DSP work in the form of principal andsubordinate style on the whole, management CPU is principal and

DSP is subordinate, executing task and obtaining parameters have toget the commands from management CPU at any time, if DSP need

to upload data forwardly, it has to send notice signals tomanagement CPU, and the management CPU will check DSPwhether there is command to deal with.

2.1 Analog experiment

In the analog experiment, the original analog output fromtransformer in dynamic simulation laboratory or relay protection

testing system is connected to this tester, then the tester will send

sampling value messages according to IEC61850 protocol to relay protection in real time one by one.

Considering the protection configuration and IEC61850 protocol requirements, analog experiment can complete on single,double side of current ,distance, longitudinal distance , longitudinalorientation and longitudinal differential line protection test, and

element protection test with two sides or three sides in transformer

protection.In order to record the condition of disturbance and protection

action in the experiment in real time, a disturbance recording tacheis added which records the changes of system voltage ,current,

analog input and GOOSE input in the experiment fully, to provide

proof for experiment and analysis of protection action. The structureof analog experiment is shown in figure 2-1.

The interface from dynamic

simulation experiment or

relay protection testing

system

Digital protective relay tester

Digital relay protection

Switch signals

Analog signals of voltage and

current

S w i t c

h s i g n

a l s

o p t i c a l f i b

e r

( G O O S E m

e s s a g e

t r a n s m i s s i o n

)

o p t i c a l f i b

e r

( s a m p l i n g v

a l u e


)

Fig.2-1 The structure of analog experiment

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2.2 Transient simulation

A transient simulation software test platform base on

ATP/EMTP is established in the tester, when the transient simulation

software runs in the background in test system, it can collecttransient current and voltage data from protected device, then thesedata is grouped frame and transmitted according to IEC61850

protocol, so the closed loop experiment is realized by detecting protection action and controlling the simulation calculator program,the structure of transient simulation is shown in figured 2-2.

Digital protective

relay tester Digital relay

protection

1. Send simulation experiment data

2.Change model and send

simulation experiment data

3.Change model again and send

simulation experiment data

Trip

Reclose

Trip forever

4.Change model at last and send

simulation experiment dataFault,Trip,Reclose,Trip forver

o p t i c a l f i b

e r

( G O O S E m

e s s a g e


)

o p t i c a l f i b

e r

( s a m p l i n g

v a l u e


)

Fig.2-2 The structure of transient experiment

Considering the ease-of – use for user operation, several kinds

of conventional pre-set system models are provided for users tochoose, such as line fault and transformer fault model. Meanwhile,

considering the user-opening in simulation experiment, thissimulation platform also provides all the simulation software

interface for user operation and management, if users define breaker node according to prescribed format, then a complex system modelwith their own need is built freely and put into normal operation.

2.3 Realization of sampling value transmission

To ensure the stability of the standard, IEC61850 uses

separation method of application and communication. The abstractmodel of sampling value is defined in 7-2, whose specific

communication service mapping(SCSM) is defined in 9-1 and 9-2.As the 9-1 protocol is carried out easier than 9-2 protocol, but lack

the flexible configuration like 9-2. Considering present applicationstatus, this tester will adopt the realization way of 9-1.

For the realization of 9-1 protocol, in order to ensure the hard

real-time of message transmission, without delay in communicationstack, the PDU at application layer will be encoded at presentation

layer, then it is mapped to data link layer and physical layer directly, both the transport layer and network layer is empty.(1) Application layer

According to achievement function for the tester, only 9

channel data in 12 will be realized in 9-1 protocol(because

three-phase current for protection is same with three-phase currentfor measurement), in this tester, 27 analog input channel is predefined, so before the application protocol data unit(APDU) is

placed in sending buffer, 3 application service data unit(ASDU) will

be connected for an APDU. The frame format of APDU is shown infigure 2-3.

TagASDU number

（3）Length ASDU1 ASDU2 ASDU3

APCI（Application

Protocol Control

Information）

ASDU（Application

Service Data Unit）

Fig.2-3 The APDU frame format of tester

(2) Presentation layer The data in sampling value buffer is encoded by abstract

syntax notation 1(ASN.1), the encoding format is TLV whichconsists of tag, length and value. But the APDU in 9-1 protocol uses

simple encoding, writing 0x80 for mark value, it represents thecontext class.

(3) Data link layer The Switching Ethernet is chosen, by default, the destination

of message is broadcast. The Ethernet type is set as 0x88BA, andthe priority service for message transmission is supported.

2.4 Realization of GOOSE information model

transmission

In order to ensure the reliability and real-time among kinds of intelligent electronic device(IED) communication with each other,

generic substation event(GSE) model is defined in IEC61850.Generic object oriented substation events(GOOSE) model as a kindof GSE, is mainly for trip command transmission in process bus. In

order to avoid the delay in communication stack and ensure the

rapidity for message transmission, a PDU is defined specially inapplication layer ,like sampling value transmission model, which ismapped to data link layer and physical layer without TCP/IP protocol, after encoded in presentation layer.

(1) Application layer Being different from sampling value model transmission, the

PDU on the layer uses ASN.1 standard, and it can ’t be simplified, soit depends on the support of MMS type to describe. For example,

the IMPORTS components need reference Data parameters in MMSto be described in ASN.1.(2) Presentation layer

Using ASN.1 basic Encoding Rules(BER) to encode PDU in

application layer.(3) Data link layer

It follows ISO/IEC 8802.3 protocol (Ethernet protocol),Ethernet type is set for 0x88B8, and the message transmission

priority service is support, whose default priority is 4. The particular

range of distribution of multicast addresses is allocated from01-0C-CD-01-00-00 to 01-0C-CD-01-01-FF.

2.5 Multitask scheme design under µC/OS

µC/OS is a kind of open source and free embedded operatingsystem for small and medium-sized system development [15], in

which a task is a thread and each task using CPU exclusively. Everytask is an infinite loop, it is always in the following one among 5kinds of states: dormancy state, ready state, running state, hang-up

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state(waiting for event to occur), and interrupted state. Theconversion relationship among 5 states is shown in figure 2-4.µC/Os can manage 64 tasks, and 56 tasks can be used by users.Each task priority must be different, on the condition of ready state,

µC/OS always run the highest priority task, 0 for the highest, and 63

for the lowest.

hang-up

state

interrupt

ed state

ready

state

dormancy

state

running

state

interrupt

Depriving

permission

waitting

Interrupt

stop

Getting CPU

permission

Registering

task

Canceling

task

Task is

cancelled

T a s k i s

c a n c e l l e d

Resuming

task

Fig.2-4 The status switch of mission

According to the functional need analysis, two system tasks,

and three user tasks are set.

(1) "Watchdog" task: This is the highest priority task in system level,it’s also the highest priority task in the entire system, setting priority5. To ensure the stable operation of the system, the system feed thedog timely, if suddenness occurs, "watchdog" program will send a

reset signal to the system.

(2) GOOSE signal received task: another system level task, setting

priority 6. Received from the network interfaces for GOOSE signalsand delivered to the user task 2 through the message queue.

(3) User task1: it checks and verifies the command from themanagement CPU in the dual-port RAM, the priority level is set to16, and it’s delivered to user task3 through message queue, then

informs user task3 download data from dual-port RAM.

(4) User task2: GOOSE signals is received from the message queueto analyze and output through output port. Its priority is set to 17.(5) User task3: it downloads and uploads data from dual-port RAM,its priority is set to 18.

Each task transferring relationship is shown in figure 2-5.

Watchdog

GOOSE

received

Checking and

verifying data from

dual-port RAM

Receiving and

outputing GOOSE

Downloading and

uploading data

from dual-port

RAM

Fig.2-5 task priority and transferring relationship

3 Transient simulation experiment test

To check the transient simulation function of the tester, we

take ” phase-to-phase fault section I input, and recloser input” for

example, control and schedule simulation experiment after establishing the power system electromagnetic transient simulationmodel, then input corresponding message to the digital protection in

accordance with IEC61850-9 protocol, and observe the action of digital protection.

After checking and testing, the simulation experiment results

is shown in table 3-1.

Table 3-1 The simulation experiment results

Setting value（Ω） Imposed conditions Action conditions

2.85 chronic fault2.669Ω

Protection tripping

without reclosing, asshown in figure 3-1

2.54Protection doesn’t

trip

2.85transient fault

2.669Ω

Protection tripping

with reclosing, as

shown in figure 3-2


trip

2.85transient fault

2.669Ω

Failure again after

reclosing

Protection tripping

with reclosing, then

tripping forever, as

shown in figure 3-3


trip

Fig.3-1 The phase current and voltage waveform describing Protection

tripping without reclosing


tripping with reclosing

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tripping with reclosing, then tripping forever

These waveforms tell that the transient simulation experimentfunction can complete closed-loop transient simulation testing ondigital protection successfully.

4 Conclusions

The emergence of IEC61850 to realizes interoperability

between relay protection of different manufacturers, so that moreand more Digital protection based on optical fiber communicationgradually replaced traditional protection devices.

Periodic testing on relay protection will play an extremely

important role to ensure the safe operation of power system,however, the traditional relay protection is impossible to completethe testing mission for digital relay protection. To establish a digital protective relay tester which suits new digital protection and inherits

the traditional testing method is important to ensure reliable action

on digital protection and comprehensive promotion of digitalsubstation.

The tester based on IEC61850 protocol, with two functions of

analog experiment and transient closed-loop simulation experiment,and can conduct a comprehensive digital test on digital protection.After being tested and used , it can meet using requirement in

worksite well.

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Biography

CHEN Hui(1985-)，male，JiangXi Nanchang，Han，Master ，the main

research directions for the Power System and its Automation。

Email:[email protected]

CHEN Jiong-cong(1979-)，male，GuangXi Wuzhou，Han，Master ，

the main research directions for the Power System and its

Automation。Email:[email protected]

LIANG Xiao-bing(1973-)，male，HeBei Tangshan，Han，Master ，

the main research directions for the Power System and its

Automation。Email:[email protected]

YU Nan-hua(1976-)，male，JiangXi Jiujiang，Han，Doctor ，the main

research directions for the Power System and its Automation。

Email:[email protected]

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