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Presentation 6.1

OMICRONelectronics GmbH 2009 International Protection Testing Symposium

PTL: A solid basis for building customized line protection test standards

Eugenio Carvalheira / Michael Albert / Oliver Janke, OMICRON, Germany

Introduction

Relay testing has been changing over the years. The

technological evolution of protective relays and test sets

has driven these changes and the way how the tests

are performed. Protective relays have evolved from the

electromechanical to the multifunctional numerical

technology. The test sets have also evolved along the

time, from the passive to the solid state and dynamic

test sets [2].

Ten to twenty years ago the tests were performed by

the testing personnel almost manually. The relay testquantities were hand calculated and a passive test set

(comprised of resistive loads, mechanical phase shifters

and variable autotransformers) was manually operated.

The operating characteristics of electromechanical

relays were shaped by resistor, inductor and capacitor

networks while springs and levers defined the operating

times. A small number of parameters had to be checked

[4].

Nowadays modern test sets include electronically

regulated voltage and current sources and have the

capability to run automated tests controlled by computer

software [2]. This allows the realization of more

sophisticated tests. With the appearance of modern

multifunctional numerical relays the number of

parameters and the complexity of protection functions

have increased drastically. Knowledge about the relay

algorithms and functions are required for testing [3].

All this evolution of relays and test sets has a big impact

on the testing practices and on the definition of testing

standards. Which tests are necessary for our relay?

How can we increase the effectiveness and quality of

testing while saving time of protection engineers?

These are some questions that should be done whendeveloping a customized testing standard. This paper

will discuss how the use of the OMICRON Protection

Testing Library (PTL) can help you to accomplish this

target.

Keywords: protection testing, test standards, auto

reclosure, power swing.

Possibilities for standardization

As the diverse ways of testing has risen with moderntest equipment also the need for standardization

increased. The reasons for that are different testing

philosophies, historically grown testing approaches and

not at least different knowledge, opinions and skills of

the testing person. The advantages of a standardized

way of testing are:

- The test person saves time for developing a test.

- As all test plans include the same tests, the testing

quality can be better controlled and improved.

- Working together as a team is easier, as everyone

is working in a similar way. For example reading a

colleagues test protocol is easier, if it is formatted

in the same way and has the same order and

content.

- Company know-how can be added to the standard.

However there are different levels where unifying ofrelay testing can be realized. Mainly two types of test

standards can be differentiated on the field of

application:

- Standard for testing a dedicated protection function

- Standard for testing a dedicated protection

application (e.g. line protection for highest voltage)

An example of a standard for testing a dedicated

protection function is the definition of a test plan for

testing the transformer differential protection function. A

standard for testing this protection function can be:

- Configuration or stabilisation test

- Pickup test

- Operating characteristic test

- Trip time test

- Harmonics blocking test

The standard also should include the fault loops,

transformer sides or combinations of transformer sides,

which have to be tested. Additionally the number and

position of test shots have to be defined.

Within a company internal unification and standard-ization is getting more and more important. Additional to

the "How to test" demand of a test standard some

general points can be added:

- A test plan can contain general text information like

safety rules or telephone numbers.

- The wiring of the test equipment can be

standardized to fit for every relay of the protection

application.

- Announcement tests can also be integrated.

- A test with circuit breaker is done.

- The test protocol is unified.

The development of a standard strongly depends on the

testing philosophy of the test designer. As an example,

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Presentation 6.2


the standard way of testing a designated protection

function will be different if defined by a relay

manufacturer or by a utility engineer.

Protection testing philosophies

The testing practices and consequent definition of a

testing standard, which states how the protective relay

system should be tested, depends on different factors:

- Testing purpose

- Region / Company culture

First of all the reason for testing should be considered.

According to its purpose, the testing routines may be

divided into three different stages:

-

Factory or Type tests- Commissioning tests

- Maintenance or Routine tests

The factory or type tests are realized by the device

manufacturers or by the utilities when they select a new

relay type for an intended application. In a type test, all

the relay functions should be tested. It includes detailed

tests of the relay characteristics and algorithms to verify

that it works according to its specification.

The commissioning tests are performed to prove the

correctness of the protective relay system of an

installation before setting it into operation. The

requirement for detailed relay characteristic testing is

reduced in comparison to type tests. Tests should be

performed to check relay operation based on the setting

values. The correct operation of the whole protection

scheme logic should also be checked, e.g. through an

end-to-end test or an automatic reclose test with the

circuit breaker.

Maintenance tests are performed periodically or after

relay setting changes or firmware updates. The goal is

to verify that the relay is operating correctly and

minimize the risks of malfunction.

A second factor that influences the development of a

standardized test plan is the region or even company

culture differences. These cultural differences result in

different testing philosophies:

- Test of discrete protection functions as single

elements by re-routing their signal directly to a

relay output or test of combined elements taking

the resultant tripping characteristic of different

elements [4].

- A complete test should be performed after a relay

firmware update; or is it sufficient to rely on the

manufacturer information [4].

- Incorporation of some tests based on the history of

failures experienced by the company.

Independent of the testing philosophy used by the test

designer, the OMICRON Protection Testing Library

(PTL) provides a good basis for designing new testing

standards. The PTL items can be customized to fit thevariedly company requirements.

Customizing PTL

OMICRON provides preconfigured test plans for

specific relay types. These test plans contain a XRIO

converter to control the behavior of the template and to

build up the characteristics out of the relay settings. All

of these templates are summarized in the protection

testing library (PTL). Every PTL item consists of an

OCC file (called PTT, protection testing template) and aXRIO converter. The PTT contains tests for the main

protection function and the most important backup

functions [1] [3].

The PTTs are OMICRON's suggestions how the relay

can be tested. However customization may be required.

The test plans of PTL are based on the standard

features of the Test Universe software. Therefore the

users have the possibility to adapt the test plans to their

needs.

Adapting the XRIO Converter

The structure of the XRIO converters is shown in

Picture 1.

Picture 1: XRIO-Converter of the PTL.

The XRIO converter is divided in five different parts,

whereas the most important parts for customizing work

are:

- Relay parameter section

- Additional Information

- Template Controller

The XRIO converter contains the relay settings in the

same structure as in the relay manufacturer software.

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Presentation 6.3


The relay characteristics are automatically calculated at

the given parameterization.

The other parts of the XRIO converter must not be

changed by the user. These blocks (RIOplus and RIO)

are needed for the communication to the advanced test

modules of the Test Universe software.

Picture 1 shows the possibility to add a new block

(Customer specific). This block can be used for entering

additional data which is not recognized in the XRIO

converter, e.g. settings of protection functions controlled

by individual logic.

Adapting the PTT

The test plans provided by the PTL are prepared for

testing different parameter settings of a relay. This

automation is realized by using the LinkToXRIO

functionality, predefined test shots and the visualization

of the relay characteristic. To adapt the PTT to a test

standard it will be necessary to change the range of the

tests or the way of testing dedicated protection

functions.

Therefore the following mechanisms can very easily be

used by every user without influence on the automation

of other test modules in the test plan:

- Deleting unnecessary test modules

- Changing the predefined test shots- Copying test modules

- Inserting new test modules

The handling of the PTT does not differ from a general

OCC-file. So every functionality of the Test Universe

software can be used and it is possible to include every

test module which is needed to fullfill the testing

purpose.

The use of the import filter

Some relay manufacturer software supports the exportof the parameter settings. This export can be imported

in the XRIO converters of the PTL by using the import

filters also offered in the PTL. The customizing work

has to consider the mode of operation of the import

filters. These rules are recognized in the relay

parameter section by entering the correct IDs or

ForeignIDs of the relays.

The following chapter shows how to change and adapt

a given PTT to special needs.

Examples for PTL Customization

According to the user specifications or standards,

customizations of the test plan may be necessary as

illustrated in the following examples.

1stExample: Schweitzer SEL-421

This example shows the specification of a utility

including tests of auto reclose function (ANSI 79) in

their test plans for a SEL 421 distance relay.

The protection functions covered by the available PTL

item are [5]:

- 21 Phase/Ground Distance protection

- 50/67P Phase Instantaneous Overcurrent

- 50/67G Residual Ground Inst. Overcurrent

- 50/67Q Negative Sequence Inst. Overcurrent

- 51 Time Overcurrent

It is important to mention that the user may rearrange

the complete test template, change the predefined test

points or delete test modules if the test strategy does

not fit his demands.

Picture 2: Reclosing settings in converter

As it is described above, testing of the auto reclose

function is not supported. However, the user can find

the complete relay settings in the converter, even the

settings related to functions which are not supported

(see Picture 2). With the necessary data and also the

distance characteristic already available in the

converter, the addition of the new test is simplified.

Picture 3: Close Cmd signal in Hardware Configuration

First of all, the Hardware Configuration should be

checked to see if all necessary signals are available for

the test. For the testing of the auto reclose function, the

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Presentation 6.4


close command signal from the relay is needed to

evaluate the function's closing time. This signal should

be added as a binary input in the Hardware

Configuration and correctly routed to the relay during

the test (see Picture 3).

One option for this test is to use the State Sequencermodule to simulate a successful auto reclose cycle. The

states necessary to simulate a 1-shot re-closure are:

- Pre-Fault: simulates a nominal load condition; it

should be run for a time enough to guarantee the

auto reclose function goes to a reset stage.

- Fault: simulates a Zone 1 trip condition. This state

is triggered by the trip signal.

- Pole open interval: circuit breaker opened

condition; during this state the close command is

expected from the relay, that will trigger the

sequence to jump to next state.- Successful reclose: nominal load condition after the

circuit breaker has been closed.

The time between the circuit breaker opening and the

receiving of the close command signal can be

measured and automatically assessed by the module.

Picture 4: State Sequencer with LinkToXRIO

All the necessary testing parameters can be

automatically set in the State Sequencer module using

the LinkToXRIO functionality, as illustrated in Picture 4.

These links are done to the relay settings that are

already available in the converter. The definition of the

fault condition (State 2) is very easy since the distance

characteristic is already modeled by the converter. It is

only necessary to define the fault location relative toZone 1 impedance.

Picture 5: Detail and Impedance View of Fault state

The new created modules can be added to the test

template. The user can configure the module to be

enabled only if the reclosing function is enabled at the

specific site by using LinkToXRIO. If desired, other

modules can be added to test the auto reclose function

when it is used with two or more numbers of re-closure

cycles.

Picture 6: SEL 421 PTT with new Auto-Reclose tests

As the XRIO converter of the SEL 421 supports the use

of an import filter the tests of the auto reclose function

integrated in the existing PTT can also make use of this

feature. Changed relay settings will be updated

immediately in all test modules of the test plan.

2nd

Example: Siemens 7SA6x

In the second example the requirement of a utility to

test the Power Swing function (ANSI 68) of the 7SA6distance relay is described. As in the previous example,

the test will be based on the OMICRON PTT available

for this relay to take all the advantages provided by the

existing converter and template.

The protection functions covered by the Siemens

7SA6x PTT are [6]:

- 21 Distance protection

- 50/51/50N/51N Backup Overcurrent

- Switch onto fault (SOTF)

Testing of the 7SA6x Power Swing detection function is

not implemented in the PTT. However, the relay

settings for this function are built in the converter.

Picture 7: Power Swing settings in converter

The power swing detection in the 7SA6 relay allows theblocking of trips by the distance protection following

dynamic events which result in an oscillatory behavior

of the system. The power swing can also be set to trip

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Presentation 6.5


during unstable power swings, when system stability is

lost. Then, both blocking and tripping should be tested.

One option for implementing this test is to use the

NetSim module (network simulation module). NetSim

uses a numerical network model to simulate processes

in an electric power network, enabling testing underclose to realistic conditions. Different network

topologies are provided (called test cases). Two NetSim

modules can then be added to our template with the

correspondent test case for power swing blocking and

tripping simulations.

For the power swing blocking test, the test case "Power

Swing Synchronous" should be used (shown in

Picture 8).

Picture 8: Power Swing Synchronous NetSim test case

The line data necessary in the module is already

available in the converter (Power System data in DIGSI

software) and can be easily set using LinkToXRIO

functionality. This can be seen in Picture 9.

Picture 9: NetSim Line Data using LinkToXRIO

The data of the two sources are not available in the

relay settings. In this case, this data should be entered

to allow a correct simulation. A new block in the XRIOconverter can be created by the user to store the

additional data. Two new parameters are added to this

block for entering the short-circuit power of the two

source sides. Other three parameters are created to

calculate the impedances of both sides which are

necessary to be defined in NetSim. As shown in

Picture 10, these parameters are blocked (dark gray),

since formulas are defined to automatically calculate

their values. The formulas are based on the powers

defined in this block and other data already available in

the converter (like voltage, CT and VT ratios). The

resulting values are used in the sources tab(Picture 11).

Picture 10: New System Data block in converter

Picture 11: NetSim Sources Data using LinkToXRIO

In this test case, three states are simulated: pre-fault,

synchronous power swing and post-fault. During the

power swing state, the slipping sources does not fall

out-of-step and returns to a synchronous state.

Picture 12 shows the voltages and currents over time

while Picture 13 is showing the trajectory in the

impedance plane.

Picture 12: NetSim time signal view for power swing blocking

Picture 13: Impedance trajectory for power swing blocking

For the power swing tripping test, the test case "Power

Swing Asynchronous (multiple turns)" should be used.

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Presentation 6.6


Picture 14: Power Swing Asynchronous NetSim test case

The Line and Sources data are defined in this module

using LinkToXRIO in the same way as in the blocking

test. Also three states are simulated: pre-fault, unstable

power swing and post-fault. In the power swing state, a

complete pole slip (out-of-step) is simulated.

Picture 15: Impedance trajectory for unstable power swing

The 7SA6x PTL item is used as basis for the test plan

and the two new NetSim modules are added to the test

template as shown in Picture 16.

Picture 16: 7SA6x PTT with new Power Swing tests

An additional Pause module is also included to give the

testing personnel prior testing instructions (see

Picture 17).

Picture 17: Power swing test information using Pause module

The examples show that with a solid base it is possible

to enhance and optimize the predefined test templates

of the PTL and at the same time minimize the effort for

preparing the test plan.

Summary

The protection functions of modern numerical relays aremore complicated than in the older ones and the

number of functions is increasing with every new relay

version.

For this reason standardization of testing these

functions is getting more important. The traceability and

the interchangeability is an important factor for an

effective work.

With the PTL (Protection Testing Library), OMICRON

offers a powerful tool to realize standardized protection

testing within every company. As shown in two

examples it is very easy to adapt a PTL item to specialneeds. Through the open structure of every PTL item, it

is possible to change the given test plans to a

customized standard for protection testing.

Literature

[1] Training material PTL.T270.1 "Testing with the

OMICRON PTL (Protection Testing Library),

OMICRON electronics Deutschland GmbH, July

2009

[2] A Survey of Relaying Test Practices, IEEE Power

Systems Relaying Committee Report, January

2002

[3] B. Bastigkeit, OMICRON, How a library of Relay

Specific Test Templates Can Support the

Protection Engineer, OMICRON IPTS 2007,

Austria

[4] C. Araujo, F. Horvath, J. Mack, A Comparison of

Line Relay System Testing Methods, by National

Grid Co., FPL Seabrook Station, and Schweitzer

Engineering Laboratories Inc., September 2006

[5] SEL-421 Distance Protection Test Template User

Manual, OMICRON electronics GmbH

[6] 7SA6x Distance Protection Test Template User

Manual, OMICRON electronics GmbH

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