Reles de Proteccion II

Secondary distribution protection relaysAre you familiar with:c the precautions to be taken in installing them?c in commissioning and maintaining them?

date

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WHAT YOU NEED TO REMEMBERThere are two types of protection device on the market:

c protection relays without auxiliary power supplywhich are generally integrated in breaking devices and requirespecific sensors and trip units.

c protection relays with auxiliary power supplywhich are used with standard sensors and trip units.

The implementation and use of these protection chains involveseveral phases:

c installation; c setting; c commissioning; c operation and maintenance. The approaches differ according to whether or not the relays havean auxiliary supply.

PROTECTION RELAYSWITHOUT AUXILIARY POWER SUPPLY

THE PROTECTION CHAINS ARE GENERALLY INTEGRATED IN THE BREAKING DEVICES

There are two types of protection chain according to the type of protection (phase-to-phase fault, phase-to-earth fault).

They are simple to implement and use, but still requirea few precautions.

Secondary distribution protection relays

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The relays are designed to be integrated in the breaking devicesin the factory. They are insensitive to electromagnetic disturbances.The power needed to operate the relays is supplied by the networkitself via specific current sensors.

The low-power trip unit fits the characteristics of the output relay.

The sensors are suited to the protection system (relays andtrip units); these sensors are capable of delivering the powerneeded to operate the trip unit. Their transformation ratios fit the relay settings.The sensor (current transformer) characteristics are defined to protectthe relays when short-circuits occur.

Only specific sensors may be used. The use ofconventional sensors is liable to destroy the relayinputs when a mains short-circuit occurs.

The trip units must match the characteristics of the relays and breaking devices, or else there is a risk of a failure to trip.

Relay

Trip unit

Phase-to-phase fault

Breaking device

Relay

Trip unit

Phase-to-earth fault

Corebalance

CT

Breaking device

Sensors Sensors

PROTECTION RELAYSWITHOUT AUXILIARY POWER SUPPLY (contd)

THIS TYPE OF PROTECTION CHAIN IS SIMPLE TO INSTALL

Installation precautionsThe devices are simple to install, however we advise you to take the following precautions: c follow the connection instructions and recommended wire positioning;c comply with grounding connections when necessary;c check the choice of low-power trip unit and sensor connection mode(according to ratings); c check the crimping of lugs and clips, tightening of the screws andpresence of all the protection accessories supplied with the relay.This guarantees resistance to vibrations and disturbances; c and, of course, comply with the protective relay installations rules(refer to the installation manual of the relay concerned).

THE PROTECTION CHAIN IS FACTORY-TESTED IN TWO STEPS


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RelayCurrentinjection

box

Trip unit

Testzone

Corebalance

CT

Sensors

These sensors are optional, see MT Partenaire C.3.1


box

ChronometerTrip unit

Testzone


Corebalance CT

Sensors

2 - Checking of the operation of the protective relay and trip unit The injection of current at the relayterminals simulates a fault.

The tests are carried out in the factory using specific test facilities(particular current injection boxes). Generally speaking, the teststake into account the tolerance limits of the sources, measuringinstruments and protection chain. The calibration and appropriate choice of test facilities are essential.The factory tests guarantee the quality of the protection chain.

1 - Checking of the sensors The installation, connection and operationof the sensors are checked by injectingcurrent into the primary circuit.


THE DETERMINATION OF THE SETTINGS IS A JOB FOR SPECIALISTS

To correctly define the relay settings for an installation, it is essentialto call in a protection specialist (network protection study, see appendix 2).

Setting of the protection chain: The protection settings must take into account:c operating conditions of the network to be protected;c standards in effect in secondary distribution;c discrimination requirements;c protection chain tolerances;c transient phenomena or interference (transformer no-load energisingcurrents, parallel transformers or networks,....);c technical characteristics of the components to be protected (overheating, harmonics, non-sine wave currents, altitude derating,);c

The protective devices are implemented in 4 steps:c definition of sensor ratings;c determination of sensor wiring;c choice of types of protection curves and values (setting current and time delay);c saving of the parameter settings of each relay to facilitatemaintenance.


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Warning! Relays do not have the same dielectricwithstand conditions as switchgear. It is importantto comply with the test conditions announced,which may require disconnection of the protectionchain during switchgear testing.


box


Testzone


Corebalance CT

Sensors

COMMISSIONING IS QUICK

Since the protection chain is factory-tested with the switchgear,commissioning operations are limited to:

c checking of protective relay tripping at characteristic pointsaccording to the specified settings by injecting current into thesecondary circuits of the sensors.

At the same time, the installation of the protection chain, the setpoints, time delays and circuit breaker tripping times are checked.The checking measurements must take into account the tolerancelimits of the sources, measuring instruments and protection chain.The calibration and appropriate choice of test facilities are vital.(Block diagram similar to the second factory test).

c added to this check are the tests stipulated by local procedures.


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OPERATION AND MAINTENANCE ARE SIMPLIFIED

The protective relays are simple to use. If tripping occurs, the relay is simply charged again after the origin of the fault has been eliminated. When a fault occurs, the simultaneous openingof the 3 phases guarantees effective protection of the loads.

Maintenance tests are generally carried out an a yearly basis.Specific equipment is used to test the relays without disconnectionor tripping of the circuit breaker.

If a relay is faulty, it should be replaced by an equivalent relay, takingthe usual safety precautions. The precautions depend on the utility,for example: de-energising of switchgear and protected equipment,customary complete isolation of feeder ways and earthing rules,

For information purposes, current sensor secondary circuitsshould never be disconnected on load (i.e. with the MV networkenergised).The commissioning procedures described above are necessaryafter all operations on switchgear relating to the protection chain.

Please note: this type of self-powered relay requires a minimumof operating power, which is attained for a sensor primarycurrent of between 10 and 20 Amps depending on the model.This criterion must be taken into account in the test values.

PROTECTION RELAYS WITH AUXILIARY POWER SUPPLY

THESE PROTECTION CHAINS ARE MADE UP OF STANDARDCOMPONENTS

Our digital relays are designed to be mounted very quickly on all typesof cubicles. Digital relays accept signals from standard currentsensors. Sensor performance affects the performance of the entireprotection system. These relays are insensitive to electromagneticdisturbances.


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Relay

Trip unit

Monitoringand

control systemCommunicationSensors

Core balance CTThese sensors are optional, see MT Partenaire C.3.1

All types of sensorsTo guarantee optimal performance of the protection system sensors,please refer to the CG0021X document (medium voltage protectionguide) and MT Partenaire: folder B. The design of our relays allows negligible consumption of the sensorsecondary circuits (1 to 25 mVA), but be careful not to overlook the consumption of the wiring. The use of a special current sensorconnection accessory enables the sensors to be disconnected on load (i.e. with the MV network energised) and without any othershort-circuiting system. A wide range of CT and core balance CTsensors may be connected to our relays. The factors which determine the choice of current sensors are:accuracy, current rating, power and size.For further information on the sensors, please refer to chapter B-1-3of MT Partenaire.

Trip unitOur relays operate with all types of trip coils. The choice of the typeof control, by shunt trip or undervoltage coil, may be parameterised.

PROTECTION RELAYS WITH AUXILIARY POWER SUPPLY (contd)

THIS TYPE OF PROTECTION CHAIN IS QUICKLY INSTALLED

Installation precautions These devices are simple to install; all it takes is a simple rectangularcut-out in the door of the LV compartment of the cubicle.However, we recommend that the following precautions be taken:

c comply with the connection instructions, type and positioning of therecommended wires; c comply with the grounding connections when necessary; c check the choice of connection mode in accordance with the desired setting ranges and the types of sensors used; c check the crimping of lugs and clips, tightening of screws andpresence of all the protection accessories supplied with the relay.This guarantees resistance to vibrations and disturbances; c and, of course, comply with the protective relay installations rules(refer to the installation manual of the relay concerned). Disconnectable relays enable prefabricated cabling and immediateinstallation of the relay in the cubicle.


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THE PROTECTION CHAIN IS TESTED IN TWO STEPS

1 - Checking of the sensors The installation, connection and operation of the sensors are checkedby injecting current into the primary circuit.


box

Trip unit

Testzone

Corebalance

CT

Sensors



box


Testzone


Corebalance CT

Sensors

2 - Checking of the operation of the protective relay and trip unitThe injection of current at the relay terminals simulates a fault.

Generally speaking, the checking measurements must take into accountthe tolerance limits of the sources, measuring instruments and protectionchain. The calibration and appropriate choice of test facilities areessential. The writing of a test procedure based on the commissioningprinciple described above improves the quality of commissioning.


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THE DETERMINATION OF THE SETTINGS IS A JOB FOR SPECIALISTS

To correctly define the setting characteristics, it is essential to callin a protection specialist (network protection study, see appendix 2).

Setting of the protection chain:The protection settings must take into account:

c operating conditions of the network to be protected;c standards in effect in secondary distribution;c discrimination requirements;c protection chain tolerances;c transient phenomena or interference (transformer no-load energising currents, parallel transformers or networks,) ; c technical characteristics of the components to be protected (overheating, harmonics, non-sine wave currents, altitude derating,);c

Proper use of our protection systems is made by:

c the choice of the performance of the sensors and connection wiring;c the choice of sensor ratings;c the choice of the sensor connection mode (sum of currents or residual current measurements via specific corebalance CTs,);c the choice of types of curves according to the application andprotection values;c the choice of the operation of any indication/automation/discriminationdigital inputs/outputs (program logic suited to the application:transformer, motor);c the saving of the parameter settings of each relay to facilitatemaintenance.


COMMISSIONING IS EASY

Commissioning operations are reduced since our digital relaysperform all the metering and protection calculations with analoginput values, which are continuously self-calibrated, to confirm theoperation of the entire protection system. At the same time, the setpoints, time delays and circuit breaker tripping times are checked,within the announced tolerance limits. The calibration and appropriatechoice of test facilities are vital.


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date

04/00

- C32 -

revised

04/00

Warning! Relays do not have the same dielectricwithstand conditions as switchgear. It is importantto comply with the test conditions announced,which may require disconnection of the protectionchain during switchgear testing.


box


Testzone


Corebalance CT

Sensors


OPERATION AND MAINTENANCE ARE SIMPLIFIED

The relays are easy to use. If tripping occurs, the relay is simplycharged again after the origin of the fault has been eliminated.Optional settings may be used to latch fault tripping and for remoterelay resetting.

Depending on the model, integrated metering functions provideinformation on currents, tripping currents, These measurements may be accessed directly with the relatedmeasurement units (current in A, breaking current in kA,).

The presence of an integrated, continuous self-testing systemimproves relay up-time through real time indication of failures. If a failure occurs, the relay may be very quickly and simplyreplaced by an equivalent relay, taking the customary safetyprecautions. The precautions depend on the utility, for example: de-energising of switchgear and protected equipment, customarycomplete isolation of feeder ways and earthing rules,

Systematic relay checking procedures can therefore be lightened.

The commissioning procedures described above are necessaryafter all operations on switchgear relating to the protection chain.


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APPENDIX 1

PROTECTION STUDYPRINCIPLE

Protection studies are carried out in two steps: c a protection plan study, prior to the order; c a protection coordination study, generally carried out when the order is placed.

1 - Protection plan studyThis preliminary study consists of proposing protective deviceswhich meet the needs of the electrical network. It includes: c the limits of the study, according to the elements available; c the overall philosophy of the protection plan, which may be basedon assumptions when applicable; c a list of the protective relays required, accompanied by operatingrecommendations.

It is very important for the protection plan study to be carried out asearly as possible in a project since it provides the information neededto choose the appropriate protective devices and may indicateoperating assumptions linked to the particular characteristics of thenetwork. In addition, it is a powerful specification tool for Schneider.It may be carried out using: c a single-line diagram of the electrical network; c a description of the installation operating conditions and constraints;c technical characteristics of the network components when available:cables, transformers, generators, motors;c and may be accompanied by a technical sales proposal for a protection coordination supply.2 - Protection coordination studyThis study gives a comprehensive description of the protectionsettings to be made in order to guarantee tripping of the breakingdevice closest to the fault, while keeping the fault-free parts energised.It is used to complete the choices of protective devices made at the time of the protection plan study, by: c a presentation of the objectives and limits of the study;c a technical description of the network to be designed, with theproposal of operating assumptions or characteristics when applicable;c calculation of short-circuit currents at characteristic points;c a presentation of the protection plan with the fault discriminationprinciples;c the protection setting chart: curves, set points, time delays,It is carried out in several chronologically complementary steps: c collection of technical data relating to all the network componentsand operating modes;c calculation of short-circuit currents at different points in the network;c determination of the setting values;c a report comprising: calculation assumptions, curves, operationsimulations and protection setting sheets. This study, which represents a commitment on Schneiders part and entails a large investment, must be valued in the framework of the project order.


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Training courses are available, the references of which you may find on the MV INTRANET site. They cover: c protection plan study;c protection coordination;c MV network calculation using SELENA software.

Documents

Reles de Proteccion II