2 transmission schemes 2010

8/2/2019 2 Transmission Schemes 2010

1/29

Transmission Schemes Part 12 Limited

Introduction

Some Terminology's in Power system Protection

Protection system

Complete arrangements of Protection equipments & protectionSystem based on a protection principal (IEC 60255-20)

Protection Equipment

A collection of protection devices (relays, fuses, etc.). Excludedare devices such as CTs, CBs, Contactors, etc.

Protection Scheme

Collection of protection equipment providing a defined functionand including all equipment required to make the scheme work(i.e. relays, CTs, CBs, batteries, etc.)

LEGENDS-

CT- Current transformer

VT- Voltage transformer

TE- Telecommunication equipment/Teleprotection

DC- Direct current

CB Circuit breaker


2/29


Introduction

Topics covered

Overview of different types of schemes

Different principles & philosophies of Protection schemes

Different elements of Protection Schemes

Engineering practices used by different utilities

Factors to consider for engineering

Simple & reliable

Ease of Maintenance

Economical

Integration of protection equipments and correctoperation of the Protection relays depend upon thescheme design


3/29


Different types of Protection

Feeder ProtectionCurrent Differential

Distance Protection

Phase Comparison

Directional Earth Fault

Over Current & Earth Fault

Circuit Breaker Failure

Thermal Over Load Protection

Voltage Protection

Transformer Protection

Biased Differential Transformer Protection

Over Current & Earth FaultRestricted Earth Fault Protection

Standby Earth Fault Protection

Over Flux (V/F Protection)

Transformer Mechanical Protection

Circuit Breaker Failure

Busbar Protection

High Impedance Busbar Protection

Low Impedance Busbar Protection

Reactor Protection

Differential Protection

Over Current Protection

Restricted Earth Fault Protection

CB Fail Protection

Voltage Protection


4/29


Current Transformer arrangements

Feeder two Main & Back up protections

Generally above 132 kV Levels

Main Protection Relays with the same Principles or different (Distanceor Current differential)

Backup Protection providing coverage for uncovered faults by the MainProtection and delayed trip for unclear remote faults

Current transformer connections to Main 1 & Main 2 from independent

cores

Voltage transformer connections are to be supervised by fuse failuresupervision relays

Built in functions for Main &Back up protection will have the risk that acommon relay element failure (e.g. the power supply) will resultin loss of both the protections

Bus BAR arrangements can be

Double Bus Bar

Double Main &Transfer

Double Main cum Transfer

One & A Half Breaker Scheme

Mesh Corner layout


5/29



Feeder single Main & Back up protections

Generally up to 132 kV levels

Bus BAR arrangements can be

Single Main & Transfer

Double Bus Bar


6/29



One & A Half Breaker System (4 CT Arrangements)

The main protection will be connected by the currenttransformers on Main CB & Tie CB in parallel

Separate Stub bus connection is not required LineIsolator interlocked over current will be used to protectthe Stub Bus area if the feeder is not on live

Four sets of CTs are sufficient to cater for the complete

protection

Economical


7/29Transmission Schemes Part 18 Limited



Ratio of CT can be selected to circuitrating

No problem of matching parallelconnected CTs

Separate Stub bus Protection is available

For a Fault between the Tie CB & Bus 2side Tie CB Isolator bus 2 CB will havedelayed tripping



Current transformer arrangements


CTs will be there on both side of the Tie CB ,

except the connection to the Stub Bus protection

all other protection remains same as five CTarrangements

Over lapping Stub bus protection CT on the BusTie CB



Current transformer arrangements

Bus Coupler & Bus Section CT arrangements



Tripping Overview Example of two Main & transfer feeder schemes

MTR Main Trip relay



Tripping Arrangements

Protection Systems will be grouped in two different

systems Group A & B Both systems will be connected with different DC supplies

for redundancy & to enable protection system

maintenance with the equipment live

Group A & B will be electrically separated & physicallysegregated except relays associated with the CBs

Direct Inter trip receive contacts are duplicated in both theGroups A & B

Main 1 & Main 2 Protections give trip impulses to Single

Phase trip units of respective CB Poles & All otherprotections give trip impulses to three phase trip units ofrespective Breakers



DC Supply Arrangements

Each bay will have dual DC supplies for protection &

control purposes with individual DC supervision systems DC Supply one is for Main 1 protection relays &

respective trip circuits and control schemes,

DC Supply two is for Main 2 & respective trip circuits,Backup, Bay control system and CB auxiliary supplies

In addition to this one separate DC circuit may be providedfor alarm & signalling purposes

Separate DC circuit will be provided for Busbar protectionscheme

Dual DC supply arrangements can be feed from the sameBus or different bus

Different Battery arrangements

Single Battery with Single Float ,Float & Boost charger

Double Battery with Two independent chargers



Supervision

Continuous Supervision of the protection devices /

important elements required

Trip Circuit

Master Trip Relay

DC Supply & Main Protection Relay

MTR MAIN TRIPRELAY



Supervision Trip Circuit Supervision

1. Lamp Method

2. TCS using Relay

PR- Protective relay

TC- CB Trip coil

52 a & 52 b CB Auxiliary contacts

A, B, C - Trip Circuit supervision relays



Supervision

Trip Circuit Supervision

3.Implementation using numerical relays

The Connection of relay A should be made in such a way that it detects the discontinuity of Tripcircuit. It is desired to have the trip circuit supervision relay to be as a last equipment in the circuit)

The Trip circuit healthy contact is wired on circuit breaker closing circuit to make sure the CB tripcircuit is health/available to trip

The alarm supply should be independent of tripping supply so that the indication is obtained in theevent of a failure in the tripping supply



Supervision Master Trip Relay Supervision

The Tripping relays are important components of thetrip systems

DC Supply will be supervised by a No Volt relay for eachtrip relay

DC Supply & Main Protection Relay Supervision Both the DC supplies will be supervised

For Static & Numerical multifunction relays it is veryimportant to monitor the self supervision watch dogcontacts, to indicate any failures occurring in the relaysinternal circuits

Normally closed watchdog contact are used for remotealarms

MVAX11 or MVAX12 relays are generally used for triprelay supervision & DC supply supervision relays areconnected at end of wiring run



Inter tripping Types of Inter tripping

Direct tripping

Permissive tripping

Blocking scheme

Direct Inter tripping

To ensure that protection at both the ends of faulted circuitsoperate to isolate the equipment

Some instance of Direct Inter tripping

CB Fail protection operations or faults between CB & CTs

Operational Inter tripping for system stability conditions

Over voltage Direct trips on EHV Networks



Inter tripping



Inter tripping Points to consider

The system protection interface shall provide the DTT send initiationinputs from external trip contacts

DTT signaling equipment should have switching and test facilities.

Operation of the tripping outputs shall be conditioned by the lineDisconnector auxiliary switch on banked and teed circuits.

The trip output contacts will have sufficient rating to activate thefollowing

Master Trip relays

CB Direct trip coils if required

Alarm & CB fail initiation Circuits

Alarm outputs from the equipments

Signal Receive Signal Receive Trip relays operated

Signaling channel Equipment / Communication channel Faulty

Signal Send



Switches & LinksSwitches

Used to perform various control/Protection operations in the scheme

Broadly it can be classified in to standard & Special PurposeStandard switches examples

Protection In/OUT or Test Normal switch

Bus bar Protection In/Out

Auto Re closure In/Out

Intertrip In/Out

CB Trip/Close

AC or DC Supply Selector

Special Purpose switches examples

Trip transfer switch

Bus VT Selector switches for Distance protection schemes

Synchronizing selection functions



Switches & Links Links

To isolate certain functions/circuits without removing

any wiring & to carry out Maintenance activities

Examples

Alarm Isolation

Trip relay Isolation

CB Fail initiation blocking

Test terminal Blocks

To isolate the relays from the Primary Plant circuits(Current, Voltage, DC & Trip circuits)

It facilitates the short circuiting of CT secondary circuitsto allow the secondary injection testing of the relays



ON Load By Pass arrangements CTs Out side the By Pass Zone

Transfer buses are designed for on load bypassing of circuitbreakers

CB Maintenance can be done without Load interruption

The protection needs to be transferred to Transfer Bus Coupler &is done through Trip transfer switch

The following also needs to be selected

LBB of TBC is to be initiated.Auto Reclose initiation and lockout of TBC.

The line voltage has to be taken to TBC for synchronising


23/29


ON Load By Pass arrangements CTs in the By Pass Zone

Transfer buses are designed for on load bypassing of circuitbreakers for maintenance from the Main Bus to transfer Bus

CB & CT Maintenance can be done without Load interruption

Protection is not affected , so no trip transfer switch required

Inter tripping needs to be re routed to TBC


24/29


Voltage selection scheme

Required in double busbar Substations when Bus voltage transformers are used

Achieved using set of Voltage selection relaysVTs are not to be paralleled due to the fact that the difference in secondary voltagecan cause circulating current between the VTs cause the winding to over heat.

However for distance protection schemes momentary paralleling of VTs is essentialfor the protection stability

The schemes can be built using self reset or using electrical reset relays

In some cases the selection can be done manually through Selector Switches


25/29


Output Relays

Variety of electrical outputs provided in relays fortripping, interlocking and remote indication purposes

Majority of the applications employ self reset type contacts

Hand reset types are required when it is necessary tomaintain a signal or lockout condition.

Some of the protection relays having high speed trippingcontacts for direct tripping of Circuit breakers

Relay contacts are not designed to break the Circuitbreaker trip coil currents


26/29


National Grid Protection philosophy in UK Standard Solutions

The standard bay solution shall support the specified functionsappropriate to a Specific Plant type ( Feeder, transformer etc..)

Standard bay solutions shall be engineered in a way thatminimises the number of design variants

Each tier will have Plug & Socket arrangements with externalmounted in 19 rack system connected via pre-manufacturedcables to a marshalling wall box.

All inter panel wirings done through cables, The purpose ofthis is to minimise the amount of site work & Easy replacementof faulty unit

Each Main Protection tiers may have

Separate DC supply MCB

Test terminal blocks

Alarm & Trip Isolation links

Protection Test /Normal switch

Main Protection Initiation Test facilities

Auxiliary & Control Relays


27/29


National Grid Protection philosophy in UK

STANDARD NICAPTIER

Typical Protection Panel

NICAP- Numerical IntegratedControl & Protection

E i i d d


28/29


Engineering standards

General guidelines followed in Protection cubicaldesigns

Various standards followed by different utilities

Type of terminal blocks

Equipments symbols & Protection Device codes

Standard wire numbering for panels

Colour codes to represent the Mimic

C l i


29/29

Conclusion

Factors Driving the Engineering

Utilities Standards

System Requirements

Functions Vs Cost

User Preferences

The acceptability of various engineering practices must beevaluated on a case-by-case basis

2 transmission schemes 2010

Documents