of 29
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
8/2/2019 2 Transmission Schemes 2010
2/29
Transmission Schemes Part 13 Limited
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
8/2/2019 2 Transmission Schemes 2010
3/29
Transmission Schemes Part 14 Limited
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
8/2/2019 2 Transmission Schemes 2010
4/29
Transmission Schemes Part 15 Limited
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
8/2/2019 2 Transmission Schemes 2010
5/29
Transmission Schemes Part 16 Limited
Current Transformer arrangements
Feeder single Main & Back up protections
Generally up to 132 kV levels
Bus BAR arrangements can be
Single Main & Transfer
Double Bus Bar
8/2/2019 2 Transmission Schemes 2010
6/29
Transmission Schemes Part 17 Limited
Current Transformer arrangements
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
8/2/2019 2 Transmission Schemes 2010
7/29Transmission Schemes Part 18 Limited
Current Transformer arrangements
One & A Half Breaker System (5 CT Arrangements)
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
8/2/2019 2 Transmission Schemes 2010
8/29Transmission Schemes Part 19 Limited
Current transformer arrangements
One & A Half Breaker System (6 CT 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
8/2/2019 2 Transmission Schemes 2010
9/29Transmission Schemes Part 110 Limited
Current transformer arrangements
Bus Coupler & Bus Section CT arrangements
8/2/2019 2 Transmission Schemes 2010
10/29Transmission Schemes Part 111 Limited
Tripping Overview Example of two Main & transfer feeder schemes
MTR Main Trip relay
8/2/2019 2 Transmission Schemes 2010
11/29Transmission Schemes Part 112 Limited
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
8/2/2019 2 Transmission Schemes 2010
12/29Transmission Schemes Part 113 Limited
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
8/2/2019 2 Transmission Schemes 2010
13/29Transmission Schemes Part 114 Limited
Supervision
Continuous Supervision of the protection devices /
important elements required
Trip Circuit
Master Trip Relay
DC Supply & Main Protection Relay
MTR MAIN TRIPRELAY
8/2/2019 2 Transmission Schemes 2010
14/29Transmission Schemes Part 115 Limited
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
8/2/2019 2 Transmission Schemes 2010
15/29Transmission Schemes Part 116 Limited
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
8/2/2019 2 Transmission Schemes 2010
16/29Transmission Schemes Part 117 Limited
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
8/2/2019 2 Transmission Schemes 2010
17/29Transmission Schemes Part 118 Limited
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
8/2/2019 2 Transmission Schemes 2010
18/29Transmission Schemes Part 119 Limited
Inter tripping
8/2/2019 2 Transmission Schemes 2010
19/29Transmission Schemes Part 120 Limited
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
8/2/2019 2 Transmission Schemes 2010
20/29Transmission Schemes Part 121 Limited
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
8/2/2019 2 Transmission Schemes 2010
21/29Transmission Schemes Part 122 Limited
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
8/2/2019 2 Transmission Schemes 2010
22/29Transmission Schemes Part 123 Limited
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
8/2/2019 2 Transmission Schemes 2010
23/29
Transmission Schemes Part 124 Limited
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
8/2/2019 2 Transmission Schemes 2010
24/29
Transmission Schemes Part 125 Limited
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
8/2/2019 2 Transmission Schemes 2010
25/29
Transmission Schemes Part 126 Limited
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
8/2/2019 2 Transmission Schemes 2010
26/29
Transmission Schemes Part 127 Limited
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
8/2/2019 2 Transmission Schemes 2010
27/29
Transmission Schemes Part 128 Limited
National Grid Protection philosophy in UK
STANDARD NICAPTIER
Typical Protection Panel
NICAP- Numerical IntegratedControl & Protection
E i i d d
8/2/2019 2 Transmission Schemes 2010
28/29
Transmission Schemes Part 129 Limited
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
8/2/2019 2 Transmission Schemes 2010
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