NETWORK OPERATING DIVISION

Operating EffectivenessTransmission Lines Protection Overview

Transmission LinesLH1 Protection OverviewOperating EffectivenessTraining & Development Hydro One Networks Inc49 Sarjeant DriveBarrie, OntarioCanada, L4N 4V9Phone (705) 719-3528Revised: November 4, 2008 The information in this document is for reference and is to be used as a guide only. The OE Training Section makes no representation or warranty, expressed or implied, that the information contained within is current. The information included is subject to change. It is solely your responsibility to ensure that you are using up-to-date documents, prints and information. Please notify the HONOC Operating Effectiveness Training Section of required updates and/or modifications.

ObjectivesThrough the use of this presentation participants will learn and understand Transmission Lines Protection. Emphasis is on:FunctionalityLimitationsInstructions and ProceduresSupport Services.ContTransmission Lines Protection

Transmission Lines Protection Overview.This presentation will cover:What transmission line protection is,Why the need for line protectionPrinciples of Operation ( Impedance), Different Operational zones Various types or schemesExceptions and AnomaliesTransfer Trip ChannelsPermissive Echo

Transmission Lines Protection Overview.This presentation will cover:LH1 configurationMicro-wave communicationsPower Line Carrier communications Fibre-Optic Digital communications Various types or schemes

Transmission Lines Protection Overview.We first must understand what a transmission line is.A transmission line is a high voltage circuit designed to carry a high amount of power over great distances between points.In some cases, this could be simply between two points as shown.

Transmission Lines Protection Overview.In more complicated configurations there could be:Multiple terminal stationsMultiple tap stationsCombinations of bothStation AStation BPower flowStation CStation DStation EStation F

Transmission Lines Protection Overview.To begin, we will look at a simple two ended circuitStation 'Z'Station 'Y'

Station 'Y' is a terminal that has two breakers on the circuit.

Station 'Z' is also a two breaker terminal for the circuit.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'The circuit that travels between Station 'Y' and Station 'Z' is a high voltage open air transmission line and as such is vulnerable to external influences.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'A fault could develop anywhere along the circuit causing fault current to flow between phases and/or to the ground.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'If there is no way of removing this faulted equipment from service, it will remain faulted eventually causing danger to the public, damage to equipment or even lead to a system wide disturbance.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'Protection systems will sense the fault and clear the circuit removing it from service.How does the protection system see the fault?

Transmission Lines Protection Overview.Simple two ended circuitThere are many ways in which faults can be detected. For transmission circuits the most common method is by using impedance .

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'At each end of the line there are both voltage sensing devices and current sensing devices Voltage (CVT)Current (CT)

Transmission Lines Protection Overview.Simple two ended circuitThese sensing devices monitor line voltage and line current on a continuous basis.

Under normal circumstances, the current will be at expected normal values and the voltage will be at the system normal.

Transmission Lines Protection Overview.Simple two ended circuitThe Impedance is derived by placing the voltage and current into a ratio using OHMS law.Impedance =VoltageCurrentVoltage = 230,000 voltsCurrent = 2,000 amps230,0002,000= 115 ohms

Current = 50,000 ampsTransmission Lines Protection Overview.Simple two ended circuitIf a fault occurs then these quantities will be disrupted causing the ratio to greatly change.Impedance =15000050000Voltage = 230,000 voltsCurrent = 2,000 amps230,0002,000= 115 ohms= 3 ohmsVoltage = 150,000 volts

Transmission Lines Protection Overview.Simple two ended circuitThe impedance is set to a certain range. Anything outside of that set range is considered a fault and will trip the circuit.230000 Volts2000 Amps150000 Volts50000 AmpsImpedance is outside of preset range Circuit will trip.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'The idea is to set the impedance such that for any fault on the line, the protections will see the changes in voltage, current and the ratio between them, covering 100% of the circuit.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'With this type of impedance detection, it would be very difficult to set the range to exactly cover 100% of the circuit due to tolerances in measuring equipment.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'The settings could be set:Too short. Under protectedToo long. Over protected

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'To correct this problem, specific zones of protection have been created.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'Zone 1 Is set to cover 80-85% of the circuit and is instant.Zone 1 80-85%Zone 2 Is set to cover 125-150% of the circuit but is generally a timed protection.Zone 2 125-150%

Transmission Lines Protection Overview.Zone 1 ProtectionStation 'Z'Station 'Y'Zone 1 Is set to cover 80-85% of the circuit and is instant.Zone 1 protection is generally known as Direct UnderreachZone 1 80-85%

Transmission Lines Protection Overview.Zone 1 ProtectionStation 'Z'Station 'Y'There is a limit to the protection when using Direct Underreach

Transmission Lines Protection Overview.Zone 1 ProtectionStation 'Z'Station 'Y'To overcome this limit communication is used between ends.Transfer Trip

Transmission Lines Protection Overview.Transfer TripStation 'Z'Station 'Y'At Station 'Y' both Zone 1 and Zone 2 will see the fault.Station 'Y' Zone 1 will trip instantly and send Transfer TripStation Z' will receive Transfer Trip and trip its terminal breakers instantly. Communication is accomplished by a variety of media but will not be discussed right now.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'There is another limit to the protection when using Direct UnderreachThe answer is to use another zone designed to reach all the way across the circuit.

Transmission Lines Protection Overview.Simple two ended circuitStation 'Z'Station 'Y'The protection will overlook into adjacent zones and could cause erroneous trips for faults outside of the zone.To prevent this Zone 2 protection is generally made to be timed.Zone 2 is set to see 125-150% of the circuit. Zone 2

Transmission Lines Protection Overview.We will look at Zone 2 independent of Zone 1Station 'Z'Station 'Y'Although Zone 2 is normally timed, there is a need for the Zone 2 protection to be instantaneous in order to satisfy rapid removal of the transmission circuit in a faulted condition.Zone 2 is set to see 125-150% of the circuit. Zone 2

Transmission Lines Protection Overview.Zone 2 ProtectionStation 'Z'Station 'Y'The rapid removal will be by using Zone 2 in a:Permissive Overreach scheme orDirectional Comparison scheme

Transmission Lines Protection Overview.Permissive OverreachStation 'Z'Station 'Y'In Permissive Overreach each Station has a timed Zone 2.If a fault occurs outside of Station 'Z' Zone 1 as shown above, only the Station 'Z' Zone 2 will see it.When the Zone 2 sees the fault it starts a timer (400ms).Zone 1 Limit

Transmission Lines Protection Overview.Permissive OverreachStation 'Z'Station 'Y'At Station 'Y' both Zone 1 and Zone 2 will see the fault.Station 'Y' Zone 1 will trip instantlyStation 'Y' Zone 2 will see the fault and will send Permission to Station 'Z' Zone 2 to trip instantly instead of timed.Zone 1 Limit

Transmission Lines Protection Overview.Directional ComparisonStation ZStation YIn Directional Comparison each Station has Instant Zone 2 coverage.If a fault occurs outside of Station Z Zone 1 as shown above, only the Station Z Zone 2 will see it.When the Zone 2 sees the fault it will trip instantly.Zone 1 Limit

Transmission Lines Protection Overview.Directional ComparisonStation ZStation YThis Instantaneous tripping, however, could pose a problem if the fault is outside of the protected circuit, but still inside the Zone 2 reach.The fault will be seen by the Zone 2 protection and will cause the circuit to erroneously trip for this out of zone fault.Zone 1 Limit

Transmission Lines Protection Overview.Directional ComparisonStation ZStation YFor example: The fault is located on the adjacent circuit.Station Z Zone 2 sees the fault and will trip instantlyOnly the circuits breakers of the faulted circuit should tripZone 1 Limit

Transmission Lines Protection Overview.Directional ComparisonStation ZStation YTo correct this a 3rd Zone is employedThis is the Directional Comparison element which employs a relay known as an OM3 relay and is set to look backwardsIf a fault occurs out of zone it trips its local breakers.The Zone 2 at Station Z will also see the fault and try to trip its breakers instantly.The OM3 will sense the fault as well and send a block signal to the opposite Zone 2 preventing it from tripping instantly.X

In some cases Zone 2 may be different in each Group, Group A Zone 2 could have Permissive Overreach where Group B could have Directional ComparisonEach Station has a Zone 1 Direct Underreach covering 80-85% of the circuit.Each Station Zone 1 will send Transfer Trip to opposite end station tripping its breakers.Each Station has Zone 2 covering 125-150% of the circuit.Zone 2 can be Permissive Overreach or Directional ComparisonPermissive Overreach is Timed unless it receives a Permissive Signal from the opposite end Zone 2 protection where it will then trip instantly.Directional Comparison is Instant unless it receives a Block Signal from the opposite end Zone 3 OM3 element where it will then trip timed.The protections will all have a Zone 1 Direct Under reach and Zone 2 will have either Permissive Overreach or Directional Comparison but not both.These protections are referred to as Groups. Each terminal will have duplication of each group and will be known as Group A and Group B.Each Group A and Group B are generally clones of each other with a Zone 1 Direct Underreach and a similar Zone 2. Station Y Zone 2Station Z Zone 2Transmission Lines Protection Overview.Protection reviewStation 'Z'Station 'Y'Station Y Zone 1Station Y Zone 3 OM3Station Z Zone 1Station Z Zone 3 OM3

Station Y Zone 2Station Z Zone 2Transmission Lines Protection Overview.Protection reviewStation 'Z'Station 'Y'Station Y Zone 1Station Y Zone 3 OM3Station Z Zone 1Station Z Zone 3 OM3This is what represents a basic line protection. Two Zones with a dual redundancy built in.

Station Y Zone 2Station Z Zone 2Transmission Lines Protection Overview.Station 'Z'Station 'Y'Station Y Zone 1Station Y Zone 3 OM3Station Z Zone 3 OM3The line switch at Station Y is OPENAs a result, Station Y Protections no longer see the circuit.Station Z Zone 1Lets look at when a terminal is Out of Service with its line disconnect open

Station Z Zone 2Transmission Lines Protection Overview.Lets look at when a terminal is Out of ServiceStation 'Z'Station 'Y'Station Z Zone 1If a fault occurs within the Zone 1, both Zone 1 and Zone 2 protections will see the fault and the Zone 1 will high speed trip the terminal at Station Z.Transfer Trip is Blocked to opposite terminal breakers

Station Z Zone 2Transmission Lines Protection Overview.Lets look at when a terminal is Out of ServiceStation 'Z'Station 'Y'Station Z Zone 1If a fault occurs outside of Zone 1, only Zone 2 protections will see the fault and will timed trip the terminal at Station Z.To correct this, the Permissive Signal is returned or Echoed back to the sending terminal and it will then trip instantly. This signal is keyed on at all times.B Pallets

Transmission Lines Protection Overview.CommunicationStation 'Z'Station 'Y'In order for the Protection signals to travel from one station to another, a communications medium is required.There are several types used today.Powerline Carrier- Wave TrapMicroWaveFibre-Optic Digital Tele-protection

Transmission Lines Protection Overview.Micro-Wave CommunicationStation 'Z'Station 'Y'A large microwave transmission tower is built at each end of the circuitMicrowave signals are transmitted between points.These are known as Guard TonesThe Guard Tones typically consist of 4 Transfer Trip Tones and 2 Permissive / Blocking TonesWe will call them

Transmission Lines Protection Overview.Micro-Wave CommunicationStation 'Z'Station 'Y'Transfer Trip Channel #1Transfer Trip Channel #2Transfer Trip Channel #3Transfer Trip Channel #4Permissive / Block Channel #1Permissive / Block Channel #2

Transmission Lines Protection Overview.Micro-Wave CommunicationStation 'Z'Station 'Y'The question arises.

Why so many Tones?Heres why.Microwave is:- influenced by external forces- a line of sight communication

Transmission Lines Protection Overview.Micro-Wave CommunicationStation 'Z'Station 'Y'Microwave is a radio signal and uses air to travel through.When the air changes properties, it distorts the path of the microwave. This is known as-Microwave Fading

Transmission Lines Protection Overview.Micro-Wave CommunicationStation 'Z'Station 'Y'Distortions in the air can be caused by changes in:Temperature Pressure Humidity Precipitation Fog and many other atmospheric factors.

Transmission Lines Protection Overview.Micro-Wave Communication Station 'Z'Station 'Y'Microwave is also a Line of Sight communicationsAny type of physical obstruction will affect the path of the signalBuildingsTrees

Transmission Lines Protection Overview.Micro-Wave Communication Station 'Z'Station 'Y'To correct for these limits.Pathways are carefully determined to minimize external influences.

Transmission Lines Protection Overview.Micro-Wave Communication Station 'ZStation 'Y'Bodies of WaterHills and MountainsTall BuildingsPathways will go around avoiding large obstaclesAnother method to secure transmission of the signal is sending along redundant pathwaysMain PathwayAlternate Pathway

Transmission Lines Protection Overview.Micro-Wave Communication Station 'ZStation 'Y'Bodies of WaterHills and MountainsTall BuildingsSometimes signals will be split. 2 T/T chs, 1 Perm on Main path 2 T/T chs, 1 Perm on Alt PathMain PathwayAlternate PathwayT/T ch#1 T/T ch#2 Perm#1T/T ch#3 T/T ch#4 Perm#2

Transmission Lines Protection Overview.Transmission CircuitPower Line Carrier - PLCPower Line Carrier employs a high frequency signal injected into the transmission circuit. At each end of the circuit, wave traps are employed which are tuned to trap the frequency and shunt it away to communications equipment.Wave TrapWave TrapCVT shunts signal to communications equipment60hz passes, high hz does not

Transmission Lines Protection Overview.Digital Tele-protection Fibre OpticDigital Tele-protection employs light signal injected into fibre optic cable. The fibre could be buried or even in the sky wire of a transmission circuit.Fibre OpticDigital Tele-protection had once utilized microwave tone equipment for the LH1 configuration but for the most part has since been replaced with all digital equipment.This is a true Digital Tele-Protection scheme and is beyond the scope of this presentation.

Transmission Lines Protection Overview.Micro-Wave CommunicationStation 'Z'Station 'Y'T1 G1T2 G2T3 G3T4 G4T5 G5T6 G6R1 G1R2 G2R3 G3R4 G4R5 G5R6 G6TRIPFrequency ShiftFaultRelay/Microwave buildingsWatch carefully how this works

Trip #1Guard #1CH #1FailTrip #2Guard #2CH #2FailTrip #3Guard #3CH #3FailTrip #4Guard #4CH #4FailCH #2CH #1CH #3CH #4A Battery DC +B Battery DC +A ProtectionB ProtectionGuard #1FailPermissive A LogicFailPermissive B LogicPerm #2Guard #2Transfer Trip ChannelsPerm #1Permissive ChannelsDisconnect SwitchCloseOpenDisconnect Switch - A Pallet SupervisionTrip CircuitTransmission Lines Protection Overview.LH1 ConfigurationClick These

To conclude you learned:What a circuit isWhat circuit protections are and why they are neededThe different zones of protection and how they workTransfer Trip, Permissive & Block signalsMicrowave, Power Line Carriers and Fibre-Optic Digital Tele-Protections communicationsLH1 configuration for protection tripping

Transmission Lines Protection Overview.

The End

Transmission Lines Protection Overview.