SCE Property - PowerPoint Presentation

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SCE Property

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Tribhuwan Choubey – SCE/TDBU/ECQ

Pilot Relay Schemes

Communication Aided Protection SchemesSlide2

IntroductionRelays at the Transmission terminals talk with each other using telecommunication media.Pilot relays do not pick up for faults outside their defined zone of protection.Pilot relays pick up instantaneously for faults within their defined zone of protection.For increased reliability some type of backup protection is also providedSCE Property2Slide3

2- Zone Distance RelaySCE Property3Slide4

Pilot relay telecommunicationSCE Property4Slide5

Relay communicationSCE Property5Leased Telephone Line ( 56 or 64kbps over copper)Power Line Carrier (PLC – 64kbps) – Twisted copper wire for 2/ 3 terminalsMicrowave or UHF radio (Multiplexed – 1.544 mbits/ sec DS1 signal – 24 channels)Dedicated Optical Fiber (Single Mode – 10 miles or Multi mode – 60 miles)SONET (Multiplexed Symmetrical Optical Network - Synchronous)T1 Multiplexing – 1.544 mbits/ sec (Asynchronous – voice and data communication)Slide6

Microwave TowerSCE Property6Slide7

Microwave TowerSCE Property7Slide8

Microwave Telecom EquipmentMicrowave Radio frequency spectrum: 1850-19909, 2130-2200, 6525-6875 and 12200-12700 MHzOperation: Two frequency duplex operationTelecom Equipment: Transmitters, Receivers, Order wires, Filters, Power Supplies, switching devicesMicrowave RF Apparatus specifications: T-8505Carrier Frequency and Bandwidth : FCC Rules 94.65 and 94.71Frequency Stability: FCC rules 94.67Baseband I/O level: < -35dBm/ -15dBm per channelPower Supply: 48V DCSCE Property8Slide9

Microwave Telecom EquipmentEach terminal is equipped with hot standby transmitter.Switching circuitry is bilateral in between transmittersThe input to the receivers from the antenna is connected through an RF HybridSwitching time for manual operation < 20 msec.Switching time for automatic operation < 25 msec.Operation of either or both of these switches cause a “Guard” or “Off Normal” lamps Hot standby operation of Transmitters and Receivers allows uninterrupted operation on failure of one equipmentSCE Property

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SONETcommunicationSCE Property10SONET - Synchronous Optical NetworkSlide11

SONET Data ServiceSCE Property11Slide12

Fiber optic communicationSCE Property12Slide13

Fiber optic Data LossesSCE Property13Slide14

T1 Extended Super FrameSCE Property14Slide15

Categories of Pilot RelayingFollowing categories of protection schemes are typically applied in pilot relaying.Phase comparisonDirectional comparison blockingRemote trippingTransfer trip Line differentialSCE Property15Slide16

Pilot Relaying Philosophy500 KV Pilot Relaying Schemes:Redundant Pilot relaying systemsRedundant Transfer Trip relaying systemsOne set of electromechanical relays as backup protection system.Mix of communication system like Power Line Carrier (PLC) and Microwave are used for communication redundancy SCE Property16Slide17

Pilot Relaying Philosophy220 KV Pilot Relaying Schemes:One Pilot relaying systemsOne set of electromechanical relays or another Pilot relaying scheme with microwave as communication channel are used as backup protection systemMix of communication system like Power Line Carrier (PLC) or Microwave are used for communication redundancy SCE Property17Slide18

Pilot Relaying PhilosophyPrinciple of Differential Relaying is applied for instantaneous tripping for in zone faultsFour wires, normally termed as Pilot Wires, run in between substations to compare current between terminals (Typical F/C 15ms – 25ms)HCB Relays from Westinghouse (ABB) are predominantly used as Pilot relays for lines up to 20 miles.HCB relay contains Sequence filters, DC polar unit with Operating and Restraining coils, Insulating and Saturating TransformersSCE Property18Slide19

Differential Relaying PhilosophySCE Property19Slide20

Pilot Relaying PhilosophySCE Property20Slide21

Pilot Relaying PhilosophyWestinghouse (ABB) LCB relays are used for Pilot Relaying for Transmission lines from 20 to 250 miles length.The communication medium is Fiber OpticsThe relay contains Sequence Filter, Transmitter Modulator ( 1 Ph -> FM), Receiver De Modulator (FM –> 1Ph), Phase comparison Unit (compare currents at Local/ Remote terminal)For out of zone fault, the signals would be out of phase and in phase for fault in the zone.SCE Property21Slide22

Pilot Relaying PhilosophySCE Property22Slide23

Phase Comparison RelayingRelay combination used with phase comparison systems are SLD or SKBU carrier relaying and CO( Residual Ground)/ ICC (Directional ground).Phase comparison relaying compares current phasors at local and remote terminals. Line and Neutral potential are not required.Faults in the protected zone would cause the currents to trip in less than 3 cyclesFault detector turns on carrier signal during FaultTransmitter generates blocking pulse during negative half cycle. During external fault both transmitters produce additive blocking pulse for the full cycle.During internal fault out of phase pulse cancel blocking pulse, allowing the relay to trip. SCE Property23Slide24

Phase Comparison RelayingSPCU relays are used for Phase comparison for Phase and Phase to Ground faultsMicrowave is used for communication of current phasors. Guard signals are transmitted for communication health. Relay trips in 9 cycles on loss of guard signal. Noise on communication channel will block tripping.SRU/ UIO as auxiliary relay for annunciation purposeDirectional comparison blocking ( SLYP/ SLYN) compares current direction at both terminals to determine in zone or out of zone faults to block trippingSLYP provides Zone1 element ( 80% of line: instantaneous trip with TT), Zone2 (125% of Line) (Instantaneous for in zone fault and TT or blocking signal for out of zone faults) and Zone3 (180% of line sends blocking signal out of zone faults)SLYN provides Directional overcurrent, trip for in zone faults and block for out of zone faultsSCE Property24Slide25

DCB PhilosophyImpedance relays trip instantaneously for z1 faults covering 80% of lineOver reaching impedance relays with z2 faults operate with time delay covering 125% of the lineDirectional comparison Blocking (DCB) allows over reaching relays to trip instantaneously by blocking out of zone faultsThus Phase Distance Relays and ground over current relays can provide instantaneous protection for in zone faultsOnly one Communication channel is used for sending blocking signal only , used with PLC schemesSCE Property25Slide26

DCB Relaying PhilosophySCE Property26Slide27

Typical Transfer Trip Relaying Transfer Trip schemes are another flavor of Directional comparison schemes, where two relays communicate to trip rather than block.The two frequencies transmitted through two communication channels are:Guard frequency to keep guard relays closed to block tripping over channel noiseTripping Frequency to allow tripping relay to pickup and trip circuit breakersBasic Transfer trip Schemes:Direct Transfer Trip (DTP)Direct Overreaching Transfer Trip (DOTT) – 125%Direct Under reaching Transfer Trip (DUTT) – 80%Permissive Transfer TripPermissive Overreaching Transfer Trip (POTT) – 125 %

Permissive Under reaching Transfer Trip (PUTT) –80%SCE Property27Slide28

Typical PUTT Relaying SchemeTypical PUTT Relaying Scheme would have following components:3 GCX (Directional Distance Relays ( Z1, Z2 and Z3 protection)Z2 and Z3 timer provides backup delayed tripping to POTT1 JBCG directional Ground Relays2 Transmitter and Receiver systems2 Transfer Trip communication channels 1 Ground Fault detector relay (SC)1 HD Balance relay to be used as backup for Transfer TrippingTrip signal at Remote terminal is enabled only when both transmitters are keyed to trip simultaneously, if Local and Remote permissive trip signal is availableLoss of Guard signal for six cycles continuously will disable the channel equipment and if it continues for more than 2 seconds resulting into alarm and if alarm is continuous, then the relays are made inactiveSCE Property

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PUTT Relaying PhilosophySCE Property29Slide30

Typical POTT Relaying SchemeTypical POTT Relaying Scheme would have following components:3 CEY (Impedance relay with zone 2 timer- starts at fault detection)1 SLYG directional Ground Relays2 GE Type 40 Transmitter and Receiver systems2 Transfer Trip communication channels (Primary/ Secondary)When a terminal receives the shift from Guard to trip frequency and a trip signal is present from Local relay, the local CB will tripZone 2 timer is reset after the fault is clearedIf zone 2 timer times out it will trip the local CBs irrespective of Tone signals from receiver to provide a backup protectionIf the fault is out of zone, then relay at the remote terminal will not pickup and removes the Guard frequency, preventing local relay to tripLoss of Guard signal for six cycles continuously will disable the channel equipment and continuous alarm will deactivate the relaysSCE Property

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POTT Relaying PhilosophySCE Property31Slide32

Digital POTT Relaying SchemeSome of the new microprocessor based relays being used in the industry are as follows:D60 Hybrid POTT Relays from GEL90 Differential with DTT from GEPLC Transfer Trip via RFL-9780MW Transfer Trip via RFL-9745FO Transfer Trip via RFL-9745SEL 421 – POTT/ DTT with PLC from Schweitzer ElectricSEL-311L – Differential with DTT from Schweitzer ElectricSEL-311C – POTT from Schweitzer ElectricCommunication Details:Serial RS485 communication PortEthernet full duplex networkModbus communication ProtocolIEC61850 communication data architectureCommunication speed 9600MB/sec

SCE Property32Slide33

Issues in Relay CommunicationOptical fiber cable damage or too high output from communications interface causes loss of channel signal alarm and may need attenuation or proper splice tray connection.T1 communication standard (DS1) requires transmittal of at least one pulse within any eight bit sequence. Loss of synchronization and unlocked frequency clocks could result in frame slips. Resulting in data loss.Leased Phone Lines need CSU channels as demarcation point between vendor and customer’s communication terminals. Interference on the cable/ CSU may cause loss of signal.SCE Property33Slide34

Issues in Relay CommunicationHigh induced voltages across pilot wire possibly caused by faults or lightning could cause induced fluxes and rise in ground voltage. This is remediated through provision of neutralizing reactors, voltage limiting circuits or surge suppressors.Open or shorted pilot wires are monitored and resulting erroneous trip signals are blocked.SCE Property34