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Carrier Aidded Protection

Phase comparison relaying compares current phasors at local and remote terminals to determine if a fault is internal or external without requiring line and neutral potentials. It uses carrier relaying like SLD or SKBU and directional ground relays like CO/ICC. Faults within the protected zone cause currents to trip in less than 3 cycles. Microwave communication is used to transmit current phasors, with guard signals checking communication health and tripping in 9 cycles if lost. Directional comparison blocking relays like SLYP/SLYN compare current directions to block tripping for external faults. Transfer trip schemes use two communication channels, one transmitting a guard frequency to block tripping during noise, and the other a tripping frequency to

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642 views4 pages

Carrier Aidded Protection

Phase comparison relaying compares current phasors at local and remote terminals to determine if a fault is internal or external without requiring line and neutral potentials. It uses carrier relaying like SLD or SKBU and directional ground relays like CO/ICC. Faults within the protected zone cause currents to trip in less than 3 cycles. Microwave communication is used to transmit current phasors, with guard signals checking communication health and tripping in 9 cycles if lost. Directional comparison blocking relays like SLYP/SLYN compare current directions to block tripping for external faults. Transfer trip schemes use two communication channels, one transmitting a guard frequency to block tripping during noise, and the other a tripping frequency to

Uploaded by

Thirumal
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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CARRIER AIDDED PROTECTION

Phase Comparison Relaying


Relay 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
cycles

Fault detector turns on carrier signal during Fault

Transmitter 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

SPCU relays are used for Phase comparison for Phase and Phase to
Ground faults

Microwave 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 purpose

Directional comparison blocking ( SLYP/ SLYN) compares current direction


at both terminals to determine in zone or out of zone faults to block
tripping

SLYP 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 faults
DCB Philosoph

Impedance relays trip instantaneously for z1 faults covering 80% of line

Over reaching impedance relays with z2 faults operate with time delay covering
125% of the line

Directional comparison Blocking (DCB) allows over reaching relays to trip


instantaneously by blocking out of zone faults

Thus Phase Distance Relays and ground over current relays can provide
instantaneous protection for in zone faults

Only one Communication channel is used for sending blocking signal only , used
with PLC schemes

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 noise

Tripping Frequency to allow tripping relay to pickup and trip circuit


breakers

Basic Transfer trip Schemes:

Direct Transfer Trip (DTP)

Direct Overreaching Transfer Trip (DOTT) 125%

Direct Under reaching Transfer Trip (DUTT) 80%

Permissive Transfer Trip

Permissive Overreaching Transfer Trip (POTT) 125 %

Permissive Under reaching Transfer Trip (PUTT) 80%

Typical PUTT Relaying Scheme

Typical POTT Relaying Scheme


Typical POTT Relaying Scheme would have following components:

3 CEY (Impedance relay with zone 2 timer- starts at fault detection)

1 SLYG directional Ground Relays

2 GE Type 40 Transmitter and Receiver systems

2 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 trip

Zone 2 timer is reset after the fault is cleared

If zone 2 timer times out it will trip the local CBs irrespective of Tone
signals from receiver to provide a backup protection

If the fault is out of zone, then relay at the remote terminal will not pickup
and removes the Guard frequency, preventing local relay to trip

Loss of Guard signal for six cycles continuously will disable the channel
equipment and continuous alarm will deactivate the relays

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