carrier direct trip

Dear Guest,

Normally the overhead transmission lines are protected at both ends by identical distance protection relays. The distance protection relay has zone settings (i.e. dividing the line into zones, Z1=80%, Z2=100% & Z3=120% of the line length) according to the requested schemes and the capability of the relay itself.

Let us assume a transmission line between two substations (A & B) and protected by distance relays at both ends.

1- Without Carrier Direct Trip Feature

Suppose a fault occurs close to substation A, both relays at A & B detect the fault. However, the relay at A detects it as first zone, while the relay at B detects it as a second zone fault. Accordingly, the relay at A substation will instantaneously (normally within 20 ms), trip its corresponding breaker trying to clear the fault, while the fault still being fed from the remote end till the relay at B substation trips its breaker after an elapsed time corresponds to second zone time (normally 400 ms). I.e. the fault has been cleared out after a time corresponds to second zone preset time of remote end relay.

2- Incorporating Carrier Direct Trip Feature

In order to avoid feeding the fault till the remote breaker clear it, trip logic has to be introduced in the system to overcome such problem. This function is known as Carrier Direct Trip or Direct Transfer Trip.

Let us now study the same system after incorporating this feature. The relay at A substation detects the fault as first zone, while the relay at B substation detects it as second zone. The relay at A will send an "Aided Trip Signal" to the remote end to accelerate tripping of remote end breaker via "Power Line Carrier" system. I.e. the two breakers shall clear the faults as first zone (instantaneously tripping).

Hoping the above clears your question.

Regards,

yOUR EXPLANATION WAS REALLY GOOD. THANKS FOR THE DETAIL EXPLANATION.

CAN YOU KINDLY EXPLAIN WHAT IS CARRIER PERMISSIVE TRIP? AND WHAT IS THE DIFFERENCE BETWEEN CARRIER DIRECT AND PERMISSIVE TRIP; IF THERE IS ANY.

Dear Prasenjitsen,

In carrier direct trip, the trip signals are sent directly to the main trip relay at remote end of the transmission line for direct tripping of the breaker. While, permissive trip commands are always monitored by the protection relays. The circuit breaker is tripped when receipt of the command coincides with operation of the protection relay at the receiving end responding to a system fault. Accordingly, to trip the breaker the following conditions must be available:

1- Permissive command (permission to trip);

2- Operation of protection relay at that end.

Best regards,

There are 4 terms on the relay

Carrier Send

Carrier Receive

DT send

DT receive

Under what conditions these operate in which zone?

Whether all zones ?

'Carrier Send' will appear when the protection zone that is set to send the carrier communication signal to remote end operates.

The protection zone is Z1 in case of PUR schemes and Z2 in case of POR schemes.

'Carrier Receive' will appear when carrier communication signal from remote end is received and suggests that the remote end protection has operated.

DT refers to 'Direct Trip' and the signal is generally used for tripping the remote end in case of BF protection operation or busbar protection operation at local end (Vice versa).

Some times, manual or feeder protection trip also may be wired for DT at emote end. It depends on the type of feeder and protection philosophy followed.