Direct Transfer Trip Scheme

Direct Transfer Trips (DTT) are initiated from station relays when a severe event occurs in the substation. Some of these events are breaker failure, bus faults, transformer failure, etc. A lockout relay (86 device) is assigned to each event.

The lockout relay in the station is pretty essential. When operated due to any of the events indicated above, it trips all the breakers connected to it. So for example, for a bus fault, the bus differential relay will operate the bus lockout relay which will trip and blocks re-closing of all the breakers connected to the bus. If the breaker is at a remote location and can’t be physically wired, a DTT signal is sent to it via the protective relays using the pilot channel.

The figure below shows which all lockout relays are typically used to initiate the DTT. The substation design affects this. For example, a ring bus substation or a breaker-and-a-half substation has a breaker failure lockout assigned to each breaker. For other designs, a breaker failure event trips the bus lockout relay. Whichever case you are presented with, a contact from the lockout is assigned to the relay that can key the DTT signal to the remote end breaker.

Direct Transfer Trip
Figure 1: Direct Transfer Trip

Note that lockout relays are typically used to initiate DTT. In which case, the intent is to trip all breakers without any delay. There is no logic or reasoning – just trip. Remaining events like faults on lines are taken care of by the pilot schemes which have intentional delay for coordinating the breaker trips.

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Direct Transfer Trip Scheme 1

Direct Transfer Trip Quiz

Get ready to learn this topic like never before.

For a transformer fault at substation 2, would you transmit DTT to substation 1?

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For a fault on the transmission line, would you transmit DTT from either one substation?

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Assume circuit breaker 3CB2 fails at substation 3. DTT is transmitted to Substation 2 to trip 2CB1 and 2CB3. Which auxiliary relay would you install at Substation 2 to trip breakers 2CB1 and 2CB3?

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For what kind of fault at Substation 1 would you transmit a DTT to Substation 2 (to trip breaker 2CB1)?

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For a fault on Bus 1, would you implement a direct transfer trip (pilot) scheme to trip breakers tied to the same bus?

 

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ahammed

Dear sir,
Please leave me a test mail to [email protected]

adit

hi . sir i want to ask you, about DTT , in my plant we used Relay UR GE L90 for line Upstream – Downstream arround 4 Kilometer. which event trip by DTT and force to 87 L trip and then Lockout relay 86 , but in may event record relay we not having any problem about diffrensial current it so normal , but DTT was aktif and trigger for DTT from Asym DET and LOSTPKT. can you explain to me why DTT its aktif ? and how about trigger DTT like ASYM DET & LOSTPKT because in my logic… Read more »

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