Trip Circuit

usually master trip(86) relay used where more than one trip singal used for trip the breaker . if you want to trip the 50/50N alone .you can directly conned to trip coil. if your triping unit shall trip like DC fail , Ups Power fail,etc .thenbetter you use 86 relay.

It all depends upon the making capacity of the relay's contacts and the switching inrush current of the breaker trip coil. If the making capacity of the relay contact is more than the switching inrush of the trip coil, then relay contact can be directly connected. But, please have a manual reset of the relay in this case.

Else, if the making capacity is less, then go for tripping thro 86. And, ensure 86 contact has the making capacity.

There seems to be a misconception here regarding the purpose of an 86 relay. Device 86 is a lockout function. Once tripped, operator intervention (either locally or remotely) is required to reset the lockout. The 86 is typically used for trips which should be investigated prior to re-energization. For example, a differential relay (87) trip on a substation power transformer may indicate damage to the transformer. It would be prudent to physically inspect the transformer and associated equipment before restoring it to service. The appropriate design is for the 87 relay to trip the 86 lockout, which will in turn trip all breakers connected to either side of the transformer.

As for a trip or interlock signal from one breaker to another, I favor simplifying trip schemes as much as possible. An interposing relay is just another device which can fail when you need it most. If the auxiliary contacts on the 33kV breaker are rated to carry the current necessary to trip the 6.6kV breaker, connect them directly. If the auxiliary contacts are not rated for such current, then I would use an interposing relay.

CAUTION: If you decide to use the interposing relay, give careful consideration to abnormal contact configurations during maintenance. A few years back I investigated a fire that was caused by the maintenance crew "slow-closing" a breaker to check contact travel. They had pulled the control power fuses for close and trip. When they manually closed the breaker, the breaker-mounted aux. contacts operated. Without control power, the interposing relay contacts did not change state, resulting in a short circuit and fire in the relay panel.