The protection device is built into the main alternator circuit breaker to safeguard both the individual alternator and distribution system
When an overcurrent is not so high a delay with inverse time characteristic allow an interval of time (or a time delay )before the breaker is opened during this time delay the overload may be cleared, hence allowing the supply of power for as long as possible giving rise to IDMT RELAY(inverse definite minimum time Relay)
1)Overcurrent protection
The alternator has overcurrent protection but the main consideration is to maintain the supply of power for as long as possible. The breaker is designed in such a way that is trip instantaneously only in the event of high overcurrent due to a short circuit.When an overcurrent is not so high a delay with inverse time characteristic allow an interval of time (or a time delay )before the breaker is opened during this time delay the overload may be cleared, hence allowing the supply of power for as long as possible giving rise to IDMT RELAY(inverse definite minimum time Relay)
REASONS FOR OVERLOAD
- Due to serious fault in the switchboard causing the high current fault
- Partial/Straight overload due to starting of big motors
2)Preferential trips
This trip is designed to disconnect non-essential load (like ventilation fan, HVAC, reefer system, etc) in the event of partial/straight overloading with the aim to prevent operation of main breaker trip an loss of total power failure.
- Non-essential load are grouped together and disconnected at timed intervals arranged at 5,10,15 seconds
- Operated at a relay set at about 110% of normal fault load
Das pot arrangement is an older design provided to give a time delay or time lag for the relay to operate, it consists of a piston moving in a cylinder with silicone fluid. The piston moves up or down as the silicone fluid is displaced from top to bottom through a small hole or by the way of clearance around it.time delay can be adjusted bu the size fo the hole or clearance
3)Reverse power trip
It is intended when the alternator is running in parallel operation, this trip will release the breaker and prevent the motoring of the alternator if a reversal of power occurs.
Such a device is used to prevent physical damages to the prime mover, which has shut down due to mechanical faults.
For a detailed explanation
4)Under voltage trip
- It helps to prevent the closure of the circuit breaker by mistake when the alternator is dead.
- This is fitted in the alternator which is arranged for parallel operations, the instantaneous operation of this trip is necessary to prevent the closure of the breaker.
- It also gives protection against the loss of voltage while the machine is connected to the switchboard.
No comments:
Post a Comment