Over Current Protection [Video Lesson]

The over-current protection works by removing power supplies to nonessential services on a preferential basis.‭ ‬This is done with the help of preferential trips which decide the load that is to be removed in case of overloading of the distribution system.

Reverse power trip and under voltage trip are required only if there is more than one alternator on board which requires the working of two alternators on load.

Over Current Protection

The overcurrent trip protects the alternator distribution system from various faults however the main characteristic of this trip is to maintain power to the distribution system till the time the alternator trips on any other protection devices. ‭

There a time delay is provided by an inverse definite minimum‭ ‬time‭ (‬IDMT‭) ‬relay to protect devices, which prevents the alternator from tripping if the over-current‭ ‬values reduce‭ ‬back to normal within the IDMT characteristics. However, in case of a major fault such as a short circuit, the alternator will trip instantaneously without any delay to protect all devices on the distribution system.

Overload of the alternator is caused by either increased switchboard load or a serious fault causing a very high current flow.

Video Lesson:

If sudden overload occurs then, the load is reduced with the help of preferential trips which removes nonessential load such as air conditioning,‭ ‬ventilation fans, etc., from the switchboard.

These preferential trips are operated by relays which are set to about‭ ‬110%‭ ‬of the normal full load of the alternator.