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MKA IDMT Overcurrent Relay User’s. Guide. A BRIEF OVERVIEW a b c d h g f e a – Auxiliary power supply indicator b – High-set start/trip status indicator. OVERCURRENT RELAY WITH IDMT. ○ Test and reset facility. ○ Convenient C. T. connections. ○ Double pole double throw 10A VAC Relay Output. Setting calculation is separated for overcurrent and eart fault relay with input parameters: Name of Feeder, Load Current: (IL) in Amps, Min Fault.

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Inverse time over current relay. April 29, at 3: Therefore, relay connected for earth fault protection is different from those for phase to phase fault protection. Le Xuan Binh Jan 08, Inverse time over current relay or simply inverse OC relay is again subdivided as inverse definite minimum time IDMTvery inverse timeextremely inverse time over current relay or OC relay. But there is always an inherent time delay which we cannot avoid practically.

Now a days we have options idm set many stages of fault current for tripping. The overcurrent protective device rating can be higher than the system voltage but never lower. Types of Over Current Relay Depending upon time of operation, there are various types of Over Current relayssuch as, Instantaneous over current relay.

The non-unit schemes, while also intended to protect specific areas, have no fixed boundaries. To achieve this, the time delay is provided in case of inverse relays.

From this phenomenon, it is clear that from trick value to certain range of faulty level, an inverse time relay shows specific inverse characteristic. Overcurrent protection protects against excessive currents or currents beyond the acceptable current ratingswhich are resulting from short circuits, ground faults and overload conditions.


As well as protecting their own designated areas, the protective zones can overlap into other areas. For feeder protection, there would be more than one over-current relay to protect different sections of the feeder. Why have seperate relays when a single relay can be used to implement multiple elements such as protection against ground faults, as well as ac instantaneous overcurrent?

Over Current Relay Working Principle Types

Ibrahim Kurdi Feb 19, Current limiting can be considered as another overcurrent protective device rating, although not all overcurrent protective devices are required to have this characteristic.

Neil Govender Nov 03, Pankaj kushwaha Oct 19, If the fault is severe, it will clear the fault faster. He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. Over Current Relay and Its Characteristics. It is also clear that the time of operation at Pick-up value is nearly very high and as the fault current increases the time of operation decreases maintaining some definite time.

Very Inverse Relay is one in which the range of operation is inverse with respect to fault current over a wide range. As the relay current does not increase further, there would not be any further reduction in time of operation in the relay.

Over Current Relay and Its Characteristics | Electrical Concepts

The protection should not operate for starting currents, permissible overcurrent, current surges. Overcurrejt relays can be used to protect practically any power system elements, i. There are standard inverse, very inverse and extremely inverse types. This happens so as the CT saturation occurs at a later stage but as soon as CT saturation occur there will not be any flux change and hence the current output of CT will become zero and hence the time of operation will nearly become constant.


Types and Applications Of Overcurrent Relay (part 1)

This relay is referred as instantaneous over current relayas ideally, the relay operates as soon as the current in the coil gets higher than pick upsetting current. Any deviation from this must indicate an abnormal current path. The secondary current enters the relay current coil. The non unit type protection system includes following schemes: Over-current Relay gives protection against: Tech Power System Control ,B.

October 27, at 2: When the power system is not radial source on one side of the linean overcurrent relay may not be able to provide adequate protection. The most simple of these schemes measures current and incorporates an inverse time characteristic into the protection operation to allow protection nearer to the fault to operate first.

These are the most important purposes of overcurrent relay: OverCurrent Relay gives protection against: