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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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But when the CT becomes saturated, there would not be a further proportional increase of CT secondary current with increased system current.

IDMT (Inverse Definite Minimum Time) Relay Calculation

The non unit type protection system includes following schemes: In our co-gen Plantwe are facing the problem of frequent tripping of grid breaker on stand by earth fault protection due to KV line earth fault or even due to small disturbance at KV line or at KV substation where we are exporting the power.

Pankaj kushwaha Oct 19, Please suggest us to idmh these frequent tripping of relay, what will be the characteristics of relay to voercurrent set definite time, normal inverse or very long inverse etc.

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? These ratings include voltage, ampere and interrupting rating.

As well as protecting their own designated areas, the protective zones can overlap into other areas. While this can be very beneficial for backup purposes, there can be a tendency for too great an area to be isolated if a fault is detected by different non unit schemes. Over-current Relay gives protection against: While, the overload protection protects against the situation where overload current causes overheating of the protected equipment. The accuracy of the operating time may range from 5 to 7.


Time graded overcurrent protection Current graded overcurrent protection Distance or Impedance Protection. Short-circuit currents are generally several times 5 to 20 full load current. Depending on the time of operation of relays, they are categorized as follows: Use time, current and a combination of both time and current are three ways to discriminate adjacent overcurrent relays.

The general practice is to employ a set of two or three overcurrent relays and a separate overcurrent relay for single line to ground fault.

Delcev Feb 01, A piece of iron is so fitted by hinge support and restraining spring in the relay, that when there is not sufficient current in the coil, the NO contacts remain open. Please develop the app at most and website too….

Over-current relays can be used to protect practically any power system elements, i. But when the current through the coil increases, the magnetic overcurret increases, and after a certain level of current, the deflecting force generated by the magnetic effect of the coil, crosses the restraining force. It has a limitation that udmt can be applied only to simple and non costly equipments. This site uses Akismet to reduce spam.

October 27, at 2: As the relay current does not increase further, there would not be any further reduction in time of operation in the relay.

Types of Over Current Relay Depending upon time of operation, there are various types of Over Current relayssuch as, Instantaneous over current relay. In these schemes, the effects of any disturbance or operating condition outside the area of interest are totally ignored and the protection must be designed to be stable above the maximum possible fault current that could flow through the protected area.


The relay operation time is inversely icmt to the fault current.

Types and Applications Of Overcurrent Relay (part 1)

As well as protecting their own designated areas, the protective zones can overlap into other areas. This relay is idt as instantaneous over current relayas ideally, the relay operates as soon as the current in the coil gets higher than pick upsetting current.

Overcurrent relaying is very well suited to distribution system protection for the following reasons:. So, high current will operate overcurrent relay faster than lower ones.

The directionality of current flow can be identified using voltage as a reference of direction. Hence fast fault clearance is always desirable on short circuits.

Over Current Relay Working Principle Types

Leave a Comment Click here to cancel reply. 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.

Separate earth fault relay provided makes earth fault protection faster and more sensitive. Instantaneous, in old days used to be high set i. These are the types of overcurrent relay: Subscribe to our mailing list and get interesting stuff and updates to your email inbox.

The secondary current enters the relay current coil.