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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Div Aug 19, Normally it has more inverse characteristic near the pick-up value which in turn means that if fault current is equal to pick-up value then the relay will take infinite time to operate. The relay operation time is inversely proportional to the fault current.

The non-unit schemes, while also intended to protect specific rela, have no fixed boundaries. Inverse time over current relay. Your email address overcurrnt not be published. In order for an overcurrent protective device to operate properly, overcurrent protective device ratings must be properly selected. Instantaneous, in old days used to be high set i. We define this time as the minimum time of operation.

If the interrupting rating is not properly selected, a serious hazard for equipment and personnel will exist.

Over Current Relay and Its Characteristics | Electrical Concepts

But there is always an inherent time delay which we cannot avoid practically. The voltage rating of the over-current protective device must be at least equal to or greater than the circuit voltage. Types of protection Protection schemes can be divided into two major groupings: October 27, at 4: Hence fast fault clearance is always desirable on short circuits.


Current limiting can be considered as another over-current protective device rating, although not all over-current protective devices are required to have this characteristic. The directionality of current flow can be identified using voltage as a reference of direction. It has a limitation that overcurrrnt can be applied only to simple and non costly equipments.

Single phase fault currents are NOT always lower than Phase fault currents. Inverse definite repay time IDMT over-current Relay is one in which the operating time is approximately inversely proportional to the overdurrent current near pick-up value and then becomes constant above the pick-up value of the relay.

We refer the pre-set value of current in the relay coil as pickup setting current. Separate earth fault relay provided makes earth fault protection faster and more sensitive.

It depends on the zero sequence impedance of the system. Types and Applications Of Overcurrent Relay 1.

Over Current Relay Working Principle Types

Any deviation from this must indicate an abnormal current path. April 29, at 3: While this can be very beneficial for backup purposes, there can be a tendency for too great an area to be isolated ovrrcurrent a fault is detected by different non unit schemes. The voltage rating of the overcurrent protective device must be at least equal to or greater than the circuit voltage.

Earth fault current is always less than phase fault current in magnitude. Overcurrent protection protects against excessive currents or currents beyond the acceptable current ratingswhich are resulting from short circuits, ground faults and overload conditions.

Types and Applications Of Overcurrent Relay. Most frequently used in utility and industrial circuits. First of all i would like to thanks you very very much, your lesseon are so valuable To introduce myself, my name Binh, i am Vietnamese, i work for shipyard that many electrical issue i met everyday make me many questions about it. Based on the inverseness it has three different types: Over Current Relay and Its Characteristics.


The other terminology used for overcurrent is hi-set and low-set.

Jignesh Parmar Jignesh Parmar has completed M. This relay is referred as instantaneous over current relayas ideally, the relay operates as soon as the current in overcurrebt coil gets higher than pick upsetting current. Instantaneous Over-current Relay is one in which no intentional time delay is provided for the operation.

Over Current Relay Working Principle Types

Although time inverse characteristic is inherent to electromechanical induction disc relay, the same characteristic can be achieved in microprocessor-based relay also by proper programming.

There are standard inverse, very inverse and extremely inverse types.

Working Principle of Over Current Relay In an over current relaythere would be essentially a current coil. To achieve this, the time delay is provided. These are the types of overcurrent relay: When the current in the coil crosses a preset value, the attractive force becomes enough to pull the iron piece towards the magnetic core, and consequently, the no contacts get closed.

Inverse time over-current Relay is one in which the time of actuation of Relay decreases as the fault current increases.