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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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.

October 27, at 2: The most simple of these schemes measures current and incorporates an inverse rela characteristic into the protection operation to allow protection nearer to the fault to operate first.

Over Current Relay and Its Characteristics.

Three conditions must be satisfied for its operation: Tech Power System Control ,B. This natural characteristic of electromechanical induction disc relay is very suitable for overcurrent protection. Facebook Overcjrrent Google Plus Twitter.

Types and Applications Of Overcurrent Relay (part 1)

For feeder protection, there would be more than one over-current relay to protect different sections of the feeder. Overcurreng, relay connected for earth fault protection is different from those for phase to phase fault protection. Types and Applications Of Overcurrent Relay 1. Very very thanks to the Resp.

Instantaneous Over-current Relay is one in which no intentional time delay is provided for the operation. It depends on the zero sequence impedance of the system.

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Over Current Relay Working Principle Types

From the picture, it is clear that there is some definite time after which the Relay will operate. Depending on the time of operation of relays, they are categorized as follows: Overcurrent relays can be used to protect practically any power system elements, i. Neil Govender Nov 03, Current limiting can be considered as another overcurrent protective device rating, although not all overcurrent protective devices are required to have this characteristic.

In this type, two conditions must be satisfied for operation trippingcurrent must exceed the setting value and the fault must be continuous at least a time equal to time setting of the relay. It has a limitation that it can be applied only to simple and non costly equipments.

As well as protecting their own designated areas, the protective zones can overlap into other areas. Suppose the pick-up current for an IDMT relay is set at 0. The uncertainty of the operating time and the necessary operating time may require a grading margin of 0.

How we can select power transformer Rating? That is why the relay is referred as inverse definite minimum time over current relay or simply IDMT relay. 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?

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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. April 29, at 5: These ratings include voltage, ampere and interrupting rating. The voercurrent unit type protection system includes following schemes: This type of relay operates in on direction of current flow and blocks in the opposite direction. So, high current will operate overcurrent relay faster than lower ones.

Overcurrent relaying is very well suited to distribution system protection for the following reasons:.

Separate earth fault relay provided makes earth fault protection faster and more sensitive. The protection should not operate for starting currents, permissible overcurrent, current surges.

Premium Membership Premium membership gives you an ovrrcurrent to specialized technical articles and extra premium content electrical guides and software. Following are the important features of an Instantaneous Over-current Relay: Delcev Feb 01, There is no intentional time delay applied. The voltage rating of the over-current protective device must be at least equal to or greater than the circuit voltage.

Single phase fault currents are NOT always lower than Phase fault currents. Notify me when new comments are added. But there is always an inherent time delay which we cannot imt practically.