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

Types and Applications Of Overcurrent Relay (part 1)

The other terminology used for overcurrent is hi-set and low-set. It become so helpful for relaj. OverCurrent Relay gives protection against: Here generally a magnetic core is wound by a current coil. For feeder protection, there would be more than one over-current relay to protect different sections of the feeder.

The voltage rating of the overcurrent protective device must be at least equal to or greater than the circuit voltage. If the interrupting rating is not properly selected, a serious hazard for equipment and personnel will exist. But when the CT becomes saturated, there would not be a further proportional increase of CT secondary current with increased system current. The over-current protective device rating can be higher than the system voltage but never icmt.

Shashidhara TM May 21, Why have seperate relays when overcurrent 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

Inverse time over current relay. 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. Instantaneous, in old days used to be high set i.

Types and Applications Of Overcurrent Relay 1. Neil Govender Nov 03, Modern relays may contain more than one stage of protection each stage includes each own current and time setting.

Hence fast fault clearance is always desirable on short circuits. The overcurrent protection is a bigger concept So that the overload protection can be considered as ocercurrent subset of overcurrent protection.

This is the simplest of the ways to protect a line and therefore widely used. This type of relay operates in on direction of current flow and blocks in the opposite direction. Unit type schemes protect a specific area of the system i. The accuracy of the operating time may range from 5 to 7.

Ibrahim Kurdi Feb 19, Over-current Relay gives ovrcurrent against: 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.

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Short-circuit currents are generally several times 5 to 20 full load current. If the fault is severe, it will clear the fault faster. Although there are different types of overcurrent relays but basic working principle of overcurrent relay is more or less same for all.


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

Protection schemes can be divided into two major groups: Inverse Time Over Current Relay Inverse time is a natural character of any induction type rotating device.

Based on the inverseness it has three different types: Overcurfent is overcurrenf 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. Inverse definite minimum time IDMT over-current Relay is one in which the operating time is approximately inversely proportional to the fault current near pick-up value and then becomes constant above the pick-up value of the relay.

These are the types of overcurrent relay: 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. Pankaj kushwaha Oct 19, When the current in the coil overcurrnet a preset value, the attractive force becomes enough to pull the iron piece towards the magnetic core, and consequently, the no contacts get closed.