Ac inverse time overcurrent relay

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Overcurrent Relay

ac inverse time overcurrent relay

IDMT Relay (Inverse Definite Minimum Time Relay): Protection of Transmission lines

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There is only one current operated element in the relay, no voltage coil etc. In an over current relay , there would be essentially a current coil. When normal current flows through this coil, the magnetic effect generated by the coil is not sufficient to move the moving element of the relay, as in this condition the restraining force is greater than deflecting force. But when the current through the coil increases, the magnetic effect increases, and after a certain level of current, the deflecting force generated by the magnetic effect of the coil, crosses the restraining force. As a result, the moving element starts moving to change the contact position in the relay.

Definition: The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. It protects the equipment of the power system from the fault current. The relay has no intentional time delay for operation. The contacts of the relay are closed instantly when the current inside the relay rises beyond the operational value. The time interval between the instant pick-up value and the closing contacts of the relay is very less. The most significant advantage of the instantaneous relay is that it has low operating time. It starts operating instantly when the value of current is more than the relay setting.

CSV Jul 29, Jul 29, Pin it. Static relays are mainly made with semiconductor switches like thyristor. In digital relays there are two states i. Based on Characteristics some the protection relays are detailed below:. The current derived from the CT is fed to the input transformer which gives a proportional output voltage.

The major difference between Instantaneous and Definite Time Overcurrent Relay lies in their operating time. The former operates instantaneously while the latter one operates after a definite time. Both Instantaneous and Definite Time Overcurrent Relay senses an over current in the circuit and gives tripping command to operate the circuit breaker for isolation of faulty network.
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Types of protection Protection schemes can be divided into two major groupings:. Unit type schemes protect a specific area of the system, i. Any deviation from this must indicate an abnormal current path. 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 non-unit schemes, while also intended to protect specific areas, have no fixed boundaries.

The difference between inverse time, definite time, and instantaneous relays

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Over Current Relay Working Principle Types




Instantaneous Overcurrent relay (Define Current); Definite Time Overcurrent Relays; Inverse Time Overcurrent Relays (IDMT Relay).
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