How does an overcurrent relay work?
Overcurrent relay. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. The ANSI device number is 50 for an IOC relay or a DTOC relay.
What is CT and PT in relay?
They are devices that measure the voltage and frequency in a circuit. Like CTs, PTs are needed because the voltage in a circuit is much higher than the relay can handle, so they step it down to a much lower level for the relay.
What are the different types of overcurrent relay?
Types of Overcurrent Relay:
- Instantaneous Overcurrent relay (Define Current)
- Definite Time Overcurrent Relays.
- Inverse Time Overcurrent Relays (IDMT Relay) Normal Inverse Time Overcurrent Relay. Very Inverse Time Overcurrent Relay. Extremely Inverse Time Overcurrent Relay.
- Directional Overcurrent Relays.
How do I set up an overcurrent relay?
Calculation of Over Current Relay Setting:
- Over Load Current (In) = Feeder Load Current X Relay setting = 384 X 125% =480 Amp.
- Required Over Load Relay Plug Setting= Over Load Current (In) / CT Primary Current.
- Required Over Load Relay Plug Setting = 480 / 600 = 0.8.
What is overcurrent relay in simple words?
An overcurrent relay is an electrical protection device designed to cut off the power supply to a circuit, appliance, or machine in the event of an overload or failure. These devices typically consist of a manual circuit breaker or contactor and a current sensing relay which interlocks with it.
What are the disadvantage of overcurrent relay?
The use of IDMT overcurrent relay has some disadvantages. Most of the problems relate to the coordination between the main and the backup relay. One of the problems faced by the overcurrent relay is fault severity variation.
What are CTs and PTS used for?
CT’s, or current transformers, and PT’s, or potential transformers are used in metering to step down current and voltage to safer and more manageable levels. Many people want to know what is a current transformer and potential transformer.
What is the difference between CT and VT?
CT is a current transformer. From its name, it transforms high current to low current and vise versa. VT is a voltage transformer. From its name, it transforms high voltage to low voltage.
What is the difference between earth fault relay and overcurrent relay?
Over load relays are used in control and power circuits to protect the motor from over load /over current. Earth fault relay that means phase to ground fault will occur the relay gets activated but phase relay means phase to phase fault, open circuit fault and short circuit fault occuring that relay gets activated.
What is overcurrent and earth fault relay?
Over current/Earth fault relays are the basic protection relays. Used for protection of transformers and feeders from over current and earth faults. When excessive current flows in a circuit, it is necessary to trip the circuit breaker protecting that circuit.