What is overcurrent protection relay?

What is overcurrent protection relay?

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.

How do you calculate TMS?

(2) TMS <= Minimum Fault Current / CT Primary Current. For Condition (1) 0.8 > =(480/600) = 0.8 >= 0.8, Which found OK. For Condition (2) 0.125 <= 11000/600 = 0.125 <= 18.33, Which found OK. Here Condition (1) and (2) are satisfied so.

What is time dial setting?

The time dial setting adjusts the time delay before the relay operates whenever the fault current reaches a value equal to, or greater than, the relay current setting.

Where is overcurrent relay used?

Application: Definite time over current relay is used as: Back up protection of distance relay of transmission line with time delay. Back up protection to differential relay of power transformer with time delay. Main protection to outgoing feeders and bus couplers with adjustable time delay setting.

What is TSM and PSM?

TSM is time setting multiplier which comes into role only when pick-up value is reached. Practically PSM tell us about the magnitude of fault. The more the value of fault current, the more will be the PSM and hence the relay should clear the fault more quickly.

What is IDMT overcurrent relay?

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.

How is relay pickup current calculated?

From CT ratio, we first see the rated secondary current of CT. Say the CT ratio is 100 / 1 A, i.e. secondary current of CT is 1 A. From current setting we calculate the trick current of the relay. Say current setting of the relay is 150 % therefore pick up current of the relay is 1 × 150% = 1.5 A.

How is overcurrent protection calculated?

The feeder overcurrent protection device must be sized not less than 125% of 184 amperes, So, overcurrent protection device size = 184 amperes x 125% = 230 amperes. According to Section 240-6(a) for “Standard Ampere Ratings of overcurrent devices”, we must select a minimum 250 ampere overcurrent protection device.

What is PSM and TSM in relay?

What is relay setting?

Relay settings means actual value of the energizing or characteristic quantity at which the relay is designed to operate under given conditions.