What is PSM in relay?

james_clark's picture


Joined: Jun 14, 2019

Replies: 0
What is PSM in relay?
June 14, 2019 - 8:14pm

In the field of electrical engineering, a relay is a relay device designed to trip a switch when an error is detected. The first protection relays were electromagnetic devices based on mobile coils in motion to guarantee abnormal operating conditions such as over current, over voltage, inverse flow, over frequency and reduced frequency.

The digital protection relays based on microprocessors now emulate the original devices, in addition to providing non-practical protection and non-mechanical monitoring with electromechanical relays.


Shivkumar's picture


Joined: May 28, 2019

Replies: 4
What is PSM in relay?
June 15, 2019 - 12:39pm

Plug setting multiplier of relay is referred as ratio of fault current in the relay to its pick up current.

Suppose we have connected on protection CT of ratio 200/1 A and current setting is 150%.
Hence, pick up current of the relay is, 1 × 150 % = 1.5 A
Now, suppose fault current in the CT primary is 1000 A. Hence, fault current in the CT secondary, i.e., in the relay coil is, 1000 × 1/200 = 5A
Therefore PSM of the relay is, 5 / 1.5 =3.33