# Inverse time lag relays in protection

I'm dealing now with the different types of time responses of electromechanical relays: instantaneous, definite time lag, inverse time lag, and inverse definite minimum time lag.

My question is: What's the difference between the last two time response? What are the advantages/disadvantages ? Is it "bad" to have a definite minimum in an inverse time lag delay?

• I didn't know the answer so I searched and found an article on Electrical4u which should answer your question. Feb 25, 2020 at 18:33
• I read that article earlier, it doesn't answer the question, I'm asking about the "inverse definite minimum relay", a electromechanical relay that is inversely proportional to the current until some minimum where the time response remains constant for any increase in the current magnitude. Feb 25, 2020 at 18:56
• The article states, "Inverse time delay is achieved in induction disc relay by providing a permanent magnet in such a way, that, when disc rotates, it cuts the flux of permanent magnet. Due to this, current is induced in the disc which slows down the movement of the disc. A solenoid relay can be made inverse time relay, by providing a piston and an oil dash-pot. A piston, attached to the moving iron plunger, is immersed in oil in a dash-pot. When the solenoid relay is actuated, the piston moves upwards along with iron plunger." It sounds awfully close to your terminology. Feb 25, 2020 at 18:59
• Yes it's close because it deals with inverse time delay, meaning that the time response is always inversely proportional with the increase in the current magnitude. However, inverse time delay with a definite minimum is another type of time response that is inversely proportional until it reaches a certain minimum, where any increase in current magnitude would NOT lead to any decrease in time response. My question asks what are the advantages/disadvantages of each. Feb 25, 2020 at 19:04