Standard formular for IDMT Relay Curve 1

[Darrick]

Anyone know the required standard for IDMT Relay Curve? What is the Equation/Formular? Thanks.

 

[johnspark]

Darrick, there are many many IDMT curves about. You need to ask yourself the question: which one do I want to use?

cheers Johnspark

 

[Darrick]

I am referring to the 3/10 curve. I would like to check using manual calculation say for a required setting after reading off the graph.

 

[5P10]

By 3/10, I believe you are talking about the Normal Inverse (NI) curve. Formulas below:-

t = (k.B)/((I/Is)^a - 1)

where t = operating time (sec)
k = TMS (time multiplier settings)
I = measured current value (A)
Is= set current value

a B
Normally Inverse 0.02 0.14
Very Inverse 1.0 13.5
Extremely Inverse 2.0 80.0
Long Time Inverse 1.0 120.0

NI = 3/10, VI = 1.2/10, EI = 0.8/10, LTI = 12/10.

You can also refer to BS142.1966 or IEC 255-4.

 

[piterpol]

For more information see:

http://www.selinc.com/instruction_manual/551/551_4.pdf

Refer to pages 4-2 to 4-6 for different US and IEC inverse-time curves equations and graphics.

 

[Darrick]

Thank you so much for the information guys. Been really helpful.

 

[piterpol]

Oops! My former post has a server error. Let me try again.

http://www.selinc.com/instruction_manual/551/551_04.pdf