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Standard formular for IDMT Relay Curve

Standard formular for IDMT Relay Curve

Standard formular for IDMT Relay Curve

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

RE: Standard formular for IDMT Relay Curve

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

cheers Johnspark

RE: Standard formular for IDMT Relay Curve

(OP)
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.

RE: Standard formular for IDMT Relay Curve

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.

RE: Standard formular for IDMT Relay Curve

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

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