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The IDMT trip time calculator

  The calculated IDMT trip times on this page are based on the IEC standards for inverse curves.
The IEC formula for calculating trip times is -
T = K * TMS/(Mα-1)
Where
  • K and α are constants depending on the curve selection
  • M is the multiple of fault current
  • TMS is the relay time multiplier setting
Some relay manufacturers express the time setting on the relay as being the ACTUAL trip time at 10 times fault current. In these cases, the value of K needs to be modified.  Before using the calculator below you will need to know how your relay expresses its trip time. If it expresses it as being the time at 10 times  setting then you must select the 10x option in the options box. Otherwise select the TMS option.  For a more detailed understanding of the curves click here.

M =  TMS =  Curve = 

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