ABB distribution protection unit 2000R defines inverse-time characteristics not according IEEE Std C37.112-1996. Still they call their curve for example "IEEE Very Inverse". The eqation is the same, but the parameters don't match.
Parameters: IEEE Std C37.112-1996: A=19.61, B=0.491, p=2
ABB 2000R: 2.855, B=0.0712, p=2
"Extremely inverse" parameters don't match either.
What is this ABB version of IEEE inverse-time?
O.B.
Best to get in touch with ABB, Allentown PA.
They don't use the same equations. The IEEE formula is multiplied directly by the time dial, while the ABB formula multiples it by (14n-5)/9 where n is the time dial. Note that the A and B parameters are off by the same multiple. Curve shape is the same, it just varies with the time dial differently.
Also note that C37.112 first gives the equations and parameters, then uses them to define the center of the conformance band. I suspect you'll find the ABB curves lie within this band. Both formulas were intended to emulate an induction disk, something ABB should know about.
Indeed, the ratio A/B is about the same for both parameter sets. Thank you for a good answer.
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