Synchronous Reactance for Induction Motors?

[BigMotorGuy]

Is the synchronous reactance a parameter for asynchronous induction motors or does it only apply to synchronous machines? If so, how does one calculate it from typical equivalent circuit info?

Also, how does one determine the transient time constant on an induction motor in the event of a fault?
Is my assumption that this parameter is the time it takes for the initial subtransient fault current to reduce to the transient fault current correct?

 

[dpc]

I don't think synchronous reactance has any purposeful meaning for an induction machine - at least for short circuit calculations. The time constant would need to be provided by the machine manufacturer. ANSI C37 has an approach for dealing with induction motor fault contributions for purposes of circuit breaker duty calculations. For large motors (>1000 hp or >250 hp @3600 rpm) they use 1.5 Xd" at interrupting time (2-8 cycles). For 50 to 250 hp they use 3 Xd" and for <50 hp, they use 4 Xd".