1 Phase Motors and Fault Calc's 2

[mpparent]

Hey All,

I didnt' think about it much, but IEEE red book does not give any guidance about the inclusion of single phase motors in fault calculations. Am I missing something,...any reason for this?

Mike

 

[dpc]

Any contribution from a single-phase motor would be extremely small and short-lived. In most industrical facilities, anything larger than 1/2hp would be three-phase. Since most of these are 120V or 208V, any contribution beyond the transformer would have to be insignificant.

I've always neglected single-phase motor contributions. I think this is an allowed assumption per ANSI C37 procedures.

 

[mpparent]

Thanks again dpc,

Mike

 

[cuky2000]

Several years back,

Several factors contribute to make less critical the performance of SC for single phase motors:

- The power source is usualy a small transformr, producing small available SC.
- Cost of SC study was difficult to justify for small installation.
- Single phase motors are relative small capacity typically up to 5 HP.

- At LV the cable impedance is relativelly high. Therefore the SC is damping rapidly to safe levels.
- The contribution to SC is relatively small.