Power Factor Correction Caps

[ndzied1]

Well, as usual, the answer to the question is not as it first appears. The caps had nothing to do with it, but, as the most "unknown" element in the system got the first blame.

Turns out we were unwittingly trying to perform an experiment talked about in http://patchn.com/forum1/viewtopic.php?t=612.

The system has no relief!!!! and due to a miswired unloading valve, we were trying to create infinite pressure... as you might expect, this takes a lot more current than a 40hp motor can handle.

Anyway, I have learned a lot about pf correction caps and I'm sure others have also. Thanks to all for your answers.

 

[leitmotif]

Power factor correction on a motor applies only to the line.
Total impedance = Ir +(IXl-IXc). If the reactive current (IXc) drawn by the capacitors is equal to the reacive current (IXl) of the motor winding they are opposite and line current is only Ir (resistive) with a power factor of unity.

Read back a few posts to Norms response to me where he said the motor would only do a partial rotation stop and then do a partial rotation. Sounds mechanical to me. I would surely check for free rotation and split the pump and motor coupling to be double sure.

Using the average VOM to read motor windings will only confirm you have a good winding or bad winding (open) which is important of course. If you really want to know the resistance use a low volt supply (6 volt battery may work OK) across each winding and read the amperage - resistance can be calculated. That is how we calculated the contact resistance on large circuit breakers.

Dan Bentler

 

[guest1]

info

Using the average VOM to read motor windings will only confirm you have a good winding or bad winding (open) which is important of course. If you really want to know the resistance use a low volt supply (6 volt battery may work OK) across each winding and read the amperage - resistance can be calculated. That is how we calculated the contact resistance on large circuit breakers.

Dan this is some very good information.
Thanks

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