It looks like this post didn't go out as intended a couple of hours ago. Anyway, here it is again.

Bob Swinney

DrollTroll sez:

"Do multiple small rpc's have any inherent advantage over 1 big one--other
than easier starting, more economical operation?"

AFAIK, there is no theoretical reason why multiple small RPCs won't perform as well as one large one
providing the HP count is the same. However, like most things electrical and mechanical, efficiency
favors the larger package. The disadvantages of a single, large unit would include the possible
problem of the supply source being robust enough to provide the high surge current necessary to
start.

"Are five 2hp units in fact as powerful as one 10hp unit?"

Yes. Power is power, no matter how many increments the total is divided into. In some cases, it
might be an advantage to start multiple units in sequence to avoid the large surge current required
by a single unit of the same HP. Bringing the idler up to speed with a pony motor before throwing
the switch, is one way to start larger RPCs.

"Is it better to cap each smaller rpc, or just cap the net collection?"

Considering cost, It might be more economical to use individual caps in a collection of idler motors
There could be availability and cost issues with a single large cap. Otherwise, it's a wash.

"Is delta/wye an issue? One preferable to the other? OK to mix?"

Most 3-phase motors in the sizes you would consider for RPC idler motors are apt to be wye wound
machines. Mixing delta and wye motors in RPC's is probably possible, but well outside my range of
experience. Because of phase-voltage difference between delta and wye, a mixed unit might be
difficult to balance.

"If current pathways are complicated in multiple delta wound capped motors,
it must be really crazy in wye-wound."

Current pathways would be very similar. That is to say the 3rd leg connections to caps would all
come from the same electrical points on respective motors.



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