I assembled a 5 hp converter using a Baldor 3600 rpm motor as the idler. To test it a connected a 5 hp Hico (Korean) Motor. The Hico is 1725 rpm, four pole, 60 cycle 230 volt and considerably larger than the Baldor. After the converter is started, I connected the test load via a knife switch. The Hico turns but will not come up to speed. I then connected the Hico up to a 10 hp converter and it runs fine. What’s with that??? I welcome your responses. My learning curve increases. Ha ha
Ignore.. We'll come back to it...HOW a load-motor
gets "up to speed'..
WHEN it has done that, it is a "consumer".. but only when actually UNDER "load".
UNTIL.. it IS "loaded', it actually functions just as much as a supplement TO the "pilot" idler as it does a "consumer" of power.
PM is full of situations where a guy turns-on OTHER 3-Phase machines to run
idle.. so as to get enough total reserve online to START a heavier load than the idler alone can haul. Then once his problematic load IS up and running, shut's down those other machines and goes and does the work.
If the workload is a LIGHT one? The "load motor" is STILL contributing partly to the overall stability.
So we have situations where a 3 HP idler is powering a 5 HP machine motor. Which might only see a "real" load asked of but 1.5 -2.5 HP from it.
"Back to"...
In this case, even though your test motor was NOT loaded, it was not that easy to "start".
So it never reached the "happy place" where it was actually aiding the idler...until it DID have a heavy load demanding service. it's like water skis. FIRST you have to get "up".
JST mentioned the 66% or idler @ 1.5 times the HP for load HP .. a very common rule of thumb.
- That works more often that not.
- One can STILL add the temporary - or even full-time - contribution of another machine. Or even several. And "get by".
More often than not.
Even so, some of the longer-serving commercial makers of RPC have published examples of progressively harder-starting types of load.. that call for FAR greater multiples of RPC idler to load motor.
Four
and more times oversize, even.
At which point?
Finding POWER to get the idler ITSELF up to speed may have become a "non-trivial exercise". Even with "pony start".
"Works well, and lasts a long time" RPC
generalizations are still subject to "TANSTAAFL"