I have an issue with a phase converter fed by 238 v phase to phase. In the morning the phase converter will trip the 100 a breaker because the idler motor goes into LRC and will not start.we meggered the motor and the windings were fine . I’m fairly certain it’s the start capacitor bank that is the issue but I do not know the correct sizing of the capacitors and cannot get a definitive answer from the manufacturer on the size of the starting bank. The motor is a 230v, 3phase, 30hp, 70.8a, sf 1.25, design B motor, the phase is good for up to 80a . Can anyone tell me what size the capacitor bank should be?
Phase converter capacitor bank
- Thread starter Jnewell
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junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Read the value off the caps that are in the converter now.... 
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
I've seen various recommendations ranging between 100 μF to 200 μF per HP for the start capacitor with a 230V motor.
Is this a new installation, or has this problem just appeared on a previously working setup? If it was working before then the cap bank must've been sized reasonably well, and something has failed or changed. Did you check whether the phase converter motor can be rotated manually and isn't binding?
Is this a new installation, or has this problem just appeared on a previously working setup? If it was working before then the cap bank must've been sized reasonably well, and something has failed or changed. Did you check whether the phase converter motor can be rotated manually and isn't binding?
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