judylev
Electrical
- Jan 10, 2009
- 7
i bought a direct drive screw compressor with a 1977 Schorch 3ph 30kw 50hz, 1440rpm, 380v Y/220v delta 12 wire motor that was supposedly modified for 230v 60hz and I assumed this meant this modified motor was rewound to slip down to around 1500 rpm and so I install a 28 kva 230v delta/delta transformer.
It turns out that the importer changed nothing in the motor but only connected it YY with instruction to supply 230 volts but it is drawing 35 amps over the 220 volt nameplate FLA of 105A while pulling the supply voltage down around 210v even without full load.
i realize now that i have a 1750 rpm motor overspeeding a compressor by 20% while trying to produce 36kw but being under supplying the required 60hz voltage of 115% or 260v. I re-tapped the transformer to 240v and beefed up my cabling but this is not working out.
I can manage my overload cycling to control transformer and motor temperature but it seems i have to reduce the load and/or increase the voltage enough to get some hours out of this setup.
A bigger distribution transformer is out of the budget but i had bounced around the idea of having the tap modified by dropping primary turns or adding secondary turns to get the voltage up but i have to acknowledge that i am up against the power limit already.
From what i learned since yesterday, i dont believe an ungrounded delta boost transformer is an option.
the VFC option is out of the budget and i also wonder the quality of that solution anyway given the low supply voltage.
While i have yet find a reference, i am considering ways to add a belt drive to slow the pump down and have a sketch here of offseting the motor latterally with an adapter plate and adding a cutout of the bell housing. Any comment would be appreciated.
i found that for NEMA T frame motors a 15% undervoltage reduces max torque by around 15% and increased full load amps by around 15%.
Can i assume that my pully ratio will target the nameplate FLA of 105 amp at 220 volts? I have a rule of thumb for air compressors generally using 2.5 Amps of 230V 3ph per HP an the factory paired a 40HP motor.
Do i get any credit for supplying an additional 10 or 20 volts to the 220V nameplate voltage?
if i have a 1.2 service factor does that give me license to exceed the FLA 20%?
What are the relative affects of each an overload and an undervoltage?
I guess I am looking for numbers that will burn up this thing after a few months rather than rite away while i am shopping for another 30kw 230v motor.
It turns out that the importer changed nothing in the motor but only connected it YY with instruction to supply 230 volts but it is drawing 35 amps over the 220 volt nameplate FLA of 105A while pulling the supply voltage down around 210v even without full load.
i realize now that i have a 1750 rpm motor overspeeding a compressor by 20% while trying to produce 36kw but being under supplying the required 60hz voltage of 115% or 260v. I re-tapped the transformer to 240v and beefed up my cabling but this is not working out.
I can manage my overload cycling to control transformer and motor temperature but it seems i have to reduce the load and/or increase the voltage enough to get some hours out of this setup.
A bigger distribution transformer is out of the budget but i had bounced around the idea of having the tap modified by dropping primary turns or adding secondary turns to get the voltage up but i have to acknowledge that i am up against the power limit already.
From what i learned since yesterday, i dont believe an ungrounded delta boost transformer is an option.
the VFC option is out of the budget and i also wonder the quality of that solution anyway given the low supply voltage.
While i have yet find a reference, i am considering ways to add a belt drive to slow the pump down and have a sketch here of offseting the motor latterally with an adapter plate and adding a cutout of the bell housing. Any comment would be appreciated.
i found that for NEMA T frame motors a 15% undervoltage reduces max torque by around 15% and increased full load amps by around 15%.
Can i assume that my pully ratio will target the nameplate FLA of 105 amp at 220 volts? I have a rule of thumb for air compressors generally using 2.5 Amps of 230V 3ph per HP an the factory paired a 40HP motor.
Do i get any credit for supplying an additional 10 or 20 volts to the 220V nameplate voltage?
if i have a 1.2 service factor does that give me license to exceed the FLA 20%?
What are the relative affects of each an overload and an undervoltage?
I guess I am looking for numbers that will burn up this thing after a few months rather than rite away while i am shopping for another 30kw 230v motor.
