darronb
Aluminum
- Joined
- May 19, 2003
- Location
- Reno, Nevada, USA
Howdy all,
I bought a used 15kVA dry-type 240V / 480V transformer earlier this year. I will be using it to power 460V VFDs on several machines. I like to buy used 460V VFDs because they are often much cheaper on eBay than 200V-class models.
I bought a “10HP” GE/Fuji 460V VFD that GE tells me is fine on single-phase input, when maximum output current is de-rated 50%. The VFD’s full rated output is 18A. So my 7.5HP 4-pole lathe motor should run well on this VFD, as the motor is rated at 9.5FLA at 460V. I will rarely need to run at full load.
I used my 115V variac and a 1.5kVA control transformer (wired for 1:4 step-up) to gradually reform the VFD’s caps, just as a precaution. The seller told me it had only recently been removed from power. Though I have not yet run a motor with it, it powered up nicely and seems to be in working order. Not bad for $50…
Today I powered up the big (230+ pounds!) 15kVA transformer for the first time. After staring at the connection diagram plate on the transformer’s case, and the existing connections inside, I was quite confused. Neither connection pattern shown on the diagram seemed to match what had been done inside. Instead, it seemed that the existing connections were a combination of the two diagrams shown. So a little doping out with a voltmeter let me know that the transformer seemed to be wired for 1:1 voltage, perhaps for use as an isolation transformer. Is there a common need for an isolation transformer with this large a capacity?
After re-connecting to match the 480V/240V diagram, I wired up a 230V input to the low side. I don’t yet have the contactor needed for my high-current 230V circuit. So I used my 115V variac and 1.5kVA control transformer (wired for 1:2 step-up) to energize the 15kVA transformer from a 115V 20A circuit. Energizing with the variac at 0V, and then smoothly turning up the voltage allows powering up this huge transformer from an ordinary 115V outlet without a huge inrush current.
This method of testing a large transformer does have a distinct danger, though. If the power fails while energized at full voltage, and the variac is left on at full voltage, the inrush current spike when the power returns will definitely pop something. Hopefully just the 20A breaker on the 115V circuit, but I wouldn’t count on it…
All seemed to go well. No bad smells or excessive heat, just the “pleasant” hum of a large transformer. My 115VAC wattmeter indicated about 1100VA current flowing once 480V was reached on the high side of the 15kVA transformer, and about 210 watts. Some of the watts are being burned in the variac and 1.5kVA control transformer, of course. I don’t have any way to measure watts at 230V or 460V, though. Does anyone have an idea about how many watts are consumed by an idle 15kVA dry transformer?
I will shut off the contactor on the input side of the transformer when it’s not needed. Other than the huge inrush current load on my domestic power when energizing this transformer, is there any problem with frequent (several times a day) power cycles on a large dry transformer?
Full Load Amps on the 240V side of this transformer is 62. I ordered a 75-Amp contactor, which should be adequate. Can I get away with powering the transformer with a 60A breaker in my main panel? I will never be running the transformer at a full 62A, other than during the moment of inrush current. Any idea how much inrush current there is on a transformer this size, and if a 60A breaker can handle it? I will use a 100A breaker if needed, and appropriate gauge wire. The transformer will be located just a few feet from the main panel, so the high-current wire run will be short.
I’ll be able to use much smaller wires on the load side of the transformer, since none of my individual 460V loads will exceed even 20A.
I bought a used 15kVA dry-type 240V / 480V transformer earlier this year. I will be using it to power 460V VFDs on several machines. I like to buy used 460V VFDs because they are often much cheaper on eBay than 200V-class models.
I bought a “10HP” GE/Fuji 460V VFD that GE tells me is fine on single-phase input, when maximum output current is de-rated 50%. The VFD’s full rated output is 18A. So my 7.5HP 4-pole lathe motor should run well on this VFD, as the motor is rated at 9.5FLA at 460V. I will rarely need to run at full load.
I used my 115V variac and a 1.5kVA control transformer (wired for 1:4 step-up) to gradually reform the VFD’s caps, just as a precaution. The seller told me it had only recently been removed from power. Though I have not yet run a motor with it, it powered up nicely and seems to be in working order. Not bad for $50…
Today I powered up the big (230+ pounds!) 15kVA transformer for the first time. After staring at the connection diagram plate on the transformer’s case, and the existing connections inside, I was quite confused. Neither connection pattern shown on the diagram seemed to match what had been done inside. Instead, it seemed that the existing connections were a combination of the two diagrams shown. So a little doping out with a voltmeter let me know that the transformer seemed to be wired for 1:1 voltage, perhaps for use as an isolation transformer. Is there a common need for an isolation transformer with this large a capacity?
After re-connecting to match the 480V/240V diagram, I wired up a 230V input to the low side. I don’t yet have the contactor needed for my high-current 230V circuit. So I used my 115V variac and 1.5kVA control transformer (wired for 1:2 step-up) to energize the 15kVA transformer from a 115V 20A circuit. Energizing with the variac at 0V, and then smoothly turning up the voltage allows powering up this huge transformer from an ordinary 115V outlet without a huge inrush current.
This method of testing a large transformer does have a distinct danger, though. If the power fails while energized at full voltage, and the variac is left on at full voltage, the inrush current spike when the power returns will definitely pop something. Hopefully just the 20A breaker on the 115V circuit, but I wouldn’t count on it…
All seemed to go well. No bad smells or excessive heat, just the “pleasant” hum of a large transformer. My 115VAC wattmeter indicated about 1100VA current flowing once 480V was reached on the high side of the 15kVA transformer, and about 210 watts. Some of the watts are being burned in the variac and 1.5kVA control transformer, of course. I don’t have any way to measure watts at 230V or 460V, though. Does anyone have an idea about how many watts are consumed by an idle 15kVA dry transformer?
I will shut off the contactor on the input side of the transformer when it’s not needed. Other than the huge inrush current load on my domestic power when energizing this transformer, is there any problem with frequent (several times a day) power cycles on a large dry transformer?
Full Load Amps on the 240V side of this transformer is 62. I ordered a 75-Amp contactor, which should be adequate. Can I get away with powering the transformer with a 60A breaker in my main panel? I will never be running the transformer at a full 62A, other than during the moment of inrush current. Any idea how much inrush current there is on a transformer this size, and if a 60A breaker can handle it? I will use a 100A breaker if needed, and appropriate gauge wire. The transformer will be located just a few feet from the main panel, so the high-current wire run will be short.
I’ll be able to use much smaller wires on the load side of the transformer, since none of my individual 460V loads will exceed even 20A.