I live in Canada were most industrial machinery is run on 575V. I have
five or six such machines in my residential garage. Some of them have
motors that are not easily replaceable such as the Bridgeport and the
Swedish gearhead drill press. I used to use a rotary phase convertor in
conjunction with a three phase transformer but I got sick of the noise.

I have bought a used 1.5 KVA single phase 220 to 600v transformer which
allows me to use small 575V VFDs that I can buy ebay every once in a
while. They seem to work fine when fead with single phase instead of
three phase.

My problem is my lathe, it is 60 year old 2-1/2 ton monster. It has a
7.5 hp motor tucked under the headstock gearbox. To replace the motor I
would have to jack the headstock end of up a couple of feet off the
floor and drop the motor. I should probably replace the 575V motor with
a 5hp 208V motor that I could buy quite cheaply, but I dont relish the job.

I have been toying with the idea of using a 30 KVA 3 phase transformer
that I have to step up 220V single phase to 600V single phase and
running the lathe with a 7.5 HP 600V VFD. The problem is that I have
not been able to get the output voltage I need. The transformer's
primary is 600V and wired in a Y and the secondary is 220V and is wired
in a Delta. I beleive the transformer original use was as a step down
distribution transformer. When I apply 230V single phase to two of the
secondary connections, I measure 500V (phase to phase,no load) on the
primary side.

I am thinking of buying a 480V VFD and driving the motor with that, the
loss of power (according to my calculations) would be about 2.5 hp which
is fine by me. Anyone have any comment on this scheme, if not I'm just
going to try it and let you know how it all works out.

stan

stanley baer wrote:

I live in Canada were most industrial machinery is run on 575V. I have
five or six such machines in my residential garage. Some of them have
motors that are not easily replaceable such as the Bridgeport and the
Swedish gearhead drill press. I used to use a rotary phase convertor in
conjunction with a three phase transformer but I got sick of the noise.

I have bought a used 1.5 KVA single phase 220 to 600v transformer which
allows me to use small 575V VFDs that I can buy ebay every once in a
while. They seem to work fine when fead with single phase instead of
three phase.

My problem is my lathe, it is 60 year old 2-1/2 ton monster. It has a
7.5 hp motor tucked under the headstock gearbox. To replace the motor I
would have to jack the headstock end of up a couple of feet off the
floor and drop the motor. I should probably replace the 575V motor with
a 5hp 208V motor that I could buy quite cheaply, but I dont relish the job.

I have been toying with the idea of using a 30 KVA 3 phase transformer
that I have to step up 220V single phase to 600V single phase and
running the lathe with a 7.5 HP 600V VFD. The problem is that I have
not been able to get the output voltage I need. The transformer's
primary is 600V and wired in a Y and the secondary is 220V and is wired
in a Delta. I beleive the transformer original use was as a step down
distribution transformer. When I apply 230V single phase to two of the
secondary connections, I measure 500V (phase to phase,no load) on the
primary side.

I am thinking of buying a 480V VFD and driving the motor with that, the
loss of power (according to my calculations) would be about 2.5 hp which
is fine by me. Anyone have any comment on this scheme, if not I'm just
going to try it and let you know how it all works out.

stan

If I'm reading your description correctly and your 575V Y service is
like the 480V Y service in the US then I don't think that transformer
will work and I don't think that 500V you read is correct either.

The US 480V Y service is 480/277V as in 480V phase to phase and 277V
phase to neutral (square root of three thing). This would put your 575V
Y service as 575/332V if I'm correct.

With a Y wired primary on your transformer each transformer primary
would be expecting to see 332V across it, not the 575V phase to phase
voltage. 575V would be across a pair of the windings, not an individual
one.

The secondary winding would be for the 220V since it's for a delta
configuration, which would make each transformer section basically 332V
to 220V, not accounting for adjustment taps and losses and whatnot.

If you were to rewire and power two of the transformers sections on the
secondary side with 220V, making sure they are properly phased, you
would most likely get about 664V on the primary side across those two
sections due to the fact that you are feeding single phase so the square
root of three thing wouldn't apply to give you the 575V.

The 500V reading you got was probably a result of the magnetic coupling
to the other transformer sections. It sure doesn't seem like this
transformer would do what you want it to do. It's probably best to track
down a suitable single phase transformer.

Pete C.

In article ,
says...
I am thinking of buying a 480V VFD and driving the motor with that, the
loss of power (according to my calculations) would be about 2.5 hp which
is fine by me. Anyone have any comment on this scheme, if not I'm just
going to try it and let you know how it all works out.

Leaving aside the transformer issue, as long as you
configure the VFD properly it'll work fine. Tell the VFD
it's powering a 480V/50Hz motor, the drive will output the
proper volts/Hz, and you'll get 50/60 x 7.5HP from 50Hz up
to whatever you set as the maximum speed on the drive. IOW,
you only lose 1-1/4HP.

Ned Simmons

"Ned Simmons" wrote in message
...
In article ,
says...
I am thinking of buying a 480V VFD and driving the motor with that, the
loss of power (according to my calculations) would be about 2.5 hp which
is fine by me. Anyone have any comment on this scheme, if not I'm just
going to try it and let you know how it all works out.

Leaving aside the transformer issue, as long as you
configure the VFD properly it'll work fine. Tell the VFD
it's powering a 480V/50Hz motor, the drive will output the
proper volts/Hz, and you'll get 50/60 x 7.5HP from 50Hz up
to whatever you set as the maximum speed on the drive. IOW,
you only lose 1-1/4HP.

Ned Simmons

Ned, I'll be the first to admit VFD's aren't my thing. Can you please
explain the loss of 1-1/4 HP? Is is related to the square of the voltage
difference between 480 and 575 ; that would come out closer to 1 1/2 HP
wouldn't it?

Bob Swinney

Pete C. wrote:



If I'm reading your description correctly and your 575V Y service is
like the 480V Y service in the US then I don't think that transformer
will work and I don't think that 500V you read is correct either.

The US 480V Y service is 480/277V as in 480V phase to phase and 277V
phase to neutral (square root of three thing). This would put your 575V
Y service as 575/332V if I'm correct.

With a Y wired primary on your transformer each transformer primary
would be expecting to see 332V across it, not the 575V phase to phase
voltage. 575V would be across a pair of the windings, not an individual
one.

The secondary winding would be for the 220V since it's for a delta
configuration, which would make each transformer section basically 332V
to 220V, not accounting for adjustment taps and losses and whatnot.

If you were to rewire and power two of the transformers sections on the
secondary side with 220V, making sure they are properly phased, you
would most likely get about 664V on the primary side across those two
sections due to the fact that you are feeding single phase so the square
root of three thing wouldn't apply to give you the 575V.

Wouldn't I rewire one of the three instead of two of the three. By my
calculations the actual wiring ratio is 1.58 ((600/Sqrt 3)/220)which
means I would get about 348v from stepping up 220 single phase using a
single trnsformer coil.

The 500V reading you got was probably a result of the magnetic coupling
to the other transformer sections. It sure doesn't seem like this
transformer would do what you want it to do. It's probably best to track
down a suitable single phase transformer.

Pete C.
Thank for the explanation Pete. I did an experiment that I did not
mention in my first post that may corresspond to what you are saying. I
applied 120 V single phase across two of the secondary connections
(the delta ones). I measured the phase to neutral voltage on the
corresponding primary coil by exposing the copper bar that links the
primary coils together. The voltage reading was about 150V.

stan

In article ,
says...

"Ned Simmons" wrote in message
...
In article ,
says...
I am thinking of buying a 480V VFD and driving the motor with that, the
loss of power (according to my calculations) would be about 2.5 hp which
is fine by me. Anyone have any comment on this scheme, if not I'm just
going to try it and let you know how it all works out.

Leaving aside the transformer issue, as long as you
configure the VFD properly it'll work fine. Tell the VFD
it's powering a 480V/50Hz motor, the drive will output the
proper volts/Hz, and you'll get 50/60 x 7.5HP from 50Hz up
to whatever you set as the maximum speed on the drive. IOW,
you only lose 1-1/4HP.

Ned Simmons

Ned, I'll be the first to admit VFD's aren't my thing. Can you please
explain the loss of 1-1/4 HP? Is is related to the square of the voltage
difference between 480 and 575 ; that would come out closer to 1 1/2 HP
wouldn't it?

Bob Swinney




Simple open-loop frequency drives deliver constant torque
up to base speed (the motor's nameplate speed) by varying
the motor voltage with frequency. In order to maintain the
proper volts/Hz ratio for the motor I was suggesting that
Stan program the drive for a 480V/50Hz motor.

480V/50Hz = 575V/60Hz

Since the motor's torque won't be affected by this change,
but its redefined base speed will be 50/60 x nameplate
speed, HP will also be 50/60 x nameplate HP, or .83 x 7.5HP
= 6.25HP.

Ned