MachineryVoltages

Heres the situation.
I just received a hydraulic press from England.
We plan to set it up and run it here.
It has a 420 Volt motor (50 HZ)and what I now believe is a 110V Control circuit.

I thought that I had a replacement motor, but upon further inspection found out that the 20 HP motor is double ended. (a shaft coes out of both sides) so I don't have another motor.

Replacing this motor is going to be a royal pain.

Perhaps DickV or somebody else knows.
Is it feasable to purchase a bucking transformer, and knock down my voltage from 480V to the 420V?

Do they make some kind of VFD/transformer combo to knock down the frequency at the same time?

Attached is a picture of the motor Nameplate.
Any comments are appreciated

Dropping the voltage down to 420V is easily done with a transformer but then you would have 420V @ 60Hz, not 50Hz like the motor wants. Reducing the frequency from 60 to 50Hz is only practical thru the use of an inverter.

Setting up an inverter to run 460V 60Hz input, 420V max, 50Hz max output, is easy but involves the expense of the drive. If you want your machine to run exactly as it did in Europe, that's your only reasonable option.

However, many many 380V 50Hz motors are brought into North America and run at constant speed for years on 460V 60Hz. They run 20% faster with 60Hz but, as long as they are not fully loaded, they survive quite nicely. That is because 380/50 is the same ratio as 460/60 so the current and therefore the available torque are nearly the same.

If a 420V 50Hz motor is run on 460V 60Hz, it also will run 20% fast but the available torque will drop about 9% due to 420/50 being a larger number than 460/60. If your plant is running its ac bus high like around 490 or so, the torque difference will be reduced. As in the 380V motors, it is quite likely that this motor will also run fine on 460V 60Hz except that it will run faster. To compensate for this if it matters, you may be able to change sheave or sprocket sizes to get the machine speed down to normal. In most cases, as long as the motor is not fully loaded, the extra speed is welcomed and nothing further needs to be done.

The reason I say that the motor must not be fully loaded is because, at full load and 20% more speed, the motor hp or kw is also 20% higher. This will almost always result in motor overtemp and short life. Limit torque to 80% and the kw and hp work out the same and motor temp should be about normal.

You can run it on your 460v 60Hz with out problems, just make sure you are not going above the rated current of the motor.
If the current increase you have to change the gear ratio in 20%.
because its a pump, changing the speed mean change the flow of the pump and might increase the current.

Thank-you Dick
I singled you out because I knew I'd get the kind of answer that I could understand.


I think that We'll probably try it out and see what kind of current it draws.
Of course before I do anything i'll run it by my Boss who is a PE. and very smart.
(E'shay ookinglay overway ymay ouldershay)

ArikBY, I must disagree on the full current statement. At full current, you will have nameplate current but at the higher voltage resulting in higher kw than the motor is rated for.

The current and therefore the torque (not directly related, remember) must be reduced so the kw stays within the motor rating.

Otherwise, the motor's smoke cannister might discharge and that would be bad!

DickDV,

So, in a case like this where 380v/50hz motors
are used on 460v/60hz supply, does reducing the
overloads/heaters 20% pass the smoke test?

Is there a rule of thumb for sizing the heaters?

I would say so. If there is any error with this method, it would be on the conservative side.

One important thing to consider is wether the load can take the extra 20% speed increase...this is usually not a problem if the load is a hydraulic pump, but if it's a mechanical load, make sure it won't mess up the systems involved.
David

Dosn't the extra 10 Hz also reduce the current because of the increased inductive reactance?? About 20%? (10/50=.2) I always thought that.

John, it would if the voltage remained constant but the voltage is increasing over that extra 10Hz as well---420 up to 480

DikDV

Sorry but I disagree with you.
The current is motor parameter that indicate the current limit of the motor.the current is the ability of the motor coil to hendel certain current.over this current the motor would smoke.
When you run the motor in 60Hz the current change because the voltage
and the frequency.but not in big different.
I was looking on motors from US 60Hz and Europe 50Hz during the day
most of the motors desine for 50/60Hz have almost same current on name plat.
for example 18AWG wire can handel 6A is it important if it 24V 0r 480V? 60Hz or 50Hz?.over 6A the wire might burn.
Same for motor current.if you run the motor in this current it safe.
If the mechanical is not adjust for the motor. the load might increase
the current and burn the motor.
According to my expireance pump need to mechanical adjust because when the speed go up the flow go up and the current too.
That somthing you need to run your system and check. it depend how the system design.

Dickdv,

I understand that more V = more I (ohm's law) The point I was trying to make is that the increase in Hz (and inductive reactance) will somewhat offset the increase in voltage So the current will be similar at 480/60 to 380/50. Otherwise the 380 motors would quickly burn if connected to 480 (roughly a 25% increase in V).

I know that this is like asking which PLC is best, or who makes the best Truck.

I only have experience with two types of drives:
TB Woods, and DanFoss.

Does anybody have a favorite VFD drive?

John, the current characteristic of an induction motor is determined by the volts per hertz ratio. As I pointed out in the above post, the ratio for 380 over 50 is the same as for 460 over 60. Therefore, you can expect that the torque output and the resulting current will be the same in both cases.

Except------there is a limit! A motor designed for 50hz base frequency and thermal capacity for its nameplate kw cannot be expected to continuing increasing its speed and kw while maintaining its same torque simply by keeping its volts per hz ratio the same at higher and higher voltages and frequencies. In fact, unless a motor is specifically designed to maintain its torque from 50 to 60hz as in dual rated motors, the motor will begin to overheat at full torque loads above 50hz. If this were not the case, you could buy a 5hp 230v motor, put it on an inverter and get 10hp from it simply by running it on 460V and 120hz. If ArikBY thinks this is possible, I invite him to try it with a motor he can easily do without!

Actually, when a motor reaches its nameplate speed at its nameplate voltage, standard practice in the inverter field is to then hold the voltage constant while increasing the frequency to whatever overspeed point is desired. The volts/hz ratio begins to fall when this is done and the torque falls in inverse proportion to the overspeed so the kw remains constant. I say constant but, in the real world, many motors can not even hold constant hp up to 50% overspeed. The magnetic circuitry in the motor goes to pieces rapidly and, unless specifically designed for more overspeed, the hp or kw starts to fall.

In most cases, when operating in overspeed with constant voltage and increasing hz, the current holds constant. When the motor starts to drop hp in overspeed and the input amps and volts (kw) hold constant, guess where the excess energy is going. That's right----heat!!

The bottom line is, in my opinion, to adhere to the nameplate limitations as closely as possible. If you are pushing the limits, you must do so with your eyes wide open and your heat gun handy. Sometimes you can cheat the system a little bit due to the service factors of many motors but I wouldn't advise turning your back on the system during testing. Motors have an uncanny ability to detect when you aren't looking and misbehaving exactly then! As competitive as the motor business is, I think the manufacturers would gladly upgrade the speed and hp output of their motors if they thought there was any simple way to get away with it.

Dike

I never said that I can run motor with VFD from 5HP to 10HP.
You probably miss understand me.
My point is,if the motor run on 60H 460V instead of 50Hz 420V with out inverter, with out droping speed do you think the motor would burn?Why?