220 volts Toshiba VFd running a 600 volts 3 phase motor

[pass99]

We have a 220v variable frequency drive driving a 600v motor 3 phase.Why it was able to run the motor?

 

[CroCop]

Same reason you can have a single phase feed into a drive and run a three phase motor.

The drive is altering the voltage & the frequency.

 

[DickDV]

There are a couple of possibilities here. First, a 600V 60Hz motor requires 10V/Hz so, from zero speed up to 22Hz, the output voltage from the drive will only vary from 0v to 220V. So the drive will be able to operate the motor at full torque in that speed range. Above 22Hz, the output will vary in Hz but the voltage will not rise further. As long as the motor is lightly loaded, the speed will increase up to whatever the speed limit is but----there will be very limited torque as the motor is starving for voltage.

The second possibility is that the drive has a voltage doubler or tripler input thereby converting the 220V input to some higher voltage. In your case it would have to be 600V. Then the drive output would reach the full motor voltage at the higher frequencies and the motor would operate normally. I've seen voltage doubling drives that convert 120V to 240V single phase to operate small 230V three phase motors but have never seen anything operating at higher voltages than that. It may be that something like that is available in Canada.

Actually, there is a third possibility--a transformer in front of the drive lifting the 220v to 600V.

 

[seppoalanen]

If in DC-circuit have inductance who loaded and then after unloaded 'serailly' with DC to AC-Skiip-circuit, so AC volage can be higher than original.

http://www.semikron.com/internet/ds.jsp?file=A06_index.html&sekId=319&sekNav=228

 

[Terry Woods]

Motors and VFDs are power devices.

As long as the drive is rated for the particular output voltage required by the motor, and it can accept various voltage sources... AND (speaking very loosely) as long as the motor voltage times the current demand does not exceed the power-rating of the drive, then it should work just fine.

In this case, the available current from the drive is greatly reduced... so if that motor is subjected to heavy loads leading to a higher power demand... and that power demand exceeds the available power, then the motor will most likely experience problems.

 

[oldgearhead]

Simple Answer = A VFD converts it's AC voltage inputs to DC. Then it 'creates' an AC voltage output waveform from DC pulses. Question:
Can the direction of a motor attached to a VFD be reversed by swapping the VFD's input wires? Answer: No....

 

[geniusintraining]

Simple Answer = A VFD converts it's AC voltage inputs to DC. Then it 'creates' an AC voltage output waveform from DC pulses. Question:
Can the direction of a motor attached to a VFD be reversed by swapping the VFD's input wires? Answer: No....

oldgearhead, its no fun when you give the answers immediately...I love the Q and A thing

 

[10baseT]

Strange that ! I thought 230V AC rectified to DC was more than 230V !
If we take that the motor is 600V star , then I suppose it would be running aound 400V delta - it would still be a be a bit strange though . Not unusual to see 415 V star motors running at 220V delta from a single phase drive .

Turning is one thing , producing useful torque is another .
Bit more info ?

 

[DickDV]

It is true that 230VAC when rectified and filtered will result in about 330VDC. However, when you convert DC back to AC, what do you know but all you can make is 230VAC. That's because you need 330VDC to recreate the peak of the sine wave which is 330V.

An AC wave with 330V peak calculates to 230VAC rms. Amazing! isn't it!

 

[rsdoran]

I get confused easily.

A motor, or electrical devices, may have a rating of 600 volts but the working voltage may be less...ie as mentioned it could be "connected" for low voltage therefore if it is 600v MAX it may be wired for 300v which would be close for the V/Hz relationship. IF I remember correctly the trick here is to change the frequency parameters in the drive..ie set the max frequency to 45Hz which should provide 5.11v per Hz...300/60=5v per Hz. The motor will not get full speed but I believe full torque would be available. Please feel free to correct me, Dick or anyone, if this is wrong.

To clarify what DickDV stated;
RMS, or Root Mean Square, is the measurement used for any time varying signal's effective value: It is not an "Average" voltage and its mathematical relationship to peak voltage varies depending on the type of waveform. By definition, RMS Value, also called the effective or heating value of AC, is equivalent to a DC voltage that would provide the same amount of heat generation in a resistor as the AC voltage would if applied to that same resistor.

Since an AC signal's voltage rises and falls with time, it takes more AC voltage to produce a given RMS voltage. In other words the grid must produce about 169 volts peak AC which turns out to be 120 volts RMS (.707 x 169). The heating value of the voltage available is equivalent to a 120 volt DC source (this is for example only and does not mean DC and AC are interchangeable).

This is why you can use things like hand drills, toasters etc plugged into a gas welder with a 120v DC receptacle.

 

[Terry Woods]

And so... Voltage Doublers can't be used? They aren't used?

If Doublers are used the voltage certainly is raised, but the available ampacity is reduced accordingly.

In the end, the power is constant, or at least reasonably so.

 

[oldgearhead]

Think about this: A semi-stock, 10th scale, RC oval track race car (brush DC) motor will draw 100 amps from It's 7 cell battery pack, during acceleration, if it's equipped with an electronic drive.

However, the same motor will only draw 15 amps if equipped with a reostat or any type of analog speed controller. Why?

Answer: In order to be competive, most racers use Digital pulse drives because they are able to make a lot more current available to the motor during wind-up. The problem with analog speed control devices is the heat dissipation required at any rate less than 'full-on'. Like the RC speed controller, a VFD makes up it's output by switching amplified DC pulses rapidly. Unlike the RC digital speed controller, a VFD 'times' the release and amplitude of it's pulse train to 'fool' the motor into thinking it's getting an AC wave-form, but it's not.

 

[OkiePC]

You guys are all right.

If you run a higher voltage motor, you must derate the drive.

You can't get higher voltages without doubling. I think there are drives with that integrated, but I've never used one. I did have a DC drive that produced 300vdc from 120 vac input. I assume it used on onboard doulbling circuit of some kind.

Look at your VFD output on a scope. Can you find the sine wave that is fooling the motor?

It ain't no fooling, the motor and all the wiring sees that trash. Why do you think they whine and buzz like they do?

Oldgearhead: Check the wiring on the motor. Are you sure it isn't dual voltage, and wired for a lower voltage?

Just a WAG
Okie

 

[rsdoran]

Actually the brushless ESD's do "time" the output for better efficiency.

A VFD doesnt "fool" anything, the incoming supply is rectified to DC then PWM (most common now) is used to develop a sinusoidal waveform...ie AC proportional to the frequency. The key is that the voltage waveform may look like this, note the output "alterrnate" :

BUT the current will look like this:

If you run a higher voltage motor, you must derate the drive.

That statement confuses me; wouldnt the motor have to be derated? Not sure derated is the correct term either! The drive can offer all its capable of but some aspect of the motor will have to lower, primarily speed I would think. Like Steve mentioned a 600vac motor could use the 230vac but you would be limited to 22Hz which if it is a 4 pole 1800 rpm motor would limit it to about 660rpm. HP = torque x rpm /5250 so the slower speed would basically mean less motor HP?

 

[OkiePC]

Yes, Ron, the motor would have to de-rated if run at a lower voltage too.

I probably didn't use the term exactly as intended, just something I've read that supports Terry's statement.

The drive can only produce a certain amount of power. Changing the voltage at which this peak power is produced is what forces the derating of the drive, if I understand it correctly.