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VFD and 3ph AC Motor - Nameplate shows PWM and CSI ratings?

robert574

Plastic
Joined
Oct 13, 2019
Location
Central Florida
Has anyone looked at some of the 3 phase ABB/Reliance motors for sale. The prices on used ones seem good, then I started looking at all the name plates. The motor nameplate is normal, 3ph, 230V, 1740rpm, 60Hz and Ins class F. Then you look at the Inverter Duty plate and it has PWM - VVI - CSI on it. What's up with that? CSI is constant current and VSI would be constant voltage that I expected to see. Can someone explain. Is this just a normal 3ph motor or something else?
I want to run the motor on a standard VFD, but I'm worried it might be different.
 

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Normal motor. It just defines what the capability is on a drive. Its basically 10:1 speed range constant torque which is good. A good standard motor is typically 4:1 speed range constant torque.

Nameplate says that its good for PWM or VVI or current source. VVI is old technology where they varied the voltage along with frequency - not PWM. More heating and lower efficiency than PWM.

Its an old motor but should be a good one.
 
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And this is not an ABB motor. This predates ABB by a lot of years. This motor was made when Reliance was still independent and based in Cleveland. Baldor bought Reliance motors in 2007 and then ABB bought Baldor in 2011.
 
It should be here tomorrow. I sent an email to ABB/Reliance for some info. It looks like they closed the plant in Cleveland and the current ones are made in AR. I just haven't seen that inverter label before and don't want to go down a different road.

Edit: Motor's here. Looks like a normal 3ph motor, just has the leads inside the junction box. It must be explosion proof, the cover for the wiring is round and screws on. I read something that said the shaft is stainless steel.
 
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PWM = Pulse Width Modulation of a Voltage Source Inverter (VSI), which is what all low voltage drives use now. Any drive can be programmed to control any motor. PWM drives are around 97% efficient. PWM can however cause voltage spikes that can damage the insulation, hence needing different insulation voltage ratings.

VVI = Variable Voltage Inverter, also known as a "6-Step Inverter", a technology that pre-dates PWM control and ceased to exist in the marketplace once PWM came along because it was not as good, needed "matching" to the motor, and the drives were physically larger and only about 90% efficient. VVI drives also caused more motor heating, so motors had to be over sized (or de-rated, however you want to look at it).

CSI = Current Source Inverter, another old technology that was supplanted by PWM drives for low voltage (still used in Medium Voltage though). A CSI drive controlled the current going to the motor, the voltage was allowed to be whatever it needed to be. CSI drives were hell for stout because they were built with thyristors instead of "dainty" little transistors and used reactors instead of capacitors on the DC bus. But they too needed to be impedance matched to the motor it controlled, so when you swapped out a motor, someone had to come out and add burden resistors to the drive to tune it to the motor. Once PWM came along that allowed any drive to work on any motor, CSI fell by the wayside. CSI drives were were super easy on motors, however often less than 90% efficient. Modern versions that are used on MV motors are now using CSI-PWM, so the motor matching is no longer an issue, and the efficiency has improved to be the same as PWM - VSI. But they have size / power and voltage limitations compared to PWM.
 
The wiring head looks like a typical explosion proof head. It should have a threaded hole on a side for a metal conduit.
 
Back in the day of that nameplate... might be there for a reason. Like covering someones ass.
If somebody connects the incorrect inverter, then we told you what it should be.
 
The motor p/n is R14X9127N.
I was contacted by their support group and they told me it was just a standard 3ph motor and there was no problem operating it with a variable frequency drive VFD.
I tested the windings with an ohmmeter and everything seems ok. There are an additional 2 wires marked P1 and P2 that go to an internal thermal cutout. Since it's 3ph they have to either be in series with the contactor coil or in my case to the VFD controller.
Also, the shaft on this motor is stainless and the wiring box has a screw off cap and there is an additional threaded conduit opening on the side.
I also noticed the nameplate says it can run at 120Hz. I tried to find some HP curves and it looks like it would have around 50% HP at 120Hz. That's still usable for some work.
 
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PWM = Pulse Width Modulation of a Voltage Source Inverter (VSI), which is what all low voltage drives use now. Any drive can be programmed to control any motor. PWM drives are around 97% efficient. PWM can however cause voltage spikes that can damage the insulation, hence needing different insulation voltage ratings.

VVI = Variable Voltage Inverter, also known as a "6-Step Inverter", a technology that pre-dates PWM control and ceased to exist in the marketplace once PWM came along because it was not as good, needed "matching" to the motor, and the drives were physically larger and only about 90% efficient. VVI drives also caused more motor heating, so motors had to be over sized (or de-rated, however you want to look at it).

CSI = Current Source Inverter, another old technology that was supplanted by PWM drives for low voltage (still used in Medium Voltage though). A CSI drive controlled the current going to the motor, the voltage was allowed to be whatever it needed to be. CSI drives were hell for stout because they were built with thyristors instead of "dainty" little transistors and used reactors instead of capacitors on the DC bus. But they too needed to be impedance matched to the motor it controlled, so when you swapped out a motor, someone had to come out and add burden resistors to the drive to tune it to the motor. Once PWM came along that allowed any drive to work on any motor, CSI fell by the wayside. CSI drives were were super easy on motors, however often less than 90% efficient. Modern versions that are used on MV motors are now using CSI-PWM, so the motor matching is no longer an issue, and the efficiency has improved to be the same as PWM - VSI. But they have size / power and voltage limitations compared to PWM.
Is PWM the same as VFD? Or if not, what is the difference. And on the inverter name plate at 6Hz it lists 38V instead of 230V. I wonder why that is.
 

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Pulse width modulation (PWM) is the way most modern inverters work to create a simulated sine wave of specified frequency for the current. VFD is variable frequency drive.

Most inverters can work in V/Hz mode, where supplied volts are directly proportional to output frequency in Hz. So in case of 6 Hz the motor voltage would be lower than 230 V. I don't know why the motor nameplate says 38 V instead of 23 V. It should not matter. In VFD parameters you should setup this motor as 230 V motor.
 
Is PWM the same as VFD? Or if not, what is the difference. And on the inverter name plate at 6Hz it lists 38V instead of 230V. I wonder why that is.
Almost all vfds are pwm of an average quality algorithm.


As for the voltage, a super conducting motor would have a linear volts per hz curve.

In reality you have a resistance to the windings that requires a voltage for a given amount of current.

To maintain nameplate full load torque, you would need something like 15vac at 2 to 3 hz, full nameplate amps, and the product of nameplate amps x 15 x 1.73 will be the waste heat the motor will waste, doing no work.


That value is approximately the same as the waste heat it burns up at 60hz, but now it's producing shaft hp at an efficiency of say 85%.
 
Pulse width modulation (PWM) is the way most modern inverters work to create a simulated sine wave of specified frequency for the current. VFD is variable frequency drive.

Most inverters can work in V/Hz mode, where supplied volts are directly proportional to output frequency in Hz. So in case of 6 Hz the motor voltage would be lower than 230 V. I don't know why the motor nameplate says 38 V instead of 23 V. It should not matter. In VFD parameters you should setup this motor as 230 V motor.
Good answer. If we had a voltmeter attached to the output of the VFD, would it (in theory) show a varying voltage to the motor as you adjust the speed and output frequency (not the PWM, but the sine wave)? And I wonder how the volt meter would read a sine wave made of chopped pulses.
 
And this is not an ABB motor. This predates ABB by a lot of years. This motor was made when Reliance was still independent and based in Cleveland. Baldor bought Reliance motors in 2007 and then ABB bought Baldor in 2011.
I wonder what they will do with all the different designs. I'm liking this motor more all the time.
 
Good answer. If we had a voltmeter attached to the output of the VFD, would it (in theory) show a varying voltage to the motor as you adjust the speed and output frequency (not the PWM, but the sine wave)? And I wonder how the volt meter would read a sine wave made of chopped pulses.
I think a proper voltmeter would show a varying voltage with different output frequencies. Many voltmeters these days are TRMS (True RMS) devices, which (in theory) can measure different wave forms. A high chopping frequency will affect the accuracy of the reading, so don't expect two different meters to show an identical result.
 
Before this, it has been my understanding that with a 3ph motor the VFD controls the frequency but the voltage remains constant at all speeds and the motor will maintain constant torque at full load as the speed drops.

(Ignoring power factor and losses) at full load:
For instance a 1hp, 3ph, 60hz,1725 rpm motor, 220V, 3A will produce about 36 in-lbs of running torque
and at 30hz, 0.5hp, 220V, 1.5A, 863rpm, still produces 36 in-lbs of running torque.

basically constant voltage but half frequency, hp, current and speed.

Is that not how it works?
 
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Before this, it has been my understanding that with a 3ph motor the VFD controls the frequency but the voltage remains constant at all speeds and the motor will maintain constant torque at full load as the speed drops.

Is that not how it works?
No, the motor would burn up.

You have to add some volts to a linear volts per hz line in order to get the magnetic flux density needed to produce a torque. (This is mostly because of the winding resistance) Better than average vfd manuals explain all of this and will give you examples of how to set the volts per hz curve for various reasons. Most vfds default to 10 to 20% nominal voltage at 1 hz. As the frequency climbs the voltage increases linearly.

For energy efficiency, you can reduce the volts below the linear volts per hz line, if the motor is oversized, or if the load is a fan or some pumps, which have a cubic load curve.
 
At or below the design motor base speed, the motor torque remains constant as the speed changes, because the V/Hz ratio is kept constant (other than the issue johansen mentions). So voltage varies along with Hz and because HP is a mechanical description of torque and speed, the HP is changing along with the speed.. Once you get to base motor speed you will also be at the maximum available line voltage. That means if you continue to increase the Hz, the voltage can no longer increase with it, which means the torque output of the motor starts to decrease. So as you get above 60Hz (or 50Hz as the case may be with the motor design), the torque decreases with an increase in speed, so the HP remains constant. So a 1HP motor at 120Hz is still providing 1HP, but at less than half of the rated torque.
VFD-Volts-Hertz-Curves.jpg
 








 
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