VFD harmonics effects on generator set

In summary: In fact the motor has all six leads coming out so I can connect in the star or delta configuration. Problem with a starter - delta starter is that that starting current would still be very high still requiring an overly sized genset to allow for starting. That's why I was thinking along the lines of a VFD.
  • #1
Tawanda
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I would like to use VFDs for motor sizes ranging from 0.4kw to 15kw. My idea here is to reduce the generator foot print to the lowest possible value. My thinking is that, theoretically, I could use a 25kva generator set to drive a 20hp motor (80% operating capacity) and since the VFD eliminates the high starting current I should be okay. But my biggest concern is: how do I account for harmonics in this system. What harmonic factor can I use to correctly size the generator. Is there a filter solution for sizes 0.4kw to 15kw used in a similar set up as above.
 
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  • #2
Tawanda said:
I would like to use VFDs for motor sizes ranging from 0.4kw to 15kw. My idea here is to reduce the generator foot print to the lowest possible value. My thinking is that, theoretically, I could use a 25kva generator set to drive a 20hp motor (80% operating capacity) and since the VFD eliminates the high starting current I should be okay. But my biggest concern is: how do I account for harmonics in this system. What harmonic factor can I use to correctly size the generator. Is there a filter solution for sizes 0.4kw to 15kw used in a similar set up as above.
Welcome to PF.

So you are using a VFD to drive a generator? Are you using this as a motor-generator setup to change AC Mains voltages/frequencies? What are the input and output frequencies? And why would the input AC Mains harmonics generated by driving the VFD affect the AC Mains output voltage waveform?
 
  • #3
berkeman said:
So you are using a VFD to drive a generator?
Or using a generator to drive an electric motor, and think a VFD for soft-start might make it easier for the generator.
That will depend on the VFD input circuit and control.
I expect there will be a power factor control circuit on the VFD input.
 
  • #4
Baluncore said:
Or using a generator to drive an electric motor, and think a VFD for soft-start might make it easier for the generator.
Hmm, interesing. Yeah, which drives which...? Guess we need the OP to return to give us more information.
 
  • #5
berkeman said:
Welcome to PF.

So you are using a VFD to drive a generator? Are you using this as a motor-generator setup to change AC Mains voltages/frequencies? What are the input and output frequencies? And why would the input AC Mains harmonics generated by driving the VFD affect the AC Mains output voltage waveform?
I'm using the generator as the power source to run a 20hp motor and I am thinking the VFD could help to suppress the high starting current whilst still giving high starting torque. The idea is to use the smallest generator possible for the 20hp motor whilst leaving a 20% capacity headroom.
 
  • #6
Baluncore said:
Or using a generator to drive an electric motor, and think a VFD for soft-start might make it easier for the generator.
That will depend on the VFD input circuit and control.
I expect there will be a power factor control circuit on the VFD input.
That's right. The idea is to make the motor starting easier on the generator. But I'm worried about the effects of harmonics on the genset if I were to size the generator to run at 80% of it's full load capacity. The VFD has a 6 pulse rectifier input circuit.
 
  • #7
Tawanda said:
The VFD has a 6 pulse rectifier input circuit.
Do you know that the 3PH VFD has a simple 6 diode full-wave rectifier to the capacitor bank?
An expensive VFD might have input power factor control circuits.

Is your motor connected as Y or ∇ ?
Maybe a star to delta starter would be sufficient.
 
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  • #8
Baluncore said:
Do you know that the 3PH VFD has a simple 6 diode full-wave rectifier to the capacitor bank?
An expensive VFD might have input power factor control circuits.

Is your motor connected as Y or ∇ ?
Maybe a star to delta starter would be sufficient.
The motor is delta connected
 
  • #9
Baluncore said:
Do you know that the 3PH VFD has a simple 6 diode full-wave rectifier to the capacitor bank?
An expensive VFD might have input power factor control circuits.

Is your motor connected as Y or ∇ ?
Maybe a star to delta starter would be sufficient.

Tawanda said:
The motor is delta connected

In fact the motor has all six leads coming out so I can connect in the star or delta configuration. Problem with a starter - delta starter is that that starting current would still be very high still requiring an overly sized genset to allow for starting. That's why I was thinking along the lines of a VFD.
 
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  • #10
If you really need high starting torque (I don't know anything about your load), a VFD is a good choice. If your load doesn't need high starting torque (many loads don't), a soft-starter is typically a lot cheaper and will provide the same benefit to the generator.
 
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Related to VFD harmonics effects on generator set

1. What are VFD harmonics and how do they affect generator sets?

VFD harmonics are electrical distortions that are generated by variable frequency drives (VFDs). These harmonics can cause issues such as voltage fluctuations and increased current draw on generator sets, leading to potential overheating and damage to equipment.

2. How can I determine if VFD harmonics are affecting my generator set?

The most common way to determine if VFD harmonics are affecting your generator set is to conduct a power quality analysis. This involves measuring the voltage and current levels at various points in the system and analyzing the data for any distortions or abnormalities.

3. What are the potential consequences of VFD harmonics on generator sets?

VFD harmonics can lead to various consequences on generator sets, including increased heat and stress on equipment, reduced efficiency, and potential equipment failure. They can also cause issues with other sensitive electronic equipment connected to the generator set.

4. How can VFD harmonics on generator sets be mitigated?

There are several ways to mitigate VFD harmonics on generator sets, including using VFDs with built-in harmonic filters, installing external harmonic filters, and implementing proper grounding and shielding techniques. It is important to consult with a qualified engineer to determine the best solution for your specific system.

5. Are there any regulations or standards for VFD harmonics on generator sets?

Yes, there are regulations and standards that address VFD harmonics on generator sets. In the United States, the Institute of Electrical and Electronics Engineers (IEEE) has published standards such as IEEE 519-2014 that provide guidelines for acceptable levels of harmonics in power systems. It is important to comply with these standards to ensure the safe and efficient operation of your generator set.

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