Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 23 replies
  • Subscribers 32 subscribers
  • Views 2859 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Regenerative Drives - Effect of Power Factor

Former Community Member
Former Community Member

I am working on a small 16kW hydro system which is experiencing about 15% loss in the Regenerative VSD. To maximise efficiency the turbine operates at variable speed. The VSD controls a synchronous generator and supplies the grid.

The VSD is a Siemens G120. The datasheet states that the efficiency should be around 96%, whilst also stating that the Power Factor is 0.9. I am looking to replace this drive for an ABB ACS 880-11 which has similar efficiency but a unity power factor.

Firstly can I trust these datasheets since, I assume, they relate to the VSD delivering electrical energy to a motor rather receiving it from a generator? Is there an efficiency penalty for regenerative generation?

Secondly, with all else being equal, will the drive with a unity power factor equate to more electrical energy on the meter than the drive with a 0.9 power factor? 

Thanks

 

 

Parents
  • 0

    I can see several problems here. You said above “true RMS sampling rate of 64 samples a second”. You also say the meter measures kW, not kVA. I assume you are using a scope that can do a true RMS multiply of two traces that measure the voltage, and the current. The power meter cannot produce a proper result at 64 samples a second, and the waveform out of the inverter will be some kind of chopped thing at several kHz, so that sample rate is inadequate, as per Nyquist, so the result is probably meaningless.

    You have also assumed that the VSD is efficient in braking mode and that your PM motor characteristic is similar to an induction motor, which it cannot be in terms of slip. Is this VSD intended for PM motors? I suspect that the meter does not respond well to the very curious VSD waveform when returning power to the mains and that the return path PF may also not be 1.0 as you are expecting. 

Reply
  • 0

    I can see several problems here. You said above “true RMS sampling rate of 64 samples a second”. You also say the meter measures kW, not kVA. I assume you are using a scope that can do a true RMS multiply of two traces that measure the voltage, and the current. The power meter cannot produce a proper result at 64 samples a second, and the waveform out of the inverter will be some kind of chopped thing at several kHz, so that sample rate is inadequate, as per Nyquist, so the result is probably meaningless.

    You have also assumed that the VSD is efficient in braking mode and that your PM motor characteristic is similar to an induction motor, which it cannot be in terms of slip. Is this VSD intended for PM motors? I suspect that the meter does not respond well to the very curious VSD waveform when returning power to the mains and that the return path PF may also not be 1.0 as you are expecting. 

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines