Derating PFC Capacitors for 50Hz Wind Turbine Conversion | Expert Tips

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Discussion Overview

The discussion revolves around the derating of passive power factor correction (PFC) capacitor banks when converting a wind turbine from 60Hz to 50Hz operation. Participants explore the implications of frequency changes on capacitor performance and reactive power requirements.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires whether derating the capacitor banks for 50Hz operation involves simply downsizing from 15 to 12.5 kVAR.
  • Another participant suggests that due to the impedance relationship, there may be a need to upsize the capacitors to around 17.5 kVAR, indicating that they could handle more inductive reactive power.
  • A different viewpoint considers that as frequency decreases, inductive reactance also decreases, leading to a potential reduction in required capacitive reactive power.
  • One participant proposes that both previous claims could be valid, leaving room for further discussion.
  • Another participant argues that capacitors would experience less stress at 50Hz compared to 60Hz, suggesting that more capacitance may be needed at 60Hz for the same filtering effect, but asserts that using 50Hz will not damage the capacitors.

Areas of Agreement / Disagreement

Participants express differing views on whether to derate or uprate the capacitors, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

The discussion includes assumptions about the relationship between frequency, inductive reactance, and reactive power requirements, which may not be fully resolved. The implications of filtering effectiveness at different frequencies are also noted but not conclusively addressed.

Hektor
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I'm converting a first generation, fixed speed wind turbine from 60Hz operation to 50Hz operation. There are passive PFC capacitor banks in the downtower box on the turbine. How are the capacitor banks derated for 50 Hz operation? Is it as simple as, for example, downsizing from 15 to 12.5 kVAR (17%)? Thanks for any help!
 
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I think you are actually upsizing...due to the impedance of 1/JωC
So more like 17.5 KVAR. They should be able to handle more inductive reactive power...although now it may be too much in a capacitive way.

But I'm pretty sure that is wrong. Just some random thoughts.

Dice it.
 
I was thinking that because xL = jwL, inductive reactance would go down as frequency decreases. And as current will be staying the same, there will be less inductive reactive power (VAR). Then, I figured I would need less capacitive reactive power to compensate.
 
Perhaps both are correct. They are both a logical conclusion.

Or not...someone else will speak up soon...
 
Think of it this way. What is the easiest life for a capacitor? It would be having only pure DC at its inputs. 60 changes a second is more work than 50 changes a second. If you look at how much energy the device is exposed to , that would also be less. That would imply for the same level of filtering at 60 Hz you would need a bit more capacitance than at 50 Hz as the number of positive pulses per unit of time, assuming a full wave rectified output fed to the capacitor, would be less.

In a nutshell, you will not be hurting the capacitors by feeding them 50 Hz but your downstream DC will be slightly less filtered.
 

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