power factor improvement

[psozot]

thread238-135043

what is the difference in installing capacitors at HT side (transformer side) than on LT side (load side)

 

[Skogsgurra]

Cost and complexity aside, I never recommend PF capacitors to be installed on the LV (secondary) side if you have a large amount of thyristor controlled loads (DC motors, controlled heating, electrolysis rectifiers etc) or VFDs connected. A large amount of low-power lights, computers, TVs and the like is also a problem. The risk of getting resonance is very real. If you have mostly linear loads like constant speed induction motors, incandescent lamps, resistive heating etc, then LV side compensation is not a problem.

Gunnar Englund

http://www.gke.org

 

[sitl]

Besides cost and complexity, I would think about installing capacitor banks on medium voltage side when I would have many transformers (or one transformer with substantial power) and measuring is on the medium voltage side.

When resonance is concerned, there are on the market capacitor banks with anti-resonant and filtering abilities.

 

[cflatters]

Personally I agree with Skogscurra

Cost is the main point though I have used a number of 3.3kV PFC units in the past for MV MCC's, though there were no power electronics drives involved.

When specifying PFC for LV MCC's and switchboards I always advocate using detuned banks. These are larger and more costly as the cabinets have to house the rejection reactors as well as the capacitors (and the heat load is higher).

 

[stevenal]

Think of capacitors as var generators. To keep losses low, capacitors should go closest to the var loads. These losses include transformer losses. Capacitors can also free up system capacity if located properly. If placed on the high side of a transformer to supply vars to equipment on the load side, you've done nothing to reduce the transformer loading or transformer losses.

 

[dewone]

Allways heard two schools of thought on this issue.
1) Place the correction as close to the inductive load. ie the motor condulet.
2) Correct the entire system as close to the point of sell. ie utility metering.
Both have pros and cons.
You need to know what your trying to accomplish with the correction. As stated earlier more effecient, or avoid the lagging current penalties from the power company.