Synchronous compensator vs capacitor PFC

[Pafi]

I need some help in preparing my answer for one client who needs PFC for a 6kV network. I proposed an automatic bank but he asked me why not synchronous compensator. He has no synchronous motor installed, so if would be to choose this method he will have to buy one.
Maybe someone can explain, breafly, the differences and problems for synchronous compensator.
Thank you!
Pafi

 

[jraef]

Quick version:

Automatic Power Factor Correction (APFC) capacitor systems = step control. You add or subtract capacitance by turning fixed capacitance devices on or off. Good for small incrementqal and / or predictable changes and not much problem with inaccuracy or overshoot that will result. Other potential problem is transients causing damage to sensitive devices every time a cap bank is switched on or off.

Synchronous CONDENSER (proper term, not compensator AFAIK)= analog control, i.e. PF is altered in direct proportion to what is needed without overshoot and with a high degree of accuracy. Can accomodate a wide swing of operation at any time, and creates no switching transients (except when motor is first turned on. There is even a case to be made for the SC being used to reduce harmonics. Drawbacks are power consumption of synchronous motor if not being used for some other purpose, and initial cost if one does not already exist, although a good engineer can probably make a case for payback.

Quick and dirty rule-of-thumb,
500kVAR and under, Capacitors
Over 500 - 1000kVAR, consider SC,
Over 1000kVAR, SC for sure

6kV system may warrant SC since APFC capacitor systems are more expensive in MV, but then again, so is everything else.

Try searching for info on synchronous condensers. People that can supply them usually will supply APFC systems as well, but not vice-versa. Quando Omni Flunkus Moritati

 

[DougMSOE]

What he said.

 

[neps3]

Pafi

Agreed with all above answers. Consider installing / replacing an induction motor with a syn motor and operate in leading power factor. This compensates for teh lagging pf but depends on the Vars.

If you install a SC it has no load except the windage and the losses.

Dynamic response is better.

 

[kssschsekhar]

all the above suggestions are correct. Any ways the system is 6kv. IF Capacitors requirement is >500 KVAR then

replace/install a syschrous motor of required capacity in place of the present induction motor. Then no load losses can be avoided.

 

[Pafi]

Can not be replaced only one motor. He has 16 motors, 250 kW each and the total reactive power needed is 2000 kVAr. So, has to be a new synchronous condenser capable to deliver 2000 kVAr.
Pafi

 

[neps3]

Pafi

Does your tariff has a separate charge for MVA.

I suggest you should install the one SC, but to prove the benefit do a Cost Benefit Analysis. (NPV).