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Capacitor placement problem

Capacitor placement problem

Capacitor placement problem

(OP)
Our system is approximately 60% underground.  It's a 12.47 kV system.  The problem is the placement of capacitor banks.  Since our system is underground, Ferro-resonance is a problem.  Capacitive more than inductive in our system.  We need to correct power factor, but is very difficult to say the least.  Has anyone dealt with this type problem and come up with a successful solution?

RE: Capacitor placement problem

It is possible. What has been tried and what is the issue? Is this an anticipated problem or a study show that?

Ferro-resonance can be avoided by adjusting the reactances, ensuring 3 phase switching (avoiding single phasing), keeping some load, etc.
 

RE: Capacitor placement problem

(OP)
rbulsara, We have tried to correct power factor, but areas within pad mounts, switchgear, etc. don't allow much additional equipment inside them.  Plus, upon adding even small capacitor units, at the end of the primary tap, where the new building is being built, it seems to increase the power factor instead of bring the system toward unity.

RE: Capacitor placement problem

Too many unknowns from your post. What is the existing power factor? leading or lagging? what type of loads are there?

What type and size of caps you added? What do you mean no room in side the switchgear? Any MV capacitors will be in its own enclosure and most likely fed by a separate breaker and controls. Not sure what is attempted in your case.

 

RE: Capacitor placement problem

Also where in relation to the capacitor connection point, are you measuring the pf?

RE: Capacitor placement problem

If you are simply trying to improve the power factor to reduce power factor penalties for purchased power, the caps can be place in your substations.  

You should also be able to install caps at service points to major customers that have three-phase switching.   

 

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

RE: Capacitor placement problem

(OP)
dpc and rbulsara,
We have the vast majority of capacitor banks located within our substations.  Wanted to improve at the delivery point.  Plus reduce purchased power penalties.  That's why I am looking at small units only.  Say 3-100- 3-150 KVAR units.  Measuring PF at station.  This could be 1000' to 2.5 miles away from delivery point.
Thanks for your assistance.

RE: Capacitor placement problem

Do you mean load such as motors, when you say delivery point?

You can do that, but then you will have to reduce equivalent caps at the substations. Substations caps are adequate for reducing penalty, adding more caps at the load will not help.

Perceived reduction is copper losses are usually negligible. Why do you want to do that? Is there a benefit?

RE: Capacitor placement problem

There's an old adage - "A problem well defined is a problem half solved."  I think it applies here because you haven't defined the problem very well.

What everyone has been trying to pull out of you is more details, like
- what is the present load at the substation (kW and kvar)
- what is the load at light load conditions
- substation transformer MVA rating
- substation capacitor bank rating(s)
- what does the existing voltage profile look like
- what would it look like with more capacitors along the line
- what power factor would you want

It may very well be that the substation capacitor banks is the best you can possibly do for the circuit.  I can't really tell from what has been provided so far.

The ferroresonant circuit is mainly initiated by single-phase switching.  Eliminate that and you virtually elliminate ferroresonance.

Would like to help further, but need a lot more input.

RE: Capacitor placement problem

Quote:

Capacitive more than inductive in our system.  We need to correct power factor, but is very difficult to say the least.
What does this mean?  If the system is capacitive, you don't add capacitors to correct the power factor.

RE: Capacitor placement problem

As MAGOO2 is telling you start by modeling the feeders.
If you have a system such as this, then you need to get the line analyisis software and start modeling.  
JIM
 

RE: Capacitor placement problem

Quote:

Plus, upon adding even small capacitor units, at the end of the primary tap, where the new building is being built, it seems to increase the power factor instead of bring the system toward unity.
Isn't increasing the power factor bringing it toward unity?  Is the system leading without the line capacitors because of cable capacitance?

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