power factor correction on 1&3 phace motor 3

[gunz]

I am very interested in the assembly and construction of "tank circuits", the ability to increase the power factor of every individual motor by using mathmatical formulas, and adding capacitors to increase KVAR of the motor. My questions are how and what formulas do I need to follow?

 

[redtrumpet]

Motors need magnetizing current that is 90 degrees out of phase with the torque-producing current. This magnetizing current can be provided by the power system, or by capacitors connected in parallel with the motor. Capacitors should be applied only on induction motors (synchronous motors don't require capacitors to adjust their power factor).

The general rule is that the amount of capacitance added to a motor should not exceed the value required to raise the no-load power factor of the motor to unity. This is to prevent self-excitation overvoltage at the motor terminals.

Most, if not all, motor manufacturers will list the maximum capacitor kvar to be added. This avoids having to calculate the maximum kvar. If it is an existing motor, the no-load current can be measured with a clamp-on ammeter and the load disconnected.

Example: assume 100 hp, 575 V motor with measured no-load current of 29.6 A. For safety factor, assume 90% of that is magnetizing current. Then capacitor kvar = (0.9(E)(I)3^0.5)/1000. Use 600 V for E because that will be the nameplate rating of the capacitor. capacitor kvar = 27.7 kvar @ 600 V. You would probably use a 25, 27, or 27.5 kvar capacitor depending on what is available.

Capacitors selected in this manner will typically boost power factor to .95 at full load and even higher at reduced loads.

 

[jbartos]

Suggestions:
1. Low voltage capacitor banks tend to be connected in Delta connection
2. Medium voltage capacitor banks tend to be connected in Star connection
3. Check this Forum for similar posting and calculations
4. Visit

http://www.thomasregister.com

and type Banks: Capacitors under Product / Service which will return 6 companies to inquire about capacitors. These companies have very good tech support with software fine tuned for various capacitor banks applications. However, what you do, as your homework will be to your advantage in any case.

 

[SooryaShrestha]

Further to the above querry, please enlighten us by posting the following querries.
1) In high voltage capacitors for reactive compensation, why are the insulating transformers used?
2) How to calculate the sizing the insulating transformer?
3) What are the other equipment required for the complete package of the capacitor unit for the reactive compensation?
4) How are the other equipment selected?

 

[jbartos]

Suggestions to the previous posting marked by ///\\\:
1) In high voltage capacitors for reactive compensation, why are the insulating transformers used?
///They can trap tripplen harmonics, reduce voltage if needed, isolate zero sequence current, and isolate the capacitors from the grid.\\2) How to calculate the sizing the insulating transformer?
///The rated line current of the capacitor bank + design margin = rated line current of the transformer.\\\
3) What are the other equipment required for the complete package of the capacitor unit for the reactive compensation?
///Discharge resistors, switching equipment to adjust capacitance and thereby compensation, in star connection in-line resistors to reduce inrush currents, safety disconnects, protective devices, and switchgear.\\\
4) How are the other equipment selected?
///According the capacitor banks rated values, and compensation VAR size, compensation steps, capacitors connection, type of capacitors, power quality, etc.\\

 

How to size PF Cap. For 4160 Volt Motor 500 HP

 

I have a 2 pole capacitor start impeller fan motor 230V/60hz/1 and 65W. The manufacturer calls out for a 2uf capacitor. What are the ramifications for using a 10uf capacitor. We have 10uf in stock.

Thanks,
Charlie