How Will You Design Your Capacitor Bank ?

A) KVAR DESIGN :-

1) Carry out a 24 hour load survey. Note down hourly KWs, P.F. and voltages.

2) Divide this into three sections :

a) No load or light load - but fixed KWs & its P.F.

b) Average load and its P.F.

c) Peak load and its P.F.

 

3) Design the bank for its, peak load conditions. Hold your desired p.f. at 0.95. Work out the capacitor bank KVAR by referring to the tables.

4) If the load is small (less than 50 KWs), then split the bank in two sections corresponding to conditions (2a) and (2b).

5) If the load is of medium size and (say up to 200 KWs), then split the bank in three sections corresponding to conditions (2a), (2b) and (2c).

6) If the laod is large sized and complex, then split the bank into a simple sections corresponding to (2a) and combine sections (2b) and (2c) and rearrange them in a multi - step, automatically controlled bank.

B) VOLTAGE CHOICE :-

1) Capacitor under A- 2a must be specified at higher range of voltages. Thus an energised transformer, with practically no load - except for 4-6 hours in a day, eg. (transformers under Garrison Engineers, MES) will require a capacitor rated at 500 Volts.

2) Capacitors under A-2b and A-2c fall in two categories :-

1. Category where electrical service is poor and the best voltages seldom cross 400-405. Specify 415 voltage.
2. Category where loads fluctuate and voltages vary and also where you suspect harmonics, specify 440 volts.

SPECIFYING 415 VOLTS FOR CAPACITORS MERELY TO GET HIGHER KVAR, IRRESPECTIVE OF LOAD AND SYSTEM CONDITIONS, IS SHORT-SIGHTED-LEADING TO SHORT-LIVED CAPACITORS.

C) MODE OF OPERATION :-

1. Capacitors under A-2a should be left on permanently, on a 24 hour basis. An adequately rated switch-fuse is good-enough for this.
2. Capacitors under A-2b, may be switched on and off, once in twenty four hour basis - covering the duration of the average load. These need not be switched off during recess-intervals since generally the load conditions on supply mains are fairy stable.
3. Capacitors under A-2c serve mainly to reduce the maximum demand in KVA and may be switched on and off more than once during the day - probably twice, if the peak load appears twice - during the day.
4. Capacitors under A-2c might not lead to satisfactory, reliable, manual operation.Automatic capacitor control - combining both 2b and 2c is more desirable.While the control panel will be on for twenty hour in a day, individual sections might come on or go off many times in 24 hours as per load conditions.

D) Design of switches, fuses MCCBS, contractors and also types of automatic controls and steps KVAR sizes are discussed in our serial on Automatic Power Factor Control Panels.

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