sinotech.org – Power factor can be improved by installing capacitors correcting power factor in electric distribution systems / electrical installations in factories / industries. Capacitors act as reactive power generation and therefore will reduce the amount of reactive power, as well apparent power generated by the utility.

An example showing the improvement of power factor by installing capacitors is shown below:

Example 1. A chemical plant installed a transformer 1500 KVA . The plant needs in the first 1160 KVA with power factor 0.70. The percentage of transformer loading about 78 percent (1160/1500 = 77.3 percent). To improve the power factor and to avoid penalties by electricity suppliers, the plant adds approximately 410 kVAr the motor load. This improves the power factor up to 0.89 and this can reduces the KVA that required becomes 913 KVA , which is the sum vector of KVAR and KW. 1500 kVA transformer and then only under load 60 % from the capacity. So that the plant will be able to increase the load on the transformer in the future

Example 2. A group of incandescent lamps with a voltage of 220V/58 W, coupled with a fluorescent lamp 12,, 11 W, there are 30 pieces of incandescent and fluorescent lamp. Power factor measured by cos alpha1 = 0.5. Calculate the apparent power of the load and the magnitude of current I1 before the compensation, if desired work factors becomes cos alpha2 = 0.9. Calculate the magnitude of current I2 (after compensation).

1. The amount of the combined light

PG = (58 W x 18) + (11 W x 12) = 1176 watts = 1.176 KW

Cos phi 1 => PG/S1 > S1 => Pg / Cos phi 1 => 1.176 KW/ 0.5 => 2.352 kVA.

I1 = S1 / U = 2.352 V = 10.69 kVA/220 ampere (A) -> before compensation

2. The amount of power after compensation (cos phi = 0.9)

S2 = PG / Cos phi2 = 1.176 kW / 0.9 = 1.306 kVA

Then I2 = S2 / U = 1.306 V = 5.94 kVA/220 A -> after compensation

sinotech.org – Before discussing about the power factor improvement by using a capacitor, we should recall about the general sense of Pseudo Power, Active Power and Reactive Power.

In alternating current system there are three types of power that must be known, especially for load impedance (Z), namely:

• The pseudo-(S, VA, Volt Ampere)
• The active Power (P, W, Watt)
• The reactive power (Q, VAR, Volt Ampere Reactive)

For AC power circuit, the voltage waveform and sinusoidal current, the amount of power is not same in every time. Then the power which is the average power measured in Watts, this power form the active energy per time unit and can be measured with a kWh meter and also the real power or active power (shaft power, real power) used by load to perform a specific task.

While the apparent power is expressed in units of Volt-Ampere (abbreviated, VA), stating the capacity of electrical equipment, as indicated on the generator and transformer equipment. At some installations, particularly in factories / industries there are also certain expenses such as electric motors, which require other forms of power, i.e. reactive power (VAR) to create a magnetic field or in other words, the reactive power is used as an energy power generating magnetic flux, so causing the magnetization and this power is restored to the system due to the effects of electromagnetic induction itself, so that power is actually a load (demand) in an electric power system.

Understanding Power Factor

Power factor is the ratio between active power (watts) to apparent power / total power (VA) or the cosine corner between active power and apparent power / total power. High reactive power will increase this corner, and as a result, the power factor will be lower. The power factor is always less than or equal to one.

Theoretically, if the entire load power is supplied by the power company has a unity power factor then, the maximum power that transferred is equivalent to the capacity of the distribution system. So, the load-induced and if the power factor ranged from 0.2 to 0.5, then the electricity distribution network capacity to become depressed. So, reactive power (VAR) should be as low as possible for the same kW output in order to minimize total power requirements (VA).

Power factor describes the phase corner between the active power and apparent power. Low power factor detrimental because it resulted in a high load current. This power factor improvement is using a capacitor.