Cap Bank

Power factor is a measure of how efficiently electrical power is being used in an AC (alternating current) system.

Electricity in AC systems has two components:

1. Real Power (kW) – does actual work (turns motors, lights bulbs, runs machines)
2. Reactive Power (kVAR) – doesn’t do work but is needed to create magnetic fields (used by motors, air-conditioners, transformers)
3. Apparent Power (kVA) – the combination of both

Power Factor = kW ÷ kVA

Why does it matter?

• If your power factor is low, you are drawing more total current than necessary
• TNB penalize commercial/industrial customers for low power factor.
• When your power factor is high, current rating decreases
• Good PF reduces load on cable and transformer and lower Voltage drop
• Improving power factor saves money and reduces strain on electrical equipment
• Avoid frequent breakdown and increase equipment efficiency with good PF

Power Factor Penalty

Penalty charges are incurred on your electricity bill when your PF falls below 0.85

• 1.5% surcharge of the current bill - for every 0.01 less than 0.85 PF
• If your PF falls below 0.75 the penalty charge increases
• 3% surcharge of the current bill - for every 0.01 less than 0.75 PF

Sample TNB bill with Power Factor Penalty

Click To View Table Image

Calculation of Penalty charge
Bill Amount: RM 3,949.50 – 1,045.46 = RM 2,904.04
Power Factor: 0.68
0.85 – 0.75 = 10 x 1.5% x RM2,904.04 = RM435.60
0.75 – 0.68 = 7 x 3% x RM2,904.04 = RM609.85
RM435.60 + RM609.85 = RM1,045.45

What should I do to avoid being charged a Penalty?

• Install a capacitor bank. A capacitor bank supplies capacitive reactive power to your electrical system to counteract the inductive reactive power from loads, which improves the overall power factor.

How does a capacitor bank work?

Will my TNB bill increase after installing a capacitor bank?

• No, installing a capacitor bank will not increase your bill. The capacitor bank does not need any power supply because the reactive power is already stored inside the capacitor itself. The reactive power is discharged automatically to your electrical system as and when it is needed.

Does the capacitor bank need to be charged?

• No, a capacitor bank does not need a power supply, and does not need to be charged.

What is the life span of a capacitor bank?

• It depends on how frequently it discharges reactive power to your electrical system. In general, a well maintained and properly sized capacitor bank can last for up to 5-10 years. After this time the capacitor cylinders may need to be replaced.

Does a capacitor bank need to be maintained?

• Yes, we recommend all our customers to conduct periodic preventative maintenance to ensure all parts are functioning well, and to avoid incurring any future penalties.

Below are extracted from TNB webpage on low power factor. Attach the Bahasa version, the English, and Mandarin.