What is Power Factor and How to improve power factor

Power factor

In AC circuits, the power factor is the ratio of the real power that is used to do work and the apparent power that is supplied to the circuit.

The power factor is equal to the real or true power P in watts (W) divided by the apparent power |S| in volt-ampere (VA):

PF = P(W) / |S(VA)|

PF – power factor.

P   – real power in watts (W).

|S|   – apparent power – the magnitude of the complex power in volt⋅ amps (VA).

 power factor

There are one another term is apparent power which are the sum of actual power & reactive power, It is denoted as KVAR. So that we can say that

Apparent Power = Actual Power + Reactive Power

Total KVA = KW + KVAR

Power factor = KW / KVA = KW / (KW+KVAR)

In an ideal system KVAR would be very small and KW and KVA would be almost equal, so we are trying to design an electrical system with power factor 1 than only we are able to get the maximum output from a system. This phenomenon can also be shown as power triangle as below:

power factor

Where Cos Ɵ  is power factor angle i.e. Cos Ɵ = KW/KVA

Reasons of Lower Power Factor:

Since power factor is defined as the ratio of KW to KVA, we see that low power factor results when KW is small in relation to KVA. Now the question arises what causes a large KVAR in a system? The answer is…inductive loads.

Inductive loads (which are sources of Reactive Power) include:

  1.  Transformers

2.  Induction motors

3.  Induction generators (wind mill generators)

4.  High intensity discharge (HID) lighting

These inductive loads constitute a major portion of the power consumed in industrial complexes. Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in our distribution system. This increase in reactive and apparent power results in a larger angle θ (measured between KW and KVA). Recall that, as θ increases, cosine θ (or power factor) decreases. So, inductive loads (with large KVAR) result in low power factor.

Power factor correction:

Power factor correction is an adjustment of the electrical circuit in order to change the power factor near 1. Power factor near 1 will reduce the reactive power in the circuit and most of the power in the circuit will be real power. This will also reduce power lines losses. The power factor correction is usually done by adding capacitors to the load circuit, when the circuit has inductive components, like an electric motor.

Benefits of power factor correction:

1. Reduced Demand Charges

Most electric utility companies charge for maximum metered demand based on either the highest registered demand in kilowatts (KW meter), or a percentage of the highest registered demand in KVA (KVA meter), whichever is greater. If the power factor is low, the percentage of the measured KVA will be significantly greater than the KW demand. Improving the power factor through power factor correction will therefore lower the demand charge, helping to reduce your electricity bill.

2. Increased Load Carrying Capabilities In Existing Circuits

Loads drawing reactive power also demand reactive current. Installing power factor correction capacitors at the end of existing circuits near the inductive loads reduces the current carried by each circuit. The reduction in current flow resulting from improved power factor may allow the circuit to carry new loads, saving the cost of upgrading the distribution network when extra capacity is required for additional machinery or equipment, saving your company thousands of dollars in unnecessary upgrade costs. In addition, the reduced current flow reduces resistive losses in the circuit.

3. Improved Voltage

A lower power factor causes a higher current flow for a given load. As the line current increases, the voltage drop in the conductor increases, which may result in a lower voltage at the equipment. With an improved power factor, the voltage drop in the conductor is reduced, improving the voltage at the equipment.

4. Reduced Power System Losses

Although the financial return from conductor loss reduction alone is seldom sufficient to justify the installation of capacitors, it is sometimes an attractive additional benefit; especially in older plants with long feeders or in field pumping operations. System conductor losses are proportional to the current squared and, since the current is reduced in direct proportion to the power factor improvement, the losses are inversely proportional to the square of the power factor.

5. Reduced Carbon Footprint

By reducing your power system’s demand charge through power factor correction, your company is putting less strain on the electricity grid, therefore reducing its carbon footprint. Over time, this lowered demand on the electricity grid can account for hundreds of tons of reduced carbon production, all thanks to the improvement of your power system’s electrical efficiency via power factor correction.

 

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