Method of improving power factor correction?

Answer 1

In AC electric systems, electrical energy is consumed by resistive loads. An AC generator sends out energy, and a resistive load takes the energy in.

But in AC systems, electrical energy is not consumed by pure capacitor loads. Neither is it consumed by pure inductive loads. Instead these loads reflect all energy back to the generator. They don't consume any electrical energy themselves. Ideally this shouldn't cause problems. However, in the real world a pure capacitor load will cause the power lines to become warm. While the energy flows out and back, there is an electric current in the lines. The same thing also happens with a pure inductive load. The loads reflect all energy and consumes none, but the utility company must use up fuel to keep sending out the reflected power and warm the power lines.

If large industrial customers place inductive or capacitive loads on the power grid, the utility company installs special electric meters to measure this. The electric company then charges them a fee. The industrial customer must pay for the energy losses they cause in the warm power lines.

In AC electrical mathematics, the reflected power effect is described as REACTIVE POWER, and is measured in terms of POWER FACTOR. A resistive load consumes the incoming energy, and it has a power factor of 100%. On the other hand, pure capacitors and inductors reflect all the incoming energy, and they have a power factor of 0%.

There is a way for industrial customers to fix the problem. There is a way to correct the power factor and bring it to 100%. If the customer is using an inductive load, they can place just the right value of capacitor across that load. The energy then stops reflecting back to the electric company generators. No longer do the power lines suffer excess heating. The electric company measures this, then stops charging the extra fee. (Actually the energy still reflects back and forth between the inductive load and the added capacitor. The excess heating in those short local wires is insignificant.)

Since large industrial customers commonly use AC motors containing coils, they commonly create inductive loads on the power grid. Power-factor correcting capacitors are the solution. They eliminate the extra fee charged by utility companies, so a PFC capacitor will eventually pay for itself. However, such capacitors cannot save money for individual homes or small businesses. These customers don't have the special electric meters, and the utility companies aren't charging any special fees for bad power factor. Those PFC capacitors don't save any money, and can never pay for themselves.

Power factor is the cosine of a circuit's phase angle, i.e. the angle by which the load current lags or leads the supply voltage. When they are in phase (phase angle is zero), the power factor is unity (i.e. 1); when they are 90-degrees out of phase, the power factor is zero. 'Poor' power factor (i.e. when it is closer to zero than to unity) results in excessively-high currents for a given value of load; power-factor correction (or 'improvement') acts to move the power-factor towards unity, thus reducing the value of that load current. This is desirable, as it reduces the necessary amount of copper (i.e. the cross-sectional area) of conductors and other equipment supplying the load. For inductive loads, power-factor correction is achieved through the use of capacitor banks.

Answer 2

'Poor' power factor causes a load to draw more current from the supply than is necessary, causing greater voltage drops and losses along that line. The most common form of power-factor correction is through the use of a capacitor connected in parallel with the load. The poor power factor is caused by the load's

reactive power, caused by the inductance of that load. By adding a capacitor, which provides leading reactive power, the net reactive power is reduced and less current is drawn from the supply without effecting the operation of the load itself.

Answer 3

Using capacitor banks, or if fast correction for varying loading conditions is needed, a D-VAR system can be used (basically a bunch of power transistors).

There are a lot of gimmics in existence for power factor correction. Be careful of these.

Answer 4

Most industrial loads are inductive and, therefore, represent an lagging reactive power which draws more load current than is necessary. By adding, for example, a capacitor bank to the load, the additional leading reactive power acts to reduce the overall reactive power, causing the resulting current to reduce to a lower value.