Power Factor Controller.

Power Factor Definition : Power factor is the ratio between the KW and the KVA drawn by an electrical load where the KW is the actual load power and the KVA is the apparent load power. It is a measure of how effectively the current is being converted into useful work output and more particularly is a good indicator of the effect of the load current on the efficiency of the supply system.

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Bulk Correction (Bulk Compensation).

The Power factor of the total current supplied to the distribution board is monitored by a controller which then switches capacitor banks In a fashion to maintain a power factor better than a preset limit. (Typically 0.95) Ideally, the power factor should be as close to unity as possible. There is no problem with bulk correction operating at unity, however correction should not be applied to an unloaded or lightly loaded transformer. If correction is applied to an unloaded transformer, you create a high Q resonant circuit between the leakage reactance of the transformer and the capacitors and high voltages can result.
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Power Factor Controllers

Power factor controlers are typically panel mount and used like a panel mount meter, indicating the power factor at the point of supply. Power factor controllers are programmable and range from quite simple to very complex.
A simple power factor controller monitors the displacement power factor (the angle between the voltage and current commonly referred to as COS(Ø) ). The controller displays the power factor on a digital display and compares the measured power factor with the desired power factor. If the power factor is less than the desired power factor, another bank of capacitors is switched on via a relay output on the controller. If the power factor is leading, or above a threshold point, a bank of capacitors is switched OFF.
The controller has a number of relay outputs for controlling contactors switching capacitors. Typically, the number of outputs will range from 6 to 14 relays.
The number and size of the banks being switched is dependent on the type of load, the range of control required and the designated power factor range.
Some controllers expect that equal stages will be used, and others are quite flexible.
The top end controllers, measure the size of each step and calculate which step combinations will give the best results. In this case, it is possible to use a combination of step sizes.

A good configuration is to use at least two small steps and at least four large steps. For large installations, up to 14 stages can be used.

The number of times that a bank can be switched is limited with delay ON and delay OFF times that are programmable. Some controllers keep the numbers of operations equal across all banks. There are a number of other options that can be included such as harmonic current alarms and low current thresholds to prevent capacitors being connected under very light load.

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Power Factor Calculations
Power Factor Information

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