Good Voltage Regulation and Justified Power Factor Correction
Good Voltage Regulation and Justified Power Factor Correction (photo credit:

Commercial Building Case

Power factor correction and voltage regulation are closely related. In many cases, the desired voltage regulation is costly to obtain. Larger or paralleled conductors to reduce voltage drop under load are, in many cases, the proper solution.

However, power factor correction may also be justified for four reasons:

  1. To improve voltage
  2. To lower the cost of electric energy, when the electric utility rates vary with the power factor at the metering point
  3. To reduce the energy losses in conductors
  4. To utilize the full capacity of transformers, switches, overcurrent devices, buses, and conductors for active power only, thereby lowering the capital investment and annual costs

Voltage Regulation

The goal of good voltage regulation is to control the voltage of the system so that it will stay within a practical and safe range of voltage tolerances under all design loads. Voltage at any utilization equipment should be within the guaranteed operative range of the equipment.

The type and size of wires or cables, types of raceways, reactances of transformers and cables, selection of motor-starting means, circuit design, power factor correction, and the means and degree of loading will all affect voltage regulation.

Voltage regulation in any circuit, expressed in percentage, is:

Voltage regulation formula

When it is not economical to control voltage drop through conductor sizing, circuit design, or other means, voltage regulators may be needed. Several types of voltage regulators, either automatic or manual, are available for all types and sizes of loads from individual electronic devices to the equipment for an entire laboratory or department store.

Voltage regulators are frequently used by electric utility companies in their distribution system feeders and are seldom needed within commercial buildings, except for use with electronic equipment.

Normally, the power and light distribution system within large commercial buildings can be designed economically and adequately without the use of large voltage regulators.

Power Factor Correction

When the type of load to be installed in the commercial building will result in a poor power factor, then an evaluation should be made to determine if installing capacitors is justified, either to stay within the power factor range specified by the electric utility in order to avoid penalty payments or to obtain a reduction in the electric bill.

Care should be taken when adding capacitors to ensure that no resonant conditions could exist with the fundamental or harmonic frequencies. This is particularly true if SCR drives are used.

When large machines (like blowers, or refrigeration or air compressors) are to be installed, a study should be made to determine whether it would be economical to install a synchronous motor and utilize it for power factor correction.

Capacitor banks in low voltage switchgear
Capacitor banks in low voltage switchgear

The cost of the synchronous motor with its controller should be compared with the cost of a squirrel-cage motor with its simpler controls plus separate static capacitors.

Better utilization of electrical machines

Generators and transformers are sized according to the apparent power S. At the same active power P, the smaller the reactive power Q to be delivered, the smaller the apparent power.

Thus, by improving the power factor of the installation, these machines can be sized for a lower apparent power, but still deliver the same active power.

Reduction of losses

The power losses of an electric conductor depend on the resistance of the conductor itself and on the square of the current flowing through it.

Since, with the same value of transmitted active power, the higher the cosφ, the lower the current, it follows that when the power factor rises, the losses in the conductor on the supply side of the point where the power factor correction has been carried out will decrease.

References //

  • IEEE Recommended Practice for Electric Power Systems in Commercial Buildings
  • Power factor correction and harmonic filtering in electrical plants – ABB

About Author //


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on


  1. Heena
    Nov 17, 2015

    This is my favorite topic! Switching capacitors in telecom industry affect voltage regulation and phase angle. I came across a case in telecom industry where significant asset damage happened when building was operating on generator and power factor happened to lead. Luckily no one was injured.

  2. E.saro br
    Jun 14, 2015

    Any articles about circulating currents?

  3. abdaslam
    Apr 07, 2015

    Is it possible to install diesel generator 1G on the busbar 30 kV transformers that feed the 30/11 kV?

  4. A.Taghian
    Apr 07, 2015

    thank you for your useful and handy informative articles.
    I suggest to add some articles about practical problem solutions approved to be routine in electrical industry.

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