EnviroVAr Power Factor Control System

The EnviroVAr power factor correction provides effective reactive power compensation for all industrial, commercial and large retail environments where excess charges are being applied and or where current availability is limited and the cost of a replacement transformer or increased supply is prohibitive.

The Problem

Most three phase electrical loads draw not only active power (kW, the part that does useful work), from the supply, but also reactive power (kVAr, essential, but ‘Wattless’ power); examples of these loads would be induction motors, motor drives (both AC and DC ) , switch-mode power supplies, and most forms of lighting.

To make a very crude example of an induction motor, the active power is what comes out of the shaft and does work, whilst the reactive power is what is used by the coils of the stator to create the magnetic field. This magnetic field is essential for the operation of the motor, but does no actual work, only permitting the transfer of power from the stator to the rotor.

The total demand on the supply for a load of this type is called the apparent power, and is the vector sum of both the active and reactive components of power. The ‘power factor’ of a load is the ratio of active power to apparent power, kW to kVA, sometimes referred to as Cos ( f ). When a load draws reactive power from the supply, its power factor is said to be lagging, when the reactive power is exported to the supply, its power factor is said to be leading. This is a reference to the phase of the load current with respect to the supply voltage.

This is the ‘Displacement Power Factor’ or DPF, more commonly known as just the ‘Power Factor’ and only takes into consideration the frequency components of voltage and current.

When seeking to improve the power factor of a load, what is actually being done is to supply a proportion of the reactive power demand of this load locally. This results in a greater proportion of active current being drawn from the supply.

With a capacitor installed electrically adjacent to a load, the supply is required only to provide the active power demand, and a smaller proportion of the reactive power demand.

Physical Benefits of Power Factor Correction

The reduction in demand on the supply from the installation of Power Factor Correction equipment results in:

• ‘Spare’ supply capacity which may be used to connect additional load without the necessity of network reinforcement
• Reduced losses and hence reduced heating in transformers, cables and switchgear, increasing reliability, useful service life, and reducing servicing costs
• Reduction in reactive power demand from the supply improves voltage regulation, as to a first approximation, the voltage drop in a supply network is proportional to the reactive power supplied by that network ( D V @ QX, where D V is the voltage drop, Q the reactive power demand, and X the system reactance)
• An increase in Power Quality, as the presence of a large capacitor bank gives significant attenuation of mains borne voltage spikes, and can also reduce the effects of short duration dips or notches in the supply voltage
• Reduction in distribution system losses means that fewer kWh are required from the electricity generators, resulting in lower carbon dioxide emissions

Contractual benefits of Power Factor Correction

• Most contracts for the supply of electricity stipulate a minimum power factor for the load to be connected, though this is often ignored by both supplier and consumer until problems occur, at which point the solution is more costly than would have been the case had the situation been addressed initially
• Engineering Recommendation G5/4, (relates to planning levels for harmonic voltage distortion and the connection of non-linear equipment to transmission systems and distribution networks in the United Kingdom), is now enforceable legislation. The use of detuned capacitor banks has the effect of absorbing a proportion of any harmonic currents produced by the load, and can often result in compliance with G5/4 without the need for further harmonic reduction equipment.
• Engineering Recommendation P28, (relates to planning limits for voltage fluctuations caused by industrial, commercial and domestic equipment in the United Kingdom), details limits on ‘Voltage Flicker’. As the majority of flicker is caused by voltage drop due to sudden reactive power demand, the installation of power factor correction capacitors can reduce the levels of flicker to within acceptable limits without the need for supply reinforcement.
• Organizations having or seeking approval under ISO14001 (Environmental Management) can easily show increased electrical efficiencies and reduction in carbon emissions by implementing an appropriate Power Factor Correction scheme.

Financial Benefits of Power Factor Correction

• Reduction in kVA required to supply a given kW load means that initial capital expenditure can be reduced, as the primary distribution network components (transformers, switchgear etc.) can be reduced in rating and hence Cost.
• Reduction in losses in distribution equipment due to reduced demand on the supply is reflected in the kWh usage for the site. Whilst this reduction in kWh consumption may at first appear to be small, it can amount to between 1% and 3% of the total consumption, with the associated savings in electricity charges.
• The tariff under which charges are made for electricity may include items which relate directly or indirectly to poor power factor. These are usually specific to the consumer, and hence generalizations are difficult. Items falling into this category which may be affected include Authorized Supply Capacity, Metered Monthly Maximum Demand, and Reactive Unit charges.

EnviroVAr systems are available as both "standard" systems and also as "detuned" systems with additional inductive reactive filters to limit harmonic currents within a circuit. For a full understanding of these systems go to the links above and then contact your local EMS (European) representative to arrange a site survey to best advise you as to how you can benefit from effective power factor correction