What is VAR Management?

VAR management can reduce a utility’s costs and ensure that the system is operated in an efficient manner. This article reviews fundamental power principles to give the reader an understanding of VARs and why VAR management is an important consideration for optimized power delivery systems. Before we delve into understanding the concept of VAR Management, let’s review some fundamental power principles.

There are 3 basic types of power. For a 3-phase circuit:

Apparent power: S = √3 × Volts × Amps, (VA)
This is the product of rms (root mean square) volts and rms amps. Most electrical equipment is rated in apparent power. Apparent power is also the combination of real power and reactive power.
Real power: S = √3 × Volts × Amps × K1 , (Watts)
This is the power that performs real work — the time average of the instantaneous product of voltage and current. K1 is the power factor which will be described later.
Reactive power: √3 × Volts × Amps × K2 , (VARs)
This is power that exists in the electrical distribution and transmission system due to the inherent capacitive and inductive elements in the system. Reactive power performs NO real work and is often associated with power that is converted to magnetic fields such as in motors. In technical terms, reactive power is the time average of the instantaneous product of the voltage and current, with current phase shifted 90 degrees. K2 is a constant that will be described later.

The three components of power can be represented by the Power Triangle below.

Power triangle.

The angle “Θ” (Greek letter “theta”) represents the phase angle between real power and apparent power in the power triangle. The size, in degrees, of that angle determines the size of the reactive power leg of the triangle.

This angle comes into play when calculating K1 and K2:

K1 = Power Factor (pf) = cosine Θ = Watts, Real PowerVA, Apparent Power

K2 = sine Θ = VARS, Reactive PowerVA, Apparent Power

In the Power Triangle, and in the formulas, when Θ is equal to 0 (zero), the cosine of which is equal to 1 (one), and the sine of which is equal to 0 (zero), apparent power and real power are on the same plane and there is NO reactive power. This is called Unity Power Factor.

Unity Power Factor means that all the electrical energy is being transferred into real power or real work and none is being wasted as reactive power (VARs). Resistive loads such as heaters and lights have a power factor equal to one making them ideal in real world electrical power consumption.

However, in the real world, there are motors in washing machines, dryers, air conditioners etc that are all inductive loads — meaning they have a power factor less than 1. Typically, inductive loads such as motors run at a pf around 0.8.

How does all this affect the electrical transmission and distribution system? Say that a motor is rated at 10,000W at 0.8 Power Factor. At 480V, the motor will require the following amount of current:

I = 1 / √3 = (10,000 / (0.08 x 480)) = 15.03 Amps

The same motor rated at 0.6 power factor will require:

I = 1 / √3 = (10,000 / (0.06 x 480)) = 20.05 Amps

This example can also be illustrated in the power triangle as shown below.

Power triangle examples.

Notice that for a given amount of power it follows that for the same amount of voltage, the current required for a low power factor load is higher than for a high power factor load. This also translates into a higher amount of VARs required to run a load with lower power factor.

The effect of this is that even though the load is not using this reactive power, the higher current resulting from the low power factor loads will put a strain on the electrical transmission and distribution system and may lead to equipment failure. The cumulative effect of a number of loads with poor power factor would be to reduce the overall power supply capacity of a given network. This would mean increased investment will be required in equipment such as cables and transformers than would otherwise be necessary if all loads had a good power factor. Also, the power generating capacity of generators is reduced due to the VARs that need to be supplied, or power factor correction capacitors need to be applied to improve the power factor and increase generation capacity.

VAR Management is the process whereby VAR flow between the power producer and the power consumer is optimized.

S&C’s Power Systems Services can provide VAR Management Services that includes the identification and realization of inefficient power flow by performing system studies and the correction of excess or deficient VARs by implementing power factor correction equipment such as capacitor banks or reactors to allow generation, transmission, and distribution companies to achieve their bottom line business goals. Contact your local S&C sales office to learn how PSS can help you implement an effective VAR management program.