NRG

Power Factor Correction and System Design

 

There has been and will continue to be a variety of measures developed to increase the efficiency of electrical systems and reduce electrical cost.  Very few, by themselves, address the demand cost and power quality as effectively as our GE/Ultravar Power Factor Correction and Harmonic Suppression System. Our system employs the principals of low voltage power factor correction to dramatically reduce an electric bill while actually increasing the electrical system capacity.  This will allow commercial and industrial users of electricity to save appreciably on their power cost and to add new equipment without a costly electrical system upgrade.

What Is Power Factor?

The power used by commercial consumers has two components:    

  • Real Power, which produces the actual work, which is measured in Watts (kW).
  • Apparent Power which is the combination of kW and reactive power (kVAr) which is measured in kVA.

Reactive power is needed to generate the magnetic fields required for the operation of an inductive piece of equipment, sometimes called wattless power.  The load does not consume this component of electricity.  A good analogy of this is purchasing a beverage that is packaged in a recyclable container. We need the container to consume the product but we do not consume the container.  The inductive component is relative to the container and a power factor capacitor literally recycles this non-consumed element of electricity and supplies it back to the load.

Inductive electrical equipment, such as motors and transformers, therefore must take from the electrical distribution system more current than is necessary to perform the work involved.  The ratio of kW to kVA apparent is called Power Factor.

How the System Saves Money

The power factor correction system lowers the electrical costs in three ways:

1.  In many areas of the country, electric rates include a charge for low power factor.  This is done via the demand charge portion of the bill.  The monthly demand is typically measured in both kW and in kVA.  The power company takes the highest 15 to 30 minute demand measurement (peak demand).  The billing demand is typically arrived at by taking a percentage of the peak kVA demand, (90% to 100%) and comparing it to the peak KW demand.  The higher of the two figures becomes your billing demand.

Our power factor correction system, connected within your electrical distribution system, supplies the wattless power to the inductive loads making it unnecessary for the power company to supply it.  This dramatically reduces the peak kVA demand figure.  Savings are realized in reduced kVA demand charges.

2.  The second savings possible through the use of our power factor correction system is in the form of increased capacity of the electrical distribution system. Installation of our equipment to furnish the non-productive current requirements of the facility makes it possible to increase the plant's connected load as much as 20% without a corresponding increase in the size of transformers, conductors and protective devices servicing the load.

3.  The third area of savings is improved voltage and power loss reduction.  Electrical system losses are also reduced by the reduction of total current and power that is delivered.  This would result in less KWH consumption.

How Does The Power Factor Affect My Electric Bill?

A typical industrial/commercial electric rate calculates a demand charge by taking 90% of the kVA demand figure and multiplying it by the demand rate. Letís assume the demand charge is $10.00.  If the monthly kW demand was 500 and the Power Factor was .70, the kVA would be 714.  90% of 714 equal 643, and 643 becomes the "billing demand".  To calculate the "demand cost" you multiply the billing demand by the demand charge (in this case $10.00) or 643 X $10.00 = $6,430.00.

Now letís assume the same demand rate of $10.00 and a kW demand 500.  If the power factor were .90, the kVA demand would be 556.  90% of 556=500 and 500 becomes the billing demand.  The demand cost is calculated the same way as above 500 X $10.00 = $5,000.00.  So for the same 500 KW (working power) it would cost the customer $1,430.00 less at a power factor of .90 than at a .70 power factor.

A Word About Harmonics

Most power factor correction equipment employ the use of special power factor correction capacitors.  Power factor capacitors have low impedance at the commonly generated harmonics levels of 5th, 7th and 11th.  Installing a PF capacitor in an adverse harmonic environment could damage the capacitor and/or the load generating the harmonic, such as a VFD drive.  It is important to consider the harmonic levels.  Please see Harmonic Testing for more information on this service.

 

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