Reactive Power – the hidden cost in your power bill
An article published in the New York Times, September 23, 2003 states that investigators are now pointing to a lack of reactive power, measured in kilovolt-amperes Reactive (KVAR), as the cause of last August's blackout throughout the Eastern elec...
An article published in the New York Times, September 23, 2003 states that investigators are now pointing to a lack of reactive power, measured in kilovolt-amperes Reactive (KVAR), as the cause of last August’s blackout throughout the Eastern electrical grid. Reactive power is a largely unappreciated force that flows through electrical distribution system doing no work, but without which energy would not travel down the transmission lines, alternating current (A/C) motors would not turn, transformers would not transform, etc. When shortages of reactive power occur on a transmission system, voltage drops, current increases and breakers trip. If the shortage can not be made up from other utilities on the grid, the entire grid collapses and your machinery grinds to a halt.
Plastics processing operations have high reactive power demands. Take a close look at the electric bill, and you will see two key measurements – kW and kVA, and several transmission and distribution charges based on one or both of these values. Kilowatts (kW) measure the portion of the power that produces work – “real power”. kilovolt-amperes (kVA) is the sum of real power and reactive power, with the effects of a few other gremlins in your electrical system tossed in for good measure.
Demand-based charges in the area affected by the 2003 blackout range from about $5.00 to nearly $12.00 per kW or kVA. Inefficient use of electricity will lower the ratio of kW to kVA, expressed as “power factor” or PF on the utility bill, and increase the demand charges. Some utilities bill demand charges based solely on kVA, meaning that you pay for all the reactive power demanded by your operations. Others use a factor, typically 0.9 times the measured kVA, and bill on the largest of that product or the measured kW. At least one utility, Gray Harbor, Washington, reportedly bills directly for reactive power at a rate of $0.014/KVAR-hour when a customers’ PF drops below 0.97. A customer running a continuous operation, with a good PF of 0.9, and a moderate demand of 1000 kW would face additional charges of more than $12,500 per year if their utility adopted a similar strategy.
Traditionally, capacitor banks are used to correct PF, trapping the reactive current within the confines of a plant, and relieving the utility of the burden of carrying the reactive current throughout its system. The impact of low power factor on the demand billing is reduced and significant savings can be achieved. Better than nothing, but not the best you can do. Unfortunately you may have effectively masked the impact of all that reactive power running through your distribution system — out of sight, off the bill, out of mind. Uncontrolled reactive power will still be carried on your power cables and distribution systems, increasing the heat losses caused by a number of phenomena present in all industrial facilities. These losses, which arise from hysteresis, skin effect, proximity effect, transformer losses, line losses and eddy-current losses, can combine to create an average wattage loss of 10% to 25% of the total power demanded by a typical industrial facility. Kilowatt hours of energy, for which you are billed directly, are needlessly consumed when reactive power is carried through the internal distribution system back to a main capacitor bank.
“Providing KVAR at the correct point in a facility frees up capacity and reduces kilowatt hours used to move the additional power through the distribution system. Reactive power won’t register on your kilowatt hour meter, but real power is used getting it to motors and other devices that rely on reactive power to create the magnetic fields that do the work,” says Paul Bleiweis, president of Energy Automation Systems Inc. EASI is a Tennessee-based company that has spent twenty five years honing techniques to improve power quality and squeeze savings out of existing distribution systems. “Capacitors installed at the main panel reduce power factor and demand charges but further savings opportunities are frequently overlooked. It is not unusual for an older facility to achieve savings of 15% or more, once we have optimized the existing electrical distribution system,” says Bleiweis. “Systems that were previously at capacity can handle new equipment without expensive upgrades.”
A low power factor, or power factor corrected at the main panel only, means there are energy savings waiting to be discovered in breakers, busses and boxes. Profits that could be going to the bottom line are going to the local utility, but a professional assessment of a facility’s electrical system and investment in good power conditioning equipment can reclaim those profits and pay dividends for years to come.
David Thomson is president of Sage Environmental Corp., Burlington, ON www.sageenergy.net