Quantify power waste from harmonics and unbalance.
By Frank Healy
It’s a for better or for worse scenario. For better or for worse, because of the increase in energy prices, large consumers are now aware of and monitoring their power consumption. For worse, local utilities have had to field more customer support activity—aside from the usual supply and reliability concerns. For better, customers are now willing to consider consumption-reduction options that previously would not have been cost-efficient. Reducing per-customer consumption is a significant goal for utilities in capacity-limited regions, and many utilities are well positioned to offer consulting on energy optimization.
Compared with five years ago, a large percentage of large commercial, light industrial and manufacturing facilities have conducted a level 1 energy audit, improved their general practices, and identified and optimized the largest loads and systems in their facility.
In parallel to this, more than 10 years ago the Institute of Electrical and Electronics Engineers (IEEE) began an assessment of the academic work necessary to more accurately segment and quantify energy consumption in three-phase electrical systems. It had been known for many years that there were gaps in the mathematical model underlying classical three-phase power measurement calculations. In particular, the effects of reactive power, harmonics and load unbalance were not considered in the classical methods used in most power quality and consumption monitoring.
At that time, harmonic distortion and load unbalance were viewed as imperfections in the purity of power that caused equipment performance issues, and, in the case of power factor, diminished the usability of the distributed power. Quantifying the amount of power made unusable had never been considered. Harmonics and unbalance were troubleshooting concerns, not an energy consumption issue—until energy became a premium.
Harmonics, Unbalance Require Utilities to Generate, Deliver More Power Than Necessary
If 100 kW come into a facility and a portion of those kilowatts is made unusable by poor power quality, the facility is paying for 100 kW but only able to use 100 kW minus the wasted portion.
If a utility customer service agent could quantify the waste and multiply it by the rate schedule, it would then be clear to the customer whether the waste amount was expensive enough to merit addressing the power quality issues.
The outcome of the IEEE efforts was a new standard, IEEE 1459-2000, that helped enable the calculation of waste because of power quality—but in a very academic framework. Still missing was a clear definition of the physical quantity of power waste. Shortly after the new standard was issued, two professors at the University of Valencia in Spain began developing the necessary math to quantify power waste because of harmonics and unbalance issues.
First, Professors Vincente Leon and Joaquín Montañana developed mathematical methods based on the recommendations of the IEEE 1459-2000 standard that defined specific waste sources. They then developed a measurement instrument with a computing system that calculated what they described as unified power.
Their breakthrough unified power measurement method took the best aspects of the IEEE 1459 recommendations and calculated the energy wasting effects of reactive power, harmonics and unbalance in the electrical system.
Fluke learned about the breakthrough and approached the professors about a partnership. Together, Fluke engineers and the professors transitioned the science from an academic instrument into a unified power measurement feature and an energy loss calculator, now available in a portable, handheld power quality analyzer. Both parties hold patents for different aspects of the new capability.
Unified power measures harmonics and unbalance waste in terms of kilowatts, and, by factoring in the cost of each kilowatt-hour, it’s possible to calculate the cost of waste energy over a week, month or year.
Field Testing Unified Power— How Much Waste is There?
To confirm their hypotheses about the link between power quality issues and the effect on energy waste, the team performed multiple field studies. One occurred at a mixed-use industrial park supplied by a local electrical cooperative. Some of the industrial park’s customers had significant inductive loads, and the utility had already chosen to install power factor correction to reduce the poor power factor effects. When the unified power device was connected, however, it showed significant reactive power losses in the power transformer’s secondary. The losses occurred primarily at night when the inductive loads were not operating, but the power factor correction capacitors were. The energy losses were measured at 353.6 kWh/day, on average; multiplied by the utility’s rate schedule, this amounted to $14,000 per year. With this information in hand, the utility and park manager devised a solution involving time-controlled relays that disconnected the capacitor bank at night.
Payback time was less than one year.
A Good Opportunity for Utilities
Addressing harmonics and unbalance often requires the support of an electrical engineer. Why not make that a service provided by the local utility? A utility engineer could assess the waste, identify the root cause, determine the best resolution—installing mitigation or unbalance compensation equipment, or changing loads—and wrap it up in a recommended plan of action and return on investment (ROI) time for the customer.
And, with follow-up from the utility, the customer might even come to appreciate the overall associated improvements to equipment reliability, efficiency, lifespan and downtime that come from improving power quality.
About the author: Frank Healy is power quality marketing manager for Fluke Corp.