What is Power Quality?
by Brad Gibson, P. Eng.
Welcome to a new feature in Electricity Today --- Phase Shift: The Power Quality Column. Running six times per year, this column is intended to provide valuable information to electrical industry professionals who want to learn more about the expanding field of power quality and power problem mitigation.
We will examine a number of key issues in the field and provide timely practical examples. Emerging standards and measurement methods will be discussed along with techniques for dealing with common problems economically. Your help and input is essential -- in order to cover the most relevant material we would appreciate hearing from you. Please contact the author by email, fax or post as outlined in the resource box accompanying this article, or get in touch with Electricity Today directly. There will be regular features answering your questions, recommendations for further reading and a selected Website.
Let's start by examining the key question:
What is Power Quality?
Ontario Hydro's Power Quality Committee has defined power quality as; "..the degree to which both the utilization and delivery of electric power affects the performance of electrical equipment." The IEEE Emerald Book Standards Committee defines power quality as ; "the concept of powering and grounding sensitive electronic equipment in a manner that is suitable to the operation of that equipment."
While there are some subtle differences in the two definitions, there is one strong common bond -- electrical equipment operation. The way we use the electrical supply within our facilities and, to some extent, the way it is delivered by the utility, will have an impact on the equipment connected to that supply. People have been using electricity for decades so why is it that in the past 10 to 15 years in particular we have developed a heightened operational concern for the way we are using the power resource? The simple answer is the predominance of power conversion loads which exist on the grid. Power conversion is the act of converting the electrical waveform from one type to another; for instance the converting of AC to DC for a computer power supply. Some equipment performs more than one type of conversion and the result always has some trade-offs. The side-effects of large concentrations of power convertors often leads to what are currently defined as power quality problems. There can be easy solutions to power quality problems; some as simple as moving loads to new circuits or re-installing wiring to meet modern code standards. There is, however, a school of thought which tends to react somewhat poorly to power related problems in a facility. Alex McEachern of BMI puts it this way,"Even skilled technicians will sometimes abandon rational, step-by-step, problem-solving techniques when confronted by a power problem. They shouldn't. Power problems obey the laws of physics."
Power quality today, as a field of work, often involves reactive measures. At times, power quality only becomes a concern in facilities when operational problems are encountered. In other quality initiatives, like Statistical Process Control and Continuous Improvement, quality is one of the key components in the design and production of a process -- thus most quality related endeavours are proactive. As awareness of the key issues grow, power quality is becoming more of a proactive issue. Companies are learning that preventative measures and "best practice" installations can be more economical than trouble-shooting thorny system problems.
Power quality proactivity begins when a realization develops in your plant or office that preventative and mitigating measures should be included at design time. There are a number of outstanding examples of this in modern equipment design. There are however a number of incomplete or ill-specified measures that pass for power quality solutions which appear frequently in the field. The key for us as electricity professionals is to learn the fundamentals and apply only those solutions which will maximize equipment operation. In addition, there will always be some reactive components to power quality problems. The modern power quality professional has to be one part physicist, one part analyst and one part trouble-shooter as many apparent power quality problems are really process related.
Reading Assignment: Your reading assignment for the next two months is ever informative IEEE 1100-1992; The Emerald Book. I'll be referring to this definitive standard quite frequently so dust off your cover and go straight to Chapter 2 to read the definitions which we will take a closer look at in the next column. If you do not yet own an Emerald Book, you can order it directly through IEEE in New Jersey.
Resources used in this column:
Brad Gibson is a Managing Partner of Current Thinking Inc., a leading supplier of engineered power quality services and mitigation equipment.