POWER QUALITY Q&A

Our Expert Offers Answers to Frequently Asked Questions About Power Quality

Question:
We need some help establishing a Power Quality Specification for our plant. Can you recommend any sources of information?

Answer:
Having made the decision to establish a Power Quality Specification puts you farther ahead than most plants. With the increased usage of non-linear and sensitive electronic loads, it is becoming increasingly difficult to maintain a safe and reliable power system.

Unfortunately, I am not aware of a generic specification to fill all your needs as everyone has a different situation. However, there are a number of excellent sources that can provide the background information necessary to develop a successful power quality strategy.

My best advice is to engage an engineer or knowledgeable contractor to work systematically through the issues with you. It's a lonely road to go alone.

Analyze the power system you have. Determine your present level of power quality. Have in mind the loads you anticipate adding in the future.

Establish the important elements of your strategy and in a short 2-3 page document, outline the minimum quality and type of equipment you are willing to accept, the methods of wiring installation, and grounding requirements. Establish the performance tests and the results you are looking for. In this way, a contractor bidding on the job will know what is expected and will price and perform accordingly.

Most of the gains in power quality will come from the fundamentals, i.e. the proper selection and installation of standard materials. In exceptional cases, a higher tech solution is necessary. Before engaging the high tech solution, fix the fundamentals. This will minimize or eliminate the high tech component of the solution at a significantly reduced cost.

When buying equipment such as drives, rectifiers, and UPS's, clearly specify your expectations of harmonics, power factor, and other PQ issues at the quotation stage. The higher end manufacturers can be of assistance in establishing the desired parameters. A few extra dollars will guarantee safe and reliable performance.

The best sources for power quality information are the standards and guidelines developed by the Institute of Electrical and Electronic Engineers (IEEE).

IEEE standards are:

• STD 142-1991 IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green book)
• STD 1100-1992 IEEE Recommend-ed Practice for Powering and Grounding Sensitive Electronic Equipment (Emerald book)
• STD 519-1992 IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems
• STD 1159-1995 IEEE Recommend-ed Practice for Monitoring Electric Power Quality
  (visit www.ieee.org for more info)

Question:
We are working with a new electrical contractor on a project in our plant. The quality of the work is fine but we can't get him to follow our power quality practices. He argues that his work meets the Electrical Code which he feels is sufficient.

Answer:
Ending up with a satisfactory installation, from a power quality standpoint, results from constant attention through all stages of a project.

Firstly, the scope of the project must be established at the bid stage to ensure that all bidders fully understand your requirements. Obviously, a set of detailed drawings and specifications of your project is a necessary step. Many people try to save a little money at this point, but it is amazing that the same people routinely accept significantly higher costs due to extra's, hold-ups and commissioning problems at the end of the job.

Contractors bid and perform based on the information given to them. To receive a competitive bid, it is necessary that the contractors all have the same information. Again, here is a need for good documentation. It is not reasonable to assume that the contractor is conversant with IEEE guidelines for power quality. It is also not reasonable to expect a contractor to put extras or enhancements into a job these days when bidding is so competitive.

Another way to combat the problem is to limit your choice of contractors to those who are reputable and know what they are doing. Reputable contractors who know their business will use quality materials and methods that will result in safe and reliable installations. When you start putting price pressure on them by going to less qualified contractors, you lose. Any money you hope to save by going 'cheap' will vaporize at the first unplanned outage or hold-up. Pre-selecting reputable contractors for your project will establish your minimum accepted level of quality and allow you to adopt a low bid philosophy without being burned.

Another misconception is that you can save money by using non-union contractors. This may be the case, but generally, there is no guarantee. The hourly rates for non-union workers may be less but you have to look at the experience and qualifications of those doing the work before you make your final determination.

If you have done your homework, it is your right to have your project installed as per the drawings and specifications. Sometimes, contractors will take shortcuts and put you in a position where it is difficult to enforce the contract. "Meeting the Electrical Code" is never an acceptable out unless, of course, you haven't provided a detailed specification. Make it clear at the beginning that you want your project installed as per the specifications. Constant supervision is necessary. You can always keep the contract holdback until he complies but it may be too late. Again, documentation will be your friend in establishing a case for getting what you want. Reputable contractors will accept this. If he doesn't, you don't invite him back for the next project.

On the other hand, if things change in the field, don't expect the contractor to give you a 'freebie'. He might for a small change, if he values the relationship with your company. However, if the change is significant, it is not fair to force him into a loss position. When a change is discovered, immediately determine the extent of the change and work with the contractor to develop a strategy and extra cost. Put the agreement on paper and proceed after approval from management and purchasing.

Doing this after the fact will only lead to misunderstandings and hard feelings if everyone does not agree or the project goes over budget.

At the end of the job, do a final deficiency inspection. Itemize the deficiencies and have them corrected by the contractor. As-built drawings should be marked up by the contractor in red and returned to you for drawing updates.

The bottom line is to establish a good working relationship with several, reputable contractors who understand your needs and expectations. In this way, you can establish a reasonable cost for the project, they can receive a fair price for their work and the majority of your electrical installation issues will go away.

David is the President of Wintek Engineering. You can forward your questions or comments to him at wintek@wintek-eng.com. ET