Maintaining Your Power Distribution System

You've probably heard the athlete's proverb, "No pain, no gain." In the electrical world, it's "No maintenance, no operations." How much maintenance do you need?Your power distribution system is your backbone. Unfortunately, many organizations operate on the "if it ain't broke, don't fix it" principle. Thus, many companies underfund (and undermine) their maintenance departments. As a result, maintenance

You've probably heard the athlete's proverb, "No pain, no gain." In the electrical world, it's "No maintenance, no operations." How much maintenance do you need?

Your power distribution system is your backbone. Unfortunately, many organizations operate on the "if it ain't broke, don't fix it" principle. Thus, many companies underfund (and undermine) their maintenance departments. As a result, maintenance groups routinely make emergency repairs at excessive cost. You may have been in such a situation. And you may have said, "Now they'll listen to me. Now we'll do the maintenance we need to do."

Will your company ensure timely completion of maintenance and repairs for more than an hour after the crisis has passed? Unfortunately, the answer is usually no. The predictable result is more unplanned downtime.

What about those organizations with comprehensive preventative/predictive maintenance programs? Every electrical and mechanical device undergoes scheduled inspections and maintenance. Skilled maintenance people identify and repair potential equipment problems before they become major events. This approach actually builds the bottom line. Feel fortunate if your company prescribes to this maintenance style. Unfortunately, most companies lean toward the first example.

Typically, nontechnical managers allocate resources for a maintenance program; resulting in an overly optimistic viewpoint and a disconnect between their idea of maintenance and real needs. You must sell to management the benefits of an aggressive program (see sidebar, bottom of page 40). You must balance the must do against the "highly recommended and against the optional, prioritizing everything to stay within resource constraints. Which procedures do you really need? How often must you do them?

Are you a maintenance "freq?" Maintenance frequency is always fertile ground for confusion; and complacency. Some industries follow the guidelines of regulatory organizations that establish maintenance schedules, but most do not. Most equipment manufacturers provide maintenance procedures and schedules in their operating manuals. These recommendations are "typical" or "minimum" requirements, and serve as starting points. You need to adjust these numbers based on conditions of use and environment. For example, switchgear on a foundry floor requires more maintenance than switchgear in a retail store.

Keep it clean. Water, dust, temperature extremes, high humidity, and vibration are just some of the items that jeopardize the electrical system. Dust combined with moisture or other airborne pollutants will coat conductor insulation, contact surfaces and enclosures. This coating acts as a blanket, reducing heat dissipation into the surroundings. Premature degradation of conductor insulation and nuisance tripping of thermal protective devices is the result. This coating also provides a conduction path for tracking and flashovers. Dirt can find its way into the operating mechanisms of the equipment, causing excessive wear and impeding its ability to operate.

Before starting any cleaning procedure, you must de-energize and lock out the equipment. Use a voltmeter to ensure power is off before cleaning. Use clean, lint-free rags to clean electrical equipment. Use a vacuum cleaner to remove construction dust, metal chips, and other undesirable material. Avoid using compressed air to blow out the dirt. If you must use compressed air, makesure it's dry and oil free. Direct the dirt away from the conductors and other components. Use liquid cleaners only when the equipment manufacturer approves them. Equipment must be dry before energizing; not all "quick-dry" solvents dry quickly; even alcohol may take hours to dry out of recesses. Check moving parts for lubrication requirements.

Exercise all switches, disconnects, circuit breakers, etc. to verify they are not binding or sticking. In some instances, this procedure will also allow for a visual inspection of contact surfaces, arc chutes and the like. You should exercise this equipment at least annually, opening and closing each device several times. An emergency situation is not the time to discover the maintenance bypass switch froze in the open position.

Test your breakers. Use an on-site primary current injection test as part of the start-up commissioning procedure of every major breaker. Don't be fooled into thinking factory tests mean your equipment will be fine after shipping, handling, and installation. The only way to know it will operate properly at your facility is to test it there.

What are major breakers? Service entrance breakers, main distribution breakers, and any other circuit breakers that, if they were to fail, would jeopardize safety or stop the flow of product out the door. Test the breakers at several different load currents to verify the recorded trip times correspond with the published time-current curves. Test these devices periodically, via primary current injection, to ensure proper operation. A typical testing cycle is every five years.

You can also use secondary current injection to test circuit breakers. This procedure is less expensive than primary injection, because you typically don't have to remove the breaker from the bus. This test will verify the trip mechanism will open the device. This should be an annual test.

Test ground fault protection devices to verify they function properly. Do the test at several current and time settings to verify the device will open within the acceptable tolerance window. Conduct this test as part of the start-up commissioning procedure and periodically thereafter.

Stand on firm ground. Your grounding system is vital to the safe operation of your facility. The best way to quantify the ground resistance of your facility is to do a ground resistance test. To obtain accurate results, you must isolate the electrical system from the utility by physically disconnecting the grounded conductor at the service. This is typically not something you can do at most facilities. An alternate method is to use a clamp-on ground resistance meter. Be sure you are measuring the ground resistance and not the resistance of ground loops. You should inspect and tighten ground connections at every location on an annual basis. This is also a good time to verify you have no unintentional neutral/ground bonds in your facility.

A thermographic inspection. This is one of the most powerful tools available to determine the condition of your electrical distribution system. This method identifies hot spots throughout the electrical distribution system. Thermographic inspection uses a specialized infrared camera that displays the viewed image in temperature-dependent colors or shades of a single color. This equipment is very expensive, and effective use requires specialized training. Thus, it's a good idea to supplement a thermography program with infrared (IR) thermometers. These inexpensive, handheld noncontact temperature sensors are excellent for spot checking equipment.

The camera does a wonderful job of identifying hot spots. However, interpreting the data and identifying the source and solution of problems requires expertise. Causes of excessive heat include loose connections, corroded connections, defective equipment and dirty equipment. Each cause has unique thermographic signatures a trained thermographer can recognize. The thermographer must identify this signature and correlate it to the hot spot location if you are to have a hope of resolving the problem.

The scanning crew must document every anomaly they find, using photographs, videotape, audiotape, and even handwritten notes. This information helps you develop maintenance procedures to prevent recurrences. Assign a seriousness rating to each identified condition (see sidebar, top of page 40 in original article).

Conduct your thermographic survey when the equipment is under load and at normal operating temperature. You may need multiple inspections over the course of a year. You should scan cycling equipment such as chillers and pumps during startup to identify gross problems and after it's been operating under load for a minimum of four hours. This allows it to reach its normal operating temperature. This is easier when you develop a script to identify each piece of equipment you want to survey (see sidebar, bottom left). This document should include a tour route and a procedure for rotating redundant equipment online. Don't forget to survey emergency equipment, such as standby generators and related switchgear.

Document, document, document. To maintain a facility properly, you need service manuals, technical bulletins, and testing standards available to the maintenance people. Catalog these items in a safe location. If your information is incomplete, contact the manufacturer and request replacement documentation. Consider photocopying service manuals for use in the field. The originals will stay clean and secure and are always available to replace lost or damaged copies.

Develop clear and concise maintenance procedures. Each procedure should include required safety equipment and methods and lockout/tagout procedures. Review these procedures against comments from the field, and update as needed.

Use a computerized maintenance management system (CMMS) to keep records of test results, maintenance procedures, and emergency repairs. These records allow you to plan and budget for maintenance and testing programs, as well as capital purchases that make sense for you.

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.