Preventing Electrical Failures - EPM Archives

Lighting, motors, and plug loads are high on facility department’s watch lists, but power distribution systems (PDS) are usually taken for granted, not getting attention until all or part of a facility goes without power for a period of time. This downtime can be minimized by planning and by preventive action.

Effective preventive maintenance programs not only prevent failures, but they can also save energy. The alternative is doing nothing, also known as "run-to-failure" or "breakdown maintenance." This technique could also be called "high-risk" maintenance, because in practice it brings personnel safety and facility downtime risks. From field data, the Institute of Electrical and Electronics Engineers (IEEE) at www.ieee.org has concluded that the failure rate of electrical components is three times higher in facilities where preventive maintenance is not performed on systems.

Preventive maintenance is not a new idea—maintenance personnel have done precautionary work on motors and mechanical systems for decades, but many people believe that because PDS have no moving parts things can’t go wrong, as they know they can in mechanical systems.

Actually, a lot can go wrong when a PDS is not properly maintained. For example, thermal expansion and contraction between periods of high and low demands can eventually loosen connections. When electrical panels are not cleaned, dust and dirt accumulate on the connections, which can provide high resistance paths that experts have attributed to nearly a third of electrical failures. Moisture on exposed components can cause another 17% of failures.

Every facility should have an operations and maintenance It should identify all the components of the PDS, updating it as necessary. The facility one-line diagram should show all components (distribution transformers, metering, switch gear, and breakers, power-factor correction capacitors, transfer switches, and backup power sources, such as on-site generators and UPS) and their interconnections (busways, wire, and cable).

Next, the O&M plan should detail when major components were last replaced, repaired, and cleaned. Where there is little or no documentation, the facility department should begin keeping these important records. When management understands the importance of planned downtime, getting its cooperation becomes easier. Otherwise, a case needs to be made for scheduled outages, which are much more convenient than unscheduled outages.

Scheduling switch gear cleaning on a rotating basis and restricting the areas affected will result in shorter downtime than taking the whole facility down for longer periods, although the outages are more frequent. Performing some procedures simultaneously, such as testing the auto-start of backup generators and the operation of transfer switches, can be cost effective. Exercising all circuit breakers and disconnect switches during the outage and lubricating parts that require lubrication makes the time even better spent. This is a good time to do breaker testing, which requires specialized equipment and is best done by companies that are skilled in this testing.

These procedures should be performed regularly, at least every three years. The frequency depends on the equipment and how it is loaded and the facility environment conditions. The international Electrical Testing Association (NETA) website (www.netaworld.org) has valuable information for facilities maintenance personnel. For example NETA provides a free download for the MTS-2001 Appendix B "Frequency of Maintenance Tests" which provides a time-based maintenance frequency matrix guide. The ideal maintenance program, NETA points out, "is reliability-based, unique to each plant and to each piece of equipment. Application of the matrix, along with the culmination of historical testing data and trending, should provide a quality electrical preventive maintenance program."

The many necessary safety procedures required when working on high-voltage equipment should be prioritized. Professional, qualified personnel, who do these procedures regularly and who have a thorough knowledge of electrical safety procedures can be contracted to perform these services.

The 2002 National Electrical Code (section 110.16) requires field marking of electrical switchboards, panel boards, and motor control centers to indicate the appropriate level of flash protection that is required when maintaining such equipment. The information must identify the severity of the flash hazard and the appropriate personal protective equipment (PPE) required for the work. Many companies have contracted this service to ensure that it is done properly.

Infrared equipment or a thermography survey service should be available to locate areas that need attention during the shutdown. This non-contact infrared imaging procedure does not require turning off power but can identify overheating in transformers and arcing connections in switch gear. This equipment has improved greatly since the days of hand-held, spot measurements. Now computer-controlled scanning provides real-time temperature profiles of vital equipment. The heat profiles for normal operation and peak load conditions can be used to compare and detect abnormal equipment operation, which can aid in troubleshooting and early correction.

A portable ultrasonic instrument can also be used for locating electrical discharges, (such as corona, arcing, and tracking) before they grow into catastrophic faults. Someone in the facility department may already be using this type of equipment to locate leaks in compressed air and steam distribution systems.

When existing meters and temperature indicators are not read frequently, establishing a program of regular meter readings can result in a normal operating base and trend data that can help identify potential problem areas. Expanded metering can include automatic monitoring with trending and alarm capability.

Making sure that the circuit breakers will work is an important part of improving the power distribution system. All PDS occasionally experience high currents from short circuits, and functioning breakers can prevent explosion when these currents exceed the equipment ratings.

To ensure that this does not happen, a professional power engineer can perform a short-circuit study. The study should be done in conjunction with a breaker coordination study. The breaker coordination study will ensure that only the breaker closest to a fault will open to isolate a fault and not affect the rest of the system by opening the main breaker. Keeping breaker coordination up to date is important because loads change in a facility, and breaker settings are not always made.