Background

A term covering switching and interrupting devices and their combination with associated control, metering, protective and regulating devices is known as switchgear. It also includes accessories, enclosures and supporting structures used primarily in connection with the generation, transmission, distribution and conversion of electric power.

Switchgear, like many other types of industrial equipment, is often unnoticed and unappreciated until it fails to function normally. Because switchgear contains no actively moving parts, it is particularly subject to neglect.

The level to which switchgear is maintained in industry varies widely. Maintenance levels at one extreme might involve continuous monitoring of equipment with temperature and thermal imaging equipment. At the other end of the spectrum, maintenance might only involve running the equipment until it fails. The vast majority of appropriate switchgear maintenance programs will fall somewhere in between these extremes.

Probably the best reference for information about switchgear maintenance is the National Fire Protection Association manual 70B (NFPA 70B). This document, titled "Recommended Practice for Electrical Equipment Maintenance," is available through a variety of sources and deals with a variety of electrical equipment including switchgear.

It is difficult to define ironclad switchgear maintenance intervals and levels because so many variables are involved. These variables include equipment criticality, equipment physical environment, equipment loading level, equipment age and other variables.

Guidelines currently provided by the NFPA 70B for most low-voltage electrical distribution related equipment recommend a periodic infrared (IR) survey fairly frequently as part of inspection routines. Specifically, it states that "routine infrared inspections of energized electrical systems should be performed annually prior to shutdown. More frequent infrared inspections, for example, quarterly or semiannually, should be performed where warranted by loss experience, installation of new electrical equipment or changes in environmental, operational, or load conditions."

In addition, the NFPA 70B recommends physically checking connection tightness and torquing as necessary during major maintenance activities performed every three to six years.

As can be seen, these are fairly "loose" guidelines and should be applied intelligently to particular situations and conditions.

Establishing a Basic Program

Given all of the variables involved in establishing the appropriate level of maintenance that should be applied to switchgear, it is difficult to give specific recommendations. However, a basic program should include the following.

Annual Infrared Inspection of Active Switchgear

This inspection service is readily available through a variety of sources. One trusted option for this service is Progress Energy. It is usually not a particularly expensive service. However, some details concerning infrared inspections are very important. The following items should be considered.

First, if planned in advance, the service can be performed in a very short amount of time. It is recommended that once you choose an IR service provider, you should plan with them in advance just which switchgear should be scanned and the sequence of that scanning that will provide the best information and ensure minimal disruption of operations.

Second, IR results are most effective if the scan is performed when the equipment supplied by the switchgear is running in a fully loaded state. This will mean that the switchgear is loaded to its highest amperage level. At this condition, any resistances in the circuits will be much more obvious in the IR scan than they would be at lighter loads.

Third, when using IR, comparisons of identical connections are often of great value. For instance, if you scan a three-phase connection, you can often identify a problem area in one of the phase connections with respect to the other phase connections. Comparisons between different switchgear running identical machinery can also be of great value.

Fourth, it is always a good idea to schedule the service just prior to an annual maintenance shutdown. This will usually ensure that any conditions discovered during the IR scan are promptly corrected.

Visual and Manual Service

During annual shutdown, after following the appropriate safety and lockout procedures, switchgear should be visually inspected for any signs of overheating, wear, corrosion or other abnormalities. This inspection should be done with an adequate light source so that all connections are clearly visible. This is very important because often the location and/or enclosure of switchgear do not allow proper visual inspection using only ambient lighting.

Also, at annual shutdown, all connections should be checked for proper torque. Torque values are usually supplied with particular equipment, and those recommendations should be followed. It is very important to check all connections. This check will provide a "belt and suspenders" approach to maintenance because you can never be too sure that the IR scan gave results for all of the connections.

In summary, switchgear maintenance is important. If ignored, it can result in considerable equipment downtime and economic loss. The level of maintenance performed should be tailored to the particular loading and importance of the switchgear. Infrared scanning is probably the most valuable tool available but it needs to be coupled with visual inspection and connection tightness checking.

If you would like to receive more information about infrared scanning services or other services and service options, please contact your Progress Energy account executive.