The two main standards that maintenance and reliability professionals access for guidance when establishing procedures and best practices for inspecting and maintaining electrical equipment in facilities are the National Fire Protection Association (NFPA) 70B and the Canadian Standards Association (CSA) Z7463. Both these documents have been established to create recommended practices for inspecting and maintaining electrical assets in order to prevent accidents and reduce downtime.
According to NFPA 70B, an Electrical Preventive Maintenance program is "a managed program of inspecting, testing, analyzing, and servicing electrical systems and equipment with the purpose of maintaining safe operations and production by reducing or eliminating system interruptions and equipment breakdowns."
Airborne ultrasound is a tool often used to inspect energized electrical equipment. NFPA 70B makes mention of ultrasound in two sections: when discussing partial discharge section 11.21.3.3.2.2 and when discussing corona in substations and switchgear in section 15.1.2.2.
CSA Z463 goes into more detail when discussing ultrasound technology, saying in section 7.10.2, "ultrasound inspections use collectors that detect the high frequency produced by the emissions caused by electrical arcing, tracking and corona." This section also mentions the sound heard by the inspector can be recorded and then further analyzed in spectrum analysis software for an accurate diagnosis of what the ultrasound instrument detected.
Users of airborne ultrasound, a technology once considered just a leak detector, quickly began to realize the instruments could be used for other applications, such ascondition monitoringg rotating equipment and electrical inspection. To many, airborne ultrasound has become a necessity for inspecting energized electrical equipment. The primary driver of this application is safety. In most cases, airborne ultrasound inspection can be done without opening energized electrical cabinets. Performing an inspection without opening energized electrical equipment helps reduce the risk the inspector faces from potential exposure to arc flash hazards.
Ultrasonic equipment detects airborne and structure-borne ultrasounds normally inaudible to the human ear and electronically "transposes" them into audible signals a technician can hear through headphones and view on a display panel. On some instruments, incoming sound can also be viewed on a spectral analysis screen. With this information, a trained technician can interpret the bearing condition to determine what, if any, corrective action is needed, and the current data can be compared on the spot to the baseline data.
Ultrasound technology has many advantages: 1) It can be used in virtually any environment. 2) Learning to use ultrasound technology is relatively easy. 3) The technology is relatively inexpensive. 4) Modern ultrasonic equipment makes it easy to track trends and store historical data. 5) Ultrasonic technology has proven extremely reliable in predictive maintenance, saving thousands of dollars and hours of lost productivity. 6) There are remote monitoring options for both mechanical and electrical applications.
Airborne and structure-borne ultrasound instruments are an extension of the user's sense of hearing, enabling you to hear what you normally can't, such as compressed air leaks or electrical discharges like corona, tracking or arcing. The sounds outside normal human hearing are high-frequency sounds detected by the instrument and translated into an audible sound heard in the headset by the inspector.
The ultrasound inspection can be done by scanning any openings on the cabinet itself, such as vent openings, seals around doors, louvers, etc. Therefore, before any energized electrical cabinet is opened for maintenance or further inspection, a pre-inspection can be done with ultrasound to see if any anomaly is heard. If there is a condition like corona, tracking or arcing inside the electrical equipment, the ultrasound produced by those anomalies will be heard via those openings. Using ultrasound in conjunction with traditional infrared inspection can help find more problems and increase safety by scanning without opening the energized cabinet.
For more information, visit www.Uesystems.com or call (800) 223-1325.
