Thermographic inspections of electrical equipment detect hot-spots well before problems occur. Here's how the latest infrared scanning systems at a major hospital work and fit into a typical electrical preventive maintenance program.
Infrared inspections are a key element of a thorough electrical preventive maintenance (EPM) program at a major Northeast hospital. An electrical testing firm, Northeast Testing, Inc., Wallingford, Conn., comes into the hospital annually to search for hot-spots on electrical equipment, uncovering potential trouble sites, and providing a complete report on the condition of equipment.
Using a "thermal-sensitive" camera and related equipment, an operator can see equipment hot-spots immediately, record the hot spot on diskette, take a video or photo of the actual item, and make recommendations.
Infrared scan program
After nearly 20 years of experience at the hospital, Bill Hyland, electrical foreman, and Bob Burns, assistant electrical foreman, have gained the know-how that enables them to select which systems and equipment need to be checked and how often to do an inspection. Because of the overwhelming amount of maintenance to be done, they have judiciously selected what has to be done to obtain high reliability with practical economy. This is where infrared thermography comes in.
Certain critical equipment and systems receive an infrared scanning annually, while only a quarter of the general electrical systems and equipment are scanned each year. As a result, all equipment and systems receive an infrared evaluation every four years. Hyland explains that much of the equipment being scanned receives a routine inspection via their regular EPM program, thus a four-year cycle is appropriate.
On the other hand, he has found that infrared scanning is essential because it finds problems that normally would be missed, possibly causing an outage.
Several years ago, when Hyland called for his first infrared scan, he had the entire hospital checked. The procedure took two weeks and revealed scores of imminent problems. The necessary repair work kept his men so busy that regular work schedules fell way behind.
With this in mind, he called for regular infrared scanning; as fewer and fewer hot-spots were found, he was able to space the scanning frequency to guard critical equipment and, at the same time, watch all systems effectively and economically.
Typical infrared scanning
On a typical infrared scanning procedure, a Northeast Testing technician starts with a list of all electrical (and mechanical) equipment to be inspected. After obtaining familiarity with the hospital, an experienced technician is able to inspect and record condition of equipment quite fast. At the hospital, thousands of items are scanned. A significant advantage is that all scan inspections are done while the equipment is energized, so that continuity of power is maintained. Typical equipment to be checked include the following.
Panelboards. There are hundreds of 208Y/120V panelboards and scores rated at 480V in the hospital, all of which can develop loose connections. In particular, neutral blocks and conductors are checked for possible harmonic heating.
Fused switches. The hospital is more than a century old; however, the oldest functioning building dates to 1923. This structure has been renovated as many times as modernizations have occurred. The original hospital distribution system used fused switches, and this overcurrent protection system has been maintained. Hundreds of fused switches of all sizes need regular inspection.
Busways. The hospital stretches over many acres, and some buildings are several stories high. Primary power at 11kV is distributed to several substations, and busways from the substations carry 480Y/277V and 208Y/120V power over long distances. Thus, it's essential to scan thousands of feet of busways.
Motor control centers. Most motor starters are electromagnetic and in various sizes, some of which, though well maintained, are quite old. Also, modern variable frequency drives are installed. Infrared scanning provides early detection of trouble at these important controls.
Transfer switches. These are scanned regularly because they are essential to maintaining power to critical locations.
Other equipment. Included in the scanning program are substation transformers, primary and secondary fused switches, main 11kV power circuit breakers, and essential motors.
How infrared works
The test firm uses either black-and-white thermal scanners, which require liquid-nitrogen cooling, or a modern, multicomponent color thermal-camera system. The color camera in this system is self-cooled, eliminating the need to transport liquid nitrogen.
The principle of operation is that operating electrical equipment gives off heat. This heat can be detected by the thermal camera and viewed and interpreted by an operator. The temperature of the scanned object can be calibrated in black-and-white or in color. Immediate action can be taken to correct the problem, or a picture called a thermogram can be taken and recorded for future reference.
Basic components of the color system are the thermal-sensing camera and a portable, rechargeable battery pack. With just these two components, effective real-time detection of hot-spots can easily be done.
Northeast Testing, however, makes use of several additional components to obtain fast, reliable data. These items are a camcorder/monitor, 3 1/2-in. computer disk system built into the thermal camera, rolling camera support, personal computer, color printer, customized software, and sometimes a VCR.
The thermal camera with built-in disk drive, camcorder/monitor, and battery supply is mounted on a rolling table. This unit is used (the camera can be handheld when desired) in the field when thermal scanning equipment.
The thermal camera has multiple function controls but is easy to operate. Control buttons include freeze-frame, store to disc, temperature level set, and four buttons for sensitivity level adjust: rough and vernier, cross-hair adjust, manual focus, date, time, etc.
Another control allows the operator to view the color thermogram on the camcorder/monitor screen, permitting a sharp, well-defined thermal image with color values. He or she can also use the camcorder to take "real-life" videos of the subject under test while speaking into the unit to describe details that can be permanently recorded.
When scanning is completed, the disk, which holds up 70 thermograms, is downloaded into a computer equipped with special software. Also, the actual video can be loaded into the computer so full-color, hardcopy records can be printed out along with any pertinent data and recommendations for action.
Infrared survey report
After completion of infrared scanning of electrical equipment, Northeast Testing provides a five-part report. Part 1 provides an overview of the facility inspected, pertinent details of the structure, environment and power systems, and a discussion of infrared thermography. Part 2 provides specifications of scanning techniques and a general summary of the results of the infrared scan survey. Part 3 contains a list of all equipment scanned, each identified by number with related results and recommendations. Part 4 contains an infrared survey report sheet on each item scanned. Each sheet has a thermogram, correlated photo, item identification and number, problem description, probable cause, recommended action, and pertinent data so that future thermograms can be accurately compared. Part 5 provides details of NETA (inter-National Electrical Testing Association) infrared test standards.
RELATED ARTICLE: HOSPITAL PREVENTIVE MAINTENANCE
The hospital is very large with more than 50 buildings on nearly 100 acres, requiring a very extensive electrical system. Also, numerous critical facilities, such as operating rooms, intensive care, heart units, etc., demand highly reliable power.
The challenge to assure dependable power is aptly managed by Bill Hyland, electrical foreman, and Bob Burns, assistant electrical foreman. With a crew of 18 electricians, the firm utilizes a computerized maintenance plan to keep electrical systems and equipment up and running. Routine maintenance is carried out by in-plant electricians. This plan includes weekly testing of several emergency generator systems, visual inspections of equipment as dictated by computer scheduling, and repair or replacement of scores of smaller electrical systems, equipment and items throughout the hospital.