Archive | March, 1997

266

2:59 am
March 2, 1997
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The Maintenance Mission

What exactly is the purpose of the maintenance function? In a world of endless reorganizations, shifting technological paradigms, growing expectations, and increasingly onerous regulatory constraints, all of which must be dealt with urgently, it is easy to lose the way. Most major corporations have developed formal mission statements to help them maintain a steady course through this ocean of distractions. It may be worth developing a formal mission statement for maintenance to help us do likewise.

Perhaps a good place to start would be to look at the meaning of the word maintain, which the Oxford dictionary defines as “cause to continue.” Cause what, you may ask, to continue what?

The first “what” is easy to answer. Maintenance exists because we have physical assets that need maintaining. So our mission statement must reflect the fact that maintenance is first and foremost about physical assets.

Continue “what”? What is it that we wish to cause to continue? The answer lies in the fact that every physical asset is put into service because someone wants it to do something. In other words, it is expected to fulfill a specific function or functions. Therefore, it follows that when we maintain an asset, the state we wish to preserve must be one in which it continues to do whatever its users want it to do. This shift in emphasis from preserving what it is to preserving what it does should be acknowledged in the mission statement.

Our maintenance mission statement also should recognize our customers: the owners of the assets, the users of the assets, and society as a whole. We satisfy owners by ensuring that their assets generate a satisfactory return on the investment made to acquire them. We satisfy users by ensuring that each asset continues to do whatever they want it to do at a standard of performance that the users consider to be satisfactory. Finally, we satisfy society as a whole by ensuring that our assets do not fail in ways that threaten the environment.

If things didn’t fail they wouldn’t need maintenance. The technology of maintenance is all about finding and applying appropriate failure management techniques: predictive maintenance, preventive maintenance, failure-finding, run to failure, and once-off changes to the design of the asset or the way it is operated.

Each category represents a host of options. A major challenge facing us nowadays is not only to learn what these options are, but to decide which are worthwhile and which are not, in our own organizations. If we make the right choices, it is possible to improve asset performance and at the same time contain and even reduce the cost of maintenance. If we make the wrong choices, new problems are created and existing problems only get worse. Our mission statement should remind us of our obligation to try to make the right choices from the full array of options.

However, when considering failure management options, we must bear in mind that we worry about failures because they have consequences. Failures incur consequences in the form of repair costs. They also can affect safety, environmental integrity, output, product quality, customer service, loss of protection, and operating costs. The severity and frequency with which a failure incurs any of these consequences dictates whether any failure management technique is worth applying. Our mission statement needs to acknowledge the pivotal role that consequence avoidance plays in maintenance.

We also must acknowledge that most of us work in a highly resource-constrained environment. The most effective maintainers are those who apply the resources they need (people, spares, and tools) as cost effectively as possible, but not so cheaply that they damage the long-term functionality of their assets. In other words, we must minimize the cost of ownership of the assets throughout their useful lives, not just to the end of the next accounting period.

Finally, our mission statement should recognize that maintenance depends on people, not only maintainers, but also operators, designers, and vendors. It should acknowledge the need to create an environment where everyone involved with our assets shares a common and correct understanding of what needs to be done and is able and willing to do whatever is needed right the first time, every time.

These criteria suggest the following as a possible maintenance mission statement:

  • To preserve the functions of our physical assets throughout their technologically useful lives
  • To the satisfaction of their owners, of their users, and of society as a whole
  • By selecting and applying the most cost-effective techniques
  • For managing failures and their consequences
  • With the active support of all the people involved. MT

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234

2:13 am
March 2, 1997
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Visual Aids Speed Maintenance

Suggestions from a maintenance professional for point-of-use maintenance information delivered by visual aids and equipment manuals.

Diagrams, charts, labels, signs, and other visual aids attached to plant equipment, printed in procedures and documentation, and posted throughout the plant speed maintenance and operating tasks as well as contribute to plant safety.

While attending a recent total productive maintenance (TPM) conference, I was reminded of the importance of visual aids in the classic approach to TPM. Work efficiency is increased when team members and other personnel can quickly see whether gauges are reporting normal or abnormal values and when adjustments are within suggested operating ranges, or when they can see which grease fitting is the one to be charged daily.

Visual aids help reduce downtime and safety incidents. If an employee is new to the plant or area and must turn off a machine or fluid supply, the process is quicker and safer if everything is properly labeled. The ready availability of an experienced craftsperson for the job cannot be taken for granted. It is not an insult to anyone to have too much labeling.

The visual aid suggestions that follow have been collected from seminars, training courses, articles, and experience, and are offered with the thought that they can be adapted for purchasing documents or added to maintenance checklists.

Labeling equipment
Components of new equipment should be labeled before they are brought into the plant, when possible, to provide visual assistance to installers, maintainers, and operators. The supplier could be asked for the following:

  • Identify each valve by name and unique number. The name should indicate the equipment served by the valve. All valves–hydraulic, air, power, drain, etc.–should carry an identifying label, especially dump valves.
  • Identify fluid flow directions at the source and frequently along the flow circuit as appropriate.
  • Identify each gauge with a unique number and name that identifies the equipment it serves.
  • Permanently mark gauges, sight glasses, and other instruments with the safe operating range. Gauges also should be marked with the normal operating value or range. It must be immediately obvious to operators or maintainers when pressures or other parameters are out of tolerance, especially if such an operation presents dangerous consequences.
  • Mark appropriate travel points on equipment that moves with the product or during the processing of a product. The equipment may need marks indicating the minimum and maximum travel points to help avoid “maxing out” the component.
  • Distinguish lubrication points with a visual code indicating frequency. If some items need lubricating daily and some weekly, the different points should be easily identified, typically by color coding.
  • Provide labels with lubricant specification at lubrication points. Labels should state special lubrication procedures or cautions.
  • Post warning signs on equipment if there is a danger from stored energy such as air or hydraulically operated rolls that can fall when de-energized.
  • Apply appropriate visual aids to components that require adjustment.
  • Mark tanks and chambers with appropriate fluid levels. Consider signs that indicate appropriate levels under various operating conditions such as hot, cold, running, or full.

Visual aids can be anything from a line scribed or painted on a gauge or machine base to special engraved signs cemented to the component; however, all marks must be permanent and easy to see.

Safety or danger signs, however, should include standard materials, colors, and lettering styles throughout the plant.

The visual aid concept can be easily extended to manuals supplied by vendors with their equipment. If needed information is not contained in the manuals, personnel should be assigned to search out the information and append it to the manual to make it a complete reference package. The following items are suggested.

Operating manuals

  • Description of the “design intent” of the equipment and an overview of the equipment
  • Identification of all controls and instruments
  • Midrange settings for any adjustable items, such as air settings on cylinders, pressure settings on hydraulic cylinders, and measurements for setup on adjustable assemblies or subassemblies; a minimum/maximum approach to putting a machine together to run (distances and tolerances for position where position is adjustable)
  • Complete safety information including warnings, lockouts, precautions, do’s and don’ts, and material safety data sheets where applicable
  • Normal operating procedures, cleanup frequency, and lubrication frequencies
  • Material flow
  • Operator’s role
  • Startup and shutdown procedures
  • Setup procedures
  • Troubleshooting procedures
  • Emergency shutdown procedures
  • Special cold or hot weather procedures.

Parts manuals

  • Complete bill of materials with manufacturer part numbers
  • Drawings when possible
  • Recommended spares
  • Recommended critical spares
  • List of long delivery items
  • List of 24 hour delivery items
  • Recommended quantities
  • List of company contacts, including engineers who provide technical advice on parts (two minimum)
  • List of startup parts (parts that are typically consumed at startup).

Maintenance manuals

  • Preventive maintenance procedures
  • Preventive maintenance frequencies
  • Troubleshooting guide (appropriate for craft personnel, more in-depth information than in operator manual)
  • Lubrication routes with recommended frequencies and types of lubricants
  • Special maintenance safety warnings and procedures
  • Maintenance warnings (example: do not weld on scanner without covering lens, or lower rolls and insert pin before doing maintenance so rolls do not fall)
  • Procedures for subassembly repair and replacement (list common wear components); any particular rebuild procedures
  • Tolerances for misalignment, pressure readings, chain and belt tension
  • Setup procedures
  • Stored energy hazards
  • Recommended frequencies for chain replacement; flights where appropriate
  • Alignment procedures
  • Calibration procedures
  • Special tool requirements, including safety equipment. MT

Ron Hardee is maintenance lead at Weyerhaeuser, P.O. Box 250, Ayden, NC 28513; (919) 746-7235; e-mail lghardee@ecu.campus.mci.net.

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321

12:57 am
March 2, 1997
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Qualify and Certify Staff for Shaft Alignment

Companies should determine the skill level of personnel responsible for alignment, arrange for appropriate training for proficiency, and use qualification testing for certification.These examples show the need for certification in shaft alignment.

A maintenance technician at a chemical plant was asked to align a motor and a pump with a newly purchased laser shaft alignment system. Shaft position measurements were captured with the instrument. Corrections required to align the motor (assigned as the movable machine) with the pump indicated that the outboard end of the motor had to be lowered 85 mils and the inboard end of the motor had to be lowered 37 mils; there was no shim stock under the motor feet. After completely removing the motor, the technician began grinding away the baseplate. The motor was placed back on the base and shaft position measurements were captured again. Because too much metal had been ground away, the technician then added shims under the motor feet. Several side-to-side moves were made to bring the equipment into alignment.

A manufacturer of gas turbines was installing several large air compressors to expand the capacity of a system used to test jet engines. Requests for bids to install the 11,000 hp motors, gearboxes, and compressors were sent to several general contractors. Detailed specifications including instructions for installing foundations and sole plates and for correcting soft foot conditions were provided, along with rough alignment procedures and final hot and cold alignment procedures. The general contractor was told to subcontract the alignment work to companies specializing in machinery alignment. The specifications were sent to the subcontractors; however, several of the contractors submitted bids although they did not understand many of the detailed specifications. Toward the end of the project, the company discovered that the alignment work was not performed to the written specifications and payment was withheld from the contractors who performed the work.

A company that was in the process of becoming ISO 9000, 9001, and 9002 compliant requested information on certification testing for maintenance personnel who perform shaft alignment. Several employees had been certified in vibration analysis and thermography. The company wanted documentation that personnel were adept at finding and fixing problems.

A petroleum company decided to sell one of its facilities. Several prospective buyers were interested in retaining as many employees as possible. However, they wanted to retain only people who were adequately trained and were certified to do specific tasks. When asked to provide information on task certification of its employees, the petroleum company was unable to do so.

A steel company was having problems with a fairly complex multiple-element drive train. Misalignment was found to be the root cause of the failures. No one in the plant knew how to align the drive system. An alignment service company was contacted; although a technician said he could align the drive system in less than 4 hours, the job actually took several days to complete.

An electric utility company experienced several failures on a critical pump. Inhouse maintenance personnel had been using a laser shaft alignment system to measure the positions of the shafts. The pump was being driven by a variable speed hydraulic clutch. In the instruction manual, the clutch manufacturer stated that the clutch would rise upward 15 mils once it attained normal operating conditions. Maintenance personnel set the clutch 15 mils lower than the pump shaft assuming that the pump would not move from off-line to running conditions. A survey showed that the pump shaft rose upward far more than the clutch did, forcing the unit to run under severe misalignment conditions.

Equipment for vibration analysis and infrared thermography has improved dramatically over the past 20 years, and the number of people working in these areas has increased substantially. With a small investment, anyone can buy a personal computer and a vibration data collector or an infrared camera and be in business. However, the learning curve for this equipment is long and steep.

Over the past 5 years, there has been an effort to determine the skill level of people working in vibration analysis and infrared thermography through qualification and certification testing by several companies and institutions. Many companies are requiring their employees to become certified.

Certification for other tasks in the workplace such as correcting rotating machinery problems including balancing, shaft alignment, and tribology also has been discussed. With certification testing comes questions. Who has the authority to provide certification? What is the best way to determine if people are qualified to perform shaft alignment? How can trainees prove what they learn from training courses? And how qualified are contractors who are installing new rotating machinery?

Who to train and qualify
Many organizations feel that the responsibility for shaft alignment rests solely in the hands of tradespeople (mechanics, millwrights, pipefitters, and electricians). However, are tradespeople responsible for the following tasks?

  • Selecting training courses they feel they need and for sending themselves to the courses
  • Researching types of shaft alignment measurement systems and purchasing a system that best fits the needs of their organization
  • Telling a contractor that he is not installing rotating machinery correctly
  • Hiring staff or contractors to help with the work overload
  • Rebuilding a piece of rotating machinery that is malfunctioning because of excessive runout conditions
  • Determining that a rotating machinery foundation or baseplate that has been removed and reinstalled has deteriorated excessively or been installed improperly
  • Redesigning and reworking improperly installed piping that is putting excessive strain on the rotating machinery it is attached to
  • Purchasing and installing piping supports, or designing a custom piping anchor on a CAD system, purchasing the materials, and installing the anchor
  • Selecting a new flexible coupling design to replace one that fails often or does not work well
  • Picking a pump as the movable machine and leaving the motor as the stationary machine
  • Issuing work orders to check the alignment of all the rotating machinery every year
  • Shutting a machine down on the basis of vibration and temperature data that indicate a misalignment or soft foot condition
  • Determining which machinery might require a hot alignment check, selecting an off-line-to-running machinery movement measurement technique, installing the equipment on the machinery, measuring and analyzing data, and altering the cold alignment position on the basis of data collected
  • Maintaining records of alignment work performed and saving records in the equipment files or a computer database
  • Installing X-Y proximity probes on a machine supported in sliding type bearings to analyze the Lissajous orbit for signs of running misalignment.

Shaft alignment training should be mandatory for managers, engineers, technicians, front-line supervisors, and tradespeople to provide them with the minimum working knowledge needed to achieve accurate alignment and to know the process. Engineering and maintenance managers, rotating equipment and maintenance engineers, maintenance technicians, vibration specialists, foremen, and front-line supervisors, as well as the trades personnel, all should be trained and qualified to do their respective tasks.

Assessing and verifying knowledge and experience
Before qualification testing begins, shaft alignment knowledge can be assessed using a Field Experience Evaluation form that queries employees’ or contractors’ knowledge and experience on specific types of machinery. Individuals can then be tested on specific tasks to determine if they are capable or if they need supplementary training to raise the level of proficiency.

The form can be used to determine required training for personnel installing, maintaining, or aligning rotating machinery. But how can experience and proficiency be verified?

Written or oral examinations can verify the knowledge level for each item in the form. One comprehensive test might encompass every facet of shaft alignment, or a series of tests can be given for discrete blocks of information. If the overall body of information is broken down into separate blocks, personnel with little or no experience can be tested incrementally as their level of knowledge grows. The accompanying section, “Test Requirements for Alignment Knowledge Assessment,” outlines possible test subjects.

Written or oral exams can test knowledge but are inadequate to determine skill level in performing specific tasks. Perhaps the most effective means to verify knowledge and skill level is to have employees perform tasks on a simulator or directly on an operating rotating equipment drive system. However, using process machinery as a test platform may not be possible. Having simulation equipment available allows testing to occur at any time without affecting production or maintenance schedules. For accurate skills assessment, test equipment must simulate real life circumstances.

Qualification and certification testing in tasks such as vibration analysis, thermography, and shaft alignment is necessary. Establishing the requirements for qualification or certification can be accomplished by appraising the experience level of personnel through an evaluation form that addresses all aspects of the task. Skills of each individual can then be assessed and appropriate training can be administered. Written or oral exams and task simulation tests can be conducted to determine the true proficiency of personnel. MT


John Piotrowski is president of Turvac Inc., an alignment training and consulting company, 125 Settlemyre Rd., Oregonia, OH 45054; (513) 932-2771; e-mail turvac@your-net.com; Internet http://www.ncinter.net/~turvac/. He is the author of Shaft Alignment Handbook.

TEST REQUIREMENTS FOR ALIGNMENT KNOWLEDGE ASSESSMENT

Basic test

  • Consequences of poor alignment on rotating machinery
  • Detecting misalignment on running rotating machinery (vibration, infrared methods)
  • Use and care of measuring tools and instruments (feeler gauges, dial indicators, optical encoders, proximity probes, laser/detector system, etc.)
  • Finding and correcting excessive runout conditions
  • Finding and correcting soft foot
  • Finding and correcting excessive piping strain
  • Foundation and baseplate design, installation, and care
  • Concrete and grouting installation
  • Alignment tolerances
  • Rigid and flexible coupling design, installation, and care
  • How to perform the reverse indicator method
  • Basic mathematical or graphical/modeling principles for realignment
  • How to determine effective alignment corrections using the reverse indicator technique
  • Keeping records of alignment work.

Intermediate test

  • How to perform the face and rim method
  • How to determine effective alignment corrections using the face and rim technique
  • How to perform the shaft to coupling spool method
  • How to determine effective alignment corrections using the shaft to coupling spool technique
  • How to perform the double radial method
  • How to determine effective alignment corrections using the double radial technique
  • How to perform the face-face method
  • How to determine effective alignment corrections using the face-face technique
  • Mathematical or graphical/modeling principles for all of the methods listed.

Advanced test

  • How to align multiple-element drive trains
  • How to align right angle drives
  • The four categories for measuring OL2R machinery movement
  • Calculating machine case thermal expansion
  • Inside micrometer-tooling ball-angle measurement methods
  • Proximity probes with water cooled stands technique
  • Using optical alignment tooling for OL2R machinery movement
  • Alignment bars with proximity probes OL2R method
  • Using laser-detector systems to measure OL2R machinery movement
  • Using the ball-rod-tubing connector system to measure OL2R machinery movement
  • Using the vernier-strobe system to measure OL2R machinery movement
  • Mathematical or graphical/modeling principles for all of the methods listed
  • How to align rotating machinery to compensate for OL2R machinery movement.

 

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1231

12:52 am
March 2, 1997
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Using Ultrasound for High Voltage Insulation Testing

Ultrasound is an effective, low cost method for evaluating the condition of insulation components on high-voltage transmission and distribution equipment. Conventional testing methods require the equipment to be shut down. Ultrasonic testing can locate failing insulation components in live electrical distribution and transmission equipment.

Ultrasonic testing is suitable for outdoor substation and aerial transmission equipment, particularly when coupled with a parabolic concentrator. Enclosed switchgear equipment also can be tested. Spectrum analysis of the ultrasound signal allows tracking to be distinguished from other sources of ultrasound in the gear or adjacent areas. Listening ports permit the safe inspection of any type of switchgear.

Overhead transmission lines
The night shift electrical supervisor at a petrochemical refinery received reports of visible arcing at porcelain insulators on a 69 kV power pole. The power line supplied a wastewater treatment facility. If the facility lost power, the refinery would be unable to operate.

From the symptoms described by the supervisor, it was likely that an insulator was failing. The failure of insulators on high-voltage (greater than 4 kV) power transmission and distribution equipment can often result in electrons discharging into the air, a phenomenon known as tracking, corona, or partial discharge. Under the right conditions, the discharge can find a path to ground, resulting in a highly destructive ground fault.

The electrical supervisor wanted to know if a recent infrared test had identified any problems at these insulators. He also wanted to know if the problems had disappeared, because arcing could no longer be seen. The supervisor was told that, except for severe cases where a current path to ground was established, infrared testing would not detect high-voltage insulator failures because the corona or tracking typically produces little or no heat. He also was informed that this situation might be extremely dangerous and that it warranted immediate attention.

A UE Systems Ultraprobe 2000 was used to evaluate the problem. The instrument hears ultrasound (sound above 20,000 Hz) and converts it to audible frequencies. High-voltage discharges that accompany the breakdown of insulation cause ionization of the air and the ionization produces ultrasound. Thus, the presence of tracking or corona can be readily detected by an ultrasonic instrument.

The instrument is simply pointed at the area of concern. If tracking or corona is present, a buzzing noise similar to static on a radio is heard through the instrument headphones. The instrument is directional, allowing the location of the insulation fault to be determined by listening from several locations until the high sound source is pinpointed.

Power pole insulators at the refinery were located about 60 ft above ground. In addition, the area around the pole had discharging steam traps and several compressed air leaks. The traps and air leaks produced high levels of background ultrasound that would ordinarily overpower the ultrasound produced by insulator failure. A parabolic concentrator was used to overcome these problems. This device has a seven element ultrasonic detector array mounted in the center of a parabolic dish. The dish features an optical sight that expedites pinpointing the source of ultrasound.

The concentrator provides two advantages:

  • Instrument sensitivity is more than doubled. As a result, even low-level discharges occurring at a substantial distance can be detected.
  • The concentrator is extremely directional. Adjacent ultrasound sources are rejected and the precise source of ultrasound is easily determined.

The ultrasound instrument immediately indicated that corona discharge was occurring at each of the insulators. The C phase insulator had a very high level of discharge.

In addition, the insulators were checked with an infrared imager using a 3x telescope. The imager revealed a ring of heat on each insulator. The ring of heat was about 2 deg F above adjacent surfaces and it occurred at a different location on each insulator. There were no connections near any of the rings. It was determined that the heating probably corresponded to the location of the discharge at each insulator. Temperature differences were very small and could be overlooked easily during a typical infrared survey.

When both ultrasound and heat are detected from a failing insulator, the problem has reached a potentially dangerous stage and requires immediate shutdown. The presence of heat indicates a current flow to ground. This flow will precede catastrophic failure.

Although the insulators were subjected to periodic inspections and cleaning, they obviously were failing. Backup generators were brought in to power the facility while the insulators were replaced.

Enclosed switchgear
A combination of infrared and ultrasonic testing is often used on high-voltage electrical equipment, particularly enclosed switchgear. Infrared equipment can locate resistive faults such as dirty switch contacts or loose joints. The ultrasonic instrument locates developing insulation faults. In enclosed gear, tracking is a particularly serious problem because the distance from current carrying components to ground is usually small. Failure of insulating components can cause switchgear components to vaporize. Ultrasonic testing in enclosed switchgear may be more important than infrared testing.

At a multi-use 1 million sq ft facility, access doors to a 13 kV switch were locked and no keys were available. The internal current carrying components could not be inspected. This switch was critical; its loss would shut down the entire complex.

Because ultrasonic sound can pass through small cracks at doors or through ventilation openings, an ultrasonic test was performed. The test revealed extremely high internal ionization. Bolt cutters were used to remove the locks. With the lights out, arcing was visible where the bus passed through a supporting barrier board.

Infrared testing also revealed a track of heat leading directly to a support bolt, indicating that current was already flowing to ground. Building tenants were notified and an orderly shutdown was conducted the next evening to correct the problem. The complex was back on line the following morning.

Often, when enclosed high-voltage switchgear or transformers are inspected, it is difficult to distinguish between ultrasound produced by insulation failure and ultrasound produced by vibration of mechanical components. However, spectral analysis of the ultrasound signal can be used to distinguish tracking and corona from mechanically produced ultrasound.

Output from the ultrasound instrument is fed into a spectrum analyzer. The spectrum analyzer can be the same portable data logger used for monitoring vibration in mechanical equipment. Mechanical vibration produces a spectrum in multiples of 60 Hz (electrical field frequency). Tracking and corona ultrasound results from ionization of air. This process produces broadband noise. There may be a 60 Hz component because the arc will rise and collapse with the voltage cycle. However, distinct 60 Hz multiples are not present.

Mechanical vibration produces an easily discerned spectral pattern while tracking or corona produces a noise pattern. Thus, for example, spectral readings can be taken at a dry-type transformer to determine whether an insulation fault is developing. Alternatively, the spectral readings can distinguish between potential transformer or switchgear case vibration and tracking.

On many types of enclosed high-voltage gear, front or rear panels can be removed to provide access for ultrasonic testing. (All appropriate safety procedures must be observed during removal of panels on energized high-voltage switchgear. See National Fire Protection Association 70E, “Standard for Electrical Safety Requirements for Employee Workplaces.”)

However, high-voltage switchgear is often totally enclosed. Access is through interlocked doors that cannot be opened when the gear is energized. This type of gear can be easily tested for insulation breakdown through the use of a listening port.

Ultrasound easily passes through an opening but is readily blocked by a solid surface. On switchgear, a listening port can often be provided by removing a few bolts from the housing. The ultrasonic instrument is then held near the open bolt holes to detect the distinctive buzz of internal tracking or corona. On totally sealed gear, a 4 in. dia capped hole can be cut into the switchgear housing during an outage. The port cover can be removed for inspection. The ultrasonic instrument is then positioned at the hole and operated to detect any internal tracking. MT

Information supplied by Mid Atlantic Infrared Services, Inc., Bethesda, MD; (301) 320-2870. Continue Reading →

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