Electrical Maintenance and Safety (part 1)

Introduction:

All maintenance and testing of the electrical protective devices addressed in this section must be accomplished in accordance with the manufacturer's instructions. The ANSI/NETA 2011 Standard for Maintenance Testing Specifications is an excellent source of information for performing the required maintenance and testing of these devices. Visit the NETA website (https://www.netaworld. org) for further information.

Because of the electrical hazards to which they may be exposed, all workers involved in electrical testing and maintenance must be qualified personnel as defined in the OSHA and NFPA standards. NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, states that equipment deterioration is normal, but equipment failure is not inevitable. Normal deterioration begins as soon as new equipment is installed and if unchecked can eventually cause equipment failure. Deterioration can be accelerated by factors such as environment, overload, or severe duty cycles. A periodic maintenance program can identify these factors and provide measures for coping with them. Other potential causes of equipment failure can also be detected and corrected. Among these are load changes or additions, circuit alterations, improperly set or improperly selected protective devices, and changing voltage conditions.

Without an effective maintenance and testing program, management assumes a greatly increased risk of a serious electrical failure and its consequences. An effective electrical preventive maintenance program can reduce accidents, save lives, and minimize costly breakdowns and unplanned shutdowns of production equipment. Failures can be averted by identifying and correcting impending troubles before they become major problems requiring more expensive, time-consuming solutions.

The Safety-related Case for Electrical Maintenance

Overview:

The relationship between safety and preventive maintenance is not a difficult one to establish. Properly designed equipment that is properly installed is well capable of doing its job when it is new. As equipment ages, however, several factors begin to take their toll on electrical equipment.

• Dust, dirt, and other contaminants collect on equipment, causing the equipment to over heat and bearings and other moving parts to bind.

• Vibration causes hardware to loosen. Subsequent operations of equipment can cause joints and equipment to fail explosively.

• Heat and age can cause insulation to fail, resulting in shock hazards to personnel.

• Increased loads, motor-starting surges, and power quality issues such as harmonics combine to increase the aging process and set the stage for equipment failure.

• Electronic components can drift or fail, causing unstable operation of protective equipment.

Unfortunately, the ultimate failure of unmaintained equipment usually occurs when the equipment is needed the most-during electrical faults. Such failures result in arc and blast events that can and do harm workers in the area. They also result in significant downtime, loss of equipment, and construction cost incurred in rebuilding the equipment.

The only way to ensure that electrical equipment continues to operate in an optimal manner is to maintain it so that it stays in factory-new operating condition.

Regulatory:

As discussed above and in previous sections, the catastrophic failure of electrical equipment creates severe hazards for personnel working in the area. Recognizing this, the Standard for Electrical Safety in the Workplace (NFPA 70e) requires that electrical equipment be properly maintained to minimize the possibility of failure.

Relationship of Improperly Maintained Electrical Equipment to the Hazards of Electricity

Improperly maintained equipment may expose workers to any of the electrical hazards. For example:

1. Improperly maintained tools or flexible cord sets (extension cords) can have frayed insulation that exposes the energized conductors and allows them to contact the worker or the metallic tool the worker is using. The result is an electric shock.

2. Improperly maintained protective devices, such as circuit breakers or fuses, can fail when interrupting an overcurrent. Such a failure is likely to be explosive; consequently, the worker is exposed to electrical arc and electrical blast.

3. Improperly maintained connections can overheat, resulting in any of the following:

a. Melted insulation, exposed conductors, and the attendant electrical shock hazard

b. Fire

c. Failed connections resulting in electrical arc and blast

4. Improperly maintained switchgear, motor control centers, or panelboards can fail explosively when an arc occurs internally. This exposes workers to the effects of electrical blast and possibly electrical arc.

Maintenance and the Potential Impact on an Electrical Arc-Flash

Maintenance of the circuit-protective devices can have a significant impact on the incident energy of an arc-flash. NFPA 70e states, "the arc flash hazard analysis shall take into consideration the design of the overcurrent protective device and its opening time, including its condition of maintenance." In a Fine Print Note following this requirement, it states, "Improper or inadequate maintenance can result in increased opening time of the overcurrent protective device, thus increasing the incident energy." Maintenance must be a major consideration in an arc-flash hazard analysis because a major component of the analysis is the clearing time of the protective device. When the arc-flash hazard analysis is performed, the ratings and settings of the overcurrent protective devices are used, based on what they are supposed to do. The following example is provided to further validate the NFPA 70E requirement for maintenance.

Example:

In this example, we use a low-voltage power circuit breaker that has not been operated or maintained for several years. The lubrication has become sticky or hardened so the circuit breaker could take several additional cycles, seconds, minutes, or longer to clear a fault condition. Two arc-flash hazard analyses will be performed using a 20,000-amp short circuit with the worker 18 in from the arc: (1) Based on what the system is supposed to do, we will use a clearing time of 0.083 second (5 cycles), and (2) due to lack of maintenance, and the resultant sticky mechanism the circuit breaker now has an unintentional time delay and a clearing time of 0.5 second (30 cycles). The following NFPA 70E equation will be used to calculate both conditions:

EMB = 1038.7DB

-1.4738 tA (0.0093F2

- 0.3453F + 5.9675).

Calculation #1:

EMB = maximum 20-in cubic box incident energy, cal/cm^2 DB = distance from arc electrodes, inches (for working distances 18 in and greater) tA = arc duration, seconds F = short-circuit current, kA (for the range of 16 kA to 50 kA) (1) DB = 18 in (2) tA = 0.083 second (5 cycles) (3) F = 20 kA EMB = 1038.7DB

-1.4738 tA(0.0093F2

- 0.3453F + 5.9675)

= 1038 × 0.0141 × 0.083(0.0093 × 400 - 0.3453 × 20 + 5.9675)

= 1.4636 × 2.7815

= 3.5 cal/cm^2

According to NFPA 70E, the required arc-rated Fr clothing and other PPE to be selected is based on this incident energy exposure level. Therefore, the arc-rated Fr clothing and PPE must have an arc rating of at least 3.5 cal/cm^2. Calculation #2:

EMB = maximum 20-in cubic box incident energy, cal/cm^2

DB = distance from arc electrodes, inches (for working distances 18 in and greater) tA = arc duration, seconds

F = short-circuit current, kA (for the range of 16 kA to 50 kA) (1)

DB = 18 in (2) tA = 0.5 second (30 cycles) (3)

F = 20 kA EMB = 1038.7DB

-1.4738 tA(0.0093F2

- 0.3453F + 5.9675)

= 1038 × 0.0141 × 0.5(0.0093 × 400 - 0.3453 × 20 + 5.9675)

= 7.3179 × 2.7815

= 20.4 cal/cm^2

According to NFPA 70E, the required arc-rated Fr clothing and other PPE to be selected is based on this incident energy exposure level. Therefore, the arc-rated Fr clothing and PPE must have an arc rating of at least 20.4 cal/cm^2.

FIG. 2 Preferred required warning label for posting on electrical equipment to warn of hazards.

FIG. 3 Effect of electrical maintenance frequency on overall costs.

Decreasing Maintenance Effort

Conclusion:

If the worker is protected based on what the system is supposed to do (0.083 second or 5 cycles) and an unintentional time delay occurs (0.5 second or 30 cycles), the worker could be seriously injured or killed because he or she was under-protected.

As can be seen, maintenance of circuit-protective devices is extremely important to an electrical safety program. Maintenance must be performed according to the manufacturer's instructions to minimize the risk of having an unintentional time delay in the operation of the circuit-protective devices.

Hazards Associated with Electrical Maintenance

Any time workers approach electrical equipment, they might face one or more of the electrical hazards. This includes activities associated with electrical maintenance. Both the National Electrical Code (NFPA 70) and the Standard for Electrical Safety in the Workplace (NFPA 70E) require that "Switchboards, panelboards, industrial control panels, and motor control centers that are in other than dwelling units and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment." FIG. 1 illustrates an example of the minimum labeling requirements, and FIG. 2 shows a preferred label for the application. Refer to Section 4 for details on the methods for determining the extent of the hazards.

FIG. 1 Minimum required warning label for posting on electrical equipment to warn of hazards.

The Economic Case for Electrical Maintenance

Although a complete discussion of the economics of an electrical maintenance program is beyond the scope of the handbook, FIG. 3, taken from Recommended Practice for Electrical Equipment Maintenance (NFPA 70B), provides a clear definition of the economic importance of such maintenance.

This diagram charts the relationship between costs and maintenance. As can be seen, the cost of electrical preventive maintenance (EPM) decreases as the interval between inspections increases. In other words, the cost of maintenance decreases as less maintenance is done. The cost of equipment repair and replacement, on the other hand, increases as less maintenance is done.

Unfortunately, many managers focus only on the cost of maintenance without taking the costs of equipment repair and replacement into consideration. The correct way to approach the economics of a maintenance program is to look at the total cost as shown in the figure.

Little or no maintenance (right-hand side of the figure) results in very high repair and replacement costs. As the electrical maintenance program is intensified (moving to the left on the figure), repair and replacement costs decrease.

At some point, the minimum total cost is realized. This is the point at which the maintenance program should be operated to provide for the best overall efficiency of the system.

Reliability-Centered Maintenance ( RCM)

What is reliability-centered Maintenance?

Reliability-centered maintenance ( RCM) is the process of determining the most effective maintenance approach. The RCM philosophy employs preventive maintenance (PM), predictive maintenance (PDM), real-time monitoring (RTM), run-to-failure (RTF; also called reactive maintenance), and proactive maintenance techniques in an integrated manner to increase the probability that a machine or component will function in the required manner over its design life cycle with a minimum of maintenance. The goal of the philosophy is to provide the stated function of the facility, with the required reliability and availability at the lowest cost. RCM requires that maintenance decisions be based on maintenance requirements supported by sound, technical, and economic justification.

A Brief history of RCM

RCM originated in the airline industry in the 1960s. By the late 1950s, the cost of maintenance activities in this industry had become high enough to warrant a special investigation into the effectiveness of those activities. Accordingly, in 1960, a task force was formed consisting of representatives of both the airlines and the Federal Aviation Administration (FAA) to investigate the capabilities of preventive maintenance. The establishment of this task force subsequently led to the development of a series of guidelines for airlines and aircraft manufacturers to use when establishing maintenance schedules for their aircraft.

This led to the 747 Maintenance Steering Group (MSG) document MSG-1, Handbook: Maintenance Evaluation and Program Development from the Air Transport Association in 1968. MSG-1 was used to develop the maintenance program for the Boeing 747 aircraft, the first maintenance program to apply RCM concepts. MSG-2, the next revision, was used to develop the maintenance programs for the Lockheed l-1011 and the Douglas DC-10. The success of this program is demonstrated by comparing maintenance requirements of a DC-8 aircraft, maintained using standard maintenance techniques, and the DC-10 aircraft, maintained using MSG-2 guidelines. The DC-8 aircraft has 339 items that require an overhaul, versus only seven items on a DC-10. Using another example, the original Boeing 747 required 66,000 labor hours on major structural inspections before a major heavy inspection at 20,000 operating hours. In comparison, using standard maintenance programs of the day, the DC-8, a smaller and less sophisticated aircraft, required more than 4 million labor hours before reaching 20,000 operating hours.

In 1974, the U.S. Department of Defense commissioned United Airlines to write a report on the processes used in the civil aviation industry for the development of maintenance programs for aircraft. This report, written by Stan Nowlan and Howard Heap and published in 1978, was titled Reliability-Centered Maintenance and has become the report upon which all subsequent reliability-centered maintenance approaches have been based. What Nowlan and Heap found was that many types of failures could not be prevented no matter how intensive the maintenance activities were. Additionally it was discovered that for many items the probability of failure did not increase with age. Consequently, a maintenance program based on age will have little, if any, effect on the failure rate.

RCM in the industrial and utility arena

As with any philosophy, there are many paths or processes that lead to a final goal. This is especially true for RCM where the consequences of failure can vary dramatically.

Rigorous RCM analysis has been used extensively by the aircraft, space, defense, and nuclear industries where functional failures have the potential to result in large losses of life, national security implications, and/or extreme environmental impact. A rigorous RCM analysis is based on a detailed Failure Modes and Effects Analysis (FMEA) and includes probabilities of failure and system reliability calculations. The analysis is used to determine appropriate maintenance tasks to address each of the identified failure modes and their consequences.

While this process is appropriate for these industries, it is not necessarily the most practical or best approach to use for industrial and utility systems maintenance. For these systems, a streamlined or intuitive RCM analysis process may be more appropriate. This is due to the high analysis cost of the rigorous approach, the relative low impact of failure of most industrial systems, the type of systems and components maintained, and the amount of redundant systems in place. The streamlined approach uses the same principles as the rigorous but recognizes that not all failure modes will be analyzed. For most industrial and utility systems, the most economical and efficient approach is to use a combination of rigorous (formal) and intuitive analysis depending on system criticality and failure impact.

Failure modes that result in high costs or personnel injury, or where the resultant reliability is still unacceptable in terms of safety or operational impact, still receive the rigorous approach, but all other failure modes will use intuitive analysis.

The primary RCM principles

1. RCM is Function Oriented--It seeks to preserve system or equipment function, not just operability for operability's sake. Redundancy of function through multiple equipment improves functional reliability but increases life-cycle cost in terms of procurement and operating costs.

2. RCM is System Focused--It is more concerned with maintaining system function than individual component function.

3. RCM is Reliability Centered--It treats failure statistics in an actuarial manner. The relationship between operating age and the failures experienced is important. RCM is not overly concerned with simple failure rate; it seeks to know the conditional probability of failure at specific ages (the probability that failure will occur in each given operating age bracket).

4. RCM Acknowledges Design Limitations--Its objective is to maintain the inherent reliability of the equipment design, recognizing that changes in inherent reliability are the province of design rather than maintenance. Maintenance can, at best, only achieve and maintain the level of reliability for equipment, which is provided for by design.

However, RCM recognizes that maintenance feedback can improve on the original design. In addition, RCM recognizes that a difference often exists between the perceived design life and the intrinsic or actual design life, and addresses this through the age exploration (AE) process.

5. RCM is Driven by Safety and Economics--Safety must be ensured at any cost; thereafter, cost-effectiveness becomes the criterion.

6. RCM defines dailure as any unsatisfactory Condition--Therefore, failure may be either a loss of function (operation ceases) or a loss of acceptable quality (operation continues).

7. RCM uses a Logic Tree to Screen Maintenance Tasks--This provides a consistent approach to the maintenance of all kinds of equipment. See FIG. 4.

FIG. 4 RCM logic tree.

8. RCM Tasks Must Be Applicable--The tasks must address the failure mode and consider the failure mode characteristics.

9. RCM Tasks Must Be Effective-The tasks must reduce the probability of failure and be cost-effective.

10. RCM Acknowledges Three Types of Maintenance Tasks

a. Time-directed (PM)-Scheduled when appropriate.

b. Condition-directed (PDM and real-time monitoring)-Performed when conditions indicate they are needed.

c. Failure finding (one of several aspects of proactive maintenance)-Equipment is run-to-failure. This is acceptable for some situations and some types of equipment.

11. RCM is a Living System-It gathers data from the results achieved and feeds this data back to improve design and future maintenance. This feedback is an important part of the proactive maintenance element of the RCM program.

The RCM analysis carefully considers the following questions:

1. What does the system or equipment do; what is its function?

2. What functional failures are likely to occur?

3. What are the likely consequences of these functional failures?

4. What can be done to reduce the probability of the failure, identify the onset of failure, or reduce the consequences of the failure?

Answers to these four questions determine the actions required to maintain the systems or equipment. FIG. 4 shows the RCM logic tree used to answer these questions.

Failure

Failure can be defined in many ways. In a broad sense, failure is simply an unsatisfactory condition. RCM, however, requires us to look at failure from not just an equipment stand point, but from a system standpoint as well. A piece of equipment can be operating (an HVAC unit in a clean room, for example), but if its output is less than required, it would be considered failed. On the other hand, a protective relay in a power system can have failed, but if it has not taken the circuit off-line (the circuit is still energized), the function of the system is unchanged. Essentially, defining failure depends on the function of an item or system and the operating context in which the item or system is used.

Functional Failure. A functional failure is essentially the inability of an item or system to meet its specified performance standard. A complete loss of function is a functional failure; however, in the HVAC example above, if the system's output is less than specified, a functional failure has occurred even if the system is still operating.

Consequences of Failure. The consequences of failure determine the priority of maintenance activities or design improvement required to prevent occurrence. If failure of an item results in little or no consequence, minimal maintenance activities are generally required.

If, however, failure of an item results in a large economic hardship, personnel injury, or environmental damage, maximum maintenance activities or a redesign may be called for.

Maintenance actions in an RCM program

RCM goals are to identify the most cost-effective and applicable maintenance techniques to minimize the risk and impact of failure in facility and utility equipment and systems.

This allows systems and equipment functionality to be maintained in the most economical manner. Specific RCM objectives as stated by Nowlan and heap are:

• to ensure realization of the inherent safety and reliability levels of the equipment.

• to restore the equipment to these inherent levels when deterioration occurs.

• to obtain the information necessary for design improvement of those items whose inherent reliability proves to be inadequate.

• to accomplish these goals at a minimum total cost, including maintenance costs, support costs, and economic consequences of operational failures.

To this end, there are four outcomes from an RCM analysis:

1. Perform No Maintenance-this is referred to as reactive maintenance, repair, fix-on fail, or run-to-fail (RTF). This type of maintenance assumes that failure is equally likely to occur in any part, and that a failure is not detrimental to the operation. When this is the sole type of maintenance practiced, high failure rates, large parts inventories, and excessive amounts of overtime become common. A purely RTF maintenance program ignores many of the opportunities to influence equipment survivability.

2. Perform Preventive Maintenance (PM)-PM consists of regularly scheduled inspections, adjustments, cleanings, lubrication, and replacement of components and equipment. PM is also referred to as time-driven or interval-based maintenance. It is performed without regard to equipment condition. PM schedules inspection and maintenance at predefined intervals in an attempt to reduce equipment failures. However, as Nowlan and heap discovered, a PM program can result in a significant increase in inspections and cost without any increase in reliability.

3. Perform Condition-Based Maintenance (CBM)-CBM consists of predictive maintenance (PDM) and real-time monitoring. PDM primarily uses nonintrusive testing techniques to mea sure and trend equipment performance. Real-time monitoring uses current performance data to asses machinery condition. CBM replaces arbitrarily timed maintenance tasks with maintenance that is scheduled only when warranted by equipment condition. Continuing analysis of equipment condition data allows for planning and scheduling maintenance activities or repairs prior to functional or catastrophic failure.

4. Redesign-When failure of a system or piece of equipment is an unacceptable risk and none of the above tasks can help mitigate the failure, a redesign of the equipment or system is in order. In most cases, adding redundancy eliminates the risk and adds very little to overall maintenance costs.

An RCM program will include all four of the above analysis outcomes, as no one is more important than another. FIG. 5 shows the relationship that maintenance activities have to RCM.

FIG. 5 RCM structure.

FIG. 6 life-cycle phases.

Impact of RCM on a Facilities Life Cycle

A facilities life cycle is often divided into two broad stages: acquisition (planning, design, and construction) and operations. RCM affects all phases of the acquisition and operations stages to some degree.

Decisions made early in the acquisition cycle profoundly affect the life-cycle cost of a facility. Even though expenditures for plant and equipment may occur later during the acquisition process, their cost is committed at an early stage. As shown conceptually in FIG. 6, planning (including conceptual design) fixes two-thirds of the facility's overall life-cycle costs. The subsequent design phases determine an additional 29 percent of the life-cycle cost, leaving only about 5 percent of the life-cycle cost that can be impacted by the later phases.

Thus, the decision to include a facility in an RCM program, including condition monitoring, which will have a major impact on its life-cycle cost, is best made during the planning phase. As RCM decisions are made later in the life cycle, it becomes more difficult to achieve the maximum possible benefit from the RCM program.

Even though maintenance is a relatively small portion of the overall life-cycle cost, typically 3 to 5 percent of a facility's operating cost, RCM is still capable of introducing significant savings during the O&M phase of the facility's life. Savings of 30 to 50 percent in the annual maintenance budget are often obtained through the introduction of a balanced RCM program.

Conclusion

Reliability-centered maintenance is the process of determining the most effective maintenance approach. As the airline industry showed 40 years ago, RCM can not only improve the reliability of a system, it can significantly reduce the required maintenance. In today's competitive world economy, that translates into monies saved, both from reduced failures and reduced work. And a properly implemented RCM program will continue saving money year after year. To remain competitive, most companies can no longer afford to remain on the sidelines doing things like they've always done.

The Eight-Step Maintenance Program

Some facilities, especially very small ones, may not want to embark on such an ambitious process as a complete RCM program. For such locations, a minimal program such as the one described below may be more desirable. This information in the following paragraphs is taken from The Eight Step Maintenance Program:

Introduction:

There are eight simple steps that should be at the heart of an electrical maintenance pro gram. These key steps are plan, inspect, clean, tighten, lubricate, test, record, and evaluate.

The following paragraphs briefly describe each step and illustrate the part that they play in a good preventive maintenance program.

Step 1-plan:

Before working on anything, take time to think about what you are going to do and how you are going to do it. A few minutes of thought before the job is started results in a safer and more efficient job. This step is especially important when you are performing emergency repair work.

Start by identifying the specific task or tasks that you intend to perform. In this initial stage, you do not need to go into too much detail; rather, concentrate on the broad goals that you need to accomplish. List each goal, the personnel that you will use, the equipment that you will need, and the amount of time that will be required.

Be certain that you obtain and use the proper instruction manuals and design drawings before you start. The joke of "getting the manual after smoke is present" has too much basis in fact to be very funny for experienced electricians. Troubleshooting without accurate and correct schematics and wiring diagrams is close to impossible in all but the simplest circuits.

Develop detailed plans and procedures from the preliminary plans discussed above.

Steps should be detailed as much as required by the complexity of the job and the experience of your personnel.

Always start any procedure with a job briefing as described in Section 4.

Step 2-inspect:

Periodic inspections should be set up on a routine basis. Inspection can be done with the senses that nature gave us, called unaided inspection, or with instruments such as infrared viewers, ultrasound transducers, and so on.

Unaided Inspection. Your eyes are your most important inspection tools. They can detect dirt, note current readings, determine levels, discover discolored, overheated insulation, determine the presence of insects and rodents, and find a whole host of other problems. The more experienced you become, the more information your eyes can provide; however, even the most inexperienced electrician can detect spider webs in a circuit breaker operating mechanism. Always observe what you are working on and look for any abnormalities that can give you an idea of anything that can cause these problems.

Your ears can also be useful inspection tools. Overloaded transformers are normally noisier than lightly loaded ones, corona has a distinctive hissing sound, and motors with unbalanced voltages or bad bearings vibrate. Any change in sound should be investigated.

Nothing in electrical systems is more distinctive than the odor of overheated or burning insulation. Your nose can detect such problems long before your other senses. Again, the most useful indicator of problems is a change in odor.

Touch may also be employed to inspect electrical equipment. Feeling for excessive vibration or heating is a time-tested technique. Of course, you should be extremely cautious before touching any piece of equipment. If the equipment is not de-energized, contact should be made only when wearing appropriate insulating PPE, such as rubber gloves.

Inspection with Tools or Instruments. Except for your own senses, infrared viewers are the most cost-effective maintenance tool in existence. Annual infrared scans of your power system invariably uncover problems that, if allowed to continue, could result in severe problems. Whether this service is done "in house" or contracted to an outside service, you should perform an annual (minimum) infrared scan of your system.

Ultrasound transducers are normally used on major overhauls to evaluate the condition of metals that are subjected to constant vibration.

Many other such tools and instruments are available to help in the performance of maintenance tasks. Such tools should be used as required by qualified personnel trained in their proper and safe use.

Step 3--clean:

Dirt and electricity don't mix. After you have completed the inspection of your electrical equipment, the next step is to clean all components.

The first step is general cleanliness. Dust, dirt, and foreign material must be cleaned from motors, switchgear, transformers, and other such electrical equipment. For such cleaning, we recommend the use of high suction; insulated hose shop vacuum, clean, lint-free wiping cloth; and general-purpose solvents. A citrus-based general-purpose solvent is effective and biodegradable.

Each insulator or conductor has its own way to be cleaned. Porcelain, for example, can be cleaned with soap, water, and appropriate cleaning brushes or pads. Plastic insulation, on the other hand, cannot take any abrasion. Always refer to the manufacturer's recommendations for specific techniques. Also, always avoid using steel wool or other conductive abrasives in any area where contact with energized conductors is possible.

Conductor connecting surfaces need special attention. Contact surfaces of copper conductors should be cleaned to a bright finish where they are connected together.

Aluminum must be cleaned and a protective lubricant must be applied immediately after the cleaning. The lubricant cuts through any aluminum oxide (a good insulator) that may be present and prevents the formation of additional aluminum oxide. (See the section on lubrication.) Refer to the manufacturer's instruction books, which sometimes specify the cleaning material to be used for its equipment. Be sure to consult this literature before attempting to clean electrical components.

Step 4--tighten

Tightening fasteners on electrical equipment takes special care and should be done to the torque recommended by the equipment manufacturer. Electrical connections are especially critical. Recommended torque values can be found in the maintenance and acceptance testing specifications published by the International Electrical Testing Association.

Be certain to torque connections per this table and/or the manufacturer's recommendations.

Step 5--lubricate

Lubrication of electrical system components is an often-overlooked or improperly per formed procedure. Too much lubricant can be worse than no lubricant at all. This is especially true of devices such as protective relays and circuit breakers, which may go for years without operating. Be especially careful of conductive lubricants to make sure they do not cause a short circuit. Always use the lubricants recommended by the equipment manufacturer or one that has the same characteristics. Lubrication falls into two important areas:

1. Nonconductors

Nonconductive joints or moving members should be lubricated using an appropriate material. In some cases, grease, oil, or some synthetic lubricant may be recommended.

Motor bearings, mechanism pivots, and other such equipment fall into this category. Remember that some pieces of equipment, such as protective relays, do not require any lubricant at all.

2. Conductors

Most manufacturers make and/or recommend a lubricant to be used on conductors, stabs, and other such equipment. The ubiquitous "black grease" has been and continues to be a good lubricant when used properly. The correct approach to lubrication of electrical conductors is to apply a small amount and then wipe the contact surface clean with a clean, lint-free cloth. Do not scrub the surface, however. You wish to leave a fine film of lubricant in place.

Remember: Use the proper lubricants in the proper amounts.

Step 6--test

Electrical equipment should be tested periodically. Insulation resistance should be measured, breaker trip times should be checked, relays should be calibrated, and a variety of other procedures should be performed. The only exercise that many protective devices get is during the test interval.

A detailed review of all procedures is beyond the scope of this course; however, the recommendations made by the International Electrical Testing Association (NETA) in its publication titled Maintenance Testing Specifications should be reviewed and applied as appropriate.

Step 7--record

Doing work without keeping records is almost useless. Recording test and other data can help set maintenance intervals, isolate troublesome equipment (or manufacturers), and pro vide a baseline that helps to indicate when insulation or other components are starting to fail. Besides test results, records should always include the date, equipment identification, and all pertinent data on any problems discovered. System conditions like load current, voltage, temperature, and other such information can help determine how close components are to being overloaded.

Test and record forms should be developed and tailored to your company's specific needs. Examples of such forms may be found at the back of the NFPA 70B Electrical Equipment Maintenance. Review that document for ideas and examples.

Step 8--Evaluate

Evaluation of the test results is, possibly, the single most important step in the entire process. Since 1990, significant progress has been made in the statistical analysis of small population data such as that gathered during maintenance intervals. Whether the analysis is done using sophisticated mathematical techniques or simple field rules of thumb, no program is complete without it. Analysis of records allows the company to determine what, if any, additional maintenance needs to be performed and to pinpoint problems that might otherwise go unobserved.

Summary

The organization of an electrical preventive maintenance program may be greatly enhanced by adhering to the simple, eight-step program outlined in this section. These steps contain all of the elements required for a comprehensive program. If you plan, inspect, clean, tighten, lubricate, test, record, and evaluate, you will be well on your way to a safe, efficient, and profitable preventive maintenance program.

Frequency of Maintenance

How often should a power system be maintained? If your facility is using a preventive maintenance (PM) program as described in the RCM section and shown in FIG. 5, you are basing your intervals on the calendar. For example, you might maintain your large transformers every July, you split your circuit breaker maintenance between May and October, and you maintain one-third of your protective relays once per year.

Referral to FIG. 3 shows the problem with that approach. You may be spending away too much money on your maintenance. Moreover, if you do not keep good records, you really do not know if you are maintaining often enough to prevent catastrophic failure.

For many years, maintenance intervals were determined as shown below.

Determining testing intervals

1. Start initially with a once-per-year test program. Continue this procedure for the first two intervals.

2. Review the test records from your maintenance intervals.

3. If frequent and/or severe problems are evident, decrease the maintenance intervals.

4. If no major or frequent problems are evident, increase the maintenance intervals.

5. Repeat steps 2 through 5 throughout the life of your maintenance program.

The average maintenance interval in industrial systems is about two years. This means that every two years, most industrial plants completely maintain their electrical system. Electrical utilities have similar intervals, although their average is probably closer to 1 1/2 years. Recent advances in statistical analysis have enabled maintenance programs based on technology rather than "estimate." Such condition-based maintenance programs will be the way maintenance is done in the 21st century.

Condition based Maintenance (CBM) -- The condition-based maintenance material is extracted largely from Condition Based Maintenance.

Introduction:

As discussed earlier in this section, condition-based maintenance (CBM) is one of the key building blocks in a reliability-centered maintenance ( RCM) program. In a CBM environment, maintenance efforts and expenditures are based on the actual condition of the maintained equipment; that is, equipment that is consistently in good to superior condition does not need to be maintained as frequently as equipment that is deteriorating or has reached an age where deterioration is anticipated. The use of test or running data to statistically model and predict the future condition of the equipment is at the very heart of CBM. Consider the effect that such an approach would have on the task of changing lubricating oil in an automobile. Car owners know that lubricating oil should be changed every few thousand miles. For example, the car manufacturer may specify that oil should be changed every 3000 miles or every six months, whichever comes first. Such a procedure is purely time (or mileage) based and does not take into consideration the condition of the lubricating oil.

If a CBM approach were employed to this task, chemical tests would be performed on the oil. If the tests predict that the oil has another 1000 miles of life, the owner can extend the oil change interval, thereby reducing operating costs. Conversely, oil that shows rapid deterioration will be replaced ahead of time. Used this way in an electrical power system, CBM is much more cost-effective than PM alone; moreover, CBM will identify incipient failures and allow timely and safe corrective actions when required.

The ability to predict and thereby prevent unplanned downtime is the major strength of CBM. To work properly, data collected either on-line or off-line must be analyzed mathematically. CBM is further broken down into elements or subsets. When implemented properly, CBM offers both technical and/or financial advantages over the more classic methods such as PM or RTF.

cont. to part 2 >>

Also see: Electrical safety systems