The relationship between maintenance and repairs is almost an inverse function. The more effective maintenance is, the fewer repairs you need. This, of course, doesn’t account for failures that cannot be prevented through maintenance. Consider the following examples:
- Post-mortem on failed motors shows a high percentage had pitted bearings. You can have perfectly executed maintenance and it will make no difference in stemming this problem. The cause is undesired current trying to find its way back to the source without an effective bonding path to get it there. Much of it flows through bearings, causing tiny arcs and, thus, the pitting.
- Motors are overheating enough to degrade the varnish on their windings but not enough to trip overload protection devices (e.g., heater strips). Chronic overload, even if within limits previously deemed acceptable, still takes its toll. Possible causes include lack of cooling air resulting from design or installation mistakes, coupling alignment is slightly off, power factor is too low, triplen harmonics are too high, supply waveform is flat-topped, or a process or other configuration changed such that certain motors have too low a heat rating for the application. Though deficiencies in maintenance can cause this overheating, look at how many causes are not related to maintenance.
- A 400A breaker failed to open upon overcurrent, causing damage to some conductors and utilization equipment. Another 400A breaker regularly provides nuisance trips, even though it never sees more than 352A of load. While the first issue sounds like the breaker was not properly lubricated and exercised (a maintenance basic for breakers), the problem could have resulted from misadjustment of the breaker. So can the second problem. If you have adjustable breakers, perform a study to determine exactly how each one should be set. If there is a change to the utilization equipment, a new study should be performed.
- In one area of the plant, electronics fail frequently. Unlike the situation with many mechanical components, there’s no lubrication to change in an electronic power supply or circuit board. Frequent failure of electronics is almost certainly not due to a maintenance failure. However, it could be due to such things as a poorly designed surge suppression system, inadequate bonding, transformer connection errors (in one plant, they removed the grounding strap inside each distribution transformer in a misguided effort to “isolate spikes”), or the presence of materials or processes that generate static electricity and yet there’s no bleed-off system.
The typical maintenance department lacks the resources to identify the exact cause(s) of each failure that occurs. But it’s also true the typical maintenance department has the resources to identify the causes of the most expensive failures.
Prioritize the top three and solve for the root cause. The solution might be to change the maintenance practices or procedures related to what failed, but more likely the solution will involve changing something structural or systemic about the conditions in which the equipment is operating.
