Sucha simple question with such a complex answer. Uptime magazine has many related articles to this subject.
Cables fail the most often, transformers fail the least often, but when a transformer fails it has the longest replacement time so it has about the highest failure "rate" in a power system, and they usually get the least attention from a maintenence aspect.
NFPA 70B and ANSI/NETA have recommended intervals for a relibility centered maintenence program, those intervals are based on the most economical factors for establishing a program.
The moment that the equipment in your substation is installed it will begin to deteriorate. This process is inevitable and if not checked will eventually lead to equipment failure and costly downtime. Additionally, changes that are made to the system, including loading, will result in improper equipment coordination and operation.
The function of an Electrical Preventive Maintenance (EPM) program is to recognize problems and to provide a means to correct them before failure occurs. Additionally, an EPM program will help ensure the safety of personnel operating or working near the equipment.
A good EPM program should consist of routine inspections, testing, repairs, and servicing of switchgear assemblies, transformers, circuit breakers, switches, relays, and support equipment.
A well organized program not only reduces costs of repairs, downtime, and hazards, it also help improve employee morale, increase productivity, and help find system deficiencies from installation or modifications.
Maintenance basics
Proper maintenance of electrical distribution equipment can be summarized by four simple rules:
1. Keep it tight
2. Keep it cool
3. Keep it clean
4. Keep it dry
These four rules will prevent many of the most common problems found in power distribution systems. The biggest contributors to equipment failure are:
? Overheating caused by high resistance connections
? Insulation deterioration from high temperatures
? Binding of mechanisms from dirt accumulation
? Tracking caused by surface contamination
? Reduced insulation properties from moisture absorption
Many facilities have some type of EPM program in place that falls under one of four basic philosophies.
Run to failure
This method can be summarized by the old saying, “If it Ain’t broke, why fix it?” Equipment is essentially allowed to degrade until a failure occurs, at which point the question “Why did it fail?” is asked. It never ceases to amaze experienced maintenance personnel why the same people that are opposed to performing preventive maintenance on multi-million dollars distribution system change the oil in their cars every 3,000 miles religiously.
Service as necessary
This method is simply done by observations and regular, informal inspections. Under this approach, obvious problems are addressed and corrected before failure occurs but no formal testing is conducted unless a problem is suspected. This method can be compared to taking your car into the shop when your service engine light comes on or a strange noise is heard while driving. Many industrial plants use this approach and find it to be a semi effective and economic choice.
Scheduled preventive maintenance
In this approach, established EPM is performed at fixed intervals of time, operations, or running time. These procedures are usually based on manufactures recommended maintenance intervals or industry standards. While this type of program ensures that equipment gets regular attention it does not take into account reliability, safety, or productivity significance.
Reliability Centered Maintenance
This approach utilizes such factors as reliability requirements, current equipment condition, and manufactures recommendations. RCM is the most reliable and cost effective approach to EPM because it improves plant reliability and reduces maintenance costs by focusing efforts on items that are most important or likely to fail. RCM is used extensively by the military and nuclear industries and is gaining acceptance in manufacturing plants where productivity and safety are a major concern.
