Inspection and testing
The condition of electrical equipment is generally affected by the atmosphere and conditions under which the equipment is operated and maintained. Water, dust, temperature, humidity, corrosive fumes, vibration, and other environmental factors can adversely affect electrical equipment.
Electrical equipment life can be extended dramatically by simple precautions that promote cleanliness, dryness, tightness, and the prevention of friction. The thoroughness of maintenance procedures can be categorized into three different levels:
Level 1-General inspection and routine maintenance;
Level 2-Inspection, general tests, and preventive maintenance;
Level 3-Inspection, speciÞc tests, and predictive maintenance.
Testing would include
a) Insulation tests;
b) Protective device tests;
c) Analytical tests (e.g., time travel analysis, dissolved gas analysis, infrared, and contact resistance);
d) Grounding tests;
e) Functional tests.
The following equipment should be in the maintenance program:
-Switchboards and switchgear assemblies
-Batteries and battery chargers
-Meters and other instruments
-Alarms and alarm systems
-Ground detection schemes
-Motor control center and motor starters
-Motor protective devices
-Transformer auxiliary systems
-Uninterruptible power supplies
-Test and safety equipment
Repairs can be categorized by their sense of urgency. Some repairs must be accomplished before the equipment can be returned to service. Other repairs may require material items that are not stocked, and cannot be accomplished until those items have been received and properly installed.
Some repairs can be postponed, thus allowing the electrical system to go back into service without undue risk. In this method, the repair could be scheduled for a future date when it is more convenient to the plant.
A part of EPM is determining which spare equipment or parts should be kept in stock, such as fuses, circuit breakers, and other components, in order to be able to repair critical items and return a shut-down facility to operation. This, like the maintenance procedure itself, is an economic
benefit vs. cost of inventory balancing act.
When equipment fails, it is important to understand the reason why. Failure analysis, when done properly, locates the root cause of the failure. This is important in order to take the necessary steps to prevent similar failures in the future.
Failure analysis involves an effort to reconstruct, at least mentally, the conditions that existed prior to failure and the events that led to the nature of the failure. It is through this process that the root cause can be determined.
There are engineers that specialize in forensic and failure analysis. These people, through their experience, are generally able to recognize failure patterns and to draw accurate conclusions much more readily than the untrained person. This is a specialty that is generally contracted when firms do not have that capability in-house.
Inspection and test frequency
Equipment in a critical service would generally receive maintenance attention more frequently than other equipment. Manufacturer's service manuals should be consulted in determining an adequate frequency.
They generally give frequencies that are based upon a standard, or average, or upon operating conditions. This is a good basis from which to start in determining the frequency for a given facility. A good guide for both maintenance frequency and routine inspections and tests is found in NFPA 70B-1994 [B3].