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
-Disconnecting switches
-Circuit breakers
-Capacitors
-Surge arresters
-Current transformers
-Voltage transformers
-Protective relays
-Network protectors
-Fuses
-Batteries and battery chargers
-Meters and other instruments
-Alarms and alarm systems
-Grounding
-Ground detection schemes
-Transformers
-Insulating liquids
-Cables
-Busways
-Busducts
-Motor control center and motor starters
-Motor protective devices
-Motor drives
-Transformer auxiliary systems
-Rotating equipment
-Lighting
-Wiring devices
-Uninterruptible power supplies
-Transfer switches
-Test and safety equipment
Repairs
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.
Failure analysis
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].
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