In this post we shall discuss about few periodic inspections and tests that must be done as a routine maintenance for power transformers of a substation.
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- Gauge readings
It is essential to note the reading for ambient temperature and KVA load and it must be recorded, too. In case you find the reading is abnormal then it is a sign that something is wrong with tank leaking and further checking is recommended.
- Cooling fans
You need to check all cooling fans by setting the control switch of fan “auto/manual” control to “manual” position. Let the fans rotate at its full speed for approximately for 5 seconds. There must be smooth rotation of fan without much vibration.
- Control wiring
Check the control wiring to ensure that all the insulation of the wire is in proper condition. Also, control cabinet and other associated conduit must be inspected to make sure that all weather seals are properly intact.
Also, check the control voltages and compare it to the voltage as stated on wiring diagram.
- Paint finish
Paint finish must be inspected for damage or any weathering, which exposes the primer coating or bare metal. If any paint damage is found then repair it.
- Fluid dielectric test
Take a sample of insulating fluid and measure its dielectric strength at 26KV. This checking must be done annually and preferably sample of oil must be taken from bottom of tank.
- Bushing and the surge arrester insulators
Make sure that bushing and also surge arrester insulators must be clean. If you find the surfaces in excessively dirty condition, then they must be cleaned while transformer is not in energized condition.
- Bushing terminals
While the transformer is in energized condition and under load, measure temperature of bushing terminal by using certain infrared scanner.
Too much bushing terminal temperature will indicate a loose/dirty connection. In case transformer is not in energized condition, then use torque measuring device for ensuring that terminal connections are fully tight.
Check all the gaskets visually to find any sign of cracking or any other deterioration. In case you find any then replace it. While replacing make sure that mating surfaces are fully clean. Remove any rust or dust present.
Never use any old gasket while replacing them and retighten them after checking, if required.