In our practice life, there is no device which efficiency is 100%. Electrical Transformer is extraordinary here. As it is static and have no rotating or dynamic parts. That is why transformer efficiency is 99.99%. Some loss may happen for any internal or external factor which is rare.
Transformer Cooling System
3
types of cooling system we generally use for cooling a transformer. They are-
- ONAN:
Oil Natural Air Natural.
- ONAF:
Oil Natural Air Forced.
- OFAF: Oil Forced Air Forced.
If we can develop better cooling system of a transformer, we will get more output and efficiency from a transformer.
Transformer Cooling Components
We
can use different method and equipment for the cooling system of a transformer.
But the main components of transformer cooling system is-
- Fan
- Oil
- Radiator
- Pump: For oil pass.
Did
you ever think, if we use water as
cooling liquid of a transformer?
As water is electric conducive, that's why if we use water as cooler, it will be short circuit and the transformer will be destroyed. So we must have to use transformer oil for cooling the transformer. Commercially transformer oil is also called as Piranor.
Transformer Oil Dielectric Strength Test
Besides cooling, transformer oil will be a good insulator. If the insulation break down, there will be short circuit. To measure the dielectric strength of Transformer oil we have to make a test by a device given below the figure. In this device, this two knob is kept in very similar distance that is almost 2.5mm – 4mm. Then we apply voltage and increase slowly.
Transformer cooling oil dielectric test machine
If the oil is good insulator, not current will flow due to applied high voltage, though it also have a limit. Up to 25kV, if there is no short circuit or no current flow, we can say the oil is good. If this voltage is higher, than we can say, it is a good cooling and insulation oil. If the knob is at 4mm distance, applying 45kV, if there is no short circuit, we can say it is good oil.
The closer two knob for dielectric test
Once the transformer is filled with cooling well, we use
it for many years. If we ever want to take out the oil and test its dielectric
strength, we have to take it out and test it by opening the transformer immediately.
Otherwise if we leave the transformer open or leave the oil out and wait and
then test, we will not get the desired result. This is because the dielectric
strength of the transformer oil decreases when left open. We can increase the
strength a bit by hitting of centrifuging later. That is not so enough. So if
you ever leave the oil open and get low dielectric strength, don't be too
scared. You can fill oil to the transformer. However, it should not be less
than 15 KV. So be careful when you are testing the oil.
Written
Jeion Ahmed
Chittagong, Bangladesh
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