Lesson 1.dau bienap

Oil, which is used in electrical apparatus, known as transformer oil, serves several very important purposes. Above all, it is a reliable insulator, a thing of vital importance in high voltage apparatus. Oil, as a liquid, can also easily circulate and act as the coolant for the winding and the core of the transformers. In oil circuit breakers, oil extinguishes the act which appears when the circuit breaker is tripped open. the that transformer oil must satisfy are listed below:

The oil must have high dielectric strength, i.e. the ability to withstand a specified voltage without a breakdown. Transformer oil for electrical apparatus rated for up to 6 KV must withstand a test voltage of 20 KV when it's in service, and not less than 25 KV when it's clean and dry. Oil for apparatus rated for upwards of 6 KV must withstand a test voltage of 25 KV. (the test voltage is applied to the testing electrodes spaced 2.5 mm apart).

The oil should have a low viscosity for good circulation.

The oil must have a high flash point (not less than 1400 C).

In mine transformers, oil may only be used in high-voltage apparatus, (transformer and distribution boxes), which operate at higher than 700 V. in the case of voltage below 700 V, it may only be used in controller, autotransformer...and starting rheostats of stationary plants which are located in fireproof chambers.

Purification of oil:

During it service, the oil becomes fouled with sludge and impurities such as moisture, insulation fibbers, carbon particles, and resinous matter. Such impurities, even in very small quantity, considerably lower the dielectric strength of the oil. It is therefore very important to treat the oil in oil purifiers at regular interval of time.