The velocity measurement of cooling gas in SF₆ gas-transformer by reflective type of ultra sonic wave method

Abstract

The improvement of the cooling-gas velocity distribution over the coil windings in SF₆ gas transformer is very important to get the high quality for designing.
In this paper, the application results of the reflective type ultra sonic wave method to measure the cooling gas distribution in the SF₆ gas transformer are reported.
This measurrement can be performed without disturbance of the gas flow by the presence of the sensors, and this method is proved to be more effective than the conventional fluid velocity measuring method. In this measurement, it is found that the velocity of gas flow at some locations in the transformer was not proportional to the volume of the input gas flow. It can be divided into three patterns corresponding to the location as follows.
(a) Gas velocity increases with the increase of the input gas flow amount.
(b) Gas velocity is constant regardless of the increase of the input gas flow amount.
(c) Gas velocity decreases with the increase of the input flow in the first, and changes to increase with the further increase of the input flow.
These characteristics are well compared to the computational results of gas flow analysis.