This paper analyzes a misoperation case of double-floating ball gas relay of a 220 kV transformer in Zhengzhou Power Supply Company

Henan Province.The operation mechanism of the gas relay is described

and the cause of this misoperation is discussed.The misoperation is found to be due to lower reverse start value of the double-floating ball gas relay

leading to its misoperation under impact of small oil flow.A test is conducted to verify this conclusion.Some suggestions about selection

acceptance and checkout of gas relay are offered:1) Pay more attention to the selection and acceptance of transformer accessories.2) The newly installed gas relay

pressure release device

and thermometer

etc.should be checked before putting them into operation

e.g.

double-contact gas relay needs the reverse operating test.3) The radiators of main transformer

specially of indoor transformer ought to be cleaned before high-temperature load.4) During the period of high-temperature load

monitoring of transformer and its oil level must be carried out

and aeration and heat dissipation of indoor transformer be strengthened.