In view of insufficient dielectric online detection technology of existing minimum oil electrical equipment

in recent years

some scholars have proposed pressure-based online monitoring technology of minimum oil equipment. However

internal pressure variation characteristic of minimum oil equipment at overheat defect has not been experimentally studied by scholars. In this paper

110 kV oil immersed vertical currnt transformer is taken as prototype to study by experiment the internal pressure variation characteristic of minimum oil equipment at the temperature of 100 ℃

150 ℃

200 ℃

250 ℃ and 300 ℃ respectively. It is shown by the result that（1）the pressure variation by mild and low temperature overheat defects is small and the maximum increments in 50 hours is 1.33 k Pa

1.65 kPa

2.01 kPa

2.51 kPa

and 2.70 kPa

respectively；（2）the pressure variation due to overheat defect shows exponential increase. In the initial 10 hours

the pressure rises sharply and gradually in 10～20 hours. The pressure remains basically unchanged after 20 hours.（3）The increase range the maximum pressure with 50 hours is several hundreds of Pascals at every 50 ℃ rise in the temperature of the overheat spot. At the same time

three reasons with different pressure variation characteristic due to overheating and discharge defects are pointed out by theoretical analysis.