The insulating spacer

an important part of GIS

is mainly fixed by flange bolts

but the looseness of bolts will cause such problems as uneven force and even gas leakage of the insulating spacer

which will seriously affect reliability and safety of GIS operation. In this paper

a kind of ultrasonic wave monitoring method for the looseness of flange bolts of GIS insulating spacer is proposed

the excitation and reception of ultrasonic signal is performed by using the piezoelectric sensor

and the piezoelectric sensor is installed on both sides of the flange connected by the bolt to be tested

and the degree of bolt looseness is judged in accordance with the energy attenuation rate of the ultrasonic response signal. The variation of ultrasonic response signal energy and its attenuation rate under different working conditions are studied through experiments. The results show that with increase of bolt looseness

the amplitude of the response signal decreases gradually and the signal energy attenuation rate gradually increases

the annentuation rate of the signal energy

in case of single bolt looseness and the looseness grade is 3

can be up to 40.8% and

at the same time

it is found that the annenuation rate of the receiving signal energy of the piezoelectric sensor which is closest to the bolt looseness is maximum. The method proposed in this paper can monitor the looseness of flange bolts of GIS insulating spacer

and has certain engineering application.