An abnormal noise defect occurred in operation of a 220 kV gas insulated switchgear（GIS） is analyzed in detail by means of overhaul inspection

and the possible causes of the abnormal noise are discussed.The result shows that both the abnormal vibration of the GIS due to loose of the internal fastener and the internal discharge can cause the abnormal noise and make the partial discharge exceed the standard.This abnormal noise defect is due to that the spring was not put into the spring slot in the GIS installation

so it was clipped on the guide rod to suffer non-recoverable deformation during long-time operation process.Although the weak displacement between the spring and the guide rod caused by thermal expansion and cold contraction made the spring eventually fall into spring slot

the deformation led the spring not to match the spring slot.Consequently

abnormal vibration of the shield and spring happened under high voltage and large current as well as the effect of electromagnetic force

resulting in the abnormal noise of the equipment.To avoid this kind of defects

some precautionary measures are suggested as follows:1) In the equipment manufacturing phase

the control of equipment installation should be improved;2) In the equipment operation and maintenance phases

the detection and diagnosis analysis of discharge and mechanical defects should be strengthened;and 3) Once defect is detected

the cause of the defect should be clearly defined in time

and pertinent measures should be taken to prevent the defect from developing to a failure.