Partial discharge detection technology is one of the effective means of insulation detection of switchgear cabinet. In this paper

an insulation defect of 35 kV switchgear cabinet is detected by using such methods as transient earth voltage (TEV)

air ultrasonic wave

ultra-high frequency (UHF) and infrared thermal imaging. The surface discharge at multiple places inside the busbar compartment of the switchgear cabinet is judged in combination with its discharge pattern and characteristic. It is found through power off and disassembly of the switchgear cabinet that the heat-dissipating wire mesh on the top of the cabinet is severely corroded due to the salt mist. And the rust and salinity attached to the surface of the insulating part cause a serious reduction of insulation level of the busbar. For preventing the occurrence of similar defects

it is suggested that the indoor environmental conditions of the high-voltage room of substations located in the coastal areas need to be strictly controlled

and partial discharge detection shall be performed regularly. In the design stage of the switchgear cabinet

the salt mist corrosion resistance performance shall be strengthened

and the straight-through air ducts on the top of the cabinet shall be strictly prohibited.