Investigation of the Possibility of Using X-Rays to Control the Technical Condition of High-Voltage Low-Oil Switches

Abstract

The capabilities of the X-ray method of nondestructive testing of high-voltage oil-filled equipment are investigated using the example of a low-oil switch of the VMT series of 110-kV voltage class (VMT-110) with porcelain external insulation. A list of characteristic types of defects based on the analysis of the causes of failure of VMT-110 switches was compiled, and a special defective sample (SDS) for laboratory research was created. The following types of defects were simulated: contact bar deformation, contact wear, burning of the contact surface and reducing the height of the contact part of the movable contact, cracks in the casing of the fixed contact, crimping failure and rope unwinding, mechanical damage to the bottom rollers, fracture of the upper roller spring, bearing defects, cracks in the insulating rods of the control system of the movable contact, and cracks on the inner and outer surfaces of the porcelain insulator of the arcing chamber. The X‑ray examination of SDS was performed using a monoblock X-ray device with a constant voltage on the tube and directed radiation output. The optimal parameters of the X-ray device were selected experimentally. The information content of the SDS radiographs for monitoring the SDS technical condition was evaluated by comparing the actual defects with the images obtained on the radiographs. The results of the SDS study have shown that the proposed technical solution can detect at least 75% of the characteristic types of defects in the internal structural elements of the VMT-110 switch. The proposed instrumentation can be used to monitor the technical condition of other types of high-voltage equipment (gas-insulated switches, gas-insulated switchgear, measuring transformers, and cable couplings) onsite without disassembly.