Maintenance, Test and Detection Technology of PT HV Bushing

Introduction: In recent years, power transformer HV bushing has broken down and electric organizations paid high attention to the operation of bushing. Countermeasures against faults are taken to ensure secure operation of bushing. On-site test monitoring technologies are presented here. 

1. About Oil-paper Capacitive Bushing   

The 110kV and above power transformer HV bushing is mostly oil-paper capacitive bushing, which relies on capacitive core to change the electric field distribution. The capacitive core is composed of layers of insulation paper with aluminum foils between layers according to the requirement, forming a series of coaxial cylinder capacitor. The insulation paper is immersed into the mineral oil.      

2. Preventive Test Technology

Main insulation test. The dielectric loss measurement of main insulation uses positive connection. The bushing get worse or dampened, resulting in an increase in dielectric loss. Reasons for why the value of dielectric loss becomes abnormally small or negative are as follows: bushing base flange is poorly earthed; bushing surface is dirty and affected with damp; end shield or standard capacitor is dampened.The increase in capacitance may be caused by poor sealing. or free discharge of bushing burns part of insulation and leads to electrode shortcircuit. However, oil leakage or incoming air is likely to bring about he decrease in capacitance.