How to Measure the Porcelain Bushing Leakage in MV

A megger is the cheapest and easiest way to measure the insulation resistance (and therefore leakage current) to ground. That, along with regular preventive maintenance (inspection, cleaning, tightening of bolted connections, etc.) are your basic tools to prevent equipment faults and failure.

If you want more comprehensive (and more expensive!) measures, you can do several things:

1. You can perform Doble insulation power factor (or equivalent Tan-delta / dissipation factor) tests, which include the "hot collar" tests on bushings to get an AC evaluation of leakage current and possible damage or contamination of the porcelain.

2. You can install a partial discharge measurement system to determine if there are places where electrical discharge / corona / breakdown of insulation is happening in your switchgear.

But really, the most value for your money comes from regular maintenance and basic megger tests.

Also FYI, arc flash does not come from leakage current. It comes from a fault. You can reduce the severity of arc flash and associated effects (arc blast, etc.) through proper protective device coordination, and equipment maintenance and testing. That way your circuit breakers, fuses, and protective relays operate per specifications so that the arc is extinguished in the shortest amount of time with the least damage done to your equipment and least hazard to your personnel.