Protection Engineering Basics and Schemes Protection Engineering | Page 56

I = 0.000000009A

I = 9 nano A Which means it is far safer for the operator also.

Now we need to see what is the need of guard?

Look when we testing any equipment, we inject 3 currents in circuit � Charging current � Absorption current � Leakage or conduction current Charging current is for the capacitance of under test insulation object Absorption current is flow in the insulation material Conduction current is further divided in two parts � Current flows in outer surface of insulator � Current flows in conduction path of the insulator When we are testing any equipment, we are more concern with the current flows in conduction path of the insulator but not the current flows in outer surface of insulator Now what guard is doing, guard is actually a shunt circuit, when we connect our insulator tester in our circuit, the guard will carry out that outer surface current and isolate it from measurement in insulation resistance measurement, and we will get the exact reading of

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