Why earth resistance can be found by only clamping it?
|Rx, is defined as earth resistance under test, and R1, R2...Rn are defined as earth resistance of other measuring objects.
|These earth resistances, R1, R2, Rn can be considered that they are connected in parallel.
And they can be regarded as a combined resistance Rs. The Rs can be regarded small enough against Rx since a combined resistance consists of several resistances. Following is an equivalent circuit diagram of this circuit.
|Voltage V is applied to the object (Resistance Rx) measured from the voltage injection transformer CT1, and the current I corresponding to the earth resistance is flowed.
The current I is detected with detection transformer CT2, and object (Resistance Rx) measured can be put out by the calculation. (refer to the right diagram)