Question

What is the most common type of grounding on primary distribution systems ?

Short answer

The most common type of grounding is three phase four wire system.

Step-by-step solution

Define grounding

The grounding is defined as giving the path for the fault current in the circuit. The circulating fault current is grounded and the grounded path is generally less resistive. If the operating person touches the body of the equipment the person does not feels the shock as the current is grounded.

Determine the type of grounding.

Consider for the star connected system, there are 3 wires and the 4^th wire is for the neutral wire for both the secondary and the primary side. The voltage on the primary and the secondary side has the same magnitude and they are out of phase by 120 degrees in case of the balanced load. In order to limit the current during the short circuit fault and to let the protective device in conjunction to work properly the neutral wire of the transformer are grounded with the impedance. The most common connection system use for the case is three phase four wire multi grounded system in the primary grounded system

Therefore, the most common type of grounding is three phase four wire system.