Friday, June 27, 2014

Understanding Neutral,Neutral connections, fault current paths, and grounding

Understanding Neutral

Neutral is the common reference point in electrical systems with respect to whom all voltages are measured. Neutral in electrical system is used to carry unbalance currents. Neutral is generally grounded so to get rid of the unbalance voltages generated in electrical systems. In single phase systems Neutral is used as return path. In Three phases it is used for carrying unbalance voltages. With introduction of Non-linear loads such as PC’s, TV’s, and other electronic equipment’s requirement of neutral is increased considerably.

Neutral connections:-
In case of star connections neutral is common point of all three phases connections. In delta connections there is no need for neutral. Usually delta-star connections are used in Transformers so as to get neutral for domestic and industrial supplies.
Neutral flow in conjunction with all three phases.  In MCCB’s also neutral is provided without overload protection so as to bypass all fault current without affecting MCCB.
In Single phase systems Neutral wire/conductor diameter is same that of phase wire/conductor. But for three phase power supply neutral is uses half size of phase conductor sizes for cables above 70 mmsq.

Fault current paths:-

Fault in an electrical system always follows low resistance path.  In case of Phase to phase fault current will rise to very high values in two phases which will leads to unbalance voltages/currents to flow in neutral which than get flow to earth. So whenever any fault occur in electrical systems fault current get flow into neutral. So neutral and earth should be strong enough to take that fault current/voltages load.

Ground represents an electrical path which is used to carry fault currents whenever there are insulation breakdown occur in electrical equipment. Usually neutral is grounded as to flow fault/ unbalance currents into ground. Grounding and earthing are same. Usually there value should be kept as low as possible