ABSTRACT

In today’s digital driven world, current in a neutral conductor is one of common problem faced by the electrical engineers in most of the commercial buildings, hospitals, IT/ITeS sector. Apart from these buildings, electronic load in an industry like CNC machines, UPS, robotics which also have excessive neutral current. In present load scenario of switch mode power supply (SMPS), even though loads are 100% balanced, current in the neutral conductor could be more than the phase conductor. In case of linear loads, for a three phase system current in the neutral conductor flows due to unbalance of loads in the three phases. However, in case of non linear loads, current in the neutral conductor is not only a function of unbalancing in the load but also harmonic current generated by the load. In SMPS loads like computers, UPS, electronics etc, triplen harmonics are major component of total harmonics generated. Triplen harmonics have a tendency to flow in the neutral of the conductor, thus giving rise to neutral current in the system. If neutral conductor is not adequately sized, excessive neutral current could cause over heating of neutral conductor which could even lead to failure and eventually accidents involving fire. Even if the neutral is adequately sized, then high neutral current in the system causes rise in neutral to ground voltage. In some equipments where neutral to ground voltage is reference point for operation of electronic equipments, this rise in neutral current can disrupt operation of the equipment.

This case study presents a unique way of suppressing neutral current in the system using Line / Neutral Inductances and Neutral Current Compensator.

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