Floating neutral is a condition, in which the neutral wire of any circuit is disconnected from the ground. In AC system, the neutral wire is permanently grounded to the earth. However, floating neutral may occur in a power system due to loose connection, braking of neutral flat, wrong circuit connection, or due to short circuit.
What is Neutral and why it is grounded?
In 3 phase AC system, we know the phase difference is 120 degrees for all the phases. In Delta-Star Transformer, a center or common point is available from where the same potential difference with a shifting of phase angle 120 degrees is found for all the three winding of R, Y & B Phase.
During the balance condition, the voltage at the neutral point is zero. Due to unbalance load or fault condition, if the phase angle of any phase is shifted, the unbalance voltage or current is generated at the neutral wire.
To protect the system, the neutral wire of every start winding transformer is permanently grounded. If any unbalance or phase to ground occurred at the load end, the unbalance or fault current will flow to the neutral wire due to a close-loop by using the ground. By sensing the neutral current, the protection relay operates and isolates the load.
Effects of Floating Neutral:
Floating neutral is very dangerous in an AC system. Following disturbances may observe
- Unbalance voltage can develop at a neutral point and it will affect the stability of the system and connected equipment
- Due to floating ground unbalance or faulty current may not detect by the relay and the connected protection system will not operate.
How to Test for a Floating Neutral?
As we know the neutral is always grounded, and the voltage at the neutral point with respect to the ground always should be zero in normal conditions. If a floating neutral condition appears, some unbalanced voltage should be present at the neutral point with respect to the ground. By checking voltage between neutral and ground, it can test in the system.
How to fix floating Neutral?
Floating neutral is very unsafe for the system. Floating neutral can be attended by the grounding of the neutral wire of the system.