Describe the consequences of a 'floating neutral' in a three-phase system and what protection measures mitigate its impact.

A "floating neutral" in a three-phase system occurs when the neutral point of the system is not properly grounded or connected to a low-impedance ground. In a balanced three-phase system, the neutral point should be at or near ground potential. However, if the neutral connection is lost or becomes high impedance, the neutral voltage can shift away from ground, leading to voltage imbalances across the phases. The consequences of a floating neutral can be severe. Unequal phase voltages occur because the voltage to ground on each phase depends on the load connected to that phase. Lightly loaded phases will experience higher than normal voltages, while heavily loaded phases will experience lower voltages. This can cause equipment connected to the lightly loaded phases to be overstressed and potentially fail. Overvoltage on some phases damages equipment sensitive to voltage fluctuations. Undervoltage can cause motors to overheat and malfunction. Increased neutral current flows. Even with balanced loads, a floating neutral can cause significant current to flow in the neutral conductor. This current can overheat the neutral conductor and potentially damage it. If the neutral conductor is undersized, it can become a fire hazard. Harmonic distortion increases. A floating neutral can exacerbate harmonic distortion in the system, leading to further equipment problems. Intermittent faults can occur. Intermittent connections in the neutral path can cause the neutral voltage to fluctuate, leading to intermittent equipment malfunctions and nuisance tripping of protective devices. Several protection measures can mitigate the impact of a floating neutral. Proper grounding of the neutral point is the most important measure. This can be achieved by connecting the neutral point to a grounding electrode system with a low impedance path to ground. Ground fault protection detects ground faults and quickly disconnects the faulted circuit. This helps to limit the voltage imbalance caused by a floating neutral. Neutral overcurrent protection monitors the current in the neutral conductor and trips the circuit if the current exceeds a pre-set threshold. This protects the neutral conductor from overheating. Voltage monitoring relays detect voltage imbalances and trigger an alarm or trip the circuit. This provides early warning of a floating neutral condition. Regular inspection and maintenance of the grounding system is essential to ensure its integrity. Therefore, preventing and mitigating the consequences of a floating neutral requires a combination of proper grounding, protective devices, and regular maintenance.