What is loss of neutrality?
Definition:
The neutral line (zero line) is disconnected or the connection fails in the circuit, causing the current to be unable to flow back to the neutral point of the transformer normally.
Key role:
In the turbine system, the neutral line balances the voltage of each phase and provides a return path for single-phase equipment.
In a single-phase system, the neutral line is the only way for the current to return.
Loss of Neutrality
Hazards to power grid and equipment
| Type of hazard | Specific manifestations |
| Voltage imbalance | In a three-phase system, a broken neutral line causes the voltage of the phase with a lighter load to soar (up to 400V or more) and the voltage of the phase with a heavier load to drop suddenly. |
| Equipment overvoltage damage | Electrical appliances are subjected to overrated voltage (such as 230V equipment suddenly subjected to 400V), causing capacitors to burst and motors to burn (such as refrigerator compressors). |
| Fire risk | Lines overheat and insulation melts, causing electrical fires. |
| Data loss | Precision electronic equipment (servers, PLCs) crash or hardware damage due to sudden voltage changes. |
Personal safety risks
● Electric shock hazard: Current is grounded through alternative paths (such as water pipes, metal frames), and touching these conductors may cause fatal electric shock.
● Arc damage: A break in the neutral wire may cause an arc, causing an explosion or burns.
Common causes of neutral line break
| Cause classification | Specific scenarios |
| Natural factors | Lightning strikes and storms cut off power lines; fallen trees crush the neutral line. |
| Human damage | Construction digs up cables; steals neutral copper (especially during power outages). |
| Equipment aging | Oxidation and loosening of joints (common in old communities); cracking of overhead line insulation. |
| Design defects | Three-phase load distribution is seriously uneven, and the neutral line is overloaded for a long time and breaks due to heat. |
Typical phenomena when neutrality is lost
Home scenario:
● Abnormal lighting: some bulbs are extremely bright (voltage is too high), and some are dim (voltage is too low).
● Electrical appliances are smoking/tripping: TVs, computers, etc. suddenly shut down and emit a burning smell.
Industrial scenario:
● Abnormal motor noise: The three-phase motor speed is unstable and makes a buzzing sound.
● Frequent protection device operation: circuit breaker trips or voltage relay alarms.
Solutions and Preventions
Emergency treatment
● Immediate power off: When abnormal voltage is found (such as light bulbs flickering), quickly turn off the main switch.
● Avoid touching conductors: Stay away from water pipes, metal doors and windows, and other objects that may be electrified.
Long-term protection equipment
● Special protection device:
○ AVS30 (anti-neutral line break protector):
◇ When the neutral line is broken or the voltage is >400V, the power is cut off within 0.1 seconds.
◇ After the voltage returns to normal, the automatic reclosing is delayed for 60 seconds to avoid repeated shocks.
○ Three-phase voltage relay: Real-time monitoring of the voltage of each phase, triggering protection when the imbalance exceeds 15%.
System optimization
● Three-phase load balancing: Industrial users need to regularly adjust the load difference of each phase (recommended <10%).
● Upgrade the line: Change the overhead neutral line to an underground cable to prevent theft and natural disasters.
Frequently Asked Questions by Users
Q: Why do some appliances burn out when the neutral line is broken, but others are fine?
A: Voltage distribution depends on the load impedance. A voltage surge in a lightly loaded phase (such as connecting only a light bulb) may burn out the device; a voltage drop in a heavily loaded phase (such as running an air conditioner) may only cause a shutdown.
Q: How do I determine whether the neutral line in my home is normal?
A: Use a multimeter to measure the socket voltage: If the live-neutral voltage is >250V or <180V, or the live-ground voltage is abnormal, the neutral line may be faulty.
Summary
Loss of neutrality is one of the most dangerous faults in the power grid, and its suddenness and destructiveness far exceed ordinary undervoltage. Home users should install special protectors such as AVS30, and industrial users need to combine three-phase monitoring + automatic switching devices. Prevention is better than cure, and regular inspection of lines and load balance is essential.
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