Vaihepuuttuu

Vaihepuuttuu is a Finnish term used in electrical engineering to describe a fault in which one phase of a three-phase power system is not energised. The condition is indicated when the voltage on one phase falls toward zero while the other phases remain alive, resulting in an unbalanced supply.

In a normal three-phase system, equipment such as motors and transformers expects balanced input. If a phase is missing, the system effectively operates on two phases. The remaining line-to-line voltages exist between the two active phases, but the third phase voltage collapses. The result is an unbalanced load, which can cause reduced torque, overheating, abnormal vibrations, and potential damage if the condition persists. Protective controls and power electronics may trip or enter fault states in response to undervoltage or phase-loss signals.

Causes of phase loss include a broken conductor, blown fuse, failed contact or breaker, loose connections, or faults in a generator or transformer. Detection is commonly provided by protection relays or monitoring equipment that flags phase voltages or currents outside acceptable ranges, and by alarms in control systems.

Prevention and response focus on reliable wiring and protection: regular inspection of cables and connections, phase-failure protection relays, and redundant or monitored feeds for critical loads. Equipment such as variable-frequency drives can also be configured to detect phase loss and respond safely.