Overvoltage

Overvoltage is a condition in which the voltage supplied to electrical equipment exceeds its rated or design voltage. It can be transient, lasting a fraction of a second, or sustained, continuing for longer periods. In power systems, overvoltage includes brief surges from switching operations or lightning and longer-lasting elevations caused by faults, switching transients, or grid disturbances. In electronic equipment, overvoltage can occur at input stages due to power-supply faults, external surges, or protection device failures.

Common causes of overvoltage include lightning strikes on power lines, switching of transformers or capacitor banks, faults such as short circuits, rapid changes in load, and power-quality issues like voltage sags followed by rebounds. Equipment with inadequate insulation margins or poor protection coordination is more susceptible to damage from overvoltage events.

Excess voltage stresses insulation and can lead to dielectric breakdown, insulation aging, capacitor dielectric damage, semiconductor junction failure, and shortened equipment life. Components may fail suddenly or exhibit degraded performance, increased dissipation, or erratic operation. In sensitive systems, overvoltage can trigger protective relays or cause data corruption and malfunction.

Protection and mitigation strategies focus on preventing or limiting overvoltage exposure. Design practices include adequate insulation margins and clearances, proper grounding, and coordination of protective devices. Surge protection devices such as metal-oxide varistors, gas discharge tubes, and transient voltage suppressors are commonly used at service entrances and sensitive circuits. Fuses, circuit breakers, voltage regulators, and crowbar circuits provide interruption or regulation during overvoltage events. Standards and testing programs define withstand levels and immunity requirements to guide equipment selection and system design.