Voltage Swell
What distinguishes a swell from overvoltage?
A swell lasts 0.5 cycles to 1 minute; overvoltage persists more than 1 minute.
What is the most common cause of swells?
A single line-to-ground (SLG) fault in ungrounded or floating ground delta systems.
How are swells classified by duration?
Instantaneous swell: 0.008333–0.5 seconds; Momentary swell: 0.5–3 seconds.
What mitigation devices are used?
Voltage regulators, capacitor bank controllers, and surge protectors rated for 1.1–1.8 p.u.
A voltage swell is a short-duration increase in RMS voltage to 110%–180% (1.1–1.8 p.u.) of nominal at power frequency, lasting 0.5 cycles to 1 minute, as defined by IEEE 1159. Also termed momentary overvoltage, it is a power quality disturbance that can damage sensitive equipment.
In manufacturing and shop floor environments, voltage swells are detected by power quality monitors integrated with CMMS like ServiceGrid, triggering asset reliability alerts. Swells often occur when large motors are switched off or during single line-to-ground faults, causing un-faulted phase voltages to rise temporarily. Maintenance teams use this data to schedule preventive inspections of voltage regulators, transformer taps, and capacitor banks, ensuring equipment longevity and minimizing downtime.
Burnout of electronic equipment such as PLCs and sensors due to voltage exceeding device ratings.
Variable frequency drive (VFD) failure from overvoltage stress, especially in sensitive electronics.
Poor maintenance of voltage regulators or loose/damaged neutral connections, allowing swells to persist unchecked.