The problem

Supply voltage moves. Where it moves beyond the tolerance of the connected equipment, the equipment either protects itself by shutting down, or degrades. Motors overheat on low voltage, electronics fail on high voltage, and both fail faster than they would at nominal.

Types

Servo-motor (SBW) regulators — a motorized variac corrects the voltage continuously; used for larger industrial loads with a wide correction range.

Static or electronic regulators — solid-state correction, faster and with no moving parts, but a narrower correction range and lower power ratings.

SVC-type regulators — electronic correction for smaller and commercial loads.

Ferroresonant and tap-changing designs — used in specific applications.

Selection inputs

Connected load and its starting characteristic

The actual input voltage range at the site, measured over time — not the nominal figure

The output accuracy the equipment requires

Single-phase or three-phase

Whether the load is balanced across phases

Ambient conditions and the space available

What trips people up

Sizing a stabilizer on nominal voltage when the site actually swings much wider.

Forgetting that the regulator must also pass the starting current of motors.

Installing a three-phase unit on an unbalanced load without checking the effect.

Ignoring the efficiency loss at very low input voltage, which reduces the available output.