The Mechanical (Type) Voltage Regulator

The mechanical type voltage regulator has the greatest number of different names often reflecting their means of operation and/or purpose:

  • Auto-boost regulator
  • Electromechanical voltage regulator
  • Electromechanical voltage stabilizer
  • LDC
  • Line voltage regulator
  • Line drop compensator
  • Magnetic induction voltage regulator
  • Mechanical tap changing regulator
  • Motorized variable transformer
  • Magnetic induction voltage stabilizer
  • Motorized variac
  • Motor-driven variable autotransformer
  • OLTC
  • On load tap changer
  • Servo voltage regulator
  • Servo voltage stabilizer
  • Step voltage regulator
  • Tap changer
  • Tap-switching voltage regulator
  • Variable autotransformer

This type of voltage regulator has been in use for more than 50 years and has seen refinements throughout the years primarily with advances in control technology and servo drive systems. This type of voltage regulator dominates the electric utility market and is the most popular type outside of North America for power quality applications. As more electronics are deployed in industrial settings worldwide, the mechanical voltage regulator is being displaced by the electronic voltage regulator.

While the mechanical voltage regulator comes in a broad variety of designs they all share the characteristics of having one or more servomotors to physically move some component(s) within the unit. The purpose of this movement is to affect voltage regulation by changing the turns ratio or magnetic coupling of a transformer. Included in this type of voltage regulator are devices for power quality control as well as devices used by electric utilities for correcting voltage (line) drop in distribution lines (see Power Quality versus Line Drop Compensation below).

The two primary methods of operation used by mechanical voltage regulators are: (A) by changing the turns ratio, or (B) by altering the magnetic induction between the primary and secondary coils of a transformer by physically changing their orientation.