Voltage Regulators in Power Systems: Single-Phase vs Three-Phase Fundamentals

Voltage regulators (szsger.com) play a crucial role in power systems. Whether single-phase or three-phase, they serve to regulate voltage, stabilize power supply, and protect equipment within their respective application scenarios. Understanding the basic principles and main structures of these two types of voltage regulators is of great significance for the design and operation & maintenance of power systems. This article will discuss the basic principles and main structures of single-phase and three-phase voltage regulators.

1.Basic Principle
This voltage regulator adopts a variable autotransformer structure. A coil is uniformly wound on a toroidal core. A carbon brush, actuated by a handwheel shaft and brush holder, makes close contact with the polished surface of the coil under spring pressure. Rotating the shaft drives the brush holder, causing the carbon brush to slide along the coil surface. By changing the contact position of the carbon brush, the turns ratio between the primary and secondary windings is altered, enabling smooth, stepless adjustment of the output voltage within the regulation range, thereby achieving voltage regulation.

2.Main Structure:

A. Unit Structure: Single-phase voltage regulators from 0.5 kVA to 10 kVA adopt a unit structure. A coil with a polished surface of certain width on its upper end is fixed onto the base. The carbon brush of the contact assembly, pressed by a spring, maintains tight contact with the polished surface of the coil. Turning the handwheel moves the carbon brush along the polished surface for voltage regulation. These unit-type regulators are typically bench-mounted and enclosed in a protective ventilated housing.

B. Single-Phase Assembled Structure: Large-capacity single-phase voltage regulators are assembled from several identical units. The carbon brushes of all units are mounted on the same main shaft. The input terminals of the coils are connected in parallel, while the output terminals are connected to a balancing reactor to equalize current distribution among units and suppress circulating currents.

C. Three-Phase Assembled Structure: A three-phase voltage regulator is assembled from three identical units mounted on a common shaft, with windings connected in a star (Y) configuration.

D. Carbon Brush Structure: For unit voltage regulators rated at 3 kVA and below, 1–2 pieces of copper-graphite composite carbon brushes and a metal brush holder with good heat dissipation are used. For units rated at 5 kVA and above, more than two copper-graphite composite carbon brushes are employed. The pressure plate of the carbon brush assembly is fixed to the upper end of the coil to limit its axial position and is secured to the main shaft with screws. When disassembly, replacement of the main shaft, or extension of the shaft from the bottom of the regulator is required, simply loosen the screws to proceed.

The above is an introduction to the basic principles and main structures of single-phase and three-phase voltage regulators. We hope this helps readers gain a clear understanding of their operating principles and construction. A deeper comprehension of these aspects enables better utilization and maintenance of the equipment, ensuring stable operation of the power system.