Automatic Regulation of Excitation

a process of varying, according to a given set of conditions, the excitation current of electrical motors. It is used in synchronous generators, synchronous motors, synchronous compensators, generators and motors operating on DC, and other special electrical motors. Varying the voltage of the excitation coil changes the current intensity of excitation of the electric motors and, consequently, the main magnetic flux and electromotive force (emf) in the armature winding. Automatic regulation of excitation of synchronous generators is basically used to ensure a given voltage in the electrical grid and also to increase stability of its operation in parallel within the overall grid. Automatic regulation of excitation is widely used in DC electrical drives in order to maintain stability of the rotational speed of the shafts by means of regulating the excitation current of the drive or the supply generator.

Automatic excitation controls operate in proportional and power modes. The proportional automatic mode is characterized by a change in current intensity of the excitation proportional to the deviation from a given value of voltage at the terminals of the motor (negative voltage feedback). Excitation controls operating in a proportional mode may contain compound circuits (positive current feedback) and stabilization circuits (flexible negative excitation voltage feedback). Proportional automatic regulation of excitation does not guarantee sufficient accuracy for maintaining the voltage of electrical power stations feeding into transmission lines nor in cases where rapidly changing loads in the system cause significant voltage variations.

In such cases the power mode is used, which increases effectiveness by introducing excitation control based on the deviation of the voltage and on derivatives of current, voltage, frequency, and other characteristics selected on a predetermined basis; its characteristics are rapid response and high excitation power of the system. Automatic excitation control of the power mode was first devised by Soviet energy experts; this development allowed the solution of one of the most important problems in the electrical energy field—the transmission of large blocks of power on AC lines over long distances. The first application of automatic regulation of excitation operating in a power mode was at the Lenin Volga Hydroelectric Station in 1955–57.