Improvement of Method of Control of Insulation of Generator–Transformer Unit

Abstract

In the conditions of significant aging of the main production capacities and prolongation of the service life of electrical equipment of power plants of Ukraine, the question of development and implementation of methods of continuous control of the technical condition of the generator–transformer unit equipment is urgent. Modern information-measuring systems and relay protection terminals, operated on generator–transformer units, enable control of electrical, thermal, mechanical parameters and parameters characterizing the status or position of technological fittings and auxiliary equipment, as well as providing relay protection of electrical equipment a wide range of possible damage.

However, the existing information-measurement systems do not allow the tracing of the following electrical parameters of the stator winding isolation such as resistance, capacitance and tangent of angle of the dielectric loss, and relay protection may be insensitive to the occurrence of single-phase ground fault near the neutral point of the stator winding and symmetric decrease of parameters of the stator winding insulation, and does not allow detecting the occurrence of damage at an early stage of its development and signal this to the service personnel. There is also the possibility of false actuations at unit start-ups due to the asymmetry of voltages in the machine phases, which is especially acute in synchronous hydrogenerators.

The paper proposes a method of controlling the isolation of a stator winding of a synchronous generator operating in a block with a transformer, a block diagram and basic formulas for signal processing and calculation of electrical insulation parameters. The proposed method is based on the overlay on the circuit containing the stator winding, alternating voltage signals with a frequency lower than the rated network frequency, DC voltage, the use of energy of the pre-charged capacitor and the calculation of the isolation parameters of the generator–transformer unit. The proposed solutions will allow increasing the efficiency of operation of power units by providing operational and repair personnel with reliable information on the technical condition of isolation of equipment in the scheme of power unit output.