Evaluation of the Probability Parameters of Insulation Control of the Stator Windings “Generator-Transformer” Unit

Abstract

It is shown that significant aging of electrical equipment of power plants, high cost of failures, the need to continue its operation, compliance with safety rules requires increasing the reliability of monitoring the technical condition of insulation. Analysis of existing methods of continuous monitoring of the technical condition of the insulation of the stator winding of a synchronous generator operating in a unit with a transformer showed their significant shortcomings, namely the low sensitivity to changes in insulation damage near the neutral of the stator winding and symmetrical reduction of insulation parameters. This does not allow to detect damage at an early stage of its development. In addition, there is a faulty operation of the controls due to asymmetries of phase voltages.

To increase the probability of controlling the insulation parameters of the stator winding of the synchronous generator, the method, principle of construction, algorithm of diagnostic control complex, as well as software algorithm used to process measurement data and determine the insulation parameters of the stator winding based on microprocessor.

The probability of control of the proposed method of controlling the insulation of the stator winding of a synchronous generator operating in a unit with a transformer based on the superimposition on the circuit containing the stator winding, AC signals with a frequency lower than the rated frequency, DC voltage, use the energy of the pre-charged capacitor and the calculation of the insulation parameters of the "generator-transformer" unit.

Expressions are given to determine the total active resistance relative to the ground and at the place of formation of the shunt connection with the ground, the equivalent insulation capacity, the tangent of the dielectric loss angle in the insulation, the probability of false and indefinite failure, the probability of “suitable” multiparameter control.

The expressions necessary for calculating the probability of control of active resistance relative to ground, transient resistance at the place of shunt formation, insulation capacity relative to ground, tangent of dielectric loss angle of stator winding of synchronous generator operating in block with transformer are obtained. Based on the obtained expressions, the probability of the result “suitable” is calculated. The results of calculations can be used in the design of relay protection and diagnostic systems for electrical equipment of new power units, as well as in the reconstruction of existing power units of power plants.