Standards Development

Scope

This part of IEC 61857 describes a procedure for the thermal evaluation and classification of an electrical insulation system (EIS) in dry-type resin-encapsulated high-voltage windings operating at voltages of 1 kV and above. The dielectric diagnostic applied uses AC breakdown of the insulation as the failure criterion. This test standard evaluates only the thermal decomposition of the solid part of any electrical insulation system which undergoes thermal decomposition during operating conditions. This document is also applicable when the windings in the application are constructed with multiple rated voltages, using different electrical insulation systems.

The performance of any transformer designed and constructed using the EIS established in accordance with this document shall be evaluated in accordance with the application requirements set by the appropriate IEC Technical Committee.

Purpose

This part of IEC 61857 describes an evaluation procedure of an electrical insulation system (EIS) to be used for windings constructed using an EIS evaluated for applications with an operating voltage above 1 kV. The approach is to evaluate the EIS using the dielectric diagnostics of the evaluation of the EIS. The test is designed to establish the thermal classification of the EIS.

This test standard evaluates only the thermal decomposition of the solid part of any winding electrical insulation system. This is not intended to be an evaluation of any winding design or to convey expected operating life. As presented in IEC 60505, expected operating life of any component such as any dry-type winding is the result of a combination of stress factors:

• thermal

• electrical, both normal and abnormal

• ambient = environmental, and

• mechanical.

These four types of stress factors in combination with duty cycle and other real-world factors all are part of the actual life performance. The combination of stress factors, known as multi-factor evaluations, is outside of the scope of this standard.