Overview

Various aspects shall be observed when conducting lightning impulse tests for determination of the electric strength of solid insulating materials under impulse voltage stress. Insulating materials used in high-voltage equipment can be subjected to transient voltage stresses, resulting from such causes as nearby lightning strokes. This is particularly true of apparatus such as transformers and switchgear used in electrical-power transmission and distribution systems. The ability of insulating materials to withstand these transient voltages is important in establishing the reliability of apparatus insulated with these materials. Transient voltages caused by lightning may be of either positive or negative polarity. In a symmetrical field between identical electrodes, the polarity has no effect on the breakdown strength. However, with dissimilar electrodes there can be a pronounced polarity effect. When asymmetrical electrodes are used for testing materials with which the tester has no previous experience or knowledge, it is recommended that comparative tests with both polarities are conducted. Because of the very short time involved, dielectric heating and other thermal effects are largely eliminated during impulse testing. Thus, the impulse test gives values closer to the intrinsic breakdown strength than longer time tests. From comparisons of the impulse dielectric strength with the values obtained from longer time tests, inferences can be drawn as to the modes of failures under the various tests for a given material. This standard DIN EN 60243-3 (VDE 0303-23) gives requirements additional to those in IEC 60243-1 for the determination of the electric strength of solid insulating materials under impulse voltage stress (1,2/50 µs). The responsible committee is DKE/K 183 "Bewertung und Qualifizierung von elektrischen Isolierstoffen und Isoliersystemen" ("Evaluation and qualification of electrical insulating materials and systems") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 183 - Bewertung und Qualifizierung von elektrischen Isolierstoffen und Isoliersystemen