A Preliminary Study on the Formation Mechanism of Microcracks in Dry-type Air-core Shunt Reactors

Abstract

As an important reactive power compensation equipment in power system, dry-type air-core shunt reactor is widely used in power grid because of its low cost and small maintenance. In operation, the failure rate and defect rate are relatively high. One of the typical failures is that the interturn insulation fault finally causes the fire. It is found that the cracks in the operation of dry reactor are one of the main causes of insulation failure. In this paper, through theoretical analysis and experimental research, the mechanism of microcracks in dry-type air-core reactor is preliminarily explored, and some of the causes of cracks are experimentally studied. The effects of main material characteristics and temperature conditions on cracks of dry-type air-core reactor are given. The low temperature environment has a great influence on the mechanical properties of the dry-type air-core reactor winding, which mainly shows that the overall stress of winding increases with the decrease of temperature, and the stress on each encapsulated winding is also unevenly distributed; however, the bonding performance of the encapsulated material and the conductor decreases obviously with the decrease of temperature. When the reactor is switched in low temperature and cold state for many times, under the combined action of two factors, it is possible to crack the enveloping insulation at the place with the largest winding stress, make the external moisture intrude, and cause partial discharge. After a long time of cumulative effect, the local turn-to-turn fault is finally formed, which leads to equipment accidents.