How to Diagnose the Fault of Power Transformer Secondary Winding

Han Weizhong, Yang Junhai, Wang Shuo, et al 
HIMALAYAL - SHANGHAI - CHINA

Abstract: Taking a fault of power transformer secondary winding in some substation as an example, the paper analyzes how the oil chromatography changes during the operation of broken transformer and high voltage test data from many aspects ranging from protective action, causes, winding damage condition to the selection of test method. Combing with disassembling and inspection results, it is believed that single-phase no-load test is an effective method of diagnosing whether the winding has developed inter-strand(interturn) short circuit fault after the transformer is out of order.  

Key words: power transformer, secondary winding, short circuit, single-phase no-load test 

Introduction 
The fault in power transformer secondary winding is very common. Causes of secondary winding fault should be figured out from many aspects, including protective action, damage condition, the choice of test method, transformer disassembling and checking. On July 17th , 2013, No.1 main transformer in some 66kV substation in Jilin province suddenly broke down. The paper analyzes how the fault occurs and develops through data of oil chromatography and high voltage test and disassembling inspection results. It is found that there is a fault in power transformer secondary winding. Some tips on transformer operation, maintenance and test are provided. 

On July 17th, 2013, No.2 main transformer in some 66kV substation was being overhauled. At nine twenty-eight, No.1 main transformer carried all the loads and No.2 main transformer was off. The total load of substation is 24MW, and the total current of 10kV side is 1345A, accounting for 77.6% of No.1 main transformer rated capacity. At five to ten, No.1 main transformer had heavy gas protection action; primary and secondary breakers tripped; the power failure of the whole station occurred. At ten five, No.2 main transformer restarted and carried all loads. The No.1 main transformer left the factory at September 1st 2000 and was put into use on September 10th 2001. The primary rated current is 275A and secondary rated current is 1732A. Before the breakdown, the No.1 main transformer carries 10MW load, and secondary current is 585A; the No.2 main transformer carries 14MW load and secondary current is 760A.