A New Method of Measuring DC Resistance of Large-sized Transformer LV Winding

Abstract: The paper presents several methods of measuring DC resistance of large-sized transformer LV winding. The test process and test results are elaborated and analyzed. Against the disadvantages of available measuring methods, a new method is proposed by combing two current methods - saturated magnetic method and full-voltage constant current power supply method. Based on steady condition of circuit, the full voltage (high voltage) is applied to increase the current of coil rapidly and shorten the transition process; then constant current source stabilizes the current for measurement. The saturated magnetic method connects high voltage winding with low voltage winding in series. The number of high voltage winding turns is much more than that of low voltage winding. Hence, low current can make iron core saturate and reduce winding inductance greatly with the help of HV winding turns. The goal of rapid measurement is achieved. 

Key words: Large-sized transformer, DC resistance, saturated magnetic method, winding, rapid measurement    

Introduction

The transformer winding DC resistance measurement is one of important tests and serves as a benchmark for assessing short-circuit loss. Hence, it is necessary to conduct the test after delivery, pre-use, overhaul and tap changer adjustment. As electrical and mechanic production level has been rising in recent years, the capacity of electrical system is becoming increasingly larger, and the same goes for the capacity per transformer. The capacity of large-sized transformer coil and voltage stage are proportional to the ratio of inductance and resistance. The large-sized transformer winding DC circuit can keep steady for minutes even longer. How to measure the transformer winding DC resistance quickly and accurately is always attracting the attention of people.