Research On Short-circuit Test Of Impedance-matching Balanced Traction Transformers

Impedance-matching balanced traction transformers (balanced transformers in this paper for short) are step-down transformers , they transfer symmetrical three phase voltage in primary side to perpendicular two phase voltage in secondary side . They are different from any other transformers, so their short-circuit current analysis and short-circuit test method must be taken into special account.GB1094.5-85 Power transformers Part 5 Ability to withstand short circuit only applies to power transformers , not to balanced transformers . If short-circuit test on balanced transformers can be performed by means of single phase supply instead of three phase supply, and other special transformers can also be done in this way ,so it is very significant to improve test capacity of transformer laboratory in our country.The relation among all short-circuit current in each winding is described , and the rms value and peak value equation of short circuit current are concluded in this paper.Single-arm short-circuit fault, both-arm short-circuit fault, both-arm sequent short-circuit fault, short-circuit fault under no load, short-circuit fault under on load, short-circuit fault in primary side may occur in balanced transformers in power system, which short-circuit fault is the most serious is decided according to calculation and test.Under some conditions, short-circuit test on balanced transformers can be performed by means of 1.5 phase supply . It is proved to be equivalent to the short-circuit fault during their operation. The test results comply with GB1094.5-1985.The equation among peak factor, quality factor, switch initial angel is concluded . On the basis of the equation, peak factor curve has been programmed . The rms value, peak value and switch initial angel can be shown in the screen of computer . Switch initial angel can be corrected automatically to make the peak value in each winding comply with requirements. This program has been applied for short-circuit test on all kinds of transformers.The short circuit test method in this paper applies to balanced transformers, such as Y/V impedance-matching balanced transformer and YNA impedance-unmatching balanced transformers . The analysis method of short-circuit current applies to all special transformers, for example, split winding transformers, Z connection winding transformers.Finally, a SF2-QY-25000-110/27.5 GY balanced transformer has been tested, the result is approved by China National Transformer Quality Supervision Testing Center.