To compensate for the current inadequacy of large capacity rectifier transformers with only overcurrent protection but no longitudinal differential protection at home and abroad

the key contents of setting up longitudinal differential protection for rectifier transformer are proposed. First

the special treatment methods for the sampled secondary current values of current transformer on the valve side of the longitudinal differential protection are put forward and demonstrated. And it is also shown what value of effective three-phase current values on the grid and valve sides in the calculation of differential current and brake current for longitudinal differential protection should be adopted

i. e.

the best compensation(or angle)equation is demonstrated

which is different from the compensation equation of the conventional power transformer

converter transformer

electric furnace transformer

etc. A unique calculating method of phase and modulus value of grid-side current is proposed and demonstrated when a two-phase short circuit fault occurs on the valve side of the rectifier transformer. The action characteristics of differential protection for rectifier transformer are analyzed when a two-phase short circuit fault or a single-phase grounding fault occurs. The characteristics of setting calculation of differential protection can make the protection action sensitivity significantly increase during the internal short-circuit fault

and make the differential protection range significantly expand

while protecting the valve-side short-circuit of the rectifier bridge and the DC side short-circuit.