Analysis and discussion of a dead-zone protection mal-operation case in Brazil

A mal-operation case of busbar protection caused by a dead-zone protection abnormality in the Brazilian Midwest Grid on September 19th, 2012, is briefly described. The operation process of pilot distance, automatic re-closure, busbar differential and dead-zone protection, and the emphasis on the logic scheme of dead-zone protection are analyzed. The time delay between the breaker's main pole and auxiliary contact during re-closure was the main cause in this case, and a defect in the logic allowed it to occur. The differences in dead-zone protection logic between Brazil and China are discussed. A test platform was constructed in the laboratory, and a site simulated experiment was also performed. Possible causes are suggested and test activities are carried out to verify them. Results show the values of practical engineering approaches to the solution. Experience also contributed to avoiding future mal-operations and strengthening the reliability of the protection system, and thus of the power supply in Brazil.