One early short circuit current detection (ESCD) method based on the energy change

To reduce the pressure on contacts and circuit breaker and realize the ZSI function above the instantaneous protection threshold (e.g., >10In), the short circuit current needs to be early detected. At short circuit (SC) current, the change of i(exp 2)t (DeltaE) is bigger than normal case. So the change of i(exp 2)t (DeltaE) is taken as the evaluation criterion for forecasting short circuit current. Based on the analysis of the short circuit condition, the change of i(exp 2)t (DeltaE) can be approximately represented as the product of i(t) and integral of i(t). Further based on a series of deducted formulas, an outline to discriminate the abnormal case and non-SC case can be got. With non-SC condition, the DeltaE should be within the area surrounded by outline, otherwise it will be on the outside of the outline as the occurrence of the SC current. According to the result of simulation and test, the short circuit current can be early forecasted with the proposed method based on the energy change.