Research On Differential Current Amplitude Protection

Current differential protection principle has become the first selection of the main HV and UHV transmission line protection with its unique advantages such as absolute selectivity, high sensitivity, no malfuction in system shaking, and so on. However, when the line does not meet the synchronous measurement conditions on both sides, current differential protection is easy to cause malfuction, not conducive to safe and stable operation of power system. Therefore, this paper presents current amplitude differential protection. It will be a perfect combination of current amplitude differential protection and current differential protection.When the line does not meet the synchronous measurement conditions on both sides, current differential protection will exit. Current amplitude differential protection can achieve rapid action, play the advantages of current amplitude differential protection in the event of a short circuit outside the midpoint of the oscillation.This paper mainly analyzes current transformer transmission error (steady error and transient error), distributed capacitance current which influence current amplitude differential protection. Through setting reliable coefficient of differential current amplitude protection and adopting distributed capacitance current compensation mode so as to ensure current amplitude differential protection with higher sensitivity without the risk of malfunction. This paper also focuses on the analysis of the current transformer saturated characteristic, proposed the blocking criterion of protection when current transformer saturation. In addition, when the system impedance is less than the capacitive reactance of series compensation capacitor, this paper also analysis the effective protection range of current amplitude differential protection, make up for current differential protection dead zone.