Abstract：Synchronization errors lead to phase shifts and the phase shift restraint capacities could describe security characteristics of differential protections caused by synchronization errors. The phase shift restraint capacity of the traditional percentage differential protection gets better when the restraint coefficient increases, with the cost of the sensitivity depression to the internal faults. The paper proposes a new differential criterion whose restraint area in ρ rho plane is a sector-ring defined by the radius setting of the inner restraint circle and the open angle setting in the unit circle. The radius setting controls the limits to magnitude errors and determines the sensitivity of protection during internal faults. The angle setting controls the amount of tolerance to phase angle errors and determines the phase shift restraint capacity of the protection independently. Simulation results show the new protection could resist 3ms time shift and has good sensitivity to inner slight faults and fine capability against current transformer saturation.
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2009, Vol. 24 
