Specification of minimum short-circuit capacity for three-phase unbalance limitation based on an efficient algorithm

To regulate the nonsinusoidal or 3φ unbalance current injection into the utility systems, power utilities have to specify the minimum 3φ short-circuit current, at the point of common coupling with the customers having the distortion source. However, the present specification rules, without theoretical verification, caused controversy between the utility and the customers under regulation. To resolve this controversy, this paper presents an efficient estimation algorithm for the minimum 3φ short-circuit current. We then estimate the maximum traction load at seven 161 kV substations of the Taiwan high-speed railway system which is now being planned. Using the maximum traction load and the minimum short circuit capacity derived, we estimate the maximum unbalance of the 3φ voltage at these seven 161 kV substations, and compare our results with those of Taipower to demonstrate the effectiveness of our proposed algorithm.