Mid-voltage Distribution Research Articles

A New Approach for Single-Phase-to-Ground Fault Detection in Mid-Voltage Systems Using Low-Voltage Sensors

Single-phase-to-ground fault in low-current grounding systems represents a serious public safety concern. Low-voltage (LV) sensors, with their growing maturity, can now monitor multiple points of the mid-voltage (MV) distribution network. This paper proposes a new method for identifying single-phase-to-ground line faults and locating them using LV sensors deployed on the LV side of distribution transformers. We analyze the characteristics of the negative-sequence signal on the LV side after a single-phase grounding fault occurs on the MV side. The negative-sequence current can distinguish between fault and non-fault lines. By setting the ratio coefficient of negative-sequence voltage and positive-sequence voltage, we can use multi-point collaborative calculation and comparison to determine the section of the fault point. We consider the unbalanced load on the LV side and the special case of a fault point on one end of the line. Through simulation of combined MV and LV distribution systems in MATLAB software and dynamic model experiments, we verify that the proposed method has good robustness and accuracy. Monitoring the status information of the MV distribution network through LV sensors has great potential in practical application and implementation for realizing the fault detection of low-current grounding systems.

Two-stage ADMM-based distributed optimal reactive power control method for wind farms considering wake effects

Since the connection of small-scale wind farms to distribution networks, power grid voltage stability has been reduced with increasing wind penetration in recent years, owing to the variable reactive power consumption of wind generators. In this study, a two-stage reactive power optimization method based on the alternating direction method of multipliers (ADMM) algorithm is proposed for achieving optimal reactive power dispatch in wind farm-integrated distribution systems. Unlike existing optimal reactive power control methods, the proposed method enables distributed reactive power flow optimization with a two-stage optimization structure. Furthermore, under the partition concept, the consensus protocol is not needed to solve the optimization problems. In this method, the influence of the wake effect of each wind turbine is also considered in the control design. Simulation results for a mid-voltage distribution system based on MATLAB verified the effectiveness of the proposed method.

Dual-timescale control for power electronic zigzag transformer

Power electronic zigzag transformer is an attractive solution for the flexible interconnection of smart distribution networks. It is constituted by slow-response and low-precision thyristor converters and fast-response and high-accuracy voltage source converters. This paper models its primary circuit and addresses its basic operation mechanism. Then a dual-timescale control scheme is investigated to realize the coordinated regulation of both types of converter. A simulation case is established in PSCAD containing interconnected mid-voltage distribution networks. Simulations with poor- and well-matched control timescales are both carried out. And accordingly, the power flow controllability under these conditions is compared. When the shorter control timescale is no more than tenth of the longer one, the power electronic zigzag transformer will operate with satisfying performances.