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This paper studies the system unbalance caused by rooftop Photovoltaic Generation Systems (PVGSs) in distribution networks and proposes an improved method. The voltage and current unbalance studies for three extreme cases considering all rooftop PVGSs being connected to one single phase and then the stochastic analyses for the integration cases of rooftop PVGSs are considered. These three extreme cases lead to severe system unbalance problems. An improving method that combines the On Load Tap Changer (OLTC) and the optimal phase arrangement of distribution transformers is proposed in this paper to mitigate the system unbalance. The OLTC-based improving method is applied first. If the system unbalance is still out of range, the optimal phase arrangement of distribution transformers is further used to mitigate the system unbalance problem. The objective function of optimal phase arrangement is to minimize the system unbalance with the constraints of voltage limits, line flow limit, etc. Test results show that the proposed method can improve the system unbalance significantly even under very extreme cases.

Fault Current Indicators (FCIs) with communication interfaces have been widely used in distribution systems to reduce fault-finding time. The effectiveness of a Fault Management System (FMS) composed of FCIs greatly depends on the performance of the communication network deployed by the FCIs and the failure rates of distribution systems. The conventional techniques only focus on the issues of optimal number and location of FCIs or communication network deployment individually; therefore, the effectiveness of an FMS cannot be assessed realistically. A systematic effectiveness assessment methodology for FMS considering the performance of the communication network deployed by the FCIs and the failure rates of distribution systems is vital and is investigated in this paper. A communication evaluation platform is designed in this paper and used to acquire the field measurements of communication parameters. The communication parameters, especially the Packet Success Rate (PSR), between two adjacent FCIs are measured, and the Probability Density Function (PDF) of the PSR can be built accordingly. The effectiveness of the FMS is then assessed by stochastic analysis considering the failure rates of the distribution system and PSR PDFs between two adjacent FCIs. Due to the characteristics of easy installation, maintenance, longer battery life, lower cost, and so on of ZigBee, the ZigBee-based FCI is mainly discussed in this paper. In order to efficiently find the communication route when a fault occurs, a fast communication route tracking method is also proposed in this paper and its feasibility is demonstrated in an actual distribution system. Experimental and simulation results demonstrate the validity of the proposed systematic effectiveness assessment methodology for an FMS composed of FCIs. The proposed assessment methodology can more realistically react to the actual conditions of the FMS and therefore save on installation time and costs.