A Practical Approach to Volt Var Optimization in an Unbalanced Radial Distribution System

This paper explains and analyzes a new practical rule-based approach for Voltage VAR Optimization (VVO) which is one of the most popular techniques to improve voltage profiles and minimize feeder losses. VVO uses power system control equipment like capacitor banks and Transformer Taps to calculate new optimal operational state for these devices. The proposed algorithm first optimizes Feeder Capacitor Banks and then optimizes On Load Tap Changing (OLTC) Transformers. Typical VVO objective functions are reactive power compensation, minimization of feeder power losses, Minimum Number of Controls and Minimum Shift or combinations of these. Typical constraints include voltage at each bus within its specified limit and current flows on each feeder section within the specified limit. In this paper, the objective function used is the minimization of feeder power loss with voltage at each bus as a constraint. Feeder capacitor banks and OLTC’s are considered as control devices. The proposed algorithm is tested on 55 bus unbalanced Radial network and the results show that proper adjustments of OLTC transformers and Capacitor banks significantly reduce power losses while satisfying all the operational constraints. The results offered by the proposed algorithm are compared with those offered by the conventional Interior point method, and the superiority of the proposed algorithm is demonstrated.