EVALUATION OF DISTRIBUTION SYSTEM LOSSES DUE TO LOAD UNBALANCE TECHNICAL PAPER

EVALUATION OF DISTRIBUTION SYSTEM LOSSES DUE TO LOAD UNBALANCE TECHNICAL PAPER
A technical paper authored and completed by Luis F. Ochoa, Rade M. Ciric, A. Padilha-Feltrin, Gareth P. Harrison of UNESP – Universidade Estadual Paulista, Faculdade de Engenharia de Ilha Solteira - Ilha Solteira, Brazil University of the West of England - Bristol, UK

ABSTRACT – Distribution network losses can vary significantly depending on the load unbalance. Here, an analysis of distribution system losses is presented that considers load unbalance and the effect of explicitly represented neutral wire.

A general power flow algorithm for three-phase four-wire radial distribution networks, based on the current summation backward-forward technique is applied. Loss analysis results obtained from three-phase four-wire medium and low voltage test feeders with unbalanced load scenarios are presented and discussed considering: a) original phase and neutral wires resistances; and b) resistances obtained by performing Kron’s reduction.

CONCLUSIONS - In this paper we presented a loss analysis in distribution systems considering different load unbalance scenarios. A general power flow algorithm for threephase four-wire radial distribution networks, based on backward-forward technique was applied.

This approach improves loss calculation due to the explicit representation of the neutral conductor, which should be considered since unbalance is a common every-day occurrence in three-phase distribution systems. High levels of load unbalance produced greater losses while the same demand is maintained at each unbalance scenario.

This means that network reconfiguration considering load balancing is highly recommend in order to diminish overall system losses. Usage of reduced matrix resistances (representation of four-wire line sections performing Kron’s reduction) into the I2R formula is a procedure that should be avoided since leads to incorrect results.

The selection of the load model to be used in the analysis plays an important role in the overall loss calculations. Constant admittance load model leads to lower amounts of losses and provides higher levels of unbalance than the constant power load model within the same specified tolerance.

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