Evaluation of voltage magnitude based unbalance metric for low voltage distribution networks

TL;DR

This study compares true voltage unbalance metrics with approximate ones based on phase voltage magnitudes in low voltage distribution networks, finding that approximate metrics are reasonably accurate especially at higher R/X ratios and varying load conditions.

Contribution

It evaluates the effectiveness of phase magnitude-based unbalance metrics as practical approximations for true unbalance measurements in distribution networks.

Findings

Approximate unbalance metrics are accurate at higher R/X ratios.

Unbalance metrics slightly improve with lower power factors.

Phase magnitude-based metrics can effectively estimate true unbalance.

Abstract

Voltage unbalance in distribution networks (DN) is expected to grow with increasing penetration of single-phase distributed generation and single-phase loads such as electric vehicle chargers. Unbalance mitigation will be a significant concern as voltage unbalance leads to increased losses, reduced motor and inverter efficiency, and becomes a limiting factor for DN operation. The true definition of the unbalance metric needs phasor measurements of network voltage and current. However, such phasor measurements are generally not available in real life and as such approximate definitions are widely used due to their simplicity. This work aims to compare the true voltage unbalance definition and approximate unbalance metrics derived from phase voltage magnitude, as phase voltage magnitudes are commonly measured by digital metering infrastructure. For the comparison, multi-period power flow simulations are performed for 161 Spanish distribution feeders with R/X ratios varying from 2.87 to 14.68. We observe that phase magnitude-based unbalance metrics reasonably approximate the true unbalance for higher R/X ratios with a varying load power factor in a DN. Furthermore, the approximate unbalance metrics slightly improve for a low DN power factor due to the increase in DN unbalance. Therefore, the phase magnitude-based unbalance metric can be utilized for approximating DN unbalance.