  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.
