One of the main tasks of a power distribution company is to ensure and maintain
the nominal network voltage levels. Therefore, there is a great emphasis on the
voltage measurements. Analysing the measured data shows discrepancies between
the voltage levels in the different phases or so-called voltage unbalance. This is
a consequence of single-phase loads and is always present in small quantities,
however higher level of asymmetry can indicate a fault on the network which
results in a lower quality of energy supply.
The thesis begins with a description of the voltage unbalance, followed by a
presentation of field data measured in low voltage network. Presented is a general
graphical overview, where voltage profiles and voltage unbalance calculations in
the network are shown. Prior the analysis, we define the allowed limit values
based on the current standard.
Three common voltage unbalance causes are analsyed first; single-phase loads,
distributed energy sources and network anomalies. Alongside network condition
analysis, a few solutions for mitigating the problem are listed.
Furthermore, we have a complete analysis of the low voltage network, with a
detailed examination of the feeder, where voltage unbalance was discovered. It
turns out that analysis of voltage conditions alone isn’t enough to find the reason
for the occurring voltage unbalance.
Finally, we present the effect of overloaded distribution transformers on the
voltage conditions in the network, where we show the comparison of voltage
conditions before and after the change of the transformer, that was previously
exceeding its maximum rated power.
We discovered that it’s not always possible to determine the cause of the
voltage unbalance by only analysing voltage measurements. Such analyses are
more useful for finding low voltage networks or feeders where we haven’t yet
detected any issues while pinpointing the issue itself requires different methods.
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