Field-Based Evaluation of the Effects of Shunt Capacitors on the Operation of Distribution Transformers

This paper analyses the effects of shunt capacitors installed on the low voltage sides of 10/0.4 kV distribution transformers on the operation of these transformers. Using the results of an extensive measurement campaign, the paper compares: real and reactive power losses, secondary-side current and primary-side apparent power before and after the installation of transformer capacitors. The following four cases of reactive power compensation are considered and discussed: adequate, conditionally adequate and total compensation, as well as overcompensation. The presented analysis helps to identify transformer substations where the initial compensation should be changed or adjusted, in order to improve transformers’ operational performance. Voltage dependencies of real and reactive power demands of the transformer-supplied loads are taken into account, based on the previously identified load characteristics in the considered networks, as well as voltage dependency of reactive power of shunt capacitors. The result with and without including these voltage dependencies in the analysis are compared and discussed.