Field measurements, modelling and simulation for harmonic analysis of a large industrial power system

Harmonic distortion problems due to non-linear loads can have a significant impact on industrial customers. Voltage and current distortion levels must satisfy limits set out by Grid Code requirements. This paper details the harmonic analysis of a large mine in Ireland which is currently undergoing an extensive expansion. As part of the expansion two existing 2MW synchronous motors are to be replaced by two new 4MW asynchronous motors. As the synchronous motors also act as reactive compensation for the plant it is planned to install two sets of capacitors banks on the main 6.6kV busbar to help maintain a high power factor. As many of the motor loads around the plant are fed through Variable Speed Drives there is existing harmonic distortion currently at the plant. Also depending on their size, installation of PFC capacitor banks may cause a resonance condition to exist. This resonance condition could magnify any harmonic currents present at the resonant frequency. As part of the application for the increase in load the harmonic emission levels of the plant have to be assessed. The results of site measurements, system simulations and possible corrective actions are outlined in this paper.