Investigation into harmonic compliance with respect to the harmonic impedance envelope in the South African Grid Code (SAGC) for Renewable Power Plants (RPPs)

Abstract

The South African Grid Code (SAGC) for Renewable Power Plants (RPPs) uses a specific method for the approximation of harmonic impedance at the Point of Common Coupling (PCC). This method assumes that the harmonic impedance as seen at the PCC is composed of a purely inductive impedance. The assumption is due to the lack of availability of accurate and complete network information. Another assumption is then made that the harmonic impedance is three times the base harmonic impedance. The purpose of this research was to prove that the SAGC (for RPPs) method of approximating the harmonic impedance is too pessimistic. This was accomplished by comparing the SAGC harmonic impedance estimation to the estimation of what will be referred to as the load aggregation method and the current injection method. The finding from this research is that a new middle ground, between the impedances calculated by the SAGC method and the actual harmonic impedance, can be determined for instances where the location of capacitors adjacent to the PCC is known. It is recommended that the SAGC (for RPPs) approximation method be revised to make provision for instances where information regarding the location of capacitances in the network is available.