Power system harmonic voltage limits for the future
This paper provides a new methodology for setting harmonic limits in power systems. This approach is designed to replace the existing harmonic limits detailed in IEC 61000.3.6 and IEEE 519. The methodology provides for replacing the ~40 or more individual harmonic with three new limits. The new limits are low frequency weighed VTHD, high frequency weighed VTHD and the even harmonic components of VTHD. It is proposed to keep the VTHD limit to make a total of four limits. The four limit types have been selected because they each correspond directly to known critical physical effects on customer equipment and network components that need to be managed. The low frequency weighed VTHD limit is used to restrict harmonic losses in induction motors. The high frequency weighed VTHD is used to restrict harmonic heating in capacitors. VTHD is used to ensure the peak of the voltage waveforms is neither too low nor too high. Even VTHD is used to ensure voltage waveform symmetry and the control of DC currents. Providing a physical basis for each of the four limits removes much of the arbitrariness of the existing IEC 61000.3.6 and IEEE 519 limits. The methodology provides safeguards for customer equipment while giving network owners and customers much greater flexibility for economic mitigation. Indicative limit values have been suggested as a starting point for the further development of this approach.