A Primer On Harmonics and The Modern Grid

Over the past 20 years, the power system has undergone significant transformation. Power generation has transitioned from large synchronous machines to inverter-based resources that convert a direct current (DC) to an alternating current (AC). In addition to changes in generation, grid design now employs other active components to regulate voltage. Furthermore, the nature of power consumption has evolved from primarily resistive loads to increasingly electronic loads. Together, these developments have contributed to a grid environment that is richer in harmonics.

Harmonics on the grid are well known to cause a variety of equipment issues from overheating to malfunction to outright failure. There are many case studies that show that excessive harmonics can negatively affect grid-connected equipment. Consequently, many standards organizations have imposed limits to ensure that equipment can function properly. However, as more active electronics are integrated into the grid, the noise on the grid continues to increase, posing a challenge for standard bodies. Striking a balance between technical feasibility and economic impact has made it difficult to reach consensus on appropriate harmonic limits.

This document describes the nature of harmonics and their effects on grid-connected equipment, summarizes current standards for harmonic measurement and testing, and presents case studies involving harmonic measurements on both distribution and transmission electric systems.