Harmonic Study

Harmonic studies are performed to determine harmonic distortion levels and filtering requirements within a facility. Field measurements and computer simulations are used to characterize adjustable-speed drives (ASDs) and other nonlinear loads and simulations are then performed to determine the filter specifications and effectiveness. The application of harmonic filters will significantly alter the frequency response of the power system. An evaluation of the harmonic voltage and current limits, (e.g., IEEE Std. 519) is completed to determine the effectiveness of the proposed filter installation.

The potential for harmonic distortion problems is dependent on two important factors:

The level of harmonic generation which can be associated with loads in the plant. Harmonic currents are generated by loads which have nonlinear voltage-current characteristics. The number and sizes of these devices at a given bus determines the level of harmonic current generation.
The system frequency response characteristics. The frequency response at a given bus is dominated by the application of capacitors at that bus. Series reactors for transient control or harmonic control significantly change the frequency response. Problems occur when the system response exhibits a parallel resonance near one of the harmonic components generated by the loads on the system (usually the 5th or 7th harmonic). Resistive load provides damping near these resonant frequencies.

The combination of these two factors determines whether or not a harmonic problem will exist at a particular bus. It is also possible for harmonic problems to occur at buses remote from the harmonic source if local resonances exist. If capacitors are applied at any locations that have large adjustable-speed drives, the potential for resonance problems must be considered carefully.