Active Harmonic Filters -AHF

Due to the increasing usage of non-linear loads such as VFDs,LED harmonics are being introduced into the power grid which is contributing to poor power quality and leads to overheating of equipment and nuisance faults. Active Harmonic Filters are parallel devices that are used to mitigate harmonics to the levels defined by IEEE-519.

AHF utilizes high frequency current sensors to continuously monitor the load and harmonic currents. By utilizing highly sophisticated software and a powerful DSP microcomputer, the system is able to instantaneously inject a corrective current from its IGBT based inverter to dramatically reduce harmonic distortion. The corrective current is equal to but 180 degrees out of phase with the existing harmonic currents to cancel their effect.

Harmonics generated by non-linear loads like

• Variable frequency drives (VFD)
• LED and CFL lighting
• Switch Mode Power Supply (SMPS) 
• SCR Temparature controllers Battery chargers & Rectifiers
• UPS

Impact of harmonic

• Overheating of transformers, motors and cables
• Reduction in available capacity of transformers and switchgear
• Reduction in efficiency of power generation, transmission, and utilization
• Aging of the installed electrical plant components and shortening of their useful life
• Spurious operations of fuses, circuit-breakers and other protective equipment
• Overloading, overheating and failure of power factor correction capacitors, distribution transformers and neutral conductors.

Harmonic study
The harmonic content varies from one installation to the other. This is based on the type of loads as well as the location of the loads in the power distribution system. A proper power quality audit of the site has to be conducted to understand the harmonic distortion levels in terms of current and voltage. The typical audit will document parameters to help propose the right solution to reduce the harmonics.

Reference standard for harmonic study

• IEEE Std. 519-1992: IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems