- Harmonic Compensation Capacity
Harmonics are typically generated by non-linear loads such as Variable Frequency Drives (VFDs), DC Drives, induction heating systems, UPS systems, battery chargers, arc furnaces, computer power supplies as well as LED and fluorescent lighting. The harmonics are an undesirable consequence of using such devices which lower power factor, reduce efficiency, develop circulating currents and cause electronic devices to operate incorrectly and fail prematurely.
The electrical power system in the United States are designed to operate at a frequency of 60 Hz. The harmonics generated by a typical “6-pulse” non-linear load will reflect the highest amount of energy between 300 and 780 Hz. Which is also known as the 5th and 7th order. Since the consumers are generating the harmonics and making the electrical grid inefficient, the utility companies are starting to enforce maximum harmonic values of energy that can be reflected back onto the grid by the consumer. In the United States, this is often referred to as the IEEE-519 standard.
When electricity is generated, the current and voltage sine wave develop is rather close to perfect and has a very low harmonic distortion content. Non-linear loads consume energy in such a way that the current consumption does not follow a sine wave. Since it is repeating, it is considered a harmonic rather than a transient which does not repeat. The current waveform reacts with the impedance of the power network and, using Ohm’s law, a distorted voltage waveform is developed.
It is the voltage distortion harmonics which cause the most operating problems such as nuisance tripping of breakers and electronic equipment to malfunction. We typically lower, not eliminate, the current harmonics which produce harmonics. Our goal is to limit maximum voltage distortion to a level that mitigates equipment malfunctions and/or meets or exceeds the IEEE-519 standards. It needs to be restated that we do not wish to eliminate the harmonics but desire to reduce the level of harmonics to eliminate the harmonics would be very cost prohibited as well as unnecessary.
- Harmonic Compensation Spectrum
The standard 6 pulse VFD is designed with 6 diodes which convert energy from alternating to direct current (AC to DC). The harmonic spectrum will develop the highest harmonic energy in the 5th and 7th order or 300 and 420 Hz respectively. As can be seen in the graph below, the harmonic energy falls off rather fast as the “orders” get higher.
Multi-pulse drives are derivatives of 6 pulse drives are typically 12, 18, 24, 30, 36 pulse converters. The advantage of multiple pulse drives is that the greater number of pulses a drive has, the harmonic levels are reduced to a greater degree. The drawback to such an installation is that an expensive and large multi-pulse transformer is required as well as an increased footprint and extra diodes are required. Active Front End drives (AFEs) are another choice to reduce harmonics but it reduces the reliability as well as greatly increases the price over a standards 6 pulse drive.
- More than just Harmonics
Besides providing correction for harmonics, our filters can correct for power factor (reactive power), Unbalance, Flicker and even resonance. Unbalance and flicker are often addressed on the medium or high Voltage grid.