Minimize disturbances and maximize energy savings

Electrical equipment disturbances, such as unstable generators, flickering lights, UPS nuisance tripping, and erratic instrument readings, may be due to electrical harmonics. Harmonics are disturbances in electrical networks that affect both current and voltage waveforms. Many municipal facilities have older networks in remote locations where power quality may be poor to begin with. This adds to the impact of harmonics.

The overall net effect of harmonics, if left unmanaged, is an unstable system and increased energy costs. Controlling these electrical harmonics provides a more stable and reliable system whether you’re on utility power or generator power. This reduces energy costs and prolongs the life of the system.

There are many ways to reduce harmonics in a facility. Some solutions are designed to fix or repair the distortion after the harmonics are created, such as passive or active filters. Others are designed to minimize the production of harmonics, such as ABB’s fourth generation ultra-low harmonic (ULH) drives. When ULH drives are controlling your equipment, distortion is minimized and unity power factor is maintained. Additionally, these compact drives use less space even when installed in panels. ABB’s experts can help you determine the best solution for your facility.

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Harmonic mitigation strategies

Essentially, there are many options for handling harmonics, including reduction, cancellation, and diversion.

By adding inductance, you can achieve minor harmonic reduction. Drives with active front end (AFE) technology further reduce harmonics to meet IEEE-519 requirements. Reduction can also be accomplished by using closed loop active filters that inject an ‘anti-harmonic’ current spectrum that sums to zero (or client specific values) with the load harmonic currents. This is an engineered solution that can allow you to manage harmonics throughout the facility. What remains is a ‘clean’ current on the mains supply.

Multi-pulse drives (or harmonic filters) provide an antiquated technology for cancellation of harmonics. Diversion technology involves a standard 6-pulse rectifier with a passive harmonic filter. Currently, multi-pulse drives tend to be used if the required transformers are already on-site.

The most basic technique for harmonics management is to use line reactors, sometimes known as chokes, fitted inside or outside a drive. This is called reduction, because with correctly sized AC/DC impedance in a standard 6-pulse drive, harmonics levels can be reduced to where they cause fewer problems. Another approach to reduction is to use an active rectifier. This has an inverter working “backwards” onto the mains supply, treating the mains as it would treat an electric motor and controlling the current flow more effectively, resulting in essentially no harmonic contribution.

Cancellation is an older approach

Cancellation has traditionally been achieved using an 18-pulse drive. Total harmonic load is divided between several isolated sources sharing a common primary supply (via a 3-winding input transformer). An 18-pulse drive uses three sources, with each source phase-shifted 20 degrees relative to the other. A more modern approach is to use an ultra-low harmonic drive.

Ultra-low harmonic (ULH) drives draw clean current

An ultra-low harmonic (ULH) drive uses insulated-gate bipolar transistors (IGBT) as the rectifier and reduces the harmonics generated. This ULH technology enables drives to significantly limit the production of harmonics, eliminating any need for further reduction. Using VFDs with ULH technology, provides more stability and reliability for electrical systems and achieves the goal of ≤ 5% THiD at the drive input terminal to meet IEEE-519, regardless of speed or load.

We are experts in managing harmonics - Let’s talk

Although the subject of harmonics can be confusing, our experts are available to work with you to determine the best strategies to address harmonics in your facility. Adding ABB’s ultra-low harmonic drives can help manage harmonics to ensure the highest overall stability and productivity in your facility.

Passive filter can be less flexible and effective

A passive filter works by diverting harmonics away from the affected equipment. This is a simple solution with a few drawbacks. For example, harmonic reduction is not linear and decreases as the load decreases. Also, at low load, it may require a capacitor disconnect to protect the capacitors against overvoltage and allow for stable generator operation, which limits its harmonic mitigation.