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For factories and industrial sites, controlling the cost of operations and equipment to protect margin is a priority. Replacing equipment before its time can increase capital expenses up to 15% and operations costs by as much as 10%. Implementing an appropriate harmonic mitigation solution helps avoid such costs.
Harmonics are unwanted currents that overload wiring and transformers, creating heat and sending interference over utility lines, which can incur higher fees. In industrial environments that operate a multitude of motors, unchecked harmonics can shorten equipment life, or at minimum, weaken equipment reliability. Harmonics can overload the electrical system, increase power demand, damage equipment, and shut down systems.
A comparison of harmonic mitigation solutions
AC line reactors and DC link chokes for drives help smooth out the current flow to variable frequency drives (VFDs), expanding the flow and reducing amplitude to partially mitigate the harmonics. This is the most reasonably priced and compact solution, but it’s less effective at mitigating the harmonic distortions in total. This solution is best for applications where harmonic mitigation isn’t the first priority, but there’s a need to filter the heaviest distortions.
A 12-pulse arrangement is the most efficient for controlling power loss and is suitable for larger drives. This solution requires a 30° phase shift transformer and a six-pulse converter bridge connected to each of the outputs. The 12-pulse solution is superior in efficiency and harmonic mitigation, but it’s neither simple to implement nor the lowest price option.
A passive filter consists of reactors and capacitors set up in a resonant circuit configuration that’s tuned to the frequency of the harmonic order to be eliminated. Since a passive filter only addresses one operating point at a time, it’s a low-cost solution, but it’s not efficient at partial loads. With the unique disadvantage of low power factor at partial load, a passive filter risks causing resonances within the grid.
An active filter works by measuring the harmonic currents and generating a harmonic current spectrum in phase opposition to the measured spectrum. It requires over sizing to compensate for decreasing power factor. An active filter is a good solution at a moderate price for mitigating the harmonics of several drives operating in parallel on a network.
A low harmonic drive configuration consumes energy like a normal inverter (converts DC power to AC power). It allows the system to adjust the waveform of the mains current and avoids the impact of harmonics and idle power. Requiring more overall space, a low harmonic drive falls in the midrange in terms of cost. Compared to an active filter, the low harmonic drive is simpler and provides better value for the money, making it an effective solution.
In summary, the line choke solution is the best option for applications where the heaviest distortions should be filtered, but harmonic mitigation is not the first priority. The active filter is a good solution to mitigate the harmonics of several drives in parallel operating on one point of coupling. The 12-pulse solution is the most efficient, but also the most complex. For applications where harmonic mitigation is very important, the low harmonic drive offers the best solution.
Making the right choice
The best harmonic mitigation solution depends on the nature of the load and the power demand of connected equipment in an industrial environment. Selection factors to consider are: