Since the beginning of 21st century variable frequency drive (VFD) has become the preferred choice of controlling elevators and escalators. It replaced the erstwhile legacy of a motor generator (MG set) system which had been used practically through the entire 20th century. It used an AC motor to drive a DC generator for feeding power to a DC motor in a configuration called the Ward-Leonard system. The VFD drives have considerably reduced the lift room footprint, simplified commissioning, and improved energy efficiency. Further the ride quality has been improved significantly by employing fourth quadrant operation in the VFD drive for regenerative breaking.
VFD drives are the primary source of harmonic distortion in a building's power system. It generates a significant percentage of 5th and 7th order current harmonics which in interaction with the building's electrical system impedance creates voltage harmonic. Depending upon harmonics distortion these industrial type 5th and 7th harmonics primarily affect the elevator's position control mechanism and cause uneven floor landing. The elevator floor level does not align with its landing floor level. If harmonic distortions are high it causes failure in the VFD drive and electronic cards. Over the past 25years Encon Tuned Harmonic Filters have been providing comprehensive solutions to above problem.
VFD drive during regenerative breaking cycle creates significant percentage of 3rd harmonic current that in addition to 5th and 7th harmonic currents. Today's buildings are filled with loads those predominantly generate third harmonic current like LED lights, myriads of SMPS based electronic gadgets and computerized equipment. Unlike phase currents 3rd harmonic current also called zero sequence current or triplen harmonic current, does not get cancelled but trebled at neutral. It's all pervasive and with any infirmness in the building's neutral/ ground system; it's a serious electrical fire risk that could strike as like a bolt from the blue. Triplen harmonic currents easily penetrate into the elevator's control system and confuse its functioning. Elevator doors randomly get stuck and does not open until power reset. Its operation becomes erratic, and with a confused control system it lands at a wrong floor. Encon Triplen Harmonic Filter has been providing comprehensive solution to above problems.
That apart, Encon harmonic mitigation solutions improve power quality by reconstructing harmonically distorted waveform back into sine wave, balance 3phase voltage and currents and is an effective surge suppressor. It effects energy conservation, extends motor life and elevator performance, and protects sensitive equipment in elevator and escalator applications.