VFD Harmonic caused drive failure and Arc Flash


VFD Harmonic When VFD drive is sizeable or many, the excessive heat and power surge due to VFD harmonic generated high waveform distortion causes drive failure and unwanted tripping. Read this case study how harmonic filter for VFD solved the problem including an arc flash incident whose root cause detailed in another webpage "harmonic filter powerful with super tuned specification". VFD Harmonic forced a power plant to shutdown due to power quality failure. Starting with drive tripping it blasted switch gear, bus bar & electrical panel. This IPP with a 25mw, 11kV, 50Hz power plant and 5000TCD sugar milling unit had completed its first anniversary without harmonic problem. But during 2nd year's operation, it started-off with a massive blast of a 6300A Air Circuit Breaker (ACB). It was at the incomer of an electrical panel. The 415V PCC panel was supplying to sugar plant's process load. There were two such PCC panels connected through a 6300A bus-coupler for the boiling house loads. It had several variable speed drives (VSD). In a span of next 4-week, it sequentially blasted several other switch gears- ACBs and MCCBs. In yet another blast it caused pitting along 6300A double circuit bus bar. It was running at the top-horizontal position inside electrical panel. That also caused 6nos holes at the side cover of electrical panel, as if each bus-bar end had fired a bullet piercing through the panel's metal cover. The power plant's auxiliary VFD loads were powered through a double-secondary transformer. It's earth-pit started boiling surrounding water. A VFD drive's IGBT card failed. It belonged to a 585 kW boiler feed water pump (BFP) motor. Onsite power quality harmonic analysis revealed an unstable power system zone supplying to this industrial co generation power plant along with a CMV issue. Harmonic Filters, one each at the double secondary transformer supplying to the power plant Aux VFD drives, were installed in the year 2013. In-addition a large 2400A harmonic filter was installed at the sugar plant's process drives' panel as in Fig.1. These measures eliminated all electrical blast and VFD drives' card failure issues both with the power plant's auxiliary load and sugar plant's process drive panel. Further in the year 2014, 4nos Harmonic Filters were installed individually at sugar Mill drive 1 to Mill 4, each with one 560kw, 690v, VFD drive for reducing harmonic stress with its sugar milling units and thereby enhancing its crushing capacity by 30% to 6500tcd. Another 11kv harmonic filter was also installed at the 2x850kw, 6P, 11kv SRIM Fiberizer drive for energy conservation. Once again another unusual problem surfaced unexpectedly but this time only with the Mill-1 VFD drive and the root cause of that is bound to change the way we design and engineer dielectric insulation protection with our equipment and electrical panels. Furthermore, the improved power system operative conditions facilitated in increasing productivity sustainably with congruous reduction in the plant's SEC, the specific energy consumption, in terms of kWh/Tons by 15%. It also reduced the power plant's synchronous generator's operating temperature between 3 to 5oC, and enabled additional power export into the 33kv grid.

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