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23 September, 2013

10MW power converters interfere with wired telephones over 12 miles away

To cope with increased North Sea oil production, two new pumping stations with 6 MW adjustable speed induction motor drives were built and installed in Scotland, one in Netherly and one in Balbeggie. Soon after commissioning the local power utility and the telephone company received a flood of complaints. Geographically the complaints came from concentrated pockets spread over an area up to 12.5 miles away from the 33 kV overhead supply lines feeding the drives. A payphone over 4 miles away from the power line was noisy enough to be almost unusable, whereas just across the street a householder's telephone was relatively unaffected. Other symptoms included loss of synchronisation on TV sets (rolling pictures) and ringing on the supply to fluorescent lighting circuits.

Although the drives had been designed to, and met the supply industry's G5/3 harmonic limits, the problems turned out to be with higher order harmonics than it covered, up to the 100th in fact (i.e. 5 kHz). The problem became a public relations nightmare for all involved, and culminated in questions being raised at Government level. Remedial EMC work was urgently required and was in fact accomplished, although under extreme difficulties because the cost of any downtime of the oil pumping stations was so high.

(Taken from: “Harmonic filtering of large induction motor variable frequency drives” by M J V Wimshurst of Hill Graham Controls, High Wycombe, U.K., and Allan Ludbrook of Ludbrook and Associates, Ontario, Canada. Presented at the 7th International Conference on Harmonics and Quality of Power (IEEE) at Las Vegas, October 16-18, 1996, pages 354-359 in the Proceedings. Also presented at the "Sixth International Conference on Power Electronics and Variable Speed Drives", Nottingham, UK, 23-25 September 1996, IEE Conference Publication No 429, pp 24-29,

Originally published in "The First 500 Banana Skins", Nutwood UK Ltd 2007, Email for a copy, cost around £10 plus p&p.


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