In a recent contract undertaken at a major power generating facility, systems integrator Systems Automation & Management were contracted to provide a large VSD solution with minimal harmonic current distortion to the mains supply. The Danfoss VSD usually conforms to most harmonic distortion standards applicable to the drives market, as the units all have DC link chokes as standard in all product ranges available.
Harmonic distortion can cause significant damage to electrical equipment, especially where larger drives are installed, therefore some customers have far more stringent harmonic distortion standards, and would require that the distortion effect be minimised by the drive supplier in the way of extra filtering. This is in addition to the protection offered on the standard product.
It was found that the harmonic distortion on site was higher than the levels acceptable to the power generating facility. This meant that Danfoss needed to offer a solution to overcome the high distortion levels.
Specialised and sensitive applications will require additional mains conditioning and for this purpose Danfoss has a range of drive filters that reduce the harmonic line current distortion throughout the drive's operating range. These filters are suitable for new as well as retrofit applications irrespective of the drive OEM (original equipment manufacturer). It must be noted harmonic line currents rise significantly when a drive runs a motor at a lower load/speed than it is rated for.
On this particular application, three Danfoss Advanced Harmonic Filters (AHF)10 were retrofitted to each of the drives and this achieved suppression down to less than 10% harmonic line current during operation at all loads. This performance is better than a drive that has a 12-pulse converter and specialised power supply needs. Danfoss product manager Dave Dyce explained, "These are the first filters of this kind to be installed in South Africa. Harmonic filters are an economic alternative to using active converters and must be seriously considered with any large drive application."
The power generating facility is now able to reduce the levels of harmonic distortion to a desirable limit, thereby reducing the risk of damage to electrical equipment and consequential production losses.
Danfoss can now also provide AHF5 filters, which further reduce harmonic line current levels to less than 5%, making it comparable in performance to that of an 18 pulse converter which also requires specialised power supply components.
Both the AHF10 and AHF5 filters are available as off-the-shelf items from the Johannesburg-based Danfoss head office. These filters will still perform to specification with levels of up to 2% imbalance and 2% background distortion on the mains supply. The filter will also keep distortion under the limits at reduced loads and speeds.
The management team at Danfoss recognises the importance of a good quality power supply for all, as well as the hazards associated with harmonics reflected back to source. They regard as important the need to reduce harmonic components with every large VSD installation, in order to maintain the very best quality supply to electrical equipment as well as preserve the mains supply for all other users.
The MCT31 Danfoss harmonics calculator can be downloaded from the company's website, www.danfoss.co.za/drives - this is able to determine the level of harmonics within an electrical system.
For more information contact Dave Dyce, Danfoss, 011 803 8390, [email protected], www.danfoss.co.za
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