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Topic Title: VSD Harmonics and temporary installation
Topic Summary: Can a 6-pulse VSD be used as an interim?
Created On: 17 November 2010 09:21 AM
Status: Read Only
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 17 November 2010 09:21 AM
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peterfile

Posts: 53
Joined: 17 April 2002

I have an application which requires a 30kW VSD for a pumping station. The power supply to the site is connected to the LV side of a local distribution transformer which is shared with a number of domestic properties.
We have instigated a harmonic survey on the PCC, and awaiting the results. The initial daytime harmonics appearing were relatively low, but the evening load could be very different.
Low harmonic VSDs are the preferred option, but since deliveries of VSDs are globally difficult at the moment, would a 6 pulse inverter be an acceptable interim solution until the LH inverters are fitted, so that the project is not delayed?
Just making sure the client is not drawn into a regulatory battle.
Thanks
Pete
 20 November 2010 11:04 AM
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peterfile

Posts: 53
Joined: 17 April 2002

Result of the harmonic survey identified that to use a 6-pulse inverter would exceed the G5/4 limits on the transformer. Although we could probably get away with it, there is still the risk of damage to someone else's equipment, so the client was advised that the project completion would have to be delayed.
 22 November 2010 09:44 PM
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Nedryerson

Posts: 38
Joined: 12 December 2009

Peterfile, I'd be surprised if a 30kW inverter required mitigation. Why not download a free calculator from Mitsubishi ?
 23 November 2010 08:42 AM
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peterfile

Posts: 53
Joined: 17 April 2002

The existing measured THD is already 3.8% peak - 3.7% on the 5th. With a limit of 4% for the 5th and 7th on the LV side, a standard VSD is unlikely to stay below this limit. We're definitely moving forward with an active front end, and we can live with the delay in delivery.
Couldn't locate a calculator off the Mitsubishi site, but I probably wasn't looking hard enough.
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