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Chuck O'Donnell
G.Sibiski's question continued...

I have researched some information in the past dealing with the effects of EMF off of high voltage equipment, and distortion of video monitors. There are enclosures available that are manufactured from an alloy sheetmetal refered to as MU-Metal. But his concerns are with preventing any EMI from the frequency drive from penetrating the office area. Physically moving the drives will be expensive due to the confines of the mechanical room. Would you have any suggestions as to additional shielding or installation procedures which mave have been overlooked?
Thanks,

G Sibiski,


Dear, G Sibiski,

Regarding the computer monitor interference problem:

Radiated electromagnetic interference can certainly be a nuisance. Also, RFI which is conducted on the power lines can cause similar problems. And, in addition to drives, other electrical devices that include rapid switching devices can also contribute to this type of problem. Presumably you have isolated the problem to the drives by confirming that the problem does not exist when the drives are not running.

ABB is the worlds largest manufacturer of AC drives. Europe has passed some very serious laws to address these problems and, to provide drives in Europe, as ABB does, their drives essentially must conform to certain European directives. Most of their current drives have some degree of compliance.

We have an ABB technical guide on this subject titled EU Council Directives and Variable Speed Drives that we would be happy to send to you. It is very informative and will provide some guidance and most likely a solution to the problem. Please advise your mailing address.

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Dear Chuck,

I have noticed many motors now advertising class 'F' insulation as a feature. Doesn't that mean the motor just runs hotter?

F.W.P. Trumbull, CT

Dear F.W.P.,

Insulation Class is the designation of insulation system temperature rating. This rating is based on the thermal endurance of a particular insulation, or how long an insulation system lasts at a certain temperature. The four insulation classes used on motors and generators are Class ‘A’ (105 C), Class ‘B’ (130 C), Class ‘F’ (155 C), and Class ‘H’ (180 C).

It is beneficial to have a higher insulation classification if the motor operates within a lower classification range. It is generally accepted that for every 10 C drop in winding temperature insulation life will double. For example, if a motor had a Class ‘B’ insulation and operated in a Class ‘B’ temperature range, you could expect the insulation to last approximately 20,000 hours. The same motor with Class ‘F’ insulation (operating in a Class ‘B’ temperature range) would have an approximate insulation life of over 100,000 hours.

NEMA MG 1-1.66 and 1-12.43 were referenced for this article.




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