[Sneap] Reason for 400 Hz transformer need

[Gregory C. Harper]

Paul-

I have never had any problem using 60Hz service devices at 400Hz. Using 400Hz equipment at 60Hz, of course, presents a serious problem indeed with core saturation. The 400Hz units are nice because they are small and lightweight due to the much lower steel requirements. I designed and built an HV isolation transformer based on 400Hz operation for just this reason. Operating it at 60Hz is a disaster in about 10 seconds which, unfortunately, I know from experience.

I agree that additional hysteresis losses will occur in the core but, especially using a 120VAC 60Hz transformer loafing at 70VAC, those losses will be insubstantial. We have for longer than the 23 years that I have worked on our FN tandem used four Del HV DC power supplies rated for 120VAC 60Hz input service at the 120VAC 400Hz Georator supply for terminal steering with no ill effects whatsoever. In addition, I run a couple of 120VAC 60Hz VARIACS from the same power. When we use the terminal ion source, the power transformer used for the power supply for the RF section I am confident is also a 60Hz rated unit but you could verify that with NEC. I also have designed a 400Hz stacked voltage multiplier circuit for low voltage steering (of order +/-350VDC) which exclusively uses small 60Hz power transformers.

If your application is for impedance matching rather than power transformation I can see how you might run into some problems. However for power transformation the requirement that the impedances due to the self inductances of both the primary and secondary windings be much greater than the their respective circuit impedances will hold. Therefore, at 400Hz a 60Hz transformer can still be considered ideal.

Good luck with your project.

-Greg

Gregory C. Harper               Phone:(206) 543-4084 (Office)
Associate Director     
CENPA - Center for Experimental Physics and Astrophysics
University of Washington        
Box 354290                      email: gharper at u.washington.edu
Seattle, WA 98195-4290          FAX:  (206) 685-4634

On Fri, 22 May 2009, Jones, Paul wrote:

>
>
>
> Mr. Harper,
> The problem is that our Van De Graaf accelerator is (and has been forever) equipped with a 70VAC, 400 Hz generator on the HV head that is driven by the charging belt.
> If it becomes absolutely necessary, we may end up characterizing some 60 Hz transformer units for 400 Hz operation. Since they would be operating at approximately 7 times their rated frequency, we would have to be careful about additional hysteresis losses in the core, not to mention the drastically different impedance characteristics and possible resonances that may occur at the higher frequency. It will no doubt be an interesting problem to work on.
> If you have previous experience performing these kinds of tests then I would be very interested in hearing about it.
> Thanks,
> Paul Jones
> Engineer
> University of North Texas Physics Dept.
>
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