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60Hz resonance - additional info
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From: Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent: Monday, February 23, 1998 8:52 PM
To: tesla-at-pupman-dot-com
Subject: 60Hz resonance - additional info
All,
In my recent post I made some statements about system resonance at
multiples of the 60 Hz mains frequency. It had been a while since
the experiment and it turns out I didn't have the details recalled
clearly and completely in my mind when I posted. I have since polled more
brain cells and now have a more accurate account of the events.
I said:
>" I am more concerned on these bigger systems with
>keeping the sucker away from 60 Hz resonance in the power circuit, or
>resonance at multiples of 60."
All true but in fact I try to keep my low frequency resonance BELOW
the 60 Hz fundamental mains frequency.
I said:
>"On my twin I've recently substituted a nice little 9500-0-9500 center
>tapped, 4.5 kVA transformer(which worked superbly) with a single
>ended 16000V-at-10 kVA pig. I found that the system safety gap across
>the capacitor was suddenly going nuts, blasting frequenly over a 1.25 inch air
>gap. This had not occured before with the smaller, higher impedance
>supply transformer. I grabbed a audio signal generator and o-scope
>and determined that at 1/2 variac setting (just where the safety gap
>would start to blast) and above the pig went into
>high-Q resonance at within 4 Hz of the 6th harmonic of 60 Hz. "
I forgot an important detail. It turned out that this wild system resonance at
about 360 Hz was being excited, not by the 6th harmonic of the mains, but by
my rotary break which was setup to operate almost exactly 360 BPS by
chance at the time. The resonant rise on the output of the pig was
quite substantial, causing the safety gap across the capacitor to
fire like a machine gun. If I then increased my break rate to above 400
BPS, where the o-scope test had shown the resonance no longer
existed, all went stable and the safety gap ceased firing.
>" If I insert series R (1K ohms at 600watts) with the pig,
>this resonance is swamped out (verified by instrument measurements)
>and the safety gap firing is almost completely stopped. At least a
>very noticeable improvement was obtained.
The resistor went in the HV side of the pig (obviously). The improvement from
this damping was seen at the previously troublesome break rate of 360 BPS.
Hope this helps.
Robert W. Stephens
Director
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel: 1-519-925-1771 Fax:
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