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Re: The worlds Largest Coil
<big snip>
>
>I note that these sorts of resonance problems cause HUGE problems for the
>folks running long distance power lines, which are a resonant circuit (of
>sorts), and have fairly high Q. Switching transients of 4 or 5 times the
>line voltage are not unheard of.
List
This is one reason why I'm generally wary of measuring mains voltages with
other peoples hand-held multi-meters. Although the mains supply voltage is
usually held at a nominal level (say 240 volts here in NZ), lightning
strikes and swtiching transients can cause momentary surge voltages far
greater than 1200 volts. I have actually seen a cheap multi-meter catch on
fire while measurements were being made on an industrial motor supply circuit!
Obviously the people who service high-voltage high-current electrical
equipment need test equipment that protects them from injury, so an
equipment rating standard called IEC 1010-1 was created. It defines four
overvoltage levels - CAT I, CAT II, CAT III and CAT IV.
If you are going to buy a new meter to measure mains voltages and/or
currents, I would recommend you spend a few extra dollars and buy a IEC
1010-1 rated meter. A 600V CAT II rated meter will be ok for mains
measurements on domestic outlets but a 1000V CAT III rated meter will be
required for any HVAC or distribution board work.
If you can't afford a good meter, then you might like to consider
hiring/leasing one. Since I make mains measurements infrequently, I hire a
Fluke 87-III (1000V CAT III) from a local hireage firm for 95NZD (approx
44USD) per month when required. I use an older (but still good) AVO
analogue meter for all other electrical measurements.
Safe coiling,
Gavin Hubbard