MooseFET wrote:
Till the dragon flies swarm in and start eating the mosquitos. Some
of the dragon flies are bigger than the birds.
[.....]
They are amazing things to watch. They can move any which
way change direction in an instant. They seem to work a lot better
than anything we can build.
The most amazing thing about dragonflies is when they land, and line
up at a 45 degree angle, like miniature bi-planes, all in the same
color.
I've seen that same sort of thing too. I think it must be the first
step in the mating or something. They expend everything they have
when they do mate.
The tiny ones are a different type. When the dragonfly emerges from
the water it is nearly or perhaps fully its final size. In the water
they are a complete terror in small scale. They are a jet powered
predator with a special set of jaw parts that can reach out and grab
small fish and tadpoles etc.
Actually no, they preferentially eat insect larva like mosquitoes, and
crane flys. Only very few dragonfly species are large enough to eat
small tadpoles or very small fish.
You must have very wimpy dragon flies where you live. I've seen them
pull a duck under water. They are huge nasty things. Watch out for
them if you go swimming.
[....]
[.... ESD etc ...]
A lot of plants still have an undersized neutral on their three phase
panels.
I wouldn't put "still" in there. I'd bet that one built today would
have the same problem. Perhaps it would be even worse today because
of the price of copper wire.
Actually no, recent chances in the NEC in 2002 and 2005 mandate larger
neutral and grounding conductors. Competent reviewers and inspectors
will insist on things being built to code.
This is good to know. I'll have to get a copy.
I've seen how little looking the inspector did. I've seen many things
that could not have been to code on the day they were built. What the
inspectors catch may get fixed but with the high price copper I'd
still expect people to make the bet. In the past it wasn't a
violation of code today it would be a bet on the part of the
contractor.
[....]
Delta windings in power transformers pretty well wipes out third
harmonics and reduce other odd harmonics, but much of the harmonics
are even order. For that you can use active harmonic correctors.
I don't think that is true. The 3rd harmonic usually starts out in a
single phase circuit. This means that it ideally ends up in the
ground return going to the local transformer where it all cancels
out. A large part of it ends up in the soil, taking the long way
around. As a result, near the local untilities 3 phase power lines I
always see more 180Hz than the 60Hz. The 60Hz cancels nearly
perfectly at even fairly small distances.
Measurements near Moffet field in the SanFransisco area usually come
up with about 3 times as much 180Hz than 60Hz radiated. On the far
side of the bay far from power lines, the ratio is about 2 to one.
Down near Morgan Hill there are some good sized transmission lines.
You have to go south of them by quite a ways if you want to find a
180Hz field under about 20nTp-p. Within the bay area it is fairly
hopeless.
[1] I really wish that a different term was used for the harmonic
content part of power factor and that power factor was reserved for
phase.
For people that care to use correct terminology it is, it is the twits
that keep confusing it.
PFC for power supplies is not about phase angle. Everybody seems to
call it PFC.
[....]
Any properly designed and used 4 terminal milliohmeter should be able
to do that, even at 100 foot lead lengths.
I wasn't after the type of meter. I was after the points being
measured.
At about 1.9mOhm per foot (IIRC) that only works out to a 50 foot
length of #12 wire. From bench to bench that would be reasonable.
From bench to ground rod it may not be. Between two ground rods at
any distance it wouldn't be for certain.
