120V-20Kac Transformer source

[John Larkin]

like the header said.
i am looking for a source to get
120V in 20K AC out transformers at
60 Hz. to generate no more than 20 Ma
NON-Auto Type both leads available
at the secondary.

we are going to be building some
hi-pot units and would like these
transformers .
thanks.
P.S.
would be nice if they would have a low
voltage tape from the secondary for a
voltage level monitoring circuit but
need absolutely needed.

Sounds like a neon sign transformer to me.

John

 

[Jamie]

like the header said.
i am looking for a source to get
120V in 20K AC out transformers at
60 Hz. to generate no more than 20 Ma
NON-Auto Type both leads available
at the secondary.

we are going to be building some
hi-pot units and would like these
transformers .
thanks.
P.S.
would be nice if they would have a low
voltage tape from the secondary for a
voltage level monitoring circuit but
need absolutely needed.

 

[John Fields]

Sounds like a neon sign transformer to me.

 

[John Fields]

like the header said.
i am looking for a source to get
120V in 20K AC out transformers at
60 Hz. to generate no more than 20 Ma
NON-Auto Type both leads available
at the secondary.

we are going to be building some
hi-pot units and would like these
transformers .
thanks.
P.S.
would be nice if they would have a low
voltage tape from the secondary for a
voltage level monitoring circuit but
need absolutely needed.

---
Have you never heard of Google?

http://www.google.com/search?hl=en&ie=UTF-8&q=High+voltage+transformers

will get you something like 185,000 hits.

 

[Jamie]

well maybe a neon sign transformer could be used but
its needs to be put in a Hi-pot unit.

 

[John Larkin]

Then put an autotransformer ahead of it. They run hot anyhow.

John

 

[John Fields]

Then put an autotransformer ahead of it. They run hot anyhow.

 

[Rich Grise]

well maybe a neon sign transformer could be used but
its needs to be put in a Hi-pot unit.

If you're making a hipot, you don't want any more
than maybe .1 mA, and preferably more like 5 uA, full-
scale. This is also called a megohmmeter or megger.
Is it possible to make an adjustable flyback from,
say, < 100V to 20 KV?

20 KV at 20 mA will kill you right now. I've heard
that it's so fast that it even beats your reflexes -
you're dead before you can flinch.

Do not ever under any circumstances have allow
equipment capable of voltages/currents like that
that people will be holding in their hand while it's
in use.

I'd say, adapt a TV flyback, and be sure to use at
least 1M series resistance.

Good Luck!
Rich

 

[Rich Grise]

They run hot at 15 mA. If you're running that kind of
current out of a hipot, you're running a death trap.
Put a 10M resistor in series to limit the current to
1.5 uA, and then I'd consider it usable by a competent
tech. And I'd imagine that when they pot the thing,
the primary gets just as much insulation as the secondary,
so it probably wouldn't mind running overvoltage at all,
as long as the core doesn't saturate, and you keep the
VA down.

Good Luck!
Rich

 

[John Fields]

They run hot at 15 mA. If you're running that kind of
current out of a hipot, you're running a death trap.
Put a 10M resistor in series to limit the current to
1.5 uA, and then I'd consider it usable by a competent
tech. And I'd imagine that when they pot the thing,
the primary gets just as much insulation as the secondary,
so it probably wouldn't mind running overvoltage at all,
as long as the core doesn't saturate, and you keep the
VA down.

1. You can't get 15mA out of a 20mA NST at 15kV,
you can only get it with 0V out. I.e.,shorted secondary.

2. 15000V/10000000 ohms = 1.5mA

3. You imagine?

4. It probably?

5. Any more guesses?

 

[Jamie]

i wasn't planing on allowing the full load to the
test fixture, i just want that load factor to
prevent over load on the transformer because
there are 2 things are taking place, one is
the material passing through the beed box covers
a large area and thus large amounts of capacitance
is a problem which loads its and the material is
passing at a high rate of speed.
the units we have now simply turn the voltage off
as soon as a short is detected and an alarm is sounded.
as far as 20 Ma being a problem , i can see it could be a
problem if it was constant but if what you are saying is true
then we would have had a good many people dead by now from operators
not discharging a high capacitance real of wire with lots
of footage on it after a test. some times they don't allow for the
crow bar to operate.
most of our older units have a simple current fold back using a
incandescent lamp.
Like i said, i don't plain on delivering that amount of current
at that voltage, i would just looking for a transformer that could
coast. in the units i am designing there will be current limited already
in place and what i am doing measuring the output voltage to slowly
apply the needed current which will bring the required voltage needed
to the set point. this way on low drain applications the current will be
very low..
and upper apps will be increase as needed to a max set point which would
constitute a a short out in any case. the circuit actually uses a choke
on the return side for the ground on the output and the sensor pulse
is used there to fire off an alarm because most of the time a pin hole
will generate the short spike you need., the 60 Hz will be shunted by
the choke.

 

[legg]

the units we have now simply turn the voltage off
as soon as a short is detected and an alarm is sounded.
as far as 20 Ma being a problem , i can see it could be a
problem if it was constant but if what you are saying is true
then we would have had a good many people dead by now from operators
not discharging a high capacitance real of wire with lots
of footage on it after a test. some times they don't allow for the
crow bar to operate.
most of our older units have a simple current fold back using a
incandescent lamp.

There is no telling what actual voltage is stored on the wire reel's
capacitance, at the time it is disharged accidentally by the operator
(anywhere from zero to +/- AC test peak). Depending on the
capacitance, this could represent a serious hazard.

I think you would find that one injury was sufficient proof of
supervisory incompetence.

How does the operator bypass the crowbar, and why haven't you
corrected the safety feature so that it cannot be bypassed?

RL