High voltage arc gap design

[David Frantz]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top View
http://bayimg.com/hajGBaAbm

Side View
http://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

 

[ScadaEng]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top View
http://bayimg.com/hajGBaAbm

Side View
http://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

Are there any signs of pitting, uneven surface area? If it ligitimately
arced once and pitted it may become more subceptable to lower voltages. I
would expect to see some sort of pitting showing there was in fact an arc,
otherwise I would suspect the arc detection circuitry. If it is pitted you
might try carefully restoring the surface with fine sandpaper or equivilant.

 

[John]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top View
http://bayimg.com/hajGBaAbm

Side View
http://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

Air breaks down at about 40kV per inch so you would expect a 3/4" spark gap
to flash over at about 30kV, so the 3/4" gap for a 32kV supply would seem
too small.

What does the transmitter manual say for setting up the spark gap?

Does this spark gap protect the power supply or is it at the base the
antenna?

 

[Jamie]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top View
http://bayimg.com/hajGBaAbm

Side View
http://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

is the point smooth and rounded like it should be?

Do you have Debris flying around like dust particles

is it possible you have rodents running around getting in there
and tripping it off? )

We deal with over 1 Mvolt units at work and one the problems is
sharp edges due to a valid arc at some point. Also, air quality
has a lot to do with it.

The round tip designed are more prone to this problem via the
ball tipped types.
Static build up in the air can cause a build up of electrons on the
tip and discharge much like how it does on an antenna which is why they
use ball tips to help reduce the static noise.

Just a thought..

http://webpages.charter.net/jamie_5"

 

[Ecnerwal]

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Not using a dry gas certainly adds to the variables.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

You might check for any surface quality issues on the electrodes - any
pitting, surface defects, or tendency to be pointy rather than rounded
and smooth will reduce the holdoff voltage. As drawn, it does not look
too terrible ("points" not actually pointy).

 

[Tom Bruhns]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top Viewhttp://bayimg.com/hajGBaAbm

Side Viewhttp://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

I'm curious--what's the radius of the tube and of the "points"? Where
are you (what elevation above sea level)? What's the temperature of
the air around the gaps? At sea-level and 25C, 0.75" is not enough
for 30kV and needle-point gap, and could be a problem if the radius on
the tips is too small; and of course, at higher elevations and higher
temperatures things get worse. Sams' "Reference Data for Radio
Engineers" has a section on gaps in the "Miscellaneous Data" chapter.

Cheers,
Tom

 

[mpm]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top Viewhttp://bayimg.com/hajGBaAbm

Side Viewhttp://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

Are you sure the arc event is happening at the base of the tower?
I am assuming this is an AM Station?
What make & model transmitter do you have? What type of antenna?

 

[ScadaEng]

Are there any signs of pitting, uneven surface area? If it ligitimately
arced once and pitted it may become more subceptable to lower voltages. I
would expect to see some sort of pitting showing there was in fact an arc,
otherwise I would suspect the arc detection circuitry. If it is pitted you
might try carefully restoring the surface with fine sandpaper or
equivilant.

If all else fails, replace the tecnology! Ditch the present spark gap and
install a proven type arestor. Check the usual vendors that utilities use,
G.E., Westinghouse to name a few. Buy an arrestor rated for the same
voltage, 32KV and all is good. No second thoughts of an original miss -
design.

 

[Don Kelly]

----------------------------

Hi David,

The other posters have already mentioned cleaning/polishing the surfaces
of the gap.

However, because the smaller radius electrode is positively charged, this
design will also tend to more easily form positive streamers, and will
thus be more prone to flashovers, than a simple sphere gap that uses a
pair of larger equally sized electrodes. If your drawing was approximately
to scale, the positive electrode diameter appears to be about 1/2 - 5/8"
in diameter, and the radius of curvature (ROC) is perhaps only ~0.75 cm.
When operated at 30 kVDC, the E-field at the tip of the positive electrode
is well above threshold to initiate positive corona, even if the electrode
is polished.

I suspect that the design is causing the problem. A sphere gap, using a
pair of 2" diameter electrodes will provide more consistent performance.
You can use a standard spark gap table to calibrate estimated breakdown
voltage such as or IEEE 4-1995 or the table below:

http://home.earthlink.net/~jimlux/hv/spherev.htm

Good luck,

Bert
--
***************************************************
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, Lichtenberg Figures (our "Captured
Lightning") and out of print technical Books. Visit
Stoneridge Engineering at http://www.teslamania.com
***************************************************

 

[James Arthur]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top Viewhttp://bayimg.com/hajGBaAbm

Side Viewhttp://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

All else failing, you could just measure the arc-over voltage: ramp up
high voltage through a resistor and see when and where she snaps.

That'll give you an answer that covers both questions of gap-setting,
and of gap & surface conditions.

Why wonder when you can measure?

Cheers,
James Arthur

 

[James Arthur]

I am an engineer working for a local radio station. One of our
transmitters has a repeating problem. For no apparent reason, it shuts
itself down, and the fault monitor indicates that an arc has occurred
at the transmitter's built-in arc gap. These appear to be nuisance
problems, as a thorough search has revealed no faulty components, and
the transmitter resets and goes back on the air when an operator
acknowledges the error. It will then run for several hours before the
problem repeats.

I have noticed that the transmitter uses an unusual arc gap design,
unlike any of our other units. The other transmitters use the
traditional round ball style arc gap. This transmitter uses a pipe and
point arc gap. I have constructed these diagrams to better illustrate
the problem.

Top Viewhttp://bayimg.com/hajGBaAbm

Side Viewhttp://bayimg.com/HAjgAAabM

It should be noted that the dielectric is ordinary atmospheric
pressure air, of varying temperature and humidity. The arc gaps are
set to the original manufacturer's specifications. Unfortunately, the
manufacturer has since stopped supporting this model transmitter.

Is the arc gap distance too small? Or is this arc gap design prone to
problems? None of the other transmitters have this problem. Any help
would be very greatly appreciated. Thank you for your time.

Oh, another question: any fried bugs piled up beneath this thing?

Cheers,
James Arthur

 

[Tom Bruhns]

Oh, another question: any fried bugs piled up beneath this thing?

Cheers,
James Arthur

;-) At that power level, they tend to vaporize rather than just fall
down dead. Used to have a problem with flies getting into the air-
variable neutralizing capacitor in a 1kW AM broadcast transmitter, and
vaporizing themselves while drawing a pulse of current large enough to
engage the over-current relay. Things got more exciting one day when
the protection circuits didn't. One of the results was a track melted
in the ceramic core of a 200W wire-wound resistor, molten ceramic
dripped down on the deck below. Didn't find the fly carcass, though.

Cheers,
Tom

 

[James Arthur]

;-) At that power level, they tend to vaporize rather than just fall
down dead. Used to have a problem with flies getting into the air-
variable neutralizing capacitor in a 1kW AM broadcast transmitter, and
vaporizing themselves while drawing a pulse of current large enough to
engage the over-current relay. Things got more exciting one day when
the protection circuits didn't. One of the results was a track melted
in the ceramic core of a 200W wire-wound resistor, molten ceramic
dripped down on the deck below. Didn't find the fly carcass, though.

Cheers,
Tom

Molten ceramic? That's good stuff! (But don't show this to Tim
Williams ;-)

Grins,
James Arthur

 

[JosephKK]

Feh. Examine the remains of three 20 kV lightning arrests mistakenly
connected across a 66 kV transmission line.

The fireball looked pretty cool too. But not to the lineman who was
standing practically underneath them closing the switch.

Ouch! That close, did that person live through that/et seq.?

 

[[email protected]]

| From reliable soft failure analog to crappy on/off digital.
| TV is the first frontier...

It is the tradeoff we get for more efficient use of the spectrum.

 

[[email protected]]

| Feh. Examine the remains of three 20 kV lightning arrests mistakenly
| connected across a 66 kV transmission line.
|
| The fireball looked pretty cool too. But not to the lineman who was
| standing practically underneath them closing the switch.

Wish you had videos/pictures.

Which kind of mistake was make? Wrong type of protectors? Wired the wrong way?

 

[Bill Shymanski]

| From reliable soft failure analog to crappy on/off digital.
| TV is the first frontier...

It is the tradeoff we get for more efficient use of the spectrum.

But how efficient is it to have several hundred megahertz of on-air
spectrum used for selling soap, anyway? Couldn't there just be one
station in each district running all the commercials and we could get by
with much less spectrum, power consumption and overall cost. I'm
surprised TV has lasted this long - every time I visit someone with
cable, a random flip through the available channels lands on a
commercial more than half the time, it seems. Maybe people like watching
commercials?

Bill

 

[Tim Williams]

But how efficient is it to have several hundred megahertz of on-air
spectrum used for selling soap, anyway? Couldn't there just be one
station in each district running all the commercials and we could get by
with much less spectrum, power consumption and overall cost.[? sic]

They have that, it's called QVC. And it's still not enough. ;-)

Tim

 

[JosephKK]

It was a portable substation, mounted on a semi trailer, used when it
was necessary to de-energize a fixed station for maintenance.

The portable unit has a high side switch, lightning arresters, high side
fuses, a transformer and low side breakers. The transformer has primary
and secondary windings with taps so that it can be reconfigured for
multiple uses. The substation maintenance group's responsibility is to
reconfigure it as we specified and then our crews connect and energize
it.

The substation group took a unit that had previously been used for a 12
kV to 4 kV step-down and rewired it for 66 kV to 12 kV. They did a turns
ratio test to verify the work and then shipped it.

Unfortunately, the lightning arresters consist of three 20 kV units per
phase, stacked in series. When this station had been used with a 12 kV
input, the bottom two sections of each phase were jumpered to ground.
Nobody noticed this (there's a whole story behind the problems at this
utility that lead up to this f*k-up worthy of another post.

When the unit was delivered, due to its construction, nobody could see
the jumpers. Our crew hooked it up and, Blam!

To answer Joseph's question, nobody was hurt. The handle of the high
side switch was accessible by swinging a panel up. Our (tall) lineman
bitched about this, having to bend over to operate the switch. But the
end result was that he was standing underneath a steel roof.

The portable substation was well grounded, so nobody got shocked.

It was quite an event. I was standing about 100 feet away. After the
initial fault, the system breaker (about 20 miles away) de-energized the
entire line. We stood there for a few seconds and, just as a few people
were thinking about walking up to it, someone shouted, "Wait for the
reclose!" Sure enough, the system operators had neglected to disable the
reclose operation. About 15 seconds later, another fireball.

Wow. Only one reclose? Or was some system monitor person really on
the ball?

 

[Fred Bartoli]

Paul Hovnanian P.E. a écrit :

But how efficient is it to have several hundred megahertz of on-air
spectrum used for selling soap, anyway? Couldn't there just be one
station in each district running all the commercials and we could get by
with much less spectrum, power consumption and overall cost.[? sic]

They have that, it's called QVC. And it's still not enough. ;-)

There's always the 'Jesus channels'. When they are able to keep their
transmitters on the air, that is.

You mean they resurrect it (the transmitter) every 33 year?