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Old 22nd Dec 2016, 2:05 pm   #21
threeseven
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Default Re: What was the highest HT voltage you ever experienced?

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400kV DC. 1kV/4000A thyristor bricks,
How big are those?!
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Old 22nd Dec 2016, 2:07 pm   #22
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Default Re: What was the highest HT voltage you ever experienced?

In my youth I serviced equipment for RF heating.
The power supplies varied but the larger ones were often between 5KV and 15KV and at 10 amps or more.
The smallest units used a voltage doubler from the mains, so about 700 volts.

The high voltage rectifiers were of various designs, one type had an ES cap like an electric lamp, with a top cap for the anode.
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Old 22nd Dec 2016, 2:19 pm   #23
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Default Re: What was the highest HT voltage you ever experienced?

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How big are those?!
About 50cm by 20cmm by 25cm, if I remember correctly with air blasted through the middle, stacked up in a very high building. You can see it on google earth, 51deg, 6min, 20sec N, 0deg, 58min, 32sec E.
Graham
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Old 22nd Dec 2016, 2:31 pm   #24
Malcolm G6ANZ
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Default Re: What was the highest HT voltage you ever experienced?

Craig, I worked for the NHS at the Bristol Oncology Centre. The machines were linear accelerators used to generate very high energy x-rays for the treatment of cancers.
The HT was produced from a pulse network from a big SMPSU giving 5Kv which was pulsed through a transformer using a thyratron to give the 40Kv for the magnetron. TheRF (3GHz and ~5MW peak power) was used to accelerate electrons to the target producing X-rays. Simple!

Malcolm
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Old 22nd Dec 2016, 3:46 pm   #25
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Default Re: What was the highest HT voltage you ever experienced?

Professionally I worked with some gear that used 30KV at about an amp average (though the peak current was rather more than that...)

For hobby stuff, 2.1Kv at about 350mA peak: a pair of 813s in parallel make a fine HF linear amp, I wish I'd kept it. The juiciest I've still got here is a grounded-grid 805 triode linear that has 800V on the anode.
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Old 22nd Dec 2016, 3:51 pm   #26
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Default Re: What was the highest HT voltage you ever experienced?

Apart from the 'everyday' 25Kv on CTV's, my most risky one was around 2.5 kV on the top of a pair of 813's in a MW AM transmitter (don't ask). This was in the mid 70's when I was a young fella and one day I switched off and without waiting for the voltage on the reservoir caps to drain away I stuck my hand in....wow, that packed a massive punch. It was like someone had hit me around the head with a cricket bat. Everything went red and the next thing I knew I was picking myself up off the floor about 10 feet away from the transmitter. Serves me right.
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Old 22nd Dec 2016, 5:11 pm   #27
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Default Re: What was the highest HT voltage you ever experienced?

Not radio or TV related, when I was at Mercury Communications we looked into using a pylon for a microwave link. Long before the cherry picker was at a useful height you could draw arcs off the cage and my hair was standing up.
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Old 22nd Dec 2016, 7:12 pm   #28
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Default Re: What was the highest HT voltage you ever experienced?

The highest I ever dealt with was 25 KV at about 30 milliamps it was an insulation tester at the transformer factory I worked in and the worst belt was from 3 KV mains derived supply at the same factory
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Old 22nd Dec 2016, 7:15 pm   #29
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Default Re: What was the highest HT voltage you ever experienced?

Wow! there's a few near misses there, that's increadable, so some of you are really lucky to be here then.

I know they always say, those 1936 television and radio table top models are lethel!

Paul.
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Old 22nd Dec 2016, 8:07 pm   #30
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Default Re: What was the highest HT voltage you ever experienced?

I once read an article about the use of earthed chain-mail type suits for live pylon working. I have never seen them in use or heard much about them since. I wonder if the Health and Safety people deemed it to be too risky? My worst experience of high voltage was actually quite recently, when I touched a 500VDC supply on a live open chassis mounted fuse holder while working on an amplifier. I actually felt shocked physically more than electrically and had to sit down for a while. It served as a good reminder on how dangerous the gear that we work on is.
Alan.
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Old 22nd Dec 2016, 9:06 pm   #31
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Default Re: What was the highest HT voltage you ever experienced?

I think pylon workers do wear conductive safety clothing to allow working on live lines.
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Old 22nd Dec 2016, 9:20 pm   #32
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Default Re: What was the highest HT voltage you ever experienced?

Although it's not the exact meaning of the post, by proxy are we not 'glamorising' who had the biggest, baddest electric shock? Some people reading this will have had friends who have lost their lives as a result of electric shocks. What the voltage is is immaterial, it's not 'big' to have withstood a high voltage electric shock, accidental as it may be. Electric shocks are dangerous and can be lethal, there's no bragging rights associated with the activity. Just my opinion.
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Old 22nd Dec 2016, 9:35 pm   #33
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Default Re: What was the highest HT voltage you ever experienced?

Hi all,

Got to agree with the last post (stevehertz), I think what we've all managed to survive is down to luck rather than good judgement! There has been some deaths in the past with service engineers working on microwave ovens, just because they are now so ubiquitous does not mean we should treat these things with contempt.

My own personal 'worst belt' was from a valve PA amp, where I managed to get one hand on the chassis and the other on the HT 500v from what I recall.
Not a great voltage of course but low impedence... I somehow was picking the amp up live and must have made good contact with both very hot hands - this was summer 1976!

SJM
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Old 22nd Dec 2016, 9:58 pm   #34
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Default Re: What was the highest HT voltage you ever experienced?

I don't think anyone is bragging, Steve. The OP asked what was the most terrifying voltage we had worked on and we have told our stories. We survived our foolish blunders by sheer luck, so maybe anyone reading our tales will take a lesson from our mistakes.
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Old 22nd Dec 2016, 10:45 pm   #35
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Default Re: What was the highest HT voltage you ever experienced?

Hi Gents, in "Supergrid" stations the operating voltage is 400KV in the UK ( about 230KV to ground) and the highest current rating of the breakers is in excess of 2000A.
Under fault conditions it is many times higher than that.
Grid workers often wear thermal suits to protect then from any sprayed, motel copper in case or an arc when a breaker opens.

The "small " 11 KV lines often seen in rural areas have a fault rating of 22KA for 5 secs. This can be sufficient to cause temp increases of over 200C in some of the busbars.

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Old 22nd Dec 2016, 11:12 pm   #36
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Default Re: What was the highest HT voltage you ever experienced?

My previous shed was a lean-to, the rear brick wall of which was the enclosure to an 8 Ton 11kv step-down transformer. In some ways it was my best ever shed as it benefited from never freezing in winter.
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Old 22nd Dec 2016, 11:28 pm   #37
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Lightbulb Re: What was the highest HT voltage you ever experienced?

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Originally Posted by threeseven View Post
I think pylon workers do wear conductive safety clothing to allow working on live lines.
This reminded me of this. Though I have feeling that I saw it somewhere on this forum first…
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Old 23rd Dec 2016, 12:07 am   #38
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Default Re: What was the highest HT voltage you ever experienced?

Hi Steve, hi Andy,

no i didn't want it to turn into a glamerising excersise, i think i inervertably perhaps used the wrong word when i said "terrifying" what i ment was, or what would of sounded a lot better was "suprisingly high HT voltage you ever came accross"

Meaning, did you encounter an exceptionly high voltage that shouldn't have been the case, perhaps due to a fault that you hadn't traced yet. But then, it's sort of sliped onto these other verious pylon stories, wich are very interesting, and truley amazing, but yes perhaps we should also bare in mind other factors

And yes that's a very good point, lets hope that anyone reading this (and there will be many)
lets hope it will give a good insight, as to the many dangers there are all around us.

And of course, more inportantly, all our hearts would always go out to anyone, who has suffered tragady in this way.

Paul.
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Old 23rd Dec 2016, 12:13 am   #39
threeseven
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Default Re: What was the highest HT voltage you ever experienced?

Yeah, I've seen that one too, there is also one showing UK workers doing the same thing. It looks so dangerous!
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Old 23rd Dec 2016, 1:44 am   #40
Stylo N M
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Default Re: What was the highest HT voltage you ever experienced?

You certainly need your wits about you, to do that job that's for sure.

Paul.
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