A rather nice German website

[ppppenguin]

A posting in the Electrokinetica forum brought me to this website. I used google translation since I know very little German.
http://www.hts-homepage.de/hts-homepage.html

This set of pages has some very nice mercury arc photos. Follow the yellow arrows for navigation.
http://www.hts-homepage.de/Klingerpark/Klinger1.html

[raditechman]

I agree Jeffrey, nice mercury arc rectifier pictures,especially the slow motion one! I don't think I have come across a 3 phase mercury arc rectifier before. We had some supplying the carbon arc lamps and an organ console lift DC motor when I worked in a cinema in the 1960's but I'm sure they were single phase.
John

[ppppenguin]

Originally Posted by raditechman

...I don't think I have come across a 3 phase mercury arc rectifier before....

3 phase probably more common than single phase. I have one - see my website. There are also pictures on the Electrokinetica website. The Energetica Museum in Amsterdam has a couple. Picture attached taken by Lucien Nunes of a 3 phase MAR in service. I think he rescued that one and its friends.

[Don Collie jnr]

I briefly [I`ll be back] visited the site and noticed some of the valves were garanteed for 100,000 hours. I`ve never heard of any being specified for more than 10,000 Hours - can anybody comment? [I have some SQ valves in the equipment I have]

[Don Collie jnr]

I remember while on my first technician block course in 1975 in Dunedin [New Zealand] at the Dunedin Polytech, when our class was taken into a back room to look at a large 6 phase mercury arc rectifier in operation [1 phase only]. It was about 2 metres across, had a 25 cm diameter pool of mercury at the bottom, and 6 dog leg anodes. It was explained to us that it had been used to rectify the AC from a large transformer [presumably a special to produce 6 phases] to make 1800 Vdc @ several 10`s of amps, for the local tram service which presumably used a DC shunt motor in each tram. So the thing was capable of high current at high voltage. The current flowed from a point on the surface of the mercury pool. This exit point danced around the pool in an unstable way - facinating to watch!............................................ ...........................................Don.

[Ed_Dinning]

Hi Gents, 6 phase rectification is quite common, it is achieved using both a Star and a Delta secondary on the same transformer (often know as 6 pulse rectification). The direct output from the rectifier only has 4% ripple and is frequently used without any smoothing caps if a batttery is on the line (Aircraft transformer rectifier units).

Modern aircraft now use 18 pulse or higher rectification all in the name of reducing harmonics and improving power factor (at the expense of efficiency)

Ed

[Herald1360]

Isn't 6-pulse rectification using a Mercury arc simply done using three centre tapped secondaries on a three phase transformer with the centre taps commoned? The common cathode makes any other configuration problematic.

I guess if you fed the rectifier from a star delta input, you would still get 6 pulses, but they would not be evenly spaced, but in pairs- I guess the hum would sound a bit like a V6 engine!

I think 6-phase full wave (two bridges, one fed from the star and one from the delta is actually a form of 12-pulse rectification.

[Lucien Nunes]

Wow - a thread about mercury arcs - I like this even if it is a little OT
100,000h = 11.4 years - there are probably many arc rectifier bulbs that have served four times this duration. No part actually needs to wear out although there are various failure modes that eventually set in after extended use, depending on the kind of load it has been subjected to. I am a little wary of the quoted build date of that rectifier though, I'd have put it a couple of decades later.

One of the nice things at Klingerpark that you don't often see surviving is the exciter Motor-Generator set (Erregermaschine) that converts line voltage AC to power the alternator field. This is an alternative to a direct-drive exciter, although either a dependable source of AC from the mains or an additional genset or battery is required to enable it to start up.

The quoted exciter speed got me thinking for a minute. 1500 rpm? It's an induction motor, it can't do that, surely they mean 1450 or so. Oh wait, look at the alternator plate - 51.5 Hz! What a fun frequency, makes average 4-pole motors run at 1500 rpm and 2-pole at 3000, not so good for powering TV receivers though!

Lucien

[Lucien Nunes]

Ah, missed Chris' post. Actually rectifier transformer winding configuration is a complex issue and there were various solutions. A rectifier bulb with six anodes can be used in different ways, depending on how many groups the secondary is divided into. Three single-phase, two three-phase and one six-phase were all used. Where multiple groups are used, each can support one conducting anode simultaneously, by means of an interphase transformer that provides the commutating volt-seconds to each group in turn. This improves the utilisation factor of the transformer copper at the expense of voltage droop.

Another factor in the design of rectifier transformers that arises with mercury-arcs but not with solid-state is that practical arc rectifiers have multiple anodes but a common cathode. This leads to circuits in which DC passes through the secondary, limiting the winding configurations to those which cancel DC within each group and preferably those which share harmonic current between primary phases to avoid slipping the neutral. Overall there are five different valid secondary winding arrangements for 6-phase MAR transformers; 6-phase, double Y, triple single-phase, Y-star and triple star.

Sorry, a bit OT since the MAR at Klingerpark is 3-phase. This was much more common for battery charging duty. I wonder why they removed the left hand (lower rated) cabinet? And why they drained the mercury from the bulb? Perhaps it was unsealed, but you would think they could have put it back after draining?

Lucien

[Don Collie jnr]

No, it wasn`t the mercury vapour rectifier that was quoted as having a 100,000 hour life, but rather some of the other valves mentioned on the site.
I`ve never heard of a valve with a predicted life of more than 10,000 hours [the philips SQ valves] - I was wondering if any group member could confirm this 100,000 hour figure?........................................... ..................Don.

[Herald1360]

How long did the Post Office expect the valves in undersea repeaters to last? That must have been pretty much for ever, given the expected replacement costs!