Ingenious Isolation ! ! ! !

Horses for courses. Wonderful solution at the time.

GA= Good Alternative

How about throwing the switch in the trash and putting in a proper unit that meets current code before someone gets killed.

No a better idea is to get the apprentices to polish off the verdegris, on that lovely brass..

Make it look real nice

....and at the perfect height for crawling toddlers.

Hmm - like riding a horse! (thanks, Ky - post #1)

GA... when I started as an electrical apprentice in the local steel works, it was drummed into me.. keep you hands in your pockets until you need to work on something, then check its dead before you do!

I remember walking into a switchroom FULL of these knife isolators in the older parts of the steel works, and these were still in use right up until the day it was demolished.

All we needed was a sign.. LIVE EQUIPMENT.

That did it for me, and several decades later, I'm still here :)

anyone following this posting should click on the link from TonyS and take the tour... there are photos of equipment I've not seen for years, and if you can read German even better.

I'm sure there is a circuit diagram for a mercury arc rectifier. Not seen one of those since '82...

Ahh.. memories!

I saw this

which oddly enough is not unlike the latest multi-pole alternators in 'gearbox free' wind turbines.

Hey Tony - 'old ways' are worth understanding!

There was one bit of kit we had while I was an apprentice I could never get my head around, the rorary converter. Starting it was a black art. You could run it up to speed two ways.
A/ starting with the pony motor and then switch to synconous followed by paraleling with the DC system.
B/ starting with DC and then synconising with the AC system.

Method A was the safest.
It was a wonderful bit of kit but it scared the life out of me. We also had MAR's feeding in to the same system, they facinated me.

There was a rotary converter that ran military radios and what not, in the days of valves (vacuum tubes), that gave the span of voltages out of 24 or 12 Vdc. "Neat" you would say back then, "only (about) 9" diameter and 20" long, and 50 lbs!"

Probably worth around 150W, but lots and lots of short circuit current available in a rotating mass. _{(insert fear emoticon here)}

Our 220V DC system had 100KW MAR's and 200KW rotary converters so a bit of a flash and bang if the sycronising was out.

At Westinghouse we had a 70kVA WWII 50/60Hz synchronous rotary converter in the test shop which kept the maintenance guys pretty busy. It had been updated with electronic controls for the exciter and when I was there they tried a soft start system - unsuccessfully. I had to investigate this.

The set drew approx 100A per phase under load, but as one would expect peaked at 900A starting off load. This peak did not blow the 100A rewireable fuses. The soft start was initially set low which just blew the fuses. Turning it up not only blew the fuses but partially melted the ceramic carriers as well. It turned out the set was so stiff that it could not me made to move with anything less than 300A, but it drew this current for so long it was damaging the installation. In the end we just gave it up as a bad job starting it with the fusebox switch, the 900A peak being the lesser evil.

Mercury arc rectifier - imagine my surprise as a young engineer to see those still around in 1990! They were all phased out in 1991. If I recall, there were two pots in series, to make one 12-pulse 3kV, 3MW traction rectifier. All sorts of vacuum pumps, gauges, back-flash detectors, exciter/energising? circuit, etc. http://www.electricstuff.co.uk/mar.gif

And in line with the topic of discussion - all the 400V AC power & 110V DC control busbars and wires were accessible from the open rear of the cabinet. No-one got injured, not even the illiterate assistants, they were taught well (and we were lucky!). New panels much safer, but a pain to work in due to the small size!

MAR's.. we had hundreds of them in the steel works as all the OH cranes were DC. I hated doing the maintenance on them.

But not a lot of people know about them...

In 1984/85 I was working at Westinghouse where we were building solid state rectifiers for London and Glasgow Underground traction supplies. These were replacing mercury arc units. I believe mercury arc rectifiers were still being used in traction supplies into the 90's. I think the London Underground had 6 phase rectifiers whereas the Glasgow Underground had 12 phase rectifiers when (at least when it was rebuilt). However it was some time ago and my memory may not be accurate.

The mercury arc system lent itself to building multiphase rectifiers without using additional components.

Actually.. very on topic.. its good to know that I'm not the only one who remembers open panels with the equipment fixed to the front of Bakelite panels with the wiring all open and exposed at the back.

and for a further trip down memory lane...

Note the Wipp & Bourne hand isolators bottom right of photo.

I'm getting all weepie...

I am sure that many of us who started our apprenticeships in maintenance back in the 60/70s remember such gear.

I did and this thread is like a walk down memory lane...

This was a rotogravure printing plant built in the 40s and modernized by the addition of new stuff in the 60s and 70s. We had...

Six phase MARs running 400 HP DC motors turning printing presses.

Old C-H wound rotor drives, three motors on the same press shaft, so we had ganged motor driven vertical wound rotor controllers with "shorting trucks" that ran up and down between brass bars on worm screws. All three towers shuttles were tied together with common drive shafts and clutches on them. This get up had a 1.5 HP motor that turned the shafts that turned the worm screws that lifted the shorting trucks. There was a whole room full of plate resistors. The heat in the summer was wild.

Great big huge "blue glow" thyratron's" that ran 25 HP motors on paper reel stands.

Whole rooms filled with open motor controls and the associated wiring and knife switches mounted on phenolic/slate backboards. Beautiful wire work. Wish I had pictures...

The wildest... was an explosion proof 500 HP "Star/Delta" oil bath manual starter. Took two of us to throw the "arm" from "start" to "run" mode.

This plant was a 230 volt delta corner grounded facility, so EVERYTHING was huge.

You should have seen the size of the contactor on the old hydraulic elevator, each phase contact was a silver puck of about 3" diameter. The arm on the starter was about 2.5 feet wide.

I miss the printing plant to this day...

There was one beauty of the old systems, you could repair them. I wonder how many maiteance guys cary a file with them now for dressing contacts. When I moved from quarrying to the steel industry the young "lads" thought I was mad when I'd dress live slip-ringss or a comutator with a Martindale stone. It saved changing motors though.

Happy times

lets be real honest to each other... we're all old farts!!

Yeah, yeah.. I know speak for ya self!! :)

I'm not sure age (ours, or the gear) has that bigger bearing - just length and breadth of learning might infer 'more calender years'.

How about "experienced farts"

"Experienced" old farts it is!!

Have a great Christmas everyone.

At my uncle's fertilizer plant was a pretty big hammer-mill, 60hp at least. It was my job to start it, using a large start/run switch. It was quite the thrill to go to start and hear the hammers rattling about, and then go to run when they flung out and got quieter. It gave us a pretty good feel on the speed of the motor, and made it easy to learn when to make the change.

_{Um - I wonder if that was a star/delta starter}

Gee, I dunno. It took both hands to move the switch up for start, then down through the middle to run. The hammer-mill was a good twenty feet tall, an awesome piece of machinery.

We were processing leather scraps into high-nitrogen fertilizer, a rather stinky process, as the blow-down tube from the pressure cooker had a leak at a turn.

11KV RMU incoming switch.

Known as an OLD 3 pole double throw switch. It was made to carry lots of current and probably 3-phase current since 3 switches. Since double pole, has 2 sides to switch 3 single inputs between 2 loads. Of course since it is old it might not carry much current. Seems in the ole days, back in 1920s and before they built every thing big. I guess to make sure it lasted. Being exposed would be considered a safety factor, definitely not UL, but then back long ago safety was not considered much and this is why we got unions. Of course the switch could have been mounted inside a cabinet, but never know. ron

I remember when I started work at a local foundry as an electronic tech in the 70's, we had 2 Brown Brovaries (ya, I know, not spelled right) induction melters. Both were motor/generator sets, both MG's were water cooled, so an ocasional water leak got real interesting. The best one that allways scared the crap out of me, was the panels were missing on the control cabinets and the operators would change capacitor taps by kicking the ceramic contactors with their steel toe boots, and yes, the leather on the steel toes was missing. This cap circuit ran at 3Kv to the induction furnace.

One furnace was small one at 200Kw and the other was a 350Kw. Both had the arm on the side that you had to pull down to start the MG, and then throw the handle to run position. Once in a while, an operator would miss and the switch would destroy the contacts.

I know, I am showing my age!

Jim