Good Link.

[John]

Here's a link to an online paper, covers a lot of coal mining electrical history etc..


content.yudu.com/Library/A1t8op/CoalInternationalJul/resources/65.htm

[colly0410]

Thanks for the link John, interesting stuff on there.

[John]

I was aware of the 11kv face in NSW, but scares the crap out of me, I worked with 11Kv at Angus Place. There was a flexible wire armoured cable between the last main armoured feeder to the transformers at the face feeding 11Kv to the primary of the two face transformers. I hated handling that pliable wire armoured cable, always worried it would blow out where my hands were.

It's also a voltage I never took for granted either, I had an urgent job one Sunday night shift on the 11Kv side of a transformer, I was leading hand, but the engineers rules were a permit to work was to be issued by an engineer.

I broke that rule, took one of my electricians with me for safety's sake, we both did a triple check on the visible isolator, and both checked the earthing of the circuit before we proceeded with the job
I did it safely, but we didn't take any chances, I fully expected to get my rear end well and truly kicked next morning, but the Engineer was quite happy with me.

[tunnelbuilder]

I enjoyed reading the link, but don't agree with everything. Sensitive Earth Leakage protection was developed for gate end boxes after the Walton Pit methane explosion in 1959, and has nothing to do with the development of electronic equipment in gate ends.
The description of failures of high voltage plugs is also interesting and relevant. I now work in the tunnel industry in the USA, and we use 15kV, 600 amp plugs on all our jobs, and we have experienced failures due to capacitance building up across the plug on long tunnel runs where 4 or 5 miles of cable are connected. All the cable conductors are individually protected with a copper tape shield, this has to be stress relieved with a stress cone to discharge the corona at the termination point when we make the plugs up. We do not fill or compound the plugs either.
The other interesting point of the paper is the use of high voltage motors. I agree with the use of high voltage equipment up to a point. Using a 600kw motor at 10kv seems like a science project to me, it would only draw a nominal 31 amps. The smallest high voltage cable you can buy in the States is a #2 Awg. which is rated for over 100 amps. Seems to me using a 4160 volt system for 600 kw would develop 81 amps would be fine and you would not need 10kv rated gear which is more expensive. Voltage drop would not be an issue either because isolation transformers or step down transformers would be part of the power skid anyway.
Just my thoughts.

[John]

Why didn't you fill the plugs??? I've always been obliged to fill the plugs with either compound or two part resin or a special silicon for HV cables.
Back in the UK days it was mandatory in both M&Q Acts.. Plus in damp mines not filling a plug would lead to moisture issues too.
NSW in Australia had some refinements, all the pins in both trailing cable plugs and the pins in armoured cables were required to be sweated, so were surface jobs.
I have jointed an armoured cable in NSW on a main 6.6Kv underground feeder with a joint box, the cores had a crimped sleeve then insulated normally, but at that mine we used a silicon filler that we pumped into the joint box with a grease gun of all things!! All approved by the NSW Mines Inspectorate.
I've also terminated 6.6Kv double wire armoured cables when I worked at Boulby in North Yorks, standard type NCB couplers filled with the two part resin we were used to with the NCB.

I found 11Kv was a different kettle of fish, there was always some corona discharge, pretty evident from the smell in substations, and visible when I turned my caplamp off viewing visible isolators.

I'm surprised you didn't have problems with plugs not being filled.. Obviously they must have been in very dry roadways.

I think what the author is aiming at, electronics in UK coal industry started in E/L circuits, notably B&F GEB's with the thyratron circuits for E/L in the old SM2/2X boxes, then moving up to the solid state E/L circuits of the SM2 range of boxes, with Wecol following suit, then Brush with their transformer secondary protection.
Then came Winster and Davis of Derby with their face control equipment, leading to the Winster MTP conveyor control, then all the BS about ROLF...LOL I think anyone who was either an electrician or an apprentice elec during the early 60's knew about that fiasco and all the BS the NCB put out regarding it.

[tunnelbuilder]

I did my time in the NCB and obviously was trained with 3.3/6.6 kv cable couplers and bitumen compound both hot and cold. The SWA cable, pvc jacketed, pvc insulated cable did not require any stress relieving in the plugs just a 2 pass layer of empire tape to stop the hot compound burning the conductor insulation. The most popular plugs we use here are the PLM 500 amp 15kV rated. These are MSHA approved and have 3 power pins, 1 ground pin, (earth) and a ground check pin ( pilot circuit). They come with a stress relieving termination kit and are a threaded male and female assembly as against a bolted coupler. The plug body is made from aluminum and is not designed for filling. Bearing in mind we don't use armoured power cable over here the plug is well sealed. However they can sweat internally and I have experienced failure because of this but not too many.
They are however widely used in all environments both wet and dry, there are plenty of wet tunnels mined using these plugs.
The plugs are aslo used on large high voltage drag lines and shovels, the cable we sue underground is often referred as shovel cable.

[rob52]

Hi tunnelbuilder re post Mar 20, 2013 at 8:52pm

You Mention the PLM 15kV rated plug….are these per NEMA 7 Catalogue

"The plug body is made from aluminum and is not designed for filling." ?? are you talking about the coupler pin interface area….. would have thought the rears of the plugs/couplers where cables term into thimbles would be filled?

Pg9 noted COLDPOUR Compound
Compound filling can prevent condensation and provide added protection in wet locations.
=>> However you mention above not compound filling?  Have you completed a Partial Discharge Test of the Couplers following coupler/plug fitment with and without filling compound installed in the rear of the plug?… could prove interesting.

Pg10 shows a Coupler Contact Insulation Cleaning Kit
…is it just Isopropyl Alcohol?
=>> Have you used this cleaning kit? What sort of improvement do you get in "Insulation Surface Creepage Distance Resistivity" following cleaning? ie place some fuse wire 100mm apart and 5kV Megger test across the Surface Creepage Path with a 5TOhm FSD Megger.

**********
=>> Assume you get the same sort of Lung Effect with subsequent internal condensation that leads to Water Drop Corona and acidic conductive products surface film we get here?  

The Newer Units we have
 Catalogue 2
& Catalogue 3 (AA803TPB2 & AB803TPB2 are superior to the "old polydoe" type AB404SPB2 with air wedges typical of pre Year 2000 11kV Units.  We use Manganese Bronze for U/G Coal.  Aluminium Plugs/couplers are permissible in Open Cut Coal for Shovels and Draglines.

**********
You may be interested in the 1981 Mining Industry Tech Conf  Paper
An Evaluation of High-Voltage Cable-Coupler Performance for Underground. Mine Power Systems CHRISTOPHER J. BISE AND LLOYD A. MORLEY, SENIOR MEMBER, IEEE
=>> A Discussion on poor performance of 15kV Cable Couplers for 12.47kV, 13.2kV & 13.8kV Systems compared with the earlier 1940's 5kV Couplers and 1957 8kV Couplers

The following paper is more readily available
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS. VOL. IA-18.NO. 4,JUI.Y/AUGUST 1982
An Evaluation of High-Voltage Cable-Coupler Performance for Underground
Mine Power Systems
CHRISTOPHER J. BISE AND LLOYD A. MORLEY, SENIOR MEMBER, IEEE

Rob

[rob52]

2009 WMEA Conference - Worry Free High Voltage Couplers
 - Achieved with Air Exclusion at the coupler male to female interface, radial E Field Stress grading & 3M Cold Filling of rear of Plugs.

Rob