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Post by tonys on Apr 29, 2011 3:10:06 GMT -5
Transformers
Knocking about in our quarry were 2 or 3 ex pit transformers 100KVA 3.3/.55KV. I got involved with a couple of them when we tried to start a limestone mine (don’t ask, it was meant to be a disaster from the start).
What is puzzling me is they had tertiary windings, anyone any idea why?
God alone knows where they came from in the first place. They were from the 30’s. I was resurrecting one of them in the 70’s.
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Post by John on Apr 29, 2011 6:32:24 GMT -5
Transformers Knocking about in our quarry were 2 or 3 ex pit transformers 100KVA 3.3/.55KV. I got involved with a couple of them when we tried to start a limestone mine (don’t ask, it was meant to be a disaster from the start). What is puzzling me is they had tertiary windings, anyone any idea why? God alone knows where they came from in the first place. They were from the 30’s. I was resurrecting one of them in the 70’s. No idea Tony, that's even smaller than the ones I was accustomed to, smallest I ever recall was 150Kva. The NCB ones had just primary and secondary windings, older were oil cooled and set up as a "mobile substation" ie flanged wheeled and rail mounted, with HV OCB one end and a termination FLP box the other end carrying 300A outlets, plus the safety circuits, ie E/L protection, O/L circuits. The Sec side was always star connected with the star point bonded to earth, some pits went restricted neutral with an inductor between star point and earth, some went "free neutral" or better known as multi point earthing in the early 60's when sensitive earth leakage protection arrived on the scene. I should also state, later transformers were air cooled, and totally flame proof, OCB's went out and ACB's replaced them, these ranged from 250Kva upwards, last ones I worked on were Brush 650Kva, 6.6Kv to 1.1 Kv with Brush SF6 breakers on the HT side and control gear on the 1.1Kv side.
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Post by tonys on Apr 29, 2011 7:56:11 GMT -5
Most likely they would be 150KVA (it is 35 years ago). These were rail mounted originally but mounted on skids in later life. I recall testing the .55 O/L and E/F circuits and they were restricted earth. I will have to dig out my old logbooks for the tests we did.
It’s the tertiary windings that confuse me. I’ve a feeling they restricted fault current but I can’t find out how.
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Post by John on Apr 29, 2011 11:04:46 GMT -5
On the restricted neutral Tony, you should find a large iron cored choke connected between the star point of the windings and earth. It limits fault current to five amps. As an outgoing earth fault, lets say a trailing cable gets crushed, the impedance of the fault will be very low, so practically, one could get thousands of amps flowing through the fault, which in turn could weld the contacts of an OCB or ACB together, not a pretty sight underground if there are gasses around!! The "choke" limits that fault current for long enough for the main breaker to trip. Though even five amps could ignite an air methane mix or worse, raised coal dust. That was the reason the NCB brought sensitive earth leakage systems in, to limit fault current to 250mA or less.
I looked up tertiary windings, but as I say, never came across them in mining transformers, either at the pit, or after I'd left and was overhauling transformers and switchgear in outside companies.
Seems they have several functions, from reducing harmonics, to balancing phase voltages, to several other functions.
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Post by tonys on May 2, 2011 3:55:37 GMT -5
My logbooks didn’t help. And I’m beginning to think my memory is at fault. A star point choke could be what I confused for the tertiary winding.
The only thing I did find in my books is where the transformers came from, a potash mine in Nidderdale, Yorkshire. God alone knows how old they were when we acquired them.
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Post by John on May 2, 2011 6:14:23 GMT -5
There's only ever been one Potash mine Tony, that's Cleveland Potash'r Boulby Mine in North Yorks. They used Brush 650Kva dry type FLP transformers, 6.6Kv/1100 for most of the mine, and 6.6Kv/550 for shuttlecars and 6.6Kv/3.3Kv for the continuous miners.
Now there were several other companies set up during the early/mid 70's, one to solution mine potash near Whitby and a couple that were to have sunk shafts. Nothing materialized of those. Maybe they were purchased by one of those companies and never used???
The choke would have been mounted on the secondary side chamber of the transformers Tony, large unit, can't recall the size of them now, been too long, but must have been 8-10 inches long, by almost that wide across the windings and about 8 inches high. Two heavy leads, one have been fastened to the star point, the other to the metal carcass of the chamber.
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Post by garryo on Dec 20, 2011 10:05:14 GMT -5
A tertiary delta winding is sometimes fitted when both the primary and secondary windings are connected in star. Most distribution transformer are delta/star either Dyn1 or Dyn11 with the neutral either solidly or impedance earthed. Some large power transformers are star/star with in this case the tertiary winding is used as a power winding along with its main purpose of reducing third harmonic current. However it is unusual to find a Tertiary winding on such a small transformer unless it was a dual secondary ie 3300/550 and 3300/440 where the T/Fs capacity of 150kva could be used on both windings along as the total primary load did not exceed 150kva. This arrangement is used in Australian metal mines where the primary is 11kV and two secondaries, one at 1JV and the other at 415v. The 1JV being used for jumbo drills etc and the 415 for small loads.
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Post by nixter on Jan 1, 2012 10:32:40 GMT -5
Business Mining
Two men seriously injured in colliery explosion
Security guards suffer severe facial burns after electrical explosion at former Welbeck colliery in Nottinghamshire
reddit this
Press Association guardian.co.uk, Sunday 1 January 2012 14.33 GMT Article history
Welbeck colliery, Nottinghamshire Welbeck colliery, Nottinghamshire, employed around 1,400 miners in its heyday, but closed in May 2010. Photograph: David Sillitoe for the Guardian
Two security guards are in a critical condition after being seriously injured in an explosion at a former colliery in Nottinghamshire.
The two men, aged 38 and 26, suffered serious facial burns in the blast at the former Welbeck colliery site, near Meden Vale, on Saturday. They have not yet been identified but are being treated in the Queen's Medical Centre, Nottingham, where they are both said to be in a critical but stable condition.
Nottinghamshire police said: "It is understood the men were working at the site as security personnel. Detectives are liaising with the site owners, UK Coal, with the fire service and the Health and Safety Executive to determine the sequence of events leading up to the incident."
The explosion was reported at around 7.30pm on Saturday and involved an electrical sub-station above the ground.
Nottinghamshire fire and rescue service said the explosion was from an electrical component in the 40m x 30m single-storey building.
She added: "The fire itself was very small. The main issue was the explosion itself and the two people injured. Investigations are ongoing."
According to UK Coal, the Welbeck site has not been a working colliery since May 2010. Shafts have been filled and a small team has remained on site decommissioning the mine which has exhausted three seams of coal since work on sinking the twin shafts began in 1912.
In its heyday, Welbeck employed around 1,400 miners and had an annual output of around 1.5m tonnes.
any ideas/copper theft
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