Fluid Couplings replaced by VVVF Drives creates challenges

[rob52]

Re CMPB> Long and Shortwall mining> History Post Jul 14, 2013 at 6:46am

"Fluid coupling drives are at last on their way out and direct drive variable drive motors are replacing them. These are speed controlled via sophisticated electronics, which monitor speed, load and other factors."

Fluid Couplings Voith or other served their intended purpose well…simple, serviceable (fluid change) no dodgy electronics solder joints to be damaged by vibration or repetitive thermal expansion and contraction….just did not work well with undulating seams or if fill viscosity and level was not adhered to or if undersized with insufficient cooling capability for the actual number of starts per hour etc

Note that High Power >1kV VF & VVVF Drives create new challenges which the industry is just starting to investigate….the system capacitance creates a leakage path for the 8kHz-10kHz carrier frequency currents and the dV/dt of the switched pulse train with IGBT's used to reconstruct the variable frequency waveforms can easily damage the motor windings, weakened insulation systems at cable repairs or impedance discontinuities/transitions per travelling wave theory of Electrical System Transients……
=>> Questions to ponder include…
[1] Are your core balance earthleakage relays sensitive to the frequency produced by your VVVF Drive?…
[2] jXL (inductive reactance) = 2*pi*f*L so the voltage rise on the earth return conductors is different, thus for U/G mining equipment the touch voltages under fault conditions are larger than for 50Hz…sparking at metalwork discontinuities due to voltage differential due to earthing conductor inadequacy
[3] "What safety criteria/protection clearance time to apply in the wet dirty U/G Coal Mine for rubber tyres shuttle cars, steel tracked CM's, AFC motors etc capable of producing higher touch voltages
[4] The use of semi-conductive rubber sheaths on mining trailing cables to CM's and S/C's does not offer EMC screening/shielding….interference/induced voltage concerns?

2011 DPI EESS Presentation discussing some of the issues

The question being asked is who is going to fund the required research? UK Coal Industry does not have the $ or the industry to support it, MSHA provides only limited funding, ACARP is dead….Tic…Tic…Tic

Rob

[John]

The last two pits I worked at didn't use fluid couplings on the belts, Angus Place used them on the AFC and Stage Loader.
All trunk belts used slip ring motors and step resistance starters, Angus Place used a "soft start" set up on the longwall gate belt, that was about as close as I got to electronic starting of AC motors in practice.

My last mine in the UK was Boulby, in North Yorks, they had Huwood Belts with dual motor drives, TB 120's, all had "Aqua Fil" couplings" Fluid couplings with water instead of oil.
The Conveyor in pit bottom that fed the skip pockets had a scoop coupling.

Like you say Rob, looks like we have a build up to a disaster without lots of R&D...

[rob52]

1996ish Chain Valley (Wallarah was similar)
* 760HP (from Memory) wound rotor Main Slope "Cable Belt" down the Drift , it was a stepped resistance starter but had the project to change it over to a liquid rheostat starter (LRS), would still have the resistance steps overlaid on the LRS curve for the different fill solutions in the shed.

1998ish Appin
* used 450kW (from Memory) 6.6kV Main Gate and Main Headings Belt Drives with scoop fluid couplings,
* 3.3kV AFC motors had 266kW/522kW pole changing to soften the starting impact on the 6.6kV Backbone System off the back of 3 x 1.5MVA Longwall Txf Pantec as well.
* Main Slope belt down the drift was 6.6kV 2MW wound rotor with liquid rheostat start.

New CAT (swallowed Bucyrus International which swallowed DBT) Longwall uses CST on the 1200kW to 1650kW AFC motors.

DOL was/is simple however you need something to reduce the startup shock loads on the belt/AFC chain.

Wound Rotor meets the smooth non shock load start criteria and gives fantastic Torque on start and through the acceleration range to Sync Speed - the slip%, problem is brush gear maintenance and Commutator Skims required + necessity to avoid sparking U/G so not really suited to U/G use, the skill set to complete this work is disappearing. Squirrel Cage Induction Motors (SCIMs) are cheaper and have no brush gear, and if Frequency (f) can be varied so can the speed Ns = 120f/p, where p = number of poles.

However, with SCIM's Torque is proportional to voltage^2 makes torque on start a concern if volts drop to far eg Class A Squirrel Cage Induction Motor typically 1.6PU torque on start drawing 6-8xFLC, so at 80% volts on start = [(0.8^2)*1.6] = [0.64*1.6] = 1PU.

Rob

[John]

Feb 15, 2014 22:04:59 GMT -5 rob52 said:

1996ish Chain Valley (Wallarah was similar)
* 760HP (from Memory) wound rotor Main Slope "Cable Belt" down the Drift , it was a stepped resistance starter but had the project to change it over to a liquid rheostat starter (LRS), would still have the resistance steps overlaid on the LRS curve for the different fill solutions in the shed.

1998ish Appin
* used 450kW (from Memory) 6.6kV Main Gate and Main Headings Belt Drives with scoop fluid couplings,
* 3.3kV AFC motors had 266kW/522kW pole changing to soften the starting impact on the 6.6kV Backbone System off the back of 2 x 1.5MVA Longwall Txf Pantec as well.
* Main Slope belt down the drift was 6.6kV 2MW wound rotor with liquid rheostat start.

New CAT (swallowed Bucyrus International which swallowed DBT) Longwall uses CST on the 1200kW to 1650kW AFC motors.

DOL was/is simple however you need something to reduce the startup shock loads on the belt/AFC chain.

Wound Rotor meets the smooth non shock load start criteria and gives fantastic Torque on start and through the acceleration range to Sync Speed - the slip%, problem is brush gear maintenance and Commutator Skims required + necessity to avoid sparking U/G so not really suited to U/G use, the skill set to complete this work is disappearing. Squirrel Cage Induction Motors (SCIMs) are cheaper and have no brush gear, and if Frequency (f) can be varied so can the speed Ns = 120f/p, where p = number of poles.

However, with SCIM's Torque is proportional to voltage^2 makes torque on start a concern if volts drop to far eg Class A Squirrel Cage Induction Motor typically 1.6PU torque on start drawing 6-8xFLC, so at 80% volts on start = [(0.8^2)*1.6] = [0.64*1.6] = 1PU.

Rob

A lot of the problems you mention were surfacing in the 1960's when I was serving my apprenticeship as an elec with the old NCB, main U/G supply back then was 3.3Kv, belts were all 3.3Kv DOL starting except the Cable Belt, which was 3.3Kv slip ring motor, resistance stepped start.
Faces back then were 550 volt, max allowed by law was 660 volts on the face. You can just imagine the problems with an advancing face if we didn't keep the transformer as close as possible to the face. Which raised another problem, oil filled none FLP transformers!!! No closer than 300 feet from a face!!
That later changed with FLP transformers starting to hit the market.
But, all GEB control transformer taps had to be altered when the tx started to get too far back, or the pilot relays would drop out on undervoltage.
Irony is, we only had 195HP of AFC motors of which 125HP was on the MG tx, 65Hp stage loader motor, 125Hp shearer and two AB undercutting machines, one on the M/G tx and approx 50HP.
So the problems with mechanization were starting to give the engineers headaches back then.

Now it appears we are back to the same problems with todays high HP faces.

When I started at Boulby, 6.6Kv seemed strange, but I guess now they have so much U/G horsepower they are at almost max loading.
I'd imagine "Wongawilli" has upgraded all U/G power to accommodate the longwall equipment, they used to be on 6.6Kv supply.

I'll have to ask Kerry, what they finished up with at Angus Place, he was the elec engineer when I started there and for many years afterwards, all I know is they now have a high speed belt system new conveyor drift and a Joy face package.
When I was leading hand elec on dogwatch, Kerry had a new 11Kv switchboard installed underground and way inbye off the main transport road.

[rob52]

Angus Place:
July 2011 to June 2012 - 3.525M Tonnes LW Face Coal, 0.202M Tonnes Other Coal
July 2012 to June 2013 Forecast - 3.5M Tonnes LW Face Coal

2.4-3.4M Lithgow Seam
250-380m Cover
31MT Marketable Reserves
LW Ops 3 x 8Hr Shifts 5 Days 2 x 12Hrs Shifts, 3 Days 14 Unit SHifts

Commenced Longwall Ops August 1979

Longwall Block - Width = 282m, Length = 3.317km

Shearer Joy 7LS DERDS March 2010 Install
Drums M/G & T/G 2.2m
Cutting - Height 3.2m, Bi-directional
Web Depth - 1m
Installed Power 1440kW
Roof Supports - 163 of Joy 2 Leg Chock Shield, 1100 Tonne Yield Load, working range 1.63m to 3.6m, Joy RS20-S
AFC - 2 x 630kW Bucyrus, 1032mm Wide, twin inboard 42mm chain,1.29m/s
BSL - 1 x 250kW Bucyrus
Coal Crusher - 1 x 250kW Bucyrus
Coal Clearance to surface - 2500tpHr

**************************

At Appin Longwall commenced May 1969ish when not gassed out....per 1982 AJ Hargraves Key Note Address re CH4 Drainage.... "Although pillar extraction goaves was known to release gas from adjoining seams, only with the commencement of Longwalling at Appin was the commencement of conventional CH4 post-drainage seen"...Appin presently runs 54 x 1MW Gas reciprocating Engines on pre block drainage & goaf recovery...also have VAM unit and still have to flare residual!!!! mid 1990's with Coal price crash to $70 US for Coking Coal (pre the 2001 onwards price rise to $400 per Tonne in 2008) we were mining CH4!!!! Existing contracts for Hard Coking Coal are $210 per tonne, talk is of $180 per Tonne moving forward this year....even with High Quality Hard Coking Coal its cyclic & a hard road to maintain margin.
Coal Contract Prices

......by early 1990's Longwall fed by 3 x 1.5MVA <3% Txfs Txf Pantec 266/522kW AFC motors, Electra 600 Shearer with 2 x 275kW Cutter Heads.....really pushed the boundaries 6.6kV 70mm2 cables....No Volts coils drop out at nominal 70% volts......6.6kV Supply System used single point suspension cables to pit bottom at 520m of cover 70mm2 PILC was the biggest cable we could run self supporting the cable support head frame was not designed for larger, .the 70mm2 PILC Cables changed 1996ish to 95mm2 PILC Cable for the Longwall only.......was also friggin cold in winter standing at the bottom of the down cast shaft.

=>> There is 11kV U/G supplying the Newer Appin Longwall, using boreholes for the LW drop down cables, detail posted elsewhere on CMPB.

Appin/Appin West (ie swallowed Tower Colliery in the race for recoverable reserves)
July 2011 to June 2012 - 3.193M Tonnes LW Face Coal, 0.437M Tonnes Other Coal
July 2012 to June 2013 Forecast - 3.656M Tonnes LW Face Coal

Appin:
2.8-3.4m Bulli Seam
550-600m Cover
42MT Marketable Reserves
LW Ops 4 x 9Hr Shifts 4 Days 2 x 12Hrs Shifts, 3 Days 16 Unit Shifts

Longwall Block - Width = 319m Nominal, Length = 2.316km

Shearer Joy 7LS-2A DERDS
Drums M/G & T/G 2.25m & 1.9m
Cutting - Height 3.2m
Web Depth - Variable Web Depth 0.8m Nominal
Installed Power 1130kW
Roof Supports - 180 of Joy 2 Leg Chock Shield, 1100 Tonne Yield Load, working range 2.4m to 3.6m, Joy RS20
AFC - 3 x 855kW Joy, 1000mm Wide, twin inboard 48mm chain,1.68m/s
BSL - 1 x 375kW Joy
Coal Crusher - 1 x 375kW Joy
Coal Clearance to surface - 1600tpHr

Rob

[John]

You forgot to point out Rob, Angus Place had the first successful longwall installation in LW1, using the Anderson Strathclyde shearer, Gullick Dobson shields, there's a couple of photos of that machinery I took on LW7 posted on this site.
I started there during LW5 block extraction. The two transformers were pressurized with Freon, as a coolant and to comply with hazardous zone rules.

Pre that I think Australia's first mechanised longwall was at Bellambi, single fixed drum AB 16/125 with modified Gullick Seaman five leg chocks..Total failure due to roof supports not being strong enough for the Illawarra sandstone