INVESTIGATION INTO THE DESIGN OF A 6600V LONGWALL MINING SYSTEM

Presented by Adrian Trevor

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Overview

• What is a Longwall?• Why bother moving to 6600V?• Predicted Future Power Requirements• Cable size selection• Power flow modeling of proposed system• Future work

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• Used because of efficiency ( Cutting and recovery rates)• Continuous process once started

Overview

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• All Drives at 3300V• Shearer > 2MW• AFC (Armoured Face Conveyor) 2.55MW• BSL (Beam Stage Loader) 300kW• Crusher 300kW• Hydraulic Pumps 600kW • Shearer Water Pump 200kW

Electrical Overview

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• Ultimate reason is to improve torque for motors

• Also allows increase in installed power without extremely large cable sizes

• Allows longer monorail hence less flits

Why 6600V?

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Motor Torque

• The torque of a motor is proportional to the voltage squared.

• At 3300V, ↑ currents are drawn which causes voltage drops in all supply cables

• At 6600V, ↓ currents, and any voltage drop is a ↓ % of rated voltage

• Ideally in new system we want torque to remain above 90% at all times.

Motor Torque Vs Terminal Voltage

0%

20%

40%

60%

80%

100%

0%20%40%60%80%100%

Voltage (% rated)

To

rqu

e (%

Rat

ed)

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• An increase in voltage allows power increases to be obtained without increases in conductor sizes– E.g Type 240.3 cable with 50sq mm conductor can

carry 170A which at 3300V is approx 970kW compared to 1940kW at 6600V

– However physical dimensions and mass of cable ↑ marginally due to extra insulation required

• In most cases cable sizes will be reduced

Increased Power

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• ↑ Voltage allows potential length of monorail to be increased by ↓ voltage drop

• If monorail length is doubled this has the potential of reducing monorail flits from approx 8 per block to 4– Each flit takes approx 8 hrs– 8hrs production = 14000 tonnes x 4 flits

= 56000 tonnes– 56000 tonnes x $40 = $2.24 million!! per block

Longer Monorail

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• Predicted future power requirements

• Cable sizing calculations

• Power flow study

Work Completed

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• Future power requirements can not simply be increased linearly. i.e. increase all items by 10%

• Each piece of machinery requires it’s operation to be analysed to determine what, if any power increases are required.

• Shearer– Increase in cutter motors to 1000kW each– Increase in traction motors to 165kW each– Total installed shearer power of 2.4MW

Future Power

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• AFC– Considering increase in face width to 400m from 265m– Increase in power to 4 x 1000kW motors (2@tg,2@mg)

• BSL– Increase in power to 2 x 300kW motors

• Crusher– Increase in power to 1 x 300kW motor

• Hyd Pumps and Shearer Water Pump– Increase hydraulic pumps to a total of 1000kW (Fat Face)– Determined that current SWP is suitable

Future Power

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• This will result in a total installed power of 8.6MW, which is an ↑ of approx 50% on present

Future Power

LONGWALL POWER RATINGS

Equipment Present Rating (kW) Future Rating (kW)

Shearer 2050kW 2385kW

AFC 2250kW 4000kW

BSL 300kW 600kW

Crusher 300kW 400kW

Hydraulic Pumps 600kW 1000kW

Shearer Water Pump 200kW 200kW

Total 5700kW 8585kW

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• Cable selection is dependant on 2 main conditions– Current carrying capacity– Voltage drop

• Current carrying capacity relates to the thermal limit of the cable– Heating effect of current in a cable (I2R losses)– Ability of insulation to dissipate this heat

• Voltage drop is dependant on cable size, length and current– Must remain below 5% to keep torque above 90%

Cable Selection

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• The heating effect on a cable occurs over a continuous time, and instantaneous values are not of a large concern.

• FLC of motors NOT used to determine this.• Future average currents are used by projecting

present averages to future Voltage and Power levels.

• Present averages determined via Scada over a fixed period of time.

Current Carrying Capacity

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Cable Selection

TG AFC MOTOR CURRENT

020406080

100120140160180

0 1000 2000 3000 4000

Time (Approx 3 Hrs)

Cu

rren

t (A

mp

s)

• Example of Scada Data for TG AFC Motor with calculated average.

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• Most important at motor startup• Full Operational Load (FOL) currents were

determined by using the future FLC of the motor and allocating each motor a load factor.

PF=0.85% and n=0.9%

• Voltage drop calcs performed using FOL in that cable plus the starting current (6xFLC) of the largest motor.

Voltage Drop

V

LFPIFOL

3

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• Main Limiting factor was the voltage drop, most cables are significantly overrated in current carrying capacity to achieve acceptable voltage drop levels.

Cable Selection

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• A load flow simulation was completed at future levels using “EasyPower” simulation software.

• Results confirmed calculated values• 3 scenarios were simulated

– Full operational load– Full operational load with TG AFC Motor starting– Full operational load with 1 Shearer Cutter Motor

starting

Load Flow Simulation

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Load Flow Simulation

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• Investigate issues that DMR has– Presently CMRA prohibits voltages >4kV

• Investigate availability of equipment e.g motors, plugs, cables switching gear etc– Also sizing due to ↑ creepage and clearance values

• Investigate issues with fault current energy, in relation to flame proof enclosures.

• Investigate effects of EMI on control systems– Clearances inside enclosures– Effect on pilot core communication systems

Future Work

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• Questions??