School for Electrical and Electronic Engineering

Die doel van die proses was gebaseer op 'n dringende oproep tot verandering - Sasol Mining moes sy winsgewendheid as 'n steenkoolmyngroep verbeter. Die doel van die studie was om die produksiekapasiteit (ton/mededinger/skof) te bepaal wat deurlopend met behulp van bestaande toerusting en kabels in stand gehou kan word.

INTRODUCTION

B ACKGROUND
P URPOSE OF STUDY
I SSUES TO BE ADDRESSED
R ESEARCH METHODOLOGY
B ENEFICIARIES

The section electrical system of the mine consists of various pieces of mining equipment and a distribution network. All the equipment and sub-components of the in-section electrical system will be discussed more thoroughly in Chapter 2.

LITERATURE STUDY

B ACKGROUND

Production targets

The Renewal initiative helped Sasol Mining win the International Coal Company of the Year 2002 at the Platts/Business Week Global Energy Awards, and the Vuselela initiative will aim to keep Sasol Mining in that position.

C OAL MINING

Strip Mining
Board and pillar
Longwall mining
Environmental Hazards in Coal Mining

The first is to ensure that the cutting drum of the continuous miner is well ventilated at all times. It clears all the headers and is exhausted at the other end of the section (see Figure 2.2-2.

Figure 2.2-1: Dragline used to remove overburden [1].

S TANDARD SECTION

Operational description

The cut coal falls into the shovel at the front of the continuous miner. At the end of the continuous mine, the tail conveyor unloads the coal into the waiting car (see Figure 2.3-2).

Figure 2.3-2: CM unloading coal onto a shuttle car [3], [4].

E LECTRICAL D ISTRIBUTION NETWORK

Mobile Switching Unit
Flameproof Section Transformers
Gate end boxes
Cables and flameproof couplers

The flameproof transformer does not supply power to conveyor belt motors or conveyor belt transformers. Feeder and follower cables form the actual distribution network in the section and supply power to various parts of the mining equipment.

Table 2-1: Supply and trailing cables used in a section.

M INING EQUIPMENT

Continuous Miner
Shuttle car
Feeder breaker
Roofbolter

The difference between JNA 1 and JNA 2 continuous miner affects the cutting cycle control. A conveyor belt feeds the coal to the breaker of the metering breaker, which crushes the coal into smaller particles to prevent clogging of the conveyor belts' chutes.

Figure 2.5-2: Location of cutter motors on continuous miner [3].

E LECTRIC MOTORS

Motor ratings
Effect of voltage regulation on motors
Thermal models for electric motors

The current capacity of the motor will now become a limitation and there will be excessive heat. Thermal equilibrium will be reached after a certain time depending on the thermal time constant (Tth) of the motor. ) 1.

Figure 2.6-1: Protection against solid objects [17], [18].

W ORK - STUDY

The non-cutting part of the cutting cycle involves pulling the continuous miner back, raising the cutting boom and moving it forward, and some time for debugging. Any unusual activity that increases the duty cycle of the equipment or the load on the equipment will not be classified as ordinary and normal and will not affect the results of the investigation.

C ONCLUSION

MEASURING STRATEGY

P ROPOSED M EASURING S TRATEGY

In-section electrical distribution network
Mining Machinery
Measurement schedule

Transporter Motor 1 Voltage, Current and Power Breaker motor 1 1 Voltage, Current and Power Breaker motor 2 1 Voltage, Current and Power Robber Bolter**. Feed Crusher – The more common configuration for feeder crushers at Sasol Mining is one feed motor and two crusher motors. Robber Bolter – The flameproof case where the gauges are to be inserted is very small, and a very small gauge will have to be used.

Figure 3.1-1: In-section electrical system with proposed measuring points indicated.

M EASURING INSTRUMENTATION

Available measuring instruments
Additional measuring instruments

The ION 7700 is a larger and more sophisticated model of the ION series meters. The ION 7700 is programmed in the same way as the ION 7330, but comes standard with many additional features. The ION 7700 can record three AC voltages and three AC currents and the power factor or operating power for each phase, along with four analog values at a two-second sampling interval for over 20 hours.

S ECTIONS TO BE STUDIED

It was decided that the coal transport method should be three shuttle cars and that JNA 2 continuous miners would not form part of the investigation as Sasol Mining felt that the future still lay with the JNA 1 continuous miners. This requirement limited the sections that could be used for the study, as only 20% of the shuttle cars used at Sasol Mining have large flameproof enclosures. If we look at the practical execution of the investigation, it was easier with all the divisions that were in one mine.

Table 3-4: Production sections with highest to lowest cumulative production.

A CTUAL M EASURING S TRATEGY

Mining equipment
Measurement schedule

Measurements on the inter-district power distribution network were carried out by order of the company MAS Condition Monitoring. Section 61 mining equipment measurements were taken on Section 51 mining equipment. Section 51 feeder measurements were also not taken with the ION 7700 meter.

Table 3-8: Actual measuring points for in-section electrical distribution network.

W ORK STUDY

S UMMARY

MAS Condition Monitoring was contracted to carry out the measurements on the transverse electrical distribution network, as there were not enough measuring instruments to measure at all points simultaneously. The shuttle car in department 51 was measured, but data on the pump motor's consumption could not be used. Measurements were then made for an additional day on the shuttle car in section 50 to obtain useful data on the pump motor in a shuttle car.

IN-SECTION ELECTRICAL DISTRIBUTION NETWORK

M EASURING SUMMARY

The measuring instrument was placed on a switch that supplied power to a particular transport car or roof rack. The transport car or roof rack supply circuit breaker sometimes tripped immediately after the start of the shift for unknown reasons, normally after repeated earth fault tripping.

P RODUCTION RESULTS

M OBILE S WITCHING U NIT

The current consumed during shifts in both sections correlates well with the tons produced during the shift. The average consumption per phase was about 40A for a good shift, and it drops for the worst shift. Neither the cables supplying power to the MSU nor the MSU itself has been a limitation and should not become a limitation unless there is a dramatic change in the number of equipment used in the sections or the size of the motors on the equipment.

Figure 4.3-1: Load current and voltage for an MSU – Afternoon shift 18 May 2005.

F LAMEPROOF TRANSFORMER

It can be seen that the peak currents consumed by the flameproof transformers were quite high and the load consumed is very cyclical. The continuous miner is clearly the largest contributor to the total load at the flameproof transformer and therefore the largest consumer of the total load of a section. The average and peak currents consumed by section 61 were much higher than those consumed by section 21.

G ATE END BOXES

The busbar of the gate end boxes was undercharged more than 99.8% of the time, although it drew much higher currents than the section 21 gate end box. There was considerable variation in the average current drawn in the gate end boxes in the section 21 and in section 61. Another possibility is that submersible water pumps were powered from the gate end boxes to pump excess water out of the section.

Figure 4.5-1: Load current and voltage for a GEB – Afternoon shift 17 May 2005.

CONTINUOUS MINER TRAILING CABLE

Cables were overloaded 30% of the time when a continuous miner was used. The cable of the continuous miner gets very hot during the use of the continuous miner. Temperature measurements on the towed cable of the continuous miner show that the external temperature of the cable sometimes exceeded 55°C.

Figure 4.6-2: Load current and voltage for a CM – Morning shift 25 May 2005.

S HUTTLE CAR TRAILING CABLE

The largest consumption of the shuttle car is between the 3-layer and 5-layer rating of the cable. The average consumption and peak consumption of the shuttle cars were almost the same in both sections. This cable amperage was exceeded between 8% and 13% of the time a shuttle car was used in Section 21.

Figure 4.7-1: Load current and voltage for a SC – Morning shift 18 May 2005.

F EEDER B REAKER TRAILING CABLE

Feeder consumption was very consistent except for the tips which were occasionally used. The next cable of the supply circuit breaker was under load more than 99.9% of the time. At least 99.9% of the time, the pull cable of the power circuit breaker was also under-stressed.

Figure 4.8-1 and Figure 4.8-2 show the total consumption of a feeder breaker during a shift in sections 21 and 61 respectively

R OOFBOLTER TRAILING CABLE

The current consumption of the motors increased only slightly when the feeder breaker was fully loaded with coal. The consumption of the roofers varies considerably as it depends on whether the roofer has stepped or drilled, for example. The average consumption of a rapier while working was about 13 A if the rapier was used for a large part of the shift.

Figure 4.9-1 and Figure 4.9-3 show the total consumption of a roofbolter during a shift in sections 21 and 61 respectively

N ETWORK V OLTAGES

Once production begins, the voltages drop to around 1000 V and fluctuate at that level depending on the size of the load in the section being measured as well as other sections in the area. The voltages were lower in section 61 because the consumption was much higher than in section 21 due to higher production. If the voltages exceeded the lower voltage limits, it would only be for a few seconds.

S UMMARY

Control of the power factor correction unit was not optimal, although undervoltage problems were prevented. The continuous miner contributes almost two-thirds of the total load consumed by a section. The voltage level varies according to the size of the load consumed by the sections.

PRODUCTION EQUIPMENT

M EASURING SUMMARY

This car was measured for a day to obtain data on the consumption of the pump motor of a shuttle car. Engines should be adjusted to 92% of rated power or operated at a maximum ambient temperature of 32°C, as Sasol Mining's coal mines are located at an altitude above 1000 m above sea level. Transport motor 1 Current and power LH Traction motor 1 Voltage and current RH Traction motor 1 Voltage and current Shuttle car.

Table 5-1: Actual measuring points on mining equipment.

C ONTINUOUS MINER

Conveyor Motor
Pump motor
Gathering head motors
Cutter motors
Traction motors

Engines were overloaded between 25% and 35% of the time the engines were used. The table shows that the operator has a large influence on motor overload. This again shows the influence that the operator has on the operation of the continuous miner.

Table 5-3: Production figures for shifts where the conveyor motor was monitored.

S HUTTLE CAR

Conveyor motor
Pump motor
Traction motors

It can be seen that the transport motor was overloaded only about 18% of the time. The average current consumption of the transport motor was between 10 A and 11 A, with the shuttle car in Section 50 (afternoon shift on July 4, 2005) consuming higher currents on average. The temperature of the motor windings and the average consumption of the motor clearly showed that the motor was not overloaded.

Table 5-18 shows the production rates in the respective sections when the consumption of the conveyor motor was measured

F EEDER BREAKER

Conveyor motor
Crusher motors

The peaks experienced by the conveyor motor of the feeder breaker were much smaller than, for example, those experienced by the cutter motors of the continuous miner. The conveyor motor consumption in section 51 (morning shift on 28 June 2005) differed significantly from that measured in section 21. The crusher motors are located in the breaker section of the feeder breaker (see Chapter 2).

Table 5-27: Production figures for shifts when the conveyor motor was monitored.

R OOFBOLTER

Pump motor

The load used by the pump motor fluctuates quite a bit, but the average consumption was still below the full load current. The table shows that the motor was under load more than 90% of the time. The thermal time constant for the pump motor is 40 minutes and has Class F insulation (operating in Class B).

C ONCLUSION

Changing the duty type of the traction motors will help the traction motors maintain higher production rates. The conveyor motor and pump motor of continuous miners are already a limitation, especially the pump motor. The ship's drive pump motor is constantly loaded within the engine step.

CONCLUSION AND RECOMMENDATIONS

D ISCUSSION OF RESULTS

Production equipment

C ONCLUSION
S UGGESTIONS FOR FURTHER INVESTIGATION
D UTY TYPE S1 – “ CONTINUOUS DUTY ”
D UTY TYPE S2 – “ SHORT TIME DUTY ”
D UTY TYPE S3 – “I NTERMITTENT PERIODIC DUTY ”
D UTY TYPE S4 – “I NTERMITTENT PERIODIC DUTY WITH STARTING ”
D UTY TYPE S5 – “I NTERMITTENT PERIODIC DUTY WITH ELECTRIC BRAKING ”
D UTY TYPE S6 – “C ONTINUOUS OPERATION PERIODIC DUTY ”
D UTY TYPE S8 – “C ONTINUOUS OPERATION PERIODIC DUTY WITH RELATED
D UTY TYPE S9 – “D UTY WITH NON - PERIODIC LOAD AND SPEED VARIATIONS ”
D UTY TYPE S10 – “D UTY WITH D ISCRETE CONSTANT LOADS ”

Increasing the size of any of the motors on the continuous miner will also increase the limit. However, the instantaneous load on the motors generally exceeded the full load rating of the motors. Most of the motors on the mining equipment are replaced well before 20 years of service.

CM CONVEYOR MOTOR