In Australia, coal-fired power generation has established itself as a valuable power source, providing vast quantities of inexpensive and reliable electricity.
It accounts for approximately 75% of the country’s annual electricity production. Keeping Australia’s coal-fired power generation infrastructure online–from the coal mine through to the generating plant and distribution grid–goes some way to ensuring the nation’s industrial wheels remain turning. As in all production processes, stoppages, breakdowns and unscheduled downtime can be crippling to the power generating process. Such outages can have a devastating effect, impacting both the energy producer’s and end-users’ bottom lines in a matter of minutes.
One energy industry stakeholder leading the way in providing industry with an uninterrupted supply of electricity is Victoria’s largest energy producer, Loy Yang Power. Located within the heart of the Latrobe Valley, 165 km east of Melbourne, Loy Yang Power provides reliable and efficient energy for industry and consumers right across south-eastern Australia.
As part of the company’s ongoing commitment to producing reliable cost-efficient energy, Loy Yang Power recently embarked on an upgrade of its four-level open-cut coal mine facility, Loy Yang Mine.
The ‘in progress’ upgrade includes the redesign and progressive changeover of the mine’s existing coal transfer conveyor drive systems. To obtain a drive solution capable of withstanding the rugged mine environment while delivering premium around-the-clock performance, Loy Yang Power enlisted Rockwell Automation.
With an annual output of approximately 30 million tonnes of brown coal and four million cubic metres of overburden, Loy Yang Mine is the largest coal-producing mine in the southern hemisphere.
The mining process and the transportation of the coal from the bottom of the mine to the power stations is largely automated and features a range of sophisticated mining and materials handling technologies.
Huge electric-powered bucket-wheel dredgers, 50m high and 190m long, patrol the open-cut mine ‘benches’, each excavating up to 4,000 tonnes of coal per hour on average. The bucket wheel of each dredger feeds on-board dredger conveyors, which in turn deposit the coal onto main transfer conveyor systems on level of the mine. Each transfer conveyor system comprises multiple separate conveyors, each with a belt-width of two metres and a travel speed of 5.2 metres/second (19 km/h). With a combined length in excess of 25kms, the mine’s conveying system transfers the freshly mined coal from the mine floor to the surface.
The transfer conveyor systems transfer the coal to a raw coal bunker, which has a 70,000-tonne capacity. The coal is then transported directly from the bunker (also by conveyor) to two separate power stations located at the ‘mouth’ of the mine. These are Loy Yang Power’s 2,100MW power station and International Power’s Loy Yang B 1,000MW power station.
According to Loy Yang Mine senior electrical engineer Steve Cleaver, providing a steady flow of coal feedstock to the coal bunker is essential to keeping the power generation process online and producing cost-effective electricity.
“The coal bunker only has enough capacity to fuel twenty hours of power generation. Therefore, the pressure on the conveying system to perform is relentless,” he said.
The legacy transfer conveyor drive systems at Loy Yang Mine were based on water-cooled eddy-current coupling (ECC) technology. When first installed many years ago, the ECCs were the ideal drive solution for providing high torque over a wide speed range–perfect for hauling enormous quantities of coal from the bottom of the mine to the surface.
However, in recent years, it had become clear to the Loy Yang Power mine engineering team that the legacy drive systems were struggling to move the coal as efficiently as they believed was now possible. Furthermore, the existing drive cooling systems were not coping with the production demand and were frequently overheating.
“We can’t afford to have a conveyor go off-line, especially given the ever-increasing demand for electricity during peak-load periods,” Cleaver said.
“When we’re off-line we’re not selling electricity, so downtime is catastrophic. It was time to make a change.”
According to Cleaver, the ongoing maintenance and performance of the ECC drive cooling systems complicated matters.
“The water tends to corrode the metal on the moving parts and contributes to an increased air gap between rotor and drum, and drum and stator. This increased air gap reduces the machine efficiency,” he said.
“In addition to this, the cooling systems were increasingly unable to cope during periods of peak demand in the summer months. We needed to upgrade.”
The mine upgrade provided Loy Yang Power with the opportunity to implement a drive solution incorporating the latest technology.
“Our legacy drive system had served us well over the years, but it was time for a more reliable system with advanced capabilities,” he said.
“With so many conveyors on-site, it was important that the new drive technology could be brought online gradually and was able to integrate with our existing drive systems and control architecture. We enlisted the services of control and automation specialists.”
In a collaborative effort, Rockwell Automation and the Loy Yang Power engineering team developed a new drive solution, founded on the Allen-Bradley PowerFlex 7000 medium voltage (MV) AC drive.
Featuring ‘Direct-to-Drive’ technology–a technology that helps eliminate the need for isolation transformers on applications with either new or existing motors–the Allen-Bradley PowerFlex 7000 MV AC drive provides space-efficient speed and torque control across a range of drive applications.
The mine engineering team came up with an idea to equip each conveyor with a fully self-contained, cooled and removable drive package that could be easily installed or uninstalled on any of the mine’s conveyors.
“This level of portability provides us with improved production flexibility,” Cleaver said.
“It allows us to physically locate the drive package at any of the conveyors on any level of the mine, as conveyor length or lift requirements dictate.”
Cleaver also stipulated that the drive packages be housed in an IP67 stainless steel enclosure equipped with a closed-loop air-conditioning cooling system.
“We wanted to protect the drive electronics from the extremely dusty conditions experienced down in the mine,” he said.
“It was also imperative that the drive packages be equipped with a reliable cooling system to avoid the costly shutdowns we had experienced with the water-cooled ECC systems.”
According to Rockwell Automation technical consultant Gary Spotswood, the compact nature of the PowerFlex 7000 drive simplified the development of the portable drive packages.
“The transformerless configuration of the PowerFlex 7000 meant we were able to help minimise the footprint of the drive package,” he said.
“We developed a partitioned stainless steel IP67-rated enclosure, equipped with an air-conditioned cooling system, to house each of the 6.6 kV PowerFlex drives.”
Four drive packages have been installed on the Loy Yang Mine site to-date; two on the lower level and one each on the middle and upper levels.
One of the challenges here was integrating the new Rockwell Automation drive technology with the mine’s existing drive technology and control architecture.
Each of the PowerFlex 7000 drive packages is interfaced with a Programmable Logic Controller (PLC) located in the neighbouring switchroom. Each PLC is, in turn, linked to the mine’s Supervisory Control and Data Acquisition (SCADA) system, through the mine’s existing communications network.
Each drive package is equipped with an Allen-Bradley Electronic Operator Interface (EIO) located on the front panel of the drive enclosure.
“The drives can be interrogated via these EIOs or through the mine’s SCADA system,” Spotswood said.
“The locally mounted EOIs make it easier for site personnel to access drive diagnostics without opening the dust-proof enclosures and exposing the drives to the elements.”
The Rockwell Automation/Loy Yang engineering team developed a strategy that allowed the new drive packages to seamlessly synchronise with the existing ECC drives.
According to Cleaver, all conveyors were set up to run in sequence.
“Where appropriate, the drives have been configured to operate in a ‘master/slave’ configuration,” he said.
“We set up one master drive to control the speed, while the other drives become ‘torque followers’. With the conveyor speeds perfectly matched, the transfer of coal from one conveyor to another is seamless.
“In a process such as ours, we can’t afford to wait around for specialised service teams. We need to be familiar with the product and its inner workings so we can set it up, monitor it and troubleshoot it if necessary.”
With the mine upgrade at Loy Yang Mine only partially complete, there is much work ahead. Cleaver and his team are planning to progressively replace many other ECC drives across the mine with PowerFlex 7000 drives.
Loy Yang Mine also has plans to implement a downhill conveying system to begin filling in certain portions of the mine.
“The Active Front End (AFE) rectifier and regenerative braking capabilities of the PowerFlex 7000 drive will be incredibly valuable here,” Cleaver said.
“As the overburden is backfilled downhill into the mine, electricity will be generated and fed back into the grid. It’s solutions like this that make our job easier.”
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