As part of its commitment to producing reliable, cost-efficient electricity, Loy Yang Power started an upgrade of its four-level opencut Loy Yang Mine.
The in-progress upgrade includes the redesign and progressive changeover of the mine’s coal transfer conveyor drive systems. The company turned to Rockwell Automation to help it develop a drive solution that could perform in the rugged mine environment.
With an annual output of about 30 million tonnes of brown coal and 4 million cubic metres of overburden, it lays claim to being the southern hemisphere’s largest coal mine.
Situated in the Latrobe Valley about 165km east of Melbourne, Loy Yang Power is Victoria’s largest energy producer.
The mining process and transportation of coal from the bottom of the mine to the power stations is largely automated and features a range of mining and material handling technologies.
Huge electric bucket wheel excavators 50m high and 190m long patrol the opencut mine benches. Each excavates up to 4000 tonnes of coal an hour on average.
Each excavator feeds on-board conveyors that, in turn, deposit the coal onto main transfer conveyor systems. Each transfer conveyor system comprises several separate conveyors. These conveyors each have a 2m belt width and travel at 5.2m per second. With a combined length of more than 25km, the mine’s conveying system transfers the mined coal from the pit floor to the surface.
The transfer conveyor systems transfer the coal to a raw coal bunker with a 70,000-tonne capacity. That coal is then taken from the bunker, again by conveyor, to two separate power stations at the “mouth” of the mine. These are Loy Yang Power’s 2100MW power station and International Power’s Loy Yang B 1000MW station.
Loy Yang Mine senior electrical engineer Steve Cleaver said a steady flow of coal to the coal bunker had to be maintained to keep the generators running.
“The coal bunker only has enough capacity to fuel 20 hours of power generation,” he said. “Therefore, the pressure on the conveying system to perform is relentless.”
The legacy conveyor drive systems at Loy Yang Miner were based on water-cooled eddy-current coupling technology. When first installed many years ago the ECCs were the ideal drive solution. They provided high torque over a wide speed range, which is perfect for hauling enormous quantities of coal from the bottom of the mine to the surface.
However, in recent years it had become clear these systems were struggling to move the coal as efficiently as the mine engineering team believed was possible. The drive cooling systems were also not coping with the production demand and frequently overheating.
“We can’t afford to have a conveyor go offline, especially given the ever-increasing demand for electricity during peak-load periods,” Cleaver said. “When we’re offline we’re not selling electricity so downtime is catastrophic.”
He said 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,” Cleaver said.
“This increased air gap reduces the machine efficiency. In addition to this, the cooling systems were increasingly unable to cope during periods of peak demand in summer.”
In a collaborative effort Rockwell Automation and the Loy Yang Power engineering team developed a new drive solution. It was founded on the Allen-Bradley PowerFlex 7000 medium voltage AC drive.
These drives feature direct-to-drive technology, which helps eliminate the need for isolation transformers on applications with new or existing motors.
The mine engineering team came up with an idea to equip each conveyor with a self-contained, cooled and removeable drive package. The package 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 the conveyor length or lift requirements dictate.”
Cleaver also stipulated that the drive packages be housed in IP67 stainless steel enclosures equipped with a closed-loop air-conditioning 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.”
Rockwell Automation technical consultant Gary Spotswood said the PowerFlex 7000’s compact nature simplified the development of 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 portioned stainless steel IP67-rated enclosure, equipped with an air-conditioned cooling system to house each of the 6.6 kilovolt PowerFlex drives. Not only was it a more elegant drive set-up, it also eliminated the mixture of water and electricity used with the ECC cooling systems.”
Cleaver said having a “minimal component count” helped too. “Fewer parts means there are fewer things to go wrong and fewer spares to keep onsite,” he said. “Most component changeovers take less than 30 minutes – a real time saver.”
Four drive packages have been installed at Loy Yang Mine – two on the lower level and one each on the middle and upper levels.
One challenge was to integrate the Rockwell Automation drive technology with the mine’s existing drive technology and control systems.
Each PowerFlex 7000 drive package links to a programmable logic controller located in the neighbouring switchroom. Each PLC is, in turn, linked to the mine’s supervisory control and data acquisition system via the mine’s communications network.
The drive packages are each equipped with an Allen-Bradley electronic operator interface, located on the front panel of the drive enclosure. This allows site personnel to access drive diagnostics without opening the dust-proof enclosures.
The Rockwell Automation and Loy Yang engineering team also put together a plan that allowed the new drives to synchronise with the ECC drives.
Cleaver said the conveyors had been set 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.”
Cleaver said he had been impressed by Rockwell’s round the clock support and willingness to fully explain the inner workings of the drives.
“We didn’t want any proprietary ‘black box’ technology,” he said. “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 if necessary.”
The four PowerFlex 7000 drives are only a start. There are plans to replace many of the other ECC drives with the Rockwell offering.
Loy Yang Mine also has plans to implement a downhill conveying system to begin filling in certain parts of the mine.
Cleaver said: “The active front-end rectifier and regenerative braking capabilities of the PowerFlex 7000 drive will be incredibly valuable here. As the overburden is backfilled downhill into the mine, electricity will be generated and fed back into the grid.”
