DRIVES & CONTROLS
generators needed to be replaced . They could upgrade to new DC equipment that would maintain productivity for another 25-plus years with similar operating costs . However , the DC system required regular maintenance and was at a high risk of extended periods of machine downtime due to waiting for parts and maintenance techs , both of which were harder and harder to find .
Another option was to retrofit the DRE28 with an AC system . AC dragline systems were already known to have safety advantages and reduced maintenance costs compared with DC systems , according to FLANDERS . They also had the same service life expectancy of 25-plus years . The team decided to move forward with an AC retrofit from FLANDERS . In July 2019 , the boom was lowered on DRE28 DC 8050 and the on-site retrofit began . After 90 days , the DRE28 AC 8050 was back online .
“ AC systems are designed with safety built in ,” FLANDERS said . “ Hardware compatibility , simpler and safer operating mechanisms and scalability are benchmarks of FLANDERS ’ AC system design .”
One of the key features of the AC system is the unique , easy-to-access drive cabinet designed to replace DC motor-generator sets , FLANDERS says . Water-cooled semiconductors remove heat , so the cabinets keep parts protected from debris . This results in a substantial reduction in noise , dust , heat , and rotating parts , and reduced exposure of employees and maintenance technicians to these safety hazards associated with DC systems . The drive cabinet also eliminates the need for on-site machining to blow out dust , balance parts , clean brushes and other regular maintenance DC systems require .
The 690 V AC hoist / drag motors are designed to fit in the same size box as the DC motor , with the same footprint , allowing for easy drop-in installation . No modification to brakes , gearing , or coupling is necessary . Class H insulation and high-output blowers help the motors safely produce a 25 % higher kilowattage than the DC motor can achieve .
The FLANDERS AC system design mimicked the DC design in generating low- and mediumvoltage interactions . The motors and drive cabinet have a category zero arc flash rating , requiring little intervention with specialists or the need to manually isolate systems within the machine .
From September 2019 through June 2021 , the DRE28 AC 8050 operated at the previous DC 8050 electrical , mechanical and structural settings . In July 2021 , after system optimisation , the AC 8050 surpassed the limits of DC 8050 machines , reaching output levels closer to the 8200 DC draglines models , and continued to bank gains in reduced maintenance costs , increased productivity and improved energy efficiency . A side-by-side comparison of DC and AC dragline operations over 12 months and including three months of data reported after the July 2021 upgrades , shows the results .
The DRE28 AC 8050 is – operationally and electrically – the safest dragline in its fleet , according to FLANDERS , with the drive cabinets and motors maintaining a category zero arc flash rating since installation . “ The overwhelming response from our client was related to the safe and easy operation of the AC system ,” Owen Uebel , Strategic Business Development Manager for FLANDERS , said . “ Operators were vocal with management about the improved work conditions .”
In terms of productivity , the lowmaintenance design of DRE28 AC system has resulted in reduced machine downtime and proportional gains in machine availability . A twelve-month comparison study confirmed that , compared with the DC 8050 , the AC 8050 moved an additional 2 million bank cu . m ( BCM ). With the July 2021 optimisation , the AC dragline is expected to reach a minimum of 15 million BCM annually for the full year 2022 , setting a record for this mine . An independent study confirmed an 11 % boost in power efficiency over the DC 8050 dragline over an operating period of January 1 to December 31 , 2020 , meanwhile . IM
Torque limiters in mining
Torque limiters provide an important protection level that is needed for powerful mining industry geared drive applications and there a number of specialised players in this market .
With more than 80 years ’ experience in providing overload protection , Regal Rexnord ' s Autogard Torque Limiter is an optimal solution for heavy duty high-shock loading applications . Autogard attaches to a high-speed drive shaft and guards equipment by providing disengagement protection . With a wide range of mounting configurations , Autogard makes it easy to fit a standard torque limiter onto a new or existing drive without having to re-engineer the drive train . Acting like a mechanical circuit breaker , Autogard protects the drive train and reduces or eliminates downtime . The Autogard can be easily reset after tripping . By reducing the likelihood of gear drive damage during an overload , Autogard makes operations less costly over time . Users can combine Autogard with Rexnord Falk V-Class gearboxes to enhance uptime and productivity .
Bibby Turboflex is another leading innovator in engineered torque limiting overload protection solutions . Bibbigard safety element torque limiters incorporate a number of safety element modules of a specific size mounted between two flanges and preset to release at a specified torque value in order to protect the drive system from expensive damage and lost production . They can be used with various types of drive mediums , many of which are available from Altra Industrial Motion . Bibbigard has been successfully utilised in many different industries including mining where , subject to space availability , the release torque capacity is virtually unlimited . This includes large grinding mill drives .
Timken-owned PT Tech ’ s SL series torque limiter products are specially designed and manufactured to be integrated into mining applications . Each SL torque limiter as capable of protecting critical mining applications when torque reaches dangerous levels in critical equipment . While slipping , this torque limiter is still able to transmit torque equal to the unit ’ s torque setting , which results in safer and more predictable operations .
Bibbigard ® torque limiters from Bibby Turboflex are designed for high and low speed applications
Additionally , since this is a friction-type torque limiter , it is not necessary to reset the torque limiter after a slip occurs . This saves time and expenses by avoiding costly equipment repairs . The SL series torque limiter is designed to operate at motor speed . In most drive systems the prime mover represents approximately 90-95 % of the equivalent inertia .
56 International Mining | NOVEMBER / DECEMBER 2022