When superior power-to-weight ratio is critical

The Clermont Coal In-Pit Crushing and Conveying (IPCC) system was one of the first to be designed in Australia within the past 20 years. SKM, who were responsible for the mining solution and detailed design, chose ABB for its slip-ring motor technology.

Efficiency requirement
SKM were very conscious of the need to specify equipment that offered the greatest efficiencies. In particular for the mobile conveyor head (Crawler), there was a major need to minimise the drives systems weight, as the power-to-weight ratio had a direct impact on performance and construction costs. This was a key factor in ensuring the overall mining method was not only economically feasible, but capable of delivering the sustainable outcomes desired by the project owners, Rio Tinto Coal Australia.

Rio Tinto Coal Australia had a strong commitment to the adoption of the IPCC system for the Clermont mine. One of the main benefits of the system was that it enabled most of the top 45m of overburden material, to be crushed in a mobile in-pit crusher, and then conveyed to the dump sites. This has significant sustainable value, in that it halves the number of haul trucks required to remove the overburden.

Tim Atchison, SKM IPCC Area Manager says "We were keen to have all aspects of the Clermont mine operations designed to maximise efficiency. As part of our evaluation process, equipment vendors were invited to submit recommended solutions, along with their equipment specifications. This assessment process was adopted to ensure that any efficiency gains were identified early, and then incorporated into both the mechanical equipment and structural design."

"In particular, we were looking for an electric motor that was not only reliable and robust, but also of a light weight construction. Motor weight is a critical factor in the design of conveyor drive applications. A poor power-to-weight ratio has significant negative cost implications for the design and construction requirements. Additional allowances would have had to be made for the structure, lifting gear and size of mobile machinery like the mobile transport crawler."

ABB motors provided the solution
Csaba Szabo, ABB Product Manager adds "We were able to satisfy the clients need for a reliable, light weight and high efficiency motor solution, by offering eight ABB 1350kW 11000V slip-ring electric motors as the main conveyor drive system; along with eight liquid resistance starters manufactured by NHP."

"The motors were supplied to Hansen Transmissions, the appointed drive module manufacturers for the drive head. The drive module consists of a large base plate which mounts the gearbox, gearbox auxiliaries, break unit and high voltage motor. This module is then installed in the drive head, and its primary role is to drive the conveyor head pulleys which are also housed inside the drive head."

Slip-ring motors are commonly used in applications requiring high starting torque or low starting current. These motors provide maximum availability, and are especially recommended for heavy load inertia applications, like mill drives or situations where network conditions are weak.

"The efficient design of the ABB motors meant our offer represented the best possible solution. We believe our machines weigh approximately 20 percent less than the closest competitor. The high reliability of these motors is of utmost importance, and the physical dimensions of the motor are also a major factor, due to the limited space available on the drive heads."

The NHP liquid resistance starters and cabinets provide external resistance for the rotor circuit to control starting torque. Additional cabinets accommodate permanent resistors to ‘trim’ motor speed. This is required when conveyor pulley’s wear, which creates the need for slightly different drive speeds, in order to avoid belt traction problems.

The high voltage motors are manufactured at our 'Centre of Excellence' in Italy, which specialises in mid to large size slip-ring motors. The contract also included several smaller low voltage motors for the auxiliary duties.

"ABB invests largely into research and development, to ensure that we have equipment with the highest possible efficiency ratings. Our high voltage machines are extensively used in applications where power-to-weight ratio is a paramount factor, such as in windmills and ship propulsion drives; demonstrating our commitment to meeting industry demand," concludes Csaba.

Some key project facts:

• The Clermont mine is planned as an open cut truck/shovel operation with the IPCC system.
• The deposit has a mine life of 17 years.
• Once extracted from the pit, the coal is transported via a 13.3km conveyor to the existing product stockyards, stacker/ reclaimers and train load out facilities, at the Blair Athol mine in Queensland.
• The coal is then transported by rail 278km to the Dalrymple Bay Coal Terminal.
• The overall project value for Clermont Coal development is $950 million.