Su versatilidad, fiabilidad y capacidad para adaptarse a diversos tipos de cargas han convertido a los variadores de frecuencia en una pieza fundamental de la industria en general – Alcanzando una gran importancia dentro de los proyectos con operaciones de alta demanda como los de la industria minera.
Mining Industry Processes:
- Grinding
- Milling
- Industrial conveyor belt
- Among others
Machinery/Equipment:
- Ball mills
- SAG mills
- High-pressure grinding rolls
- Conveyors belt
- Pumps
- Fans
Typical Power Range: 200 – 2000 kW / Typical Use of Drives in Low Voltage (LV)
Areas within the Mining Process and Their Typical Powers:
Excavation
- Bucket wheel excavator: High starting torque and high overload
- Power range: 50-150 kW (small) / 300 – 2000 kW (medium/large)
Typical Use of Drives in LV
Primary Grinding
Material processing stage: High starting torque and high overload
Main Processing and Refining
Ball mills, semi-autogenous mills (SAG), high-pressure grinding rolls (HPGR), Ring Motor Drives (RMD), and Gearless Mill Drives (GMD).
Ball mills/SAG mills with up to 8,000 kW per motor, typically gear-driven (‘high speed’) using asynchronous motors with 6-8 poles and nominal speeds of 1,000 – 1,800 rpm.
- HPGR with nominal power 1,500 – 3,000 kW.
- RMD con hasta 000 kW como piñón simple y hasta 18.000 kW como piñón doble
- GMD with typical power exceeding 5,000 kW, using special low-speed ring motors.
- High overloads during start-up.
Typical Use of Drives in Medium Voltage (MV) Material Handling and Transport:
- Cintas transportadoras para el «transporte horizontal» (minas a cielo abierto)
- Upward conveyors
- Downward conveyors
- Typical power range: 500 – 3000 kW Required braking capacity
- Multiple drive concept can be advantageous Master/follower control
- Hoists for vertical transport (underground mines) Typical power range: 500 – 5000 kW
- Wide speed range 10% – 100% High starting torque and high overload
- Required braking capacity
- Slurry pumps, cyclone feed pumps
CHALLENGES:
Mining applications present specific challenges for operating systems.
Harsh Environment
Environmental conditions are often severe. The most relevant factors are dust, extreme ambient temperatures, and the presence of vibrations and impacts. These conditions primarily affect motors, but VFDs may also be partially exposed. Therefore, a robust design and adequate maintenance are desired. Liquid-cooled units may be more suitable due to enhanced ingress protection (IP rating) and easier integration into a container (where applicable).
Sudden Load Changes
Load torque is not always smooth. In addition to short-duration overloads, abrupt load changes occur, especially in conveyors, crushers, and certain types of mills. These affect mechanical components and are transmitted to the electric motor. In addition, the control system must handle such dynamic torque requirements effectively.
High Starting Torque
Many mining and mineral industry applications involve constant torque characteristics. Moreover, additional overloads occur at low speeds during startup. The torque required to turn the mill depends on the angle relative to the steady-state. Maximum torque can be reached at approximately 60° to 70° of inclination. Handling peak overload can challenge VFD sizing, as some VFDs have reduced current capacity at low output frequencies. Operating with high torque at low speed also poses challenges for the control system, particularly due to the motor's highly nonlinear behavior.
High Altitude Installations
Some mines are situated at high altitudes, often exceeding 4,000 meters above sea level. Therefore, the impact of altitude on system design and VFD sizing must be considered. High altitude reduces air density, affecting air cooling efficiency. This generally impacts all drive system components (e.g., increased BIL level for transformers). Moreover, high altitude affects the air's dielectric insulation property, potentially reducing the system voltage.
Weak Grid
Most mines are located in remote or extreme locations, resulting in a frequently weak power grid (i.e., low short-circuit capacity). This affects the propulsion system in at least two ways. Firstly, the VFD topology must be grid-compatible, leading to low harmonic distortion. Secondly, a weak grid tends to have greater voltage variation (fluctuation), noticeable during larger load changes. Additionally, a weak grid is another compelling reason to use VFD-driven motors instead of direct-on-line starting methods.
Conclusion:
VFDs help reduce energy consumption, promoting sustainability in mining. They provide soft start capability, making them grid-friendly compared to direct starting methods. VFD-driven motors offer superior control, especially in dynamic situations such as sudden load changes, supporting plant automation and enhancing mining profitability. minas sean más rentables.
Use of VFDs in the Mining Industry.
- Ing. Juan Francisco Mariscal Mejines
- Dirección comercial
- At VMS ENERGY, we specialize in the design and construction of these distribution systems.
