Motor Control for Mill Startup with Sedimentation
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Solution Overview
Problem
The high starting torque required to restart a mill after prolonged downtime due to material sedimentation leads to the need for oversized and expensive electric drives, as the sedimentation increases the torque demand significantly at low speeds.
Innovation Solution
A method involving a first converter with a maximum output voltage lower than the network voltage is used to dissolve sedimentation, then the motor is connected to the network for further operation, allowing for reduced power consumption and cost-effectiveness by switching to a higher voltage for grinding speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor is oversized to provide high starting torque for sedimented material, then the mill can be restarted after prolonged downtime, but the electric drive becomes very expensive
Solution Approach 1:
The starting process is divided into two distinct phases: first, a low-voltage converter provides high starting torque to dissolve sedimentation, then the motor is switched to direct network connection for normal operation. This segmentation allows each phase to be optimized independently, avoiding the need for an oversized motor that would be required if a single system had to handle both conditions.
Solution Approach 2:
The system dynamically switches between two operating modes: converter-fed mode for starting with sedimented material, and direct network connection mode for normal operation. This dynamic adaptation allows the motor to operate efficiently in both conditions without requiring oversizing for the worst-case scenario.
2Power
If a converter with maximum output voltage matching network voltage is used, then the motor can operate at full voltage for grinding, but the converter becomes more expensive and network load increases
Solution Approach 1:
The operation is segmented into starting phase (using low-voltage converter) and running phase (using direct network connection). This allows the converter to be specified for lower voltage and power, reducing its cost, while the motor still receives full network voltage during normal operation through direct connection.
Solution Approach 2:
The function of providing high voltage during starting is extracted from the converter and instead provided by direct network connection during the running phase. This allows the converter to be designed for lower specifications, reducing its cost while maintaining full voltage capability when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the starting torque requirements after sedimentation is dissolved, allowing for more economical operation and lower network load, with the motor being connected to the network for efficient grinding, thus reducing overall costs and power consumption.
Implementation Method 1
A method is proposed for controlling a motor for starting a mill with ground material
Implementation Method 2
the motor for dissolving sedimentation of the ground material of the mill first being fed by a first converter
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention relates to a method for actuating a motor (16) for starting up a mill (6) with material (20) to be milled. In order to permit more cost-efficient starting up of the mill in comparison to the prior art, it is proposed that the motor (16) for triggering sedimentation of the material (20) to be milled of the mill (6) be initially fed by a first inverter (25), that the motor (16) be subsequently disconnected from the first inverter (25), and that in a further step the motor (16) be connected to a first power system (21) which has a first power system voltage, wherein the maximum output voltage of the first inverter (25) is lower than the first power system voltage.