The ball mill is a mechanical device that continues to crush ore or other materials after the crusher to obtain finer particle products required by the process. Its basic principle is to load a certain number of steel balls into its cylinder as grinding media to crush the ore. When the cylinder rotates, the steel balls installed in the cylinder are lifted to a certain height as the cylinder rotates under the action of friction and centrifugal force, and then thrown down at a certain linear speed. The ore is crushed by the impact of the falling steel balls, as well as the additional crushing and grinding between the steel balls and between the steel balls and the liner. At present, there are two types of drive forms for ball mills used in domestic mines:

1. Small-tonnage ball mill: winding asynchronous motor + reducer + large and small gear rings + drum;

2. Large-tonnage ball mill: high-voltage three-phase synchronous motor + large and small gear rings + drum;

No matter which form drives the ball mill, there will be long transmission chains, low operating efficiency, high motor energy consumption, and heavy maintenance and overhaul workload. In the context of energy conservation and emission reduction, it is urgently needed to upgrade energy-saving technology.

With the advent of high-performance NdFeB permanent magnet materials, permanent magnet motors have achieved milestone development. NdFeB has a very high magnetic energy product, and its residual magnetic induction intensity/coercive force is large. Using fewer NdFeB permanent magnets can produce enough motor magnetic energy product, so the motor volume/size can be greatly reduced. Permanent magnet synchronous motors are suitable for designing with multiple poles, which significantly reduces the height of the stator/rotor core yoke, thereby reducing the amount of core and the size of the motor.

The new line start permanent magnet motor has a cage-shaped conductive bar in the rotor, which is the same as the induction motor rotor structure, in addition to the permanent magnet embedded in the motor rotor, so that it can generate asynchronous torque to achieve rotor acceleration when powered on. During normal operation, the permanent magnet on the rotor generates an excitation magnetic field that maintains a certain power angle and rotates synchronously with the rotating magnetic field generated by the three-phase winding. When the synchronous speed is stable, since the stator magnetic field speed is consistent with the rotor speed and there is no relative motion, no induced current will be generated, and the squirrel cage bar (copper bar) will not work. The permanent magnet and stator winding jointly generate driving torque.

Differences from the asynchronous motor structure rotor: the asynchronous motor is squirrel cage copper excitation, while the LSPM is rotor permanent magnet excitation.

Asynchronous motor rotor copper winding structure

Synchronous motor rotor permanent magnet structure

Low-voltage medium-speed direct-running permanent magnet motors (also called “self-starting permanent magnet motors”) have the same advantages as variable-frequency permanent magnet motors:

1. The new direct-running series of permanent magnet motors have strong load-bearing capacity, fast dynamic recovery time, and high stable operating performance;

2. It has the characteristics of constant speed, high efficiency and power factor, and wide economic operation range;

3. Using high-performance NdFeB rare earth permanent magnet materials and low-loss non-oriented electrical steel, the motor is small in size and light in weight;

Compared with variable-frequency permanent magnet motors, it also has the following advantages:

4. When a large load is suddenly added or unloaded, there will be no power angle oscillation, no loss of step and inability to operate, and no damage to the motor;

5. This product can be started directly at industrial frequency without a frequency converter, can be V/F controlled, and can also be driven by frequency converter speed regulation; (limited to products above 750 rpm)

6. It can be used in fan and water pump applications where one frequency converter can drive multiple motors;

7. Asynchronous frequency converters can be used to directly drive this series of motors without replacing permanent magnet dedicated frequency converters;

The high-voltage direct-drive new direct-operation permanent magnet motor has the same voltage and rated speed as the three-phase high-voltage excitation synchronous motor, and the starting system has all the functions of variable frequency starting, industrial frequency operation and one-to-many. First, the ball mill at the rear end is driven to start slowly at a low speed through the starting cabinet. When the rated speed is reached, the permanent magnet direct-drive motor is cut into industrial frequency operation through the conversion system. After normal operation, it is the same as the original three-phase high-voltage excitation synchronous motor, and no adjustment is required. The motor saves efficiency according to the change of material load.

Therefore, in the actual normal operation process, there is no loss of high-voltage frequency conversion and transformer (accounting for more than 4.5% of the system energy saving), and the whole system has higher power saving efficiency. The starting cabinet can achieve the effect of starting multiple three-phase synchronous high-voltage excitation motors with one cabinet, realizing one-to-many comprehensive control. Multiple motors can share a set of starting switching system, which can effectively reduce costs.