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Application of SLANVERT SB70 Inverter in Hoister of Lead Zinc Ore

1. General
Mine hoister is widely used for hoist of vertical shaft and inclined shaft of coal mine, nonferrous metal, ferrous metal and nonmetal mines. Hoister system is used for hoist of minerals, equipment, etc. Hoister takes an important role in the whole process of production. Mine hoister system of a company adopts traditional wound type motor rotor resistance for speed regulation. Motor is 185kW wound type 6-level motor, of which the speed regulation is conducted through multi-gear switchover with rotor resistance. As the electrical control system is congenitally deficient, it often results in fault shutdown after many years' operation and severely affects normal operation of the production. In mining process, safe and reliable operation of equipment is very important. In order to enhance reliability of equipment, technical transformation for mine hoister is very necessary.

2. Transformation Solutions
Conduct transformation of variable-frequency speed regulation for the hoister through investigation and demonstration and in accordance with the practical situation of the mine hoister site, and use autosyn which is widely used in the machinery industry for control of speed setting of inverter. Autosyn outputs analog quantity signal through angular displacement transmitter. Operator handles the angle of control lever of the hoister, and angular displacement transmitter outputs analog quantity signal accordingly so as to control the operation frequency of inverter and then to control operation speed of hoister. Theoretically, the hoister can operate at any speed and operation is more convenient; and operation is similar to original experiences, so it is easy for operators to master.

Series Angular Displacement Transmitter  is selected to be as the autosyn. The main characteristics are as follows. First, high degree of accuracy: it can output 256-65536 absolute codes at one circle, without temperature drift and time drift, can measure 30,000 circles. Second, high reliability: absolute position and reliable software lap technology of the sensor ensures the high reliability; and it is free of the defaults of optical code disc that is liable to be damaged or interfered. Third, convenient to use: plug and play, no need to adjust null position of the sensor, only 5 wires are needed between module and sensor, wiring is convenient. Fourth, powerful function: it can not only measure the angle but also the position, and it is equipped with the function of switchover between angle and position. All functions of the transmitter are set by Angular Displacement Transmitter programmer.

Select SB70G250KW High Performance Series Vector Control Inverter produced by Hope Senlan Science & Technology Holding Corp., Ltd. Its main characteristics are: integrated high-accuracy rotor field vector control calculation method, equipped with 250% instantaneous torque control capacity to realize rapid response and accurate control of torque, and can perform wide scope of speed regulation with high accuracy; original multi-mode PLC operation function which is especially suitable to industrial manufacturing equipment and other applications; practical multi-section and multi-speed function: provide coding, direct, superposition and number selection method; powerful PID function; equipped with powerful programming function, the User can define internal I/O module; slip compensation, AVR automatic voltage stabilization function. Input analog quantity can be set at 10V. When input analog quantity signal changes from positive to negative, operation direction of motor will change accordingly, vice versa. Set corresponding parameters at the autosyn to make control lever output positive signals forward from central null position and output negative signals backward. It provides convenience for use.

Block diagram of variable-frequency speed regulation solution for hoister is shown in Fig. 2 as below:

Fig. 2: Variable-frequency Speed Regulation Solution for Mine Hoister

3. Plan Implementation
The load of inclined shaft lift features frictional potential energy load and belongs to the load with constant torque characteristic. Hoister has five buckets. When started and moving upward with full materials along the bevel face, the hoister should be gradually accelerated to full speed running, because torque of the power needs to overcome the resisting torque of the load and the friction; when near to well head, speed of the hoister should be gradually reduced. Due to heavy load and big inertia, short time required for speed reducing will lead to “overvoltage” of the inverter resulted from increasing AC side voltage, thus braking unit for energy consumption plus braking resistor or feedback unit is required to deal with recovered energy; recovered energy still produces during lowering process, so recovered energy also needs to be dealt with. 

Motor of the previous system is a Cascade-VI 185KW wound-rotor motor and usually works at the current of 280-380A. To guarantee safety, the hoister should be braked to some extent in time of upward or downward startup and the brake should be loosened immediately after completion of startup. Under this operation situation, the current will exceed the rated current of the motor sometimes and reach to more than 400 A. After speed is adjusted by frequency conversion, the hoister still needs to be braked to some extent in time of upward or downward startup and the brake should not be loosened until the output frequency of the inverter reaches to 0.3Hz and has sufficient torque. Motor is in a locked rotor state at the output frequency below 0.3Hz, however the output frequency is low and the output voltage is also low, so the motor will not be over current. During production, overload may occur sometimes for the loaded materials. Considering that the acceleration time in heavy-load condition is short, capacity of the inverter should be increased in type selection. In this case, a 280kW inverter is selected so that the inverter has sufficient overload capacity in time of overload of the motor.

Change of hoister is conducted according to the following steps:
(1) Equipment state when the frequency-conversion system operates is different in some degree from that of the previous power frequency system. On the console of the hoister, there is a cam controller (Utilizing the multiple contacts of the controller to act as the gear of the hoister, it controls the contact and adjusts the resistance of the rotor to respond to the low and high speed gear.). All the springs at the contacts except the control contacts of oil have been removed, thus facilitating to reduce the operation resistance when angle position control is used.

(2) Then short-connect all rotor windings of the wound-rotor motor.

(3) Utilize the previous cam controller and install natural Selsyn on the rear axial of cam controller with its center in line with central axial of the cam controller, thus the previous operation mode, lifting and lowering operation mode, can be used. The positive and negative angles of corresponding cam controller are 108° and -108° respectively. The natural Selsyn sends the signal of angle position in form of pulse to angle position inverter who in turn outputs the analog voltage signal of 10V and -10V corresponding to 108° and -108° according to the positive and negative angles. 10V and -10V received by the inverter acts as normal/reverse running signals.

(4) Cam controller is used to control brake oil system and the first contact must be used from the central point to the corresponding two sides on the cam controller. After passing the contacts of both sides, the contact is smoothly transit to 108° and -108° with the pushing of control lever. Before control lever is turned to the contact of oil system, Selsyn has already realized the variation of angle position and positive and negative voltages will be output from the corresponding inverter of angle position because the inverter has very low frequency output (0-0.3Hz) before oil system is turned on. When oil system is not turned on, the brake system is in the braking state. Through setting of the relevant functions of logic unit, arithmetic unit and comparator, etc., clear position of two contacts is transit, thus operation of the inverter at the frequency below 0.2Hz when the control lever is passing oil system contact is controlled every efficiently.
Setting of Inverter Parameters:

For application of the inverter to the system, we set the following parameters for the inverter.
F0-01=7, F0-02=1, F1-00=7, F1-01=3, F1-18=1.0, F1-25=1, F2-01=2, F2-04=90, F4-01=16, F4-08=0, F5-00=49, F5-01=14, F5-03=5, F6-00=6, F6-15=1, F6-16=101.1, FE-00=10, FE-01=28, FE-02=11, FE-03=25, FE-05=44, FE-06=10, FE-07=29, FE-08=1, FE-09=0, FE-12=1, FE-13=50, FE-14=0, FE-16=14, FE-18=7, FE-44=29, FE-46=8, FE-48=27, FE-49=31, FE-50=3, FE-51=70, FE-52=10, FE-53=28, FE-54=1, FE-56=10, FE-57=28, FE-72=21, FE-73=22, FE-74=48.
In the above basic parameters set for the inverter, parameters in motor parameters volume (FA-01~FA-05) must be input according to the identification on motor name plate. After input of motor parameters, set F0-01 as 0, F0-02 as 0 and then set FA-00 as 11 where the motor is in a static and self-regulation state, and then check the motor. After check of the inverter to the motor, change the setting of F0-01 and F0-02 to 7 and 1 and then the inverter converts the control to startup and control through external signals.

Operation of Power Frequency:
In case of failure, frequency conversion system can be restored to the previous power frequency system to work. The works after shifted to power frequency system include restoring rotor wiring of the wound-rotor motor and connecting it to output terminals of the power frequency system after switching off the general power supply of the system. Then install and restore all the contact springs of cam controller under the hoist console. At that time, the power frequency system restores to the condition before the frequency-conversion device is changed and hoister operators can continue to conduct control according to the previous habits of operating power frequency system.

4. Energy Saving Calculation
As for wound-rotor motor, whether in startup, brake or speed regulation, rotor-resistance mode will lead to electric energy consumption. The consumption will increase with speed reducing of and slip ratio (S) increasing. Power relation of wound-rotor motor is:

Where:
    T - Electromagnetic torque of the motor
    ω₀ -Synchronous angle speed
    I₂, R₂ - Current and resistance of each phase of the motor
    R_f - Auxiliary resistance of rotor series connection
    P₂ - Electromagnetic power of input rotor
    P_T - Mechanical output power
    P_h - Speed differential power consumed for rotor resistance

In the above formula, when S=0.5, half of electromagnetic power is consumed for rotor resistance and the efficiency of speed regulation system is very low, only about 50%. In this case, through calculation, the hoister operates in low-speed section for 30% of the time and the energy saving rate is around 24.5%, with remarkable economic benefits.