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Application of Mine Hoist


              Application of ACI Frequency Inverter in Coal Mine Hoist
 

一、Summary of mine hoisting:

   Mine hoist is an important equipment in the production process of coal, iron ore and non-ferrous metals. The safe and reliable operation of the elevator is directly related to the production situation and economic benefit of the enterprise. Coal mine mining the coal through the inclined shaft lifting machine for the car onto the ground. The winch is mounted on the ground winch room (hoist), driven by the motor through the speed reducer drives the rotating drum, the wire rope wound on the drum several weeks to hang a car, driven by the motor from the ground to the underground mine will put the car or from underground to ground drag. This drive system requires frequent positive, reverse start, deceleration brake, and the speed of the motor according to a certain rule. The mechanical structure of the inclined shaft hoisting machine diagram as shown in figure 1. Incline hoist drive motor is generally winding asynchronous motor, the rotor series resistance speed governing mode. The basic parameters of lifting machine is: motor power 55kW, reel diameter 1200mm, reducer ratio 24:1, the maximum operating speed of 2.5m/s wire rope, wire rope length is 120m.

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    Fig. 1   Schematic diagram of mechanical transmission system of hoist drum


二、Existing problems: 
   

1, at present, the majority of small and medium-sized coal mine by lifting, the traditional slope hoist is widely used AC asynchronous motor rotor series resistance speed, resistance switching relay - contactor control。 This control system for AC contactor control in the process of frequent moves, equipment running longer, AC contactor main contact oxidation heat welding or poor contact, causing equipment failure。

2, the speed control performance of the elevator in the deceleration and crawling stage is poor, often cause the parking position is not accurate。 Hoist frequent start, speed and braking, the resistance in the rotor circuit will produce a considerable power consumption。

3, the traditional shaft hoist machine adopts AC winding motor series resistance speed, the AC asynchronous motor series resistance speed control system belongs to a stepless speed regulation, smooth speed difference; low speed soft mechanical properties, static slip resistance is bigger; the slip power consumption, energy consumption; current starting process the speed and impact in the process of shifting; high speed vibration, poor safety。


三、
Principle of frequency inversion and power saving

   In order to overcome the shortcomings of the traditional AC wound rotor series resistance speed control system, the variable frequency speed control technology is adopted to improve the constant torque control in the whole frequency range (0 ~ 50Hz)。 For the treatment of renewable energy, the energy consumption braking scheme with low price or more remarkable regenerative braking scheme can be adopted。 For safety considerations, hydraulic machinery brake needs to be retained, and in the design process of hydraulic machinery brake and inverter brake to be integrated。 The principle of mine hoist frequency control scheme is shown in figure 2。

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   Fig. 2 Schematic diagram of the frequency conversion speed regulation scheme of mine hoist

  The torque of wound motor is larger than that of the squirrel cage motor, whose load capacity is strong。 So still use the original 4 pole 55kW wound motor。 In the use of frequency inverter driver, it needs to take three wires in short circuit 。In the course of operation, the underground and the wellhead must be in contact with the signal, the signal is not confirmed, the hoist can not run。 Display of the location of mine car running, using the E6B2-CW6Z 40P encoder, the motor rotation 1 rotary encoder to produce 40 pulses, so each of the two compartment through the corresponding pulse distance is 1200 * pi / (24 * 40) =3。927, about 3。9mm。 If the 6 digit calculator, set the single pulse measurement value is 3。9, and the actual distance of the impulse is error value is 4-3。9=0。027mm, a circle of error is 0。027 reel running x 40 x 24=25。29mm, known wire rope length is 120m, if the calculation of the two pulses corresponding to the distance traversed by car 3。9mm approximation, 120m total error is 25。92 pi = 825mm * 120000/1200。 Then taking into account the actual detection process there is a pulse of the error, the maximum error between 829mm ~ 821mm, for tens of meters long in the car, the error range of less than 1m, the accuracy is sufficient。 Therefore, the position of the carriage can be calculated by using the number of pulses emitted by the rotary encoder in real-time statistics。 The other question is whether there is no cumulative error in the counting process? The actual detection, in a process of ascension began before the first counter is reset, the first heavy car after a certain point, open the counter, car in inclined position in taking this point as the basis, no accumulated error。 On the operating table, with a 8 inch touch screen display AC voltage and motor operating current and the location of the car。

四、Program implementation


    Incline hoist load is the typical frictional load, which is constant torque characteristic load. When the heavy truck is up, the electromagnetic torque of the motor must overcome the load torque and some of the static friction torque in starting time. The motor is located in the first quadrant in the electric working state. When the heavy car slows down, although the heavy vehicle has a downward force in inclined rail surface, the deceleration time of heavy vehicles is short, the motor will still be in the regenerative working state in the second quadrant. When the car down, the motor is in reverse electric state is located in the third quadrant. When the heavy truck down, the motor is located in the power generation state in the fourth quadrant. In addition, the motor is in the fourth or second quadrant , when it delivers tools or equipment to the mine. At this time the motor is in the state of renewable power for a long time, and need the effective braking. The energy consumption is bound to consume a large amount of electric energy. The regenerative braking mode can save this part of electric energy. But the regenerative braking unit price is higher, the investment is big, Transportation of tools or equipment to the underground accounted for only 10% of the total running time, so we select the low cost braking scheme with energy consumption braking unit and energy consumption resistance.

   Hoist load characteristic is constant torque load potential with big starting torque. Selection of the inverter should keep the margin, so we choose ACI V11-90kW inverter. Because of the hoist motor is in the electric state for most of the time, whose renewable energy generation is not much . It can realize the regenerative braking at heavy truck down time and smooth descending by using the braking units and braking resistance in inverter. The ground winch room also has a hydraulic machinery (disc) brake, which brakes for heavy vehicle at rest. Especially when heavy vehicles parks in the slope on the slope, there must be a mechanical brake hydraulic brake. The hydraulic mechanical brake is controlled by PLC and frequency inverter, and the mechanical brake is controlled by frequency inverter. When the output torque of the inverter reaches the set value, frequency inverter TA, TB port output switching signal, which means the motor torque is large enough. And then open the hydraulic mechanical brake to let the heavy car up. In deceleration process, when the frequency of frequency inverter down to 0.2Hz,it indicates that the motor torque is small, and the hydraulic brake should be stopped. Press the emergency stop button in emergency, with the effect of frequency inverter energy consumption brake and hydraulic mechanical brake, it ensures the hoist stops running in the shortest possible time.

     Traditional operation of the hoist: operation workers ,sitting in the ground winch room operation stage, holds a joystick to control the motor speed. In order to adapt to the operation of worker, the frequency inverters (no gear) use multi speed control mode. The principle of variable frequency speed regulation is shown in figure 3.



   Fig. 3 principle of variable frequency speed regulation











五、Electricity saving rate and investment return analysis 


    
Mine hoist that is used in a coal mine regulates the speed by 132KW three phase asynchronous motor rotor series resistance with speed switching of AC contactor.

As the power is relatively large, so the impact current of starting current is large, high-speed operation is uneven, and a large number of electric energy consumes in the rotor resistance, which results in a great waste of energy. At the same time, due to the electromagnetic noise of the contactor, the operating environment of the workers is extremely poor, which is urgently needed transformation.


   The inverter has a wide range of soft start, smooth speed and obvious energy-saving effect and other advantages, so the mine decided to use the production of the V11 series 185KW inverter of Guangzhou ACI Electric Company Limited after many Investigation. After several months of operation, it proved that the effect of ideal, mainly manifests in:

1。 Achieve the start of soft start, soft stop, and reduce the impact on the power grid。

2.The frequency of the frequency inverter can be adjusted, so that the speed regulation is more convenient and reliable, and the operation is more stable.

博乐彩票开奖3。 After using the frequency converter, the original shift contactor and the speed regulating resistance are saved, the maintenance cost is saved too, the maintenance time is reduced, and the output is improved。 At the same time, the electromagnetic noise of the contactor is eliminated, and the operation environment is improved, so that workers can avoid to work under the high temperature condition caused by the speed regulating electric resistance heating in summer。

博乐彩票开奖4. At low speed, energy saving effect is very obvious. Mine that is over 300 meters deep is measured by 4/50A meter. In the same power consumption, the hoist can pull 17 hooks by power frequency, which can pull 26 hook by the use of frequency conversion. Estimated power saving rate is about 20%. Because of the use of the frequency converter, the device basically run with full load. Even if we adopt the conservative algorithm, according to the 132KW of the motor load rate is 90%, the actual power is 118.8KW, the use of only 20 hours a day, 360 working days per year, saving electricity is still as high as 171 thousand degrees (118.8KW*20%*20h*360 degrees =302400). If we use the 0.5 CNY per kilowatt as the basis, a year can save electricity more than 80 thousand CNY (17.1*0.5=8.55 ten thousand CNY).

六、Concluding remarks

      Winding type motor rotor connects resistance to achieve speed control. Resistance consumes a large amount of slip power, the lower the speed of the motor, the greater the power consumption is. The use of frequency control is a low power high speed mode. The elevator is in a state of electric power for most of the time, The elevator is in a state of electric power for most of the time ,and the stability and safety of the system is greatly improved by frequency conversion and speed regulation of it. It saves manpower and material resources, improves the coal capacity, saves  electric power more than 20%.So the economic benefit is very considerable,



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