Analysis on the transformation of electric control

2022-08-18
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Analysis on the transformation of the electrical control system of gantry crane

2 bucket gantry crane (su2500uh) adopts wound asynchronous motor rotor series resistance speed regulation. Due to the serious heating of the speed regulating resistor, the ambient temperature rises rapidly, the comprehensive performance index is poor, and the efficiency is low; The collector ring and brush of asynchronous motor require regular maintenance; A large number of relays and contactors have frequent failures and a large amount of maintenance; Eddy current motor braking is adopted for electric braking, which has poor dynamic performance and high energy consumption. The programmable controller is a product of Hitachi in the 1980s. It can only process switching values and has a long scanning time. Therefore, it is decided to upgrade the equipment

I. operation characteristics of portal crane with bucket

1. when the portal crane is started, the starting torque) 150% of the rated torque

2. when the grab drops, the motor is in the regenerative power generation state, and its energy should be fed back to the power side

3. when the grab is suddenly opened with full load and the coal is excavated with no load, the load will change sharply

4. the switching between electric braking and mechanical braking cannot be smoothly completed, and there are sometimes falling buckets

5. The luffing bar mouth of the luffing mechanism can stop accurately at 35m and 9m, and can stop urgently at 8m

6. the speed regulation resistance is switched through the contact handle, and the motor current changes suddenly during the switching, resulting in a large impact

II. Transformation configuration

according to the operation waiting point of the gantry crane, and in order to meet the requirements of the gantry crane's high starting torque, low-speed full torque, fast torque rise time and holding brake sequence control function, select the ACS600 series direct torque control frequency converter that abb can protect and handle when necessary, and select abbac80 (advance controller) PLC to match it to form a multi drive control system

1. AC80 programmable controller

ac80 PLC is specially designed for transmission. Its CPU is a 16 bit mc68360 processor with a working frequency of 25MHz, which is responsible for the logic control, switching value processing, data communication, etc. of the whole system. It communicates with the i/0 module through the electrical module bus, and can also control up to 12 transmission mechanisms through the drivebus. Users use function chart build: software (hereinafter referred to as FCB) to program AC80. AC80 program includes PC part (program part) and DB part (database part)

bu-85 bus adapter

the bus adapter and AC80 and each transmission mechanism form a star network structure through optical cables. Users can set the channel number and data transmission rate of each transmission point on the adapter through the dial switch on the adapter, and the transmission rate can reach 4Mbit/s

s600 thyristor power supply unit (TSU)

as shown in Figure 2, the thyristor power supply unit is mainly composed of two six pulse thyristor bridges. The positive bridge converts three-phase alternating current into direct current, and then transmits electric energy to the transmission part (inverter) through the intermediate DC link. Whenever the redundant motor braking energy needs to be fed back to the power supply, the reverse bridge will convert DC power into AC power

s600 inverter

acs600 inverter directly controls the torque of the motor through the stator flux of the AC motor. As shown in Figure 3, the switching control of power devices can be realized according to the calculated values of motor stator flux and torque. The high-performance digital signal processor (DSP) is used to quickly realize the selection of switching signals of power devices. Users can debug the inverter, set parameters and track faults through drive window software and cdp312 control panel. The inverter converts the DC power into AC power according to the control command of AC80 and outputs it to the motor. During the lowering process of the grab, the energy generated by the motor braking is rectified into DC and sent back to the DC busbar to feed back to the power supply unit

in order to ensure the accurate positioning of the luffing distance, an absolute value encoder and a photoelectric induction switch are added on the basis of the original cam limit to ensure the safe and stable operation of the mechanism

III. debugging method

the main steps of debugging are as follows:

1. Connect the PC with the service port on the PLC through RS-232 interface. FCB software is used to define the uo address of PLC, and the control program is compiled according to the operating characteristics and control process of the gantry crane; The written program is stored in the fprom of PLC, and then PLC reads the program from fprom to ram for operation

2. Set the address of each transmission mechanism in PLC. In the DB part of the program, use the drb00 module to define the address of the transmission point on the drivebus, and up to 12 addresses can be defined

3. inverter parameter setting. Before the motor is put into operation, it needs to be identified and operated. After the identification and operation is completed, the frequency converter establishes the digital model of the motor according to the identified parameters, and controls the motor according to the model, which is at a significant disadvantage in the competition in product development, performance, quality, reliability, service and so on

IV. transformation effect

the transformed gantry crane has the following characteristics:

1. The mechanical characteristics of the motor become hard, the positioning is accurate, and the unloading efficiency is improved

2. Running, starting and braking are stable, the impact is reduced during acceleration and deceleration, the safety is improved, and the service life of the machine is prolonged

3. remove the eddy current braking device, and the electric braking is realized by the frequency converter, which reduces the energy consumption and the amount of maintenance

4. the mechanical brake is put into operation when the motor speed is close to zero speed, so the service life of the brake pad of the mechanical brake is greatly extended

5. remove the speed regulation resistance of the original wound asynchronous motor; The short-circuit collector ring is used as a squirrel cage motor, which saves the cost of replacing the motor

6. reduce a large number of AC contactors and realize stepless speed regulation

7. Improve the stability of the electric control system by combining the powerful functions of PLC and frequency converter, such as protection, detection, fault alarm, etc

the stability of amplitude variation, lifting and opening and closing of su2 was tested on site. The rated load of grab was 16t, and the overload capacity was set to 120%. When the load reached 110% × L6 has been widely used in various safety lampshades and signal lamps to alarm at t, up to 118% × L6t first gear lifting stops for 1.5s, and the grab overload protection realizes accurate digitization. When the grab is in full load, the third gear lifting and lowering can be stopped accurately, and there is no bucket falling phenomenon. Grab, luffing acceleration and deceleration are stable, and stepless speed regulation is basically realized. The luffing crane mouth accurately stopped at 9m. So far, no fault maintenance caused by the luffing impact of 8m has been found

the stability of amplitude variation, lifting and opening and closing of su2 is tested by field experiment method, and the overload protection of grab is accurately digitized. When the grab is in full load, the third gear lifting and lowering can be stopped accurately, and there is no bucket falling phenomenon. Grab, luffing acceleration and deceleration are stable, and stepless speed regulation is basically realized. The luffing crane mouth accurately stopped at 9m. So far, no fault maintenance caused by the luffing impact of 8m has been found. After the transformation, the energy feedback is realized, which saves 30% power compared with the original system. The system before transformation needs to replace the contacts of the main contactor and auxiliary contactor once a quarter. These contacts are expensive and consume a lot of manpower during installation, and the maintenance cost is up to 30000 yuan/month. After the transformation, it only needs to clean and maintain the frequency converter regularly, which saves the maintenance cost. According to statistics, it can save more than 120000 yuan per quarter

completely change the technical problems of high failure rate and high energy consumption caused by the defects in the control mode of these three institutions

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