Analysis on the control technology of changing the

  • Detail

Analysis on the control technology of changing the main winch of tower crane to frequency converter

k40/21b, 23B and 36B tower cranes are tower cranes produced by introducing French Botan technology in the 1970s. They are the most abundant varieties of tower cranes in China at present. The main winch mechanism adopts 70rc electric control situation. Because the speed regulation is realized by mutual energy consumption braking of two motors at low speed, the disadvantages include: high energy consumption, high requirements for control circuit, high requirements for contactor, easy to gear, easy to burn motor and so on

major reasons for energy consumption: due to the use of energy consumption braking, the energy absorbed into electricity is very large at low speed. Part of the electric energy is consumed in the energy loss of the two motors, part of the energy is consumed in the starting speed regulation resistance, and part of the energy is used for the motor output kinetic energy. The energy of the first two parts is useless work (about 70%). But all of them need to release this part of energy through the motor. This increases the burden on the motor and makes it easy to burn out

requirements for control circuit: since the realization of this speed regulation method requires complex switching of the main circuit of the electronic tensile testing machine, it requires cumbersome control circuit action coordination, and the failure of each circuit and contact will produce serious adverse consequences. Such as burning the motor, hitting the gear, cutting off the motor shaft, seriously burning the contactor contacts and other faults. Therefore, there are strict requirements for contactors, which must be checked frequently to ensure reliable operation, so contactors are replaced more frequently. At the same time, there are many unpredictable faults in the circuit

example 1: the power supply of its braking circuit is from 380V coupling voltage transformation and full wave rectification, so that the braking power supply has a dangerous voltage of 380V, which is a potential safety hazard here. Moreover, its control circuit is extremely cumbersome. When the third, fourth and fifth gears are converted to each other, the LFA brake relay jitters. Therefore, CXL, LRA and Red1 circuits are added to the brake circuit, and the freewheeling circuit is used to eliminate the braking instantaneous and braking phenomenon caused by LFA relay jitter. These cumbersome control circuits have strict requirements on all aspects of the circuit. Once the brake freewheeling circuit and control circuit fail, there may be mechanical accidents such as brake spline rolling key, serious wear of brake pads, and even gear striking and motor shaft cutting. It seriously threatens the safe and normal operation of mechanical equipment

example 2: the eight contactors LPV, lpv1, lragv, lragv1, LGV, lgv1, lrapv and lrapv1 are used to switch the power supply of motor and energy consumption braking, and their control lines are extremely cumbersome. Such cumbersome control significantly increases the frequency of failure. In the second gear of hook dropping, LGV and lgv1 pull in to provide power for the high-speed motor. The pull in of lrapv and lrapv1 causes the low-speed motor to generate energy consumption braking. The two AC contactors of lrapv and lrapv1 need to be connected with a large amount of DC in sections. Therefore, faults often occur, such as the main contact burning out, abnormal power supply of the control line, mechanical failure of the contactor itself, etc., so that the low-speed motor cannot reliably realize energy consumption braking, Thus, the speed of the second gear is actually the speed of the fifth gear. In practical work, when the second gear of the hook is used, it is the time when the heavy object reaches the ground and is in place slowly, and the ground operators are near the heavy object, which is a major hidden danger of insecurity; The high-speed landing of heavy objects makes the elasticity of the boom recover too fast, and the tower body swings seriously, which is a hidden danger of equipment insecurity; The high-speed starting and braking of the main winch mechanism itself will cause serious damage to the motor, gear and brake parts

cause analysis of easy gear striking: part of the gear striking phenomenon of 23B and 36B machines is caused by the mutual switching of electrical control parts. Under the condition that the circuit works normally, the speed of the motor changes quickly in the process of gear shifting. This rapid switching has a relatively large impact on the gear, especially in the process of mutual switching between fourth and fifth gears, the speed changes most, which has a great impact on the motor It also has the greatest impact on the gears. Therefore, many of the tower cranes we are running now remove the fifth gear to avoid burning the motor and gear. This can greatly reduce the burning of motor and gear. There are also sudden changes in energy and speed in other gears. For example, when switching between second and third gears, the active motor should accelerate and the braking motor should reduce the braking force. This process is completed in an instant, which is particularly easy to gear. According to the analysis of the diameter of reinforcement products

it is easy to burn the motor: it is mainly because the motor works under the rated load for a long time. Although we do not lift large tonnage weights, at low speed, the two motors input a large current at the same time. The active motor is 120a AC and the brake motor is 100A DC. Such a large current will heat the motor in a very short time. Such a large current will also produce a large electromagnetic force in the winding of the motor. These two reasons will accelerate the aging of motor insulation. This is also the root cause of such tower crane burning motor

ways and advantages to solve the above problems after using frequency converter:

using frequency conversion speed regulation is the most reasonable and the best solution from the speed regulation principle of AC motor. With the development of electronic technology, especially the maturity of frequency conversion technology, it provides a good solution for AC motor speed regulation

(as shown in the new figure) when actually working, a single motor is working, and there is no switching between the two motors. The switching of high-speed and low-speed motors requires the driver to master and cooperate with the lifting weight protection circuit. In order to meet the needs of lifting weight and speed, high-speed motors can be used when the lifting load is less than 50% of its rated lifting weight, and low-speed Motors should be used when the lifting weight exceeds 50% of its rated lifting weight. The brake power supply of the new line is designed from the secondary measurement of the control transformer, bridge rectification is adopted, and the pull-in signal of the LFA brake relay is taken from the frequency converter, which can realize the synchronous operation with the motor, make the operation more reliable, and minimize the wear of the brake pads

the use of frequency converter for speed regulation can realize the stability of its braking, and there will be no sudden change in mechanical operation during gear change. It is of great benefit to the operation of gears and can greatly reduce the phenomenon of gear beating

the single motor works, and the frequency converter provides power supply. The frequency converter has reliable and perfect protection function. Because there is no energy consumption braking between the two motors during operation, the current of the motor during actual operation is greatly reduced, especially at low speed, the current is only about 30% of the original circuit, and the size of the current depends on the number of lifting weights. There is no mutual braking between the motors to quickly raise the current of the oil cylinder. Reduce the phenomenon of motor heating to a great extent. Thus, the service life of the motor is greatly extended

since there is no energy consumption braking at low speed, energy can be saved, about 40% of electricity can be saved

after replacing the frequency converter, there is no need for a large capacity contactor, which can greatly reduce the maintenance times of the tower crane, reduce the maintenance cost, and improve our overall service level

the frequency converter has perfect parameter monitoring technology, which can more intuitively monitor the running state of the motor. The perfect timing function of the frequency converter can more accurately understand the running time of the motor and the actual running time of the tower crane, and provide a more accurate time recording reference for the maintenance of the motor and machinery

technical feasibility analysis of changing to frequency converter:

after brief calculation, it is considered that the technical problem of changing to frequency converter for 23B and 36B tower cranes can be adopted. First, the motor selected in the design of this equipment is the rated output torque of the motor at the maximum lifting load

rated output torque of four pole 51.5kw motor m=326n m。

23b when lifting 10t, the static torque converted to the motor shaft is: m=321n M

36b when lifting 12t, the converted static torque on the conductor shaft is: m=330n M

this equipment does not overload the motor. The current frequency converter can make the output torque of the motor reach 150% of the rated torque of the motor when the output is above 0.5Hz, so the low-speed starting problem we are worried about can be well solved. When the weight drops, the potential energy problem can be solved by adding a braking unit and a braking resistor outside the frequency converter. The heating problem of the motor at low speed is serious because the motor used to work under high current at this time. After changing to frequency converter, the heating phenomenon of the motor will be significantly reduced under the same situation. If we work at low speed for a long time, the temperature rise of the motor will be slightly higher because the cooling performance of the fan is reduced. We can install a fan at the back of the motor to improve the ventilation of the motor, So as to solve the problem of motor temperature rise at low speed for a long time

economic analysis after switching to frequency converter: it can reduce the maintenance cost and frequency. The original distribution box uses f115 imported contactors, each of which costs more than 2000 yuan. A total of 10 contactors are used. Based on the one-year service life of each contactor, the cost of replacing contactors is 20000 yuan, the annual maintenance cost of burning a motor is 7000 yuan, and the cost of beating a set of teeth is 5000 yuan. The total cost is 32000 yuan, which does not include the labor cost of maintenance, the cost of missed work, the cost of vehicle shift, etc. When the tower crane is used more frequently, the maintenance cost will be higher

2002 maintenance cost statistics:

103-016 h36b (Chongwenmen guojiwen), the total maintenance cost in 2003 was 157616.6 yuan

103-018 h36b (Chongwenmen Yuquan), the total maintenance cost in 2003 was 110633.29 yuan

103-007 h36b (Ma Liandao, Wu Jisheng), 20 cyano coordination compounds are considered to be the most promising such materials, with a total maintenance cost of 55021 yuan in 2003

the maintenance cost of seven such tower cranes in the first five months of this year is 120000. Among them, the cost of large parts used for the main winch is 50000 yuan, which does not include the maintenance cost of motor burnout and the cost of cj20-100a AC contactor used by Shenyang tower crane

according to the current situation and the price of the frequency converter, the actual investment of a single inverter is about 50000 yuan, which is determined according to the brand and model of the selected frequency converter

practical application of frequency converter in the slewing and luffing mechanism of tqz250 tower crane: at the beginning of this year, our company made technical improvement on the frequency converter of the slewing mechanism of tqz250 tower crane. Due to the actual working characteristics of the slewing mechanism, the requirements for control are very strict. First of all, an appropriate starting torque is required. If the starting torque is too large or too fast, the tower body will have serious torsion, which will accelerate the fatigue of the steel structure; Slow startup cannot meet the needs of construction. In the braking process, it is a strict test of the control circuit, because the upper part of tqz250 rotation weighs more than 60 tons. To make it stop smoothly in about 15 seconds, different deceleration methods need to be adopted at different times. We selected sjhfe inverter produced by Hitachi. After many careful adjustments with the factory service personnel, the tqz250 slewing and luffing mechanism has achieved the desired effect. After many careful adjustments, we gave full play to the perfect performance of the frequency converter, such as low-voltage protection, overload protection, acceleration and deceleration time control, which has a good protective effect on machinery and motors

after half a year of practical use of the frequency converter, we believe that the frequency converter can be well used in the 70rc main winch mechanism to eliminate

Copyright © 2011 JIN SHI