introduction

　　AC asynchronous motors have been widely used in my country's coal mines, petroleum, chemical industry, steel, power generation, water supply, cement and building materials due to their simple structure, high operational reliability, strong environmental adaptability and excellent drag performance. . But the fatal disadvantage of AC asynchronous motors is that they have a large starting shock, which will have an adverse effect on the system. The main impact is reflected in two aspects:

　　(1) Electrical problems:

　　5-7 times the rated current when starting, causing the motor windings to overheat due to the current, thereby accelerating the insulation aging, causing voltage fluctuations in the power supply network, and affecting the normal operation of other equipment under the same power grid.

　　(2) Mechanical problems:

　　Excessive starting torque produces mechanical shock, which causes a large impact on the driven equipment, shortens the service life, and affects accuracy. Such as damage to the coupling, tearing of the belt, etc. Causes abnormal wear and impact of mechanical transmission components, accelerates aging, shortens life, and increases maintenance workload.

　　Jiangsu Kangjie Environmental Engineering Co., Ltd. is an environmental protection enterprise specializing in the design and development of air pollution control projects, equipment manufacturing, installation and commissioning, and operation and management. This case is the two dust removal fans provided by Kangjie Company to Xuzhou Southeast Steel. Due to the relatively large motor power (10KV/1250KW, 500KW), the mechanical impact on the fan during the start-up process is relatively large, which increases the workload of system maintenance. ; The starting current is 6 times the rated current. Secondly, when the motor is started directly, the power grid drops more seriously. When the power grid voltage drop reaches 85%, other equipment cannot work normally.

　　1. Plan selection

　　After communicating with Jiangsu Kangjie Environmental Engineering Co., Ltd. in many aspects, I chose our company's GSDQ series high-pressure water resistance soft starter. The main parameters of the field equipment are as follows:

　　Dust removal fan: YKK630-6

　　Rated power: 1250KW

　　Rated voltage: 10KV

　　Dust removal fan: YKK500-6

　　Rated power: 500KW

　　Rated voltage: 10KV

　　Working principle: After the high-voltage switchgear is closed, the water resistance starter PLC (programmable controller) receives its auxiliary normally open contact closing signal (called start command), and after being arranged into the PLC logic to judge, the starter runs according to the program . At this time, the servo motor drives the transmission mechanism and the electrode plate to move down, the distance between the electrode plate and the fixed electrode plate gradually decreases, the resistance value between the two electrode plates gradually decreases, and the main motor gradually accelerates. When the movable electrode plate moves to the lowest end, The resistance value is close to zero, and the vacuum switch is short-circuited to make the main motor run at full pressure, while the moving plate moves up to the uppermost end, ready for the next start

　　2. Technical features

　　(1) The starting current is small, not more than 2~3.5 times of the rated current of the motor, which reduces the starting heat of the motor and effectively prolongs the service life of the motor.

　　(2) Smooth start, reduce the impact on mechanical equipment, and extend the service life of mechanical equipment and motors by about 20%.

　　(3) Simple structure and easy maintenance.

　　3. Operation status

　　The following is the comparison between GSDQ soft start and full voltage start:

　　(1) Causes voltage fluctuations in the power grid, affecting the operation of other equipment on the same power grid

　　When the AC motor is started directly at full voltage, the starting current will reach 5-7 times the rated current. When the capacity of the motor is relatively large, the starting current will cause a sharp drop in the grid voltage and affect the normal operation of other equipment on the grid.

　　When using GSDQ soft start, the starting current is generally 2~3.5 times the rated current, and the grid voltage fluctuation rate is generally within 10%, which has very little impact on other equipment.

　　(2) Impact on the power grid

　　The impact on the power grid is mainly manifested in two aspects:

　　A. The impact of the large current directly started by the motor on the power grid is almost similar to the impact of a three-phase short circuit on the power grid, which often causes power oscillations and destabilizes the power grid.

　　B. The starting current contains a large number of high-order harmonics, which will cause high-frequency resonance with the grid circuit parameters, causing malfunctions such as relay protection malfunctions and automatic control failures.

　　When using GSDQ soft start, the starting current is greatly reduced, and the above influence can be completely eliminated.

　　(3) Damage the insulation of the motor and reduce the life of the motor

　　A. The Joule heat generated by the large current repeatedly acts on the outer insulation of the wire, which accelerates the aging of the insulation and reduces the service life.

　　B. The mechanical force generated by the large current causes the wires to rub against each other, reducing the insulation life.

　　C. When the high-voltage switch is closed, the vibration of the contacts will produce operating overvoltages on the motor stator windings, sometimes reaching more than 5 times the applied voltage. Such high overvoltages will cause great damage to the motor insulation.

　　When using GSDQ soft start, the maximum current is reduced by about half, and the instantaneous heat generation is only about 1/4 of straight up, and the insulation life will be greatly extended; the motor terminal voltage can be adjusted from zero during soft start, which can completely avoid overvoltage damage.

　　(4) The damage of electric power to the motor

　　The large current produces a great impact on the motor stator coil and rotor squirrel cage bar, which will cause the clamping loose, the coil deformation, and the squirrel cage bar breakage.

　　When using GSDQ soft start, because the maximum current is small, the impact force is greatly reduced.

　　(5) Damage to machinery and equipment

　　The starting torque during full pressure direct starting is about twice the rated torque. Suddenly adding such a large torque to stationary mechanical equipment will accelerate the fatigue of the blades or even break the blades.

　　The torque of using GSDQ soft start will not exceed the rated torque, and the above drawbacks can be completely overcome.

　　When using decompression starting, the above-mentioned hazards are only reduced to a certain extent; when using GSDQ soft start, the above-mentioned hazards almost completely disappear; independent transformer power supply directly starting can only be mitigated in terms of grid voltage fluctuations, and other hazards All still exist.

　　4 Conclusion

　　The two dust removal fans started smoothly and fully achieved the expected results, which not only improved the equipment efficiency, but also met the production process requirements, and therefore greatly reduced the equipment maintenance and repair costs, and the direct and indirect economic benefits were obvious.