Soft start and local compensation method of asynchronous electric motor and device thereof

Abstract

The invention discloses a soft start and local compensation method of an asynchronous electric motor and a device thereof. A control system of an asynchronous electric motor is internally provided with an electrical switch of a high voltage thyristor; the soft start of the asynchronous electric motor and the switching of the local reactive power compensation of the asynchronous electric motor is completed by the on-off of the electrical switch of the high voltage thyristor to realize the local reactive power compensation of the asynchronous electric motor. The device at least comprises one detecting controlling unit and one compensating capacitor set, wherein the detecting controlling unit is internally provided with the electrical switch of the high voltage thyristor, and the output of the electrical switch of the high voltage thyristor is respectively connected with a controlled electric motor and the local compensation capacitor set. Under the coordinate control of the detecting controlling unit, the electrical switch of the thyristor completes the soft start of the electric motor and the switching of the local compensation capacitor set of the electric motor.

Description

technical field [0001] The technical invention relates to a control device of an industrial motor, in particular to a soft start of the motor and an in-situ compensation device of the motor. Its application fields are occasions where high-power high-voltage motors in metallurgy, mining, building materials, petrochemical, water supply and drainage industries need soft starting, local compensation, and infrequent starting. It is especially suitable for loads with one-way rotation, such as water pumps, fans, compressors, ball mills, etc. Background technique [0002] There are two main ways to start the motor, one is the direct starting method, and the other is the step-down starting method. For the direct starting method, due to many restrictions, it is mainly manifested in the following three aspects: [0003] (1) The starting current can be as large as 4 to 7 times the rated current of the motor, and the actual measurement of the starting current of some domestic motors is...

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Problems solved by technology

If a large motor is directly started, the excessive starting current will cause a significant drop in grid voltage, which will affect the normal operation of other electrical and electronic equipment in the same grid. The line relay protection device trips due to the overcurrent protection action, which interrupts the line power supply

[0004] (2) Direct starting will cause mechanical impact on the dragged working machinery. For water pump loads, too high starting torque will cause soft damage (mechanical deformation, fatigue aging, etc.) to blades, bearings, flaps, etc. ) and hard damage (cracks, fractures, etc.) are relatively common, and may even cause severe water hammer damage to the equipment due to excessive impact force (and reaction force) of the water flow on the pipeline

[0005] (3) The direct start requires a large capacity of the power supply transformer, and the capacity of the transformer for supplying power to the farmland drainage and irrigation pumping station is often not up to the requirement of the direct start for the capacity of the power grid

[0008] (1) The degree of current and torque drop cannot be controlled, and these values ​​are fixed at 1 / 3 of the rated value

[0009] (2) When the starter is switched from star connection to delta connection, there will usually be large current and torque changes

[0011] (1) The step change of the voltage (generated during step conversion) causes large current and torque changes, which will lead to frequent mechanical and electrical failures just like the performance limit "2" of the star / delta starter

[0012] (2) Limited output voltage types (limited number of starting voltage taps), which limits the choice of ideal starting current

[0014] (1) Starting characteristics are difficult to optimize

The reason is that the resistance value is determined when the starter is manufactured, and it is difficult to change it during use. Although it is possible to perform graded starting by converting taps, when the number of stages is large, it will inevitably increase the complexity of the control system, and the manufacturing cost, failure The efficiency will also be greatly increased accordingly, so the general resistance starter is between 2 and 5 levels.

In this way, the main power parameters such as voltage and current applied to the stator winding of the motor still fluctuate greatly when starting in stages.

[0015] (2) The starting characteristics are not good in frequent starting occasions

[0016] (3) When the load is large or the starting time is long, the operating characteristics are deteriorated because the resistance value changes with the temperature of the resistor

[0027] (1) When the compensation device is switched on, a large inrush current is generated, and an overvoltage is generated when it is cut off, reducing the service life of the switch and compensation equipment

[0028] (2) High cost and large volume

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