A high-power motor starting system and method

Abstract

The invention discloses a high-power motor starting system and method. The high-power motor starting system which is combined with a PLC, a thyristor soft starter and a permanent magnet coupler with an adjusting device is designed, and the high-power motor starting method that no-load starting is carried out first, when currents are lowered to a set value and a rotor does not reach a set rotating number under a motor no-load state, currents are stabilized, and loading is increased gradually is designed. According to the scheme, the system and method have the advantages that structure is simple, and designing is reasonable. During a no-load starting process, motor starting power is lowered, influence on a power grid is reduced, peak currents are lowered, motor rotating number increasing is fast, then when the currents are lowered to a set value and the rotating number does not reach the set value, current value gradual increasing is maintained, effective power is improved, and accordingly starting speed is improved.

Description

technical field [0001] The invention relates to a motor starting system and method, in particular to a high-power motor starting system and method. Background technique [0002] The start-up of three-phase asynchronous motors, especially the direct start-up of high-power, heavy-duty motors, will produce large torque shocks and current shocks (generally 4 to 7 times the rated current, or even higher), excessive shocks It will have a serious impact on motors, power distribution equipment, other electrical equipment, transformers, and power grids. The main impacts are as follows: (1) It affects the stability of the power grid. ① The impact of the large current directly started by the super-large 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 oscillation and destabilizes the power grid; Contains a large number of high-order harmonics, which will cause high-frequency resonance with the grid circu...

AI Technical Summary

Problems solved by technology

The main impacts are as follows: (1) It affects the stability of the power grid. ① The impact of the large current directly started by the super-large 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 oscillation and destabilizes the power grid; Contains a large number of high-order harmonics, which will cause high-frequency resonance with the grid circuit parameters, resulting in faults such as relay protection malfunctions and automatic control failures

(2) Affect the normal operation of other equipment in the same power grid. When the AC motor is started directly at full voltage, the starting current will reach 4 to 7 times the rated current or higher. When the capacity of the motor is relatively large, the starting current will cause The sharp drop of the grid voltage will affect the normal operation of other equipment on the same grid

(3) Cause damage to the motor insulation and reduce the life of the motor. ①The Joule heat generated by the high current repeatedly acts on the outer insulation of the wire, which accelerates the aging of the insulation and reduces the life; ②The mechanical force generated by the high current causes the wires to rub against each other, reducing the insulation life ;③ When the high-voltage switch is closed, the shaking phenomenon of the contact will generate an operating overvoltage on the motor stator winding, sometimes reaching more than 5 times the applied voltage, such a high overvoltage will cause great damage to the motor insulation

(4) Cause damage to the mechanical parts of the motor. The high current will generate a great impact on the motor stator coil and the rotor squirrel cage, which will cause faults such as loose clamping, coil deformation, and squirrel cage breakage.

(5) It will cause damage to the load equipment. The starting torque when the full pressure is directly started is about 2 times the rated torque. Such a large torque is suddenly added to the stationary mechanical equipment, which will accelerate the wear of the gears and even drive the teeth and speed up the belt. Wear or even break the belt, accelerate wind blade fatigue or even break the wind blade, etc.

For example: (1) Increase the possibility of resonance in the power grid, resulting in high overcurrent or overvoltage and the risk of accidents

(2) Increase additional loss, such as current harmonics will increase the copper loss of the transformer

Voltage harmonics will increase iron loss

(3) Abnormal use of electrical equipment (such as motors, capacitors, transformers, etc.), resulting in heat loss, mechanical vibration, noise, and output power loss; resulting in overheating of the motor, accelerating insulation aging, and shortening their service life

(4) Make measuring and measuring instruments, meters, automatic devices, computer systems, and many electrical equipment operate abnormally, affect the measurement accuracy of equipment, cause malfunctions or errors, and reduce the processing quality of mechanical products

(5) Interfere with the communication system, reduce the transmission quality of the signal, destroy the normal transmission of the signal, or even damage the communication equipment

(6) In some cases, it not only generates harmonics, but also causes power supply voltage fluctuations and flickers, and even causes unbalanced three-phase voltages, which will endanger the safe and economical operation of the power grid and affect the normal use of electrical equipment

(2) When the temperature is too high and the temperature changes greatly, condensation is prone to occur inside the inverter, and its insulation performance will be greatly reduced, which may even cause a short circuit accident

(4) When the control cabinet equipped with frequency converter is subjected to mechanical vibration and impact, it will cause poor electrical contact

However, the thyristor soft start still has a certain amount of harmonic pollution. Since the torque decreases according to the square of the voltage ratio during start-up, the start-up torque is very small, which is not conducive to the start-up of high-power motors.

Images