Brushless DC motor refers to an explosion-proof stepping control motor with a rated voltage above 1000V. The voltages of 6000V and 10000V are often used. Due to the differences in the study of foreign power grids, there are also voltage technical levels of 3300V and 6600V. Brushless DC motors can produce because the working power of our motors is proportional to the product of voltage and current. Therefore, the driving power of low-voltage motors continues to increase to a certain degree of influence (such as 300KW/380V). The current will be subject to the wires and allow students to take risks. It is difficult to develop and expand due to the limitation of capacity, or the cost is too high. We need to be able to achieve high-power output by effectively increasing a voltage.
The main advantages of DC brushless motors are large power and strong impact resistance; the disadvantage is large inertia, which makes it difficult to start and brake.
1.When ordinary squirrel-cage explosion-proof stepper motors are directly started at no-load and full voltage, the starting current will reach 4-7 times the rated working current. When the explosion-proof stepper motor capacity is relatively large, the starting current will cause the national grid voltage to drop sharply, and the voltage signal frequency will also change. This will seriously damage the normal economic operation of other technical equipment of the grid company, and may even cause damage. Caused the power grid company to lose social stability, causing even greater accidents for students.
2.The large current of the explosion-proof stepper motor when the full voltage is started will have a great impact on the stator coil and the rotor squirrel cage bar, which will damage the winding insulation, cause the squirrel cage bar to break, cause the motor to malfunction, and the large current will also produce a lot of Joule heat damages the winding insulation and reduces the life of the motor.
3.The start of the series reactor is a step-down start. When the full voltage switch torque jumps, a mechanical shock will occur. Compared with direct full-voltage start, the probability of operating over-voltage is smaller. However, due to the random nature of high-frequency oscillations, large operating overvoltage may occur.
4.When the same starting torque is obtained, the starting current of the autotransformer step-down starting is smaller, which is suitable for the situation of larger resistance torque.
5.Use a medium voltage inverter as a soft start device to start a brushless DC motor. The performance of the starting system is very good, but the medium voltage inverter is more expensive. In addition, because the inverter technology is still in the historical period of social development, its reliability It is not very high, and the user's maintenance information technology can't keep up. This is the reason why our teaching method has not been applied and researched a lot. Generally, students use imported products and equipment. Using the inverter to start the motor can truly achieve no operating overvoltage, but the output working voltage of the inverter contains a large number of higher harmonics, which will also cause serious damage to the motor.
6.The consistency requires the use of silicon series technology medium voltage motor soft starter with high component parameters, low screening rate components, and high price screening equipment, which leads to a higher price than the device. In addition, after a period of use, the parameters of each component will change, so that the reduced performance of the pressure component can easily cause damage to the entire string of components, for example, the reliability of the device is reduced.
