Y Necessary conditions for buck start up

Here's how I understand it.

Q1The stator phase current of the motor is synthesized by two components: the excitation current and the rotor current (this relationship can be applied to the transformer, the stator current is the current on the power side of the transformer, and the rotor current is the current on the load side of the transformer).

At the time of start-up, due to the low equivalent impedance of the rotor (similar to the short circuit on the load side of the transformer), the rotor current increases, and the stator current increases, so "in order to limit the starting current" is indeed to limit the "current" in the rotor winding or copper strip, but at the same time, it is also to limit the stator phase current of the motor, the two cannot exist independently, but in the application of estimation, detection and discussion, the stator phase current is simpler than the rotor current, so the limitation of the starting current is based on the stator current. Then the voltage drop caused by the large current generated by the rotor is related to the entire power grid, because the stator current comes directly from the power grid, the stator current becomes larger, the current on the load side of the power grid transformer increases, and the impedance of the transformer itself reduces the voltage on the load side, affecting the operation of other equipment.

Q2It is certainly not correct to say that the electromagnetic torque is proportional to the square of the stator winding voltage, for example, when the constant torque load is running stably, the frequency does not change, and the u decreases, but the load torque does not change, so that the speed decreases, the slip rate rises, and the electromagnetic torque does not change. It can be seen that to discuss the electromagnetic torque is proportional to the square of the stator winding voltage, firstly, the motor parameters cannot be changed, secondly, the frequency of the power supply does not change, and the slip rate does not change again, the first two conditions are easy to meet, and the slip can be approximated constant in three cases:

No load, maximum torque, starting torque.

When there is no load, the slip rate is approximately 0, and the electromagnetic torque is approximately 0; When discussing the maximum torque, it is possible to derive a constant slip rate; When finding the starting torque, the slip rate is 1. In all three cases, the electromagnetic torque can be considered proportional to the square of the voltage, but the first one is meaningless. The formula is not given, as long as the relationship is known in practical application.

Q3The reason why it is necessary to check the starting current, in fact, it has been discussed in question 1, that is, the starting current is required to be less than the requirements of the power grid, no matter how the starting current is adjusted, the starting torque must change, and the starting torque is generally required to be greater than the double load torque, so it needs to be checked at the same time.

Q4The number of poles refers to the sum of the number of poles of the rotating magnetic field n,s in the air gap. The number of stator and rotor windings or the number of copper strips is determined by the number of magnetic poles, the number of slots, the winding method, etc.

Q5Line voltage = root 3 phase voltage, which means that the effective value of the line voltage is 3 times the root value of the phase voltage. Symmetrical three-phase is necessary to derive the formula.

Phase voltage refers to the voltage of each phase uan, ubn, ucn. Line voltage refers to the voltage difference between each phase, e.g. UAB = UAB-UBN.

It is easy to conclude from the vector method that the UAB vector UAB amplitude is 3 times that of UAN, UBN because the amplitudes of UAN and UBN are equal and the difference is 120 degrees. UBC, UAC are similar.

The normal operation of the motor is a triangular connection.

Y- (star angle) buck starting, also known as y- transformer start or star angle starting, is a method used to mitigate the current impulse during motor starting. It is mainly used in large three-phase asynchronous motors.

The effect of y- buck start is as follows:

Reduce the starting current: in the Y- step-down start-up process, the motor is initially started in the Y (star) connection mode, and the voltage is reduced to 1 3 times of the line voltage, so that the starting current is reduced and the impact on the power grid start-up block is reduced. When the motor reaches a certain speed, it is switched to a (triangle) connection mode to make the motor run normally.

Reduced torque during start-up: As the starting current decreases, so does the starting torque of the motor, which helps to protect the mechanical parts of the motor and equipment.

Improve the success rate of starting: Y- step-down start can improve the success rate of the band plex of large motor starting, and reduce the loss caused by starting failure.

Reduce the impact on the power grid: Due to the reduction of the starting current, the Y-step-down start can reduce the load on the power grid, reduce voltage fluctuations, and improve the stability of the power grid.

In short, Y-step-down start can effectively reduce the current impact when the motor starts, reduce the starting torque, improve the success rate of starting, and reduce the impact on the power grid. This starting method is suitable for large motors and occasions where the starting current is limited.

Summary. Hello dear, briefly describe the reasons for step-down start and the principle of Y-D step-down start as follows, 1. The motor starting process, the motor winding is wired in a star-shaped way, and the motor winding is converted into a triangle wiring mode after the start process is completed2. Compared with the motor control circuit of normal start-up operation, there are two more contactors and a time relay, and the role of the three contactors is the star-shaped starting contactor, the sealed motor winding star point contactor, and the angular running contactor, The time relay is used to control the conversion time of the star angle start, 3, between the star start control and the angle operation control, the auxiliary contact of the respective contactor should be interlocked, in case of short circuit accidents, I wish you a happy life! Hope mine is helpful to you!

Briefly describe the reasons for step-down start and the principle of Y-D step-down start.

Hello dear, briefly describe the reasons for step-down start and the principle of Y-D step-down start as follows, 1. The motor starts the filial piety process, and the motor leakage winding is wired in a star-shaped way, and then the motor winding is converted into a triangular wiring method after the start process is completed2. Compared with the motor control circuit of normal start-up operation, there are two more contactors and a time relay, and the role of the three contactors is the star-shaped starting contactor, the sealing motor winding star point contactor, and the angular running contactor, The time relay is used to control the conversion time of the star angle start, 3, the star start control and the angle operation control should be interlocked through the auxiliary contacts of the respective contactors to prevent short circuit accidents, I wish you a happy life! Hope mine is helpful to you!

Hello, I am Mr. Liu, who is good at digital, and has been engaged in the digital industry for 10 years now, and I am happy to serve you.

y-- The step-down start-up method is only suitable for ().

a.Fully loaded. b.Overload.

c.Light load, coarse kai or empty load.

d.Let the stool bury the conditions of the macro ants.

Correct answer: c