How does the current change of the induction motor from the start to the rated working state?

When the induction motor is in a stopped state, from an electromagnetic point of view, just like a transformer, the stator winding connected to the power supply is equivalent to the primary coil of the transformer, and the rotor winding of the closed circuit is equivalent to the secondary coil of the transformer being short-circuited; There is no electricity between the stator and rotor windings.

There is only a magnetic connection, and the magnetic flux is closed through the stator, air gap, and rotor core. When closing, the rotor has not yet rotated due to inertia, and the rotating magnetic field cuts the rotor winding at the maximum cutting speed - synchronous speed, so that the rotor winding induces the maximum possible.

The high electric potential, therefore, flows through the rotor conductor with a large current, which generates magnetic energy that cancels out the stator magnetic field, just as the secondary magnetic flux of a transformer cancels out the primary magnetic flux.

In order to maintain the original magnetic flux that is compatible with the power supply voltage at that time, the stator automatically increases the current. Because the current of the rotor is very large at this time, the stator current also increases very much, even up to 4 7 times of the rated current, which is the reason for the large starting current.

Why is the current small after starting: as the speed of the motor increases, the speed at which the stator magnetic field cuts the rotor conductor decreases, the induced potential in the rotor conductor decreases, and the current in the rotor conductor also decreases, so the stator current is used to offset the influence of the magnetic flux generated by the rotor current.

That part of the current also decreases, so the stator current goes from large to small until it is normal.

Direct start starts large and slowly becomes smaller until it stabilizes at the rated current.

Hello, glad to answer for you. The starting current of the motor is generally 4-7 times of the rated current, and the starting current refers to the impulse current of the electrical equipment (inductive load) when it is just started, and it is the amount of current change in the short period of time from the moment the motor or inductive load is energized to the stable operation. Hope mine is helpful to you.

As soon as the magnetic flux passing through a closed circuit changes, an induced current is generated in the closed circuit. Therefore, "a part of the conductor of a closed circuit cuts the magnetic inductance line in the magnetic inductance line, and the current generated is called the induced current" is one-sided, and the conductor can also generate the induced current without cutting the magnetic inductance line.

The magnitude of the induced current is proportional to the magnetic induction intensity b, the length of the wire l, the speed of motion v, and the sine of the angle between the direction of motion and the direction of the magnetic inductance line. Increasing the magnetic induction intensity B, increasing the length of the wire L of the cutting magnetic inductance line, increasing the cutting speed v and cutting the magnetic inductance line as perpendicular as possible (=90°) can increase the induced state current.

Whether at start-up or running, the power of the motor is mainly provided by the working windings. Therefore, the smaller the resistance, the better, and the main task of the starting winding is to assist the working winding to generate a rotating magnetic field, and it does not require much power;

The current is also smaller than that of the working winding, so in order to save some material and to give space to the working winding, a small line is used, so the resistance is large. In addition, some starting windings have a large number of turns, and the wire diameter can only be reduced in a limited space, so the resistance is larger than that of the working winding.

For ordinary motors, the starting current is 4-7 times of the rated current, and if it is a first-class energy efficiency motor, the multiple will be larger.

When the three-phase rolling return induction motor starts, the starting current is very large, and the rated current can reach ().

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Correct answer: 4--7 times.

In an instant, from small to large, and then from large to small, the start is complete. Normal operation.

The starting current is greater than 2-4 times the rated current.

It depends on how to start, if the frequency conversion start, the frequency is from low to high at the same time, the voltage is also adjusted from low to high, and the current can be relatively gentle. In the case of direct start, the instantaneous current is larger. The following is a curve chart of the single-cycle effective value of voltage and current when a three-phase asynchronous motor is started, for reference!

The starting current is generally 4-7 times the rated current.

Starting current refers to the impulse current of electrical equipment (inductive load) at the beginning of starting, is the current change in the motor or inductive load from the moment of energizing to the short period of time when the operation is stable, this current is generally 4-7 times the rated current, the state stipulates that in order to run the line safely and the normal operation of other electrical equipment, the high-power engine must be equipped with starting equipment to reduce the starting current. Inrush current is the maximum instantaneous current that passes through the input voltage before it reaches a steady state when the input voltage is turned on or off at specified intervals. The common starting methods of AC motor include direct start, string resistance start, self-coupling transformer start, star-delta decompression start and inverter start to reduce the impact on the power grid

1. The reason why the starting current is very large is that when it is just started, the slip rate s is the largest, and the rotor electromotive force e is also the largest, so the starting current is very large.

2. There are two reasons why the starting torque is not large: one is that the electromagnetic torque depends on the active component of the rotor winding current, when starting, s=1, the rotor leakage reactance is the largest, and the power factor on the rotor side is very low (left and right), therefore, the active component of the rotor winding current is very small when starting;

3. The large starting current leads to the increase of the leakage impedance voltage drop of the stator winding, and if the power supply capacity is small, it will also lead to the decrease of the output voltage of the power supply, and the result is that the magnetic flux of each pole air gap decreases, and then causes the reduction of the starting torque.

In the case of no load, the starting current is 4 to 7 times of the rated current, and it will generally not be started at full load, and the switch will definitely trip.

Generally, the three-phase squirrel cage motor does not stop after starting, and the load is driven by electromagnetic clutch control Where the fall height is more than two meters (including two meters) from the reference ground for operation, it is a safety regulation for high-altitude operations: generally wear a safety belt and have a special person to supervise. Give it satisfaction, hehe.

The motor is wound type, and the squirrel cage type is divided into no-load, light-load and heavy-load starting. The starting mode is different, the starting current is different, the winding general starting current is selected according to 2 4 times of the rated current, and the starting time is 8 15 seconds. Squirrel cage motors are generally selected by 4 8 times, and the starting time is 15 to 20 seconds.

The fuse is short-circuit protected, and when selected, it is about 7 times the rated current. The low-voltage circuit breaker has overload protection and short-circuit protection, and each switch is different, and the overload curve is different. i.e. the overload capacity is different.

Overload protection is selected as a multiple of the rated current. Some electrical operating regulations stipulate that more than 2 meters is at a high altitude. Aerial work must be fastened with safety belts, safety helmets, safety ropes, etc.

Throwing objects is strictly prohibited. It depends on what kind of homework you are, and you must check the operating procedures.

The starting current of the motor is 5-7 times of the rated current, and the load of the motor should also be considered; The starting time and the size of the starting current are related to the load driven2Select 3In order to meet the overload protection in the normal operation of the motor, the thermal relay setting value is generally multiple of the rated value of the motor, 4

Where there is more than 2m at the reference point of the fall height (exposed 2m) whether there is a high place to enter and stop the operation, are called high-altitude work, the regulations are: erect and dismantle scaffolding around the building, hang safety nets, install and disassemble tower cranes, gantry, well-shaped frames, construction elevators, pile frames, ascending and installing steel structural components, etc.

The starting current of the general asynchronous motor is 5-7 times of the rated current, and the starting time is related to the size of the starting current, and the load is driven; The selection of the fuse to protect the motor is generally selected according to the multiple of the rated current; High-altitude work is to stipulate that the vertical distance from the ground is more than 2 meters, and the safety regulations are: there must be a firm scaffolding, safety belt, safety helmet, safety rope!

1. Necessary conditions: there must be an intersection between the mechanical characteristics of the motor and the torque characteristics of the load, that is, there is t=tz.

2. Sufficient conditions: the intersection meets (dt dn-dtz dn) <0.

The automatic control device can realize the automatic control of mechanical equipment through the control of motor starting, braking, motor speed adjustment, motor torque control and control of certain physical parameters according to certain laws. Sun with potatoes.