What is a series motor and what is the specific principle?
A series-excited (series-excited) motor is a series of stator windings and rotor windings.
Working principle: When the AC power supply is supplied, the principle of generating rotational torque can still be explained by the operation principle of the DC motor. When a current flows through a conductor, a magnetic field is generated around the conductor, and the direction of the magnetic field lines depends on the direction of the current.
Put the energized conductor into a magnetic field, and the magnetic field interacts with the magnetic field generated by the energized conductor, which will cause the conductor to be subjected to a force f, and thus cause movement. , when a coil composed of two conductors facing each other is placed in a magnetic field, the two sides of the coil are also subjected to a force, and the two forces are in opposite directions, resulting in a torque.
When the coil rotates in the magnetic field, when the corresponding two coil sides turn from one magnetic pole to the other, the direction of the acting force on the conductor will change due to the change of the magnetic field polarity, which also makes the The direction of the torque changes, causing the coil to turn in the opposite direction, so the coil can only swing back and forth around the central axis.
A submersible pump with a rated current of 12a has a maximum starting current of 227a, which will cause the thermal and magnetic protection action of the upstream switch to trip. The instantaneous value of the starting current has nothing to do with the load, even if the pump blade is jammed, it should not cause the maximum value of the instantaneous value of the starting current to change. If the pump leaves are really stuck, it will only cause the starting current to last for a long time and not fall down (this may cause the thermal-magnetic protection action of the upstream switch to trip).
If the insulation of the motor windings is normal to the ground, the reason why the maximum value of the starting current is too large is likely to be caused by the decrease of the insulation resistance value between the winding phases or between the turns. It is easier to check the insulation drop between phases, but it is difficult to check the insulation drop between turns.
There are two types of motor overload:
One is mechanical load overload, which means that the driven load exceeds the rated value or the transmission system has a jamming phenomenon, which has nothing to do with short circuit.
The second is that the load is normal and the motor current is overloaded, which may be a short circuit between the motor windings locally to the ground and between turns.
What is the application of frequency conversion speed regulation? What are the benefits?
Before the realization of frequency conversion speed regulation (theoretically realized, but the real realization is after the invention of power electronic devices) the traditional speed regulation adopts DC
The disadvantages of DC speed regulation are:
1) The structure of the DC motor is complex and the maintenance cost is high
2) Due to the existence of the commutator, there is not much room for improvement in the power of the DC motor.
Therefore, the advantages of variable frequency speed regulation are:
1) Make the AC motor get the same excellent speed regulation performance as the DC speed regulation
2) The maintenance of AC squirrel-cage asynchronous motor is simple and convenient
3) There is no limitation of the commutator on the power of the AC motor
25. Is it enough to use a 100kva transformer to supply a total power of 300kw electrical appliances (maximum 37kw)?
How much load can a 100kva transformer carry? Look at the formula to know:
p=capacity*power factor*80%=100*0.9*80%=72kw
Generally, 20% overload operation for 1 hour is allowed, so it is enough.
It mainly depends on whether the total current exceeds or not. The high-voltage current of the 100kva transformer is 5.8a, and the low-voltage current is 150a. It doesn't matter even if it is overheated occasionally, the main thing is that the temperature rise should not exceed 55 degrees. The temperature rise is equal to the actual temperature minus the ambient temperature.
There are many types of motors, but according to the power supply, they are nothing more than AC motors and DC motors. So is there a motor that can use both AC power and DC power?
The answer is: yes, the single-phase series excitation (series excitation) motor to be introduced below is one such motor.
Single-phase series excitation (series excitation) motors are quite common. Various hand-held power tools such as hand drills, angle grinders, and small household appliances mostly use single-phase series excitation (series excitation) motors. The most obvious feature of this motor is There are carbon brushes.
