Motor knowledge
16. The transformer ratio is equal to the turns ratio of the primary winding to the secondary winding. The ratio of the single-phase transformer can also be expressed as the ratio of the rated voltage of the primary and secondary sides.
17. During normal excitation, the power factor of the synchronous generator is equal to 1; keep the output active, so that the excitation current is less than the normal excitation (underexcitation), then the nature of the direct-axis armature reaction is magnetically assisted; When the excitation current is greater than the normal excitation (overexcitation), the nature of the direct-axis armature reaction is demagnetized.
18. In DC motors, the iron loss is mainly present in the rotor core (armature core) because the stator core magnetic field is essentially unchanged.
19. In a DC motor, the first pitch y1 is equal to the number of slots between the first side and the second side of the component. The composite pitch y is equal to the number of slots between the upper edge of the two elements in series.
20. In a DC motor, when saturation is not considered, the cross-armature armature reaction is characterized by shifting the position of the magnetic field to zero, but the magnetic flux per pole is unchanged. When the brush is on a geometric neutral, the armature reaction is magnetic.
21. In a direct current motor, a component that converts external direct current into internal alternating current is a commutator. The purpose of the commutator is to convert DC to AC (or vice versa).
22. In the synchronous motor, when the field flux F0 of the stator winding is at the maximum value, the back E0 reaches the minimum value. When F0 reaches zero, E0 reaches the maximum value, and the phase between F0 and E0. The relationship is F0 ahead E090o. And the relational expression between E0 and F0 is: E0=4.44fNkN1F0.
23. In a motor, the leakage flux refers to the flux of only the winding winding itself, and the back electromotive force generated can often be equivalent to a leakage voltage drop (or negative reactance drop).
24. Asynchronous motor rotors are: - squirrel cage, winding type and so on.
25. The slip s of an asynchronous motor is defined as the ratio of the difference between the synchronous speed and the rotor speed to the synchronous speed. When the asynchronous motor operates in the motor state, its slip rate s ranges from 1>s>0.
26. The relationship between the electromagnetic torque Tem of the asynchronous motor and the slip rate s There are three key points in the Tem-s curve, namely the starting point (s=1), the maximum electromagnetic torque point (s=sm), and the synchronization point (s =0). When the rotor resistance of the asynchronous motor changes, the magnitude of the maximum electromagnetic torque Tem and the slip rate sm are characterized by the same size and the s position change.
27. Asynchronous motors must absorb the hysteresis of reactive power from the grid for excitation.
28. A coil assembly is energized with alternating current, and its magnetomotive force has a pulse-vibration property with time. A single coil is connected to an alternating current, and its magnetomotive force also has a pulse-vibration property with time.
29. When the synchronous generator is connected to the grid, the three-phase terminal voltage is required to have the same voltage as the grid three-phase voltage: frequency, amplitude, waveform, phase sequence (and phase).
30. The rotor of the synchronous motor has two types: hidden pole and salient pole.
