Electrical knowledge that electrical people need to master

Electrical knowledge that electrical people need to master

1. The current of the single-phase transformer under no load is different from the main magnetic flux, and there is a phase angle difference aFe because there is a current consumption. The no-load current is a cusp waveform because there is a larger third harmonic.

2. The AC current flows in the armature winding of the DC motor. However, the current flowing in the field winding is a direct current. The excitation mode of the DC motor includes other excitation, shunt excitation, series excitation, and compound excitation.

3. The back EMF expression of the DC motor is E=CEFn; and the electromagnetic torque expression is Tem=CTFI.

4. The number of parallel branches of a DC motor is always paired. The number of parallel branches of the AC winding is not necessarily the same.

5. In a DC motor, the components of a single-stack winding are connected in series by one on top of the other. Whether it is a single-wave winding or a single-stack winding, the commutator segments connect all the components together to form a single closed loop.

6. Asynchronous motors are also called induction motors because the rotor current of asynchronous motors is generated by electromagnetic induction.

7. When the asynchronous motor is stepped down, the starting torque is reduced, and the starting torque is reduced in proportion to the square of the starting current of the winding.

8. When the amplitude and frequency of the primary side voltage are constant, the saturation degree of the core of the transformer is basically constant, and the excitation reactance is also basically unchanged.

9. The short-circuit characteristic of the synchronous generator is a straight line. When the three-phase symmetrical short circuit occurs, the magnetic circuit is unsaturated; when the three-phase symmetrical steady-state short circuit, the short circuit is a purely demagnetized direct-axis component.

10. The current in the excitation winding of the synchronous motor is DC current. The excitation mode mainly includes excitation of the excitation generator, excitation of the static rectifier, and excitation of the rotary rectifier.

11. There is no even harmonic in the three-phase synthetic magnetomotive force; the symmetrical three-phase winding is symmetrical three-phase current, and there is no multiple multiple of 3 in the synthetic magnetomotive force.

12. Three-phase transformers generally want to have a side connected by a triangle or a grounded point on one side. Because the winding connection of the three-phase transformer is expected to have a path of the third harmonic current.

13. When the symmetrical three-phase winding is symmetrical three-phase current, the fifth harmonic in the synthetic magnetomotive force is reversed; the seventh harmonic is forward.

14. The mechanical characteristics of the series-excited DC motor are relatively soft. The mechanical characteristics of the DC motor are relatively hard.

15. The transformer short-circuit test can measure the leakage impedance of the transformer winding; the no-load test can measure the excitation impedance parameter of the winding.