45 motor knowledge, quickly identify and fill in the gaps!

1. When a single-phase transformer is unloaded, the current is out of phase with the main magnetic flux, resulting in a phase angle difference aFe due to the presence of iron loss current. The no-load current is a sharp waveform due to the presence of significant third harmonics.

2. The current flowing in the armature winding of a DC motor is also AC current. But the current flowing through its excitation winding is direct current. The excitation methods of DC motors include separate excitation, parallel excitation, series excitation, compound excitation, etc.

3. The expression for the back electromotive force of a DC motor is E=CE F n; The expression for electromagnetic torque 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 winding are connected in series by stacking one on top of another. Whether it is a single wave winding or a single stack winding, the commutator connects all components in series to form a single closed circuit.

6. Asynchronous motor, also known as induction motor, generates rotor current through electromagnetic induction.

7. When an asynchronous motor starts with voltage reduction, the starting torque decreases, and the starting torque and the square of the starting current of the winding decrease proportionally.

8. When the amplitude and frequency of the primary voltage remain constant, the saturation degree of the transformer's iron core remains basically unchanged, and the excitation reactance also remains basically unchanged.

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

10. The current in the excitation winding of a synchronous motor is direct current, and the excitation methods mainly include excitation generator excitation, static rectifier excitation, and rotating rectifier excitation.

11. There are no even harmonics in the three-phase synthesized magnetomotive force; Symmetrical three-phase windings carry symmetrical three-phase currents, and there are no multiples of 3 magnetic harmonics in the synthesized magnetic electromotive force.

12. Three phase transformers generally hope to have a triangular connection on one side or a midpoint grounded on one side. Because the winding connections of three-phase transformers all require a path for third harmonic current.

13. When a symmetrical three-phase winding is subjected to symmetrical three-phase current, the 5th harmonic in its synthesized magnetomotive force is reversed; The 7th harmonic is forward rotating.

14. The mechanical characteristics of series excited DC motors are relatively soft. The mechanical characteristics of his DC motor are relatively hard.

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

16. The transformation ratio of a transformer is equal to the turns ratio of the primary winding to the secondary winding. The transformation ratio of a single-phase transformer can also be expressed as the ratio of the rated voltage on the primary and secondary sides.

17. During normal excitation, the power factor of the synchronous generator is equal to 1; When the output active power remains constant and the excitation current is less than normal excitation (under excitation), the property of the direct axis armature reaction is magnetic assistance; When the output active power remains constant and the excitation current is greater than normal excitation (overexcitation), the property of the direct axis armature reaction is demagnetization.

18. In DC motors, iron loss mainly exists in the rotor iron core (armature iron core) because the magnetic field of the stator iron core remains basically unchanged.

19. In a DC motor, the first pitch y1 is equal to the number of slots that differ between the first and second sides of the component. The synthetic pitch y is equal to the number of slots that differ between the upper edges of two components connected in series.

20. In DC motors, when saturation is not considered, the characteristic of the armature reaction of the cross axis is to shift the position where the magnetic field is zero, but the magnetic flux of each pole remains unchanged. When the electric brush is located on the geometric neutral line, the armature reaction is cross magnetic.

In a DC motor, the component that converts external DC power into internal AC power is the commutator. The function of a commutator is to convert DC into AC (or vice versa).

In a synchronous motor, when the excitation magnetic flux F0 of the stator winding is at its maximum value, the back electromotive force E0 reaches its minimum value. When F0 reaches zero, E0 reaches its maximum value. F0 leads E0 by 90o. The relationship expression between E0 and F0 is: E0=4.44 f N kN1F0.

In a motor, leakage flux refers to the magnetic flux generated only by the winding itself, and the back electromotive force generated can often be equivalent to a leakage voltage reduction (or negative voltage reduction).

24. There are two types of rotors for asynchronous motors: squirrel cage and wound rotor.

25. The slip rate 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 an asynchronous motor operates in the motor state, the range of its slip rate s is 1>s>0.

The Tem-s curve of the electromagnetic torque Tem and slip rate s of asynchronous motors has three key points, namely the starting point (s=1), the maximum electromagnetic torque point (s=sm), and the synchronization point (s=0). When the rotor resistance of an asynchronous motor changes, the magnitude of its maximum electromagnetic torque Tem and the characteristic of the slip rate sm are: the magnitude remains unchanged, while the position of s changes.

27. Asynchronous motors must absorb reactive power with hysteresis properties from the power grid for excitation.

28. When an alternating current is applied to a coil assembly, its magnetic potential exhibits pulsating properties over time. When a single coil is subjected to alternating current, its magnetic potential also exhibits pulsating properties over time.

When a synchronous generator is connected to the grid, it is required that its three-phase terminal voltage has the same frequency, amplitude, waveform, phase sequence (and phase) as the three-phase voltage of the grid.

30. There are two types of rotors for synchronous motors: hidden pole and salient pole.

31. The equivalent number of phases of the squirrel cage rotor is equal to its number of slots, and the equivalent number of turns for each phase is 1/2.

32. Three phase symmetrical AC winding, passing symmetrical three-phase AC current, its fundamental synthesized magnetic electromotive force is a circular rotating magnetic electromotive force, and its rotation direction is from the axis of the leading phase winding to the axis of the lagging phase, and then to the axis of the next lagging phase.

33. There are two connection methods between the three-phase windings of a three-phase transformer: star and triangle; There are two types of magnetic circuits: group type and center type.

34. The six odd numbered connection group numbers of the three-phase transformer are 1, 3, 5, 7, 9, and 11; And the six even connected group numbers are 0, 2, 4, 6, 8, and 10.

In the AC winding, the number of slots per pole and phase is q=q=Z/2p/m (assuming the number of slots is Z, the number of pole pairs is p, and the number of phases is m). In AC windings, there are both 120o and 60o phase bands used. The fundamental winding coefficient and back electromotive force of the 60o phase band are relatively high.

36. The symmetrical component method can be used to analyze the asymmetric operation of transformers and synchronous motors. The prerequisite for its application is that the system is linear, so the superposition principle can be applied to decompose the asymmetric three-phase power system into three symmetrical three-phase systems: positive sequence, negative sequence, and zero sequence.

The formula for calculating the short distance coefficient is ky1=sin (p/2 × y1/t), which physically means the discount (or reduced coefficient) of the back electromotive force (or magnetomotive force) caused by short distance compared to the entire distance. The formula for calculating the distribution coefficient is kq1=sin (qa1/2)/q/sin (a1/2). Its physical meaning is the coefficient (or discount) that decreases when the back electromotive force (or magnetomotive force) is relatively concentrated when q coils differ by an electrical angle of a1 in sequence.

38. Current transformers are used to measure current, and their secondary side cannot be open circuited. Voltage transformers are used to measure voltage, and their secondary side cannot be short circuited.

39. A motor is a device that converts mechanical energy into electrical energy (or vice versa), or changes one AC voltage level to another. From the perspective of energy conversion, motors can be divided into three categories: transformers, electric motors, and generators.

The calculation formula for the distance between slots and the electrical angle a1 is a1=p × 360o/Z. The visible slot distance electrical angle a1 is equal to p times the slot distance mechanical angle am.

The principle of transformer winding calculation is to ensure that the magnetic potential of the winding remains unchanged and the active and reactive power of the winding remain unchanged before and after calculation.

The characteristic of the efficiency characteristic curve of a transformer is the existence of a maximum value, which is reached when the variable loss equals the constant loss.

The no-load test of transformers is usually conducted by applying voltage and measuring on the low voltage side. The short-circuit test of transformers is usually conducted by applying voltage and measuring on the high voltage side.

When transformers are operated in parallel, the condition for no no-load circulating current is that the transformation ratio is the same and the connection group number is the same.

When transformers are operated in parallel, the principle of load distribution is that the per unit value of the transformer load current is inversely proportional to the per unit value of the short-circuit impedance. The condition for fully utilizing the capacity of transformers during parallel operation is that the per unit value of short-circuit impedance must be equal, and their impedance angles must also be equal.