1. When a single-phase transformer is at no‑load, the current and the main flux are not in phase; there is a phase angle difference α_Fe because of the iron‑loss current. The no‑load current has a peaked waveform because it contains a significant third harmonic.

2. In a DC machine, the armature winding carries alternating current, but the field winding carries direct current. The excitation methods of a DC motor include separately excited, shunt, series, and compound excitation.

3. The back‑EMF expression for a DC machine is E = C_E Φ *n*, while the electromagnetic torque expression is T_em = C_T Φ I.

4. The number of parallel branches in a DC machine is always even. In AC windings, however, the number of parallel branches is not necessarily even.

5. In a DC machine, the coils of a simplex lap winding are connected in series one on top of another. Whether it is a lap winding or a wave winding, the commutator segments connect all coils in series to form a single closed circuit.

6. An induction motor is also called an asynchronous motor because its rotor current is induced by electromagnetic induction.

7. When an induction motor is started with reduced voltage, the starting torque decreases, and it decreases in proportion to the square of the starting current in the winding.

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

9. The short‑circuit characteristic of a synchronous generator is a straight line. Under symmetrical three‑phase short circuit, the magnetic circuit is unsaturated. Under steady‑state symmetrical three‑phase short circuit, the short‑circuit current is a purely demagnetizing direct‑axis component.

10. The current in the field winding of a synchronous machine is direct current. The main excitation methods include excitation by a separate exciter, static rectifier excitation, and rotating rectifier excitation.

11. The resultant three‑phase magnetomotive force (MMF) contains no even harmonics. When symmetrical three‑phase currents flow in symmetrical three‑phase windings, the resultant MMF contains no harmonics that are multiples of three.

12. In three‑phase transformers, it is generally desirable to have a delta connection on one side or a neutral point grounded on one side, because the winding connection of a three‑phase transformer requires a path for the third‑harmonic current.

13. When symmetrical three‑phase currents flow in symmetrical three‑phase windings, the 5th harmonic of the resultant MMF rotates in the reverse direction, while the 7th harmonic rotates in the forward direction.

14. The mechanical characteristic of a series‑excited DC motor is relatively soft. That of a separately‑excited DC motor is relatively hard.

15. The short‑circuit test of a transformer can measure the leakage impedance of the windings; the open‑circuit test can measure the magnetizing impedance parameters.

16. The turns ratio of a transformer is equal to the ratio of the number of turns of the primary winding to that of the secondary winding. For a single‑phase transformer, the turns ratio can also be expressed as the ratio of the rated primary voltage to the rated secondary voltage.

17. Under normal excitation, the power factor of a synchronous generator is 1. When the field current is reduced below normal (under‑excitation) while keeping the output active power constant, the direct‑axis armature reaction is magnetizing. When the field current is increased above normal (over‑excitation), the direct‑axis armature reaction is demagnetizing.

18. In a DC machine, iron losses mainly exist in the rotor core (armature core), because the magnetic field in the stator core is essentially constant.

19. In a DC machine, the first pitch *y*₁ is equal to the difference in the number of slots between the two sides of a coil. The resultant pitch *y* is equal to the difference in slots between the upper sides of two series‑connected coils.

20. In a DC machine, when saturation is neglected, the cross‑axis armature reaction shifts the zero‑field position but does not change the flux per pole. When the brushes are on the geometric neutral axis, the armature reaction is of a cross‑magnetizing nature.

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

22. In a synchronous machine, when the excitation flux Φ₀ linking the stator winding reaches its maximum, the back‑EMF E₀ reaches its minimum; when Φ₀ reaches zero, E₀ reaches its maximum. The phase relationship between Φ₀ and E₀ is that Φ₀ leads E₀ by 90°. The relationship is expressed as E₀ = 4.44 *f* N *k*_N1 Φ₀.

23. In electrical machines, leakage flux refers to the flux that links only its own winding. The back‑EMF produced by leakage flux can often be represented by a leakage reactance voltage drop (or a negative reactance voltage drop).

24. Induction motors have two types of rotors: squirrel‑cage and wound‑rotor.

25. The slip *s* of an induction motor is defined as the ratio of the difference between synchronous speed and rotor speed to the synchronous speed. When the induction motor operates as a motor, the slip *s* is in the range 1 > *s* > 0.

26. The electromagnetic torque T_em versus slip *s* curve of an induction motor has three key points: the starting point (*s* = 1), the maximum torque point (*s* = *s*_m), and the synchronous point (*s* = 0). When the rotor resistance is changed, the magnitude of the maximum torque T_em remains unchanged, but the slip *s*_m at which it occurs changes.

27. An induction motor must absorb lagging reactive power from the grid for excitation.

28. When a coil group is supplied with alternating current, its MMF pulsates with time. The same applies to a single coil.

29. When a synchronous generator is connected to the grid, its three‑phase terminal voltages must have the same frequency, magnitude, waveform, phase sequence (and phase) as the grid voltages.

30. Synchronous machine rotors are of two types: cylindrical‑rotor and salient‑pole.

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

32. For a symmetrical three‑phase AC winding carrying symmetrical three‑phase AC currents, the fundamental resultant MMF is a circular rotating MMF. Its rotation direction is from the axis of the leading phase winding toward the axis of the lagging phase winding, and then to the next lagging phase.

33. Three‑phase transformer windings can be connected in star or delta. The magnetic circuit can be either core‑type or shell‑type.

34. The six odd connection group numbers of a three‑phase transformer are 1, 3, 5, 7, 9, 11. The six even connection group numbers are 0, 2, 4, 6, 8, 10.

35. In AC windings, the number of slots per pole per phase is *q* = Z / (2*p* *m*) (where Z is the number of slots, *p* is the number of pole pairs, and *m* is the number of phases). Both 120° phase belts and 60° phase belts are used; the 60° phase belt gives a higher fundamental winding factor and back‑EMF.

36. The symmetrical component method can be used to analyse unbalanced operation of transformers and synchronous machines. Its application is based on the linearity of the system, allowing superposition to decompose an unbalanced three‑phase system into three symmetrical systems: positive‑sequence, negative‑sequence, and zero‑sequence.

37. The pitch factor is given by *k*_y1 = sin(π/2 × *y*₁ / τ), where it represents the discount (or reduction factor) of the back‑EMF (or MMF) due to short pitching compared with full pitching. The distribution factor is *k*_q1 = sin(*q*α₁/2) / [*q* sin(α₁/2)], which represents the reduction factor of the back‑EMF (or MMF) when *q* coils are successively displaced by an electrical angle α₁ relative to a concentrated arrangement.

38. A current transformer is used to measure current, and its secondary side must not be open‑circuited. A voltage transformer is used to measure voltage, and its secondary side must not be short‑circuited.

39. An electrical machine is a device that converts mechanical energy to electrical energy (or vice versa), or changes one AC voltage level to another. From an energy‑conversion perspective, electrical machines can be classified into three types: transformers, motors, and generators.

40. The slot electrical angle α₁ is calculated as α₁ = *p* × 360° / Z. Thus, the slot electrical angle α₁ is equal to *p* times the slot mechanical angle α_m.

41. The principle of transformer winding conversion (referred values) is that the MMF of the winding, as well as the active and reactive powers, must remain unchanged before and after conversion.

42. The efficiency curve of a transformer has a maximum point, which occurs when the variable losses equal the constant losses.

43. The open‑circuit test of a transformer is usually performed by applying voltage and taking measurements on the low‑voltage side. The short‑circuit test is usually performed on the high‑voltage side.

44. For transformers to operate in parallel without circulating current at no‑load, the conditions are: same turns ratio and ... (the original text is incomplete; it likely continues with “same connection group” or “same phase displacement”).