1 . The current of a single-phase transformer when it is not loaded is in a different phase than the main flux, and there is a phase angle difference aFe because of the iron current consumption. The no-load current is a spire waveform because there is a large third harmonic in it. 2 . AC current also flows in the armature windings of DC motors. However, the current in the excitation winding is a direct current. The excitation methods of DC motors include separate excitation, parallel excitation, series excitation, compound excitation, etc. 3 . The back EMF expression of a DC motor is E = CE F n; The electromagnetic torque expression is Tem = CTFI. 4 . The number of parallel branches of a DC motor is always in pairs. The number of parallel branches of the AC winding is not necessarily. 5 . In DC motors, the elements of a single stack winding are stacked in series on top of the other. Whether single-wave windings or single-stack windings, commutators connect all components in series to form a single closed loop. 6 . Asynchronous motors are also known as induction motors because the rotor current of asynchronous motors is generated by electromagnetic induction. 7 . When the asynchronous motor is started with bucking, the starting torque decreases, and the starting torque and the square of the starting current of the winding decrease in direct proportion. 8 . When the amplitude and frequency of the primary voltage remain unchanged, the saturation degree of the core of the transformer is basically unchanged, and the excitation reactance is basically unchanged. 9 . The short-circuit characteristic of the synchronous generator is a straight line, and the magnetic circuit is unsaturated when the three-symmetrical short circuit is shorted; When the three-relative symmetrical steady-state short circuit, the short circuit circuit is a straight axis component of pure demagnetization. 10 . The current in the excitation winding of the synchronous motor is DC current, and the excitation methods mainly include excitation generator excitation, static rectifier excitation, rotary rectifier excitation, etc. 11 . There are no even-order harmonics in the three-phase synthetic magnetomotive force; Symmetrical three-phase windings pass symmetrical three-phase currents, and there is no magnetic harmonic in multiples of 3 in its synthetic magnetomotive force. 12 . Three-phase transformers generally want to have a delta connection on one side or a midpoint ground on one side. Because the windings of three-phase transformers are expected to have a third harmonic current path. 13 . When the symmetrical three-phase winding passes the symmetrical three-phase current, the 5th harmonic in the synthetic magnetomotive force is reversed; The 7th harmonic is forward-turning. 14 . The mechanical characteristics of series excited DC motors are relatively soft. The mechanical characteristics of separately excited DC motors 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 parameters of the windings. 16 . The transformation ratio of the transformer is equal to the turns ratio of the primary winding to the secondary side 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 . When excitation is normal, the power factor of the synchronous generator is equal to 1; When the output is kept active and the excitation current is less than the normal excitation (under-excitation), the nature of the straight-axis armature reaction is magnetic; When the output remains active and the excitation current is greater than the normal excitation (overexcitation), the nature of the linear armature reaction is demagnetized. 18 . In DC motors, iron consumption mainly exists in the rotor core (armature core), because the magnetic field of the stator core is basically unchanged. 19 . In DC motors, the first pitch y1 is equal to the number of slots that differ between the first and second sides of the element. The synthetic pitch y is equal to the number of slots that differ between the upper component edges of two elements in series. 20 . In DC motors, when saturation is not considered, the orthostatic reaction is characterized by a position shift where the magnetic field is zero, but the magnetic flux per pole is unchanged. When the brushes are on the geometric neutral line, the armature reaction is crossmagnetic. 21 . In a DC motor, the component that converts the external direct current into the internal alternating current is the commutator. The role of the commutator is to convert DC to AC (or vice versa). 22 . In synchronous motors, when the excitation flux F0 of the stator winding cross-chain is the maximum value, the back EMF E0 reaches the minimum value, when F0 reaches zero, E0 reaches the maximum value, and the phase relationship between F0 and E0 is F0 ahead of E0 90o. And the expression of the relationship between E0 and F0 is: E0 = 4.44 f N kN1F0. 23 . In motors, leakage flux refers to the magnetic flux of only the cross-chain winding itself, and the back EMF generated by it can often be equivalent to a leakage reactance voltage drop (or negative reactance voltage drop). 24. The rotor of asynchronous motor has: - squirrel cage type, winding type and so on. 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 the asynchronous motor works in the motor state, its slip rate s ranges from 1>s>0. 26 . The relationship between the electromagnetic torque Tem and the slip rate s of the asynchronous motor has three key points, which are 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 size of its maximum electromagnetic torque Tem and the slip rate SM are characterized by: the size does not change, and the position of S changes. 27 . Asynchronous motors must absorb reactive power of hysteresis properties from the grid for excitation. 28 . A coil pack is connected to alternating current, and its magnetomotive force changes over time with pulsation properties. A single coil is connected to alternating current, and its magnetomotive force changes over time also have pulsation properties. 29 . When the synchronous generator is connected to the grid, its three-phase terminal voltage is required to have the same as the three-phase voltage of the power grid: frequency, amplitude, waveform, phase sequence (and phase), etc. 30 . The rotor of synchronous motor has two types: hidden pole type and salient pole type. 31 . The equivalent number of phases of the squirrel cage rotor is equal to its number of slots, while the equivalent number of turns per phase is 1/2. 32 . Three-phase symmetrical AC winding, symmetrical three-phase AC current, its fundamental synthetic magnetomotive force is a circular rotating magnetomotive force, the direction of rotation is from the leading phase winding axis to the hysteresis phase axis, and then to the axis of the next hysteresis phase. 33 . There are two connection methods such as star and triangle between the three-phase windings of the three-phase transformer; The magnetic circuit has two structures: group type and core type. 34 . The six odd coupling numbers of three-phase transformers are 1, 3, 5, 7, 9, 11. The 6 even-numbered linkage numbers are 0, 2, 4, 6, 8, and 10. 35 . In the AC winding, the number of slots per phase per pole 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 the AC winding, there are both 120O and 60O bands. Among them, the fundamental winding coefficient and back EMF of the 60O phase band are high. 36 . The symmetric component method can be used to analyze the asymmetric operation of transformers and synchronous motors, and the premise of 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 groups of symmetrical three-phase systems such as positive order, negative sequence and zero order. 37 . The shortness coefficient is calculated as ky1 = sin(p/2×y1/t), which is physically defined as the discount (or reduction factor) of the back EMF (or magnetomotive force) caused by the short distance compared to the full distance. The distribution coefficient is calculated as kq1 = sin(qa1 /2) / q / sin(a1 / 2), and its physical meaning is the coefficient (or discounted) of the relative concentration of the back electric potential (or magnetomotive force) when q coils differ from the a1 electric angle in turn. 38 . Current transformers are used to measure current, and their secondary side cannot be open. The voltage transformer is used to measure the voltage, and its 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, motors, and generators. 40 . The slot distance electrical angle a1 is calculated as a1 = p×360o/z. The visible slot distance electrical angle a1 is equal to p times the slot distance mechanical angle am. 41 . The principle of transformer winding calculation is: before and after the calculation, ensure that the magnetomotive force of the winding does not change, and ensure that the active and reactive power of the winding do not change. 42 . The efficiency characteristic curve of the transformer is characterized by the presence of a maximum value, i.e. when the variable loss is equal to the constant loss. 43 . No-load testing of transformers is usually performed with voltage applied and measured on the low side. The short-circuit test of transformers is usually carried out by applying voltage and measuring on the high voltage side. 44 . When the transformers are operated in parallel, the conditions for no-load no circulating current are: the transformation ratio is the same and the coupling group number is the same. 45 . When the transformer is operated in parallel, the load distribution principle is: the nominal unit value of the transformer load current is inversely proportional to the nominal unit value of the short-circuit impedance. The capacity of transformers can be fully utilized in parallel operation if the unitary values of the short-circuit impedances are equal and their impedance angles are equal.