Electrical motor knowledge
31. The equivalent phase number of the squirrel cage rotor is equal to the number of slots, and the equivalent number of turns per phase is 1/2.
32. Three-phase symmetrical AC winding, symmetrical three-phase AC current, whose fundamental wave synthetic magnetomotive force is a circular rotating magnetomotive force, whose direction of rotation is from the axis of the leading phase winding to the axis of the lag phase, and then to the next The axis of a lagging 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, a group and a heart.
34. The six odd-numbered junction groups of the three-phase transformer are 1, 3, 5, 7, 9, and 11. The 6 even numbered group numbers are 0, 2, 4, 6, 8, and 10.
35. In the AC winding, the number of slots per phase per pole 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 the AC winding, both the 120o phase band and the 60o phase band are used. Among them, the 60o phase band has a higher fundamental winding coefficient and back electromotive force.
36. The symmetrical component method can be used to analyze the asymmetric operation of transformers and synchronous motors. The premise of the application is that the system is linear, so the superposition principle can be applied to decompose the asymmetric three-phase power system into positive sequence and negative sequence. Three sets of symmetrical three-phase systems such as zero sequence.
37. The calculation formula of the short-range coefficient is ky1=sin(p/2×y1/t), and its physical meaning is that the short-distance causes the back EMF (or magnetomotive force) to be discounted (or reduced) compared with the whole distance. Coefficient). The calculation formula of the distribution coefficient is kq1=sin(qa1/2)/q/sin(a1/2), and its physical meaning is that when the q coils are in phase difference a1 electrical angle, the back EMF (or magnetomotive force) is relatively concentrated. The coefficient of reduction (or the discount).
38. Current transformers are used to measure current and the secondary side cannot be opened. The voltage transformer is used to measure the voltage, and the 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 of the alternating voltage levels to another alternating voltage level. From the perspective of energy conversion, motors can be divided into three categories: transformers, motors, and generators.
40. The calculation formula of the slot electrical angle a1 is a1=p×360o/Z. It can be seen that the slot electrical angle a1 is equal to p times the slot mechanical angle am.
41. The principle of transformer winding reduction is: before and after the reduction, ensure that the magnetomotive force of the winding is constant, and that the active and reactive power of the winding are not changed.
42. The characteristic curve of the transformer is characterized by the existence of a maximum value, that is, the maximum value is reached when the variable loss is equal to the constant loss.
43. The no-load test of the transformer is usually done by applying voltage and measuring on the low voltage side. The short-circuit test of the transformer is usually done by applying voltage and measuring on the high voltage side.
44. When the transformers are operated in parallel, the conditions of no-load uncirculated flow are: the ratio is the same and the joint group number is the same.
45. When the transformers are operated in parallel, the load distribution principle is that the value of the transformer load current is inversely proportional to the value of the short-circuit impedance. The capacity of the transformer can be fully utilized when operating in parallel: the values of the short-circuit impedance are equal, and their impedance angles are equal.
