The structural difference between ac motor and dc motor
rating: generally understand and grasp the rated frequency and rated speed, the frequency of 50 hz. (3) connection methods: Y type and angular type. (4) insulation level and temperature rise: mastery allows the definition of temperature rise. (5) works: general understanding. 4. Mechanical properties of three-phase asynchronous motor Master rated torque, maximum torque and start torque. The relationship between the book's formula to grasp and can be flexibly used to calculate. At the same time, remember the following content: (1) at constant speed rotation, the torque of the motor must be balanced and resistance torque. (2) when the load torque increases, the initial moment motor torque T (3) general three-phase asynchronous motor overload coefficient is 1.8-1.8. (4) motor has just started n = 0, s = 1.5. Three phase asynchronous motor starting
the structure of the synchronous motors have to be different. Compared with asynchronous motor (objective) (2) the principle of synchronous motor Understand the synchronous motor speed is constant, not change according to the load. Synchronous motor speed cannot adjust. 1, the working principle of dc motor General understanding of 2, the structure of the dc motor is divided into two parts: the stator and rotor. Remember the stator and the rotor is composed of a few parts, note: don't confuse commutating pole and commutator, remember the two of them. The stator includes: main pole, stand, commutating pole, brush device and so on. The rotor includes: the armature iron core, the armature winding, commutator, shaft and fan, etc. 3, dc motor excitation method Dc motor performance is closely related to its excitation mode, dc motor excitation method usually has four kinds: dc separately excited motor, dc shunt motor, dc series motor and dc compound motor. Mastering the respective features of four ways: dc separately excited motor: exciting winding and armature contact without electricity, excitation circuit is made up of other dc power supply. So the exciting current is not affected by the armature terminal voltage or armature current. Dc shunt motor, shunt winding ends voltage is the voltage on both ends of the armature, but exciting winding with fine wire coils, the number of turns a lot, so has larger resistance, made by his exciting current is small. Dc series motor:
direct starting startup slip is 1, rotor induction electromotive force is very big, the rotor current is very big also. When under the rated voltage of the motor starting, referred to as direct start and direct start current of about 5 to 7 times of the rated current. In general, under the rated power is 7.5 kw small capacity of asynchronous motor can be directly starting. Direct starting control circuit used appliances including combination switch, button, intermediate relay contactor, thermal relay, and fuse. Mastering their respective characteristics, at the same time grasp the fuse fuse rated current calculation. Starting control circuit directly: to grasp its control principle. (2) the squirrel-cage asynchronous motor step-down starting. Master star - Angle starting and autotransformer step-down starting the work principle of (3) the wound rotor three-phase asynchronous motor starting General understanding. 6. The three-phase asynchronous motor and reversing control Generally understand 7. Three phase asynchronous motor speed regulation This part is important, to understand the formula. Changing the rotational speed of the motor, there are three possible change frequency and change the winding of magnetic pole logarithmic or change slip. 8. Synchronous motor
Motor converts electrical energy into mechanical energy is the function of. Motor is divided into two major categories of ac motor and dc motor. (1) ac motor and its control ac motor divided into two categories, asynchronous motor and synchronous motor. The asynchronous motor according to the number of stator phase asynchronous motor is divided into single and two phase asynchronous motor and three-phase asynchronous motor. Three-phase asynchronous motor has simple structure, reliable operation, the advantages of low cost, widely used in industrial and agricultural production. 1. The basic structure of three phase asynchronous motor There are two parts: the structure of the three-phase asynchronous motor stator and rotor. (1) of the stator, the stator is motor fixed part, the function is used to produce a rotating magnetic field. It is mainly composed of stator core, stator windings and the frame.
Rotor (2) : part of the rotor is the key to master, there are two kinds of rotor, squirrel cage and wound rotor. To master their own characteristics and differences. Cage type used for medium and small power motor (below 100 k), he has simple structure, reliable work, convenient in operation and maintenance. Wound rotor can improve startup performance and adjust the speed, size of air gap between the stator and rotor, will affect the performance of the motor, the general thickness of air gap between 0.2 1.5 mm. Grasp the connection method of stator winding. 2. The working principle of three phase asynchronous motor Master formula n1 = 60 f/P, S = (n1 - n)/n1, n = (1 - S) 60 f/P, at the same time understand the meaning of their (very important), to be able to apply these formulas, to calculate. At the same time, remember: usually motor slip under rated load of SN is about 0.01-0.06. Examples of the book to grasp key. 3. The data on the three-phase asynchronous motor nameplate models: (1) master the example of the book.
