直流电机(英文).ppt

* * Equivalent circuit of separately excited DC generator DC machines theory * * DC Generator Equivalent circuit The magnetic field produced by the stator poles induces a voltage in the rotor (or armature) coils when the generator is rotated. The dc field current of the poles generates a magnetic flux The flux is proportional with the field current if the iron core is not saturated: DC machines theory * * DC Generator Equivalent circuit The rotor conductors cut the field lines that generate voltage in the coils. The motor speed and flux equations are : DC machines theory * * DC Generator Equivalent circuit The combination of the three equation results the induced voltage equation: The equation is simplified. DC machines theory * * DC Generator Equivalent circuit When the generator is loaded, the load current produces a voltage drop on the rotor winding resistance. In addition, there is a more or less constant 1–3 V voltage drop on the brushes. These two voltage drops reduce the terminal voltage of the generator. The terminal voltage is; DC machines theory DC machines theory * DC machines theory * EN0567 DC Machines * DC machines theory * Applications The direct current (dc) machine can be used as a motor or as a generator. DC Machine is most often used for a motor. The major advantages of dc machines are the easy speed and torque regulation. However, their application is limited to mills, mines and trains. As examples, trolleys and underground subway cars may use dc motors. In the past, automobiles were equipped with dc dynamos to charge their batteries. * DC machines theory * Applications Even today the starter is a series dc motor However, the recent development of power electronics has reduced the use of dc motors and generators. The electronically controlled ac drives are gradually replacing the dc motor drives in factories. Nevertheless, a large number of dc motors are still used by industry and several thousand are