电工问答（Electrician ask）.doc

电工问答（Electrician ask） 1, a comparative study on differences in synchronous motor power factor angle and power factor angle. Answer: only for the angle between ^E0 and ^I, it is related with the load character and motor internal impedance; and the angle between ^U and ^I for the PSI, only concerned with the nature of the load. 2. What is called synchronous reactance? How does it affect the performance of synchronous generator? Answer: the reactance of the leakage reactance and armature reaction is called synchronous reactance. Its influence on the performance of synchronous generator is as follows: (1) influence terminal voltage size. (2) affect the magnitude of steady-state short-circuit current. (3) in the operation of infinite power grid, the static stability is affected. 3. What does the power limit of synchronous generator depend on? How to improve? Answer: to the hidden pole synchronous generator, for example, the power limit is: Pemmax=m*E0*U/Xt Because the grid voltage is U=C, the power limit depends on the no-load electromotive force E0 (If) and the synchronous reactance Xt. Improving method: (1) increase the exciting current (increasing the no-load EMF E0); When designing and manufacturing, the synchronous reactance can be reduced (not only increasing the air gap, but also). 4. In the salient pole synchronous motor, why is the direct axis armature reaction reactance Xad higher than the quadrature armature reaction reactance Xaq? Answer: in the salient pole motor armature air gap along the circumference is uneven. The analysis of the armature reaction, use double reaction theory, namely the armature reaction magnetomotive force is decomposed into parallel and perpendicular to the electric potential of ^E0 two components ~Fad and ~Faq, which are produced through direct axis armature reaction magnetic properties AD and the q-axis armature reaction flux by AQ, the corresponding current is decomposed into two components. Therefore Ead=IdXad Xd=Ead/Id Id / Fad or