electricalengineeringquestionanswer

Q: Why synchronous motor is not self starting? Synchronous motor is a doubly excited machine i.e two electrical inputs are provided to it. It’s stator winding which consists of a 3 phase winding is provided with 3 phase supply and rotor is provided with DC supply. The 3 phase stator winding carrying 3 phase currents produces 3 phase rotating magnetic flux. The rotor carrying DC supply also produces a constant flux. At a particular instant rotor and stator poles might be of same polarity (N-N or S-S) causing repulsive force on rotor and the very next second it will be N-S causing attractive force. But due to inertia of the rotor, it is unable to rotate in any direction due to attractive or repulsive force and remain in standstill condition. Hence it is not self starting. Q: What are the methods of starting synchronous motor? 1.     Pony motor starting( using ac or dc motor) 2.     Starting as squirrel cage Induction motor or using damper winding 3.  ...

Q: Write the most important mode of operation of power system and mention the major problems encountered with it.  Symmetrical steady state is the most important mode of operation of power system. Three major problems are encountered in this mode of operation. They are,  1) Load flow problem  2)  Optimal load scheduling problem 3) Systems control problem Q: Why power flow analysis is made? Power flow analysis is performed to calculate the magnitude and phase angle of voltages at the buses and also the active power and reactive voltamperes flow for the given terminal or bus conditions. The variables associated with each bus or node are, a. Magnitude of voltage |V|  b. Phase angle of voltage δ  c. Active power, P d. Reactive voltamperes, Q Q: What is power flow study or load flow study?  The study of various methods of solution to power system network is referred to as load study. The solution provides the voltages at various buses, power flowing in Vari...