Q choose the correct answer: 1-Brushless excitation system consisting of.... a- Stator field winding and power diodes b-stator and rotor field winding and capacitor c- stator and rotor field winding and capacitor d- Everything mentioned in the options 2- Voltage generated per phase in an alternator is proportional to a- Flux per pole b- Number of turns in armature c-Winding factors d- Everything mentioned in the options e- Frequency of waveform 3- If input mech. Power of SG constant, the functionality of AVR is a- Control flux of rotor b-Control terminal voltage c- Control flux and terminal voltage d-Control Load angle

Q3/ Chose the correct answer for the following 1. Synchronous motors are generally not self-starting because (a) the direction of rotation is not fixed (b) the direction of instantaneous torque reverses after half cycle (c) startes cannot be used on these machines (d) starting winding is not provided on the machines 2. The power developed by a synchronous motor will be maximum when the load angle is (a) Zero (b) 45° (c) 90° (d) 120° 3. An over-excited synchronous motor takes (a) leading current (b) lagging current (c) both (a) and (b) (d) none of the above 4. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on (a) d.c. excitation only (b) speed of the motor (c) load on the motor (d) both the speed and rotor flux 5. A pony motor is basically a (a) small induction motor (c) D.C. shunt motor (b) D.C. series motor (d) double winding A.C./D.C. motor

Two DC generators are running in parallel. One of the generators may run as a motor, what is the main reason such conditions occur? Explain your answer with the use of a calculation.

ANSWER ALL THE QUESTIONS: A.) Calculate the voltage induced in the armature winding of a 4 pole, wave-wound, dc machine having 728 active conductors and running at 1800rpm. The flux per pole is 30mWb. 1310.4V 468.2 V 720.4 V 236.4 V B.) The direction of rotation of a DC motor is reversed by reversing armature connections adding resistance to the field circuit interchanging the armature and field connection reversing supply connection

A. The DC motor in Figure 3 on Worksheet 8 is aa) cumulatively connected short-shunt compound DC motor b) cumulatively connected long-shunt compound DC motor c) differentially connected short-shunt compound DC motor d) shunt DC motorB. Is the DC motor in Figure 1 on Worksheet 8 turning in the same direction as that in Figure 3?a) yes b) no

(B)-ndicate whether the following statements are true or false and correct the faise statements. -When a series d.c. motor is operate without load, the armature will not run. The strength of magnetic field in d.c. shunt generator can be varied by varying the polarity of the field poles The main disadvantage of series generators is Output voltage varies as the Toad varies There is no output from the transformer under short-circuit conditions

The factors effecting the speed of dc motor are The flux p and the voltage across the armature the voltage across the armature and the applied voltage V The applied voltage V, flux p and the voltage across the armature none of the aboye Indicate whether the following statement are true or false * True False The distance between the beginnings of each cascaded two coils is called commutator Pitch

Which is the device in DC generators that converts AC into DC? stator brushes commutator armature This type of armature winding delivers high e.m.f. and low current. dummy or idle coils lap winding O frog-leg winding wave winding

DEGREE: ELECTRICAL ENGINEERING  SUBJECT/COURSE: AC MACHINES   Answer the following questions (A, B and C) depending on the topic.   1. SYNCHRONOUS MOTORS   A. What is necessary to start a synchronous motor to rotate from standstill? Describe the process.   B. What is meant by synchronous condenser?   C. Why is it possible for synchronous motors be used as a power factor correction device and what applications do synchronous motors commonly used? Describe the operation.