When the rotor is locked (or blocked), i.e. s =1, the largest voltage and rotor frequency are induced in the rotor, Why?

SUBJECT = ELECTRIC MACHINES In an induction motor, If the rotor speed becomes equal to the stator field speed, what would happen? Explain

Q2 : What the important characteristics of a d.c. generator explain briefly.

Drive the law of the Maximum Power require ment for a DC motor which state s that Eb-V 2 Ia Ra= %3D or

q4 ciii

State two reasons why a self-excited shunt dc generator may fail to build up a voltage. In each (both) case, briefly explain what can be done to correct the problem. Reason #1 Solution #1 Reason #2 Solution #2

In the magnetic system where the rotor in the figure can rotate around the center, the rotor and the stator have infinite magnetic permeability. The air gap length is 0.5 mm and it covers a 30 degree arc. The distance from the center of the rotor to the air gap is 5 cm, the number of turns of the two coils in series is equal and the total is 50, the length (depth) of the figure is 10 cm, 6; If the angle of rotation of the rotor and its value as given is zero degrees, a. How many electrical degrees is the angle at which the inductance is minimum. b. How many electrical degrees is the angle where the inductance is maximum. c. Calculate the maximum inductance value. d. If the windings are connected to a 50 V DC source over a 5 ohm resistor, calculate the air gap flux, neglecting the winding ohmic resistance. Bobin Stator Rotor

Which of the following statements regarding the principle of rotor operation are true? Select one or more: a. In horizontal axis wind turbines, it is desired that the lifting force be as small as possible. Ob. Drag pulls the wing backwards (HAWT). c. The operation of the Savonius rotor is based on drag.

× 4:03 K s.eng.ruh.ac.lk □ Û 8. Figure 4 shows the core of a simple dc motor. The magnetization curve for the metal in this core is given by Figure 5 and Figure 6. Assume that the cross-sectional area of each air gap is 18 cm² and that the width of each air gap is 0.05 cm. The effective diameter of the rotor core is 4 cm. L It is desired to build a machine with as great a flux density as possible while avoiding excessive saturation in the core. What would be a reasonable maximum flux density for this core? ii. What would be the total flux in the core at the flux density of part (i)? iii. The maximum possible field current for this machine is I A. Select a reasonable number of turns of wire to provide the desired flux density while not exceeding the maximum available current. Flux Density, B (T) 2.8 སྤྲ ཤཱ ཀ ཀཱ བྷ ཀ ཡཱཾ བ ་ 1.2 1.0 0.4 0.2 4-48cm Figure 4 0 10 20 30 40 50 100 → Depth 4 cm -0.05 cm 200 300 500 1000 2000 Magnetizing Intensity, H (A.turns/m) Figure 5 Magnetization curve…