The following columns present various modes of induction machine operation and the ranges of slip
A | B | ||
---|---|---|---|
Mode of operation | Range of Slip | ||
a. | Running in generator mode | p) | From 0.0 to 1.0 |
b. | Running in motor mode | q) | From 1.0 to 2.0 |
c. | Plugging in motor mode | r) | From $$-$$1.0 to 0.0 |
The correct matching between the elements in column A with those of column B is
The four stator conductors (A, A', B and B') of a rotating machine are carrying DC currents of the same value, the directions of which are shown in the figure (i). The rotor coils $$a$$-$$a'$$ and $$b$$-$$b'$$ are formed by connecting the back ends of conductors '$$a$$' and '$$a'$$' and '$$b$$' and '$$b'$$', respectively, as shown in figure (ii). The e.m.f. induced in coil $$a$$-$$a'$$ and coil $$b$$-$$b'$$ are denoted by $${E_{a - a'}}$$ and $${E_{b - b'}}$$, respectively. If the rotor is rotated at uniform angular speed $$\omega$$ rad/s in the clockwise direction then which of the following correctly describes the $${E_{a - a'}}$$ and $${E_{b - b'}}$$?
A separately excited DC motor rated 400 V, 15 A, 1500 RPM drives a constant torque load at rated speed operating from 400 V DC supply drawing rated current. The armature resistance is 1.2 $$\Omega$$. If the supply voltage drops by 10% with field current unaltered then the resultant speed of the motor in RPM is ____________ (Round off to the nearest integer).


A 5 kW, 220 V DC shunt motor has 0.5 $\Omega$ armature resistance including brushes. The motor draws a no-load current of 3 A. The field current is constant at 1 A. Assuming that the core and rotational losses are constant and independent of the load, the current (in amperes) drawn by the motor while delivering the rated load, for the best possible efficiency, is _______ (rounded off to 2 decimal places).
A 280 V, separately excited DC motor with armature resistance of 1 $$\Omega$$ and constant field excitation drives a load. The load torque is proportional to the speed. The motor draws a current of 30 A when running at a speed of 1000 rpm. Neglect frictional losses in the motor. The speed, in rpm, at which the motor will run, if an additional resistance of value 10 $$\Omega$$ is connected in series with the armature, is __________. (round off to nearest integer).



The external resistance to be added in the armature circuit to limit the armature current to $$125\% $$ of its rated value is
The net voltage across the armature resistance at the time of plugging will be

(i) at half the rated speed by armature voltage control and
(ii) at 1.5 times the rated speed by field control, the respective output powers delivered by the motor are approximately
Group-I(Performance variables)
(P) Armature emf (E)
(Q) Developed torque (T)
(R) Developed power (P)
Group-II(Proportional to)
1.Flux ($$\phi$$), speed ($$\omega$$) and armature current ($$I_a$$)
2.$$\phi$$ and $$\omega$$ only
3.$$\phi$$ and $$I_a$$ only
4.$$I_a$$ and $$\omega$$ only
5.$$I_a$$ only
List-I (Test)
(A) No load and blocked rotor test
(B) Sumpner’s test
(C) Swinburn’s test
List-II (Machine)
(1) Transformer
(2) Induction machine
(3) Synchronous machine
(4) DC machine

$$(i)$$ of two sections of the field coil are connected in series, and in another case
$$(ii)$$ the two sections are connected in parallel. If the motor takes the rated current in both the cases, then ratio of torque $$(1):$$ torque $$(2)$$ and speed $$(1):$$ speed $$(2)$$ respectively are