D.C Machines · Electrical Machines · GATE EE
Marks 1
1
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
GATE EE 2023
2
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 $${E_{b - b'}}$$?
GATE EE 2023
3
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).
GATE EE 2023
4
A separately excited dc motor has an armature resistance R$$a$$ = 0.05Ω. The field excitation
is kept constant. At an armature voltage of 100 V, the motor produces a torque of 500 Nm
at zero speed. Neglecting all mechanical losses, the no-load speed of the motor (in radian/s)
for an armature voltage of 150 V is _____ (up to 2 decimal places).
GATE EE 2018
5
A 4-pole, lap-connected, separately excited dc motor is drawing a steady current of 40 A while
running at 600 rpm. A good approximation for the waveshape of the current in armature
conductor of the motor is given by
GATE EE 2016 Set 1
6
A separately excited DC generator has an armature resistance of 0.1 $$\Omega$$ and negligible armature inductance. At rated field current and rated rotor speed, its open-circuit voltage is 200 V. When this generator is operated at half the rated speed, with half the rated field current, an un-charged 1000 μF capacitor is suddenly connected across the armature terminals. Assume that the speed remains unchanged during the transient. At what time (in microsecond) after the capacitor is connected will the voltage across it reach 25 V?
GATE EE 2015 Set 1
7
A 4-pole, separately excited, wave wound DC machine with negligible armature resistance is rated for 230 V and 5 kW at a speed of 1200 rpm. If the same armature coils are reconnected to form a lap winding, what is the rated voltage (in volts) and power (in kW) respectively at 1200 rpm of the reconnected machine if the field circuit is left unchanged?
GATE EE 2015 Set 2
8
A shunt-connected DC motor operates at its rated terminal voltage. Its no-load speed is 200 radian/second. At its rated torque of 500 Nm, its speed is 180 radian/second. The motor is used to directly drive a load whose load torque TL depends on its rotational speed $$\omega_r$$ (in radian/second), such that $$T_L=2.78\times\omega_r$$. Neglecting rotational losses, the steady-state speed (in radian/second) of the motor, when it drives this load, is _______.
GATE EE 2015 Set 2
9
The no-load speed of a 230 V separately excited dc motor is 1400 rpm. The armature
resistance drop and the brush drop are neglected. The field current is kept constant at rated
value. The torque of the motor in Nm for an armature current of 8 A is ____________.
GATE EE 2014 Set 3
10
A 4–point starter is used to start and control the speed of a
GATE EE 2011
11
The dc motor, which can provide zero speed regulation at full load without any controller is
GATE EE 2007
12
In a $$DC$$ machine, which of the following statements is true?
GATE EE 2006
13
A dc series motor fed from rated supply voltage is overloaded and its magnetic
circuit is saturated. The torque-speed characteristic of this motor will be
approximately represented by which curve
of Fig.
GATE EE 2002
14
In case of an armature controlled separately excited dc motor drive with closed loop
speed control, an inner current loop is useful because it
GATE EE 2001
15
A 1.8° step, 4-phase stepper motor has a total of 40 teeth on 8 poles of stator.
The number of rotor teeth for this motor will be
GATE EE 2000
16
Ratio of the rotor reactance X to the rotor resistance R for a two-phase
servomotor
GATE EE 2000
17
The compensating winding in a dc machine
GATE EE 2000
18
A 4-pole lap-wound DC generator has a developed power of P watts and voltage
of E volts. Two adjacent brushes of the machine are removed as they are worn
out. If the machine operates with the remaining brushes, the developed voltage
and power that can be obtained from the machine are
GATE EE 1999
19
The torque speed characteristic of a Repulsion motor resembles which of the following dc motor characteristic?
GATE EE 1996
20
Which type of motor is most suitable for computer printer device?
GATE EE 1996
21
A $$4$$ pole dynamo with wave wound armature has $$51$$ slots containing $$20$$ conductors in each slot. The induced $$emf$$ is $$357$$ volts and the speed is $$5800$$ $$rpm$$. The flux per pole will be
GATE EE 1996
22
A differentially compounded d.c. motor with interpoles and with brushes on the
neutral axis is to be driven as a generator in the same direction with the same
polarity of the terminal voltage. It will then
GATE EE 1995
23
A cumulative compounded long shunt motor is driving a load at rated torque and rated speed. If the series field is shunted by a resistance equal to the resistance of the series field, keeping the torque constant.
GATE EE 1993
24
Neglecting all losses, the developed torque $$(T)$$ of $$d.c.$$ separately excited motor, operating under constant terminal voltage, is related to its output power $$(P)$$ as under
GATE EE 1992
Marks 2
1
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).
GATE EE 2024
2
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).
GATE EE 2022
3
A 200 V DC series motor, when operating from rated voltage while driving a certain load,
draws 10 A current and runs at 1000 r.p.m. The total series resistance is 1 Ω. The magnetic
circuit is assumed to be linear. At the same supply voltage, the load torque is increased by
44%. The speed of the motor in r.p.m. (rounded to the nearest integer) is ________
GATE EE 2018
4
A 120 V DC shunt motor takes 2 A at no load. It takes 7 A on full load while running at 1200
rpm. The armature resistance is 0.8 Ω, and the shunt field resistance is 240 Ω. The no load
speed, in rpm, is _________.
GATE EE 2017 Set 2
5
A 220 V, 10 kW, 900 rpm separately excited DC motor has an armature resistance Ra= 0.02 Ω.
When the motor operates at rated speed and with rated terminal voltage, the electromagnetic
torque developed by the motor is 70 Nm. Neglecting the rotational losses of the machine, the
current drawn by the motor from the 220 V supply is
GATE EE 2017 Set 2
6
A separately excited DC generator supplies 150 A to a 145 V DC grid. The generator is running
at 800 RPM. The armature resistance of the generator is 0.1 Ω. If the speed of the generator is
increased to 1000 RPM, the current in amperes supplied by the generator to the DC grid is
_______.
GATE EE 2017 Set 1
7
A 220 V DC series motor runs drawing a current of 30 A from the supply. Armature and field
circuit resistances are 0.4 Ω and 0.1 Ω respectively. The load torque varies as the square of the
speed. The flux in the motor may be taken as being proportional to the armature current. To
reduce the speed of the motor by 50% the resistance in ohms that should be added in series with
the armature is _________.
GATE EE 2017 Set 1
8
A DC shunt generator delivers 45 A at a terminal voltage of 220 V. The armature and the shunt
field resistance are 0.01 Ω and 44 Ω respectively. The stray losses are 375 W. The percentage
efficiency of the DC generator is ______.
GATE EE 2016 Set 1
9
A DC motor has the following specifications: 10 Hp, 37.5 A, 230 V; flux/pole = 0.01 Wb, number of poles = 4, number of conductors = 666, number of parallel paths = 2. Armature resistance = 0.267 Ω. The armature reaction is negligible and rotational losses are 600 W. The motor operates from a 230 V DC supply. If the motor runs at 1000 rpm, the output torque produced (in Nm) is ________.
GATE EE 2015 Set 1
10
A separately excited DC motor runs at 1000 rpm on no load when its armature terminals are connected to a 200 V DC source and the rated voltage is applied to the field winding. The armature resistance of this motor is 1 Ω. The no-load armature current is negligible. With the motor developing its full load torque, the armature voltage is set so that the rotor speed is 500 rpm. When the load torque is reduced to 50% of the full load value under the same armature voltage conditions, the speed rises to 520 rpm. Neglecting the rotational losses, the full load armature current (in Ampere) is _______.
GATE EE 2015 Set 1
11
With an armature voltage of 100 V and rated field winding voltage, the speed of a separately excited DC motor driving a fan is 1000 rpm, and its armature current is 10 A. The armature resistance is 1 Ω. The load torque of the fan load is proportional to the square of the rotor speed. Neglecting rotational losses, the value of the armature voltage (in Volt) which will reduce the rotor speed to 500 rpm is ______.
GATE EE 2015 Set 2
12
A 250 V dc shunt machine has armature circuit resistance of 0.6 $$\Omega$$ and field circuit resistance
of 125 $$\Omega$$. The machine is connected to 250 V supply mains. The motor is operated as a
generator and then as a motor separately. The line current of the machine in both the cases is
50 A. The ratio of the speed as a generator to the speed as a motor is ____________.
GATE EE 2014 Set 2
13
A separately excited 300 V DC shunt motor under no load runs at 900 rpm drawing an
armature current of 2 A. The armature resistance is 0.5 $$\Omega$$ and leakage inductance is 0.01 H.
When loaded, the armature current is 15 A. Then the speed in rpm is _____
GATE EE 2014 Set 3
14
A 15kW, 230V dc shunt motor has armature circuit resistance of 0.4 $$\Omega$$ and field circuit
resistance of 230 $$\Omega$$. At no load and rated voltage, the motor runs at 1400 rpm and the line current drawn by the motor is 5 A. At full load, the motor draws a line current of 70 A.
Neglect armature reaction. The full load speed of the motor in rpm is ________________
GATE EE 2014 Set 1
15
A 220 V, 15 kW, 1000 rpm shunt motor with armature resistance of 0.25 Ω , has a rated line
current of 68 A and a rated field current of 2.2 A. The change in field
flux required to obtain a speed of 1600 rpm while drawing a line current of 52.8 A
and a field current of 1.8 A is
GATE EE 2012
16
A 220 V, DC shunt motor is operating at a speed of 1440 rpm. The armature
resistance is 1.0 $$\Omega$$ and armature current is 10 A. of the excitation of the machine
is reduced by 10%, the extra resistance to be put in the armature circuit to
maintain the same speed and torque will be
GATE EE 2011
17
A separately excited DC motor runs at 1500 rpm under no-load with 200 V applied
to the armature. The field voltage is maintained at its rated value. The speed of
the motor, when it delivers a torque of 5 Nm, is 1400 rpm as shown in the figure.
The rotational losses and armature reaction are neglected.
For the motor to deliver a torque of 2.5 Nm at 1400 rpm the armature voltage to
be applied is
For the motor to deliver a torque of 2.5 Nm at 1400 rpm the armature voltage to
be applied isGATE EE 2010
18
A separately excited DC motor runs at 1500 rpm under no-load with 200 V applied
to the armature. The field voltage is maintained at its rated value. The speed of
the motor, when it delivers a torque of 5 Nm, is 1400 rpm as shown in the figure.
The rotational losses and armature reaction are neglected.
The armature resistance of the motor is,
The armature resistance of the motor is,GATE EE 2010
19
Figure shows the extended view of a $$2$$ pole $$dc$$ machine with $$10$$ armature conductors. Normal brush positions are shown by $$A$$ and $$B,$$ placed at the inter polar axis. If the brushes are now shifted, in the direction of rotation to $$A'$$ and $$B'$$ as shown, the voltage waveform $${V_{A'B'}}$$ will resemble
GATE EE 2009
20
A $$240V$$ $$dc$$ shunt motor draws $$15A$$ while supplying the rated load at a speed of $$80$$ $$rad/s$$. The armature resistance is $$0.5$$ $$ohm$$ and the field winding resistance is $$80$$ $$ohm.$$
The external resistance to be added in the armature circuit to limit the armature current to $$125\% $$ of its rated value is
GATE EE 2008
21
A $$240V$$ $$dc$$ shunt motor draws $$15A$$ while supplying the rated load at a speed of $$80$$ $$rad/s$$. The armature resistance is $$0.5$$ $$ohm$$ and the field winding resistance is $$80$$ $$ohm.$$
The net voltage across the armature resistance at the time of plugging will be
GATE EE 2008
22
A $$220V$$ $$DC$$ machine supplies $$20$$ $$A$$ at $$200V$$ as a generator. The armature resistance is $$0.2$$ ohm. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by $$10\% ,$$ the ratio of motor speed to generator speed is
GATE EE 2006
23
In relation to DC machines, match the following and choose the correct
combination.
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
GATE EE 2005
24
A 50 kW dc shunt motor is loaded to draw rated armature current at any given
speed. When driven
(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
(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
GATE EE 2005
25
Two magnetic poles revolve around a stationary armature carrying two coils
($$c_1-c'_1$$ , $$c_2-c'_2$$ ) as shown in Figure. Consider the instant when the poles are in a
position as shown. Identify the correct statement regarding the polarity of the
induced emf at this instant in coil sides $$c_2$$ and $$c_1$$.
GATE EE 2005
26
A 8 pole, DC generator has a simplex wave-wound armature containing 32 coils
of 6 turns each. Its flux per pole is 0.06 Wb. The machine is running at 250 rpm.
The induced armature voltage is
GATE EE 2004
27
The armature resistance of a permanent magnet dc motor is 0.8 $$\Omega$$. At no load, the
motor draws 1.5 A from a supply voltage of 25 V and runs at 1500 rpm. The
efficiency of the motor while it is operating on load at 1500 rpm drawing a
current of 3.5 A form the same source will be
GATE EE 2004
28
A dc series motor driving an electric train faces a constant power load. It is
running at rated speed and rated voltage. If the speed has to be brought down to
0.25 p.u. the supply voltage has to be approximately brought down to
GATE EE 2003
29
A 200 V, 2000 rpm, 10A, separately excited d.c. motor has an armature resistance
of 2 $$\Omega$$. Rated d.c. voltage is applied to both the armature and field winding of the
motor. If the armature drawn 5A from the source, the torque developed by the
motor is
GATE EE 2002
30
An electric motor with 'constant output power' will have a torque speed
characteristic in the form of a
GATE EE 2001
31
A 240 V dc series motor takes 40A when giving its rated output at 1500 rpm. Its
resistance is 0.3 ohms. The value of resistance which must be added to obtain
rated torque at 1000 rpm is:
GATE EE 2000
32
A permanent magnet dc commutator motor has a no load speed of 6000 rpm when connected to a 120V dc supply. The armature resistance is 2.5 ohms and other losses may be neglected. The speed of the motor with supply voltage of 60V developing a torque 0.5 Nm, is:
GATE EE 2000
33
A DC shunt motor is running at 1200 rmp, when excited with 220 V DC.
Neglecting the losses and saturation, the speed of the motor when connected to a
175 V DC supply is:
GATE EE 1999
34
Match the following
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
GATE EE 1998
35
A 240 V d.c. shunt motor with an armature resistance of 0.5 $$\Omega$$ has a full load
current of 40 A. Find the ratio of the stalling torque to the full load torque when a
resistance of 1 $$\Omega$$ is connected in series with the armature?
GATE EE 1998
Marks 5
1
A $$230V,$$ $$250$$ $$rpm.$$ $$100A$$ separately excited $$dc$$ motor has an armature resistance of $$0.5\,\Omega .$$ The motor is connected to $$230V$$ $$dc$$ supply and rated $$dc$$ voltage is applied to the field winding. It is driving a load whose torque speed characteristic is given by $${T_L} = 500$$$$ - 10\omega ,$$ where $$\omega $$ is the rotational speed expressed in $$rad/sec$$ and $${T_L}$$ is the load torque in $$Nm.$$ Find the steady state speed at which the motor will drive the load and the armature current drawn by it from the source. Neglect the rotational losses of the machine.
GATE EE 2002
2
In a $$dc$$ motor running at $$2000$$ $$rpm,$$ the hysteresis and eddy current losses are $$500$$ $$W$$ and $$200$$ $$W$$ respectively. If the flux remains constant, calculate the speed at which the total iron losses are halved.
GATE EE 2001
3
A $$dc$$ series motor is rated $$230V,$$ $$1000$$ $$rpm,$$ $$80$$ $$A$$ (refer to Figure). The series field resistance is $$0.11\,\Omega ,$$ and the armature resistance is $$0.14\,\Omega .$$ If the flux at an armature current of $$20A$$ is $$0.4$$ times of that under rated condition, calculate the speed at this reduced armature current of $$20$$ $$A.$$
GATE EE 2001
4
A separately excited $$DC$$ shunt motor is driving a fan load whose torque is proportional to the square of the speed. When $$100$$ $$V$$ are applied to the motor, the current taken by the motor is $$8$$ $$A,$$ with the speed being $$500$$ $$rpm.$$ At what applied voltage does the speed reach $$750$$ $$rpm$$ and then what is the current drawn by the armature? Assume the armature circuit resistance to be $$1\,\,\,\Omega .$$ Neglect brush drop and mechanical losses.
GATE EE 1999
5
A $$DC$$ shunt generator delivers $$60$$ $$KW$$ at $$240$$ $$V$$ and $$360$$ $$rpm.$$ The armature and field resistances are $$0.015\,\,\,\Omega $$ and $$60\,\,\,\Omega $$ respectively. Calculate the speed of the machine running as a shunt motor and taking $$60$$ $$KW$$ input at $$240$$ $$V.$$ Allow $$1$$ volt per brush for contact drop.
GATE EE 1998
6
At $$50\% $$ of full load, the armature current drawn by a $$d.c.$$ shunt motor is $$40$$ A when connected to a $$200$$ $$V$$ $$d.c.$$ mains. By decreasing the field flux, its speed is raised by $$20\% $$ this also causes a $$10\% $$ increase in load torque. Calculate the percentage change in field current. The armature resistance including the brushes is $$1$$ $$Ohm.$$ Neglect saturation and armature reaction.
GATE EE 1997
7
The field coil of a two-pole $$d.c.$$ series motor is made up of two identical sections In one case
$$(i)$$ 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
$$(i)$$ 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
GATE EE 1997
8
A $$5$$ $$kW,$$ $$200V$$ $$d.c.$$ shunt motor has an armature resistance of $$1$$ $$ohm$$ and shunt field resistance of $$100$$ $$ohms.$$ At no-load, the motor draws $$6A$$ from a $$200$$ $$V$$ supply and runs at $$1000$$ $$rpm.$$ The rotational loss of the machine is ______________ $$W$$ and the no load torque is ____________ $$N$$-$$m$$
GATE EE 1997
9
A $$200V$$, $$10$$ $$kW$$ lap-wound $$d.c.$$ generator has $$10$$ poles and $$500$$ conductors on it's armature. If the pole face covers $$80\% $$ of the pole pitch, the pole face conductors required to fully compensate for armature reaction will be ___________________ conductors/pole.
GATE EE 1997
10
A separately excited $$d.c.$$ motor has an armature resistance of $$0.5$$ $$ohm.$$ It runs off a $$250$$ $$V$$ $$d.c.$$ supply drawing an armature current of $$20$$ $$A$$ at $$1,500$$ $$rpm.$$ The torque developed for an armature current of $$10$$ $$A$$ will be __________ for the same field current.
GATE EE 1992