A DC series motor with negligible series resistance is running at a certain speed driving a load, where the load torque varies as cube of the speed. The motor is fed from a 400 V DC source and draws 40 A armature current. Assume linear magnetic circuit. The external resistance, in , that must be connected in series with the armature to reduce the speed of the motor by half, is closest to

A  DC shunt motor has  armature resistance including brushes. The motor draws a no-load current of . The field current is constant at . 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).

The four stator conductors  and  of a rotating machine are carrying  currents of the same value, the directions of which are shown in the figure (i). The rotor coils  -  ' and  -  ' are formed by connecting the back ends of conductors '  ' and '  ' and '  ' and '  ', respectively, as shown in figure (ii). The e.m.f. induced in coil  -  ' and coil  -  are denoted by  and , respectively. If the rotor is rotated at uniform angular speed  in the clockwise direction then which of the following correctly describes the  and  ?

fig. (i) cross-section view fig. (ii) rotor winding connection diagram

A separately excited DC motor rated  A, 1500 RPM drives a constant torque load at rated speed operating from  supply drawing rated current. The armature resistance is 1.2Ω . If the supply voltage drops by  with field current unaltered then the resultant speed of the motor in RPM is __________ (Round off to the nearest integer).

A 280 V, separately excited DC motor with armature resistance of 1 Ω and constant field excitation drives a load. The load torque is proportional to the speed. The motor draws a current of 30A 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 Ω is connected in series with the armature, is ___________. (round off the nearest integer).

A belt-driven DC shunt generator running at 300 RPM delivers 100 kW to a 200 V DC grid. It continues to run as a motor when the belt breaks, taking 10 kW from the DC grid. The armature resistance is 0.025 Ω, field resistance is 50 Ω, and brush drop is 2 V. Ignoring armature reaction, the speed of the motor is _________ RPM. (Round off 2 decimal places)

A 250 V DC shunt motor has an armature resistance of 0.2 Ω and a field resistance of 100 Ω. When the motor is operated on no-load at rated voltage. It draws an armature current of 5 A and runs at 1200 rpm. When a load is coupled to the motor, it draws total line current of 50 A at rated voltage, with a 5 % reduction in the air-gap flux due to armature reaction. Voltage drop across the brushes can be taken as 1 V per brush under all operating conditions. The speed of the motor, in rpm, under this loaded condition, is closest to:

A 220 V DC shunt motor takes 3 A at no-load. It draws 25 A when running at full-load at 1500 rpm. The armature and shunt resistances are  and  respectively. The no-load speed in rpm (round off to two decimal places) is _________.

A separately excited dc motor has an armature resistance. The field excitation is kept constant. At an armature voltage of 100V, 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).

A 200V DC series motor, when operating from rated voltage while driving a certain load, draws 10 A current and runs at 1000r.p.m. The total series resistance is . 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 ________

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 . If the speed of the generator is increased to 1000 RPM, the current in amperes supplied by the generator to the DC gird is ___________. (Give the answer up to one decimal place).

A 220 V DC series motor runs drawing a current of 30 A from the supply. Armature and field circuit resistances are  and , respectively. The load torque varies as the square of the speed. The flux in the motor may be taken as being proportional to 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 _________. (Give the answer up to one decimal place).

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  and the shunt field resistance is . The no load speed, in rpm, is ___________.

A 220 V, 10 kW, 900 rpm separately excited DC motor has an armature . 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

A 4-pole, lap-connected, separately excited dc motor is drawing a steady current of 40 A while running at 600rpm. A good approximation for the waveshape of the current in an armature conductor of the motor is given by

A DC shunt generator delivers at 45A at a terminal voltage of 220V.The armature and the shunt field resistance are  and  respectively. The stray losses are 375W. The percentage efficiency of the DC generator is________________.

A separately excited DC generator has an armature resistance of 0.1Ω 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 voltages across it reach 25 V?

A separately excited DC motor runs at 1000 rpm on no load when its armature terminals are connected to a 200V DC source and the rated voltage is applied to the field winding. The armature resistance of this motor is 1Ω. 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 ________________.

A DC motor has the following specifications: 10 hp, 37.5A, 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 ____________.

A shunt-connected DC motor operates at its rated terminal voltage. Its no-load speed is 200 radian/sec. At its rated torque of 500 Nm, its speed is 180 radian/sec. The motor is used to directly drive a load whose load torque  depends on its rotational speed  (in radian/second), such that . Neglecting rotational losses, the steady-state speed (in radian/second ) of the motor, when it drives this load, is_________.

A 4-pole, separately excited, wave wound DC machine with negligible armature resistance is rated for 230V and 5kW at a speed of 1200 rpm. If the same armature coils are reconnected to form a lap winding, what is rated voltage (in volts) and power (in kW) respectively at 1200 rpm of the reconnected machine if the field circuit is left unchanged?

With an armature voltage of 100 V and rated field winding voltage, the speed of a separately excited DC motor driving a fan is 1000rpm, and its armature current is 10 A. The armature resistance is 1 . 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 500rpm is ___________________.

A 15kW, 230V dc shunt motor has armature circuit resistance of  and field circuit resistance of . At no load and rated voltage, the motor runs at 1400rpm and the line current drawn by the motor is 5A. At full load, the motor draws a line current of 70A. Neglect armature reaction. The full load speed of the motor in rpm is_____________.

A 250V dc shunt machine has armature circuit resistance of  and field circuit resistance of . The machine is connected to 250V 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 50A. The ratio of the speed as a generator to the speed as a motor is_____________.

The no-load speed of a 230 V separately excited dc motor is 1400rpm. 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 ________.

A separately excited 300V DC shunt motor under no load runs at 900 rpm drawing an armature current of 2A. The armature resistance is  and leakage inductance is 0.01H. When loaded, the armature current is 15A. Then the speed in rpm is __________.

A 220V, 15kW, 1000rpm shunt motor with armature resistance of , has a rated line current of 68A and a rated field of 2.2A. 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 1.8A is a

A 4-point starter is used to start and control the speed of a

A 220V, DC shunt motor is operating at a speed of 1440 rpm. The armature resistance is  and armature current is 10A. If 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

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 its delivers a torque of 5Nm is 1400rpm as shown in the figure. The rotational losses and armature reaction are neglected.

The armature resistance of the motor is.

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 its delivers a torque of 5Nm is 1400rpm as shown in the figure. The rotational losses and armature reaction are neglected.

For the motor to deliver a torque of 2.5Nm at 1400 rpm. The armature voltage to be applied is

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  will resemble

A 240V, dc shunt motor draws 15A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5Ω and the field winding resistance is 80Ω.

The net voltage across the armature resistance at the time of plugging will be

A 240V, dc shunt motor draws 15A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5Ω and the field winding resistance is 80Ω.

The external resistance to be added in the armature circuit to limit the armature current to 125% of its rated value is

The dc motor, which can provide zero speed regulation at full load without any controller, is

In a DC machine, which of the following statements is true?

A 220 V DC machine supplies 20A at 200 V 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%, then ratio of motor speed to generator speed is

Two magnetic poles revolve around a stationary armature carrying two coils 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 and  

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

In relation to DC machines, match the following and choose the correct combination.

The following motor definitely has a permanent magnet rotor

For a linear electromagnetic circuit, the following statement is true.

The armature resistance of a permanent magnet dc motor is 0.8Ω. 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 1400 rpm drawing a current of 3.5 A form the same source will be

A 8 poles, 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

The speed/torque regimes in a dc motor and the control methods suitable for the same are given respectively in Group II and Group I

To conduct load test on a dc shunt motor, it is coupled to a generator which is identical to the motor. The field of the generator is also connected to the same supply source as the motor. The armature of the generator is connected to a load resistance. The armature resistance is 0.02 p.u. armature reaction and mechanical losses can be neglected. With rated voltage across the motor, the load resistance across the generator is adjusted to obtain rated armature current in both motor and generator. The p.u. value of this load resistance is

When Stator and Rotor windings of a 2-pole rotating electrical machine are excited, each would produce a sinusoidal MMF distribution in the air gap with peak values  and respectively. The rotor MMF lags stator MMF by a space angle δ at any instant as shown in Figure. Thus, half of stator and rotor surfaces will form one pole with the other half forming the second pole. Further, the direction of torque acting on the rotor can be clockwise or counter-clockwise.

The following Table gives four sets of statements regarding poles and torque. Select the correct set corresponding to the MMF axis as shown in Figure

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

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 Figure?

A 200 V, 2000 rpm, 10A, separately excited dc motor has an armature resistance of 2Ω. Rated dc voltage is applied to both the armature and field winding of the motor. If the armature draws 5A from the source, the torque developed by the motor is

A 230V, 250 rpm, 100A separately excited dc motor has an armature resistance of 0.5Ω, 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 500 − 10ω, where ω is the rotational speed expressed in rad/sec and  is the load torque in Nm. Find the steady state speed at which the motor will drive the load and the rated armature current drawn by it from the source. Neglect the rotational losses of the machine.

An electric motor with ‘constant output power’ will have a torque speed characteristic in the form of a

In a dc motor running at 2000 rpm, the hysteresis and eddy current losses are 500W and 200W respectively. If the flux remains constant, calculate the speed at which the total iron losses are halved.

A dc series motor is rated 230V, 1000 rpm, 80 A (refer to figure), the series field resistance is 0.11Ω, and the armature resistance is 0.14Ω.  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 20A.

The compensating winding in a dc machine

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:

A belt driven dc shunt generator runs at 1500 rpm delivering 10kW, at 220V bus bars. The belt breaks, following which the machine operates as a motor drawing 2kW power. What will be its speed as a motor? The armature and field resistances are 0.25 ohms and 55 ohms respectively. Ignore armature reaction and assume the contact drop at each brush to be 1V.

A 240V 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:

A DC shunt generator delivers 60KW at 240V and 360 rpm. The armature and field resistances are 0.015Ω and 60Ω respectively. Calculate the speed of the machine running as a shunt motor and taking 60KW input at 240V. Allow 1 volt per brush for contact drop.

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

A DC shunt motor is running at 1200 rpm, when excited with 220V DC. Neglecting the losses and saturation, the speed of the motor when connected to a 175V DC supply is:

A separately excited DC shunt motor is driving a fan load whose torque is proportional to the square of the speed. When 100V are applied to the motor, the current taken by the motor is 8A, 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 1Ω. Neglect brush and mechanical losses

A 240 V DC shunt motor with an armature resistance of 0.5Ω has a full load current of 40A. Find the ratio of the stalling torque to the full load torque when a resistance of 1Ω is connected in series with the armature?

A 5kW, 200V DC 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 200V supply and runs at 1000rpm. The rotational loss of the machine is… W and the no load torque is… N-m

A 200V, 10kW lap-wound DC generator has 10 poles and 500 conductors on its 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.

The field coil of a two-pole DC 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 torque (i): torque (ii) is ….. and speed (i): speed (ii) is ….. (Neglect the effect of magnetic saturation)

At 50% of full load, the armature current drawn by a DC shunt motor is 40A when connected to a 200V DC 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.

A 4 pole generator with 16 coil has a two layer lap winding. The pole pitch is

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 8500 rpm. The flux per pole will be

Out of the following factors for a dc machine,         

(i) Inter pole                

(ii) Armature resistance

(iii) Armature leakage reactance        

(iv) Armature reaction

(v) Reduction in field current

The factors that are responsible for decrease in the terminal voltage of a shunt generator are

A differentially compounded d.c. motor with inter poles 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

A 220V, 1.5 kW, 859 rpm, separately excited dc motor has armature resistance of 2.5 ohms and it draws a current of 8A at rated-load condition. If the field current and the armature voltage are fixed at the value of rated speed at rated load, what will be the no-load speed of the motor? Assume losses remain constant between no-load and full load operation.

A cumulative compounded long shunt motor is driving a load at rated torque and rated speed. If the series field in shunted by a resistance equal to the resistance of the series field, keeping the torque constant

Neglecting all losses, the developed torque (T) of a d.c. separately excited motor, operating under constant terminal voltage, is related to its output power (P) as under

The developed electromagnetic force and/or torque in electro-mechanical energy conversion systems act in a direction that tends

A separately excited d.c. motor has an armature resistance of 0.5 ohm. It runs off a 250V d.c. supply drawing an armature current of 20A at 1500 rpm. The torque developed for an armature current of 10A will be _________________ for the same field current.

Level compounded D.C generator is used for which of the following applications?

A separately excited d.c. motor has to be run at 125% of rated speed when delivering 50% torque. The excitation will be _______________.

Match the windings of a large D.C series motor and their functions:

A 10 kW, 6 pole, D.C generator develops an EMF of 200V at 1500 rpm. The armature has a lap connected winding. The average flux density over a pole pitch is 0.9 Tesla. The length and diameter of the armature are 0.25m and 0.2m respectively. Calculate

(a) The flux per pole

(b) The total number of active conductors in the armature

(c) The torque developed by the machine when the armature supplies a current of 50A.