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 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 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 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_________.

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 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 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 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

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

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 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 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

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