DC Motors

A 230 v shunt motor has a no-load line current of 7 A and a full-load line current of 46 A. The armature resistance is 0.05 Ω and the shunt field is 75 Ω Determine the motor efficiency at full load.

As the load is increased the speed of a dc shunt motor will

The armature current drawn by any dc motor is proportional to

A 400 V, 10 kW series motor drives a fan when running at 800 rpm. The motor draws 50 A from the supply. The resistances of the armature and series field are 0.2 Ω and 0.1 Ω, respectively. Determine the electromagnetic torque developed by the motor.

A 220 V series motor takes 10 A and runs at 600 rpm. The total resistance is 0.8 Ω. At what speed will it run when a 5 Ω resistance is connected in series, the motor taking the same current at the same supply voltage?

A shunt motor runs at 500 rpm on a 200 V circuit. Its armature resistance is 0.5 Ω and the current taken is 30 A in addition to the field current. What resistance must be placed in series in order that the speed may be reduced to 300 rpm, the current in the armature remaining the same?

The resistance of the field coil of a motor is 200 Ω at 15 °C. After the motor worked for a few hours on full load, the resistance increases to 240 Ω. Calculate the temperature rise of the coil, assuming the temperature coefficient of resistance is 0.0042 per °C at 0 °C.

The armature current drawn by any dc motor is proportional to

A 20-HP, 110 v dc shunt motor has an efficiency of 88% and an exciting current of 4 amperes and an armature resistance of 0.04 ohm. What is the starting resistance required for full-load torque?

A 220-volt dc shunt motor runs at 500 rpm with an armature current of 50 amperes and an armature resistance of 0.1 Ω. Calculate the speed if the torque is halved.

An external resistance is added in series with the field of a dc shunt motor. When the motor runs, the effect of resistance is

The primary reason for using carbon brushes over copper brushes in DC motors is

Power developed by a dc motor is maximum when the ratio of back emf to applied voltage is

A 110-volt shunt motor has an armature resistance of 0.8 Ω and a field resistance of 220 Ω. At full load the motor takes 10 amperes, and the speed is 1,200 rpm. At what speed must this motor run as a generator to deliver 10 amperes to an external circuit at 110 V?

When a dc motor has no load, what will happen to the back emf?

A 440-V, 70-HP shunt motor has an armature resistance of 0.185 Ω and field resistance of 350 Ω. The current drawn by this machine is 135 A at full load. If this machine is to deliver torque equal to 175 percent of that at full load, what would be the best resistance of its starter?

The current flowing in the armature conductors of a dc motor is

A 4 pole lap winding motor with 16 slots, 42 conductors per slot, 480 v runs at 1800 rpm. Find the flux produced per pole.

If the load current and flux of a dc motor are held constant and the voltage applied across its armature is increased by 10%, its speed will ___________.

A 15-hp motor operates at an efficiency of 87.5 percent at full load. If the stray power loss is approximately one-fourth of the total loss, calculate the copper loss.