DC Motors

Problem 527: A 220 V shunt motor driving its normal load draws an armature current of 50 A from a 220 V dc source. The armature resistance of this motor including brushes is 0.25 ohm. How much armature current (minimum) will this motor draw from a 200 V dc source when driving the same load with the field adjusted to maintain the same speed.

Problem 535: A DC shunt motor has a full load rating of 15 hp, 230 volts, 57.1 amperes, 1400 rpm. The armature circuit resistance is 0.13 ohm and the field circuit resistance is 115 ohms. Neglecting the effect of armature reaction, determine the no-load speed.

Problem 546: A certain shunt motor has an armature resistance of 0.05 ohm. It draws 50 A at a terminal voltage of 120 V. Assume other miscellaneous losses at 1%. Determine the output horsepower of the motor.

Problem 551: The equivalent armature resistance of a series motor is 0.1 ohm. When connected across a 110-V mains, the armature takes 20 A and its speed is 1000 rpm. Determine its speed when the armature takes 50 A from the same mains, with the field increased by 10%.

Problem 552: A 400 V series motor has a field resistance of 0.2 ohm and an armature resistance of 0.1 ohm. The motor takes 30 A of current at 1000 rpm while developing full load torque. What is the motor speed when this motor develops 60% of full load torque.

Problem 558: On full load a 500 V series motor takes 100 A and runs at 820 rpm. The armature and series field resistances are 0.1 and 0.04 ohm respectively. What will be its speed when developing half-full load torque and with a 0.08-ohm diverter connected across the series field winding. Assume flux is proportional to the field current.

A shunt motor has a rated armature current of 50 A when connected to 200 V. The rated speed is 1,000 rpm and the armature resistance is 0.1 Ω. Find the speed if the total torque is reduced to 70% of that at rated load and a 3 Ω resistance is inserted in series with the armature.

A 400 v series motor working with unsaturated field is taking 60 A and running at 840 rpm. The total resistance of the motor is 0.1 ohm. At what speed will the motor run when developing half-full load torque.

Calculate the no-load current taken by a 100 kW, 460 v, shunt motor assuming the armature and field resistance to remain constant and equal to 0.03 Ω and 46 Ω, respectively The efficiency at full load is 88%

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.

A dc shunt motor has a nameplate rating of 15 HP, 230 V, 57.1 amperes and 1,400 rpm. The field circuit has a resistance of 115 Ω and the armature circuit resistance is 0.13 Ω. Neglecting the effect of armature reaction, find the no-load line current.

A shunt motor with an armature resistance of 0.15 ohm is running at 1,200 rpm for a load which requires an armature current of 50 A from a 230 V source. At no load, the armature current is 5 A. If armature reaction has reduced the air-gap flux by 2% from no load to full load, what is the no-load speed?

A 9.6 kW, 240 V shunt generator having an armature resistance of 0.10 ohm and a shunt field resistance of 240 ohms delivers full load at rated voltage and 800 rpm. The machine is now run as a motor taking its full-load line current of 40 A at 250 V. Neglecting brush drop and assuming flux proportional to field current, what is the speed of the motor?