A 20 kW, 500 V d.c. shunt wound motor draws a current of 45 A when running at full load

6. (i) A 20 kW, 500 V d.c. shunt wound motor draws a current of 45 A when running at full load with a speed of 600 rev min-1. On no load, the current drawn from the supply is 5 A. If the armature resistance is 0.3 ohms and the shunt field resistance is 220 ohms, calculate the armature current, speed and efficiency of the motor when the torque falls to half of its full load value, assuming that the flux per pole does not change.

(Hint: don't forget that all armature current is supplying torque. One must decide at some points what is the armature current producing
torque and at others, to determine generator emfs, the total armature current).

(ii) State what you would expect to happen to the speed if a resistance is inserted into the field circuit.

(iii) If a resistance of 50 ??is inserted in series with the shunt field, calculate the armature current required to maintain half full-load
torque. Calculate also the speed of the motor when supplying this torque.

Solution Summary

The expert examines shunt wound motor drawing a current of 45A running at full load. What you would expect to happen to the speed if a resistance is inserted into the field circuit is determined.

(a) A shunt-woundmotor set was designed to run from a 250 V d.c. supply. It had an effective armature resistance of 3 m Ohm and when run at 3000 rev/min it drew 10 kA.
Find:
(i) The maximum permissible supply voltage at start-up if the motor set is not to draw more than 20 kA when started from rest.
(ii) The maximum start-

A three-phase, 60 Hz, squirrel-cage induction motordraws a current of 385 amps per phase and a total active power of 2344 kW when operating at fullload from a 4000 volt (line) supply. The corresponding speed is 709.2 rev/min. The stator is star-connected and the resistance between two stator live terminals is 0.1 ohms. The mac

A 100 hp 60 Hz six pole 460 V three phase wound rotor induction motor develops a full-load torque at 1152 r/min with the rotor short-circuited. An external noninductive resistance of 1 Ohm is placed in series with each phase of the rotor, and the motor is observed to develop its rated torque at a speed of 1116 r/min. Calculate

In the zener diode circuit calculate the value of the current through the zener diode if the power supply is rated 24 volts at 500 milli amperes. The load voltage is 12 volts and draws a current of 300 milli amperes. Also calculate the value of the series resistance R.

Q1)
Assume the torque stays constant at 120 N-m. How long will it take for the unloaded armature to accelerate from zero up to full speed of 3000 rpm? Now I am given the formular Ix = I w-wo / t. All I know is that the rotational inertia is 2.81 kg-m^2.
Q2)
What will be the power of the motorwhen it is s

What is the effect of the DMM input resistance on the measured results? Derive the voltage gain of the divider with a DMM resistance of Rm, which is also called shunt resistance (See Figure 2.3-attached file).

In the figure (attached), the winding drum of a lift is driven by an electric motor via a gearbox having a reduction ratio of 20:1. The direct inertia on the motor shaft is 0.05 kg m2 and that on the winding shaft is 20 kg m2. The drum, which has a diameter of 600 mm, moves a lift by means of a cable wound around it. If the li

A fully loaded 440V, three phase motordraws 12.4A at 86% power factor (pf). Its speed is 1730 rpm and its torque output to a mechanical load is 29.1 lb-ft*1.356=39.5Nm. What is the output HP and the efficiency?

Table 1 shows a set of torque-speed measurements for a d.c. electric motor intended for use in an electric wheelchair. Data of this type is used by manufacturers to help specify motor performance.
Table1
Speed /rpm..............600..........1200......1850..........2400.......3050.........3700
Torque /Nm..............5.51...