A 440 V dc shunt motor has a no-load speed of 2000 rpm. It is running at 1000 rpm at full load torque, reduced armature voltage and full field current. If load torque is reduced to 50% of rated value with armature voltage and field voltage held constant at previous values, the speed increases to 1050 rpm. Find the armature voltage drop at full load. Neglect the effect of armature reaction.

2Medium10 marks

An RLE load is operating in chopper circuit from a 500 V dc source as shown in Figure. For R = 0, L = 0.064 and constant E, the duty cycle is 0.2. Find the chopping frequency to limit the amplitude of load current excursion to 10 A.

3Medium20 marks

Explain the direct connection method of measurement of Q of a coil. Name the sources of error in such measurements. Compute the value of self-capacitance and inductance of a coil when the following measurements are made :

At frequency 2 MHz, the tuning capacitor is set at 450 pF

When the frequency is measured to 5 MHz, the tuning capacitor is tuned at 60 pF

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