Utilization of Electrical Energy

A single phase 220V, 50Hz supply feeds a separately excited dc motor through two single phase semi converters, one for the field and another for armature. The firing angle of the field semi converters is zero, the field resistance is 250 Ω and the armature resistance is 0.2 Ω. The load torque is 150 Nm at 1500 rpm. The voltage constant is 0.8 V/A rad/s and torque constant is 0.8 Nm/A². Assuming armature and field current to be continuous and neglecting losses, determine: (i) Field current. (ii) Firing of the converter in the armature circuit. (iii) Power factor of the converter of the armature circuit.

A single phase, 220 V, 50 Hz supply feeds a separately excited dc motor through two single phase semi-converters, one for the field and another for armature. The firing angle for the field semi-converter is zero. The field resistance is 250 Ω and armature resistance is 0.2 Ω. The load torque is 50 N-m at 1000 rpm. The voltage constant is 0.8 V/A-rad/s and the torque constant is 0.8 N/A². Assuming the armature and field currents to be continuous and neglecting losses, Determine: (i) Field current. (ii) Firing angle of the converter in the armature circuit. (iii) Power factor of the converter of armature.

A DC chopper fed from 400V supply runs a separately excited motor. The armature resistance Ra = 0.1 Ω. The motor voltage constant is 4 Vsec/radian, the average armature current Ia = 150 A. the armature current is continuous and has negligible ripple. Determine (a) The input power (b) The motor speed and (c) The developed torque for a duty cycle of 60%. Neglect the losses in chopper. If the duty cycle of chopper varies between 10% and 90%, find maximum and minimum speed.

A 3 phase fully controlled Thyristor Bridge with 400 V, 3 phase, 50 Hz supply is feeding a separately excited DC motor. Armature resistance is 0.2 Ω, armature rated current is 100 A and back emf constant is 0.25 V/rpm. Determine no-load speed if no-load armature current is 5 A and firing angle is 45°. Also determine firing angle to obtain a speed of 1500 rpm at rated current.

Draw the torque speed-characteristics of induction motor with constant V/f control for speed variation from very low up to the base speed. Describe an open loop control scheme for induction motor with constant V/f control.

A 400 V 4 pole 50 Hz3 phase star connected induction motor has the following parameters: number of stator turns/phase is twice the number of rotor turns/phase. R₁ = 0.64 Ω, X₁ = 1.1 Ω, R₂ = 0.8 Ω, X₂ = 0.12 Ω. The load torque is proportional to the square of speed and is 40N-m, at 1440 rpm. If the motor speed is 1300 rpm, find (a) load torque (b) rotor current (c) stator applied voltage. Neglect no load current.