PROBLEMS 621(b) When the load is completely removed with-
out change of excitation currents.
13.4.16The external-characteristics data of two shunt
generators in parallel are given as follows:Load Current, A: 0 5 10 15 20 25 30Terminal voltage I, V: 270 263 254 240 222 200 175
Terminal voltage II, V: 280 277 270 263 253 243 228Calculate the load current and terminal voltage
of each machine.
(a) When the generators supply a load resistance
of 6.
(b) When the generators supply a battery of emf
300 V and resistance of 1.5.*13.4.17A separately excited dc generator with an
armature-circuit resistanceRais operating at a
terminal voltageVt, while delivering an armature
currentIa, and has a constant lossPc. Find the
value ofIafor which the generator efficiency is
a maximum.
13.4.18A 100-kW, 230-V, dc shunt generator, withRa=
0. 05 , andRf= 57. 5 has no-load rotational
loss (friction, windage, and core loss) of 1.8 kW.
Compute:
(a) The generator efficiency at full load.
(b) The horsepower output from the prime
mover to drive the generator at this load.
13.4.19A dc series motor, with a design constantKa=
40 and flux per pole of 46.15 mWb, operates at
200 V while taking a current of 325 A. The total
series-field and armature-circuit resistances are
25 and 50 m, respectively. The core loss is 220
W; friction and windage loss is 40 W. Determine:
(a) The electromagnetic torque developed.
(b) The motor speed.
(c) The mechanical power output.
(d) The motor efficiency.
13.4.20A 230-V dc shunt motor delivers 30 hp at the shaft
at 1120 r/min. If the motor has an efficiency of
87% at this load, find:
(a) The total input power.
(b) The line current.
(c) If the torque lost due to friction and windage
is 7% of the shaft torque, calculate the de-
veloped torque.
13.4.21A 10-kW, 250-V dc shunt generator, having an
armature resistance of 0.1and a field resistance
of 250, delivers full load at rated voltage and
800 r/min. The machine is now run as a motor
while taking 10 kW at 250 V. Neglect the brush-
contact drop. Determine the speed of the motor.
13.4.22A 10-hp, 230-V dc shunt motor takes a full-
load line current of 40 A. The armature and field
resistances are 0.25 and 230, respectively. The
total brush-contact drop is 2 V, and the core and
rotational losses are 380 W. Assume that stray-
load loss is 1% of output. Compute the efficiency
of the motor.