Question

a three phase induction motor delivers %00 HP at the efficiency of 90% when the operating point of p.f is 0.8 lag. a loaded synchronous motor with power consumption of 120KW is connected in parallel with the induction motor. calculate the necessary and the operating power factor of the synchronous motor if the overall power factor is to be unity.

Answer #1

Q1. A 3-phase, 400 V synchronous motor having a power
consumption of 50 kW is connected in parallel with an induction
motor which takes 200 kW at a power factor of 0·8 lagging.
(i) Calculate the current drawn from the mains when the power
factor of the synchronous motor is unity.
(ii) At what power factor should the synchronous motor
operate so that the current drawn from the mains is
minimum.

4) A three-phase synchronous motor of 4000 hp nominal, 13,200 V,
60 Hz, 2 poles, connected in star, operating at 0.84 of power
factor in advance, has an efficiency of 96.5%.
The synchronous reactance per phase is 49.33 Ω:
• Draw the phasor diagram on the grid sheet
• Determine the loading angle
• Determine the load torque

Question
A 208 V 10 Hp four pole 60 Hz Y connected induction motor has a
full load slip of 5%.
a)-What is the synchronous speed of this motor?
b)-What is the shaft speed of this motor at full load?
c)-What is the frequency of rotor current at full load?
d)-What is the shaft torque of this motor at full load?
e)-If the efficiency of this motor is 90% at full load what is
the input power
f)-If the efficiency...

A three-phase, 280 V, 60 Hz, 20 hp, 1710 r/m. Y-connected
induction motor has the following impedances in ohms per phase
referred to the stator circuit:
R1=0.12 Ω.
Rˈ2=0.1
Ω
X1=Xˈ2=0.25 Ω
Xm=10 Ω
A total rotational loss are 400 W. The core loss is lumped in
with the rotational losses. For a slip of 0.05 at the rated voltage
and rated frequency. Find:
a) The numbers of poles of the motor.
b) The stator current.
c) the power factor...

A 100 KW (OUT PUT), 3300V, 50 Hz, 3-Phase star connected
induction motor has a synchronous speed of 500 rpm. The full load
slip is 1.8%and full load power factor 0.85. Stator copper
loss=2440W. Iron loss=3500W. Rotational losses= 1200W. calculate
:
The rotor copper loss
The line current
The full load motor efficiency.

A single-phase motor takes 8.3 A at a power factor of 0.866
lagging when connected to a 230 V, 50 Hz supply. Two similar
capacitors are connected in parallel with each other to form a
capacitance bank. This capacitance bank is now connected in
parallel with the motor to raise the power factor to unity.
Determine the capacitance of each capacitor

a 460-V 100-hp 60-Hz 4 pole Y connected synchronous motor has a
operating power factor 0.85 leading the aramature resistance is o.2
ohms and synchronous reactance is 12 ohms at full load the
efficiency is 85% find the sum of mechanical loss core loss and
stray loss when meachine is operating at full load

A three phase Y connected synchronous motor has negligible
armature resistance and a synchronous reactance of 12 ohm/phase.
The motor takes 12,000kW at a line voltage of 13,200V. If the line
current is adjusted so that the excitation voltage is
9000V/phase:
a. What is the torque angle?
b. At what power factor is the motor operating?
c. What is its armature current?

Q4 (a) A 3-phase induction motor having a synchronous speed of
1200rpm draws 80kW from a 3-phase feeder. The copper losses and
core losses in the stator amount to 5kW. If the motor runs at
1152rpm, calculate:
(i) the rotor input power;
(ii) the rotor copper losses;
(iii) the gross mechanical power output;
(iv) the net mechanical power with knowing that the windage and
friction losses are 2kW;
(v) the efficiency of the motor
(b) Compare the brushed motor (DC...

(360) Volt, 60 Hz, 600 hp, 0.6 pf-leading, four-pole -connected
synchronous motor has 0.9Ω synchronous reactance. Friction; wind;
core losses and armature resistance are neglected.
a) If the motor is operating under magnitude of phase current
(ia) (180)
Ampere and power factor of 0.6 lagging,
1. Find the input power of motor in hp
2. Find the generated voltage, EA
3. Find the torque and the maximum inducible torque in current
state.
b) If EA is increased by 18% find,...

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