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Transcript
Homework 4
ECE 207 – Electrical Engineering
Due: 9/27/2012
1. A three-phase, 10 hp, 208 V, 50 Hz, 4 pole, Y-connected induction motor delivers rated
output power at a slip of 2%. Determine:
a. Synchronous speed
b. Rotor speed
c. Synchronous speed and rotor speed, if the motor had 2 poles
2. A three-phase, 25 hp, 230 V, 60 Hz induction motor draws 60 A from the source at 0.866
lagging power factor. The motor losses are:
 Stator copper loss, Pcu1 = 850 W
 Magnetic core loss, Pcore = 450 W
 Rotor copper loss, Pcu2 = 1050 W
 Rotational loss, Prot = 500 W
Find:
a.
b.
c.
d.
e.
Air gap power, Pag
Slip, s
Mechanical power developed, Pdev
Output power, Pout
Efficiency of the motor, η
3. A three-phase, 50 hp, 460 V, 60 Hz, 4 pole, induction motor has the following data:
R1 = 0.1 Ω
X1 = 0.35 Ω
R2 = 0.125 Ω
X2 = 0.40 Ω
Rc = 1200 Ω
Xm = 100 Ω
This motor operates at a slip of 2.5%. Ignoring windage losses, calculate:
a.
b.
c.
d.
e.
f.
Line current, I1
Input power, Pin
Input power factor, pf
Efficiency, η
Starting current, Istart
Starting power factor, pfstart
4. A three-phase, 5 hp, 208 V, 4 pole, 60 Hz induction motor is subjected to no-load, blockedrotor, and DC tests. The following data was collected from these tests:
Variable
Voltage (V)
Current (A)
Power (W)
No-Load Test
208
4
250
Blocked-Rotor Test
35
12
450
DC Test
20
25
Find:
a. Parameters of the equivalent circuit
b. Draw the equivalent circuit with parameter values specified on it
5. For the motor of Problem 4, it is desirable to improve the power factor to 0.98 lagging.
If the slip is 5% and terminal voltage is 208 V, then calculate:
a. Reactive power of the capacitor/phase for power factor correction
b. Capacitance of the Y-connected capacitor/phase for power factor correction