Problem 3 A 208 V, 45 HP, 50 Hz, 1000 RPM, 0.8-PF leading, A-connected synchronous motor has a synchronous reactance of 4 2 and a negligible armature resistance. The friction, windage, stray, and core losses are all lumped together and approximated to 2.4 KW at rated conditions. 3-Phase Synchronous Motors If the motor is supplying a 20 HP load at 0.8 leading power factor: 1. What is the number of poles of this machine? 2. Calculate the output power and the stator copper losses in Watt. 3. Calculate the input power supplied to the motor?

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Problem 3
A 208 V, 45 HP, 50 Hz, 1000 RPM, 0.8-PF leading, A-connected synchronous motor has a
synchronous reactance of 4 2 and a negligible armature resistance. The friction, windage,
stray, and core losses are all lumped together and approximated to 2.4 KW at rated conditions.
3-Phase Synchronous Motors
If the motor is supplying a 20 HP load at 0.8 leading power factor:
1. What is the number of poles of this machine?
2. Calculate the output power and the stator copper losses in Watt.
3. Calculate the input power supplied to the motor?
4. Find the line current and the phase current of the motor?
5. What are the internal generated voltage Ea and the load angle d of this motor?
Suppose now that the shaft load is increased to 35 HP without any changes in the field
circuit of the motor,
6. Find the phase current and the line current in this case. What is the new power factor?
Transcribed Image Text:Problem 3 A 208 V, 45 HP, 50 Hz, 1000 RPM, 0.8-PF leading, A-connected synchronous motor has a synchronous reactance of 4 2 and a negligible armature resistance. The friction, windage, stray, and core losses are all lumped together and approximated to 2.4 KW at rated conditions. 3-Phase Synchronous Motors If the motor is supplying a 20 HP load at 0.8 leading power factor: 1. What is the number of poles of this machine? 2. Calculate the output power and the stator copper losses in Watt. 3. Calculate the input power supplied to the motor? 4. Find the line current and the phase current of the motor? 5. What are the internal generated voltage Ea and the load angle d of this motor? Suppose now that the shaft load is increased to 35 HP without any changes in the field circuit of the motor, 6. Find the phase current and the line current in this case. What is the new power factor?
Problem 4
A 3-phase, 381 V, 50-Hz, 50 HP, 4-pole, Y-connected induction motor has its per-phase
3-Phase Induction Motors
equivalent circuit when referred to stator side as shown below.
The total friction, windage, and core losses can be assumed to be constant at 1000 w,
independent of load. The motor is operating at rated voltage and frequency.
For a per-unit slip of 0.05, (Use the formula sheet, last page):
(a) Find the shaft speed of the motor in RPM and in rad/sec.
(b) Calculate the stator input current I1.
(c) Find the electrical input power Pin-
(d) What are the stator copper losses PSCL-
(e) Find the air-gap power PAG-
(f) What is the converted power from electrical to mechanical Peony-
(g) Calculate the induced torque t¡nd-
(h) Deduce the overall efficiency %n.
R1=0.42
jX1=j2 52
jX2=j12
+
I2
R2
S
jXm
= j24 2,
0.12
S
Transcribed Image Text:Problem 4 A 3-phase, 381 V, 50-Hz, 50 HP, 4-pole, Y-connected induction motor has its per-phase 3-Phase Induction Motors equivalent circuit when referred to stator side as shown below. The total friction, windage, and core losses can be assumed to be constant at 1000 w, independent of load. The motor is operating at rated voltage and frequency. For a per-unit slip of 0.05, (Use the formula sheet, last page): (a) Find the shaft speed of the motor in RPM and in rad/sec. (b) Calculate the stator input current I1. (c) Find the electrical input power Pin- (d) What are the stator copper losses PSCL- (e) Find the air-gap power PAG- (f) What is the converted power from electrical to mechanical Peony- (g) Calculate the induced torque t¡nd- (h) Deduce the overall efficiency %n. R1=0.42 jX1=j2 52 jX2=j12 + I2 R2 S jXm = j24 2, 0.12 S
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