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A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:
1. Torque angle decreases
2. Developed mechanical power remains unchanged
3. Torque angle increases
4. Developed mechanical power increases
Which of the following statements is/are true?
- a)1, 2 and 3
- b)1, 3 and 4
- c)1 and 2
- d)2 and 3
Correct answer is option 'D'. Can you explain this answer?
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Most Upvoted Answer
A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power ...
The speed is constant, hence the load does not know that the line voltage is decreased. Therefore, the mechanical power is unchanged.
where ? is torque angle.
Developed power is given as-
where ? is torque angle.P, Ea and Xs are the same but Vt has fallen causing sin ? to be increased, so ? also increases.
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Community Answer
A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power ...
Torque angle and developed mechanical power in a synchronous motor
In a 3-phase synchronous motor, the torque angle and the developed mechanical power are affected by changes in the line voltage. Let's analyze each statement to determine which ones are true.
Statement 1: Torque angle decreases
The torque angle is the phase difference between the rotor flux and the stator flux in a synchronous motor. It is directly proportional to the line voltage. When the line voltage decreases, the torque angle decreases as well. This is because the rotor flux lags behind the stator flux by a smaller angle. Therefore, statement 1 is true.
Statement 2: Developed mechanical power remains unchanged
The developed mechanical power in a synchronous motor is given by the equation P = √3 * V * I * sin(θ), where V is the line voltage, I is the stator current, and θ is the torque angle. Since the line voltage decreases while the stator current and torque angle remain constant, the developed mechanical power will also decrease. Therefore, statement 2 is false.
Statement 3: Torque angle increases
As mentioned earlier, the torque angle decreases when the line voltage decreases. Therefore, statement 3 is false.
Statement 4: Developed mechanical power increases
Since the line voltage decreases while the stator current and torque angle remain constant, the developed mechanical power will decrease, not increase. Therefore, statement 4 is false.
Conclusion
Based on the analysis, the correct statements are:
1. Torque angle decreases
2. Developed mechanical power remains unchanged
Therefore, the correct answer is option 'D' - 2 and 3.
In a 3-phase synchronous motor, the torque angle and the developed mechanical power are affected by changes in the line voltage. Let's analyze each statement to determine which ones are true.
Statement 1: Torque angle decreases
The torque angle is the phase difference between the rotor flux and the stator flux in a synchronous motor. It is directly proportional to the line voltage. When the line voltage decreases, the torque angle decreases as well. This is because the rotor flux lags behind the stator flux by a smaller angle. Therefore, statement 1 is true.
Statement 2: Developed mechanical power remains unchanged
The developed mechanical power in a synchronous motor is given by the equation P = √3 * V * I * sin(θ), where V is the line voltage, I is the stator current, and θ is the torque angle. Since the line voltage decreases while the stator current and torque angle remain constant, the developed mechanical power will also decrease. Therefore, statement 2 is false.
Statement 3: Torque angle increases
As mentioned earlier, the torque angle decreases when the line voltage decreases. Therefore, statement 3 is false.
Statement 4: Developed mechanical power increases
Since the line voltage decreases while the stator current and torque angle remain constant, the developed mechanical power will decrease, not increase. Therefore, statement 4 is false.
Conclusion
Based on the analysis, the correct statements are:
1. Torque angle decreases
2. Developed mechanical power remains unchanged
Therefore, the correct answer is option 'D' - 2 and 3.
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A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer?
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A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer? for Electrical Engineering (EE) 2024 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer?.
A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer? for Electrical Engineering (EE) 2024 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 2.4 kV, 60 Hz, 3-phase synchronous motor operates at a unity power factor. Now, the line voltage suddenly falls to 1.8 kV, keeping the exciting current constant. Consider the following statements:1. Torque angle decreases2. Developed mechanical power remains unchanged3. Torque angle increases4. Developed mechanical power increasesWhich of the following statements is/are true?a)1, 2 and 3b)1, 3 and 4c)1 and 2d)2 and 3Correct answer is option 'D'. Can you explain this answer?.
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