Electrical Engineering (EE) Exam > Electrical Engineering (EE) Questions > A 3 phase induction motor is controlled by vo...
Start Learning for Free
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torque
- a)will be less than 100 N-m
- b)will be more than 100 N-m
- c)may be more or less than 100 N-m depending on motor parameters
- d)very small
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
A 3 phase induction motor is controlled by voltage and frequency contr...
Introduction:
In a 3-phase induction motor, the starting torque is an important parameter that determines the motor's ability to start rotating and overcome the initial inertia. The starting torque of the motor depends on various factors, including the voltage and frequency applied to the motor.
Voltage and Frequency Control:
In voltage and frequency control, the ratio of voltage (V) to frequency (f) is kept constant. This means that as the frequency decreases, the voltage is also reduced in proportion to maintain the constant V/f ratio. This control method is commonly used to vary the speed of induction motors in applications such as variable frequency drives (VFDs).
Effect of Frequency on Starting Torque:
The starting torque of an induction motor is directly proportional to the square of the applied voltage and inversely proportional to the square of the frequency. Mathematically, the starting torque (Ts) can be expressed as:
Ts ∝ (V^2) / (f^2)
Explanation:
Given that at 50 Hz, the starting torque is 100 N-m, we can calculate the starting torque at 25 Hz using the above equation. Since the voltage and frequency control maintains a constant V/f ratio, we can assume that the voltage will also be reduced by half when the frequency is halved.
Let's assume the voltage at 50 Hz is V1 and the voltage at 25 Hz is V2 (V2 = V1/2).
Using the equation for starting torque, we can write:
Ts1 = (V1^2) / (50^2) (Starting torque at 50 Hz)
Ts2 = (V2^2) / (25^2) (Starting torque at 25 Hz)
Since V2 = V1/2, we can substitute this in the equation for Ts2:
Ts2 = ((V1/2)^2) / (25^2)
= (V1^2) / (4 * 25^2)
= (V1^2) / (100 * 25)
= (V1^2) / (2500)
Comparing Ts2 with Ts1, we find:
Ts2 = (1/2500) * Ts1
Since Ts2 is equal to (1/2500) times Ts1, it is evident that Ts2 (starting torque at 25 Hz) will be less than Ts1 (starting torque at 50 Hz). In this case, Ts2 will be 1/2500th of Ts1, which means it will be significantly lower.
Conclusion:
Based on the analysis, we can conclude that the starting torque of the 3-phase induction motor controlled by voltage and frequency control will be less than 100 N-m at 25 Hz. This is because the starting torque is inversely proportional to the square of the frequency, and the voltage is reduced in proportion to maintain the constant V/f ratio.
In a 3-phase induction motor, the starting torque is an important parameter that determines the motor's ability to start rotating and overcome the initial inertia. The starting torque of the motor depends on various factors, including the voltage and frequency applied to the motor.
Voltage and Frequency Control:
In voltage and frequency control, the ratio of voltage (V) to frequency (f) is kept constant. This means that as the frequency decreases, the voltage is also reduced in proportion to maintain the constant V/f ratio. This control method is commonly used to vary the speed of induction motors in applications such as variable frequency drives (VFDs).
Effect of Frequency on Starting Torque:
The starting torque of an induction motor is directly proportional to the square of the applied voltage and inversely proportional to the square of the frequency. Mathematically, the starting torque (Ts) can be expressed as:
Ts ∝ (V^2) / (f^2)
Explanation:
Given that at 50 Hz, the starting torque is 100 N-m, we can calculate the starting torque at 25 Hz using the above equation. Since the voltage and frequency control maintains a constant V/f ratio, we can assume that the voltage will also be reduced by half when the frequency is halved.
Let's assume the voltage at 50 Hz is V1 and the voltage at 25 Hz is V2 (V2 = V1/2).
Using the equation for starting torque, we can write:
Ts1 = (V1^2) / (50^2) (Starting torque at 50 Hz)
Ts2 = (V2^2) / (25^2) (Starting torque at 25 Hz)
Since V2 = V1/2, we can substitute this in the equation for Ts2:
Ts2 = ((V1/2)^2) / (25^2)
= (V1^2) / (4 * 25^2)
= (V1^2) / (100 * 25)
= (V1^2) / (2500)
Comparing Ts2 with Ts1, we find:
Ts2 = (1/2500) * Ts1
Since Ts2 is equal to (1/2500) times Ts1, it is evident that Ts2 (starting torque at 25 Hz) will be less than Ts1 (starting torque at 50 Hz). In this case, Ts2 will be 1/2500th of Ts1, which means it will be significantly lower.
Conclusion:
Based on the analysis, we can conclude that the starting torque of the 3-phase induction motor controlled by voltage and frequency control will be less than 100 N-m at 25 Hz. This is because the starting torque is inversely proportional to the square of the frequency, and the voltage is reduced in proportion to maintain the constant V/f ratio.
Free Test
FREE
| Start Free Test |
Community Answer
A 3 phase induction motor is controlled by voltage and frequency contr...
The Starting Torque of a 3-Phase Induction Motor with Voltage and Frequency Control
Introduction:
In a 3-phase induction motor, the starting torque is an important parameter that determines the motor's ability to accelerate the load from rest. The starting torque is dependent on various factors, including the voltage and frequency supplied to the motor. In this scenario, the motor is controlled by voltage and frequency control in such a way that the ratio V/f is kept constant. We need to determine the starting torque of the motor at a frequency of 25 Hz, given that it is 100 N-m at 50 Hz.
Explanation:
1. Voltage and Frequency Control:
- Voltage and frequency control is commonly used in applications where the motor speed needs to be varied. By changing the voltage and frequency supplied to the motor, the speed and torque characteristics of the motor can be adjusted.
- In this case, the ratio V/f is kept constant, which means that the voltage and frequency are adjusted in proportion to each other. This ensures that the motor operates within its designed limits and prevents excessive heating and damage.
2. Relationship between Frequency and Torque:
- The starting torque of an induction motor is directly proportional to the square of the supply voltage and inversely proportional to the square of the supply frequency.
- Mathematically, the starting torque (T) is given by the equation: T ∝ (V^2 / f^2), where V is the supply voltage and f is the supply frequency.
3. Comparison at 50 Hz and 25 Hz:
- Given that the starting torque is 100 N-m at 50 Hz, we can rewrite the equation as: T1 = (V1^2 / f1^2), where T1 is the starting torque at 50 Hz, V1 is the supply voltage at 50 Hz, and f1 is the supply frequency at 50 Hz.
- Similarly, at 25 Hz, the starting torque (T2) can be calculated using the equation: T2 = (V2^2 / f2^2), where V2 is the supply voltage at 25 Hz and f2 is the supply frequency at 25 Hz.
- Since the ratio V/f is constant, we can write: V1/f1 = V2/f2.
- From this equation, we can deduce that V2 = (f2 / f1) * V1.
- Substituting this value of V2 in the equation for T2, we get: T2 = ((f2 / f1)^2) * T1.
4. Conclusion:
- From the above equation, it is clear that the starting torque at 25 Hz (T2) will be more than 100 N-m because the frequency (f2) is lower than the reference frequency (f1).
- Therefore, the correct answer is option 'B': The starting torque will be more than 100 N-m at 25 Hz, when the voltage and frequency are controlled such that the ratio V/f is constant.
Introduction:
In a 3-phase induction motor, the starting torque is an important parameter that determines the motor's ability to accelerate the load from rest. The starting torque is dependent on various factors, including the voltage and frequency supplied to the motor. In this scenario, the motor is controlled by voltage and frequency control in such a way that the ratio V/f is kept constant. We need to determine the starting torque of the motor at a frequency of 25 Hz, given that it is 100 N-m at 50 Hz.
Explanation:
1. Voltage and Frequency Control:
- Voltage and frequency control is commonly used in applications where the motor speed needs to be varied. By changing the voltage and frequency supplied to the motor, the speed and torque characteristics of the motor can be adjusted.
- In this case, the ratio V/f is kept constant, which means that the voltage and frequency are adjusted in proportion to each other. This ensures that the motor operates within its designed limits and prevents excessive heating and damage.
2. Relationship between Frequency and Torque:
- The starting torque of an induction motor is directly proportional to the square of the supply voltage and inversely proportional to the square of the supply frequency.
- Mathematically, the starting torque (T) is given by the equation: T ∝ (V^2 / f^2), where V is the supply voltage and f is the supply frequency.
3. Comparison at 50 Hz and 25 Hz:
- Given that the starting torque is 100 N-m at 50 Hz, we can rewrite the equation as: T1 = (V1^2 / f1^2), where T1 is the starting torque at 50 Hz, V1 is the supply voltage at 50 Hz, and f1 is the supply frequency at 50 Hz.
- Similarly, at 25 Hz, the starting torque (T2) can be calculated using the equation: T2 = (V2^2 / f2^2), where V2 is the supply voltage at 25 Hz and f2 is the supply frequency at 25 Hz.
- Since the ratio V/f is constant, we can write: V1/f1 = V2/f2.
- From this equation, we can deduce that V2 = (f2 / f1) * V1.
- Substituting this value of V2 in the equation for T2, we get: T2 = ((f2 / f1)^2) * T1.
4. Conclusion:
- From the above equation, it is clear that the starting torque at 25 Hz (T2) will be more than 100 N-m because the frequency (f2) is lower than the reference frequency (f1).
- Therefore, the correct answer is option 'B': The starting torque will be more than 100 N-m at 25 Hz, when the voltage and frequency are controlled such that the ratio V/f is constant.
|
Explore Courses for Electrical Engineering (EE) exam
|
|
Top Courses for Electrical Engineering (EE)View all
Question Description
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? for Electrical Engineering (EE) 2025 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 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer?.
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? for Electrical Engineering (EE) 2025 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 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer?.
Solutions for A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? in English & in Hindi are available as part of our courses for Electrical Engineering (EE).
Download more important topics, notes, lectures and mock test series for Electrical Engineering (EE) Exam by signing up for free.
Here you can find the meaning of A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer?, a detailed solution for A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? has been provided alongside types of A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? theory, EduRev gives you an
ample number of questions to practice A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torquea)will be less than 100 N-mb)will be more than 100 N-mc)may be more or less than 100 N-m depending on motor parametersd)very smallCorrect answer is option 'B'. Can you explain this answer? tests, examples and also practice Electrical Engineering (EE) tests.
|
|
Explore Courses for Electrical Engineering (EE) exam
|
|
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
|
© EduRev
|
Education Revolution
|
|
Signup to see your scores
go up
within 7 days!
within 7 days!
Takes less than 10 seconds to signup