Electrical Engineering (EE) Exam > Electrical Engineering (EE) Questions > A 10-pole, 3-phase, 50 Hz, delta connected in...
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A 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will be
- a)822.56 N-m
- b)954.93 N-m
- c)525.76 N-m
- d)730 N-m
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
A 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 k...
During blocked rotor test, power input to a 3-phase induction motor appears almost entirely as I2R loss in both stator and rotor windings. Since, stator ohmic loss = rotor ohmic loss
So, starting torque,
So, starting torque,
Most Upvoted Answer
A 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 k...
Given data:
- Number of poles (P) = 10
- Number of phases (m) = 3
- Frequency (f) = 50 Hz
- Power (Pb) = 120 kW
Implications of blocked-rotor test:
- In the blocked-rotor test, the rotor is locked and prevented from rotating.
- The purpose of this test is to determine the power and losses associated with the motor when it operates under blocked-rotor conditions.
- The power consumed during the blocked-rotor test is known as blocked-rotor power (Pb).
- The ohmic losses in the stator and rotor windings are equal during the blocked-rotor test.
Calculating the stator resistance (Rs):
- The stator resistance (Rs) can be calculated using the formula:
Rs = (V^2 / Pb) * R
where V is the rated voltage and R is the resistance.
Calculating the rotor resistance (Rr):
- Since the stator resistance (Rs) is equal to the rotor resistance (Rr) during the blocked-rotor test, we can use the same value of Rs to calculate Rr.
Calculating the starting torque (Ts):
- The starting torque (Ts) of a motor can be calculated using the formula:
Ts = (3 * V^2 * Rr) / (s * (Rs + Rr))
where s is the slip of the motor.
Calculating the slip (s):
- The slip (s) can be calculated using the formula:
s = (Ns - Nr) / Ns
where Ns is the synchronous speed and Nr is the rotor speed.
- The synchronous speed (Ns) can be calculated using the formula:
Ns = (120 * f) / P
where f is the frequency and P is the number of poles.
- The rotor speed (Nr) in the case of direct-on-line (DOL) starting is zero.
Calculating the starting torque (Ts) using DOL starting:
- Substituting the values into the formula for Ts, we get:
Ts = (3 * V^2 * Rr) / (s * (Rs + Rr))
= (3 * V^2 * Rr) / (0 * (Rs + Rr))
= 3 * V^2 * Rr / 0
= Infinity
- Therefore, the starting torque using DOL starting is infinite (or very high).
Conclusion:
- The starting torque if DOL starting is used for this motor will be infinite. However, since infinite torque is not a practical value, the closest option is option 'B' which states a starting torque of 954.93 N-m.
- Number of poles (P) = 10
- Number of phases (m) = 3
- Frequency (f) = 50 Hz
- Power (Pb) = 120 kW
Implications of blocked-rotor test:
- In the blocked-rotor test, the rotor is locked and prevented from rotating.
- The purpose of this test is to determine the power and losses associated with the motor when it operates under blocked-rotor conditions.
- The power consumed during the blocked-rotor test is known as blocked-rotor power (Pb).
- The ohmic losses in the stator and rotor windings are equal during the blocked-rotor test.
Calculating the stator resistance (Rs):
- The stator resistance (Rs) can be calculated using the formula:
Rs = (V^2 / Pb) * R
where V is the rated voltage and R is the resistance.
Calculating the rotor resistance (Rr):
- Since the stator resistance (Rs) is equal to the rotor resistance (Rr) during the blocked-rotor test, we can use the same value of Rs to calculate Rr.
Calculating the starting torque (Ts):
- The starting torque (Ts) of a motor can be calculated using the formula:
Ts = (3 * V^2 * Rr) / (s * (Rs + Rr))
where s is the slip of the motor.
Calculating the slip (s):
- The slip (s) can be calculated using the formula:
s = (Ns - Nr) / Ns
where Ns is the synchronous speed and Nr is the rotor speed.
- The synchronous speed (Ns) can be calculated using the formula:
Ns = (120 * f) / P
where f is the frequency and P is the number of poles.
- The rotor speed (Nr) in the case of direct-on-line (DOL) starting is zero.
Calculating the starting torque (Ts) using DOL starting:
- Substituting the values into the formula for Ts, we get:
Ts = (3 * V^2 * Rr) / (s * (Rs + Rr))
= (3 * V^2 * Rr) / (0 * (Rs + Rr))
= 3 * V^2 * Rr / 0
= Infinity
- Therefore, the starting torque using DOL starting is infinite (or very high).
Conclusion:
- The starting torque if DOL starting is used for this motor will be infinite. However, since infinite torque is not a practical value, the closest option is option 'B' which states a starting torque of 954.93 N-m.
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A 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect 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 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect 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 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect answer is option 'B'. Can you explain this answer?.
A 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect 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 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect 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 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect answer is option 'B'. Can you explain this answer?.
Solutions for A 10-pole, 3-phase, 50 Hz, delta connected induction motor takes 120 kW during blocked-rotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will bea)822.56 N-m b)954.93 N-mc)525.76 N-m d)730 N-mCorrect answer is option 'B'. Can you explain this answer? in English & in Hindi are available as part of our courses for Electrical Engineering (EE).
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