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The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when delivering 35% of its rated load. If the stator is reconnected in star, then its
- a)pf is worsened, stator current increases
- b)pf is improved, stator current increases
- c)pf remains unchanged, stator current decreases
- d)pf is improved, stator current decreases.
Correct answer is option 'D'. Can you explain this answer?
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Verified Answer
The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when d...
We know that,
∴
Thus, stator current will decrease.
∴
Thus, stator current will decrease.
Most Upvoted Answer
The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when d...
Explanation:
To understand why the power factor (pf) is improved and the stator current decreases when the stator of a delta-connected 3-phase, 50 kW, induction motor (IM) is reconnected in star, let's break down the scenario step by step.
Initial Conditions:
- The IM is delta-connected.
- The power factor (pf) is 0.4.
- The IM is delivering 35% of its rated load.
Step 1: Calculating the Reactive Power (Q):
The reactive power (Q) can be calculated using the formula:
Q = S * sin(θ)
Where S is the apparent power and θ is the angle between the apparent power (S) and the active power (P).
Given that the power factor (pf) is 0.4, we can determine the angle θ using the power factor formula:
pf = cos(θ)
0.4 = cos(θ)
θ = arccos(0.4) ≈ 66.42°
Since the power (P) is given as 50 kW, we can calculate the apparent power (S) using the formula:
S = P / pf
S = 50 kW / 0.4
S = 125 kVA
Now, we can calculate the reactive power (Q) using the formula mentioned earlier:
Q = S * sin(θ)
Q = 125 kVA * sin(66.42°)
Q ≈ 111.8 kVA
Step 2: Converting to Star Connection:
When the stator of the IM is reconnected in star, the line voltage Vl becomes √3 times the phase voltage Vph. This means that the line current Il becomes √3 times the phase current Iph.
Step 3: Power Factor and Stator Current:
When the stator is reconnected in star, the power factor (pf) improves, and the stator current decreases. This can be explained as follows:
- Power Factor Improvement: In a star-connected system, the line current Il lags the line voltage Vl by a smaller angle compared to a delta-connected system. This results in a higher power factor (pf) since the power factor is the cosine of the angle between Vl and Il.
- Stator Current Decrease: As mentioned earlier, the line current Il becomes √3 times the phase current Iph in a star-connected system. Since the line current Il is smaller compared to the delta-connected system, the stator current also decreases.
Thus, the correct answer is option 'D': The power factor is improved, and the stator current decreases when the stator of a delta-connected 3-phase, 50 kW, induction motor is reconnected in star.
To understand why the power factor (pf) is improved and the stator current decreases when the stator of a delta-connected 3-phase, 50 kW, induction motor (IM) is reconnected in star, let's break down the scenario step by step.
Initial Conditions:
- The IM is delta-connected.
- The power factor (pf) is 0.4.
- The IM is delivering 35% of its rated load.
Step 1: Calculating the Reactive Power (Q):
The reactive power (Q) can be calculated using the formula:
Q = S * sin(θ)
Where S is the apparent power and θ is the angle between the apparent power (S) and the active power (P).
Given that the power factor (pf) is 0.4, we can determine the angle θ using the power factor formula:
pf = cos(θ)
0.4 = cos(θ)
θ = arccos(0.4) ≈ 66.42°
Since the power (P) is given as 50 kW, we can calculate the apparent power (S) using the formula:
S = P / pf
S = 50 kW / 0.4
S = 125 kVA
Now, we can calculate the reactive power (Q) using the formula mentioned earlier:
Q = S * sin(θ)
Q = 125 kVA * sin(66.42°)
Q ≈ 111.8 kVA
Step 2: Converting to Star Connection:
When the stator of the IM is reconnected in star, the line voltage Vl becomes √3 times the phase voltage Vph. This means that the line current Il becomes √3 times the phase current Iph.
Step 3: Power Factor and Stator Current:
When the stator is reconnected in star, the power factor (pf) improves, and the stator current decreases. This can be explained as follows:
- Power Factor Improvement: In a star-connected system, the line current Il lags the line voltage Vl by a smaller angle compared to a delta-connected system. This results in a higher power factor (pf) since the power factor is the cosine of the angle between Vl and Il.
- Stator Current Decrease: As mentioned earlier, the line current Il becomes √3 times the phase current Iph in a star-connected system. Since the line current Il is smaller compared to the delta-connected system, the stator current also decreases.
Thus, the correct answer is option 'D': The power factor is improved, and the stator current decreases when the stator of a delta-connected 3-phase, 50 kW, induction motor is reconnected in star.
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The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when delivering 35% of its rated load. If the stator is reconnected in star, then itsa)pf is worsened, stator current increasesb)pf is improved, stator current increasesc)pf remains unchanged, stator current decreasesd)pf is improved, stator current decreases.Correct answer is option 'D'. Can you explain this answer?
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The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when delivering 35% of its rated load. If the stator is reconnected in star, then itsa)pf is worsened, stator current increasesb)pf is improved, stator current increasesc)pf remains unchanged, stator current decreasesd)pf is improved, stator current decreases.Correct 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 The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when delivering 35% of its rated load. If the stator is reconnected in star, then itsa)pf is worsened, stator current increasesb)pf is improved, stator current increasesc)pf remains unchanged, stator current decreasesd)pf is improved, stator current decreases.Correct 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 The power factor of a delta-connected 3-phase, 50 kW, IM is 0.4 when delivering 35% of its rated load. If the stator is reconnected in star, then itsa)pf is worsened, stator current increasesb)pf is improved, stator current increasesc)pf remains unchanged, stator current decreasesd)pf is improved, stator current decreases.Correct answer is option 'D'. Can you explain this answer?.
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