In the case of power measured by two-wattmeter method in a balanced 3-...
W
1 = V
L I
L co s (30° + φ)
and W
2 = V
L I
L cos(30° - φ)
When the load is purely capacitance, then φ = - 90°.
So, W
1 = V
LI
L cos(30°- 90°)
and W
2 = V
LI
L cos (30° + 90°)
= - V
L I
L sin30° =
Hence, |W
1| = |W
2| but W
1 = - W
2
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In the case of power measured by two-wattmeter method in a balanced 3-...
Explanation:
In a balanced 3-phase system with a pure capacitive load, the power is reactive, meaning it is not consumed by the load but rather alternates back and forth between the source and the load. When measuring power using the two-wattmeter method in such a system, the following scenarios can occur:
Option A: One wattmeter will indicate zero and the other some non-zero value
This scenario is not possible in a balanced 3-phase system with a pure capacitive load. In such a system, the reactive power is equal and opposite in each phase. Therefore, both wattmeters should indicate the same value, but with opposite signs.
Option B: Both the wattmeters will indicate the same value but of opposite sign
This is the correct option. In a balanced 3-phase system with a pure capacitive load, both wattmeters will indicate the same value, but with opposite signs. This is because the power alternates between the source and the load in each phase, resulting in equal and opposite reactive power.
Option C: Both the wattmeters will indicate zero
This scenario is not possible in a balanced 3-phase system with a pure capacitive load. Although the load consumes no real power, it does consume reactive power. Therefore, the wattmeters will not indicate zero.
Option D: Both the wattmeters will indicate the same value with the same sign
This scenario is not possible in a balanced 3-phase system with a pure capacitive load. The reactive power in each phase is equal and opposite, so the wattmeters must indicate the same value but with opposite signs.
In summary, when measuring power using the two-wattmeter method in a balanced 3-phase system with a pure capacitive load, both wattmeters will indicate the same value, but with opposite signs. This is because the power is reactive and alternates between the source and the load in each phase.
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