Which of the following balanced phase-voltage phasor sets represents an abc positive- sequence system?
Va = 0°, Vb = -120°, Vc = 120°
To determine which of the given phase-voltage phasor sets represents a balanced abc positive-sequence system, it's important to understand the concept of phase sequence in three-phase systems.
In a balanced abc positive-sequence (also known as positive-sequence) system, the phase voltages are separated by 120 degrees, and the order of the phase sequence is a-b-c. This means:
- The voltage of phase B lags the voltage of phase A by 120 degrees.
- The voltage of phase C lags the voltage of phase B by 120 degrees.
- The voltage of phase C leads the voltage of phase A by 120 degrees (since C comes after B in the sequence).
This translates mathematically to something like:
- Va = 0°
- Vb = -120°
- Vc = 120°
Now, let's examine each option:
- Option 1: Va = 0°, Vb = 120°, Vc = -120°
- Option 2: Va = 0°, Vb = -90°, Vc = -180°
- Option 3: Va = 0°, Vb = -120°, Vc = 120°
- Option 4: Va = 0°, Vb = 90°, Vc = 180°
From these options, Option 3: Va = 0°, Vb = -120°, Vc = 120° matches the requirement of the abc positive-sequence system where each phase is separated by 120 degrees, and the sequence proceeds as A-B-C. Therefore, this is the correct choice.
Hence, the answer is:
Va = 0°, Vb = -120°, Vc = 120°
Important Questions from Three Phase Circuits
In a balanced three-phase, star-connected system, the phase difference between phase voltages and their respective line voltages is:
Three equal impedances are first connected in star across a balanced 3 phase supply. If connected in delta across the same supply
The power taken by a 3-ϕ load is given by the expression
A three phase circuit is connected with balanced delta connected load of impedance 100 Ω. If the current in each phase is 5 A, the voltage across each load will be
A load of three impedances each (6 + j9) is supplied through a line having an impedance of (1 + j2) Ω. The supply voltage is 400 V at 50 Hz. Determine input and output powers respectively when the load is star connected.
