Question

In a Load Flow study, which parameters are known at a PQ (Load) bus?

• A. P and V
• B. V and $\delta$
• C. P and Q
• D. Q and $\delta$

Hint:

Bus classification summary:
1. Load Bus (PQ): Knowns = \(P, Q\); Unknowns = \(V, \delta\).
2. Generator Bus (PV): Knowns = \(P, V\); Unknowns = \(Q, \delta\).
3. Slack Bus: Knowns = \(V, \delta\); Unknowns = \(P, Q\).
PQ buses make up over 85% of the buses in typical power system networks.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the pre-specified (known) variables at a PQ bus (also known as a Load bus) during a power system load flow study.

Step 2: Detailed Explanation:

• In load flow analysis, each bus in the power system is classified into one of three categories based on which two of the four primary variables are known beforehand:
- Active Power (\(P\))
- Reactive Power (\(Q\))
- Voltage Magnitude (\(V\))
- Voltage Phase Angle (\(\delta\))

• PQ Bus (Load Bus): At these buses, the active power \(P\) and reactive power \(Q\) drawn by the load are specified (known). The unknowns to be calculated are the voltage magnitude \(V\) and the phase angle \(\delta\).

• PV Bus (Generator Bus): At these buses, the active power generation \(P\) and the voltage magnitude \(V\) are specified. The unknowns to be calculated are the reactive power \(Q\) and the phase angle \(\delta\).

• Slack Bus (Swing Bus): This bus serves as the reference. The voltage magnitude \(V\) and the phase angle \(\delta\) (usually set to \(0^\circ\)) are specified. The active power \(P\) and reactive power \(Q\) are computed to account for the system losses.

• Therefore, at a PQ bus, the specified known variables are \(P\) and \(Q\).

Step 3: Final Answer:
The known parameters at a PQ bus are P and Q.