Understanding Bus Types in Power Systems

In power system analysis, particularly in load flow studies, different buses (nodes) in the network are classified based on the variables that are known or unknown at that bus. There are typically three main types of buses considered:

1. Load Bus (PQ Bus)
2. Generator Bus (PV Bus)
3. Slack Bus (Swing Bus / Reference Bus)

Each type of bus has different parameters specified and different parameters that need to be calculated during the load flow analysis. The parameters involved are typically:

• Real Power (P)
• Reactive Power (Q)
• Voltage Magnitude (|V|)
• Voltage Phase Angle (\(\delta\))

Let's look at the characteristics of each type of bus:

• Load Bus (PQ Bus): At a load bus, the real power (P) drawn by the load and the reactive power (Q) drawn by the load are known. The voltage magnitude (\(|V|\)) and the voltage phase angle (\(\delta\)) are unknown and are calculated during the load flow study.
• Generator Bus (PV Bus): At a generator bus, the real power (P) being generated and the voltage magnitude (\(|V|\)) at the bus are known. The reactive power (Q) being generated/absorbed and the voltage phase angle (\(\delta\)) are unknown and are calculated.
• Slack Bus (Swing Bus / Reference Bus): The slack bus is special. It acts as the reference bus for phase angles, and it absorbs or supplies the difference in real and reactive power to balance the total generation and load losses in the system. At the slack bus, the voltage magnitude (\(|V|\)) and the voltage phase angle (\(\delta\)) are known or specified. The phase angle (\(\delta\)) is usually set to 0 degrees, and the voltage magnitude (\(|V|\)) is typically set to its nominal value, often 1 per unit. The real power (P) and reactive power (Q) at the slack bus are unknown and are results of the load flow calculation.

Let's summarize the known and unknown quantities for these bus types in a table:

The question asks about the type of bus where the magnitude and the phase angle of the voltage are known. Based on our description, this characteristic matches the Slack bus.

Therefore, in the Slack bus, both the voltage magnitude (\(|V|\)) and the phase angle (\(\delta\)) are known.