In load flow analysis of power systems, a bus refers to a specific location or point where many lines, one or many generators and loads are connected. It is not necessary that all of these be connected at every bus.
In a power system each node or bus is associated with four quantities such as:
- Magnitude of voltage i.e. |V|.
- Phase angle of the voltage i.e. δ.
- Active or true power or real power i.e. P.
- Reactive power i.e. Q.
Buses are classified based on their characteristics:
- PV Bus (P-V Bus) or Generation Bus or Voltage-Controlled Bus: Represents a bus where real power (P) and voltage magnitude |V| are specified.
- The phase angle (δ) of the Voltages and the reactive powers are unknown.
- PQ Bus (P-Q Bus) or Load Bus : Represents a bus where real power (P) and reactive power (Q) are specified.
- The phase angle (δ) of the Voltages and Magnitudes of voltages |V| are unknown.
- Slack Bus (Swing Bus) or Reference Bus: Represents a bus where voltage magnitude |V| and phase angle (δ) are specified. It’s usually the reference bus, and its voltage angle is set to zero.
- The real power (P) and reactive power (Q) are unknown.
These classifications help in formulating the equations for the load flow analysis.