Bus

A bus (also known as a node or busbar) is an electrical junction point in a power system where multiple components, such as generators, loads, transmission lines, and transformers, connect together. Buses are the fundamental building blocks of power system network models, forming the nodes of the system graph while branches form the edges.

Key Aspects of a Bus:

• Four Defining Quantities: Each bus is characterized by voltage magnitude, voltage angle, active power (P), and reactive power (Q). Which two are specified and which two must be solved determines the bus classification.
• Bus Types: Buses are classified as PQ (load), PV (generator), or slack (reference). PQ buses make up roughly 80–85% of buses in a typical system, PV buses around 15%, and one bus is designated as the slack bus.
• Admittance Matrix: The bus admittance matrix (Y-bus), built from the network of interconnected buses and branches, is the mathematical foundation for power flow analysis, short-circuit studies, and stability assessment.
• Voltage Levels: Bus voltages in modern grids range from low voltage (below 1 kV) at distribution endpoints to ultra-high voltage (765 kV or above) at major transmission interconnections.
• Practical Role: In physical substations a bus corresponds to a busbar, a metallic bar or strip that collects and distributes current to multiple outgoing circuits.