Types of buses in power system?

Three major types of nodes or buses are identified in the power network.
 
01. Load Bus, or P-Q Bus.
At a load bus, the real and reactive power demands are given or scheduled.
 
02. Generator Bus, or P-V Bus.
The generators are connected to P-V buses. At these buses, the real power generation and the voltage magnitude are defined.
 
03. System Slack, or Swing Bus.