A bus is a node at which one or many lines, one or many loads and generators are connected. In a power system each node or bus is associated with 4 quantities, such as magnitude of voltage, phage angle of voltage, active or true power and reactive power in load flow problem two out of these 4 quantities are specified and remaining 2 are required to be determined through the solution of equation. Depending on the quantities that have been specified, the buses are classified into 3 categories. Buses are classified according to which two out of the four variables are specified
LOAD BUS
No generator is connected to the bus. At this bus the real and reactive power are specified.it is desired to find out the voltage magnitude and phase angle through load flow solutions. It is required to specify only P
d and Q
d at such bus as at a load bus voltage can be allowed to vary within the permissible values.
GENERATOR BUS OR VOLTAGE CONTROLLED BUS
Here the voltage magnitude corresponding to the generator voltage and real power P
g corresponds to its rating are specified. It is required to find out the reactive power generation Q
g and phase angle of the bus voltage.
SLACK (SWING) BUS
For the Slack Bus, it is assumed that the voltage magnitude |V| and voltage phase Θ are known, whereas real and reactive powers P
g and Q
g are obtained through the load flow solution.
