A bus (or busbar) is a node in a power system where generators, loads, and transmission lines are interconnected. For load flow analysis, buses are classified based on known and unknown electrical quantities.
Table of Contents
Basic Quantities
Each bus is associated with four quantities:
- Voltage Magnitude (\(|V|\))
- Voltage Angle (\(\delta\))
- Real Power (\(P\))
- Reactive Power (\(Q\))
Only two quantities are specified; the other two are calculated.
Types of Buses
1. Load Bus (PQ Bus)
Known: \(P, Q\)
Unknown: \(|V|, \delta\)
- Represents load demand
- No voltage control
- Most buses are PQ buses
2. Generator Bus (PV Bus)
Known: \(P, |V|\)
Unknown: \(Q, \delta\)
- Voltage is controlled
- Reactive power varies
- Also called voltage-controlled bus
3. Slack Bus (Swing Bus)
Known: \(|V|, \delta\)
Unknown: \(P, Q\)
- Reference bus
- Balances system losses
- Only one slack bus
The slack bus satisfies:
\[
\text{Total Generation} = \text{Total Load} + \text{Losses}
\]
Summary Table
| Bus Type | Known Quantities | Unknown Quantities | Common Name |
|---|---|---|---|
| Load Bus | \(P, Q\) | \(|V|, \delta\) | PQ Bus |
| Generator Bus | \(P, |V|\) | \(Q, \delta\) | PV Bus |
| Slack Bus | \(|V|, \delta\) | \(P, Q\) | Swing Bus |
Important Points
- Only one slack bus is used
- Most buses are PQ buses
- PV buses control voltage
- Bus type may change based on conditions