Voltage stability can be analyzed using P-V curve which shows the interaction between power delivered at a constant power factor and the corresponding change in bus voltage. : Where By keeping the voltage at bus 1, power angle and line impedance constant, we can plot the effect of increasing the active power on the voltage at bus 2 on a PV curve: Figure 3. PV Curve. Transmission line power flow is an integral part of power systems studies and is used to calculate steady state voltage, voltage angle, real and reactive power flow in an interconnected power system. Think of it as the voltage on the main highway that feeds electricity to everything connected to it. In load flow studies, buses are classified into three categories: generation bus, load bus, and slack bus.