Power Flow: Bus Category Possibilities

 

The various topics on the Power Flow Theory all end up describing different possibilities for the field that appears in the mismatch table called "Type" or "BusCat". This is a comprehensive list of the potential string that will appear in this field and what they mean.

 

The following BusCat strings are the standard one seen for generators and switched shunts using local voltage control as described in the Power Flow: Bus Equation Basics topic.

• PQ: buses that have no voltage control devices such as a generator at them and are also not remotely controlled by a generator will be called a PQ bus. We call them a PQ bus because we use the equations for summation of real power (P) and reactive power (Q) at these buses and the unknown variables are then voltage angle (V) and voltage angle (d).
• PV: a bus that has a generator at it which is regulating the terminal voltage to a voltage setpoint will be called a PV bus. Again this is because the equations are the summation of real power (P) and an equation for Voltage = Setpoint (V). The unknown variables are then voltage angle (d) and the extra Q injection at the bus. The extra Q injection at the bus is then used to assign the reactive power output to the generators at the bus.
• Slack: one bus in each electrical island is chosen as the island slack bus. This bus has a fixed voltage magnitude and voltage angle. Using our notation we might call it a dV bus. The unknown variables at this bus are then the real power (P) and reactive power (Q) which are then used to assign the real and reactive power at the slack generator.
• PQ (Gens at Var Limit): a bus that has a generator at it regulating the terminal voltage, however presently the generator is stuck at a maximum or minimum Mvar limit and is thus no longer able to regulate the voltage. Because we are stuck at a Mvar limit, the equations used is the reactive power (Q) equation. This is an indication that the bus type would have been PV, but is not because of the generators at Mvar limits
• PV (SVC): a bus that has a switched shunt with (ShuntMode = SVC) and (SVCType = SVSMO3 or SVSMO1) configured to regulate the voltage at the terminal bus. The voltage equation will be used just as for a generator.
• PQ (SVC at Limit): similar to PQ (Gens at Limit)
• PQ (Continuous Shunts at Var Limit):: similar to PQ (Gens at Limit), but it's a continous switched shunt at limits.

The following BusCat strings are the ones seen as a result of remote voltage regulation being used as described in the Power Flow: Remote Voltage Regulation topic.

• PV (Remote Reg Primary): the primary bus in a group of buses performing remote regulation will enforce the bus voltage equation at the regulated Bus R
• PQ (Remote Reg Secondary): secondary buses in a group of buses performing remote regulation will enforce a rather complex equation then ensures that the total Mvar output of generators at the respective bus is equal to the appropriate proportion of the summation of the Mvar outputs at all generators in the group.
• PQ (Remotely Regulated): A bus that is regulated by a group of generators at remote bus will just enforce the real and reactive power flow summation at its bus.
• PV (Local/Remote Reg Primary): This is seen when there are a group of generators at different buses that all regulate the voltage at a regulated bus and that regulated bus also has generation participating in the regulation. Thus this bus is regulating its own voltage, but doing so in coordination with generators at other remote buses.
• PQ (Remotely Regulated at Var Limit): This is seen for a remotely regulated bus if all the generators which are regulating it are at MVar limits.

The following BusCat strings are the ones seen as a result of line drop compensation being used as described in the Power Flow: Line Drop Compensation topic.

• PQ (Line Drop Comp): indicates that generation at this is configured to use Line Drop compensation so a special reactive equation is written to account for this.
• PQ (SVC Line Drop Comp): same as PQ (Line Drop Comp), but indicates a switched shunt configured as an SVC on line drop comp is present.

The following BusCat strings are the ones seen as a result of Voltage Setpoint Tolerance being used as described in the Power Flow: Voltage Setpoint Tolerance topic. The ability to use a Voltage Setpoint Tolerance was added in Simulator Version 21

• PVTol: Same as the PV, except the voltage equation for the bus is modified such that when the bus voltage is equal to (VoltSet - VoltSetTol), the generators at the bus will operate at their maximum Mvar Limit and when the bus voltage is equal to (VoltSet + VoltSetTol), the generators at the bus will operate at their minmum Mvar Limit
• PVTol (Remote Reg Primary): Same as the PV (Remote Reg Primary), except the voltage equation for the remote bus is modified such that when the regulated bus voltage is equal to (VoltSet - VoltSetTol), the generators participating in remote regulation will operate at their maximum Mvar Limit and when the regulated bus voltage is equal to (VoltSet + VoltSetTol), the generators participating in remote regulation will operate at their minmum Mvar Limit
• PVTol (Local/Remote Reg Primary): Same concept as PVl (Local/Remote Reg Primary), except this the voltage equation includes the Voltage Setpoint Tolerance again.

The following BusCat strings are the ones seen as a result of Voltage Droop Control with Deadband as described in the Power Flow: Voltage Droop Control with Deadband topic. The ability to use a Voltage Droop control with Deadband was added in Simulator Version 21

• PQ (Voltage Droop Reg Bus): this represents the remotely regulated bus of a group of generators that are assigned to the same Voltage Droop Control . The equation at this bus is a special reactive power flow equation ensuring that the droop control curve is enforced.
• PQ (Voltage Droop Remote Bus): this represents on of the remote buses in a group of buses performing voltage droop control. It will enforce a rather complex equation then ensures that the total Mvar output of generators at the respective bus is equal to the appropriate proportion of the summation of the Mvar outputs at all generators in the group.
• PQ (Voltage Droop Reg Bus at Var Limit): This is an indication that all the generators that are remotely regulating this bus using voltage droop control are at a Mvar limit.
• PQ (Voltage Droop Remote Bus at Var Limit): This is an indication that a remotely regulating bus in a voltage droop control is at a Mvar limit.