AC Loadflow

Element Model

Loadflow Bus Model

• InterPSS Bus always requires its base voltage to be entered. When bus data are entered into InterPSS in actual value, they are transfered in PU using the bus base voltage together with system base Kva.

Line Branch Model

• InterPSS requires a line to connect to two buses with the same base voltage. If you attempt to connect a line between two buses with different base voltage, you will get an error message
• When line data is entered in actual value, it is converted to PU using the bus base voltage together with system base Kva
• Yshunt is for modeling impedance device, such as reactor, at the branch terminal bus.

Transformer Branch Model

• Transformer data, including phase-shifting transformer, could be entered in PU or %. InterPSS assumes that the data is based on transformer's Kva rating and transformer's rated voltage. InterPSS allows you to enter transformer rated voltage different than the bus base voltage. You can connect a transformer rated at 115KV/10.6KV to a bus with 110KV base voltage.
• When transformer impedance is entered in Ohms, InterPSS assumes the value is measured at the high voltage side.

Advanced Loadflow Adjustment/Control

Functional Load

Functional load allows you to model a bus voltage dependent non-linear load

Pload = Pload(0) * [ Const-P-factor + Const-I-factor * Voltage + Const-Z-factor * Voltage^2 ]

Qload = Qload(0) * [ Const-P-factor + Const-I-factor * Voltage + Const-Z-factor * Voltage^2 ]

PV Bus Limit Adjustment

PV Bus Limit Adjustment allows you to define Qmax and Qmin for a PV Bus. If during the loadflow calculation process, the Q required to support the PV Bus voltage (Vspec) exceeds the limit, the bus will be changed to a PQ Bus with bus Q = Qmax or Qmin.

PQ Bus Limit Control

PQ Bus Limit Adjustment allows you to define Vmax and Vmin for a PQ Bus. If during the loadflow calculation process, the actual bus voltage exceeds the limit, the bus will be changed to a PV Bus with bus Vspec = Vmax or Vmin.

Remote Q Adjustment

Remote Q Adjustment allows you to use the bus Q to control a remote bus voltage or a remote branch Mva flow. In the above example, the bus Q is used to control Bus-4 voltage at ReVspec = 1.0. If the required Q to support the remote bus voltage exceeds the limit [Qmax, Qmin], the bus will be changed to a PQ bus with Q = Qmax or Qmin.

You can also use the bus Q to control reactive Mar flow on a remote branch. For example, in the above diagram, the bus Q is used to control reactive power flow on branch Bus2->Bus4. The Mar flow direction is From->To and Mar is measured at the to-bus side.

Transformer Tap Adjustment

You can use transformer tap to control a bus voltage. The bus could be the terminal bus of the transformer or any remote bus in the network. You need to specify the bus to be voltage-controlled is on the transformer from-bus side or to-bus side, and the control tap is on the from-side or to-side. Also, limit [max/min turn ratio] and change step length need to be specified. If the Step = 0.0, it is assumed that the transformer tap could be adjusted continuously.

You can also use transformer tap to control reactive Mar flow on the transformer branch.

Phase-Shift Transformer Adjustment

You can use phase-shift angle to control power flow on the phase-shift transformer. You need to specify power control side (From Side or To Side) and power flow direction (From->To or To-From). Angle control is within the limit [AngleMax, AngleMin].

Inter-area Power Control

(Todo ...)