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FAQs: Modelling Capacitance in PTW
Each PTW study module models capacitance in a different way. For a full discussion of how capacitance is taken into account, please refer to the manuals (available in electronic format on the SKM website).
Capacitance can be entered into different components in different ways. The choice of which method to use depends on what information you have: 
  • Enter directly into a PI-equivalent network component. 
  • Enter into a PI-equivalent network component using the Single-Core Pipe Type library model. 
  • Enter directly into a cable component. 
  • Enter into a cable component using data from the PTW cable library. 
  • Use PTW's transmission line model. 
  • Use a capacitor component attached to the busbar at either end of the cable. 
Using PTW's cable models makes sizing cables much easier, whereas the transmission line and single-core pipe type library models are more convenient if accurate cable capacitance is not known. Using a capacitor component is useful with older versions of PTW (before V6.0), where capacitance was not included in the standard cable model. 
When entering series reactance into a pi-equivalent network, positive values should be entered for inductance, and negative values should be entered for capacitance.
(Left): Screen-shot of PTW's component editor showing a Pi-equivalent component.  The series reactances should be entered into the fields highlighted in red.