How to create a second isolated ground node in Nexxim Transient (Circuit) simulation?

Ulrich Ghislain

Hello,

I'm simulating a 2-port transformer (imported as .s2p NPort
into Ansys Circuit) where I need two galvanically isolated
ground references:

• Port 1 reference → instrumentation ground (node "0")
• Port 2 reference → a separate "floating" ground for a
  cable model (W-element), NOT connected to node "0"

I used the NPort "Add individual reference pin per port"
option, then connected Port 2's reference pin to a Global
Port named "GND_2", and tied all cable-side references
(W-element Input_ref/Output_ref) to the same "GND_2".

When I add a 50 Hz AC voltage source in that isolated loop,
the voltage waveform appears almost flat instead of a proper
sine wave, suggesting the current loop isn't closing
correctly through "GND_2".

Question: Is "Global Port" the correct way to create a
second, fully isolated reference node in Nexxim Transient?
Or is there a better/standard method to model two
galvanically separated circuits in the same schematic?

Thanks for any guidance.

gia

To model two galvanically isolated ground references in Ansys Circuit with an imported NPort (.s2p) model, the recommended approach is to use the "Add individual reference pin per port" option. This allows each port to have its own reference voltage and be connected to its own net, which can represent separate ground nodes in your schematic. 

Reference Pin Configuration for Galvanic Isolation

• When you select "Add individual reference pin per port," each port's reference pin can be connected to a different net, enabling the creation of isolated ground domains (such as node "0" for instrumentation ground and "GND_2" for the floating cable ground). 
• This method is explicitly supported for NPort and state-space models, and is the standard way to represent multiple isolated references in a single schematic. 
• Each reference pin can be connected to a Global Port (such as "GND_2"), which acts as a net in the schematic. 

Potential Issues with Current Loop Closure

• If the voltage waveform is flat when you add a source in the isolated loop, it may indicate that the current loop is not properly closed. Ensure that all elements in the isolated domain reference the same net ("GND_2") and that the source is correctly connected between nodes in that domain. 
• Verify that there are no unintended connections between "GND_2" and node "0" elsewhere in the schematic, as this would compromise isolation. 

Summary Table: Reference Pin Options

Reference Pin Option	Isolation Capability	Typical Use
Implied reference to ground	No	Single ground domain
Common reference port	Partial	Shared reference for all ports
Add individual reference pin per port	Yes	Multiple isolated ground domains

Use the "Add individual reference pin per port" option for true galvanic isolation, and connect each reference pin to the appropriate net or Global Port. This is the standard and supported method for modeling multiple isolated circuits in Ansys Circuit. 

If you continue to see a flat voltage waveform, double-check your schematic for correct net assignments and ensure the isolated loop is complete within its domain.