# 2-Winding 3-Phase Saturable Transformer with Tap Changer V1\_ V\_2

**URL:** <https://community.opal-rt.com/t/2-winding-3-phase-saturable-transformer-with-tap-changer-v1-v-2/173>\
**Category:** Q&A\
**Tags:** hypersim, discussion, protection-testing, testing-approaches, grid-simulation\
**Created:** [August 21, 2026, 4:24am UTC](https://community.opal-rt.com/t/2-winding-3-phase-saturable-transformer-with-tap-changer-v1-v-2/173 "2026-08-21T04:24:00Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![cokeke](https://avatars.discourse-cdn.com/v4/letter/c/54ee81/32.png) [@cokeke](https://community.opal-rt.com/u/cokeke)\
**Post date:** [August 21, 2026, 4:24am UTC](https://community.opal-rt.com/t/2-winding-3-phase-saturable-transformer-with-tap-changer-v1-v-2/173/1 "2026-08-21T04:24:00Z")

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I exchanged the transformer in **Example Model for 87T Transformer Differential Protection Relay** for a 2-Winding 3-Phase Saturable Transformer with Tap Changer

 ![image](https://canada1.discourse-cdn.com/flex012/uploads/sps/original/1X/8832143ea92c2083227415c9c7d4117fbbf4e1f1.png)

When I open the Sensor form for the 2-Winding 3-Phase Saturable Transformer with Tap Changer **it has two sensors called V\_1 and V\_2.** what do they do?

when i enable the V\_1 and V\_2 sensors in the sensor form (left column boxes ticked) and try to add them in scopeview I get an error

 ![V_1 V_2.png](https://canada1.discourse-cdn.com/flex012/uploads/sps/original/1X/1794d012e0891b9f352f8bf7d64845fa1a29bd62.png)

I have checked the online and offline document and there is no explanation for them

Help!

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<div class="post-metadata">

**Author:** ![Parija](https://yyz2.discourse-cdn.com/flex012/user_avatar/community.opal-rt.com/parija/32/161_2.png) [@Parija](https://community.opal-rt.com/u/Parija)\
**Post date:** [September 8, 2026, 3:50pm UTC](https://community.opal-rt.com/t/2-winding-3-phase-saturable-transformer-with-tap-changer-v1-v-2/173/2 "2026-09-08T15:50:38Z")

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Hello @cokeke

Here is an explanation of what the V\_1 and V\_2 sensors do and how to resolve the ScopeView error:

1. What are the V\_1 and V\_2 Sensors?  
In the 2-Winding 3-Phase Saturable Transformer with Tap Changer block:  
V\_1: Measures the instantaneous terminal voltages of Winding 1 (Primary) across phases A, B, and C.  
V\_2: Measures the instantaneous terminal voltages of Winding 2 (Secondary) across phases A, B, and C.

Because this is a 3-phase component, enabling V\_1 and V\_2 generates three separate phase signals for each winding (Phases A, B, and C) in the solver rather than a single scalar value.

1. Why ScopeView shows Error: Cannot find signal XFMR1.V\_1  
This error typically happens for two main reasons:  
Signal Name / Phase Vector Mismatch:  
In ScopeView, signals for 3-phase components are mapped as individual phases (e.g., XFMR1.V\_1\_A, XFMR1.V\_1\_B, XFMR1.V\_1\_C or XFMR1.V\_1[0..2]). If the plot references the top-level group tag XFMR1.V\_1 directly (or an outdated reference from the original example template), ScopeView cannot resolve it during acquisition.  
Model Code Generation & Compilation:  
When you replace a transformer or enable new sensor checkboxes in the component mask, HYPERSIM must recompile the network code to generate the new signal map (.sin / dictionary file). If the simulation was started without a clean build, ScopeView looks for signal addresses that do not yet exist on the target memory.

2. Step-by-Step Resolution  
Enable Sensors & Save:  
Open the 2-Winding Saturable Transformer sensor form.  
Check the boxes for V\_1 and V\_2 (and any other desired measurements like currents I\_1, I\_2 or flux).  
Click Apply and OK, then save the schematic.

Rebuild the Model:  
Stop the simulation if it is currently running.  
Click Simulation \> Generate Code / Rebuild (or start the simulation on localhost/target) so the new sensor signals are compiled.

Update ScopeView Signals:  
Open ScopeView.  
In the signal list / browser panel, click the Refresh / Reload Signals button to fetch the newly compiled signal dictionary.  
Expand the XFMR1 signal tree. You will see the decomposed phase signals (e.g., XFMR1.V\_1\_A, XFMR1.V\_1\_B, XFMR1.V\_1\_C).  
Drag the individual phase signals onto your ScopeView plot axes (replacing any orphaned XFMR1.V\_1 tags).  
Click Start Acquisition (or enable Sync / Trigger) to view the waveforms.

Tip: You can also connect standard Bus Voltage Probes / Sensors to the primary and secondary busbars adjacent to the transformer to monitor the line-to-ground or line-to-line voltages directly.