"Why am I getting a voltage swell in Phase A during a line-to-line (A-B) fault in my Simulink model with a 11 kV, 30 MVA source, 11/0.4 kV 1 MVA Δ-Yg transformer, and a 10 kW

I am replicating a simulation from a textbook that models a line-to-line (A–B) fault. The system setup is as follows:

🔹 Source:

• Three-phase, 11 kV, 30 MVA, 50 Hz

🔹 Transformer:

• 11 kV/0.4 kV, 1 MVA, Delta–Yg (Dyn1), grounded Y-side

🔹 Load:

• Three-phase parallel RLC load
• Active power (P): 10 kW
• Inductive reactive power (QL): 100 VAR
• Y-grounded configuration at 0.4 kV side

🔹 Fault Setup:

• Line-to-line fault between Phase A and B
• Fault resistance (Ron): 8 ohms
• Start time: 0.1 s
• End time: 0.168 s
• No explicit ground connection in the fault block
• Snubber resistance (Rs) set to 1e6 ohms

🔹 Solver Settings:

• ODE23tb, Max step: 1e-5

🔹 Problem:

Despite matching the book’s description, my simulation shows Phase A swelling instead of sagging, while Phase B sags. I expect both A and B to sag symmetrically, with Phase C unaffected.

🔹 Scope Measurement:

• Measured at the 11 kV side (pre-transformer).

Code Block Example (Simplified Load Block)

matlab

Copy

% Load block setup (Three-Phase Parallel RLC Load)

Configuration: Y (grounded)

Nominal Voltage:

0.4 kV line-to-line

Active Power (P):

10 kW

Inductive Reactive Power (QL):

100 VAR

Capacitive Reactive Power (Qc):

0 VAR

What I’ve Tried

✅ Confirmed fault block connections (A-B only, ground unchecked)

✅ Checked transformer grounding and vector group (Dyn1)

✅ Adjusted snubber resistance (from 1e6 to 1e3)

✅ Balanced load and measured away from the fault node

✅ Solver settings match recommended setup (ODE23tb, step 1e-5)

Additional Information

• Simulink version: 2024

https://drive.google.com/file/d/1QqstKU2RsHP8t7LFcfSbFkpWxZ2eFXWQ/view?usp=drive_link

Request

I’d appreciate if anyone could point out:

• Possible reasons for this Phase A swelling during an A-B line fault, given the above settings.
• Whether I need to adjust snubber settings, fault resistance, load configuration, or solver settings.

Thank you!

Answer 1

[Kothuri]

Hi @Moneera,

I could not open the file though the drive link you provided.

However, you can refer the below file exchange link where they have created a Simulink model circuit for creating a L-L fault on phases A and B.

https://www.mathworks.com/matlabcentral/fileexchange/77338-voltage-sag-and-swell-caused-by-ll-fault

[Moneera]

Thank you for your help Kothuri. I have a 2024 edition maybe that is why the file is not opening with you. I will be sure to check out the link you sent.