# How transient simulations work in SPS Software ⚡

**URL:** <https://community.opal-rt.com/t/how-transient-simulations-work-in-sps-software/55>\
**Category:** Q&A\
**Tags:** sps-software\
**Created:** [March 23, 2026, 10:58pm UTC](https://community.opal-rt.com/t/how-transient-simulations-work-in-sps-software/55 "2026-03-23T22:58:35Z")\
**Posts on this page:** 1\
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**Author:** ![MariaZanutto](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@MariaZanutto](https://community.opal-rt.com/u/MariaZanutto)\
**Post date:** [March 23, 2026, 10:58pm UTC](https://community.opal-rt.com/t/how-transient-simulations-work-in-sps-software/55/1 "2026-03-23T22:58:35Z")

</div>

One of the main uses of SPS Software is to simulate electrical transients. Whether you are studying a line energization with mechanical circuit breakers or high-frequency switching with power electronic devices, SPS Software has specific tools and best practices to capture these phenomena accurately.

Here is a guide on how to approach transient simulations, choose the right line models, and set up your solver.

### 🔌 1. Simulating Transients with Circuit Breakers

Transients are usually triggered by switching events. In SPS Software, you can use the `Breaker` block to simulate line energizations, faults, or load switching.

When setting up a transient simulation (e.g., closing a breaker to energize a line), the accuracy of your results heavily depends on the physical models you choose for your components—especially transmission lines.

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### 📏 2. Choosing the Right Line Model for Transients

When studying fast transients, a simple equivalent impedance is not enough. Let’s compare three line models during an energization transient:

1. **Single PI Section Line:** A simple PI model acts as a low-pass filter. It does not respond well to high frequencies and will miss fast transient peaks.
2. **Multiple PI Sections (e.g., 10 sections):** This gives much better accuracy for transients. However, the discretization of the line into chunks can introduce artificial high-frequency oscillations.
3. **Distributed Parameters Line:** This is the **most accurate** model for transient studies. It accurately represents the wave propagation time delay along the line without introducing artificial ringing.

 ![image](https://canada1.discourse-cdn.com/flex012/uploads/sps/original/1X/b96501c4e7ecd9a52ec528ccf7135dbf09dc2548.jpeg)

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### ⏱ 3. Continuous vs. Discrete Simulation

SPS Software can simulate using either continuous (variable-step) algorithms or discrete (fixed-step) solvers.

- **Continuous (Variable-step like `ode23tb`):** Usually faster for _small_ systems because the solver takes large steps when the system is stable and tiny steps only during the transient event.
- **Discrete (Fixed-step):** Highly recommended for _large_ systems containing many states or nonlinear blocks (like power electronic switches).

**The Discretization Trade-off:**  
When you discretize your system via the `powergui` block, the precision of the transient simulation is entirely controlled by your Sample Time (Ts). If you use a time step that is too large, you will lose accuracy and miss the transient peaks.

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### 💡 4. Rules of Thumb for Choosing a Time Step (Ts)

How do you know if your time step is small enough? The best method is to run the simulation with a small step, then increase it until the results start to deviate unacceptably.

However, here are the standard industry guidelines for SPS Software:

- **20 µs to 50 µs:** Good for switching transients on standard 50-Hz or 60-Hz power systems, or systems using line-commutated devices (diodes and thyristors).
- **\le 1 µs:** Mandatory for systems using forced-commutated power electronic switches operating at high frequencies. For example, simulating a PWM inverter using IGBTs, MOSFETs, or GTOs at 8 kHz requires a maximum time step of 1 µs to accurately capture the dead times and switching transients.

 ![image](https://canada1.discourse-cdn.com/flex012/uploads/sps/original/1X/f940c4e8fcce274144f39c7a4102d47af76f7a60.jpeg)