Point on Wave Polarity Detection Method for Saturation Mitigation Timing a Switch So the Power Grid Does Not Get a Jolt

This patent describes a method for operating a self-resetting electrical switch, built around a vacuum interrupter, so that it opens and closes at exactly the right moment in the alternating current cycle. The goal is to avoid a damaging surge of current, known as a saturation-driven inrush, when the switch closes back in after clearing a fault on the electrical grid.

The Problem

Devices that automatically interrupt and restore power, similar in spirit to a recloser, have to reconnect the circuit after a fault. If they close at an unlucky point in the alternating current waveform, transformers and other equipment downstream can experience magnetic saturation) and draw a large inrush current. That surge stresses equipment, can trip protection unnecessarily, and shortens the life of components. Getting the closing instant right matters, but a compact self-powered switch in the field has limited information and limited energy to work with.

What This Invention Does

The method first detects a fault current and opens the vacuum interrupter, drawing the energy it needs to act from a current transformer on the line itself. As it opens, it records the polarity of the fault current at that moment. It then calculates a close time so that when the interrupter shuts again, the current has the same polarity that was stored, and so that the closing action finishes right at a current zero crossing. By matching polarity and aligning with the natural zero point of the waveform, the switch reconnects with minimal disturbance. The method also covers opening the interrupter a second time after reclosing, again powered from the line. This “point on wave” control reduces saturation and the inrush that follows it.

Key Features

• Polarity capture on opening. The system stores the polarity of the fault current at the instant the interrupter opens.
• Zero-crossing aligned closing. The close time is chosen so the action ends at a current zero crossing for a smooth reconnection.
• Self-powered operation. Energy to open and close is harvested from the line’s current transformer, with no separate supply required.
• Saturation mitigation. Matching polarity on reclosing limits transformer saturation and the resulting inrush current.
• Self-resetting cycle. The method handles a full open, close and re-open sequence autonomously.

Who Is Behind It

The applicant is S&C Electric Company, a long-established maker of switching, protection and grid-automation equipment for electricity utilities and industrial power systems. The named inventors are Tsvetan Rusev and Michael Stamber. The application is a divisional of an earlier S&C filing.

Why It Matters

As distribution networks add more automation and more sensitive equipment, controlling exactly when switches operate becomes increasingly valuable. Reducing inrush and saturation protects transformers, avoids nuisance tripping, and improves the reliability of self-healing grid devices. For S&C, securing this method in Australia supports its grid-automation business as local utilities modernise their networks.

Related Concepts

• Vacuum interrupter – the switching element at the heart of the device.
• Inrush current – the damaging surge this method works to prevent.
• Magnetic saturation) – the transformer effect that drives inrush.
• Recloser – the family of self-resetting protective switches this relates to.
• Current transformer – the component that both senses current and powers the switch.

---

AU 2026201898 was published in the Australian Official Journal of Patents on 2 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.