Could smarter controlled switching really elevate grid reliability?
Blog Post | 11.10.2025 | 4 min read | Alessandro Pacchioni
In high-voltage power systems, every switching operation is a test of both equipment and the transmission grid. Without precision, even routine energization can trigger harmful transients, voltage spikes, and mechanical stress, jeopardizing grid stability, and asset longevity.
For instance, during the commissioning of a 420 kV gas-insulated switchgear (GIS), energizing a 400 kV cable without controlled switching would risk high inrush currents and overvoltages. But with controlled switching in the vicinity of voltage zero, inrush currents and voltage disturbances can be minimized for all phases.
Similarly, uncontrolled energization of a 500 MVA transformer could lead to surging magnetizing currents in the range of kilo amperes and consequently a large voltage drop on the grid. Instead, controlled switching would bring the inrush current down to a few hundred amperes and eliminate the voltage dip, demonstrating its vital role in protecting critical infrastructure and ensuring reliable grid performance.
Why is controlled switching so critical?
High-voltage circuit breakers are essential for isolating faults and managing load flow in transmission networks. Yet, even scheduled operations of these breakers can unexpectedly disrupt system stability and increase operational costs.
Uncontrolled switching, where breakers operate without regard to the electrical waveform, introduces unpredictability. This randomness can result in:
High inrush currents during transformer and capacitor bank energization
Overvoltages when switching shunt reactors, cables or transmission lines
Mechanical wear and electromagnetic stress on critical equipment
On the other hand, controlled switching enables phase-wise operation of the circuit breaker at the optimal point on the reference voltage waveform. This precision minimizes electrical and mechanical stress, improves power quality, and extends the lifespan of asset equipment.
The impact goes beyond equipment health. Uncontrolled switching can compromise system reliability and increase maintenance costs - making controlled switching not just beneficial, but a strategic necessity.
Know more technical details about the principle of controlled switching of high-voltage circuit breakers and various applications here.
When it comes to tackling the challenges of uncontrolled switching, Switchsync PWC600 stands out as a game-changer.
Developed by Hitachi Energy, this advanced point-on-wave controller brings precision to high-voltage circuit breaker operations.
What makes Switchsync PWC600 such a game-changer?
Single-pole precision: Optimizes switching for each pole independently - ideal for modern single-pole operated breakers.
Residual flux estimation: Reduces magnetizing inrush currents by estimating the transformer’s residual flux and adjusting the closing strategy.
Secondary arc detection: Enhances auto-reclosing by identifying secondary arcs and ensuring successful reclosure on any type of transmission lines.
Built on Relion®: Leverages a proven platform trusted in thousands of installations worldwide.
In a high-voltage transmission environment where grid stability and protection are non-negotiable, Switchsync PWC600 is a strategic enabler. By delivering point-on-wave switching with millisecond accuracy, it minimizes transients, safeguarding critical assets, and enhancing overall grid stability.
Frequently asked questions
Controlled switching (also known as point-on-wave switching or synchronous switching) is the technique of controlling circuit breaker switching operations to occur at an optimum instant in each phase.
Controlled switching can minimize harmful electrical transients upon planned switching of loads such as shunt capacitor banks, shunt reactors, no-load power transformers, unloaded power cables, and transmission lines.
Controlled switching is highly effective in reducing switching overvoltages (SOV), especially during energization and auto-reclosure of transmission lines. It:
- Keeps SOV within safe limits (≤2.2 pu), even under faulty conditions.
- Matches the performance of pre-insertion resistors (PIR) without their mechanical complexity.
- Adapts to system variations like trapped charges and secondary arcs.
- Enhances reliability and reduces maintenance needs.
Advanced point-on wave-controllers like Switchsync PWC600 implement all these capabilities with precision and proven field performance.
Controlled switching enables phase-wise operation of the circuit breaker at the optimal point on the reference voltage waveform. This precision minimizes electrical and mechanical stress, improves power quality, and extends the lifespan of asset equipment.
