NEWS

Controlled switching (Point-on-Wave): A key ally for power system safety, resilience and stability

July 16, 2025

Modern electrical networks are evolving towards more dynamic, complex, and demanding environments. Factors such as the increasing penetration of variable renewable generation, the integration of power electronics, advanced automation, and reduced inertia margins have heightened the system’s exposure to operational disturbances. In this context, the stability, resilience, and safety of the grid are increasingly sensitive to switching operations that were traditionally considered routine.

Operations such as the energization of transformers, transmission lines, or reactive power compensation equipment can generate significant electromagnetic transients, such as:

Transient overvoltages and undervoltages

High inrush (magnetization) currents

Re-ignitions during breaker opening

High harmonic content

Subsynchronous oscillations

Undesired protection trips

These effects compromise operational reliability and equipment lifespan, and can even trigger instabilities in weak or low-inertia grids.

The implementation of controlled switching relays is an effective, mature, and high-impact solution to enhance the operational resilience and safety of modern medium and high-voltage electrical grids. Their deployment at strategic nodes directly contributes to reducing operational risks, protecting critical assets, and ensuring compliance with quality and service continuity standards.

What is controlled switching (Point-on-Wave)?

Controlled Switching, or Point-on-Wave (PoW), adds the capability to operate a circuit breaker at a specific electrical instant. It involves synchronizing the mechanical operation of the breaker with the voltage or current waveform so that current is established (during closing) or interrupted (during opening) at the optimal electrical point, minimizing electrical transients. This significantly reduces the severity of switching-induced transients such as transformer inrush current.

Benefits of controlled switching

Using controlled switching relays reduces operational risks and protects strategic assets, becoming a fundamental tool to ensure dynamic stability and resilience in modern power systems:

Overvoltage and undervoltage reduction: Switching at the optimal point prevents such transients, improving system stability and protecting HV equipment (cables, breakers) from dielectric stress.
Inrush current elimination: Energizing transformers at the right point drastically reduces magnetization currents, avoiding unwanted protection trips and minimizing thermal and mechanical stress.
Improved transient stability: Avoiding severe transients during switching helps maintain voltage and frequency stability, improves power quality, and enhances the network’s ability to withstand disturbances.
Operational and personnel safety: Reduces electrical arcs, re-ignitions, and undesired protection trips, improving both system and personnel safety.
Extended equipment lifespan: Reduces current and voltage peaks, protecting breakers, transformers, coils, and other critical substation components.
Breaker monitoring: Enables condition monitoring of the breaker and detection of electrical and mechanical issues.
Cost reduction: Lowers maintenance costs and avoids the need for more expensive alternatives like pre-insertion resistors.
Grid Code compliance: Prevents overvoltages and undervoltages exceeding regulatory limits.

What is Inrush or Magnetizing Current?

Inrush current is a very high transient current that flows into a transformer at the moment it is energized. This current contains a high harmonic content.

It mainly occurs because the transformer core requires a magnetizing current—rich in harmonics—at the time of energization. During the first milliseconds, the current can be several times the rated current (2 to 15 times, or even more), stabilizing in a few cycles or seconds. Despite its brief duration, it can cause:

Voltage sags, especially in weak grids (low short-circuit power)
Protection trips due to voltage drops or high current
Power quality issues (harmonic distortion)
Heating

Shortened lifespan of breakers and transformers

Where is Controlled Switching Used?

Controlled switching relays (PoW) can be applied to optimize the switching of the following loads in medium and high voltage systems:

Power transformers
Shunt reactors
Capacitor banks (discharged or partially charged)
Cables and transmission lines
Harmonic filters

Sectors for application include:

Transmission and distribution networks
HVDC substations
HV/MV substations
Generation
- Renewables (solar, wind)
- Storage (batteries, flywheels)
- Hydroelectric
- Combined cycle
- Coal
- Diesel/gas gensets
Off-grid applications
Industry
- Electric arc furnaces
- Transport and rail (AC/DC)
- Metallurgy
- Mining
- Cement
- Industrial furnaces
- Oil & gas

Vizimax – Controlled Switching Solutions

Since 2015, Ingelectus has been the official partner in Spain for sales, commissioning, and technical support of Vizimax controlled switching devices.

Vizimax (a PGC Company) is a Canadian manufacturer specializing in advanced substation solutions for controlled switching (PoW) in medium and high-voltage systems. Their products precisely control the switching time, optimizing service quality and protecting electrical assets from transients.

Key features of Vizimax devices

Breaker brand-agnostic
Suitable for both new and existing breakers
Compatible with single- or three-pole operated breakers (e.g., transformers)
Applicable to both medium and high-voltage breakers
IEC 61850 server included
Web-based breaker monitoring

Event logging and oscillographic analysis tools

Main products include: SynchroTeq Plus (HV), SynchroTeq Lite (HV), SynchroTeq MV (MV), and SynchroTeq STM045000 (MV). For more details, visit our website.

https://ingelectus.com/smart-switch/