Switching surges, also known as transient overvoltages or switching transients, are sudden voltage spikes that occur in electrical systems when switching operations are performed.
🔍 1. What Are Switching Surges?
Switching surges (also called switching transients) are overvoltages generated by:
- Opening or closing circuit breakers
- Switching inductive or capacitive loads
- Energizing or de-energizing transmission lines or transformers
- Fault clearing or load rejection
These surges typically have:
- Duration: microseconds to milliseconds
- Voltage Magnitude: Can exceed normal operating voltage by 2–3 times
- Frequency: High-frequency components (up to hundreds of kHz)
💥 2. Causes of Switching Surges
| Cause | Description |
|---|---|
| Capacitor Bank Switching | Sudden energizing causes high-frequency oscillations |
| Transformer Energization | Inrush current generates voltage spikes |
| Line Switching | Long lines can reflect and reinforce transient waves |
| Load Shedding | Sudden interruption can lead to voltage rise |
| Interruption of Faults | Current chopping in circuit breakers creates steep voltage spikes |
These surges can have damaging effects on sensitive equipment and can lead to insulation breakdown if not properly managed. Here are some remedial measures to mitigate switching surges:
| Remedy | How It Works |
|---|---|
| Surge Arresters | Divert excess voltage to ground; limit overvoltage at terminals |
| Controlled Switching Devices | Synchronize breaker operation to minimize transients |
| Pre-Insertion Resistors | Temporarily inserted during switching to limit surge current |
| Shunt Reactors | Absorb excess reactive power; stabilize voltage after line energization |
| Line Terminating Resistors/Filters | Damp high-frequency components of the surge |
| Proper Breaker Selection | Use breakers with low current-chopping characteristics |
| Use of RC Snubbers | Protect sensitive devices by absorbing switching energy |
Surge Arresters (Metal Oxide Surge Arresters):
- Surge arresters are devices installed at strategic points in the electrical system to divert and dissipate transient overvoltages.
- Metal oxide surge arresters are commonly used due to their high energy absorption capability and fast response time.
- Surge arresters provide a low-resistance path to the ground for transient surges, protecting the connected equipment.
Shunt reactors
- Shunt reactors are used to compensate for capacitive currents during switching operations, reducing the magnitude of transient overvoltages.
- They are particularly effective in high-voltage systems and can help control voltage levels during switching events.
Series capacitor
- Series capacitors can be installed in the system to control the rate of rise of transient voltages during switching.
- They are especially useful in reducing the effects of very fast transient overvoltages
Modern circuit breakers and disconnect switches
- Modern circuit breakers and disconnect switches are designed to have fast switching times, reducing the duration of transient overvoltages.
- High-speed circuit breakers can interrupt the current quickly, minimizing the impact of surges.
Grounding and bonding
- Proper grounding and bonding of electrical systems are essential to ensure that transient surges have a low-resistance path to dissipate.
- Effective grounding and bonding practices reduce the risk of equipment damage and electrical hazards.
Switching Schedules and Sequences:
- Careful planning of switching operations, including the sequence and timing of switching events, can help minimize the impact of transient surges.
- Proper coordination of switching operations with protective devices is crucial.
📘 Standards and Guidelines
- IEC 60099-4 – Surge arresters for alternating current systems
- IEEE Std C62.41 – Surge environment in low-voltage power circuits
- IEC 62271-100 – High-voltage AC circuit breakers
📈 Practical Considerations
- Evaluate surge protection during system design.
- Coordinate protective devices across the system.
- Use transient simulation tools (like EMTP or PSCAD) to study switching effects.
- Perform routine maintenance on arresters and switching equipment.
Summary
It’s important to note that the choice of remedial measures depends on the specific characteristics of the electrical system, including its voltage level, configuration, and the nature of the switching operations. Consulting with electrical engineers and specialists in power system protection is advisable to develop an effective switching surge mitigation strategy tailored to the system’s requirements.
