Transient Overvoltages: Causes, Effects, and Protective Measures
Transient overvoltages pose a significant threat to modern electronic devices, telecommunications systems, and data processing systems. To ensure the continuous operational readiness of critical systems when lightning strikes cause brief voltage spikes on power supply and data lines, effective surge protection is essential.
There are three main reasons for this:
High susceptibility to interference: Due to their circuit design, modern electronic components are highly sensitive to voltage fluctuations.
Economic risk: Unplanned operational interruptions and system failures are unacceptable in today’s digitalized workplace.
Widespread networking: Data transmission networks span vast geographic areas and are therefore constantly exposed to external interference.
Causes of Power Surges: The 4 Main Causes
Transient overvoltages in electrical power systems can essentially be attributed to four primary causes, which differ significantly from one another in terms of amplitude, duration, and frequency:
Lightning strike (LEMP – Lightning Electromagnetic Pulse): Extremely high-energy pulses with enormous destructive potential.
Switching events (SEMP – Switching Electromagnetic Pulse): Industrially generated voltage spikes that occur, for example, in production facilities when large loads are switched.
Electrostatic Discharges (ESD – ElectroStatic Discharge): Voltage breakdowns caused by large potential differences, resulting from static electricity (triboelectric effect) or induction.
Nuclear electromagnetic pulses (NEMP): Extremely powerful electromagnetic fields generated by nuclear weapons detonated at high altitudes.
While power surges caused by lightning strikes and industrial switching operations are classic problems in electrical engineering, ESD and NEMP disturbances represent more modern challenges. The widespread use of sensitive semiconductors has drastically increased susceptibility to ESD damage.
Direct and Indirect Electrical Effects of Lightning Strikes
Direct Lightning Strike
At the moment of discharge, a pulse current flows with a peak value between 1,000 and 200,000 amperes and a rise time of a few microseconds. This direct effect can be considered a major factor in the damage to electrical and electronic systems.
During a thunderstorm, there are three main types of indirect effects that pose a risk to electrical systems:
1. Lightning Strikes on Overhead Power Lines
Due to their exposed location, overhead power lines are particularly vulnerable. A direct lightning strike often damages the conductor cables first. Extreme surge voltages then build up, propagate along the lines, and reach the end users’ connected electrical systems. The extent of the damage correlates directly with the distance from the point of impact.
2. Increase in Earth Potential
When lightning strikes the ground, it causes a massive increase in ground potential. The magnitude of this increase depends on the current of the lightning strike and the local ground impedance. If an electrical system has multiple grounding points (e.g., in a wired network connecting different buildings), an extreme potential difference arises. The result: Connected devices and networks are destroyed or suffer long-term operational disruptions.
3. Electromagnetic Radiation (Induction)
A lightning channel acts like an antenna several kilometers high that carries a pulse current of several tens of kA (kiloamperes). The electromagnetic fields radiated in the process can still reach field strengths of several kV/m (kilovolts per meter) even at a distance of over one kilometer. These fields induce high voltages and currents in surrounding power lines and electrical systems. The actual measured values depend on the distance from the lightning strike and the physical characteristics of the power line route.
Industrially generated surge voltages and switching events
The term SEMP (Switching Electromagnetic Pulse) refers to transient phenomena caused by the intentional or faulty switching of electrical power sources in industrial and commercial settings.
Typical sources of industrial surge voltages:
Starting high-power electric motors or switching on transformers
Ignition processes of conventional fluorescent lamps (e.g., neon or sodium vapor lamps)
High-frequency switching in modern switching power supplies
Switching of circuits with high inductive loads
Boundary-value tripping of fuses and circuit breakers
Fluctuations in the power frequency caused by sagging power lines
These events generate transients of several kV (kilovolts) with very short rise times in the microsecond range. They propagate through the shared power grid and cause lasting disruption to sensitive loads.
Surge Voltage caused by Electrostatic Discharge (ESD)
The human body acts as a capacitor with a capacitance in the range of 100 to 300 pF (picofarads). When walking on synthetic carpeting, this capacitance can build up to voltages of up to 15 kV (kilovolts). When a conductive object is subsequently touched, this charge discharges within a few nanoseconds at current levels of around 10 A (amperes). Modern integrated circuits—especially those based on CMOS technology—are extremely susceptible to these ESD disturbances. However, this risk can be effectively minimized through targeted shielding and grounding measures.
The Potential Dangers of a Nuclear Electromagnetic Pulse (NEMP)
A nuclear electromagnetic pulse triggered by a high-altitude detonation (high-altitude EMP) above the atmosphere generates a strong electromagnetic field of up to 50 kV/m (kilovolts per meter) within just 10 ns (nanoseconds). This field covers an area on the Earth’s surface with a radius of up to 1,200 kilometers.
On the ground, the NEMP induces immense transient overvoltages in power lines, data networks, antenna systems, and critical infrastructure. Connected devices such as computers, telephones, and control systems are instantly destroyed, as the rise in field strength can reach several kV/ns (kilovolts per nanosecond). Achieving complete protection is complex; however, the destructive energy can be effectively mitigated through shielding, filtering, and surge protection devices (SPDs) specifically designed for NEMP effects, thereby ensuring the resilience of the systems.
