Overvoltage
Surge protection devices (SPD) are designed to limit the transitory excess voltage caused by lightning or by work being carried out on the electricity supply grid.
Lightning can cause these phenomena either directly, through a lightning strike on high voltage overhead power lines, (for example) or indirectly by coupling :
- Resistive or "galvanic" coupling due to a difference in potential
- Inductive coupling due to the magnetic fields affecting the surrounding conductors.
A & B: Indirect lightning discharge on overhead distribution lines
C : Induced lightning discharge (electromagnetic coupling on incoming power or Telecom networks)
D : Direct lightning discharge
E : Induced lightning discharge (electromagnetic coupling on internal and external conductors)
F : Choc de foudre induit (par couplage électromagnétique sur conducteurs internes et externes)
In addition, transitory overvoltage has a specific form (steaffness of the current wave, particularly with multiple return strokes), meaning other electrical safety components, such as standard circuit breakers, cannot effectively protect equipment from the "lightning risk". Surge protection devices normally use spark-gaps or zinc oxide varistors.
- Telephone networks
- IT networks
- Data transmission networks
The INDELEC product catalog lists a full range of lightning protection equipment.