Main causes of damage

 

1. Occurrence of very fast transient overvoltage (VFT)

• In GIS, when switching on and off switches, circuit breakers, etc., a sudden surge in transient voltage occurs.

• This voltage can cause insulation breakdown and, especially if foreign matter is present in the GIS or insulation deterioration has occurred, can exceed the electrical strength and cause damage to both internal and external systems.

2. Insulation breakdown and partial discharge

• When the insulation performance is degraded or partial discharge occurs in the insulator due to switching surges, the deterioration of power equipment (spacers, bushings, etc.) is accelerated, ultimately resulting in insulation breakdown and device damage.

• In real-world cases, aging of the spacer surface, moisture adhesion, and ingress of foreign metals have been linked to insulation breakdown, leading to large-scale power outages.

3. Malfunction and failure of electronic equipment due to surges

• High voltage and high frequency surges that flow in at the moment of opening and closing can directly damage or cause malfunctions in delicate equipment such as firefighting equipment, communication and control devices, sensors, and PCBs.

• If surge suppressors or protection devices are inadequate or missing, the damage can be magnified.

4. External system transfer

• Transient voltages generated within the GIS can spread to external systems through overhead transmission lines, distribution panels, etc., causing widespread damage.

 

Power leakage current

• Leakage current is a phenomenon in which a small amount of current continues to flow through a path that should not normally allow current to flow due to weakening, aging, contamination, or moisture in the cable insulation.

• At this time, leakage current can continuously deteriorate the insulation of electrical appliances within firefighting equipment, directly causing insulation breakdown and damage. Severe leakage current can cause malfunctions or overheating and fires in electrical switches, detectors, control panels, and communication equipment.

 

lightning (thunder surge)

• Lightning is a natural phenomenon that involves very high voltage and current momentarily, and lightning surges can penetrate firefighting equipment directly or induced through power lines, communication lines, etc.

• Overvoltage (surge) caused by lightning can cause instantaneous destruction of components within a circuit, especially semiconductor devices, sensors, relays, and PCBs, or can cause long-term performance degradation and shortened lifespan.

 

Opening and closing surge

• Switching surge is a momentary transient voltage (surge) that occurs during the process of switching on/off a load when operating a switch or circuit breaker.

• The main causes include inserting or breaking an unloaded line, forced breaking of an inductive load, and momentary re-lighting of a switch.

• In the case of an opening and closing surge, the voltage is smaller than that of a lightning surge, but the duration is long (tens to hundreds of microseconds) and the accumulated energy is large, repeatedly putting stress on electrical equipment (especially fire equipment systems with weak insulation performance), causing deterioration and damage.

• In particular, if the insulation strength of the equipment is insufficient, insulation breakdown may occur, causing internal circuit failure or even fire.

 

Comprehensive summary

• The switching surge of GIS in underground utility tunnels causes extremely high-speed transient voltages, which directly damages equipment with weak insulation performance and sensitive low-voltage systems (communications, control, protective relays, firefighting equipment, CCTV, etc.) within the power system.

• The main causes are lightning, switching surges, leakage current, insulation breakdown, insulation degradation due to foreign substances and moisture, and deterioration of protective device performance.

• To prevent damage, it is necessary to maintain cleanliness within the facility, conduct periodic insulation inspections, install surge protection devices (SPDs), conduct surge monitoring, and design a system division.