What Are the Factors Influencing the Impact of Lightning on 10kV Distribution Lines?

1. Induced Lightning Overvoltage

Induced lightning overvoltage refers to the transient overvoltage generated on overhead distribution lines due to nearby lightning discharges, even when the line is not directly struck. When a lightning flash occurs in the vicinity, it induces a large amount of charge on the conductors—opposite in polarity to the charge in the thundercloud.

Statistical data shows that lightning-related faults caused by induced overvoltages account for approximately 90% of total faults on distribution lines, making it the primary cause of outages in 10 kV distribution systems. Research indicates that if a 10 kV line is 10 meters above ground and lightning strikes 50 meters away, a lightning current of up to 100 kA can be induced. Without proper lightning protection, the resulting overvoltage may reach peak values as high as 500 kV. If the line’s insulation level is inadequate, this overvoltage can easily puncture or even shatter the insulation, leading to flashovers or conductor failure.

2. Insulation Level

Insulation failure, particularly due to insulator breakdown or explosion, is another major cause of distribution line faults. The performance of insulators directly determines the overall insulation strength of a 10 kV distribution line and thus significantly impacts system reliability.

Over long-term operation, insulators may degrade due to environmental pollution, moisture, aging, or mechanical stress. Without regular inspection, maintenance, or timely replacement, the insulation level of the entire line can deteriorate significantly. This degradation increases the likelihood of flashover under overvoltage conditions—especially during thunderstorms—further raising the risk of lightning-induced outages.

Therefore, routine inspection and maintenance of insulators are essential to ensure sustained insulation integrity and system safety.

3. Lightning Protection Installation

3.1 Transformer Protection

When lightning overvoltage reaches several times the rated voltage, it can easily puncture the insulation around the transformer’s neutral point. In most current installations in China, surge arresters are typically installed only on the high-voltage side of transformers, while protection on the low-voltage side remains inadequate.

Surge arresters can be installed either ahead of the main fuse or at the outgoing feeder side of the distribution line. During installation, the low-voltage terminal of the arrester must be properly grounded.

It is critical to note that the neutral conductor (N-line) downstream of a current-type protective device must not be repeatedly grounded. Otherwise, the protective device may fail to operate correctly, compromising the entire protection scheme. Therefore, the grounding lead of the low-voltage arrester should be connected to the primary terminal of the transformer’s neutral conductor, before any repeated grounding points.

3.2 Pole-Mounted Switches and Disconnectors

Installing pole-mounted circuit breakers and disconnect switches can greatly improve the reliability and safety of 10 kV distribution lines. However, in practice, many lines lack proper lightning protection for these critical devices. Without surge arresters installed on both sides of such switches, they are vulnerable to damage from lightning overvoltages, potentially leading to equipment failure and prolonged outages.

3.3 Surge Protection for Switchgear and Other Units

A 10 kV distribution system consists of multiple critical units, including switchgear, capacitor banks, and distribution panels. Surge arresters can be installed on every unit (comprehensive protection) or selectively on key units only.

While the former approach involves higher initial costs, it provides significantly higher reliability and system resilience. Selective installation reduces cost but may leave certain sections exposed. The choice should be based on risk assessment, criticality of load, and local lightning activity.