Protecting the power transmission grid

Protecting the power transmission grid

Vol. 4 Issue 4


Power transformers are vital pieces of equipment in the power grid. However, the measures taken to safeguard these critical transmission nodes from high-powered ballistics are often insufficient. This article presents the threat that ballistics attacks pose to transformers and the consequences such attacks may have on the broader power grid. Physical protection measures available to transmission system operators are then discussed, including a tank-mounted transformer protection system.

Keywords: bullet resistance, power transformers, grid resilience, high-powered ballistics


Serving as critical nodes in the power grid, transformers have been engineered over the past decades to withstand operation risks, such as lightning strikes, severe weather events and network power fluctuations. However, often housed in substations protected by a simple chain-link fence, transformers present an easier target for malicious attacks than other key network elements. Furthermore, to mitigate the threat of an attack on a transformer, current standards and guidelines generally focus on assessing, preventing, detecting and responding to unauthorised access to substations. These measures therefore do little to safeguard transformers from threats that originate outside a substation’s perimeter.

There is consensus among utility operators, governments and manufacturers that transformers are highly vulnerable to ballistics attacks. With a clear line of sight, attackers may employ high-powered rifles to disable these critical pieces of equipment from a significant distance. Such rifles are easily capable of penetrating the standard 8 mm to 10 mm thick transformer tanks, causing the loss of insulating and cooling oil (which is critical for the operation of the transformer) or potentially short-circuiting the windings and destroying the unit. Other components of the transformer, such as the bushings and cooling systems, may also be targeted.

The vulnerability of transformers has been demonstrated by several successful attacks in recent years. The most highly publicised of these assaults occurred in 2013 at a major U.S. substation in San Jose, California. Carried out with a high-powered rifle, the attack was able to knock out 17 large power transformers in approximately 19 minutes, resulting in USD 15.4 million in damages. It took utility workers 27 days to make repairs before reopening the substation.

The San Jose and other attacks have highlighted the possibility that, if carried out simultaneously on several substations, assaults with high-powered ballistics could have severe implications for reliable service over large geographic areas. The U.S. Federal Energy Regulatory Commission has noted that such an attack could cripple the U.S. electricity network and cause widespread, extended blackouts. This would have serious economic and social consequences, thereby making a coordinated attack on several substations a potential target for terrorists. Best practice to ensure the reliable operation of power transmission networks is therefore to safeguard transformers from intentional damage.

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