Protecting Critical Power Transmission Equipment

By Justin Case and Helmut Pregartner

Power transformers are essential for effective and reliable transmission and distribution of electricity. Serving as critical nodes, these pieces of equipment have been engineered over the past decades to withstand operational risks such as lightning strikes, severe weather events, seismic activity and network power fluctuations. However, despite their complexity, transformers are susceptible to malicious attacks, especially those carried out with high-powered rifles.

There is widespread agreement between governments, utility operators and manufacturers that transformers are vulnerable pieces of infrastructure in the power grid. Often housed in substations protected by a simple chain-link fence, critical power transformers generally present an easier target for malicious attacks than other electric facilities such as generation plants and control centers. To mitigate the threat of an attack, current standards and guidelines have focussed on assessing, preventing, detecting and responding to unauthorized access to substations. However, these measures do not offer protection from threats that originate outside the substation perimeter.

With a clear line of sight, attackers may disable critical power transformers from a significant distance with high-powered rifles. Such rifles are easily capable of penetrating the 8-mm to 10-mm thick transformer tanks, causing the loss of the insulating and cooling oil (which is critical for the operation of the transformer) or potentially short-circuiting the windings and destroying the transformer. Other components of the transformer, such as the bushings and cooling systems, may also be targeted. This vulnerability of transformers has been demonstrated by several successful attacks in recent years.

The latest highly published attack on a transformer occurred at a Garkane Energy substation located in Arizona on September 26, 2016. The incident, which resulted in loss of power to an estimated 13,000 customers, was carried out by at least three rounds fired from a high-powered rifle into the substation’s main transformer. Damage to the targeted unit was estimated to reach $1 million and take six months to repair.

Perhaps the best-known substation attack though occurred in April 2013 at PG&E’s 500 kV substation in Metcalf, California. The assault, carried out by multiple individuals firing .30 calibre rounds, knocked out 17 transformers in approximately 19 minutes. Of note is that the attackers appeared to intentionally target the radiators, causing the units to leak cooling oil, overheat and become inoperative.

The direct effects of the above-mentioned ballistics attacks to customers were short-lived. This is the result of careful grid planning whereby the consequences of losing a single critical substation can be negated by rerouting power flows as necessary to maintain regional service. However, a coordinated and simultaneous attack on multiple critical transformer substations could have severe implications for reliable service over large geographic areas, crippling the electricity network and causing widespread, extended blackouts. Such an event would have serious economic and social consequences, thereby making a coordinated attack on several substations a potential target for terrorists.

To protect transformers from high-powered ballistics it is necessary to erect additional shielding around the equipment. One measure currently available to utility operators is the construction of hardened concrete walls around the entire substation. Such a barrier limits the visibility of the assets while also providing a degree of bullet resistance. However, erecting a concrete wall around an entire substation may be costly, timely and limits the ability of security personnel to identify saboteurs once inside the premises. Furthermore, the effectiveness of a solid wall to prevent an attack is dependent on the height of the wall, the surrounding terrain and the elevation of the equipment within the substation.

More feasible than shielding an entire substation with a hardened concrete wall is to place a bullet resistant structure directly around critical transformers. Such bullet resistant technology may be in the form of tank-mounted panels, which protect the tank, cooling equipment, conservator, turrets, and the bottom of a transformer’s bushings. It is also effective to replace porcelain bushings with polymer or composite RIP oil-less type bushings so that even if the polymer insulator is penetrated, catastrophic failure will not result in ignition of the oil.

Tank-mounted bullet resistant panels are advantageous to other external ballistic protection measures due to their easy installation and their ability to be retrofitted onto transformers currently in operation. Furthermore, mounting bullet resistant panels directly onto the transformer assembly minimizes the space required while negating the need for foundations. This makes a tank-mounted system suitable for safeguarding equipment in confined spaces, which is becoming increasingly important with the trend of locating critical electrical infrastructure in urbanized environments.

Extensive testing and development means that the technology is available for transformers to withstand the highest class of rifle projectile specified in current ballistics standards, being a .50 calibre round. This round represents the most powerful commonly available cartridge that is not considered a destructive device under the National Firearms Act enforced by the United States Department of Justice. The .50 calibre round therefore also represents the maximum likely ballistic threat to power transmission equipment.

It’s important to continue efforts to secure our power grid, focusing on both the digital and physical security of critical pieces of energy infrastructure. With the right strategies, technologies and plans in place, manufacturers, utility operators and regulators must work together to reduce the threat of malicious attack and continue moving the grid into the 21st Century.




Justin Case works in the Noise and Mechanics R&D team for Siemens AG, Large Power Transformers, Global Technology Centre. He has received B.Eng and B.Bus degrees from the Queensland University of Technology, Australia and is studying towards his Masters of Applied Science. His research interests include the numerical analysis of transformer noise and vibration characteristics and the mechanical improvement of electrical transmission equipment.



Helmut Pregartner is the key expert for transformer noise and Head of the Noise and Mechanics R&D team for Siemens AG, Large Power Transformers, Global Technology Centre. Since 2009, he has been a member of the IEC 60076-10 working group. Mr. Pregartner received his Dipl.-Ing. degree in Telematics from Graz University of Technology, Austria in 2001.

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