EMP Digital Substation

Authors: Andre Smit, Siemens Industry, Inc., USA, Eric Easton and Kevin Bryant, CenterPoint Energy, USA

One human way an EMP can be produced is if a nuclear device is detonated in the upper atmosphere. The pulse produced by the detonation is a powerful electromagnetic field covering an unusually large area that can span hundreds or even thousands of miles. Among the most severe threats confronting modern societies, an EMP attack is an example of a malicious hazard that could cause a classic Black Sky-class catastrophe. An EMP strike could cause a large-scale blackout associated with widely distributed damage of a portion of the digital protection and control devices installed in substations throughout the grid. Another potential human-made EMP source comes from portable Intentional Electromagnetic Interference (IMEI) devices that can also produce an electromagnetic pulse strong enough to damage the protection devices in a substation.
It was decided by CenterPoint Energy Leadership to take an active role and find a solution. In 2015 a backup control center building was constructed by the company’s electric utility to the military EMP standard MIL-STD-188-125. The focus has since been moved to substations to further bolster EMP resiliency in a systemic manner.
This article will describe a resilient Protection and Control system design that CenterPoint developed while investigating EMP from 2015 to 2019.
There are several approaches that can be taken to make a substation protection and control house resilient to both nuclear detonated EMP and portable IEMI attacks. However, these approaches are extremely costly, and cost is the major challenge for electric utilities to address.  Existing solutions to EMP threats are estimated to cost over $2M per substation.
When attempting to mitigate the effects of high-power, high-frequency electromagnetic energy, the smallest details can compromise efforts to achieve the needed levels of shielding effectiveness (SE).  When using the correct components, the digital substation is uniquely capable of achieving electromagnetic resiliency against the harshest High-Altitude Electromagnetic Pulse (HEMP) and IEMI environments.

Electromagnetic Mitigation
The HEMP environment has been studied since the early 1960s when both United States and Russian scientists noted the phenomenon of electric fields capable of damaging electronics emanating from a nuclear burst at altitudes exceeding 19 miles.  The resulting 1 GHz HEMP is capable of 50kV/m which can couple to power conductors and control cables.  Significant portions of the coupled energy may be reflected though instrument transformers to secondary control cables as conducted energy.  Radiated energy can directly couple to unshielded control cables and devices compounding the effects of conducted energy.  Combined, the radiated and coupled energy can result in failures of protective relays and SCADA RTUs in the substation environment.

Conducted and Radiated energy effects on building [IEC 61000-5-10]:  The effects of such an event are experienced by space and ground-based assets within a line of site from the burst. (Figure 1). The most commonly cited methods of mitigation can be found in MIL-188-125, the United States Military Standard for Hardening of Fixed Installations Against HEMP. However, many of the provisions listed in the standard are difficult to employ in a power substation and require new construction as opposed to retrofit applications. Recent empirical testing and modeling by the Electric Power Research Institute (EPRI), concluded that a HEMP event would result in interconnection level disruptions and most likely system collapse. The Electromagnetic Defense Task Force (EDTF) however, reviewed the EPRI report and suggested that the system damage may be much more severe. Therefore, study continues and efforts to identify effective HEMP mitigation methods have increased significantly.
Alternately, an EMP attack from a portable IEMI would be a more localized event.  These devices could range from the size of a suitcase to the bed of a standard size pick-up truck.  While the energy level is lower than that produced from a HEMP, the frequency range may extend to 10 GHz.  The increased frequency enhances coupling for shorter antenna.  The enhanced coupling increases the capability of an IEMI device to disrupt electronic data transmissions such as SCADA telemetry. Operators may be misled into taking incorrect actions as a result of faulty data.

The fundamental aspects of comprehensive EMP mitigation include more robust SE for electric grid components, device power filtering, conducted energy surge suppression and high-frequency bonding and grounding.  Each of the aforementioned aspects must be accomplished to achieve systemic protection. Undoubtably, technologies exist to accomplish the stated objectives using legacy substation designs; however, they were found to be cost prohibitive, require lengthy construction processes and necessitate new construction as opposed to retrofit. 
The desired solution needed to be economical, compact, low maintenance and allow flexible protection and control configurations.  By combining proven electromagnetic mitigation techniques and Digital Substation Design technology, CenterPoint Energy has developed a CenterPoint Energy’s cost-effective EMP mitigation solution which exceeds military standards. The basis of CenterPoint Energy’s cost effective EMP mitigation solution is a module designed using the digital substation architecture. The two fundamental aspects of radiated and coupled energy are inherent to a Digital Substation design.

The physically compact design greatly reduces cost and fiber optic cables decouple primary gear from the protection and control system.  More precisely, the resulting solution increases typical shielding effectiveness from 30 dB to greater than 100 dB at one-fifth the costs of the Non-Digital Substation Designs.
The EMP Mitigation unit or module designed by CenterPoint Energy is intended to serve as indicated in Figure 2 as an online non-tripping data collection and resiliency device.  Pre-EMP the device can be used to collect operational data and serve as reference to non-hardened systems in the event of an attempted IEMI attack. In such a scenario, the values from the hardened and un-hardened systems would be compared to determine if data corruption had occurred.  Response to an EMP event would entail enabling tripping functions in the hardened system to allow operation of the substation to resume should the EMP damage traditional relaying.
CenterPoint Energy ultimately selected Siemens SIPROTEC 5 hardware for the EMP Mitigation unit due to its ability to support the design requirements of compactness and low maintenance, as well as flexible protection and control functionality.

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