[Transformers Protect Or Destroy Game
Addison Mauldin
Electromagnetic pulses (EMP) from nuclear weapon detonations at altitudes from 30 to 400 kilometers (18 to 50 miles) can damage or destroy sensitive electronic equipment at ground level. High-altitude EMP (HEMP) has the potential to seriously disrupt commercial and military communications, damage the electrical grid infrastructure, and interfere with command and control operations. These disruptions can adversely affect federal, state, or local agency missions and operations.
The effects of HEMP span a wide frequency range (very low frequency to a few hundred megahertz [MHz]), and encompass critical commercial and military frequency bands. HEMP effects also produce damaging currents within power transmission, distribution, and communications lines resembling effects of geomagnetic disturbances or storms (e.g., solar flares). These disturbances can damage or destroy both electronic control equipment and the power transformers associated with electric grid distribution. Protection from HEMP effects is, therefore, essential.
The E1 (Early-time) phase, produces a very high-intensity pulse over a large frequency bandwidth of extremely short duration - nanoseconds to microseconds. It is produced by radiation from the nuclear blast interacting with specific layers in the atmosphere. This pulse propagates a blast wave along lines feeding communication equipment; direct absorption of energy induces high voltages and currents. Each effect may seriously damage electronics and electrical and communication systems.
The E2 (Intermediate-time) phase is also a product of radiation interacting with the atmosphere, but has characteristics closely resembling the effects created by lightning strikes, lasting from microseconds to seconds. These "induction effects" differ from actual lightning in that there is no current surge produced directly as would be the case of a bolt of lightning striking an electric pole or a house. E2 induction effects resemble and are equivalent to the electromagnetic pulse that radiates from a lightning bolt that impinges during a discharge on sensitive electronics and equipment.
E3 (Late-time) is produced by the slow movement of charged particles within the heated plasma fireball from the nuclear blast as it interacts with the Earth's magnetic field. Effects of this phase last from seconds to minutes. The blast expands as it moves through the atmosphere, then lifts upward. E3 effects are very similar to those produced by solar flares, but they can be significantly more intense. They result in large current surges on the order of hundreds to thousands of amperes produced at ground level that couple onto power lines and communications lines through induction. These current surges produce various adverse effects, particularly to power lines, damaging equipment and transformers by overheating the transformer core and windings.
The combined effects of HEMP require different technologies and methods for mitigation. Fortunately, there has been significant research and development conducted that have produced many viable solutions to provide effective protection.
Providing protection against HEMP is a process-based approach that combines the application of various technologies with appropriate tactics, techniques, and procedures. Various technology options are available to provide physical protection against the three phases of HEMP; but just as important are the methods and approaches used to apply these technologies.
In general, options for mitigation source three technologies: electromagnetic shielding; HEMP special filtering; and surge protection (see illustration below). Additionally, proper grounding, and, in some instances, electrical isolation, can offer improved protection against HEMP effects.
Electromagnetic shielding provides excellent protection against direct absorption effects (i.e., electromagnetic waves impinging directly onto equipment) of the E1 and E2 phases of HEMP. Various metals and other materials with differing weights, sizes, and costs can provide very high levels of electromagnetic wave attenuation to protect equipment. The material selected ties directly to the level of protection needed and the infrastructure to be protected. Shielding can be incorporated in both new construction and renovations, and for whole structures or within specific areas or rooms, or even individual equipment items.
The most common shielding method uses metal containers and boxes, and is particularly suitable for small equipment. The most common metal employed in shielding is copper. However, other metals can be used such as aluminum or steel. In special instances, more exotic metals, such as ferromagnetic alloy metals, are used, particularly when magnetic effects come into play.
Larger areas or whole buildings may be shielded with metal sheeting, or metal foils and conductive paints can be used. Additionally, emerging technologies such as electrically conductive concretes are increasingly attracting attention. In these cases, cost must be weighed against the desired level of protection.
For military applications, special HEMP filtering technology meeting the stringent requirements of the Department of Defense Interface Standard MIL STD 188/125, High-Altitude Electromagnetic Pulse (HEMP) Protection for Ground-based C4I Facilities Performing Critical Time-Urgent Missions, Part 1 and Part 2, and MIL-STD-464C, Electromagnetic Environmental Effects Requirements for Systems are usually selected. The purpose of HEMP filtering is to prevent or "arrest" induction surge created by the HEMP pulse from coupling into sensitive equipment. While filtering specifications are extensive, capabilities typically include very high-surge Pulse Current Injection (PCI) protection and very fast rise-time response.
Particularly useful to mitigate E2 phase effects, surge protection technologies prevent damage to electronics and electrical systems from induced currents in lines. Surge protection technologies are well-established and are a standard for lightning protection. Generally, these technologies are variants on Metal-Oxide-Varistors (MOV) or Transient Voltage Suppression (TVS) diodes (also known as avalanche diodes). Other devices such as thyristor protection or gas discharge tubes are also used.
These devices limit a high voltage surge that exceeds a preset limit by shunting or blocking the current flow from being introduced into electronic or electrical systems. Their many configurations range from simple home surge protection strips to larger whole-home or building protection. It must be noted that these devices protect against induced current/voltage transients (HEMP E2 or a nearby lightning strike), not direct lightning strike to an ingress/egress power or communication line.
Two common techniques applied to electrical and electronic systems to improve resilience against HEMP effects are grounding and isolation. Both limit exposure to HEMP-generated effects, but they differ in that they are electrical configuration techniques, as opposed to applied devices or material solutions.
Other techniques to provide HEMP protection include reliance on natural shielding provided by facility infrastructure or the application of beyond cutoff waveguides for points of entry into structures.
As with grounding, electrical isolation may involve many options. However, the overarching goal is to prevent or reduce induction of HEMP-produced currents from entering sensitive systems. An area where isolation is particularly effective is in mitigation of the extremely low frequency components of E3-induced currents. As indicated, these currents are very similar to those produced by solar flares and geomagnetic sun spot storms, but with significantly more serious impact.
These are very slow time-varying currents, almost a direct current effect, and they are particularly troublesome for transformers and power lines. One example is the induction of these currents onto the neutral line of a standard configured distribution transformer system which can couple directly into the facility ground system. Currents introduced into the long transmission and distribution lines can cause serious heating in the transformers and propagate harmonic generation issues downstream that can seriously affect other equipment.
A typical mitigation method for this effect is to configure transformers to block the E3 effects from entering the facility. Another method is to insert blocking capacitors and shunt devices into the distribution lines to block the E3-induced currents before they get to the facility distribution points. A third method is to allow the infrastructure ground to be disconnected from earth ground for isolation.
A more comprehensive approach to HEMP protection involves resilience, which addresses the entire timeline of a HEMP event, from the pre-planning stage through post-event recovery. Resilience must address infrastructure robustness, such as the protections already described, as well as other tactics and techniques. These may include redundancies in capability; resourcefulness and out-of-the-box thinking to identify novel means to overcome HEMP effects; and the ability to respond with necessary manpower and equipment to affect efficient recovery.
Securing assets via dispersal and relocation, as with the EMP Protection-in-a-Box concept, can provide protection against HEMP effects. This strategy dilutes risk by moving critical assets to more secure locations, or providing HEMP protection for those assets only.
Resourcefulness as a HEMP protective tactic involves creative thinking. For example, if base infrastructure is severely affected, can nearby community capability that is still functioning be borrowed or leased? Can the commercial sector substitute for damaged capability in a timely manner? Is it possible to implement "Rube Goldberg" solutions to restore critical capability to a workable level? Key to resourcefulness is situational awareness regarding what is available for support and maintaining an open mind to identify options that would not be considered during normal day-to-day operations.
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