IEC/TS 61000 5 8 Edition 1 0 2009 08 TECHNICAL SPECIFICATION Electromagnetic compatibility (EMC) – Part 5 8 Installation and mitigation guidelines – HEMP protection methods for the distributed infrast[.]
Early-time (E1) HEMP spatial variations
The early-time (E1) High-Altitude Electromagnetic Pulse (HEMP) field primarily operates above 1 MHz, with most energy concentrated in the tens of MHz range, allowing it to travel by line of sight This field is generated at altitudes between 20 km and 50 km, where atmospheric density is sufficient for prompt gamma rays to create Compton currents Despite this, the early-time HEMP field appears to emanate from the detonation point, enabling straightforward calculations of the Earth's radius exposed to early-time HEMP based on burst height A simple formula applies when the burst height is significantly smaller than the Earth's radius, which is typically the case.
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Figure 2 – E1 HEMP tangent radius as a function of the height of burst
Figure 3 illustrates the coverage of the early-time (E1) High-Altitude Electromagnetic Pulse (HEMP), highlighting a 170 km burst affecting a specific region of the United States.
In Ohio, the early-time High-Altitude Electromagnetic Pulse (HEMP) can generate electric field levels reaching up to 50 kV/m within a specific area Typically, the highest E1 HEMP fields occur near ground zero, with intensity diminishing as the distance from this point increases However, the Earth's geomagnetic field influences this distribution, particularly close to ground zero For further insights into the variations of early-time (E1) HEMP, additional information is available.
HEMP field levels, see IEC 61000-2-9
Figure 3 – Example of the area covered by the early-time (E1)
HEMP by a 170 km burst over the United States
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An essential aspect of early-time (E1) High-Altitude Electromagnetic Pulse (HEMP) is its propagation at the speed of light from a focal point at the burst.
Figure 3 (burst height of 170 km), the time difference between the first and last arrival of the
E1 HEMP at the Earth's surface measures just 4.3 ms, indicating that disturbances caused by HEMP can affect networks, including power systems, over thousands of kilometers These impacts occur within a single power cycle, which is 20 ms for 50 Hz and 16.7 ms for 60 Hz, creating a distinct disturbance scenario for distributed infrastructures.
Intermediate-time (E2) HEMP spatial variations
For the intermediate-time (E2) HEMP environments, the E2 HEMP radiated field lasts between 1 μs and 1 s and has a peak field of 100 V/m (IEC 61000-2-9) The peak field of
Electric fields of 100 V/m are typically found within 100 km of the Earth's surface, diminishing to just a few V/m at the tangent The frequency characteristics of this pulse shape hinder effective coupling with equipment, systems, or small installations Generally, the primary impact occurs through coupling with long conductors (over 100 m) that connect to installations and the equipment they house.
Late-time (E3) HEMP spatial variations
The E3 HEMP radiated field can reach up to 40 V/km, as specified by IEC 61000-2-9, with a rise time of seconds and a pulse width around 100 seconds The peak field strength is influenced by the burst height and yield, typically affecting areas within a 250 km radius from the surface Additionally, the lower frequency components of the E3 field are primarily effective for coupling with very long cables, specifically those exceeding 1 km in length.
7 Implications for HEMP coupling to extended conductors
General
Due to the fact that the HEMP conducted environments are only produced by coupling of the
HEMP radiated environments, there are three distinct types of conducted environments: early- time (E1), intermediate-time (E2) and late-time (E3).
Early-time (E1) conducted environments
According to IEC 61000-2-10, the early-time (E1) High-Altitude Electromagnetic Pulse (HEMP) field effectively couples with extended conductors, such as cables and wires, generating significant currents and voltages with rise times around 10 ns The induced currents, which can reach up to 4 kA, depend on factors such as the polarization of the HEMP field, the angle of incidence to the Earth's surface, and the orientation of both above-ground and buried conductors relative to the incident field.
IEC 61000-2-10 presents several examples of probabilistic E1 HEMP currents that can be induced for the case of random conductor orientation over the entire area exposed by the
The upper section of Table 1 presents the findings for above-ground conductors, while the lower section details comparable results for buried conductors The currents displayed represent the flow on a conductor, categorized as either shield currents or bulk currents for unshielded cables.
The induced pulse shapes of the currents can be described by a (10/100) ns waveform (rise time/pulse width) for above-ground conductors and by a (25/500) ns waveform for buried conductors
Above-ground conductors can carry significantly larger currents compared to buried conductors, with minimal variation due to ground effects that reduce the efficiency of incident field phasing and induced current propagation Ground conductivity plays a crucial role in determining peak induced currents To assess appropriate voltage levels, it is essential to consider the characteristic impedance of the cables, which is 400 Ω for above-ground conductors compared to just 50 Ω for buried ones.
Licensed to MECON Limited for internal use in Ranchi and Bangalore, this document is supplied by Book Supply Bureau The average induced peak voltages for above-ground conductors are approximately 200 kV, while for buried conductors, they range from 10 kV to 20 kV.
Table 1 – Peak currents induced by the E1 HEMP on above-ground and buried conductors
99 4 000 20 L 20 L a Percentage of currents smaller than the indicated value
NOTE Source impedances are used in Table 1 to inject the proper ratio of voltages and currents They are the same as the common-mode characteristic impedances.
Intermediate-time (E2) conducted environments
For the intermediate-time or E2 HEMP field coupling to extended conductors, results from
IEC 61000-2-10 outlines the currents induced in long conductors based on ground conductivity, conductor length, and their positioning (above ground or buried) According to Table 2, lower ground conductivities result in larger induced currents for both types of conductors, with above-ground conductors experiencing currents that are 2 to 3 times higher, along with a greater characteristic impedance.
Note also that the currents do not increase further for above-ground conductors greater than
10 km long or for buried conductors greater than 1 km In both cases, the induced current waveform can be expressed as a (25/1 500) μs waveform
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Table 2 – Peak currents induced by the E2 HEMP on above-ground and buried conductors
NOTE 1 Source impedances are used in Table 2 to inject the proper ratio of voltages and currents They are the same as the common-mode characteristic impedances
NOTE 2 In Table 2a for values of L between 1 000 m and 10 000 m, the values provided are approximate values
This accounts for the discontinuity for values below 1 000 m For L < 1 000 m, use the formula provided.
Late-time (E3) conducted environments
The E3 HEMP waveform increases rapidly within seconds but only effectively couples to conductors that are longer than 1 km With a maximum peak field of 40 V/km, this can induce a voltage of 40 V across a 1 km conductor, provided that the conductor and its grounding system are properly configured.
When a resistance of 10 Ω is present, a current of 4 A can flow, posing a risk to fuses and protective devices due to its low magnitude and a pulse width of 100 s According to IEC 61000-2-10, a straightforward DC method can be employed to assess the currents induced by E3 HEMP This involves determining the induced voltage based on the field level and conductor length, followed by evaluating the total resistance in the ground loop The induced current is then calculated by dividing the voltage by the resistance, exhibiting the same time dependence as the incident E3 electric field.
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8 Relation of HEMP disturbances to natural EM environments
General
The E1 High-Altitude Electromagnetic Pulse (HEMP) radiates pulse fields similar to those generated by natural events, such as electromagnetic transients from arcing in power substations and electrostatic discharge (ESD) occurrences In power substations, pulsed fields exhibit rise times around 10 ns and peak field strengths of 10 kV/m Conversely, ESD tests have recorded peak fields of up to 10 kV/m at a distance of 0.1 m from the arc, with a rise time of 0.7 ns and a pulse width of 30 ns.
IEC 61000-2-9 specifies a (2.5/25) ns waveform with a peak field of 50 kV/m, indicating that electronic equipment can be vulnerable to such fields without adequate protection In power substations, high-frequency currents and voltages can induce over-voltages on equipment cables, necessitating robust protection for connected devices While HEMP fields are often likened to lightning fields, measured lightning fields typically have peak values of 10 kV/m or higher, but their rise times exceed 100 ns, making them less comparable to E1 HEMP or ESD events, as outlined in IEC 61000-5-3.
The E2 HEMP radiated fields exhibit a waveform akin to natural lightning, but with a peak field value of 100 V/m, significantly lower than that of nearby lightning electric fields However, due to the E2 HEMP field's propagation as a plane wave, it couples more efficiently to conductors, resulting in current levels approaching 1 kA.
E2 HEMP conducted environment features a waveform that rises in 25 μs with a pulse width of 500 μs, closely resembling the ITU-T immunity test waveform characterized by a pulse shape of (10/700) μs (IEC 61000-4-5) The standard performance level for equipment immunity to this electromagnetic pulse is typically 2 kV Notably, as shown in Table 2, the HEMP E2 conducted environment can reach levels as high as 300 kV on above-ground conductors exceeding certain lengths.
The E3 HEMP electric fields are very similar in their time dependence to the natural electric fields produced in the Earth due to geomagnetic storms created by enhanced solar activity
Over the years, direct measurements of geomagnetic fields, induced electric fields, and currents in high-voltage power networks have been extensively documented Recent data indicates that electric fields have reached levels of 1 V/km, with the potential for these fields to rise to 5 V/km during severe storms, despite the absence of direct measurements in such conditions.
Comparison of HEMP E1 to EFT and surge
The conducted E1 HEMP environment for an above-ground conductor is defined in
IEC 61000-2-10 as a waveform that rises in 10 ns (10 % to 90 %) and has a pulse width (50 %
– 50 %) of 100 ns (this is typically described as a (10/100) ns waveform) Of course the real
HEMP transients are influenced by the coupling angle of incidence and the conductivity of the surrounding Earth near a conductor For well-buried conductors, the expected waveform duration is approximately 25 to 500 nanoseconds In contrast, surface conductors are anticipated to exhibit HEMP waveforms with rise times and pulse widths that fall within this range.
The electrical fast transient (EFT) waveform, characterized by a (5/50) ns pulse as defined in IEC 61000-4-4, is generated from arcing events in power substations and poses a significant risk to electronic control equipment both within the substations and in nearby factories This waveform occurs in bursts with a repetition rate ranging from 5 kHz to 100 kHz It is crucial to note that the IEC test method for EFT is widely adopted, and most electronic systems undergo testing for this disturbance, albeit at lower peak voltages compared to those generated by high-altitude electromagnetic pulses (HEMP).
Typically, the test levels for EFT range between 0,5 kV and 4 kV (open circuit voltage) For
HEMP the levels can be 10 kV to 20 kV for equipment inside of buildings and much higher for fully exposed equipment
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The primary distinctions between the E1 HEMP waveform and the EFT waveform lie in their rise time and pulse width; the HEMP waveform exhibits a slower rise time and a longer pulse width Consequently, the derivative norm (\$dV/dt\$) of the HEMP waveform is half that of the EFT at the same peak value, resulting in a rectified impulse for the HEMP waveform that is twice as large as that of the EFT, again for the same peak value.
Since charge transfer and energy are not normally the primary means for causing damage
Damage to equipment often occurs due to arcs on circuit boards, which can harm low voltage components The derivative norm is crucial in this context, as the EFT test generates a derivative norm that is twice that of a HEMP for a specific peak voltage level Consequently, test level EC9 in IEC 61000-4-25 specifies a maximum open circuit voltage test of 16 kV, utilizing the IEC 61000-4-4 test method, which achieves the same maximum derivative as a 32 kV HEMP waveform.
The IEC has established a surge immunity test for electronic systems that may encounter lightning transients within buildings, as outlined in IEC 61000-4-5 This test is characterized by an open circuit voltage waveform designed to assess the resilience of these systems against nearby lightning strikes.
The 1/50 μs pulse shape exhibits a significantly slower rise time, approximately 100 times longer, and a pulse width nearly 1000 times greater than the E1 HEMP conducted transient waveform Consequently, there is no correlation between these two waveforms, and testing according to IEC 61000-4-5 cannot substitute for E1 HEMP waveform testing, despite the higher rectified impulse and energy delivered at the same peak value.
Comparison of HEMP E3 to currents induced by geomagnetic storms
The late-time (E3) HEMP electric field waveform, as defined in IEC 61000-2-9, is characterized by a (1/20) s waveform, exhibiting significant amplitude over several hundred seconds This electric field arises from the interaction between the incident magnetic field and the Earth's conductivity, effectively coupling with conductors like high voltage power transmission lines that are grounded through their transformer neutrals.
The peak electric field is around 40 V/km, which induces currents in phase wires, with the amplitude influenced by the conductor's length and resistance For instance, a 100 km power line with a resistance of 5 Ω can result in a total current flow of approximately 800 A Quasi-d.c currents can significantly disrupt the efficient functioning of large high-voltage transformers by generating harmonics due to half-cycle saturation and creating substantial inductive loads from transformer losses As many transformers can produce this inductive load quickly and simultaneously across a wide area of the power grid, it poses a serious risk to network stability, potentially leading to power blackouts, similar to past incidents in power systems.
Figure 4 – Late-time (E3) electric field waveform from IEC 61000-2-9
In the case of geomagnetic storms, which are produced by enhancements of the solar wind coupling to the Earth magnetotail, these periodic storms can create electric field waveforms
Licensed to MECON Limited for internal use in Ranchi and Bangalore, this document discusses the similarities between induced geomagnetic storm electric fields and HEMP E3 waveforms While typical induced electric fields during severe geomagnetic storms are generally lower, around 1 V/km, they can exceed 5 V/km in extreme situations In the scenario presented, with a geomagnetic storm electric field of 1 V/km, the peak induced quasi-d.c current would reach 20 A.
The saturation level of a high voltage transformer is significant, yet it is 40 times lower than the induced current from the IEC E3 HEMP waveform, highlighting the difference in peak electric fields.
Both waveforms exhibit rise times of just a few seconds and pulse widths lasting several minutes However, each geomagnetic storm can present unique characteristics, as can the late-time High-Altitude Electromagnetic Pulse (HEMP).
Significant levels of late-time (E3) High-Altitude Electromagnetic Pulse (HEMP) can affect areas within a 250 km radius from ground zero In contrast, geomagnetic storms have a much broader impact, often extending over larger geographic regions with linear dimensions that exceed this range.
The difference of 1,000 km is significant, as late-time High-Altitude Electromagnetic Pulse (HEMP) originates from a point source of energy in the ionosphere In contrast, geomagnetic storms result from a broad "curtain" of charged particles descending from space into the ionosphere, or from other extensive magnetospheric disturbance processes.
On March 13, 1989, Quebec, Canada experienced a power blackout caused by an induced electric field estimated at approximately 1 V/km.
The Soviet nuclear test experience with High-Altitude Electromagnetic Pulse (HEMP) is significant, as it involved conducting high-altitude nuclear tests over land Analyses from these tests revealed that the failures of two telecommunication systems were attributed to electric field levels induced by HEMP.
5 V/km [3] Given the similarities of the late-time HEMP and geomagnetic storm environments, it is likely that the effects created would be similar for both types of disturbances
General
The HEMP protection strategy for infrastructure encompasses four key components: first, establishing HEMP immunity standards for new electrical and electronic equipment; second, implementing selected retrofit protection with redundancy considerations; third, developing emergency operational procedures; and fourth, creating restoration plans to address potential widespread failures.
In this international publication, items c) and d) should be combined into a comprehensive
HEMP and widespread disaster plan
An important consideration for civil systems is cost A goal of this publication is to identify protection methods that provide a substantial level of protection at relatively low cost
Infrastructures implementing these protection strategies will experience enhanced reliability against non-HEMP threats, including electrical and electromagnetic transients, intentional electromagnetic interference, sabotage, and extensive physical damage from natural disasters like hurricanes and earthquakes, as well as geomagnetic storms The strategies are prioritized based on their importance and cost-effectiveness.
Electric power
Background
The electric power infrastructure is a highly interconnected and dynamic system that may consist of a single integrated utility or a combination of many public and private utilities
These utilities use a supervisory control and data acquisition (SCADA) system to automate
The control of electric power generation, transmission, and distribution is essential for maintaining balance between generation and load Power infrastructure aims to match generation with demand, utilizing stored energy in generator magnetic flux and rotating mass to accommodate rapid load changes Energy is exchanged with neighboring control areas through interconnected transmission lines Significant load changes cause generators to adjust their speed accordingly, while generator control systems automatically regulate power to turbines, ensuring stable power frequency without requiring intervention from the control center.
In SCADA systems, the master terminal unit (MTU) communicates with remote terminal units (RTUs) at substations and power stations to send commands and receive data, completing scans of all parameters within seconds These systems maintain comprehensive logs of the power system's operation and status Modern control systems address frequency variations, cost factors, transmission losses, and load-generation mismatches, with the automatic generation control (AGC) system sending corrective control pulses to generation units The AGC, integrated into the SCADA system, enhances frequency control and economic operation compared to traditional generator plant governor control However, the MTU, typically built from personal computer components, may be susceptible to radiated and conducted HEMP environments without additional protection.
A load forecast over time is essential for aligning generation with demand By utilizing historical data, date, time of day, weather forecasts, and other relevant information, the load profile can be accurately predicted The optimal generation mix is then identified to achieve the most cost-effective match to the load This process, known as economic dispatch or energy management, facilitates hour-to-hour control through an energy management system.
The Energy Management System (EMS) is an integral component of the SCADA system, facilitating communication with power plants to ensure they operate online at specified times and participation factors Accurate forecasting of generation needs is crucial for effective power system control, as some generators require time to come online.
In the event of a significant discrepancy between actual load and online generation, the control area must depend on interconnected transmission lines to meet power demand until generation adjustments are made Control centers utilize real-time load-flow and stability analyses, supported by data from the SCADA system, to monitor thermal and stability limits The operator schedules the most cost-effective energy supply and manages line maintenance Acting as a power broker, the operator can purchase cheaper power, leading to the shutdown of less economical plants to reduce operating costs Nonetheless, it is essential to maintain a certain level of spinning reserve to address potential major line losses or generator failures.
Spinning reserves are extra generating capacity that is kept running to respond to unexpected increased demand or drop in generation on the power grid
Power systems require protection from overcurrents, overvoltages, undervoltages, and instabilities High-voltage transmission lines are equipped with breakers that can be activated during faults The protective relay system detects these faults and sends signals to operate the breakers Although these protection systems operate independently of the SCADA system, they are crucial control assets that must be safeguarded against early-time HEMP waveforms.
The interconnected power infrastructure ensures high reliability and economic efficiency under normal conditions; however, it also presents significant vulnerabilities during multiple malfunctions and widespread disturbances A widespread loss of loads, triggered by line flashovers or line switching due to a High-Altitude Electromagnetic Pulse (HEMP) event, can lead to a complete system collapse.
Geomagnetic storms or late-time High-Altitude Electromagnetic Pulse (HEMP) events can lead to significant mismatches between reactive loads and generation, potentially causing massive power failures.
Emergency planning, operating procedures and restoration
In the face of imminent crises like hurricanes or geomagnetic storms, it is crucial to shift the power infrastructure from a standard economic mode to an emergency secure mode This proactive approach involves aligning load and generation within control areas and preparing for potential power network islands during system disruptions Additionally, increasing spinning reserves can help accommodate unexpected generation shutdowns Experts in the power infrastructure industry must develop detailed operational plans, and it is essential to identify the organization or government agency responsible for initiating the transition to emergency secure operations.
A major problem for the electric power infrastructure during and after widespread damage and disturbances such as those caused by a hurricane is the lack of adequate communications
Effective communication is essential during and after a High-Altitude Electromagnetic Pulse (HEMP) event Establishing an independent HEMP-resistant communications system is vital for emergency operations and restoration efforts During the restoration phase, maintaining communication between control centers, generation stations, and field operations is crucial.
The 2003 blackout in the northeastern U.S highlighted the critical role of communication during power outages, as cell phone services failed in some areas after a few hours due to insufficient battery power at cell towers This incident underscores the necessity of reliable communication systems for effective power restoration, emphasizing that such systems may become increasingly dependent on electric power over time.
An effective emergency restoration plan must address the specific challenges posed by HEMP-induced disruptions and should be validated through practice drills Given the potential for widespread HEMP blackouts, reliance on neighboring utilities or control areas for restoration may prove inadequate Therefore, restoration strategies should be self-sufficient, ensuring that they do not depend on external sources for electrical start-up power or personnel To safeguard the system and personnel, it is essential to assess key components such as power plant instruments, protective relays, and SCADA systems for damage prior to initiating restoration Additionally, maintaining DC power supplies is crucial for the recovery of the electric power infrastructure.
Backup emergency generators to recharge substation batteries may be required for extended outage times All of these aspects are required in order to achieve a black start capability.
HEMP immunity standards for new equipment
Equipment in power substations and generation plants must endure harsh environments characterized by conducted and radiated transients, necessitating the implementation of EMC immunity standards For instance, IEC 60255 outlines various withstand tests that simulate electromagnetic interference (EMI) phenomena typically found in substations These tests address fast transients, inductive load switching, lightning strikes, electrostatic discharge (ESD), radio frequency interference from portable radios, ground potential rise due to high current faults, and other electromagnetic disturbances commonly experienced in these settings.
Although IEC immunity standards for substations and generation stations will not assure
Implementing HEMP immunity standards is essential to reduce the likelihood of equipment failure across the power infrastructure within HEMP field coverage These standards should serve as a baseline for all new equipment acquisitions, particularly for critical communications and control center systems To ensure a significant level of immunity, it is crucial to adopt HEMP standards specifically tailored for power substations, generation plants, control centers, and communication systems.
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A new trend in SCADA and relay protection for power infrastructures is the adoption of an Ethernet-based utility communications architecture, aimed at achieving interoperability among various Intelligent Electronic Devices This innovative system eliminates the need for Remote Terminal Units (RTUs) and is outlined in the IEC 61850 standard Utilities must ensure that all equipment utilized within an IEC 61850 framework complies with EMC and HEMP standards.
To achieve a higher level of HEMP immunity, the power infrastructure industry should examine and improve the immunity of its equipment as defined in IEC 61000-4-25.
Selected retrofit protection
During the process of developing the emergency plan discussed in 9.2.2, critical links and systems that are necessary for the safe operation and restoration during and following a
The HEMP event must be recognized, as non-compliance of electronic boards and equipment with the latest IEC EMC standards for power infrastructure necessitates retrofit hardening.
To protect equipment within a building or facility, two primary approaches are utilized: building hardening and layered protection The building hardening method is often applied to critical military systems and is more feasible for new constructions rather than retrofitting According to IEC 61000-5-6, layered protection involves using electromagnetic shielded racks or small shielded rooms to safeguard essential equipment Additionally, it is crucial to properly bond any metallic wiring connecting the equipment to external systems, and if fiber optic cables are employed, they must penetrate the shielding using waveguides below cut-off.
There are three other IEC publications that aid in the process of retrofit hardening First
IEC 61000-2-11 outlines the varying levels of High-Altitude Electromagnetic Pulse (HEMP) environments present in different facility types based on their construction Meanwhile, IEC 61000-5-3 provides guidelines for safeguarding equipment by utilizing shielded racks and rooms, effectively minimizing potential risks.
The IEC 61000-6-6 standard outlines specific testing requirements for equipment in relation to HEMP environments, as detailed in Table 3 It establishes a 90% severity level for HEMP conducted environments, ensuring that protection concepts are effectively applied.
Table 3 – Minimum required attenuation of peak time domain external environments for the six principal protection concepts
Electric field Magnetic field Conducted current
NOTE Frequency evaluation ranges for E and H fields are 100 kHz to 30 MHz for concepts 1 and 2, and 1 MHz to
Table 3 outlines two distinct building concepts: Concept 1 features an above-ground structure made of wood or concrete without steel reinforcement and includes large windows, while Concept 2 describes an above-ground concrete building with steel reinforcement or a buried brick building, indicated by the presence of B.
MECON Limited, located in Ranchi and Bangalore, has provided internal use materials through the Book Supply Bureau The article discusses various concepts for lightning protection at the building level, emphasizing the importance of reducing conducted transients at the equipment level Concept 3 features a shielded enclosure with a minimum RF shielding effectiveness of 20 dB, while Concept 4 offers modest RF shielding effectiveness of 40 dB Concept 5 enhances protection with good RF shielding effectiveness of 60 dB, along with effective PoE surge protection and filtering Concept 6 shares similarities with the previous concepts.
Concept 5 except the shielding and PoE protection is of high quality (80 dB) Measurements should be made to confirm these levels through the use of IEC 61000-4-23 and
IEC 61000-4-24 Assessments can also be made with IEC 61000-5-9, which is being developed to provide a methodology to assess the HEMP hardness of a facility.
Application to a high-voltage power substation
Supervisory control refers to equipment that allows for remote control of a substation's functions from a system control centre or other point of control Supervisory control can be used to
• change the settings on circuit breakers,
• operate tap changers on power transformers,
• supervise the position and condition of equipment, and
• telemeter the quantity of energy in a circuit or in substation equipment
The substation control house is equipped with essential components such as switchboard panels, batteries, battery chargers, supervisory control systems, power-line carriers, meters, and relays While some relay settings can be adjusted via the SCADA system, their operation remains autonomous during disturbed conditions to ensure rapid response to over-current situations This control house offers all-weather protection and security for the control equipment, with control wires connecting the panels to various substation equipment Typically, a substation control house includes several hundred meters of conduit and extensive lengths of control wire.
The E1 HEMP cable coupling and protection issue in high-voltage substations is highlighted by the figures, which illustrate the entire system from sensor-connected cables to cable runs leading to the control house and connections within The images reveal significant concerns, including cable exposure, inadequate shielding, and the absence of high-frequency grounding procedures.
Figure 5 demonstrates that cables and conduits in a high-voltage substation are directly exposed to HEMP fields Although a conduit is depicted, it lacks electromagnetic shielding for high frequencies, resulting in some coupled currents being transferred to the control cables where the conduit terminates.
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Example of Vertical exposure of CT leads in conduit on transformer
Figure 5 – Vertical conduit geometry for a current transformer (CT)
As insulated cables enter shallow below-ground trenches, they are exposed without metallic conduits or electromagnetic shields In the scenario depicted in Figure 6, the cables are grouped together in a concrete tray, positioned just below the ground surface Although a shielded metallic conduit could provide extra protection against E1 HEMP, transients would still affect the wiring from the exposed vertical cables necessary for measuring power flow in the substation.
Cl ose -up o f trenway with cov er removed - Multipl e Control Cables
Close-up of tren wa y with co ver rem oved - Multiple Control Cab les
Figure 6 – Covered shallow trench for control cables
When cables enter the control house, ground wires and mechanical shields are connected to a grounding bar, as illustrated in Figure 7 However, the long length of these high inductance grounds fails to provide a low impedance ground for E1 HEMP conducted transients, which contain frequencies in the tens of MHz range Utilizing shorter ground wires, measuring between 0.05 m and 0.1 m, would greatly diminish the HEMP transients that affect the equipment.
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Close-up of Cables from trenway being brought into Control House Junct ion Box with ground termination details
Figure 7 – Grounding of control cables at junction box
Control cables exit the junction box and are organized in the control house on elevated cable trays, as illustrated in Figure 8 Additionally, employing shielded cables within the facility and grounding the cable shields to the racks prior to penetration offers an extra layer of protection.
Metallic cable trays, while heavier than fiber trays, effectively reduce the currents flowing to equipment Additionally, utilizing shielded equipment racks or a small shielded room can help minimize electromagnetic transients that may affect the equipment.
C ontrol Ca bles ro uted v ia ca bl e tra y ins id e Su bstati on Control hous e to v arious rel ay/contro l panel s
E xam pl e of Re lay and C on trol
Figure 8 – Control cable access to equipment
To safeguard power system equipment from HEMP transients, enhancing the immunity of the facility's equipment is essential However, this approach can be challenging and costly, particularly if new equipment with higher immunity levels is required.
Not all protection concepts discussed are typically required However, implementing a variety of protective measures can effectively minimize the HEMP transients that impact the equipment.
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Telecommunication centres
To safeguard telecommunication centers and their equipment from High-Altitude Electromagnetic Pulse (HEMP), it is essential to assess the shielding effectiveness of current structures This evaluation helps identify areas that require enhanced shielding and surge protection to mitigate the HEMP threat.
The International Telecommunication Union (ITU-T) is developing Recommendation K.HEMP in TD 611 (GEN/5) to address specific challenges related to High-Altitude Electromagnetic Pulse (HEMP) This recommendation incorporates fundamental HEMP standards from the IEC 61000 series, tailored for various installations and equipment types.
The process begins by assessing the protection concept utilized in a telecommunication center, guided by IEC 61000-5-3 standards A topological evaluation follows to recommend either global or distributed protection, or potentially both Additionally, the significance of various equipment in relation to HEMP threats is analyzed, alongside establishing performance criteria for HEMP immunity testing for each piece of equipment This comprehensive analysis culminates in the creation of a design flow chart that outlines the necessary protection measures.
This method utilizes the tables from IEC 61000-6-6 to establish the HEMP radiated and conducted immunity requirements for each equipment based on a specific protection concept Subsequently, IEC 61000-4-25 provides a detailed description of the applicable test methods.
Upon completion of this process, K.HEMP evaluates the different levels of HEMP immunity tests for equipment against the requirements outlined in other ITU-T EMC recommendations The ITU-T document reveals that protection concepts offering minimal or no electromagnetic shielding for internal electronics necessitate considerably higher equipment test levels.
HEMP than for normal EMC purposes For these cases shielded racks or rooms would be recommended along with surge arresters
NOTE Since the ITU-T K.HEMP document is still under development, the summary provided in this clause will be considered sufficient at this time.
Other infrastructures
Critical infrastructures, such as power and telecommunication systems, play a vital role in the functioning of modern society These infrastructures are equipped with control centers and sensors that monitor essential resources like water, transportation, natural gas, and oil Data from these systems is transmitted through a SCADA network to ensure effective management and oversight.
Control centres will be equipped with advanced computers connected through wired and wireless networks, which are susceptible to High-Altitude Electromagnetic Pulse (HEMP) Research shows that modern personal computers are highly vulnerable to both radiated and conducted HEMP effects without adequate protection Although commercial computer centres may have different vulnerabilities compared to personal computers, they share many similar features Furthermore, control centres are particularly at risk from brief outages that can happen even at lower HEMP levels.
Many infrastructures utilize sensor and SCADA systems that lack shielding from external electromagnetic environments The controls, primarily programmable logic controllers (PLCs), are not built to endure the effects of High-Altitude Electromagnetic Pulse (HEMP) radiated and conducted environments.
PLCs for the EMP Commission [4] has clearly indicated their vulnerability to the early-time
The unique challenge of "other" infrastructures lies in their significant reliance on power and telecommunications To safeguard these infrastructures from High-Altitude Electromagnetic Pulses (HEMP), it is crucial to acknowledge the high probability of prolonged power and communication outages This factor must be taken into account alongside the direct protection of the infrastructure itself.
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[1] IEC Guide 107, “Electromagnetic compatibility – Guide to the drafting of electromagnetic compatibilty publications”
[2] J G Kappenman, L J Zanetti, W A Radasky, “Space Weather from a User’s
Perspective: Geomagnetic Storm Forecasts and the Power Industry,” EOS Transactions of the American Geophysics Union, Vol 78, No 4, January 28, 1997, pg 37-45
[3] V Greetsai, A Kozlovsky, V Kuvshinnikov, V Loborev, Y Parfenov, O Tarasov, L
Zdoukhov, “Response of Long Lines to Nuclear High-Altitude Electromagnetic Pulse
(HEMP),” IEEE Transactions on Electromagnetic Compatibity, Vol 40, No 4, pp 348-
[4] “Report of the Commission to Assess the Threat to the United States from
Electromagnetic Pulse (EMP) Attack,” Vol 1: Executive Report, 2004
[5] J Kappenman, W Radasky, “Too Important to Fail,” Space Weather Journal, Vol 3,
[6] I Erinmez, S Majithia, C Rogers, T Yasuhiro, S Ogawa, H Swahn, J Kappenman,
“Application of Modelling Techniques to Assess Geomagnetic Induced Current Risks on the NGC Transmission System,” CIGRE Paper 39-304, 2002
[7] J Kappenman, “An Overview of the Impulsive Geomagnetic Field Disturbances and
Power Grid Impacts Associated with the Violent Sun-Earth Connection Events of 29-31
October 2003 and a Comparative Evaluation with Other Contemporary Storms,” Space
[8] J G Kappenman, “Geomagnetic Disturbances and Impacts Upon Power System
Operations”, The Electric Power Engineering Handbook, 2 nd Edition: Chapter 16, edited by L Grigsby, CRC Press/IEEE Press, pages 16-1 to 16-22, 2007
[9] MIL-STD-188-125-1, “High-Altitude Electromagnetic Pulse (HEMP) Protection for
Ground-Based C41 Facilities Performing Critical, Time-Urgent Missions, Fixed
[10] “Application of requirements against HEMP to telecommunication systems,” Draft of
K.HEMP, ITU-T, Study Group 5, TD 611 (GEN/5), 23 November 2007
[11] R Hoad, A Lambourne, A Wright, “HPEM and HEMP susceptibility assessments of computer equpment,” EMC Zurich Symposium in Singapore, Singapore, February 2006
IEC 60050-151:2001, International Electrotechnical Vocabulary – Part 151: Electrical and magnetic devices
IEC 60050-441:1984, International Electrotechnical Vocabulary – Chapter 441: Switchgear, controlgear and fuses
IEC 60050-603:1986, International Electrotechnical Vocabulary – Chapter 603: Generation, transmission and distribution of electricity – Power system planning and management
IEC 60255 (all parts), Measuring relays and protection equipment
IEC 61000 (all parts), Electromagnetic compatibility (EMC)
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IEC 61000-4-33, Electromagnetic compatibility (EMC) – Part 4-33: Testing and measurement techniques – Measurement methods for high-power transient parameters
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LICENSED TO MECON Limited - RANCHI/BANGALORE, FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.