Publications

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A report detailing commissioning activities for pulsed operations of the 4.5m GTEM at Sandia.

High-altitude electromagnetic pulse events are a growing concern for electric power grid vulnerability assessments and mitigation planning, and accurate modeling of surge arrester mitigations installed on the grid is necessary to predict pulse effects on existing equipment and to plan future mitigation. While some models of surge arresters at high frequency have been proposed, experimental backing for any given model has not been shown. This work examines a ZnO lightning surge arrester modeling approach previously developed for accurate prediction of nanosecond-scale pulse response. Four ZnO metal-oxide varistor pucks with different sizes and voltage ratings were tested for voltage and current response on a conducted electromagnetic pulse testbed. The measured clamping response was compared to SPICE circuit models to compare the electromagnetic pulse response and validate model accuracy. Results showed good agreement between simulation results and the experimental measurements, after accounting for stray testbed inductance between 100 and 250 nH.

This work developed a methodology for transmission line modeling of cable installations to predict the propagation of conducted high altitude electromagnetic pulses in a substation or generating plant. The methodology was applied to a termination cabinet example that was modeled with SPICE transmission line elements with information from electromagnetic field modeling and with validation using experimental data. The experimental results showed reasonable agreement to the modeled propagating pulse and can be applied to other installation structures in the future.

Sandia National Laboratories performed tests to address the potential vulnerability concerns of a coupled High-Altitude Electromagnetic Pulse (HEMP) inducing secondary coupling onto critical instrumentation and control cables in a nuclear power plant, with specific focus on early-time HEMP. Three types of receiving cables in nine configurations were tested to determine transfer functions between two electrically separated cables referenced to the common mode input current on the transmitting cable. One type of transfer function related the input short circuit current and resulting open circuit voltage on the receiving cable. The other transfer function related the input short circuit current and the resulting short circuit current on the receiving cable. A 500 A standard HEMP waveform was input into the transfer functions to calculate peak coupling values on the receiving cables. The highest level of coupling using the standard waveform occurred when cables were in direct contact, with a peak short circuit current of 85 A and open circuit voltage of 9.8 kV, while configurations with separated cables predicted coupling levels of less than 5 A or 500 V.

Sandia National Laboratories (SNL) is performing a test campaign for the Department of Energy (DOE) Office of Cybersecurity, Energy Security, and Emergency Response (CESER) to address high-altitude electromagnetic pulse (HEMP) vulnerability of critical components of generation stations, with focus on early-time (E1) HEMP. The campaign seeks to establish response and damage thresholds for these critical elements in response to reasonable HEMP threat levels as a means for determining where vulnerabilities may exist or where mitigations may be needed. This report provides component vulnerability test results that will help to inform site vulnerability assessments and HEMP mitigation planning.

The electric power grid is one of the most critical national infrastructures, and determining the susceptibility of power grid elements to external factors is of significant importance for ensuring grid resilience. Reliable energy is vital to the safety and security of society. One potential threat to the power grid comes in the form of strong electromagnetic field transients arising from high-altitude nuclear weapon detonation. The radiated EM fields from these can affect the operation of electronic components via direct field exposure or from the conducted transients that arise from coupling onto long cables. Vulnerability to these pulses for many electrical components on the grid is unknown. This research focuses on conducted pulse testing of digital protective relays in a power substation and their associated high-voltage circuit breaker circuit and instrumentation transformer circuits. The relays, yard cables, power supplies, and components representing yard equipment were assembled in a manner consistent with installation in a substation to represent the pulse's propagation in the components and wiring. Equipment was tested using pulsed injection into the yard cable. The results showed no equipment damage or undesired operations for insult levels below 180 kV peak open circuit voltage, which is significantly higher than the anticipated coupling to substation yard cables.

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A High-Altitude Electromagnetic Pulse (HEMP) is a potential threat to the power grid. HEMP can couple to transmission lines and cables, causing significant overvoltages which can be harmful to line connected equipment. The effects of overvoltages on various types of power systems components need to be understood. HEMP effects on trip coils were tested and presented in this report. A high voltage pulser was built to replicate the induced voltage waveform from a HEMP. The pulser was used to test breaker trip coils with increasing pulse magnitudes ranging from 20 kV to 80 kV. The State-of-Health of each trip coils was measured via mechanical operation and impedance measurements before and after each insult to identify any damage or degradation to the trip coils. Dielectric breakdown was observed at the conductor leads during testing, causing the HEMP insult to be diverted to the grounded casing. However, the dielectric breakdown did not cause interference with regular device operation.

Sandia National Laboratories sponsored a three-year internally funded Laboratory Directed Research and Development (LDRD) effort to investigate the vulnerabilities and mitigations of a high-altitude electromagnetic pulse (HEMP) on the electric power grid. The research was focused on understanding the vulnerabilities and potential mitigations for components and systems at the high voltage transmission level. Results from the research included a broad array of subtopics, covered in twenty-three reports and papers, and which are highlighted in this executive summary report. These subtopics include high altitude electromagnetic pulse (HEMP) characterization, HEMP coupling analysis, system-wide effects, and mitigating technologies.

This report describes broadband measurements of transmission-scale transformers typical in the electric power grid. This work was performed as part of the EMP Resilient Grid LDRD project at Sandia National Laboratories to generate circuit models that can be used for high-altitude electromagnetic pulse (HEMP) coupling simulations and response predictions. The objective of the work was to obtain characterization data of substation yard equipment across a frequency range relevant to HEMP. Vector network analyzer measurements up to 100 MHz were performed on two power transformers at ABB-Hitachi and a single ITEC potential transformer. Custom cable breakouts were designed to interface with the transformer terminals and provide ground connections to the chassis at the base of the transformer bushings. The three-phase terminals of the power transformers were measured as a common mode impedance using a parallel resistive splitter, and the single-phase terminals of the potential transformer were measured directly. A vector fitting algorithm was used to empirically fit circuit models to the resulting two-port networks and input impedances of the measured objects. Simplified circuit representations of the input impedances were also generated to assess the degree of precision needed for high-altitude electromagnetic pulse response predictions, which were performed in Sandia's XYCE circuit simulator platform. HEMP coupling simulations using the transformer models showed significant reduction in the voltage peak and broadening in the pulse width seen at the power transformer compared to the traveling wave voltage. This indicated the importance of the load condition when defining the coupled insult in an electric power substation. Simplified circuit models showed a similar voltage at the transformer with a smoothed waveform. The presence of potential transformers in the simulation did not significantly change the simulated voltage at the power transformer. Single-port input impedance models were also developed to define load conditions when transfer characteristics were not necessary.

There are concerns about the effects of High-Altitude Electromagnetic Pulses (HEMP) on the electric power grid. Activities to date tested and analyzed vulnerability of digital protective relays (DPRs) used in power substations, but the effect of HEMP on the greater substation environment is not well known. This work establishes a method of testing the vulnerability of circuit breaker control and protective relay circuits to the radiated E1 pulse associated with HEMP based on coupling to the cables in a substation yard. Two DPRs from Schweitzer Engineering Laboratories, Inc. were independently tested. The test setup also included a typical cable in a substation yard with return plane to emulate the ground grid and other ground conductors near the yard cable, cabinetry housing the installed DPRs, station battery and battery charger, terminal block elements, and a breaker simulator to emulate a substation yard configuration. The DPRs were powered from the station battery and the transformer inputs energized with a three-phase source to maintain typical operating conditions during the tests. Vulnerability testing consisted of a conducted E1 pulse injected into the center of the yard cable of the DPR circuits. Current measurements on the yard cable and DPR inputs indicated significant attenuation of the conducted pulse arriving at the control house equipment from the emulated substation yard. This reduction was quantified with respect to the equivalent open-circuit voltage on the yard cable. No equipment damage or undesired operation occurred on the tested circuits for values below 180 kV, which is significantly higher than the anticipated coupling to a substation yard cable.

The electric power grid is one of the most critical infrastructures in the modern world, and the continued protection and resilience of this system from threats is of significant concern. One such set of threats is nanosecond-scale transient effects generated by high-altitude electromagnetic pulses, for which the effect on the power grid is still being studied. Lightning surge arresters serve as the current grid protection against fast transients but are designed and modeled for protection against lightning and switching transients. Surge arrester response to faster transients is not well known. This work defines a scalable metal-oxide surge arrester model with specific consideration to frequencies attributed to fast transient overvoltages from electromagnetic pulses. Measurements using vector network analyzer sweeps at low and high bias as well as high-voltage I-V curve traces are presented to define arrester behavior and to parameterize it from measurement data. The proposed model is compared to the standard IEEE model for lightning arresters in this paper. Furthermore, model parameters are defined by scalable terms to be easily implemented for transmission-level devices. The scalable model enables enhanced assessment of protection levels and grid susceptibility against fast transients.

High-altitude electromagnetic pulses pose an unknown risk to the electric power grid, and the vulnerabilities will continue to arise as the structure and needs of the grid change. This is especially true with the increasing prevalence of renewable energy sources. This work investigates the vulnerability of photovoltaic modules to E1-like radiated environments with maximum field levels exceeding 100 kV/m. State of health checks via I-V curve trace measurements and physical inspection indicated no readily observable damage or degradation of the module behavior after multiple field exposures. Any variation in I-V curve data was attributable to ambient conditions at the time of measurement and was reflected in similar measurements of the experimental control. Follow-up measurements with a calibrated light source showed that all modules aligned with the experimental control and exceeding the manufacturer ratings for fill factor and efficiency, implying that no damage was incurred from field exposure. Coupled current measurements were also performed over the course of testing, showing a damped sine response in common mode and double exponential response in differential mode. The responses were observed to scale with incident field and were dependent on the module orientation.

High-altitude electromagnetic pulses pose an unknown risk to the electric power grid, and the vulnerabilities will continue to arise as the structure and needs of the grid change. This is especially true with the increasing prevalence of renewable energy sources. This work investigates the vulnerability of photovoltaic modules to E1-like radiated environments with maximum field levels exceeding 100 kV/m. State of health checks via I-V curve trace measurements and physical inspection indicated no readily observable damage or degradation of the module behavior after multiple field exposures. Any variation in I-V curve data was attributable to ambient conditions at the time of measurement and was reflected in similar measurements of the experimental control. Follow-up measurements with a calibrated light source showed that all modules aligned with the experimental control and exceeding the manufacturer ratings for fill factor and efficiency, implying that no damage was incurred from field exposure. Coupled current measurements were also performed over the course of testing, showing a damped sine response in common mode and double exponential response in differential mode. The responses were observed to scale with incident field and were dependent on the module orientation.

Abstract not provided.

This report details the test setup, process, and results for radiated susceptibility testing of multicrystalline silicon photovoltaic (PV) modules as part of the EMP-Resilient Electric Grid Grand Challenge Laboratory Directed Research and Development (LDRD) project at Sandia National Laboratories. Testing was conducted over October 10-17, 2019, where 8 photovoltaic modules were exposed to E1 transient pulses with peak field levels up to 100 kV/m. Modules were terminated in a resistive load representing connected components. State of health testing conducted via I-V curve tracing of the photovoltaic modules showed no observable loss of device function due to large electric field transients. Differential mode currents were measured on the order of 10's of amps for up to a microsecond following the radiated field pulse. Common mode currents took the form of a damped sinusoid with a maximum peak of 10's to 100's of amps with a resonance near 60 MHz.