Carlos T. Mata

Direct Lightning Strikes to the Lightning Protective System of a Residential Building: Triggered-Lightning Experiments

Lightning triggered from natural thunderclouds using the rocket-and-wire technique was employed in order to subject to direct lightning strikes the lightning protective system of a test house at the Intemational Center for Lightning Research and Testing (ICLRT) at Camp Blending, Florida. The electrical circuit of the test house was connected to the secondary of a padmount distribution transformer located a distance of about 50 m from the house. The transformer primary was connected to a 650-m long unenergized underground power cable. The test house had two ground rods, one for the lightning protective system grounding and the other for the power supply system grounding. The two rods were about 3 m apart and were connected by a metallic cable. Lightning current was injected into the lightning protective system ground rod, and the currents and voltages at different points in the test system were measured. The waveshapes of currents in the ground rods of the test house differed markedly from the current waveshapes in other parts of the overall system. The ground rods at the test house appeared to filter out the higher-frequency components of the lightning current, allowing the lower-frequency components of the current to enter the houses electrical circuit; that is, the ground rods appeared to exhibit a capacitive behavior rather than the often expected resistive behavior. This effect was observed for dc grounding resistances of the rods (driven in sandy soil with conductivity of about 2.

Triggered lightning testing of an airport runway lighting system

The interaction of rocket-triggered lightning with an airport runway lighting system has been studied. The lighting system included a buried counterpoise with attached vertical ground rods for protection of the series lighting cable from lightning. Experimental data for voltages and currents at various locations in the runway lighting system due to direct lightning strikes are presented along with the causative lightning current. The data include the first measurements of the responses of an underground bare conductor (counterpoise) to direct lightning strikes. These measurements can serve as ground truth for the testing of the validity of various counterpoise models.

EMTP modeling of a triggered-lightning strike to the phase conductor of an overhead distribution line

A triggered-lightning experiment and EMTP modeling of that experiment are used to study the responses of a two-conductor overhead power line to a direct lightning strike. The experiment was conducted at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, FL. The lightning was artificially initiated (triggered) from a natural thundercloud using the rocket-and-wire technique, and its current was directed to the phase conductor. EMTP modeling of the line behavior yields results that are generally consistent with the measurements.

Measurement of the division of lightning return stroke current among the multiple arresters and grounds of a power distribution line

A triggered-lightning experiment was conducted during the summer of 2000 at the International Center for Lightning Research and Testing (ICLRT) in north-central Florida for the purpose of studying the lightning current division in an 829 rn long, 18-pole, three-phase plus neutral, unenergized, overhead distribution line equipped with six arrester stations. Eight lightning flashes containing a total of 34 recorded return strokes, as well as low amplitude, long duration steady currents, were artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique, and the flash currents were directed to phase C (the outermost conductor of the three-phase cross-arm-configured line). Six of the eight triggered lightning flashes caused damage to one of the two closest phase C arresters. In the case when no arrester was damaged or was not yet damaged by current in the flash, it is inferred that about 40% of the return stroke peak current and about 25% or more of the return stroke charge transferred in the first millisecond passed to the neutral conductor through each of the two closest arresters on either side of the strike point. The bulk of the peak current then flowed from the neutral conductor to ground through the groundings of the two closest arresters. The charge transferred in the first millisecond from the neutral to the eight system groundings, six at arrester stations and one at each of the two line-end poles, appears to be distributed inversely to the low-frequency, low-current grounding resistances.

A Kennedy Space Center implementation of IEEE 1451 networked smart sensors and lessons learned

To meet the need for more specific and reliable information from ground support instrumentation systems and future spacecraft sensors and to support intelligent health management systems (IHMS), NASAs Instrumentation Branch and ASRCs Advanced Electronics and Technology Development Laboratory at Kennedy Space Center (KSC) have consulted the IEEE 1451 family of smart-sensor standards to develop smart network elements (SNEs). SNEs provide reliable signal conditioning to raw sensors, complex data processing, and communication capabilities with a light implementation of the IEEE 1451 family of standards. They are capable of assessing the health of the raw sensors and the electronics and the reliability and tolerance of the measurement, and they relay this information to higher-level systems. The KSC SNEs employ a scaled-down version of the IEEE 1451.1 object model for smart sensors. The sensors are capable of publish-subscribe and client-server communication over an Ethernet network using a custom on-the-wire transmission format that is bandwidth-conservative. KSC, together with NASA Stennis Space Center, has also implemented a user-defined transducer electronic data sheet (TEDS) to store health information about the sensor, defined as the health electronic data sheet (HEDS). The KSC SNEs expand upon the IEEE 1451 family of standards to include a well-defined communication protocol for high-level sensor-to-sensor interaction and a HEDS structure for passing relevant health data over the network

Direct Lightning Strikes to Test Power Distribution Lines—Part II: Measured and Modeled Current Division Among Multiple Arresters and Grounds

The division of return stroke current among the arresters and groundings of two unenergized test distribution lines, one horizontally configured and the other vertically configured, was studied at the International Center for Lightning Research and Testing in Florida. The division of return stroke currents for the vertically configured line was initially similar to the division on the horizontally configured line: at the time the return stroke current reached peak value (after one microsecond, or so) the two closest arresters/grounds on both lines passed about 90% of the total current. However, the time during which the return stroke current flowed primarily through the closest arresters to the neutral conductor was significantly shorter on the vertically configured line. On that line, the arrester current was about equally divided among all four arresters after several tens of microseconds. The arrester current division as a function of time measured on the vertical line was successfully modeled using the published VI-characteristic, while the division on the horizontal line after some tens of microseconds was only successfully modeled if the residual voltage of the two arresters closest to the current injection point was reduced by 20%. Based on the triggered lightning current division observed on our line, the minimum energy absorbed in each of the two arresters closest to the strike point during a typical natural first stroke is estimated to be 40 kJ.

A new comprehensive lightning instrumentation system for pad 39B at the Kennedy Space Center, Florida

A new comprehensive lightning instrumentation system has been designed for Launch Complex 39B at the Kennedy Space Center, Florida. This new instrumentation system includes the synchronized recording of six high-speed video cameras; currents through the nine downconductors of the new lightning protection system; four dH/dt, 3-axis measurement stations; and five dE/dt stations composed of two antennas each. The instrumentation system is composed of centralized transient recorders and digitizers that are located close to the sensors in the field. The sensors and transient recorders communicate via optical fiber. Sensor outputs are sampled by fiber-optic digitizers, which transmit the digitized data to transient recorders via fiber optics. The transient recorders are triggered by the dH/dt sensors, the dE/dt sensors, or the current through the downlead conductors. The high-speed cameras are triggered by the trigger output of one of the transient recorders when any of the recorders perceive a qualified trigger.

Direct lightning strikes to the lightning protective system of a residential building: triggered-lightning experiments

Summary form only given. Lightning triggered from natural thunderclouds using the rocket-and-wire technique was employed in order to subject to direct lightning strikes the lightning protective system of a test house at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, USA. The electrical circuit of the test house was connected to the secondary of a padmount distribution transformer located a distance of about 50 m from the house. The transformer primary was connected to a 650-m long unenergized underground power cable. The test house had two ground rods, one for the lightning protective system grounding and the other for the power sup. ply system grounding. The two rods were about 3 m apart and were connected by a metallic cable. Lightning current was injected into the lightning protective system ground rod, and the currents and voltages at different points in the test system were measured. The waveshapes of currents in the ground rods of the test house differed markedly from the current waveshapes in other parts of the overall system. The ground rods at the test house appeared to filter out the higher frequency components of the lightning current, allowing the lower frequency components of the current to enter the houses electrical circuit, that is, the ground rods appeared to exhibit a capacitive behavior rather than the often expected resistive behavior. This effect was observed for DC grounding resistances of the rods (driven in sandy soil with conductivity of about 2.5 /spl times/ 10/sup -4/ S/m) ranging from more than a thousand ohms to some tens of ohms. The peak values of: (1) the current entering the test houses electrical circuit; (2) the current flowing to the distribution transformer secondary neutral; and (3) the current flowing through the surge protective devices at the test houses service entrance were observed to be greater than in either of the two scenarios suggested by the International Electrotechnical Commission.

Fiber-optic sensor for aircraft lightning current measurement

An electric current sensor based on Faraday rotation effect in optical fiber was developed for measuring aircraft lightning current. Compared to traditional sensors, the design has many advantages including the ability to measure total current and to conform to structure geometries. The sensor is also small, light weight, non-conducting, safe from interference, and free of hysteresis and saturation. Potential applications include characterization of lightning current waveforms, parameters and paths, and providing environmental data for aircraft certifications. In an optical fiber as the sensing medium, light polarization rotates when exposed to a magnetic field in the direction of light propagation. By forming closed fiber loops around a conductor and applying Amperes law, measuring the total light rotation yields the enclosed current. A reflective polarimetric scheme is used, where polarization change is measured after the polarized light travels round-trip through the sensing fiber. The sensor system was evaluated measuring rocket-triggered lightning over the 2011 summer. Early results compared very well against a reference current shunt resistor, demonstrating the sensors accuracy and feasibility in a lightning environment. While later comparisons show gradually increasing amplitude deviations for an undetermined cause, the overall waveforms still compared very well.

Evaluation of the performance characteristics of CGLSS II and U.S. NLDN using ground-truth data from Launch Complex 39B, Kennedy Space Center, Florida

A new comprehensive lightning instrumentation system has been designed for Launch Complex 39B (LC39B) at the Kennedy Space Center (KSC), Florida. This new instrumentation system includes seven synchronized high-speed video cameras, current sensors installed on the nine downconductors of the new LC39B lightning protection system (LPS); four dH/dt, 3-axis measurement stations; and five dE/dt stations composed of two sensors each. The LPS received 8 direct lightning strikes (a total of 19 strokes) from March 31 through December 31 2011. The measured peak currents and locations are compared to those reported by the Cloud-to-Ground Lightning Surveillance System (CGLSS II) and the National Lightning Detection Network (NLDN). Results of comparison are presented and analyzed in this paper.