VLF/LF High-Voltage Design and Testing

Hansen, P.; Watt, A. D.

doi:10.21236/ada526052

Cited by 14 publications

(15 citation statements)

References 55 publications

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“…The critical breakdown gradient for a 1.5-inch-diameter pin in air is 22.6 kV/cm [10]. The calculations indicated that the gradient on the pin inside the insulator cap, with enough oil removed to partially expose the pin to air, was 6.3 E-4 kV/cm/Kv.…”

Section: Discussionmentioning

confidence: 96%

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Impulse Flashover Tests at Edgar Beauchamp High Voltage Test Facility, Dixon, California, in Support of Cutler Insulator Failure Investigation

Hansen¹,

Dann²

2006

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EXECUTIVE SUMMARYThe Naval Radio Transmitting Station, Cutler, Maine, has experienced four insulator failures in the last decade. All are believed to be the result of lightning strikes to the antenna. The insulators that failed are fiberglass-belted safety core insulators that had been installed in the late 1990s. An investigation into these failures was undertaken in order to understand the cause of the failure and the implications to other sites having the same type of insulator. At the same time, the Navy has initiated a procurement program to replace the safety core insulators at Cutler with fail-safe insulators. The first array insulators will be replaced in the summer of 2007 and the second in the summer of 2009. The cost of this replacement is significant.The safety core insulators were tested at VLF voltage prior to their installation at Cutler, but they were not tested with impulses. All flashovers in the VLF tests occurred in the air between the corona rings. As a part of the investigation, impulse tests were done at Hydro Quebec; the tests showed that flashover occurred along the surface of the insulator when the voltage rises very fast (high dV/dt). Flashover along the surface is believed to be the primary cause of damage to the safety core insulators. Our conjecture is that making the design such that the flashover takes place in the air will protect the insulator.We used a scale model insulator to investigate the flashover phenomenon using an impulse generator owned by the Navy. The objective was to see if different corona ring configurations could keep flashover away from the insulator body. The IG was successfully activated and generated impulses up to 1.2 MV with peak times as short as 0.6 µs and up to 20-kAmp peak currents. The glaze on a small safety core insulator was melted at these current levels. Flashovers along the surface initiated from the region around the triple point at the ground end of the insulator body when that area was not well shielded. One tentative conclusion is that symmetrical grading is required on both ends of the insulator to protect the insulator body from high dV/dt impulses.The scale model tests were performed with several corona ring configurations, including the unsymmetrical one installed at Cutler. These tests showed that the flashover path can be kept away from the insulator body by bringing corona rings closer together, although this reduces the VLF withstand voltage of the insulator. Symmetrical corona ring configurations with spacing up to 2/3 of the total insulator length always flashed in the air. Non-symmetrical configurations having the small (Cutler) corona ring at the ground end flashed along the insulator surface at high values of dV/dt. The surface flashovers seemed to initiate from the triple point at the ground end of the insulator body and terminated on the high-voltage end corona ring when that triple point was well shielded.A limited set of configurations was tested. The test results were promising, indicating these insulators can be protected f...

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Section: Discussionmentioning

confidence: 96%

“…Arc initiation is a function of the electric field on the electrodes at ends of the insulator [10]. Once initiated, the arc then propagates across the gap with a finite velocity.…”

Section: Basis For Scale Model Testingmentioning

confidence: 99%

Impulse Flashover Tests at Edgar Beauchamp High Voltage Test Facility, Dixon, California, in Support of Cutler Insulator Failure Investigation

Hansen¹,

Dann²

2006

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“…The corona limit is determined by the critical surface electric field on the wires for corona onset E c . The value of E c is a function of the radius of curvature of the object and is nearly independent of frequency from DC up to MF [15]. The surface electric field on a thin antenna conductor is given by, q l /2πε 0 a, where q l is the charge density along the wire.…”

Section: Radiated Power Limitationsmentioning

confidence: 99%

Terrestrial antenna for high power VLF radiation into the magnetosphere

Hansen¹

2014

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS)

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The radiated power limitations for VLF horizontal half-wave dipoles located above the Earth have been examined to determine the feasibility of using such a source to investigate wave-particle interactions in the magnetosphere. It is found that as the antenna approaches ground the maximum radiated power limits for the dipole are significantly reduced over the value for free space. The reduction is a strong function of the conductivity being less for lower conductivity. The primary reason for the reduction is lowered radiation resistance. A secondary reason is the reduction in resonant frequency from dielectric loading which increases the charge density on the antenna by the ratio of frequency reduction squared. The radiation efficiency is also greatly reduced by the presence of the Earth, however this does not affect the radiated power limit but does increases the transmitter power required. For a practical system it will be important to find a location with low ground conductivity.

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“…6. ) [4]. Power transmission lines are often designed to operate in corona, especially during inclement weather.…”

Section: Design Considerations and Analysis Techniquementioning

confidence: 99%

“…Power transmission lines are often designed to operate in corona, especially during inclement weather. However, since the energy dissipated in corona is proportional to the frequency it is not practical to operate in corona at VLF and higher frequencies [4].…”

Section: Design Considerations and Analysis Techniquementioning

confidence: 99%