FRP hot stick flashovers during EHV live line work
24 Nov 2003-pp 7-11
TL;DR: In this paper, a FRP hot stick was found to flash over during live line work at 550 kVac in 2002 and a second flashover occurred during live-line work at 650 kVAC in 2002, both occurred during work from the tower on "v" suspension insulators.
Abstract: In 1997 a FRP hot stick flashed over during live line work at 550 kVac. A rigorous maintenance program was instituted and all FRP hot sticks used in live line work must now withstand an annual dielectric test at 105 kVdc per 305 mm with the surface wet consistent with IEEE Std 978. More frequent electrical tests are made using a hand held tester and limits have been set for the hydrophobicity of the surface. In spite of these measures a second flashover a FRP hot stick occurred during live line work at 550 kVac in 2002. Both flashovers occurred during work from the tower on "v" suspension insulators, the first at a temperature near the freezing point and the second at a temperature well below freezing. In both cases the wind was blowing from the conductor to the worker. Our investigation is trying to establish an adequate explanation for these events as well as corrective measures. The work to date is summarized in this paper. Industry standards for limits of approach are based on the switching surge withstand of air gaps and should not be equated to the minimum safe leakage distance of FRP hot sticks.
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TL;DR: In this article, a three-dimensional electric field calculation model of a fiber glass-reinforced plastic (FRP) hot stick during live-line work based on the finite element method is proposed to account for the geometry of the Manitoba site incidents at 500-kV.
Abstract: The three-dimensional FEM electric field calculation model of a fiber glass-reinforced plastic (FRP) hot stick during live-line work, which was elaborated in a previous study, could well explain some features of the flashovers that occurred during a series of cold fog tests at CIGELE. These tests have achieved the most reliable reproduction of four separate FRP hot stick flashover incidents in Canada at a voltage stress of 105 kV/m at -1.04°C, Relative Humidity (RH) of 109 % with visible fog and 2.8 μg/cm 2 Equivalent Salt Deposit Density (ESDD). However, at the incident site, the geometry is different from that of the laboratory tests. In this paper, a three-dimensional electric field calculation model of a FRP hot stick during live-line work based on the finite element method is proposed to account for the geometry of the Manitoba site incidents at 500-kV. Moreover, the influence of the tower, phase conductors and shield wires on the potential and electric field distribution around an FRP hot stick during live-line work is studied.
20 citations
Cites background or methods from "FRP hot stick flashovers during EHV..."
...They occurred at 500-kV ac line voltage working stress (9596 kV/m) in 1997 and 2002 in Manitoba [5-7] and at 230-kV ac line voltage working stress (71 kV/m) twice in 2012 in Saskatchewan [8]....
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...Figure 2 shows a re-enactment of this step of the work method [6]....
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...Thereafter many tests were carried out at Manitoba Hydro, Hydro-Quebec Research Institute (IREQ), Kinectrics and CIGELE to reproduce the flashovers [5-14]....
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...Re-enactment of the 2002 flashover experienced at Manitoba Hydro [6]....
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TL;DR: In this article, the potential and electric field distribution along a fiberglass reinforced plastic (FRP) hot stick under dry condition and non-uniform wetting were determined using a commercial software, COMSOL MultiphysicsTM.
Abstract: In February and December 2012, SaskPower experienced two flashovers of "clean" Fiberglass-Reinforced Plastic (FRP) hot stick during cold weather live-line work under steady-state 230 kV ac system conditions. As for SaskPower, Manitoba Hydro had two separate live-line tool flashover events, in 1997 and 2002. Clean-fog tests and non-uniform wetting tests at Hydro-Quebec Research Institute (IREQ), and cold-fog tests at Kinectrics and UQAC were carried out to explain these flashovers. The laboratory tests demonstrated that inadvertent contamination of clean tools at a very light level () of Equivalent Salt Deposit Density (ESDD) likely reduced voltage withstand capability of FRP hot sticks, particularly under freezing conditions. The flashover mechanism was identified when surfaces become fully wetted by the environment or surrounding fog. However, the source of moisture in field flashovers well below 0°C, i.e. as low as -19°C, was not identified. This study is based on laboratory tests and on using available pollution flashover models to explain the results. In this paper, the main objective is to determine the potential and electric field distribution along a FRP hot stick under dry condition and non-uniform wetting. A commercial software, COMSOL MultiphysicsTM, based on the finite element method (FEM), was used for the three-dimensional modeling and simulations. The results obtained will be useful to improve knowledge on the determination of discharge initiation conditions based on electric field distributions along a FRP hot stick.
16 citations
Cites background from "FRP hot stick flashovers during EHV..."
...The ambient temperature, relative humidity, average wind speed and the peak wind speed (gusts) measured at the work site at ground level were -13°C, 46%, 22 km/hr and 28 km/h, respectively[5, 12]....
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...the 2002 flashover led to the conclusion that ESDD could no longer be considered “clean” [5, 6]....
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...These four incidents led to a series of tests at IREQ, Kinectrics and UQAC to investigate factors that may have contributed to the flashovers [4-14]....
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...9 km from Dorsey under steady-state system condition and at the peak of the negative half-cycle of voltage waveform [5]....
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...Even after the flashover, most of the surface was still in good condition except for scratches that were caused when the stick fell to the ground [5]....
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19 Sep 2004
TL;DR: In spite of improvements in the maintenance and testing of the hot sticks, a second flashover occurred during live line work at 550 kV AC in 2002 and a low level of surface pollution is believed to have been the cause of the more recent flashover as mentioned in this paper.
Abstract: In 1997 a FRP hot stick flashed over during live line work at 550 kV AC. In spite of improvements in the maintenance and testing of the hot sticks, a second flashover occurred during similar work in 2002. A low level of surface pollution is believed to have been the cause of the more recent flashover. Laboratory tests have shown that the leakage distance of the FRP hot stick needs to be substantially greater than the minimum air gap approach distance.
14 citations
Abstract: A coupled computational fluid dynamics (CFD) and heat-transfer model for an ice-covered fiberglass-reinforced plastic (FRP) hot stick, elaborated in a previous study, could well explain why the flow of partial-discharge current could be sufficient to raise the temperature of an iced pollution layer just below freezing, where the cold-fog flashover mechanism prevails. However, the ice-covered hot stick was modeled as a solid “ice rod” having an equivalent cross section of ice, meaning that the exposed ice surface is smaller in the model compared to reality. In addition, the simulations were performed for a relatively low wind speed of 1 m/s, while average wind speeds of 6.1–14.4 m/s were reported for the two Manitoba flashovers. Both of these problems are addressed in this paper to deal with the site incident conditions. The ice cover is considered as a thin layer having a thickness of 1 mm on the FRP hot stick. The effects of wind speeds of 0.1–15 m/s and wind direction as parallel and perpendicular to the ice-covered FRP hot stick are studied. This paper also presents experimental investigations on the most reliable reproduction of four separate FRP hot stick flashover incidents in Canada achieved at CIGELE laboratories.
13 citations
Cites background from "FRP hot stick flashovers during EHV..."
...78 m/s, respectively, measured at the work site at ground level [4], [7]....
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09 Jun 2008
TL;DR: In this paper, a flashover mechanism has been identified that can occur at moderate values of relative humidity, with very low values of surface leakage current under direct voltages of negative polarity at gradients as low as 111 kVdc/m.
Abstract: During the investigation of the flashover of FRP surfaces a flashover mechanism has been identified that can occur at moderate values of relative humidity, with very low values of surface leakage current under direct voltages of negative polarity at gradients as low as 111 kVdc/m. A method has been developed to reliably generate such flashovers. The effectiveness of a preventive measure has been demonstrated.
11 citations
Cites background from "FRP hot stick flashovers during EHV..."
...As reported in [1], [2] two flashovers have occurred during work with FRP hot sticks at 550 kVac....
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References
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TL;DR: In this paper, the authors describe the live line work which was being done, the weather and the condition of the hot stick, and a series of tests were made to investigate factors which may have contributed to the flashover.
Abstract: In October 1997 Manitoba Hydro experienced the flashover of a FRP hot stick during live line work at 500 kV AC. The paper describes the live line work which was being done, the weather and the condition of the hot stick. A series of tests were made to investigate factors which may have contributed to the flashover. The adequacy of available tests for FRP hot sticks is discussed. The corrective measures which have been taken prior to resuming work of this type are described.
23 citations