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Induced current estimation algorithm of gas insulated line
(2018-07-02)
Thungsook, K.
;
Sontayananon, N.
;
Chuayin, C.
;
Nganpitak, T.
;
Chamnong, C.
This paper presents the analysis of induced voltage and induced current in enclosure pipe of three-phase gas-insulated transmission line. The induced current and induced voltage are carried out so that generalized mathematical model can be obtained. The current is derived based on electromagnetics theory. The estimated results are compared with the measured results. The highest error from the comparison between the computed and actual data is 12.89% because a large amount of induced current cannot be measured accurately.
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Computation program for breakdown voltages of a gas insulation under different pressures and slightly nonuniform electric fields
(2018-07-02)
Chamnong, C.
;
Chuayin, C.
;
Nganpitak, T.
;
Sontayananon, N.
;
Kittiratsatcha, S.
This paper proposes a program for computing the breakdown voltage of a gas insulation under slightly nonuniform electric field. The development of the program is based on the knowledge of gas ionization and streamer breakdown theories, so it can compute the breakdown voltage of an ideally-simulated gas-insulated system, under a certain gas pressure level that the streamer constant is known. To verify this program, several simulations of sphere-sphere electrode systems were made using COMSOL Multiphysics with differences in sphere dimensions and gap spacings referred from IEC-60052 standard. Then the AC breakdown voltage of each simulation was computed using the breakdown voltage computation function under the pressure of 101.3 kPa according to the standard. Next, the computed AC breakdown voltages were compared with the AC breakdown data from the standard. The differences between the computed and the standard AC breakdown voltages were less than 3% in all simulated cases. Then the program was developed further by creating a new function that could estimate the streamer constant of a practical gas-insulated system under various gas pressure levels and slightly nonuniform electric field. Since the streamer constant of a practical gas-insulated system with any gas pressure level could be estimated using the streamer constant estimation function, the breakdown voltage of any practical gas-insulated system should be able to be computed pragmatically. To verify the ability to compute the breakdown voltage of a practical gas-insulated system, several practical gas-insulated systems with slightly nonuniform electric field were set up under certain gas pressure levels. Then several simulations were made to represent the practical gas-insulated system those were set up. Next, the streamer constant of each simulation was estimated using the developed streamer constant estimation function. After that, the gap spacings of both practical and simulated systems were changed. Then AC breakdown test was conducted on each practical system, while AC breakdown voltage of each simulated system was computed using the breakdown voltage computation function. Finally, the computed breakdown voltages were compared with the breakdown voltages those were practically tested. The comparison was satisfactory with less than 3% differences between the computed and the tested AC breakdown voltages in all cases.
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Breakdown characteristics and partial discharge phenomena of gas-insulated system under slightly nonuniform electric field with floating object
(2018-07-02)
Chuayin, C.
;
Chamnong, C.
;
Sontayananon, N.
;
Kachachaveevong, T.
;
Nganpitak, T.
The characteristics of breakdown voltage of air under slightly non uniform field with floating object was investigated experimentally. The sphere-plane electrodes with sphere diameter of 4.5 cm and plane diameter of 10 cm were used to study. The gap spacing between the sphere-plane electrodes was fixed at 3 cm. In this paper, the floating objects were divided into 2 types according to types of materials used, i.e., aluminum material represents a conductive particle and plastic material represents a nonconductive particle. The floating object position was varied between the sphere-plane electrodes in the test chamber. It was found that both types of floating objects clearly had negative effect on the breakdown voltage. Moreover, to more understand the effect of these floating objects, an ultra-high frequency sensor was used to detect partial discharge signal occurring during the experiment before breakdown occurred.
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Experience of a partial discharge problem of electrical cables in power plant
(2018-07-02)
Kongdang, P.
;
Nganpitak, T.
;
Sontayananon, N.
;
Chamnong, C.
;
Chuayin, C.
This paper represents a Partial Discharge ("PD") problem occurred in 6.6 kV electrical cable systems in a power plant. During annual switch gear and cable termination box inspection, some parts of electrical cables were identified as burned. Using electromagnetic and PD theory, the burned electrical cables were caused by the touching and pressing of different phase cables with inadequate clearance space. The initial solutions were rearranging the cables, using heat shrink tube for jacketing to improve the cable insulation. Inspection window was installed for PD measurement with Transient earth voltage method. Periodical PD monitoring has been performed to follow up whether new cable rearrangement can reduce the problem. The core of this problem could be better and deeper understood by Root Cause Analysis (RCA). Extension of busbar, enlargement of the cable box for better arrangement and addition of environmental control was later applied with a satisfactory outcome.

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