Abstract
This paper uses practical experimentation to analyse the effect of replacing SF6 with pure CO2 in conventional gas insulated transmission line sections by studying partial discharge measurements taken with applied voltages up to 242 kV (rms). The results can also help in understanding the properties of new alternative gas mixtures which can be utilised with a ratio of up to and over 95% CO2. The experiments undertaken involved filling a gas insulated line demonstrator with 3 bars of CO2 and applying voltages up to 242 kV in both clean conditions and particle-contaminated enclosure conditions. The results demonstrate that CO2 can be used to insulate gas equipment without breakdown at high voltage, however, a higher gas-filling pressure may be needed to reduce the partial discharge found in the tests presented in this paper. Another aspect of the work showed that partial discharge (PD) measurements from internal ultra-high frequency (UHF) sensors compared with a direct measurement from a capacitive divider both clearly showed the effect of contaminating particles in CO2. However, the PD divider measurements also showed considerable external PD on the outside of the gas compartment, leading to the conclusion that UHF sensors are still regarded as having the highest sensitivity and noise immunity for gas insulated switchgear (GIS) or gas insulated transmission line (GIL) systems including when the equipment is insulated with CO2.
Highlights
The use of gas insulated busbars (GIB) and transmission lines (GIL) is common practice within the high voltage power industry when insulated with compressed sulphur hexafluoride (SF6 ) gas to enable compact electrical substations and transmit large amounts of energy across large distances or in urban locations or hard-to-reach areas such as underground river crossings that overhead power lines may not be able to facilitate
Considering the IEC/BS EN standard 62771-203 [13] and 62271-204 [14], which recommend the same method for partial discharge detection for both gas insulated transmission lines and switchgear, the test voltages shown in Table 2 were used for practical testing to show system rating voltage responses
The rest of the AC cycle shows lower partial discharge (PD) levels averaging less than or approximately 10 pC, even though this gas insulated equipment is filled with CO2 instead of SF6 which has a much higher dielectric strength
Summary
The use of gas insulated busbars (GIB) and transmission lines (GIL) is common practice within the high voltage power industry when insulated with compressed sulphur hexafluoride (SF6 ) gas to enable compact electrical substations and transmit large amounts of energy across large distances or in urban locations or hard-to-reach areas such as underground river crossings that overhead power lines may not be able to facilitate. Current research efforts are focusing on the replacement of SF6 with alternatives such as C4 F7 N [4,5], C5 F10 O [6,7] and CF3 I [8,9] in relatively small mixture quantities (1–30%) as a partial pressure gas mixture with large quantities of CO2 (up to 95%) as a buffer gas making up a component gas mixture of two or three gases It is, important that the partial discharge characteristics within high voltage gas insulated transmission lines (GIL), busbars and gas insulated switchgear (GIS). It is useful to note that studying of insulation performance of the system as a whole and a method, in this research, of assessing the the effects of pure CO2 is beneficial considering that the alternative mixtures have gases that degrade use of CO2 as a direct replacement for SF6 in practical GIB and GIL. Production processes ordercould to capture store emitted global of CO2 from other processes in order to capture and usefully store otherwise emitted global warming gases.Test Arrangement and Methods
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