C II R E D 18th International Conference on Electricity Distribution Turin, 6-9 June 2005 RESEARCH OF SF6 GAS COMPREHENSIVELY ONLINE MONITORING DEVICE Wang Chun-Ning，Luan Kai-Ning，Liu Hong-Bo，Li Ying Nanjing Electric Power Company, Nanjing, China [email protected] INTRODUCTION SF6 circuit breaker and GIS (gas-insulated switchgear) compartment in the SF6 apparatus is not allowed to exceed are important component part in substation .The 1%; and for new 126～550kV apparatus, moisture content measurement of both density (pressure) and humidity should be measured once each 3 to 6 months, if no (micro water content) in SF6 gas is two important abnormal phenomenon found, since then once one or two conditions to guarantee the normal and safe operation of years; for 40.5～72.5kV apparatus, moisture content should the equipment. In this paper a new solution for on line be rechecked annually after they are put into operation, if monitoring of SF6 gas is proposed. The influence of normal, since then once each two or three years. pressure and temperature on-site in substation on SF6 gas is a stable inert one, and most of its decomposition humidity value is simulated and studied by the test system products formed by action of corona, spark, or arc of SF6 density and humidity under pressure state discharge may combine into SF6 gas against. The SF6 gas established in laboratory.A new hi-accurate humidity in the power supply apparatus in operation, however, senso is independently designer based on the test of contains various impurities, which and the metal material of ordinary humidity sensor. The SF6 gas digital online the apparatus body very easily combine with active monitoring device for substation on-line monitoring is particles generated in high temperature condition brought developed by combining pressure, humidity and by arc light, and produce extremely harmful solid or temperature sensors in one sensor and by digital circuit. gaseous compounds, and poisonous and corrosive gases Comparison measurement and test is performed between as well. Most of the gaseous subfluorides are poisonous, the SF6 gas digital online monitoring device and the and will threaten health of maintaining and operating measurement devices at home and abroad. In result, not personnel in case a leakage accident occurs. Therefore, only online monitoring of SF6 circuit breakers in enhancing measurement of SF6 gas in the apparatus in substations and working state of SF 6 gas in GIS may be running is of significant for safe and steady operation of realized, but also environmental pollution of SF6 may be the apparatus and personal safety. For these reasons, we reduced, safety operation level of equipment may be say measuring and processing of SF6 gas is a long-term and raised .A good foundation is laid for state-inspection of important task. equipment and no-manned in substation. TABLE 1-Allowable water content in SF6 gas in the apparatus at 20℃ Compartment With arc decomposition Without arc decomposition products, µL/L products, µL/L Acceptance value =150 =500 Allowable operation value =300 =1,000 1. SF6 GAS 1.2 Leak detecting of SF6 gas Sulfur hexafluoride (SF6) is a colorless, odorless, innoxious, and incombustilble inert gas, which is synthesized form Now what used for detecting leakage of SF6 gas at home elements sulfur and fluorine, with a specific gravity of five and abroad mainly includes leak detecting and density time of that of air. SF6 gas has very strong electronegative relays. The former consists of a probe, a detector and a property, can form an inert ion after adsorbing electron. It pump. When there is SF6 gas in air, SF6 gas will be inhaled has good arc-quenching and insulating performance, and into the detector from the probe by the vacuum pump, and can meet the requirement of transformer oil for insulation makes the diode in the detector generate corona discharge, strength at a pressure within the range 2.02×105 and and so the current in the diode is weakened. A signal of 3.04×105Pa. When SF6 is used, original insulation may soon current weakened is transformed into audible/visual sound/ be recovered after arc is quenched thanks to its excellent light alarm signal by an electronic circuit. Generally thermal conductivity under the high temperature condition speaking, now each high voltage circuit breaker is equipped and strong electron-capturing capacity. with a SF6 gas density monitoring device, that is so-called density relay, with itself. The density relays equipped on 1.1 Processing of SF6 gas ex-factory high voltage circuit breaker all are of mechanical type, with a standard gasbag, can monitor pressure of SF6 In consideration of physical properties of SF6 gas, it may be gas in the gas-chamber applying the lever principle, and a concluded that measurement of both leakage of and pressure gauge on site will show pressure, where is a moisture (water content) in SF6 gas in a SF6 apparatus is an conversion curve between pressure and density values important guaranty for normal and safe running of the available. Some units at home have developed digital online apparatus. Quality of SF6 gas must be inspected prior to density-monitoring devices, and have put them into filling, and monitored and processed during the operation practical application in the substations, realizing online of the apparatus as the provided in GB 8905-1996, The monitoring of density (pressure and temperature) of SF6 guide for processing and measuring SF6 gas in power gas. apparatus, which provides that annual leakage rate in each CIRED2005 Session 1 C II R E D 18th International Conference on Electricity Distribution Turin, 6-9 June 2005 SF6 gas and remote transmission of monitored data and 1.3 Measurement of moisture in SF6 gas alarm signal to the monitoring center under the premise of no emission of SF6 gas, and meet demand for unmanned Measurement of moisture (water content) in a gas may be substations and provide technical support to state performed by measuring relative humidity or absolute troubleshoot of SF6 circuit breakers in this way, it is humidity of the gas in the expansion method, dry and wet necessary to research and develop a SF6 gas bulb method, condensation and dew point method, lithium comprehensively online monitoring device. chloride dew point method, resistance method, capacitance method, electrolysis method, and quality method as 2.1 Establishment of a proper experimental circumstance provided in national relevant standards. As main methods used in on-the-spot measurement of water content For development of a SF6 gas comprehensively online (moisture) in the SF6 gas insulated apparatus in the power monitoring device, an experimental circumstance similar to supply system, they are electrolysis method, condensation the job site must be established, in which performance and dew point method, and resistance method, capacitance characteristic of SF6 gas in the power apparatus and its method. Now dew point meters are used in regular patrol change rule are investigated. The experimental apparatus to inspection within substations on most occasions. There are be established and connection between them are as the a few of common characteristics between them, those are, shown in Figure 2. their power supplies have to be cut off during measurement; the instrument must be regularly calibrated, so that online measurement become impossible; and it is required to discharge SF6 gas for 15 to 30 min in each measurement. Taking an experience we have performed using a DP-19 dew point meter as an example, the first ten minutes at least have to be used for drying the sampling pipeline because of moisture in the sampling pipeline. The whole measurement job will take about 45 to 55min, otherwise accurate and stable data cannot be gotten. Figure 1 shows a time vs. the value found curve obtained by DP-19 dew point meter. Therefore SF6 gas in a gas chamber will require to complement after only 2 to 3 measurements usually. Figure 2 Schematic drawing of lab test apparatus connection 2.1.1 Accurate dew point meter. A DP-19 Dew Point Meter working based on the cold-trap principle, with precision =±0.2℃, ±1 digit, is used. 2.1.2 Microwater generator. A MG-101 Microwater generator with a dew point range form -82.1℃ to 5℃, is used. 2.1.3 Pressure gage. A hi-accurate pressure gage with precision of 0.5% is used. 2.1.4 Experimental gas. Nitrogen gas and SF6 gas with moisture content below 10µL/L. In the experiment, first open the gas source (usually use Figure 1 Time vs. value found curve obtained by using DP-19 Dew Point nitrogen gas for the experiment), immediately followed by Meter opening the valves on experimental devices, to let dry N2 Besides, as a fluoride, SF6 gas is one of six greenhouse gas drive out moisture existed in the pipeline and devices. gasses provided in Kyoto Protocol to phase out. In recent After the data shown on DP-19 Dew Point Meter stabilize, years, many countries have adopted new environmentally measure the first set of data, which are humidity values in protective and monitoring measures, especially some N2 gas. The measuring process lasts for at least 6 hrs. After developed countries in Europe and America pay close this, adjust the moisture valve on the microwater generator attention to emission of the gases, such as SF6 and PFC, to let moisture from the microwater generator be added into similar to HFC in accordance with the provisions in Kyoto the experimental gas. Similarly, after the data shown on DP- Protocol. On-line monitoring and minimizing of emission of 19 Dew Pont Meter get stabile, measure the second set of SF6 gas has very profound and lasting significance no data.