Keywords power system; electrical equipment; high-voltage test; problems; measures
For the power system, high-voltage test should be carried out in due course, so as to ensure the safe operation of the power system, at present, the high-voltage test is the detection of high-voltage electrical equipment is the main means of testing, mainly including: operating wave, full-wave impact, cut-off wave impact, partial discharge and other tests, which can be used to test the performance, insulation status and other characteristics of the electrical equipment of the power system. It can detect the performance of electrical equipment, insulation status and so on. However, high-voltage tests are often conducted at different times and in different locations, and each high-voltage test has uncertainty factors. Therefore, it is easy to appear some problems and hidden dangers.
1. High-voltage test problems
1.1 attention to electric shock
In the high-voltage test, in addition to cutting off the equipment, all possible incoming power supply, but also with the test power supply to the test equipment to strengthen the voltage to achieve the test purpose. Test equipment before and after the pressurization to frequent dismantling of wiring, a large capacitance or electrostatic induction of the test equipment, but also after the test discharge or grounding. The test equipment is generally higher than the operating voltage of several times the voltage, and the test wire is bare. Therefore, high-voltage electrical test work is more dangerous than general electrical equipment maintenance work. Test process of electric shock and electric injury accidents can be divided into the main reasons:
(1) no test equipment and other equipment is clearly separated, resulting in accidental contact with the charged equipment. (2) No reliable power supply chain and access control system, personnel mistakenly test area. (3) Violation of operating procedures when connecting and exchanging conductors during the test, and failure to conduct away the residual current. (4) During the test, the idle capacitor equipment is not short-circuited and grounded. (5) When reversing the wiring of the pressurized test, the regulator is not retreated to zero position, or the reversing of the wiring is carried out without pulling the knife gate of the test power supply. (6) The operator is not under the supervision of the guardian to wear a helmet, insulated boots, insulated gloves for the test.
1.2 Pay attention to fire, explosion
(1) electrical fire. In the high-voltage test short-circuit test work, due to the circuit current increases, in the short-circuit is easy to produce strong sparks and arcs, can ignite the nearby combustible materials and cause a fire. Power line, bus, switch contacts, transmission and distribution lines at the joints are contact resistance, in the current is larger due to contact loosening contact resistance, contact temperature rises, resulting in contact with the melting of the metal, caused by wire insulation and nearby combustibles on fire.
(2) oil-filled equipment explosion. Reactor and transformer and other oil-immersed equipment internal short circuit, can form a smooth discharge channel, generating arc and lead to oil degradation decomposition, generating a large number of acetylene and other gases, which can cause a sharp rise in pressure inside the tank, the pressure relief valve oil relief, which may lead to deflagration. If the pressure relief is not timely, and even the box explosion can occur. In addition, lightning strikes, overvoltage, short circuits and external sources of ignition may cause oil fires.
1.3 Pay attention to poisoning leading to asphyxiation
The circuit breaker is to sulfur hexafluoride (SF6 ) gas as insulation and arc extinguishing medium. Sulfur hexafluoride gas itself is non-toxic, odorless and non-flammable, but it will decompose under the action of the arc to form low-fluorine compounds such as S2F2, SF4, S2F10 and HF, etc. These substances are highly toxic, and if an explosion or leakage occurs in the test process, resulting in the leakage of sulfur hexafluoride gas, and the personnel enters the test site without wearing protective equipment or the protective equipment is ineffective, it will result in poisoning accidents.
SF6 recovery or filling process, if the equipment, piping, valves have quality defects, design, installation, unreasonable, unauthorized operation or misoperation, resulting in gas leakage. If the indoor ventilation is poor, SF6 gas concentration is too high can cause asphyxiation.
1.4 Pay attention to electromagnetic radiation
If the impulse current strength is too large during the test, the protection distance of the operator is insufficient or electromagnetic shielding protection measures are not taken, it can lead to personnel suffering from electromagnetic radiation hazards.
2. Main technical measures
According to the "Electricity Industry Safe Working Procedures (High-voltage Laboratory Part)" (DL 560-1995), "High-voltage AC Sulfur Hexafluoride Circuit Breaker) (JB/T 9694-2008) and "Sulfur Hexafluoride Electrical Equipment Operation, Testing and Overhaul of Personnel Safety and Protection Rules" (DL/T 639-1997), and other standards and norms, in order to address the electrical problems that exist in the high-voltage test, it is important to take measures for the safety and protection of personnel in the operation, testing and maintenance of sulfur hexafluoride electrical equipment. The grounding resistance is not more than 0.5Ω. There should be a reliable metallic connection between the grounding point of the test equipment and the grounding point of the equipment under test. All metal structures and fixed metal safety shielding fences in the test room (field) must be firmly connected to the grounding network. The grounding point should be clearly visible signs.
(2) The test room should be kept well lit, tight doors and windows, ventilation facilities are complete. Door to the test area and the test power supply should be interlocking device, when the door to the test area is open, an alarm signal should be issued, and make the test power trip.
(3) high-voltage test room should be set up in accordance with the provisions of the safety fence, signage, safety signals and alarms, control room should be laid rubber insulating mat.
(4) according to the nature and needs of the test room, equipped with appropriate safety work (equipment), as well as anti-virus, anti-radiation, anti-scald protective equipment and fire and explosion-proof safety facilities, and equipped with emergency lighting and power.
(5) in the same test chamber at the same time for different high-voltage test, the test interval must be separated by the respective safety distance with a fence, while setting up obvious signage, leaving enough safe passage.
(6) high-voltage test equipment, test items and power distribution units used to carry the type of ground wire should be multi-stranded braided bare copper wire or transparent insulating layer covered with copper soft stranded wire or copper tape made. High-voltage test equipment and specimens used on the grounding wire, its cross-section should be able to meet the test requirements, and shall not be less than 4mm2.
(7) in order to prevent high-voltage test of the electromagnetic field and ground potential rise caused by the impact of counterattack, the test room should have the appropriate safety and technical measures, the important instrumentation and weak equipment should be installed to prevent the discharge of counterattacks and induced voltages of the protective device or take other safety measures.
(8) single electrical equipment in the house, the oil volume of 100kg or more, should be set up oil storage facilities or oil facilities. The volume of oil-blocking facilities should be designed to accommodate 20% of the oil, and there should be accidental oil discharge to the safety of the facilities, when the above requirements can not be met, should be set up to accommodate 100% of the oil storage facilities, the inner diameter of the oil pipe should not be less than 150mm, the pipe should be equipped with iron grille mesh.
(9) 8h per day during the work period, any 6min continuous by the whole body average specific absorption rate (SAR) should be less than 0.1W/kg.
(10) SF6 gas insulation high-voltage test equipment and test specimens should be well sealed, the test site should be required to install a strong ventilation devices and protective facilities.
3. Safety management and protection measures
(1) Strengthen the staff's own technical training and safety awareness training. In the usual training should focus on improving the staff's business and technical level, combined with the daily work of high-voltage test professional knowledge of the training work, to lay a solid technical foundation for safe production. Electrical test is a need to be careful, careful, careful work, if the safety awareness is not strong, a small link of the error may lead to safety disaster.
(2) strict implementation of operating procedures and licensed. High-voltage test is different from other electrical tests, the test equipment is different, the required test equipment, wiring and test standards are very different, more specialized, dangerous, if the danger of unauthorized operation is also great. Therefore, the high-voltage test personnel must be done by the special operators after training, and licensed; _T work to strictly implement the relevant safety technology operating procedures.
(3)Prepare a good emergency rescue plan for accidents, and do regular drills.
The Work Safety Law establishes an emergency rescue system for accidents, which plays an important role in preventing and rescuing accidents beforehand, and can effectively reduce casualties. Therefore, enterprises should prepare emergency rescue plans for accidents in accordance with the Guidelines for the Preparation of Emergency Response Plans for Work Safety Accidents in Production and Operation Units (AQ/T 9002-2006), and conduct regular drills.
4. Conclusion
Because of the special nature of the high-voltage test work environment, the requirements of technical protection and safety management to take comprehensive, reasonable and feasible measures. All participants should strengthen the understanding of the electrical test, improve their own safety awareness, and put an end to illegal operation. This can ensure the safety of high-voltage test.
References
[1] GUO Yongchao, LI Jisheng, HUANG Liqiu, LIU Yingnan, LIU Wei. Analysis of high voltage test equipment[J]. Coal Mine Modernization.2010(4).
[2] Ma Chuanyan. High-voltage test safety assurance measures [J]. Beijing Electric Power College Journal.2009(12).