Keywords: catenary; Overpressure; Lightning protection measures
Electrified railway is an electric traction railway. Also known as electrified railway. Electric trains (trains and EMUs drawn by electric locomotives) run on electrified railways, and power supply system of electric traction, which provides power for electric locomotives and electric vehicles (hereinafter referred to as electric locomotive EMUs), is set along the railway.
Traction power supply system is mainly composed of traction substation and catenary. The traction substation reduces the transmission line voltage of the power system from 1 10kV (or 220kV) to 27.5kV, and sends the electric energy to the catenary through the feeder; Overhead catenary is erected along the railway, and the electric locomotive can obtain electricity from it after lifting the bow to traction the train. As an important part of traction power supply system, catenary is mostly exposed to the natural environment and has no backup, so necessary lightning protection measures need to be taken. If there are no protective measures or improper measures, insulators may be damaged and lines may trip, which will directly affect the operation of electrified railways. At the same time, the surge overvoltage caused by lightning strikes is introduced into the traction substation through the catenary, which may damage the electrical equipment in the substation and cause more accidents. Judging from the current operation of more than 30,000 kilometers of electrified railways in China, some lines are frequently struck by lightning. According to statistics, guangzhou-shenzhen railway double track 139.4438+0 km, in February 2000 alone, there were 45 lightning strikes on the catenary. How to effectively protect catenary from lightning strike and reduce the harm and loss caused by lightning strike of electrified railway as much as possible is a subject worthy of our study.
A, catenary line lightning phenomenon
When lightning strikes, it will produce overvoltage on the conductor of catenary, that is, lightning overvoltage, which is several hundred to several Qian Qian volts. Lightning overvoltage is generally divided into two types: one is lightning strike to the earth or pillar near the catenary line, which is called induced lightning overvoltage due to electromagnetic induction; One is the direct lightning overvoltage caused by lightning strike of catenary. No matter what lightning overvoltage, when the lightning overvoltage exceeds the insulation level of the line, the insulation flashover of the catenary line will occur. Because the traction power supply system consists of catenary, rail, earth and so on. When insulation flashover occurs on catenary lines, lightning flashover will inevitably be transformed into a stable power frequency arc, which will lead to the tripping of catenary lines, and in severe cases, catenary disconnection accidents will occur.
Second, lightning protection measures for catenary lines
General lightning protection measures for transmission lines are as follows: 1. Set up lightning conductor and lightning rod along the line to guide direct lightning to discharge to the lightning conductor, and introduce lightning current into the earth through towers and grounding devices to protect the protected objects from lightning strike. The second is to reduce the grounding resistance of towers, install line arresters on some towers, improve the lightning withstand level of lines, and reduce insulation flashover caused by lightning strikes on towers or lightning wires. (3) appropriately increase the number of insulators and reduce the power frequency electric field intensity on insulator strings. The power grid is not grounded or grounded by arc suppression coil to prevent lightning flashover from transforming into stable power frequency arc. Finally, automatic reclosing measures are taken to ensure that the power supply is restored by the automatic reclosing device after lightning flashover tripping. Four groups of coupled ground wires can shunt current, strengthen the coupling between lightning rod and conductor, and reduce the lightning trip rate. 5. Install the line arrester and connect it in parallel near the protected equipment. When the applied voltage exceeds the discharge voltage of the arrester, the arrester will discharge first, which can limit the development of overvoltage.
At present, the measures taken by catenary lines are to reclose once through the automatic reclosing device of traction substation to ensure automatic reclosing after lightning flashover trip and restore power supply. In areas with medium and above minefields, lightning arresters should be installed for lightning protection according to the design specifications of the Ministry of Railways.
1, angular gap arrester
The angular gap arrester consists of a full-angle vibrator, a half-angle vibrator and a supporting insulator device. Because of its simple structure, convenient adjustment and small maintenance workload, this kind of arrester was widely used in the lightning protection of electrified railway catenary in the early stage, but there are some defects in practical work: ① sundries blown by the wind are easy to hang on the corner gap, which makes the discharge gap short-circuit and discharge; (2) The action of lightning arrester will inevitably form power frequency aftercurrent, and the strong short-circuit arc will burn out the angular gap; (3) In foggy days, the insulation performance of the angular gap decreases and discharges, resulting in misoperation. From this point of view, the angular gap arrester is not an ideal lightning protection device.
2, tube arrester
Tube arrester is an early lightning protection device for catenary lines, which is actually a protective gap with high arc extinguishing ability. It consists of two notches connected in series. A gap in the atmosphere is called the outer gap, and both poles are fixed on the insulator. The other is installed in the arrester tube, which is called internal gap or arc extinguishing gap. When the inner and outer gaps of lightning overvoltage are broken down, lightning current and power frequency short-circuit current are grounded on the inner wall of the tube, so that the materials in the wall tube are heated and gasified, and the gas with high pressure is ejected out of the tube through the inner gap, forcing the gap to extinguish the arc. The choice of tube arrester is limited by the maximum and minimum short-circuit current at the installation site. When the maximum short-circuit current is greater than the upper limit of arrester, arrester will explode. When the short-circuit current is less than the lower limit of the arrester, the arc cannot be extinguished and the arrester may burn out. In addition, after the tube arrester is operated for many times, the inner diameter of the tube will gradually increase, and the arc extinguishing ability will decrease or even disappear.
3, silicon carbide valve arrester
Silicon carbide valve arrester has been used for a long time in China and is the main lightning protection device in current lightning protection technology. However, it has some inherent shortcomings: for example, only lightning amplitude and voltage limiting protection function, no lightning steep wave protection function, and incomplete lightning protection function; No continuous lightning impulse protection ability; The stability of action characteristics is poor, which may be harmed by transient overvoltage; The short service life is emphasized in the operation condition, so the silicon carbide valve arrester will be gradually eliminated.
4, zinc oxide arrester
Zinc oxide arrester is recognized as the most advanced lightning protection device in the world. Seamless zinc oxide arrester is widely used in China at present, but the practice shows that it is easy to be damaged, easy to explode and short in service life. The reason is that poor transient overvoltage tolerance is its fatal weakness. However, series gap zinc oxide arrester not only has the advantages of protection performance of gapless zinc oxide arrester, but also has the characteristics of withstanding transient overvoltage. Therefore, series gap zinc oxide arrester should be widely used as lightning protection device at present.
Discussion on lightning protection measures of catenary
First, advanced arrester and on-line monitoring technology of arrester are adopted.
At present, zinc oxide arrester or series gap zinc oxide arrester is the first choice for line lightning protection. Suggestion: In high and strong minefields, zinc oxide arrester should be used to protect the catenary in the following places: the insulation anchor joint at the end of the split-phase junction station, the two ends of the tunnel with a length of 2000m or more, the power supply line with a length of 200m or more, or the connection between the autotransformer power supply line and the catenary; At the joint and cable terminal of 27.5KV cable. The lightning conductor is set in a strong minefield with a protection angle of 0 ~ 45. However, in operation, the resistance of the arrester is aging due to repeated actions, which may lead to the failure of the arrester. In order to ensure the safe and reliable operation of lightning arrester, in recent years, on-line lightning arrester monitor has been gradually popularized and used. On-line arrester monitor is a monitoring device integrating arrester discharge counter and leakage current detection function. By patrolling the counter action times of the monitoring device and the leakage current value of the lightning arrester, the action situation and operation performance of the lightning arrester can be grasped in time.