Influence of Overvoltage on High-voltage Electric Equipment of Electric Locomotive

In November, he proposed to discuss the impact of overvoltage on high-voltage electrical equipment for electric locomotives He Anqing (CSR Zhuzhou Electric Locomotive Co., Ltd. Technical Center, Zhuzhou 412001, Hunan, China). The current status of the use of vehicles and proposed measures and recommendations for the suppression of overvoltages.

1 Overview With the rapid development of China's railway construction in recent years, railway transportation has increasingly become an important role in the national economy, especially for high-speed EMUs, heavy-duty electric locomotives, subway light rail and intercity trains and other electric traction equipment. The coming and coming are closely related to people's production and life. At the same time, people's demands and expectations for railway operations are getting higher and higher. Therefore, efficiency, safety, and efficiency have become the most important development requirements for railway electric traction and transportation equipment.

Taking an electric locomotive powered by single-phase AC 25kV systems running outdoors as an example, the high-voltage electrical equipment on the roof should not only be exposed to various harsh environments for a long time, but also be subject to various types of over-voltage shocks.

According to statistics, at present, during the operation of electric locomotives, especially in heavy snow and heavy fog and heavily polluted weather conditions, there are many accidents in the roof equipment. Among them, breakdown flashover accidents in the top electrical equipment account for the most part. This phenomenon has become one of the major bottlenecks restricting the normal operation of electric locomotives. The reason for the formation of roof faults, excluding the external causes caused by the harsh environment, mainly comes from various types of overvoltages. The high-voltage insulation design of electric locomotives involves the high-voltage electrical equipment of electric locomotives, and also relates to systems such as power supply contact networks and ground substations that are closely related to them. Therefore, in the grid-side circuit design of electric locomotives, only electric locomotives are concerned with the electric The parameters of the equipment are not enough, and the power supply system and electric locomotive should be considered as a whole. Because the power supply system and the on-board system are different systems in China and the standards used in their designs are different, it will inevitably lead to problems of unbalanced insulation and misconduct. Therefore, it is necessary to conduct a comprehensive analysis of the overvoltage environment experienced by electric locomotives so as to facilitate The insulation design of high-voltage electrical equipment for electric locomotives can also be targeted to formulate measures to solve the roof failure of electric locomotives.

2 Classification of Overvoltage of Electric Locomotive The electric locomotive is operated under the single-phase AC rated 25kV catenary. According to the provisions of GB1402-1998, the nominal electric voltage of the railway electric traction system is 25kV, including the electric locomotive, EMU or intercity railway. For electric locomotives, the maximum allowable voltage is 27.5 kV (effective value) and the minimum allowable voltage is 19 kV (effective value). This is the voltage fluctuation range under normal conditions of electric locomotives, but in the actual line operation, due to the different electrified power supply sections The load, especially in the electrified section of the heavy-duty electric traction, the voltage range will exceed this range, some transport particularly busy electrified sections, in order to ensure that the operation of multiple electric locomotives in the section will not lead to traction power supply network pressure Too low, often the network pressure setting will be higher than the standard value.

The overvoltages that form the electric locomotive during operation are mainly of the following types.

2.1 Overvoltage caused by over-phasing The main reason that an electric locomotive generates over-voltage when it passes through the articulated phase of the anchor segment is that: when the locomotive enters into the over-phased powerless zone, the pair of pantograph and roof high voltage leads Ground capacitance, neutral embedded wire, and high-voltage voltage transformer form a resonant circuit. Because there is also induced voltage in the phase-divided non-electrical area, the circuit structure is from "powered" to "no power" or from "no power" to "available. The transient changes that occur in electricity create high-order oscillating circuits and therefore generate oscillating overvoltages. The reason for this is not related to the normal operation of the main circuit breaker by the driver when the locomotive is overly dephased, but related to the parameter configuration of the electrical equipment of the locomotive and the articulated phase splitter. Different line sections and different electric locomotives, over-phase generated by the over-voltage amplitude is also not the same, according to the line test test of the relevant departments, over-phase generated over-voltage amplitude of up to close to 100kV, frequent over-voltage contact The high-voltage electrical equipment of the network cable and the locomotive poses a great danger. In severe cases, it even leads to the phenomenon of flashover breakdown of the contact net burning line and the insulator.

2.2 Overvoltage due to pantograph relationship The electric locomotive obtains electrical energy through the dynamic contact between the pantograph and the catenary wire, while the suspension system of the pantograph and the catenary has a certain elasticity, and the pantograph and the catenary The dynamic contact of the connector clamps, positioning clamps or pantograph arc hard points, or due to poor line conditions, low contact pressure of the pantograph, etc. will cause frequent pantograph off-line phenomenon. Inductive loads such as voltage transformer windings and transformer primary windings on the locomotives form a resonant circuit during frequent off-line transients of the pantograph, resulting in high-order resonant overvoltages; and due to saturation of ferromagnetic inductors such as locomotive voltage transformers and transformers. The role of the formation of ferromagnetic oscillations.

Generally, the over-voltage amplitude in this case will not be too high, but under severe conditions, not only will the pantograph slide and the contact cable pull arc burn, but also it will easily cause the phenomenon of high-voltage voltage transformer burn-out.

2.3 Operating overvoltage The operating overvoltage of the electric locomotive includes two types of internal and external electric locomotives. Over-voltage generated by the reclosing of the traction power supply system or the adjacent electric locomotive of the same section will cause the over-voltage of the machine to be generated, and at the same time, due to the electric locomotive. In the primary side inductive load circuit, the main circuit breaker at the current zero-crossing point of the small current will also cause the closure of the over-voltage, the locomotive's internal operating over-voltage generated by the maximum amplitude and the locomotive primary circuit parameters. Operational over-voltage has great damage to the insulation of vacuum circuit breakers and traction transformer windings. In severe cases, vacuum circuit breakers may be damaged.

Because the atmospheric overvoltage caused by climate acts on the 25kV contact network, it is mainly divided into lightning overvoltage and induced overvoltage. The lightning over-voltage is the over-voltage caused by the lightning discharge directly acting on the contact net, and its short wavelength; the over-voltage induced is the over-voltage induced when the lightning discharge occurs near the contact net, and the wavelength is relatively long.

Electric locomotives are subject to such a wide variety of overvoltages. In extreme cases, overvoltages can occur at the same time as overvoltage superposition. Therefore, the overvoltage environment that electric locomotives suffer during operation is relatively poor.

Overvoltages are harmful to vehicle-mounted high voltage electrical equipment. The high-voltage electrical equipment of single-phase AC-powered electric locomotives is divided into protective equipment and functional equipment. The protective equipment is mainly arrester. Its main function is to suppress the overvoltage of the electric locomotive onboard system; the functional equipment mainly includes supporting insulators, Pantographs, main circuit breakers, high voltage disconnectors, voltage transformers, current transformers, high voltage cables and traction transformers. The insulation strength of functional equipment mainly depends on the external insulation characteristics of the equipment. Because the internal structure of vacuum circuit breakers, high-voltage voltage transformers and transformers also exist insulation requirements for the ground, its insulation strength depends on the insulation material used inside the equipment.

3 The purpose of insulation coordination of the electric locomotive is to correctly handle the contradiction between overvoltage and insulation, determine the insulation level of the equipment, and ensure the efficient, safe and reliable operation of the electric locomotive. The current insulation matching mode is based on the protection characteristics of the valve arrester as the basis of insulation coordination. The selection of the insulation level of the protected equipment is based on this and multiplied by the corresponding matching coefficient.

The level of insulation protection of on-board equipment for electric locomotives depends on the external insulation material supporting the insulators and equipment. In the early introduction of digested imported locomotive technology, the introduction of foreign locomotives basically adopted the OV3 overvoltage category in the IEC60077-1 standard. The corresponding roof equipment and protective equipment have low insulation levels and cannot adapt to the relatively harsh climate and environment in China. For example, the external insulation of the vacuum circuit breakers and high-voltage isolation switches that were introduced earlier and the structural height of the pantograph-supported insulators did not exceed 315 mm, and the phenomenon of flashover discharge of the insulation of the roof equipments often occurred during the operation of electric locomotives.

In view of the current harsh climate environment in the country, most insulators or insulation jackets in electric equipments for roofs of electric locomotives have generally adopted silicone rubber composite materials with strong hydrophobicity, good low-temperature weather resistance, and high resistance to flashover. According to the TB/T3077.2-2006 classification regulations for composite insulators of the roof insulators of electric locomotives, insulators or insulation jackets with a structure height of 400 mm and a creepage distance of more than 1000 mm have been generally selected, and the standard lightning impulse withstand voltage (peak ) Not less than 185kV, it can be seen from the volt-ampere characteristics of the arrester that the residual voltage at the surge current of the arrester nominally operating at 10kA is generally 105 to 110 kV. Therefore, the insulation coordination coefficient K of the electrical equipment is greater than 1.6, which meets the requirements of our country's standards. Insulation coefficient K.1.4 requirements.

Volt-ampere characteristic curve of lightning arrester The insulation level of high-voltage electrical equipment can be intuitively reflected by the volt-second characteristic curve. The volt-second characteristic curve refers to the relationship between the voltage of the shock wave and the voltage action time when the insulation breakdown occurs under the shock wave or operating wave voltage. Usually through tests using different shock wave voltage insulation breakdown test, you can get the device insulation volt-second characteristic curve, as shown, the arrester as a protective device, its insulation volt-second characteristic curve should be lower than the protected high-voltage equipment The level of insulation can play a role in suppressing overvoltage and protecting functional devices.

According to the overvoltage protection mode based on the protection characteristics of lightning arresters as the basis of insulation cooperation, the main purpose of the insulation coordination of the high voltage system of the electric locomotive is to select the appropriate arrester parameters so as to avoid insulation breakdown of the protected equipment under the action of overvoltage shock waves. However, during the actual operation of electric locomotives, due to the harsh climate and the uncertainty caused by overvoltage, the residual voltage of the arrester after the action of the shock wave voltage may still exceed the insulation level of the protected equipment, and the protected equipment will also appear. Flashover breakdown phenomenon.

4 Measures and Recommendations By analyzing the examples of grid-side circuit insulation coordination applications of electric locomotives at home and abroad, the use of two-stage arrester protection is an effective solution. Through analysis, it is easy to see that when the Class I arrester acts under the overvoltage shock wave, the class arrester can effectively suppress the residual pressure generated after the Class I arrester acts, thereby avoiding the insulation breakdown of the protected equipment after the arrester action.

For example, the grid-side circuit of the Lore-Kiruna locomotive designed by Bombardier uses two-stage arrester protection, which is a successful example. The specific implementation plan is to place two arresters on the two pantograph ends of the roof, and at the same time the vacuum circuit breaker. An arrester is set at the output of the device. The arrester at the end of the pantograph selects a nominal discharge current of 5 kA and a residual voltage of 120 kV. At the output of the vacuum circuit breaker, a nominal discharge current of 5 kA is used. The residual voltage is 108 kV. Passing through the two-stage arrester Protection can effectively suppress various types of overvoltage, especially for the operation overvoltage generated on the side of the vacuum circuit breaker has a significant inhibitory effect, so as to effectively achieve the purpose of protecting high voltage electrical equipment. Only from the failure statistics of the vacuum circuit breakers applied to electric locomotives, the number of failures of vacuum circuit breakers burning in electric locomotives not protected by two-stage arresters is significantly higher than that of the two-stage arrester-protected locomotives. Because of the different types of electric locomotives, the parameters of the electrical equipment on the network side, the parameters of the transformer windings, and the distributed capacitance will be different, resulting in different operating overvoltages. When analyzing the failure of the roof vacuum circuit breaker, it was found that the number of times vacuum breakers were burned would vary greatly even if the same model was produced by a different manufacturer.

At present, due to the lack of test data for the high-voltage system of the electric locomotive roof, it is difficult to reduce the operating overvoltage by reasonably matching the parameters of the high-voltage electrical equipment, but we can effectively use the two-stage arrester protection mode in the side circuit of the electric locomotive. Reduce the over-voltage amplitude of the roof.

Taking corresponding measures can reduce the harm of overvoltage, but it is necessary to fundamentally solve the problem of overvoltage and reach the best insulation coordination of the high-voltage system of electric locomotives. The following problems still need to be solved: The insulation level of the power supply system and the on-board system The selection should not be isolated. In view of the current management system, it is recommended that the lead department organize the experts of the two systems to jointly study the standards for the insulation coordination and insulation level of the power supply system of the electric locomotive so as to achieve the purpose of selecting a reasonable insulation matching parameter.

The insulation level of the side circuit of the electric locomotive shall systematically and comprehensively consider factors such as various overvoltages, arrester protection parameters and insulation levels of various equipments in the design, and cannot only focus on the parameters of a single electrical device.

It is necessary to test and test the high voltage system of the electric locomotive side grid to study the test data of the overvoltage generated by the high voltage system of the electric locomotive, and to provide basis for establishing the high pressure system model and overvoltage theoretical calculation of the locomotive side.

5 Concluding remarks Through the analysis of the causes of the overvoltage of the electric locomotive, it can be seen that the high-voltage electrical equipment of the grid-side circuit during the operation of the electric locomotive is faced with a complex over-voltage environment, and the equipment is likely to cause insulation breakdown under the external influence of the bad weather. The phenomenon of failure has brought greater harm to the driving safety of electric locomotives. Therefore, in the design of electric locomotive network side circuit, it is necessary to systematically solve the problem of insulation coordination of electrical equipment. At the same time, a reasonable arrester protection parameter and configuration mode should be selected so that overvoltage can be effectively suppressed, thereby reducing the need for high-voltage electrical equipment. Harm to ensure the safety of electric locomotives.