Lightning Protection Configuration of Urban Rail Transit Power System

Urban rail transit communication system transmission equipment, program-controlled switches, special communications equipment, wireless communications equipment and UPS power supply are the core equipment for data transmission and processing, the external connection lines exist low dielectric strength, over-voltage and over Current tolerance is poor, sensitive to electromagnetic interference and other weaknesses. Once a building is struck by a lightning strike or a lightning strike occurs in the nearby area, lightning over-voltage and lightning electromagnetic pulse intrude into the building via power supply lines, communication lines, receiving antennas and space electromagnetic induction, which will threaten the normal operation of the urban traffic and communication system and safe operation. This article talk about urban rail transit power system lightning protection configuration.

In China, the subway is the focus of development of urban public transport, a large number of micro- electronic devices applied in underground industry, large scale integrated circuit technology enables the system has been greatly improved, but the integrated circuit itself has lightning performance As the formerly used electromechanical equipment, in general, the higher the integration, the lower the durability of equipment, most of the equipment indoors, but also susceptible to lightning, the reason is mostly due to lightning electromagnetic pulse over-voltage transmission line intrusion caused by indoor equipment of. Lightning strike and lightning will cause instantaneous high voltage and high current on the input / output power line, affecting the railway signal such as user network system, server, computer, signal relay interlocking, computer interlocking, automatic block blocking, etc. Intelligent power supply equipment and precision equipment Stable operation, will cause serious damage to equipment. In recent years, lightning protection, grounding system design concepts constantly updated, the new materials, new technology has also been greatly developed.

First, low-voltage power supply system protection

The grounding and lightning protection of low-voltage power supply system is a systematic project. According to relevant international, domestic and industry standards, corresponding lightning protection measures should be taken on the high-voltage side and low-voltage side of the AC power transformer before the power line is introduced into the UPS room, The introduction of the length of the low-voltage power cables and UPS room UPS grounding, lightning protection in the engine room, the engine room shielding and room lightning protection are all stringent requirements.

Urban rail transit communication system transmission equipment, program-controlled switches, special communications equipment, wireless communications equipment and UPS power supply are all the core data transmission and processing equipment, these devices are connected through the network and around, but the external connection lines There are low dielectric strength, over-voltage and over-current tolerance is poor, sensitive to electromagnetic interference and other weaknesses. Once a building is struck by a direct lightning strike or a lightning strike occurs in the nearby area, lightning overvoltages and lightning electromagnetic pulses intrude into the building through power supply lines, communication lines, receiving antennas and space electromagnetic induction, threatening the normal operation and safe operation of the urban traffic communication system . And the circuit closed, disconnected conversion operation, inductive and capacitive load switching operation, blocking the short-circuit current can generate switching surges on a variety of electronic equipment damage.

The various subsystems of communication include transmission system, business communication system, special communication system, special wireless communication system, public security wireless communication system, fire wireless communication system, television monitoring system, broadcasting system, clock system, power supply system, Leakage of coaxial cables, RF cables take different measures to carry out mine protection, so the protection of the entire subway system is a complex system engineering, this article only for the protection of thunder and lightning wave of the first grade protection for brief introduction:

Second, low-voltage distribution system lightning protection configuration

According to the requirements of GB50343-2004, urban rail transit belongs to Class A thunder and lightning protection level, and its SPD configuration will be configured strictly in accordance with Class A protection level:

The introduction of external power grid room should be multi-level lightning protection. The first grade is located in the introduction of outdoor AC power feeder (distribution board or level â…  in the power switch box); the first level is located in the power supply side of the screen; the third level in the microelectronic equipment (refers to the computer terminal power supply stable Pressure vessel or UPS power supply before).

The purpose of the first level of lightning protection: to prevent the direct conduction of thunder into the LPZ1 area, the tens of thousands to hundreds of thousands of surge voltage limit to 2500-3000 volts.

The purpose of the second level of lightning protection: further through the first level surge arrester residual voltage or limited to 1500-2000 volts, LPZ1-LPZ2 implementation of equipotential bonding.

The purpose of the third stage lightning protection: the ultimate means of protection equipment, the value of residual surge voltage will be reduced to less than 1000 volts, the surge of energy will not damage the equipment.

Three lightning protection because the energy needs to be discharged step by step, the transmission line will sense LEMP (lightning electromagnetic pulse radiation), for the building with information systems, three lightning protection is a lower cost, more adequate protection options.

Since the energy of the lightning strike is very huge, it is necessary to gradually release the lightning strike energy to the earth through the method of graded discharge. The first-stage SPD can discharge the direct lightning current or discharge the huge energy conducted when the power transmission line suffers direct lightning strike For the possible direct lightning strike, it is necessary to carry out CLASS-I lightning protection . The second-level lightning protection device is the residual voltage of the former-stage lightning protection device and the lightning protection device in the area, and when there is a large lightning energy absorption at the previous stage, there will be a part of lightning protection device or third-level lightning protection device It is still quite huge energy will be transmitted over, the need for further absorption of the second stage mine. At the same time, after the first-level SPD transmission line will also be induced lightning electromagnetic pulse radiation LEMP, when the line is long enough (more than 15 meters) induction lightning energy becomes large enough, the need for second-level SPD further Relieve lightning strike energy.

Similarly, after the second-level SPD transmission line will also be induced lightning electromagnetic pulse radiation LEMP, when the line is long enough induction lightning energy becomes large enough, the third-level SPD is on the LEMP and through the second Lightning protection device residual lightning energy protection.

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