Lightning protection for power systems is an important protection measure for power supply and distribution projects. If a lightning strike occurs, it will cause a large-scale blackout, which will seriously affect social production and people’s lives. The lightning protection of the power supply and distribution system should be carefully considered from the engineering design stage, and practical and feasible lightning protection schemes should be adopted according to the actual conditions of each region.
1. Lightning protection in
substations 1.1 Sources of lightning strikes in substations and solutions
(1) Sources of lightning strikes: First, lightning strikes directly on the equipment in the substation; second, lightning induced overvoltage and direct strikes on overhead lines The lightning wave formed by lightning overvoltage invades the substation along the line.
(2) The protection of direct lightning strikes in substations is generally solved by installing lightning rods or erecting lightning protection wires within a certain distance along the incoming line of the substation.
(3) The lightning induced overvoltage of overhead lines and the lightning waves formed by direct lightning overvoltage invade the substation along the line, which is the main cause of lightning damage in the substation. If no protective measures are taken, it will inevitably cause the electrical equipment of the substation. The insulation is damaged, causing an accident. The purpose of installing lightning arresters in substations is to limit the amplitude of intruding lightning waves, so that the overvoltage of electrical equipment will not exceed its impulse withstand voltage. The main purpose of installing a protection section on the incoming line section of the substation is to limit the amplitude of the lightning current flowing through the arrester and the steepness of the intruding lightning wave.
1.2 Principles substation installation of lightning rods
all protective equipment should be within the scope of the lightning rod (wire) of the order to avoid being struck by lightning. When the lightning rod is struck by lightning, the potential of the lightning rod against the ground may be very high. If the insulation distance between them and the protected electrical equipment is not enough, it may cause a discharge between the lightning rod and the protected equipment after the lightning rod is struck by lightning. This phenomenon is called counterattack. At this time, the lightning rod can still add the high potential of the lightning wave to the protected electrical equipment, causing an accident. The distance between the lightning rod and the electrical equipment that does not have a counterattack accident is called the minimum lightning protection distance between the lightning rod and the electrical equipment.
1.3 Determination of the minimum lightning protection distance between the lightning rod and the electrical equipment
When the lightning rod is struck by lightning, the lightning current flows through the lightning rod and its grounding device. In order to prevent the air gap between the lightning rod and the protected equipment or frame from being broken down and causing a counterattack accident, the air gap must be greater than the minimum safe clear distance. In order to prevent the gap in the soil between the lightning rod grounding device and the protected equipment or frame from being broken down and causing a counterattack accident, the air gap must be greater than the minimum safe clear distance.
1.4 installed lightning rod relevant provisions
for 35kV substation and below, because of its low level of insulation must be installed separate lightning rod, and meet the requirements of counter does not occur.
For substations above 110kV, due to the high insulation level of such voltage level power distribution devices, the lightning rod can be directly installed on the frame of the power distribution device, so the high potential generated by lightning strikes will not cause electrical equipment damage. Fight back against the accident. The power distribution frame equipped with lightning rods shall be equipped with auxiliary grounding devices. The connection point between the grounding device and the grounding grid of the substation shall not be less than the electrical distance from the connection point of the grounding device of the main transformer and the grounding grid of the substation. 15m. Its function is to make the high potential generated on the lightning arrester grounding device gradually attenuate during the process of propagation along the grounding grid to the transformer grounding point when lightning strikes the arrester, so that the intruding lightning wave will not cause the transformer back strike when it reaches the transformer grounding point. accident. Since the insulation of the transformer is weak, and the transformer is also an important equipment of the substation, lightning rods should not be installed on the door frame of the transformer.
Since the distance between the power distribution device of the substation and the first tower of the substation outlet may be relatively large, if the lightning protection wire on the tower is allowed to be led to the structure of the substation, this section of the wire will be protected. Use lightning rods to protect the economy. Due to the shunting effect at both ends of the lightning conductor, when lightning strikes, the potential rise caused by the lightning rod is smaller than that caused by the lightning rod. Therefore, 110kV and above power distribution devices can lead the line lightning protection wire to the outgoing door-type frame, but the area where the soil resistivity is greater than 1000Ω·m should be installed with a centralized grounding device. For 35～60kV power distribution devices, in areas where the soil resistivity is not greater than 500Ω·m, the lightning conductor of the line is allowed to be connected to the outlet door frame, but a centralized grounding device should be installed. When the soil resistivity is greater than 500Ω·m, the lightning protection line should terminate at the line terminal tower, and the first gear line protection of the substation can be protected by a lightning rod.
2. Lightning protection of power lines
Lightning protection transmission lines 2.1
Lightning transmission line, the line should be based on the voltage level, the nature of the load and system operation mode, and the combined strength of the local area lightning activity, terrain characteristics and high soil resistivity lower case, technical Economic comparison, reasonable lightning protection methods are adopted.
(1) 35kV lines are not suitable for the whole line of lightning protection lines. Generally, 1~2km lightning protection lines are installed in the incoming line of the substation, and lightning protection lines are installed in areas with strong lightning activity, or line metal oxide lightning arresters are installed.
(2) The 110kV line should be erected across the entire line of lightning protection lines, and double lightning protection lines should be used in mountainous areas; however, in areas where the annual average number of thunderstorm days does not exceed 15 days or the operation experience proves that the lightning activity is slight, the lightning protection line may not be erected.
(3) The 220kV line should be set up with lightning protection lines on the whole line, and double lightning protection lines should be adopted at the same time. For the line for erecting lightning protection lines, attention should be paid to the protection angle of the opposite conductors of the lightning protection line on the tower. Generally, the protection angle of 20°～30° is adopted. At the same time, the grounding of the tower should be done well. According to the different soil resistivity, the power frequency grounding resistance of the tower should not be greater than the value listed in Table 1.
For the technical parameters of metal oxide arresters installed on 35kV lines, the following conditions should generally be met:
①Continuous operating voltage (effective value) is not less than 40.8kV; ②Rated
voltage (effective value) is not less than 51kV; ③DC
1mA reference voltage is not less than Less than 73kV (range between 73 and 74kV);
④The residual voltage (peak value) at the standard discharge current level of 5kA is not greater than: lightning impulse 134kV, operation impulse 114kV, and steep wave impulse 154kV.
⑤2000μs square wave current (peak value) 200A.
⑥The insulation configuration is determined according to the requirements of the pollution level of the line.
2.2 Lightning protection of distribution lines
as the transmission lines, distribution lines Lightning also employ lightning arrester wire or measures for different voltage levels and take different lines are not the same.
2.2.110kV bare wire line
for 10kV bare wire line, can be used in principle, lightning lines lightning protection, but because of the high cost of construction is not convenient, basically do not currently using lightning conductor, but in some frequent lightning activity segment Install the lightning arrester, and do the grounding of the tower as required.
2.2.210kV insulated wire line
for insulated overhead lines lightning current may take the following measures:
① install lightning conductor, lightning This method works best, but the feasibility and difficult and costly.
②Improve the withstand voltage level of line insulators, and replace 10kV insulators with lightning protection insulators, which will greatly improve the lightning protection level.
③Install line arresters in minefields or according to a certain distance to reduce lightning strikes and disconnection accidents.
④Extend the flicker path, which will cause the arc to be easily extinguished, and locally increase the insulation strength, such as strengthening the insulation at the connection between the wire and the insulator, and using a long flicker path arrester.
⑤Partially strip the insulated wires to make them partially bare wires, so that the arc can slide on the stripped part instead of being fixed at a certain point for ablation. At the same time, it can also provide a grounding point for future construction.
2.2.3 low-voltage distribution lines
low voltage lines should be installed at the outlet of the transformer low voltage surge arresters or breakdown fuse, while making the grounding resistance grounding means should not be greater than 4Ω. The neutral line in the low-voltage power network where the neutral point is directly grounded should be grounded at the power point. Low-voltage power distribution lines should be grounded repeatedly at the terminals of the trunk and branch lines. The grounding resistance of the repeated grounding device should not be greater than 10Ω each year. For longer lines, the repeated grounding should be no less than 3 locations. Especially in order to prevent lightning waves from invading users along low-voltage power distribution lines, the iron angle of the insulator on the connection line should be grounded and the grounding resistance should be less than 30Ω.
2.3 Lightning protection of power cable lines
Due to its own structural characteristics and requirements for connection with other electrical facilities, power cables adopt different lightning protection methods according to different voltage levels. For power cables with voltage levels of 35kV and below, a lightning arrester should be installed near the cable terminal. At the same time, the metal shield and armor of the terminal must be well grounded. For high-voltage cables of 110kV and above, when the cable line is subjected to lightning impulse voltage, overvoltage will appear at the ungrounded end or cross interconnection of the metal sheath, which may cause breakdown of the sheath insulation. The following protections should be taken One of the solutions:
① One end of the cable metal sheath is interconnected and grounded, and the other end is connected to a protector.
②The metal sheaths of the cables are cross-connected, and the protector Y0 is connected.
③Cable metal sheaths are interconnected crosswise, protector Y wiring or Δ wiring.
④ One end of the metal sheath of the cable is interconnected with a grounding and equalizing line.
⑤ One end of the metal sheath of the cable is connected to ground and return line.
Third, the electrical equipment and lightning protection of electronic equipment
3.1 substation equipment of lightning protection and grounding
Lightning lightning substation equipment is inseparable from the building, according to the latest national mandatory standard GB50054-2010, the building The lightning protection grounding of objects and equipment should be equipotentially connected instead of using separate grounding grids in the traditional way. The so-called equipotential connection is to weld the building itself and various conductive objects inside and outside it (electrically) to ensure equipotentiality. Because the peak value of the lightning current is very large, it immediately rises to a very high potential (relative to the earth) where it flows. Therefore, the nearby electrical and electronic equipment and people that are still at the earth potential will cause side flicker, which is easy to cause the equipment And personal accidents. So equipotential bonding is the key measure for lightning protection.
3.1.1 Lightning protection of buildings in substations
The lightning protection device of the building itself is the first barrier for the lightning protection of electrical equipment and systems in the building. The lightning protection performance of the building itself directly affects the lightning protection of the internal electrical equipment. Therefore, we must first pay attention to the protection of the building itself. mine. The lightning protection of modern buildings mainly consists of the top air-termination belt and the air-termination net as the air-termination device, the beams, columns, floor slabs and the main steel bars in the surrounding walls of the building are used as down conductors, and the underground reinforced concrete foundation is used as the grounding body. In the design and construction of the building, it is necessary to consider the electrical connection between the steel bar network as the air-termination device, the down conductor and the grounding body, making it an ideal “Faraday cage” arrester. The combination of lightning protection nets and reinforced concrete of buildings has become an economically feasible lightning protection method recognized at home and abroad. Therefore, in the design and construction, it is necessary to reserve joints welded from the steel bars in each floor, beam, and column to facilitate connection with Connect indoor and outdoor ground wires.
3.1.2 outdoor lightning equipment
for preventing direct lightning, according to need outdoor installation or a lightning rod, the scope of which is calculated, in order to protect all the equipment required for the outdoor principles. At the same time, the outdoor structure busbar and the neutral point of the transformer should be installed with lightning arrester protection, and a grounding network should be made outdoor, and the grounding down conductors of all equipment should be welded to the grounding body to ensure equipotentiality. In order to prevent overvoltage caused by lightning strikes, the insulation level of various equipment should be able to meet the insulation requirements of the voltage for the equipment, and the equipment should be strictly checked during the ordering and factory test of the equipment, and the insulation withstand voltage level of the equipment should be ensured in accordance with the requirements of the regulations to prevent lightning strikes. wear. This kind of lightning protection structure has many advantages: ① can avoid “shielding”; ② can play the shielding function of “Faraday cage”, can greatly weaken the intrusion of lightning electromagnetic pulse; ③ because of the beams, columns, floors, and floors of the building The steel bars of the wall and metal pipelines and other conductors have been electrically connected into one body, so that the potentials are almost equal everywhere, thus ensuring the safety of the equipment; ④The down conductor of the “cage” lightning arrester is composed of a large number of steel bars , Greatly disperse the lightning current, and weaken the impact amplitude of the pulse electromagnetic field received by the information equipment in the building; ⑤The grounding body is the reinforced concrete foundation distributed around the underground, which can form a uniformly distributed pressure net, and the contact surface with the earth Wide, low grounding resistance and stable.
3.1.3 Lightning protection of indoor equipment
Various indoor metal screens and cabinet skins should be reliably welded or bolted to the base channel steel to ensure good contact. At the same time, the channel steel should be welded to the cable support in the cable channel with galvanized flat steel to form a whole. The grounding grid forms a complete large grounding grid.
Lightning Protection 3.2 computers, communications, and other automated equipment
in the building of the first protective barrier of the electronic device like a computer, since the communication station must be connected by a signal cable and communications antenna tower, so for communications cable sheath must be well grounded (Multipoint Repeated grounding), and connected with the grounding grid of the building to form an equipotential. At the same time, lightning arresters can be installed. Corresponding surge protectors should be installed on the communication interfaces of electronic equipment. For the electronic equipment in the building, the most important thing is to connect the independent grounding grids into a common grounding system. Other grounding schemes such as separate, independent, and dedicated grounding are not appropriate and have no practical meaning in the project. For all electrical and electronic equipment in the building, lightning protection measures should be taken step by step. First, the building and the power supply should be grounded for lightning protection, and then the corresponding lightning arrester should be installed in the computer room and each equipment port to truly prevent the intrusion of lightning waves. Fight back.