Program-controlled switch inductive lightning protection measures

Power communication is an indispensable part of modern power system. It is one of the three pillars of the safe and stable operation of modern power grids. Program-controlled switches are an important part of power communication networks. In the event of failure, the losses are not only economic. More serious is that it poses a potential threat to grid security. Therefore, it is especially important to strengthen the security protection of the program-controlled switch.

Many units now have a program-controlled switch installed, and the most important component of a program-controlled switch is an integrated circuit (IC). The IC's anti-interference ability is relatively low, and even the lightning electromagnetic pulse (LEMP) induced from the line can break down the IC components. Therefore, the program-controlled switch is prone to lightning strikes. Most of the components that are damaged are the relay board, the user board, the billing card, and the power supply unit. Because these motherboards are valuable, in order to reduce economic losses, some users want to do all kinds of ways to protect the switch, and even insured the entire switch to the insurance company, but the loss caused by the communication interruption caused by lightning strikes is irreparable. . Therefore, the lightning protection of the program-controlled switch is particularly important.

First, determine the equipotential bonding of the switch

The purpose of the equipotential bonding of switches is to reduce the potential difference between various metal components and systems in the space where lightning protection is required. Metal parts and systems that require the intersection of lightning protection zones, as well as metal components and systems inside a lightning protection zone, should be equipotentially connected at the junction of the lightning protection zone (Figure 1). For example, in the equipotential bonding zone at the junction of LPZO and LPZ1 in the lightning protection zone, all metal conductors entering the switch room should be equipotentially connected. In addition, these lines should be equipped with SPDs at the junction of LPZ1 and LPZ2.

Second, we must first determine the quality of lightning protection facilities in buildings.

According to the relevant provisions of GB50057-94 "Code for Lightning Protection of Buildings", the program control switch building must have facilities for direct lightning protection. When the height of the building exceeds 30m (a type of lightning protection), 45m (a type of lightning protection) and 60m (three types of lightning protection), the metal objects and lightning protection devices such as railings, doors and windows, etc. on the outer wall above the height shall be connection. In addition, the grounding resistance of lightning protection facilities should also meet the requirements of relevant regulations.

Third, determine the lightning protection zone inside the building (LPZ)

According to the relevant regulations of the International Electrotechnical Commission IEC1312-1 "Protection of Lightning Electromagnetic Pulses", the building is divided into four zones (Fig. 1): LPZOA zone, objects in the zone may be directly struck by lightning, and the electromagnetic field in the zone Without fading; minus the LPZOB area, objects in the area cannot be directly struck by lightning, and the electromagnetic field in the area is not attenuated; in the LPZ1 area, objects in the area are unlikely to be directly struck by lightning, and the electromagnetic field in the area may be attenuated. The LPZ2 area is the subsequent lightning protection zone. According to the above partition principle, the program-controlled switch should be placed in the LPZ2 area as much as possible to reduce the impact of lightning electromagnetic pulses on the switch.

Fourth, determine the wiring method

At present, the transmission network of the switch is used in both outdoor and underground modes. For overhead cables, the wires or cables should be buried before entering the house. The buried length is >2ρ (ρ is the resistivity of the grounding resistance, the unit is Ω*m), and the actual length is >50m. The buried ground is generally buried directly with a metal armored cable, or the non-metallic shielded cable is buried directly through the metal pipe. From the point of view of lightning protection, the cable entering the room should be buried when conditions permit.

The transmission network of the program-controlled switch should be routed along the dedicated signal cable trough in the room to avoid laying along the structural column of the building or close to the external wall; the strong and weak electric cables should not be laid in the same slot to reduce interference. For example, if there is no special signal cable trough in a central building in Guangzhou, the signal line and the power line are laid in the same slot. When the power line is struck by lightning or induced by lightning, an electromagnetic pulse is also induced on the signal line. The signal line is transmitted to the switch, causing the switch to be struck by lightning. As a result, the mainframe and computer network systems of the central building are often struck by lightning.

Fifth, the shield of the switch

The shield (including space and line shielding) of the switch, in addition to the signal line and power line, the switch room should also be shielded. The specific method is to ground the metal door, window, ceiling keel and anti-static floor.

Sixth, determine the location of the machine room

The location of the equipment room should be determined by factors such as the distance and near planning of the construction project, as well as the location of the terrain. For high-rise buildings, the general practice is to set the equipment room above the first floor below the 4th floor. In wet areas, the switch floor is not suitable for the first floor. However, some units are subject to conditions, and the switch house is not set up according to the above principles. For example, the program-controlled switch room of Guangdong Yingbin Hotel is located in the super-storey room on the sky side of the building. According to the relevant regulations of IEC1312-1 "Protection of Lightning Electromagnetic Pulse", the division of the building's sky surface in the lightning protection zone belongs to the LPZOB zone. In this zone, the electromagnetic field is not attenuated, and the switch is greatly affected by the electromagnetic field.

Seven, measures to determine the pressure limit

In terms of power supply, a three-stage shunt voltage limiting measure should be used to minimize the amplitude of the lightning electromagnetic pulse. Therefore, the first stage is installed in the low voltage part of the main power distribution room, and the 40kA power lightning protection box is installed; the second level is set at the power box of the floor, and the 20kA power lightning protection box is installed; the third level is set in the power switch of the switch room. Install a 10kA power lightning protection box or install a primary power lightning protection box in front of the UPS.

In terms of signals, measures to divide the voltage limit should also be adopted. First, install a reliable program-controlled switch arrester on the trunk line and the subscriber line, and install a network lightning arrester between the switch and the billing terminal.

Eight, determine the grounding system of the switch

The grounding of the program-controlled switch includes: DC power supply grounding; telecommunications equipment cabinet or rack shield grounding; metal sheath or shield grounding of inbound communication cable; grounding or cable in-street arrester grounding and signal cable empty pair grounding.

In order to make the grounding of the program-controlled switch, some units separately make a pair of artificial ground poles for the program-controlled switch. The grounding resistance of the ground pole also meets the requirements of the specification, but the lightning protection grounding of the artificial ground pole and the building is insufficient due to the limitation of the site. 20m. For example, the artificial ground poles of the Yunfu Hotel and the South China Building's main engine room and the lightning protection grounding of the building are less than 20m apart, which is inconsistent with the national JGJ/T16-92 "Electrical Design Code for Civil Buildings". The two networks must be larger than 20m when they are used independently. Relevant regulations. In order to solve the above problem, it is common practice to connect all the grounding of the program-controlled switch to the communication grounding device shared by the whole station, and then connect the common grounding device to the lightning protection ground of the building to form a grounding pole. After the grounding pole is used, the grounding device of the communication equipment needs to use a dedicated grounding trunk, and the cross-sectional area of ​​the trunk line is not less than 25mm2 of multi-strand copper wire.

Summary: In modern communication systems, a well-designed lightning protection system is critical to the safe operation of the equipment, not just for program-controlled switches, only in strict accordance with the principle of integrated lightning protection, from all possible lightning strikes. Introducing ways to plan and protect can ensure the safe operation of the entire communication network.