The hottest surge protector and its application

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Surge protective devices and their applications

with the rapid development of electronic technology and the extensive application of personal PCs, large and medium-sized computers and related information equipment, the lightning protection electromagnetic pulse (overvoltage) of buildings has attracted more and more attention. Therefore, more and more overvoltage protection products have been produced, and many of the scientific research achievements of measurement and control technology and related instruments have been put into the market, Surge protective device (SPD) is also gradually familiar to people

1 therefore, in addition to providing the specified environmental conditions, the environmental experimental equipment is required to provide the premise for the setting of surge protective devices

(1) for the buildings with information systems, whether lightning protection electromagnetic pulse is required should be carefully analyzed and comprehensively considered after the completion of direct and indirect loss assessment and the prediction of construction and maintenance investment, so as to achieve safety, applicability and economy. Because surge protective devices (SPDs) are relatively expensive compared with other switching devices, it is necessary to set them blindly without paying attention to investment in order to minimize the economic burden of developers

(2) without knowing the scale and specific location of the information system at the engineering design stage, if it is expected that there will be an information system in the future, natural components such as metal supports, metal frames or reinforced concrete reinforcement of buildings, metal pipelines, protective grounding system of power distribution, etc. and lightning protection devices should form a common grounding system in the design, And equipotential bonding plates should be embedded in some suitable places (such as weak motor room, etc.)

(3) reasonably divide the lightning protection area, and divide the building into lpz0a area, lpz0b area, lpz1 area... Lpzn + 1 area according to the possibility that the object may be struck by lightning and the attenuation degree of electromagnetic field intensity. It is required to make equipotential bonding on the interface of the two lightning protection areas on all metal objects passing through the interface (such as pipelines, power and communication lines), And shielding measures should be taken (note that there is no interface between lpz0a and lpz0b)

2 shielding, grounding and equipotential bonding measures

2.1 shielding

shielding is the basic measure to reduce electromagnetic interference. In the process of implementation, shielding should be set outside buildings and rooms, and laid in a suitable path to shield lines

(1) all large-size metal parts combined with buildings (such as roof metal surface, facade metal surface, steel bars in concrete and metal door and window frames) should be equipotential bonded and connected with lightning protection devices

(2) practice of shielded cable: the cable shielding layer should be equipotential bonding at least at both ends and at the junction of lightning protection area. When the system requires equipotential bonding only at one end, insulated double-layer shielding should be used, and the outer shielding should be equipotential bonding at least at both ends

(3) practice of unshielded cables: unshielded cables between separate buildings should be laid with industrial chains, cables, wires and other test pieces with a load force of 600 (3) 000kn. The experimental equipment for loading should be set in the metal pipe, and ensure that the metal pipe should be conductive from one end to the other end, and should be connected to the equipotential bonding belt of each separate building respectively

2.2 grounding

in addition to the grounding measures required by the lightning protection code, the following two points should be paid attention to:

(1) each building itself should adopt a common grounding system, including strong current system and various weak current systems

(2) when power and communication cables are connected between adjacent buildings, their grounding devices should be connected with each other

2.3 equipotential bonding

the metal objects and systems passing through the interface of each lightning protection area, as well as the metal objects and systems inside a lightning protection area, should be equipotential bonded at the interface

(1) several equipotential or local equipotential bonding strips should be set at the interface of each lightning protection area. For the interface between lpz0a or lpz0b area and lpz1 area, the equipotential bonding strip and internal ring conductor should be connected to reinforcement or metal facade and other shielding objects, and should be connected every 5m

(2) the minimum cross-section of the connecting conductor between the equipotential bonding strip and between the equipotential bonding strip and the grounding device, which flows through more than or equal to 25% of the total lightning current, is 16mm2 when copper material is used, and 50mm2 when iron (galvanized steel) is used; For the connecting conductor between the internal metal device and the equipotential bonding strip, the minimum section of the equipotential bonding conductor flowing through less than 25% of the total lightning current is 6mm2 when copper material is used, and 16mm2 when iron is used

(3) the minimum section of equipotential bonding strip of copper or galvanized steel is 50mm2

(4) when taking equipotential bonding measures, it should be connected to the nearest equipotential bonding belt with the shortest path

(5) the basic methods of equipotential bonding of information system include S-shaped star structure and M-shaped structure. When S-shaped equipotential bonding network is adopted, all metal components of information system, except the equipotential bonding point, should have more than 10kV, 1.2/50 with each component of common grounding system μ S-type and M-type combined networks can also be used in complex systems

3 performance characteristics of surge protector

(1) under normal conditions, SPD presents a high resistance state

(2) when the circuit encounters lightning strike or overvoltage, SPD presents a low resistance state, realizes low resistance conduction in nanosecond time, instantly discharges energy into the earth, and controls the overvoltage to a certain level

(3) when the transient overvoltage disappears, SPD immediately recovers to the high resistance state and extinguishes the power frequency freewheeling generated after the overvoltage passes

4 main performance indicators of surge protective device

4.1 maximum continuous operation voltage Uc

when SPD is selected in 220/380V three-phase system, its maximum continuous operation voltage Uc should be selected according to different grounding system forms, as shown in Table 1

(1) when TN system is used for power supply, TN-S system must be used for distribution lines and branch lines from the main distribution board (box) in the building

(2) in the following places, the above specified UC value of zinc oxide varistor SPD should be increased according to the specific situation:

① the power supply voltage deviation can also be used in other places where the difference of elastic components and small-scale mechanical property experiments exceeds the specified 10%

② places where harmonics increase the voltage amplitude

4.2 impulse current iimp

provisions include amplitude current ipeak and charge Q

4.3 nominal discharge

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