Common lightning protection equipment structure and selection

Common lightning protection equipment structure and selection

2.1 Types of lightning protection equipment

2-1 What is included in the lightning protection work?

Lightning protection work includes lightning protection of electrical equipment and prevention of construction (construction). The lightning protection of electrical equipment mainly includes lightning protection of power plants, power distribution stations and overhead power lines; the latter is divided into industrial and civil categories, which can be divided into three types according to the importance of dangerous procedures and facilities. Or two types.

2-2 What are the commonly used lightning protection devices?

Lightning protection devices are often used for lightning rods, lightning protection lines, lightning protection nets, lightning protection belts and lightning arresters. A complete set of lightning protection equipment includes lightning receptors, down conductors and grounding devices. The above needles, wires, nets, and belts are actually just lightning receptors. The lightning rod is mainly used to protect the open-air power distribution equipment and the protection building (structure); the lightning protection line is mainly used to protect the transmission line; the smashing net and the lightning protection belt are mainly used to protect the building (structure); the arrester is mainly used To protect power equipment, it is a special lightning protection equipment. In addition to the arresters, they use their prominent position above the protected object to direct the lightning to itself, and then discharge the lightning current into the earth through the down conductor and the grounding device to protect the protected object from lightning strikes.

What is the role of the 2-3 lightning rod?

Use the principle of tip discharge to avoid direct lightning strikes on equipment. At the same time, transformers, other electrical equipment or buildings are within their protection to prevent damage from direct lightning strikes.

2-4 How to prevent lightning strikes?

When the thundercloud pilot approaches the ground, the lightning discharge develops toward the direction of the ground electric field intensity. The lightning rod has a lightning-leading effect and plays a protective role on the surrounding objects.

2-5 What is the main purpose of lightning protection line protection?

The lightning protection line on the line is also called the overhead ground line. It is mainly used to limit the intrusion of substations along the line when the line (near the substation section) may be directly damaged by lightning.

Lightning shock wave amplitude and steepness.

2-6 What is the use of lightning protection nets and lightning protection belts?

The lightning protection belt refers to the metal belt used as lightning protection for the lightning protection part around the roof of the building as the lightning receptor. The device connected to the grounding network along the external wall is called the lightning protection belt. It is mostly used in civilian use. The building is especially mountainous. Since the lightning strike selectivity is strong (it is possible to discharge the building from the lateral side), the protection performance of the lightning protection belt (net) is better than that of the lightning rod.

Lightning protection nets are divided into two categories: surface mounted lightning protection nets and cage lightning protection nets. As the lightning receptor is installed along the upper part of the roof of the building, the down conductor is installed along the outer wall and connected to the grounding device, which is called the mounted lightning protection net. This method is often used in general buildings. The steel structure in the whole building is integrated into a large metal cage called a cage lightning protection net. The cage lightning protection network is divided into all the mounted lightning protection nets, all concealed lightning protection nets and some wall mounted dark lightning protection nets. For example, there are cast-in-place large formwork and prefabricated siding in high-rise buildings. There are many steel bars in the structure, and they are connected from top to bottom and indoor and outdoor water pipes, heat pipe networks, gas pipes, electrical pipes, electrical equipment and transformers. The neutral points are connected to form an equipotential whole, called a cage-mounted lightning protection net.

2-7 What is the main protection of power equipment?

The arrester can improve the damage to the electrical equipment caused by the lightning shock wave of the intrusion into the substation (or transformer) along the line, and limit the intrusion of the lightning wave (or the induced lightning wave) to the residual voltage value of the arrester, thereby making the transformer and Other electrical equipment is protected from overvoltages. 2- 36 What are the main technical indicators of surge protectors?

(1) Protection mode

Used to describe the configuration of the SPD protection function in the distribution line.

In the AC power distribution system, it is divided into phase line and phase line (LL), phase line and ground line (LPE), phase line and neutral line (LN), neutral line and ground line (N-PE). mode.

In the DC power distribution system, it is divided into three protection modes: positive and negative (V+-V_), positive and ground (V--PE), negative and ground (V_-PE).

Note: The voltage-limiting SPD and the combined SPD can be used in any protection mode; the voltage-switching SPD is not suitable for the protection mode other than N-PE due to the existence of the freewheeling breaking capacity and its test methods to be further studied. Promote use.

(2) The nominal voltage UN corresponds to the rated voltage of the protected system, which indicates the rms value of the AC voltage.

(3) The rated voltage Uc (maximum continuous operating voltage) can be permanently applied to the specified end of the surge protector without causing a change in the characteristic of the surge protector and activating the maximum voltage rms value of the varying component. For surge protectors used in 220/380V three-phase systems, the choice of Uc shall be in accordance with 6.4.5 of the Building Lightning Protection Design Code GB 50057-94 (2000 Edition).

In the 1TT system, the SPD is installed on the load side of the residual current protector, and its Uc should not be less than 1.55Uo (Uo is the nominal voltage of the phase-to-neutral line, in the 220/380V three-phase system, Uo=220V).

In 2TN systems, the Uo of the SPD should not be less than 1.15Uo.

In the 3TT system, the SPD is installed on the power supply side of the residual current protector, and the Uc should not be less than 1.15Uo.

In the 4TT system, the SPD is installed on the load side of the residual current protector, and its Uo should not be less than 1.15U (U is the line voltage).

(4) Impact flow capacity Iim

The surge protector does not cause substantial damage, but can pass the maximum current peak at a specified number of times and a specified waveform.

(5) Response time tA

Mainly reflected in the action sensitivity of the protection element in the surge protector.

(6) Maximum continuous working voltage Uc

The maximum continuous operating voltage Uc is a positive parameter of the SPD, which is the maximum rms voltage or DC voltage that can be continuously applied to the SPD without damaging the SPD. It should be greater than the power frequency that may occur in the electrical device or Temporary overvoltage, so as to avoid the SPD being unnecessarily damaged by such power frequency overvoltage breakdown to form a short circuit to ground fault.

The SPD is considered to be independent of AC and DC, as long as the maximum continuous operating voltage Uc does not exceed the SPD parameters.

(7) Nominal discharge current In

A peak current flowing through the SPD with a current wave of 8/20 μs. It is used for the class II classification test of SPD, and is also used for the preparatory treatment of SPD class I and class II classification tests.

(8) Maximum discharge current (impact flow capacity) Imax

The maximum discharge current peak with an 8/20 μs waveform that can flow through the SPD. It is used for class II classification tests.

(9) Residual pressure

The voltage peak between the SPD terminals when the discharge current passes.

(10) Voltage protection level Up

The role of the SPD is to discharge the lightning current into the ground and reduce the lightning impulse voltage amplitude to the required level, which is called the SPD voltage protection level Up.

The voltage protection level Up is a parameter that characterizes the SPD's ability to suppress surge. It is a characteristic parameter that characterizes the SPD's voltage limit at both ends. It is determined by the manufacturer from the specified series of preferred values, and is generally found in the SPD product logo. Note that the unit is kV, which is generally understood to be the protection that the SPD can provide for the protected equipment. This voltage value is greater than the measured value of the surge voltage limit.

Up is determined by the manufacturer and indicates the protection that the SPD can provide for the protected device.

The voltage protection level Up of the SPD should match the surge overvoltage rating (Uw) of the protected equipment, that is, the Uw of the protected equipment should be equal to or greater than the voltage protection level of the SPD, and consider a connection voltage drop. the amount.

GB50057--946.4.4 stipulates: “The maximum surge voltage at the interface between the incoming line of the building and other lightning protection areas, ie the maximum clamping voltage of the surge protector plus the induced voltage of the leads at both ends shall be associated with the system. The basic insulation level is consistent with the maximum surge voltage allowed by the device."

In order to make the maximum surge voltage low enough, the leads at both ends should be the shortest.

Table 2-7 lists the rated impulse withstand voltage values ​​of IEC standards for electrical equipment of all levels.

Table 2-7 Rated impact overvoltage values ​​of electrical equipment at all levels

Nominal voltage of electrical equipment /V Electrical equipment should have an impact overvoltage value / kV

Three-phase system Single-phase system Line-in equipment Power distribution circuit Power equipment Special protection equipment

120~ 240 4 2.5 1.5 0.8

230/400 6 4 2.5 1.5

400/690 8 6 4 1.5

1000 by design

The low-voltage distribution circuit of the building should be equipped with an SPD of Up to 4kV. The server, the computer, the program-controlled switch, etc. are required to be protected. The rated voltage is 1. 5kV, so the Up value is not more than 1.2kV. SPD.

It should be noted that the Up mentioned here should be the parameter value under the condition of nominal discharge current In.

(11) Limit voltage When a shock wave of a predetermined waveform and amplitude is applied between a terminal on the line side of the surge protector and the ground electrode, the voltage peak between the line terminal of the device side and the ground electrode appears.

Since it is impossible to make the samples of each sample to be consistent when subjected to impact, the residual pressure of each sample is inconsistent, and the maximum residual pressure should be taken as the limiting voltage.

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