Internal lightning protection system
The internal lightning protection system is installed to prevent the occurrence of dangerous spark discharges inside the protected structure due to lightning current flowing through the external lightning protection system or the conductive part of the protected structure.
Dangerous spark discharges can occur between the external lightning protection system and the following components:
1) Metal equipment
2) Internal system
3) External conductive parts and lines connected to the protected structure
Sparks with a risk of explosion occurring inside the protected structure are always dangerous. In this case, additional protective measures are required, which are currently under review.
Equipotentialization can be achieved by connecting the following lightning protection systems to each other.
1) Metal equipment
2) Internal system
3) External conductive parts and lines connected to the structure. When installing lightning equipotential bonding in an internal system, some lightning current may flow in the internal system, so its influence must be considered. Mutual connection can be made in the following way.
(1) Bonding conductor in places where electrical continuity is not provided by bonding through natural components.
(2) Surge protection device (SPD) in places where direct connection with bonding conductor is not possible.
(3) Insulation discharge gap (ISG) for locations where direct connection with bonding conductors is not permitted.
The method of installing lightning equipotential bonding is important and should be discussed with communications engineers, electricians, gas engineers, other related engineers, and agency officials, considering that there are conflicting requirements.
Surge protection devices must be installed in a way that allows inspection.
When installing a lightning protection system, metal installations outside the structure to be protected may be affected, and this should be taken into account when designing the lightning protection system. Additionally, lightning equipotential bonding for external metal equipment is necessary.
Lightning equipotential bonding in a structure must be integrated and coordinated with other equipotential bonding.
4.1.1 Lightning equipotential bonding for metallic equipment
In the case of an external lightning protection system that is separate from the protected structure, lightning equipotential bonding must be installed only on the ground surface.
In the case of an external lightning protection system connected to the protected structure, lightning equipotential bonding must be carried out in the following places:
1) An underground (foundation) area or a place near the surface. Bonding conductors must be installed so that they can be easily inspected and connected to the bonding bar. The bonding bar must be connected to a ground electrode system. In large buildings (generally over 20m in height), an annular bonding bar or two or more bonding bars must be installed and interconnected.
2) Locations where insulation requirements are not met
Lightning equipotential bonding connections should be made as straight and straight as possible.
Note) If the conductive part of the structure is subjected to lightning equipotential bonding, some of the lightning current may flow through the structure, so it is best to take this effect into consideration.
Table 4.1 shows the minimum cross-sectional areas of bonding conductors connecting bonding bars to each other and conductors connecting bonding bars to the ground electrode system. The minimum cross-sectional area of the bonding conductor connecting the internal metal equipment to the bonding bar is shown in Table 4.2.
|
Lightning protection level |
ingredient |
cross-sectional area mm2 |
|
Ⅰ~Ⅳ |
copper |
16 |
|
aluminum |
25 |
|
|
steel |
50 |
|
Lightning protection level |
ingredient |
cross-sectional area mm2 |
|
Ⅰ~Ⅳ |
copper |
6 |
|
aluminum |
10 |
|
|
steel |
16 |
If insulating material is inserted in the middle of a gas pipe or water pipe, the insulating material inserted in the gas pipe or water pipe inside the protected structure must be bridged by an insulation discharge gap (ISG) with appropriate operating conditions with the consent of the water supplier and the gas supplier. do.
The insulation discharge gap (ISG) must be tested according to IEC 62561-3 and have the following characteristics:
1) , is the lightning current flowing along the relevant part of the external lightning protection system.
2) The rated impulse discharge overvoltage must be lower than the impulse insulation withstand voltage between external lightning protection system parts.
4.1.2 Lightning equipotential bonding to external conductive parts
Equipotential bonding to external conductive parts is carried out as close to the entry point of the protected structure as possible. The size of the bonding conductor must be evaluated according to the guidelines and must be thick enough to withstand a portion of the flowing lightning current.
If direct bonding is not possible, an insulating discharge gap (ISG) with the following characteristics must be used.
1) , is the lightning current flowing along the external conductive part under consideration.
2) The rated impulse discharge overvoltage must be lower than the impulse insulation withstand voltage between external lightning protection system parts.
If equipotential bonding is required but a lightning protection system is not required, the grounding system of the low-voltage electrical installation may be used. Conditions under which a lightning protection system is not required are described in KS C IEC 62305-2.
4.1.3 Lightning equipotential bonding for internal systems
Lightning equipotential bonding must be installed in accordance with 1) and 2) of Section 4.1.1. If the internal system cables are shielded or routed within a metal conduit, it is sufficient to simply bond the shielding layer to the metal conduit.
Note) Bonding between the shielding layer and the metal pipe may not prevent failure due to overvoltage of devices connected to the internal system conductors.
If the internal system cables are neither shielded nor routed within metal conduits, the internal system conductors must be bonded with a surge protection device. In the TN system, the protective conductor (PE) and neutral protective conductor (PEN) must be bonded to the lightning protection system directly or through a surge protection device.
The bonding conductor must have the same insulation discharge gap (ISG) and allowable current.
Surge protection devices must comply with KS C IEC 61643-11 and KS C IEC 61643-21 and have the following characteristics.
1) The test conditions are the lightning current flowing along the relevant part of the external lightning protection system.
2) The protection level must be lower than the impulse insulation withstand voltage of the protected section.
If protection of internal systems against surges is required, a coordinated SPD system should be used.
4.1.4 Lightning equipotential bonding for lines connected to protected structures
Lightning equipotential bonding for power lines and communication lines must be installed in accordance with Section 4.1.2.
The conductors of each line are bonded directly or by applying a surge protection device. The charging cable should only be connected to the bonding bar through a surge protector. In the TN system, the protective conductor (PE) and neutral protective conductor (PEN) are connected to the bonding bar directly or through a surge protection device.
If the power line or communication line is shielded or routed within a metal pipe, the shielding layer and the metal pipe must be bonded. If the cross-sectional area of the shielding layer or metal pipe is larger than the minimum cross-sectional area, separate lightning equipotential bonding is not required.
Equipotential bonding of cable shields or metal pipes should be performed near the entry point to the structure.
The bonding conductor must have the same insulation discharge gap (ISG) and allowable current.
Surge protection devices must comply with KS C IEC 61643-11 and KS C IEC 61643-21 and have the following characteristics.
1) The test conditions are the lightning current flowing along the line.
2) The protection level must be lower than the impulse insulation withstand voltage of the protected section.
Note) If equipotential bonding is required but a lightning protection system is not required, the grounding system of low-voltage electrical equipment may be used.