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Designing lightning protection for a covered transitional point 110 kV

June 28, 2017

The closed intermediate station provides the air power line transition to the cable line. As in any other electrical installations, we should provide a grounding arrangement and protection against direct lightning strikes there.

Our ZANDZ Technical Center has received the following question: How to protect a closed 100 kV intermediate station? Let's consider the solution we provided below.

 

Calculation example

Facility: Closed 110 kV intermediate station

Фасад в осях 4-1 - Façade within axis 4-1
Фасад в осях B-A - Façade within axis B-A

Figure 1 - Facility dimensions.

Task: To perform calculations for the grounding and lightning protection system.

 

Protection of the buildings and structures against lightning strikes is provided by using lightning arrester. The lightning arrester is a device that is elevated over the considered object, through which the lightning current goes into the ground bypassing the protected object. It consists of a lightning rod that directly accepts the discharge of a lightning , a current collector, and a grounding electrode.

 

A set of arrangements ensuring compliance with the lightning protection requirements is based on the following solutions:

The lightning protection was made according to SO 153-34.21.122-2003 GUIDELINES FOR ARRANGEMENT OF LIGHTNING PROTECTION OF BUILDINGS, STRUCTURES, AND INDUSTRIAL UTILITIES and RD 34.21.122-87 GUIDELINES FOR ARRANGEMENT OF LIGHTNING PROTECTION FOR BUILDINGS AND STRUCTURES.

2.The facility is classified as Category 3 in terms of lightning protection. The system reliability shall be at least 0.9.

3. The facility's lightning protection is made using 4 m lightning mast (ZZ-201-004). They are connected to the current collector using a clamp ZZ-202-001. The attachment to the vertical surface is made using clamp ZZ-203-002.

4. Current collectors are installed using a clamp GL-11747A on the roof and GL-11703A on vertical surfaces. The clamp spacing is 0.8 to 1.0 m. The lightning rod are connected to each other by the roofing perimeter.

5. A multi-purpose clamp GL-11551A is used for securing rolled metal products along the distance, as well as in the grid nodes.

6. All metal elements located on the roof should be connected to the current collectors.

7. Copper-plated 3 m steel electrodes are installed as vertical ground terminals in the downdrop locations (in the corners of the facility). Horizontal ground terminal represents a copper-plated steel strip with the cross-section of 30 x 4mm gathering all vertical electrodes into the circuit. The distance to the facility foundation is at least 1 m. Strip deepening is 0.5 to 0.7 m.

8. The grounding arrangement connection is made using clamps ZZ-005-064.

 

Results of the calculations performed by using the software developed by OJSC G.M. Krzhizhanovskiy Energy Institute (OJSC ENIN):

Density of lightning discharge into the ground is 4 strikes/square km/year;

The total number of strikes into the system is 0.047 (once every 21 years);

The total number of breakouts into the system is 0.00088 (once every 1136 years).

The system's reliability is 0.981

The probability of breakout into all facilities of the system is 0.019.

 

Ground terminal resistance calculation:

Верт - Vert
Ом - Ohm
Гор - Hor
ЗУ - GA

The estimate resistance of the grounding arrangement is 2.73 Ohm.

 

The results of calculation of protection zones according to SO:

Lightning mast No. 1, 2 (ZZ-201-004):

h = 16.82 m;

Cone height according to SO, Table 3.4:

h0 = 0.85*h = 0.85*16.82 = 14.3 m;

Cone radius according to SO, Table 3.4:

r0 = 1.2*h = 1.2*16.82 = 20.18 m;

Distance between the lightning rod:

L=20 m;

Limit distance between lightning rods according to SO, Table 3.6:

Lmax = 5.75*h = 5.75*16.82 = 96.72 m;

L0 = 2.5*h = 2.5*16.82 = 41.05 m;

Zone slack is absent.

 

Figure 2 shows the equipment and protection zone layout.

Зона защиты - Protection zone
Условные обозначения - Legend
Фасад в осях 4-1 - Façade within axis 4-1
Фасад в осях B-A - Façade within axis B-A

Figure 2 - Equipment layout. Protection zone.

 

Table 1 includes the list of the required hardware and materials.

 

Table 1 – List of required hardware and materials.

№ Figure Part number Name Quantity, pcs
1. ZZ-201-004 ZANDZ Vertical lightning mast, 4 m (stainless steel) 4
2. ZZ-203-002 ZANDZ Chimney fastening for lightning rod (stainless steel) 4
3. ZZ-202-001 ZANDZ Lightning rod clamp for current collectors (stainless steel) 4
4. GL-11149-50 3
5. GL-11551A GALMAR Current collectors connection clamp (painted galvanized steel) 15
6. GL-11747A GALMAR Current collector roof clamp for the roof coated with metal shape / corrugated sheeting (painted galvanized steel) 90
7. GL-11703A GALMAR Current collector facade clamp for current collector providing 15 mm elevation over the clamp (painted galvanized steel) 60
8. ZZ-001-065 ZANDZ Copper-plated threaded grounding rod (D14; 1.5 m) 8
9. ZZ-002-061 ZANDZ Threaded connecting coupling 5
10. ZZ-003-061 ZANDZ Takeoff Tip 4
11. ZZ-004-060 ZANDZ Guide head for jackhammer attachment 2
12. ZZ-005-064 ZANDZ Conductor connection clamp (up to 40 mm) 12
13 ZZ-006-000 ZANDZ Conductive grease 1
14. ZZ-007-030 ZANDZ Waterproofing tape 1
15. ZZ-008-000 ZANDZ Attachment to the jackhammer (SDS max) 1
16. GL-11075-50 1
17. GL-11075-20 2

 

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