When designing generators, a particular attention is paid to electrical safety systems such as grounding and lightning protection. The ZANDZ Technical Center has received a request to calculate the lightning protection and grounding systems for the gas engine generator. Let us consider the proposed solution.
1. Facility: 1,500 MW gas engine generator.
2. Dimensions of the protected facility: 16 m x 8 m x 5.3 m.
3. The soil resistivity used in calculations is 150 Ohm*m.
1. Calculate the external lightning protection system.
2. Calculate a grounding device having the resistance not more than 4 Ohm.
The activities have been performed according to:
- EIC, Rev. 7. Electrical Installations Code (hereinafter referred to as the EIC);
- SO 153-34.21.122-2003 Instructions for Mounting Lightning Protection for Buildings, Structures, and Industrial Utilities (hereinafter referred to as SO);
- RD 34.21.122-87 Instructions for Mounting Lightning Protection for Buildings and Structures (hereinafter referred to as RD).
The facility is classified as Category 2. The required system reliability is at least 0.95.
A set of measures to meet the necessary requirements to the lightning protection system and grounding arrangement for the gas engine generator includes the following solutions:
The lightning protection of the facility is made using 12 m lightning arresters, which are installed at the distance at least 3 m from the protected facility, at the edges.
3 m steel copper-plated grounding devices are used as a vertical grounding device.
30 x 4 mm steel copper-plated bar combining all vertical electrodes is used as a horizontal grounding device. The distance to the facility foundation is at least 1 m. Strip deepening is 0.5 to 0.7 m.
According to the EIC, Rev. 7, item 1.7.55, grounding devices for protective grounding of electrical installations for buildings and structures and Categories 2 and 3 of the lightning protection for these buildings and structures usually should be common.
If there are reinforced concrete structures, they should be connected to current collectors/to the grounding device.
Connection to the grounding device (external and internal) is made by clamps ZZ-005-064.
The results of calculation of protection zones according to SO:
Lightning arrester No. 1-2 (ZZ-201-012):
h = 12 m;
Cone height according to SO, Table 3.4:
h0 = 0.8*h = 9.6 m;
Cone radius according to SO, Table 3.4:
r0 = 0.8*h = 9.6 m:
Distance between the lightning arresters (maximum):
L = 22 m;
Limit distance between lightning arresters according to SO, Table 3.6:
Lmax = 4.75*h = 57 m;
L0 = 2.25*h = 27 m;
There is not sagging height.
For the protection zone with the required reliability, radius rcx at height h0 =5,3 m is defined as follows:
м - m
Results of the calculation performed using the software developed by Krzhizhanovsky Energy Institute (OAO ENIN):
Intensity of lightning discharge into the ground is 4 strikes/square km/year;
The total number of strikes into the system is 0.024 (once every 42 years).
The total number of breakouts into the system is 0.000021 (once every 47,619 years).
System reliability is 0.99913;
The probability of breakout into all facilities of the system is 0.00087.
Ground terminal resistance calculation:
Vertical electrode resistance:
Ом - Ohm
where ρeq is equivalent soil resistivity, 150 Ohm·m;
L is vertical electrode length, 3 m;
d is vertical electrode diameter, 0.014 m;
T is depth, i.e. the distance from the ground surface to the ground electrode, 2 m;
м - m
where t is electrode top depth, 0.5 m.
Horizontal electrode resistance:
Ом - Ohm
where ρ is soil resistivity, 150 Ohm·m;
b is horizontal electrode width, 0.03 m;
h is horizontal electrode depth, 0.5 m;
Lгор is horizontal electrode length, 60 m.cjj
Electrical impedance of the grounding arrangement:
Ом - Ohm
where n is a number of sets, vertical grounding arrangements - 10 pcs, horizontal grounding arrangement - 1 pc;
Kutil is utilization rate, 0.69.
The calculated resistance of the grounding arrangement is 3,7 Ohms.
The layout of the equipment is shown in Figure 1.
Молниеприемник-мачта высотой 12 м (ZZ-201-012) - 12 m lightning arrester (ZZ-201-012)
Полоса омедненная сечением 30х4 мм (GL-11075) - Copper-plated bar 30 x 4 mm (GL-11075)
Электрод D=14 мм, L=3 м. - Electrode D = 14 mm, L = 3 m
Figure 1. Equipment layout.
The list of equipment and necessary materials is provided in Table 1.
Table 1. List of needed materials.
|№||Part number||Name||Quantity, pcs.||Unit weight, kg||Note|
|1.||ZZ-201-012||ZANDZ 12 m vertical lightning arrester (zinc-plated steel; with parts embedded under the foundation)||2|
|2.||ZZ-001-065||ZANDZ Copper-plated threaded grounding rod (D14; 1.5 m)||20||2,00|
|3.||ZZ-002-061||ZANDZ Threaded coupling||11||0,08|
|5.||ZZ-004-060||ZANDZ Guide head for jackhammer attachment||4||0,09|
|6.||ZZ-006-000||ZANDZ Conductive grease||2||0,10|
|7.||ZZ-008-000||ZANDZ Attachment to the hammer (SDS max)||1||0,50|
|8.||ZZ-005-064||ZANDZ Conductor connection terminal (up to 40 mm)||16||0,312|
|9.||ZZ-007-030||ZANDZ Waterproofing tape||6||0,40|
|10.||GL-11075-20||GALMAR Copper-plated strip (30 * 4 mm/ S 120 mm²; 20-meter strip bundle)||1||0,98||Вес за 1 м|
|11.||GL-11075-50||GALMAR Copper-plated strip (30 * 4 mm / S 120 mm²; 50-meter strip bundle)||1||0,98||Вес за 1 м|
Do you have any questions regarding lightning protection and grounding of the gas engine generator? Please contact the ZANDZ Technical Center!