The ZANDZ Technical Center has received a request to calculate the lightning protection and grounding system for a gas-regulating unit (GRU) in the Moscow Region. Let us further consider a solution proposed by our specialists.
facility: gas-regulating unit (GRU);
dimensions: 7 m x 2.5 m x 3 m;
soil resistivity: 100 Ohm*m.
calculate the lightning protection system;
calculate the grounding device.
Lightning protection and grounding of the building are made in accordance with:
SO 153 34.21.122 2003 "INSTRUCTIONS FOR MOUNTING LIGHTING PROTECTIONS OF BUILDINGS, STRUCTURES AND INDUSTRIAL COMMUNICATIONS", hereinafter referred to as SO;
The facility is "special, environmentally hazardous" from the viewpoint of SO and is classified as Category II of the lightning protection according to RD.
A set of measures to meet the necessary requirements to the lightning protection system and to the grounding arrangement of the GRU includes the following solutions:
Lightning protection of the facility is made using a 20 m lightning rod.
The space R = 5 m, H = 2.5 m above breathing tubes of the GRU is additionally protected.
Copper-plated steel electrodes 3 m long in the locations of the current collector downdrops are used as vertical ground electrodes. The copper-plated steel strip with a cross-section of 30 x 4 mm, combining all vertical electrodes, is used as a horizontal ground electrode. The distance to the facility foundation is at least 1 m. Strip deepening is 0.5 to 0.7 m.
According to EIC-7 issue, par.1.7.55, Grounding devices for protective grounding of electrical installations for buildings and structures and the 2nd and 3rd categories lightning protection of these buildings and structures, as a rule, shall be common.
Resistance design value of the grounding device is 3.72 Ohm.
If there are concrete-steel constructions, they shall be connected to down conductors/grounding device.
Connection to the grounding device is carried out using ZZ-005-064 clamps.
The results of calculation of protection zones according to SO:
h = 20 m;
Cone height according to SO, Table 3.4:
м - m
Cone radius according to SO, Table 3.4:
м - m
For the protection zone with the required reliability, radius rx at the height of hx = 5.5 m is defined as follows:
м - m
Ground terminal resistance calculation:
Vertical electrode resistance:
Ом - Ohm
Верт - Vert
Экв - Eqv
where ρρeq – is equivalent soil resistivity, 100 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;
where t – is deepening of the top of the electrode, 0.5 m.
Horizontal electrode resistance:
Ом - Ohm
where ρ – is soil resistivity, 100 Ohm·m;
b - is horizontal electrode width, 0.03 m;
h - is horizontal electrode depth, 0.7 m;
Lhor is horizontal electrode length, 54 m.
Electrical impedance of the grounding arrangement:
Ом - Ohm
where n – is a number of sets, vertical grounding arrangements - 3 pcs, horizontal grounding arrangement - 1 pc;
Kutil – is utilization rate, 0.75.
The calculated resistance of the grounding arrangement is 3,72 Ohm.
The location of the equipment is shown in Figure 1.
Figure 1. Equipment layout.
ГРПБ - GRU Условные обозначения - Legend
The list of necessary materials is given in Table 1.
Table 1. List of needed materials.
|№||Part number||Name||Quantity, pcs||Unit weight, kg.||Note|
|1.||ZZ-201-020||ZANDZ 20 m vertical lightning arrester (zinc-plated steel; with parts embedded under the foundation)||1|
|2.||GL-11075-50||GALMAR Copper-plated strip (30 * 4 mm / S 120 mm²; 50-meter strip bundle)||1||0,98||В метрах|
|3.||GL-11075-20||GALMAR Copper-plated strip (30 * 4 mm/ S 120 mm²; 20-meter strip bundle)||1||0,98||В метрах|
|4.||ZZ-001-065||ZANDZ Copper-plated threaded grounding rod (D14; 1,5 m)||6||2,00|
|5.||ZZ-002-061||ZANDZ Threaded coupling||4||0,08|
|7.||ZZ-004-060||ZANDZ Guide head for jackhammer attachment||2||0,09|
|8.||ZZ-005-064||ZANDZ Conductor connection terminal (up to 40 mm)||6||0,312|
|9.||ZZ-006-000||ZANDZ Conductive grease||1||0,10|
|10.||ZZ-007-030||ZANDZ Waterproofing tape||2||0,40|
|11.||ZZ-008-000||ZANDZ Attachment to the hammer (SDS max)||1||0,50|
Do you have any questions regarding lightning protection and grounding of the GRU? Please contact the ZANDZ Technical Center.