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;
RD 34.21.122 87 "INSTRUCTIONS FOR MOUNTING LIGHTING PROTECTION OF BUILDINGS AND STRUCTURES", hereinafter to as RD
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.