We have received a request to calculate grounding devices for a diesel generator set and a fire brigade station. The employees of the ZANDZ Technical Center have accepted this task and prepared the solution we are going to study below.
Facilities to be grounded:
- a diesel generator set;
- a fire brigade station intended for 2 vehicles.
soil type: soil containing crushed stone and a sandy filler with a low filling degree;
soil resistivity accepted for calculations is 1,000 Ohms*m.
According to the EIC Rev. 7, item 1.7.101. Resistance of the grounding arrangement to which generator and transformer neutral wires or a single-phase current source outputs are connected, in any time of year, should not exceed 4 Ohms, respectively, with linear voltages 380 V for a three-phase current source, or 220 V for a single-phase current source. The resistance should be provided taking into account natural grounding arrangements as well as grounding electrodes of repeated grounding arrangements for high-voltage PEN or PE wire up to 1 kV with at least two branch lines.
With soil resistivity ρ > 100 Ohms m, these standard values are allowed to be increased 0.01 ρ times, but not more than 10-fold. 1,000 * 0.01 = 10, i.e. 10 * 4 = 40 Ohms.
The allowable resistance of the grounding arrangement should not exceed 40 Ohms.
A set of measures to ensure the requirements for one grounding arrangement is based on the following solutions:
installation of 2 sets of electrolytic grounding ZZ-100-102, around the diesel set generator, a grounding circuit is made using a corrosion-resistant steel copper-plated bar 30 x 4 mm. The distance from the electrode to the facility is at least 3 m, depth is 0.5–0.7 m;
for the fire brigade station, the distance between two grounding arrangements should be at least 22 m.
Ground terminal resistance calculation:
The set ZZ-100-102 resistance:
Ом - Ohm
где C where C is a non-dimensional factor, describing the electrolyte content in the surrounding soil, 0.25;
ρ – is soil equivalent resistivity, 1,000 Ohms m;
L – is vertical electrode length, 2.4 m;
d – is vertical electrode diameter, 0.65 m;
T – is deepening - the distance from the ground surface to the ground electrode, 0.6 m.
Horizontal electrode resistance:
Ом - Ohm
Гор - Hor
where ρ – is soil resistivity, 1,000 Ohm·m;
b - is horizontal electrode width, 0.3 m;
h - is horizontal grounding depth, 0.5 m;
Lгор is horizontal electrode length, 22 m.
Electrical impedance of the grounding arrangement:
Ом - Ohm
ЗУ - GA
Исп - Util
where n – is a number of kits, 2 pcs;
Kutil – is utilization ratio, 0.99 for electrolytic grounding sets; 0.7 for horizontal grounding
Rated resistance of the grounding arrangement is 30,63 Ohms, which is less than the required value of 40 Ohms.
The layout of the equipment is shown in Figure 1.
Комплект электролитического заземления - Electrolytic grounding set
Полоса омедненная 30х4 мм - 30 x 4 mm copper-plated bar
Здание пожарного депо - Fire brigade station
ДГУ - DGS
22 м - 22 m
3 м - 3 m
Figure 1. Layout of grounding arrangement parts
The list of materials required for two facilities is provided in Table 1.
Table 1. List of needed materials.
|Item #||Figure||Part number||Name||Quantity, pcs.|
|1.||ZZ-100-102||ZANDZ Electrolytic Grounding Set (horizontal; 3 meters length)||4|
|2.||GL-11075-50||GALMAR Copper-plated strip (30 * 4 mm / S 120 mm²; 50-meter strip bundle)||1|
|3.||GL-11075-10||GALMAR Copper-clad strip (30x4 mm/S 120 mm²; 10-meter strip bundle)||1|
|4.||ZZ-007-030||ZANDZ Waterproofing tape||4|
|5.||ZZ-005-064||ZANDZ Conductor connection terminal (up to 40 mm)||10|
Do you have any questions with regards to the grounding system for the fire brigade station and diesel generator set? Please contact the ZANDZ Technical Center!