Diesel Generator Units (DGU), placed in a shipping container, are widely used for power supply of temporary facilities, as well as a backup power source. The generators in this design require the same grounding device, as well as other sources with the voltage of 380 V. Let's find out how to perform grounding and lightning protection for them?
An example of a diesel generator unit
In accordance with the EIC 7 th ed. Chapter 1.7, grounding resistance should be not more than 4 ohms. The contour can be laid around the container, and when installing lightning protection it can also be used for spreading lightning currents. The decision, which reflects the objectives of these systems doesn't require a large area - the ground electrode is located on the container perimeter at the distance of one meter and is complemented by vertical electrodes. Below you will see the detailed calculation and arrangement of grounding and lightning protection for a container with a diesel generator unit, located in Skolkovo.
Set of measures for lightning protection:
- You install two air-terminal masts for mounting to vertical surfaces 1.5m high, fixation of which is carried to the container wall. It is considered that the 0.3m of the bar length goes to the fixation.
- From each air terminal two down conductors are placed with the use of copper-bonded wire D = 8 mm, which are connected with an artificial ground electrode. Fixation of down conductors to the well is carried out by means of clamps GL-11704A (0.6-1 m setting increment). The down conductors are fixed on the roof with GL-11747A clamps.
A set of activities for grounding:
- A horizontal ground electrode is laid around the container. The ground electrode is made of corrosion-resistant stainless copper-bonded steel tape with the cross- section of 4x30 mm (GL-11075), laying depth 0.5 m, and distance to the wall of the building 1 m.
- In places of the down conductor descent, four vertical electrodes 3 m in length are installed.
- Connection of horizontal electrodes is carried out by using clamp ZZ-005-064.
- Connection of the down conductor with the output of the copper-bonded tape from the ground is carried out with the help of a control clamp GL-11562A.
Arrangement of elements of lightning protection systems and the grounding device is shown in Figures 1 and 2.
Protection zone corresponding to zone B of the AD, is shown in Figure 3.
Figure 1 - Layout of lightning protection elements and the grounding device
Figure 2 - Sketch with the location of lightning protection elements and the grounding device
Условные обозначения- notations
Стержневой молниеприемник 1,5 м – rod lightning rod 1.5m high
Вертикальный заземлитель длиной 3 м – vertical ground electrode 3 m long
Горизонтальный заземлитель – horizontal ground electrode
Токоотвод - down conductor
Зажим для подключения проводника – clamp for connecting conductor
Зажим контрольный – control clamp
Зажим на крышу, покрытую металлическим профилем для токоотвода – Clamp for the roof covered with metal profile for down conductor
Figure 3 - Protection zone corresponding to zone B of the AD
Calculation of lightning protection:
The following source data are taken for the calculation:
- Lightning density in the ground - 4 strikes / square kilometre per year for the city of Moscow region;
- The number of strikes into an unprotected object - 0.0014 1/year, period - once in 714 years.
The results of lightning protection calculation performed by the software, developed by JSC "Energy Institute to the name of Krzhizhanovsky "(JSC" ENIN ") are shown in Table 1.
Table 1 - Results of lightning protection calculation
|№||Object||Height of the lightning rod, m||Protection reliability||The number of strikes into an object
|The number of breakthroughs into the object,
|Period of srikes, year||Period of breakthroughs, year|
|once in 416 years||once in 8333 years|
Calculation of grounding device resistance:
Estimated value of the resistivity of frozen clay ground is taken to be 60 Ohm ∙ m. As previously mentioned, in accordance with the EIC 7 th ed. Chapter 1.7.101 grounding device resistance, to which neutrals of the generator or transformer or single-phase current supply terminals are connected. At any time of the year it should not exceed 4 ohms at the line voltage of 380 V of a three-phase power source.
The design resistance of the grounding device is 3.88 ohms, which is less than the required value of 4 ohms.
The list of the required materials is given in Table 2:
Table 2 - List of materials needs
Protection of power plants is very important. Their area of applicability is wide, including the use in backup and emergency power sources. If you need assistance in calculating, contact our Technical center ZANDZ.com!
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