Power engineering utilizes the most critical facilities in terms of lightning protection, including: substations, power plants, and high-voltage power lines. It is important to properly arrange lightning protection not only at a single facility but at all facilities in the industry at once. This is due to the fact that the lightning strike can result in significant process and utility consequences for the city or region, or maybe even to a catastrophe. Power supply interruptions occur before accidents are identified and eliminated. Depending on the damage degree, they can take several minutes or up to several days. Certainly, such facilities implement many measures and technical means that prevent the lightning strike to the critical equipment and minimize effects of atmospheric discharges.
The lightning protection measures include:
- Lightning protection provided using rod and wire arresters that get the strike instead of the facility. Moreover, the roof can also be used as a lighting arrester and grid, if the lightning strike directly to the facility does not cause any significant consequences.
- Proper arrangement of lightning arresters and current collectors that ensures controlled lightning current drain to the grounding arrangement. As a result of this, the lighting current, when flowing along the facility, cannot form strong electromagnetic fields and surges, which are dangerous enough for electric and electronic devices in case of the noise in their feeding cables and secondary circuits.
- Correctly designed and reliably installed grounding arrangement ensure the efficiency of other means. The proper grounding electrode structure is required to ensure the sufficient lightning current flow to the ground which results in reduced overvoltage and prevents surface discharges and sparks. To ensure proper operation, the grounding arrangement should have a particular grounding resistance which is not more than 0.5 Ohm at substations.
The technical means include:
- Surge limiting devices, such as arresters and surge protection devices (SPDs). Arresters and overvoltage limiters are used in high-voltage grids, while SPDs are used in low-voltage grids.
- Automation equipment used for restoring power supply after the lightning strike if it has not led to any irreversible damage, and if the normal operation can be continued. Such means include automatic reclosing on the line.
Substations and high-voltage power lines are vastly discussed in regulatory documents, including:
- The Electrical Installations Code (EIC).
- STO 56947007-29.130.15.114-2012 Grounding Devices Design Guidelines for 6-750 kV Substations.
- RD 153-34.3-35.125-99 Guidelines on Protection of 6-1150 kV Power Grids from Thunderstorm and Internal Surges.
This is not an exhaustive list. There are many other standards. However, note that they are not related to power plants with the rotating equipment inside. There is not a single special document, except for items 4.2.160-4.2.165 of the EIC, which are intended for the surge protection of the rotating equipment.
These items in the EIC discuss the location and capacity of valve-type arresters or non-linear overvoltage limiters for protecting motor generators against thunderstorm surges. The protection of the overhead line terminals to the buses of the switching equipment of the power plant is arranged using wire lightning arresters, as well as valve-type arresters or overvoltage limiters. Note that item 4.2.162 states accurate requirements to the grounding resistance of valve-type arresters and overvoltage limiters, which, in most cases, should not exceed 3 Ohm, and the grounding resistance of bottoms at the wire section should not exceed 10 Ohm.
Item 4.6.163 of the EIC standardizes the protection against direct lightning strikes. Thus, current collectors connecting generators and transformers, should be covered by the protection zone of lightning arresters of the structures of a power plant or substation. If the protection zone of such lightning arresters does not cover current collectors, they are protected using standalone lightning arresters or wires with the protective angle not more than 20 degrees. The grounding is ensured via isolated grounding electrodes which should not be connected to the grounding arrangement of bottoms of current collectors, or due to the connection to the grounding arrangement of the switching equipment of the power plant or substation, and the connection point should be spaced from current collector elements with the grounding by at least 20 m. The distance from current collectors or wire supports and their grounding electrodes in the air and on the ground to aboveground or underground parts of current collectors, including grounding electrodes, should be at least 5 m.
In addition to the protection against thunderstorm surges, the external lightning protection for the power plant should be arranged. To do this, let's use broader regulatory documents for the lightning protection which cover several types of facilities.
The rotating equipment, such as generators and motors, requires the lightning protection together with the building they are installed in. The preface in RD 34.21.122-87 states: "The Instructions do not cover design and arrangement of the lightning protection for power lines, electrical part of power plants and substations". Such a wording may be disputable in the following aspects: can a building be considered separately from the electrical part or should we use there any lightning protection means in accordance with this document. Table 1 in RD 34.21.122-87 aggravates the uncertainty as it contains types of buildings and structures to be subjected to the lightning protection, because it does not mention power plants.
However, we should not design the lightning protection relying on a disputable regulatory basis, so let's read the standard SO 153-34.21.122-2003. Its Table 2.1 particularly indicates power plants and even classifies them as special limited-hazard facilities. Now, we can say that this document is suitable for designing the lighting protection for power plants and rotating equipment. Let's then consider the example of calculation for the lightning protection of the hydroelectric plant according to SO 153-34.21.122-2003.
Example of calculation of the lightning protection and grounding for the hydroelectric power plant
The activities were carried out in accordance with the EIC, Rev. 7, Chapter 1.7, SO 153-34.21.122-2003 Guidelines for Arrangement of Lightning Protection of Buildings, Structures, and Industrial Utilities (hereinafter CO).
Protection of buildings against lightning strikes is provided by using lightning arresters. Lightning arrester is a device that is elevated over the protected facility through which the lightning current goes into the ground bypassing the protected facility. It consists of a lightning rod arrester that accepts the lightning discharge directly, a current collector, and a ground terminal.
The lightning protection of the facility is only provided when using ZANDZ lightning arresters having heights determined by calculations, names and product numbers of which are as stated in the specifications and the commercial proposal.
A set of arrangements ensuring compliance with the lightning protection requirements is based on the following solutions:
- installation of 2 lightning rods 7.3 m high on the wall. It is considered that 1,4 m of the rod length is used for securing.
- 4 lightning rods 7.3 m high installed on the APC are used;
- the lightning arresters are interconnected to create two current collectors using galvanized wire D = 8 mm from each lightning arrester;
- current collectors are attached (with mounting step 0.6 to 1 m):
- on the gutter using clamps ZZ-11545;
- on the roof and the wall using clamps ZZ-11747;
- on the waterspout using clamps ZZ-11514;
- current collector connection and branching are made using clamps ZZ-11551.
A set of measures to ensure the requirements for the grounding arrangement is based on the following solutions:
- installation of the grounding arrangement consisting of a horizontal electrode (steel zinc-plated bar with the cross-section 4 x 40 mm), depth 0.5 m, distance to foundations 1 m, and 4 vertical electrodes (zinc-plated steel rods having the diameter 16 mm) 3 m long;
- the vertical and horizontal electrodes are connected to each other using ZZ-202-022 clamps;
- the connection of the current collector with the output of the zinc-plated bar from the ground is made using clamps ZZ-202-023;
- design of the grounding arrangement corresponds to item 1.7.55 of the EIC. Grounding arrangements for protective grounding and grounding for lightning discharges are common.
The location of the elements of the lightning protection system and the grounding arrangement is shown in a drawing in a separate file. The protection zone shown conforms to the reliability of 0.9 according to SO.
Calculation of a ground terminal resistance
Information on the soil type and its resistivity was not provided by the customer. The estimated soil resistivity is taken to be 100 Ohm ∙ m.
Warning! In case the Customer provided erroneous and limited soil data, the above calculation of a grounding arrangement is considered incorrect. If the soil resistivity differs from the calculated one, it is necessary to perform computations with a real value. If the normalized impedance of the grounding arrangement is exceeded, there must be introduced the design corrections.
Resistance of a horizontal electrode::
where ρ is the soil resistivity, Ohm·m;
b is the horizobntal electrode bar width, m;
h is the depth of the horizontal electrode, m;
Lhor is the horizontal electrode length, m.
Vertical electrode resistance
where ρ is the soil resistivity, Ohm·m;
L is the vertical electrode length, m;
d is the diameter of the vertical electrode, m;
T is depth, i.e. the distance from the ground surface to the grounding electrode, m;
where t is the depth of the top of the electrode, m.
Electrical impedance of the grounding arrangement:
where n is the number of sets;
kutil is the utilization ratio.
The resistance of the common grounding arrangement for APC and hydroelectric power plant are calculated.
The rated resistance of the grounding device is 1.59 Ohm.
See the lightning protection layout and attachments on a separate page.
Table 1. List of required materials for the hydroelectric power plant
Do you have any inquiries concerning lightning protection for the acetone storage, the filtration pump station, or other facilities? Please, contact the ZANDZ Technical Center!
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