Introduction

Widely adopted in PV, wind power and construction power supply, compact substations, including compact mobile substations, run exposed outdoors. Non-standard lightning grounding may damage the substation transformer and trigger safety accidents. As a professional compact substation manufacturer, Chuanli’s integrated units combine all components of a substation. This article analyzes lightning risks and offers standardized lightning protection & grounding design guidelines for engineering teams.

Lightning Risks of Outdoor Compact Substation Equipment

The outdoor compact box transformer is exposed to the open air, lacks building shielding, and is exposed to direct lightning. Inductive lightning surge has dual hazards, and the fault hazard of different types of box-type equipment under thunderstorm conditions has differentiated characteristics. The whole section adopts a continuous and integrated narrative, without fragmented segmentation and disassembly, and the second-level headings are fully retained.

Lightning damage to compact substation transformer

The transformer in the box substation is the core transformer component in the box, and the insulation of the winding is extremely sensitive to lightning impulse overvoltage. When the overhead line is struck by lightning, the huge amplitude of the lightning surge will invade the transformer winding along the cable; If the surge device is not matched properly and the resistance of the grounding circuit is too high, the transient overvoltage will break through the insulation between the winding layers, causing the winding to be permanently short-circuited and the transformer to be scrapped. The oil-immersed compact box transformer will also cause the internal gas of the oil tank to expand when it is hit by lightning, triggering the action of the pressure relief valve and even causing oil leakage and trigger accidents; The insulation grade of the SF6-free dry box substation transformer of Chuanli is higher, and if there is no graded surge protection, a single lightning strike may cause a long-term power outage in the whole station, seriously affecting the power generation income of new energy projects.

Grounding hazards of mobile compact substation

Compared with the fixed box transformer with a permanent buried grounding network, the grounding construction hazards of the mobile box transformer used for temporary access to the construction site, wind power and emergency power supply are prominent. The depth of the temporary grounding stake is shallow and the contact is loose, and the grounding resistance exceeds the standard, making it impossible to quickly discharge the lightning fault current. At the same time, the mobile chassis is frequently transferred, and the ground connection copper strip is easily broken and loosened due to repeated vibration. Once the lightning strikes the outer casing of the box or the induced surge enters the circuit, the equipment casing will generate a dangerous contact voltage, causing electric shock and casualties to the on-site workers. In mountainous areas with high-resistivity soil, it is impossible to add external horizontal ground electrodes for temporary grounding of mobile substations. When a lightning discharge occurs, the voltage difference between the equipment and the ground will increase sharply, which will also damage the secondary protection and monitoring components in the box.

The fixed-type box transformer of Chuani is equipped with complete and integrated lightning protection components at the factory, and the mobile model is equipped with removable lightning protection modules, which can be disassembled and reassembled with the equipment.

Standard Direct Lightning Protection Design Rules

The complete direct lightning protection of the outdoor compact substation consists of three parts: the lead shielding system, the lead line, and the graded surge protector (SPD). According to the IEC 62 305 rolling ball method, Chuanli has formed a standardized supporting scheme for substations of different capacities. The text is fluent and coherent without fragmented points.

Air terminal layout for compact transformer substation

The lightning rod (lightning rod/lightning conductor) of the outdoor compact box substation is laid according to the 30° protection angle standard of the rolling ball method, and the ZBW series box substation provided by Chuanli offers two mature solutions for selection. 630kVA and below single small capacity box transformers, the 1.5m high integrated lightning rod is installed in the center of the top of the box, which can completely include the whole equipment in the protection range; More than 1000k VA new energy power station multi-unit large-capacity box transformer, along the four sides of the box body, the entire length of the installation of lightning rod, the corner column added auxiliary short lightning rod to eliminate the shielding blind spot. All lightning rods and the metal shell of the box are welded with hot-dip galvanized flat steel as the grounding wire, with a minimum cross-sectional area of 40 × 4 mm, using the shortest direct path to avoid bending and increase impedance, so as to realize the rapid introduction of lightning current into the underground grounding network.

Surge device matching for substation components

According to the voltage level of each substation component in the box, three-level surge protectors are equipped to realize the absorption of lightning surge gradient, which is the core measure to protect the transformer of the box substation from overvoltage breakdown. The following table summarizes the standardized SPD parameters for the high- and low-voltage circuits of the Chuanli box-type transformer.

The three-level surge is matched to form a gradient energy absorption, avoiding the failure of a single SPD due to a strong lightning surge overload, and preventing the lightning overvoltage from penetrating the transformer insulation from the root.

Standard Grounding System Design Specifications

The reliable grounding network is the foundation of the whole lightning protection system of the outdoor compact substation, which is divided into two major links: the outdoor pre-embedded main grounding network and the equal potential connection in the substation. All design parameters follow the GB/T 5 0065 and IEC 6036 4 specifications.

Ground grid layout for outdoor compact substation

The main grounding network of the outdoor box transformer adopts a closed rectangular ring layout, with a 2.5m long hot-dip galvanized vertical grounding electrode buried every 5m around the foundation of the box, and connected to form a closed loop through 40×4 mm galvanized flat steel. Under the normal medium-resistivity soil environment, the comprehensive ground resistance of the ring-shaped ground network shall not be greater than 4Ω. In the mountainous, high-resistance soil area, it is necessary to add horizontal extension strips or install graphite grounding modules to reduce resistance to meet the standard. All the lead lines of the lightning rod at the top of the box, the grounding bolts of the outer shell of the box, and the neutral point of the transformer are respectively connected to the ring ground network with two ground wires, so as to prevent the failure of grounding caused by single-point breakage. As standard accessories, a set of 1.8m long portable quick grounding posts is equipped in the mobile box substation, which can be temporarily buried on the construction site to form a temporary grounding circuit, and the temporary grounding resistance index is controlled within 10Ω.

Equal potential connection standard for substation parts

All metal components in the box must achieve complete equipotential connection, eliminate the potential difference generated by lightning current, and prevent contact voltage electrocution hazards. The box frame, the metal shell of the low-voltage cabinet, the iron core of the transformer, the cable bridge and the grounding busbar in the box use copper braid with a cross-sectional area of not less than 6 mm² to form an integral equipotential body. The neutral point of the transformer in the box substation is reliably connected to the indoor total ground bus bar, and the bus bar is connected to the outdoor pre-buried ring-shaped ground network through two independent grounding leads. In the production workshop, the pre-installed box transformer of the Chuanli factory completes all the equipotential connection processes, and the user only needs to connect the main grounding wire to the earth network on-site, which greatly reduces the hidden danger of incomplete equipotential on-site construction.

Selection Tips for Qualified Compact Substation Manufacturer

When selecting a professional box-type substation manufacturer, the anti-lightning grounding complete set capability is the core evaluation index, which can be referred to the five major selection criteria. First, verify whether the manufacturer has completed the full set of lightning protection accessories at the factory stage, such as the pre-installed lightning rod, graded surge, and internal equipotential connection, by regular manufacturers such as Chuanli, rather than purchasing lightning protection accessories separately on-site by the user. The second verification of the sample machine’s lightning impulse withstand voltage and ground resistance comprehensive inspection report, to ensure that the product conforms to the international and national lightning protection specifications. The third type of scene model is: for fixed projects of new energy power stations, ZB European/American fixed box transformers with integrated ring grounding design are selected, and mobile box transformers with portable grounding accessories are selected for temporary construction power supply. Fourth, confirm the anticorrosion grade of lightning protection grounding accessories: all lead lines, grounding flat bars, and connecting copper bars used in Chuanli box transformers are made of hot-dip galvanized/tin-plated materials, which can withstand coastal salt fog and soil corrosion in mountainous areas. The fifth requirement is for the manufacturer to provide lightning grounding construction drawings, technical briefing, and on-site guidance and after-sales service to avoid non-standard on-site construction affecting the lightning protection effect of the entire equipment.

Conclusion

Outdoor compact transformer substations suffer direct and induced lightning threats. Chuanli’s compact substation transformer adopts integrated lightning shielding, surge protection and closed grounding complying with international standards. Verify the complete lightning protection configuration during procurement to ensure reliable long-term operation of the outdoor Compact Substation.

FAQs

Q1: What is the standard ground resistance value of the fixed box transformer ring ground network?

A1: In the shared ground mode of lightning protection and equipment protection, the comprehensive ground resistance is not greater than 4Ω.

Q2: What three levels of surge protection devices are included in the compact box transformers of Chuanli?

A1: First-level SPD for high-voltage incoming lines, second-level SPD for the primary side of transformers, and third-level SPD for low-voltage outgoing lines and signal fine protection.

Q3: What kind of lightning protection accessories are included in the standard configuration of the Chuanli mobile box transformer?

A3: Removable box lightning conductor, portable quick grounding stake, mobile three-level surge protection box.

Q4: What kind of equipotential connection standard is used inside the pre-assembled box of the Chuanli factory?

A4: All metal casings, transformer cores, and bridge frames are connected with> 6 mm copper braided tape to form an integrated equipotential body.

Q5: Why can’t low-cost unpackaged transformers pass the lightning surge test?

A5: There is no factory-supplied classification surge and lightning shielding system; the internal equipotential connection is not complete, and lightning can easily penetrate the transformer.