Electric foundation bolt

Definition and function of power anchor bolts

Power anchor bolts are pre embedded bolts used in power engineering to fix power equipment such as transformers, circuit breakers, towers, distribution cabinets, etc. By connecting the equipment to a concrete foundation, they transmit equipment loads (such as gravity, wind, vibration, etc.) and protect the stability and safety of power facilities. Its core functions include:

Fixed equipment: It is crucial to prevent equipment displacement or overturning, especially in outdoor high-voltage equipment or transmission towers.

Load transmission: Transmit vertical loads, horizontal loads (such as wind force), and dynamic loads (such as vibration caused by short-circuit current) during equipment operation to the foundation concrete.

Anti seismic and anti shake: Enhance the anti overturning ability of equipment in harsh environments such as earthquakes and strong winds, and reduce safety hazards.

Common types and structural characteristics

According to the equipment type and installation requirements, power anchor bolts are mainly divided into the following categories:

1. Straight hook type anchor bolt (L-shaped)

Structure: One end of the bolt is a threaded section (used to connect equipment), and the other end is a 90 ° straight hook or bent hook, embedded in the concrete foundation.

Features: Simple construction, easy installation, suitable for equipment with small loads (such as low-voltage distribution cabinets, small transformers).

Application scenarios: indoor power equipment foundation, fixed distribution boxes in residential areas, etc.

2. Anchor plate type anchor bolt (welded anchor plate)

Structure: Square or circular anchor plates are welded at the end of the bolt to increase the contact area with the concrete and improve the pull-out resistance.

Features: Good pull-out resistance, suitable for equipment that can withstand large horizontal loads or vibrations (such as high-voltage circuit breakers, large transformers).

Application scenarios: Substation main transformer foundation, outdoor high-voltage switchgear fixed.

3. Welding plate reinforced anchor bolt

Structure: Add stiffeners (triangular steel plates) on the anchor plate foundation to further enhance the connection strength between the bolts and the anchor plate.

Features: High bearing capacity, able to resist complex loads (such as torsional forces), suitable for high-intensity earthquake areas or strong wind areas.

Application scenario: Fixed foundation for transmission line terminal towers and large-span towers.

4. Double headed bolt (through type)

Structure: Both ends of the bolt have threads, which are fixed with nuts after passing through the equipment base, and the middle is embedded in concrete.

Features: High installation accuracy requirements, bolt holes need to be reserved in advance on the equipment base, suitable for equipment that requires detailed positioning (such as GIS composite appliances).

Application scenario: Substation accuracy suitable for equipment foundation and installation of compact power equipment.

Installation process and precautions

Installation process

Positioning and laying out: Mark the bolt positions in the foundation steel mesh according to the design drawings, confirm the accuracy of spacing and elevation (error ≤ 2mm).

Fixed bracket: Use steel sections (such as angle steel and channel steel) to make positioning brackets, and weld bolts to the brackets to prevent displacement during pouring.

Concrete pouring: first pour the bottom layer concrete to 1/2 of the bolt buried depth, adjust the bolt perpendicularity and elevation before initial setting, and then pour to the design elevation.

Maintenance and acceptance: The concrete should be cured for more than 7 days, and the exposed length, spacing, and verticality of the bolts should be tested (with a deviation of ≤ 1%). Only after passing the inspection can the equipment be installed.

precautions

Anti corrosion treatment (based on actual reports): Outdoor bolts need to be hot-dip galvanized (with a zinc layer thickness of ≥ 85 μ m) or coated with anti-corrosion (based on actual reports) paint to prevent rusting and reduce strength.

Anti displacement measures: The bolts and steel mesh should be welded well (welding length ≥ 6 times the bolt diameter) to avoid displacement due to concrete flow during pouring.

Stress relief: For equipment with high vibration (such as transformers), spring washers can be installed on the top of the bolts to adjust the vibration stress.

Insulation treatment: If the bolt is close to live parts, it needs to be isolated with an insulation sleeve to prevent the risk of short circuit.

Typical application scenarios

Transmission tower foundation

The anchor bolts used to fix iron towers and steel pipe poles are usually grouped in groups of 4-8, distributed in a rectangular shape, and the burial depth needs to be combined with the tower height and wind resistance design (for example, the specifications of anchor bolts for 110kV towers are usually M30~M36).

Substation equipment foundation

Main transformer foundation: anchor plate type anchor bolts are used, and the bolt spacing is designed according to the size of the transformer base (for example, the spacing between anchor bolts for 500kV transformers can reach 2-3 meters).

Circuit breakers and isolating switches: Use straight hook type or double headed bolts, with good positioning accuracy (error ≤ 1mm), and confirm that the axis of the equipment is aligned after installation.

New energy equipment

Wind turbine foundation: Large diameter anchor bolts (such as M60~M80) are used, distributed in a circular shape, to withstand huge overturning moments and vibration loads.

Photovoltaic bracket fixation: Expansion type anchor bolts (no need for pre embedding) are used in some scenarios, suitable for temporary or small photovoltaic projects.

Quality inspection and maintenance

Construction stage inspection

Appearance inspection: There are no cracks or rust on the surface of the bolt, the threads are intact, and there is no virtual welding or slag inclusion in the welding area.

Mechanical test: Conduct a pull-out test by sampling to check whether the bolt's pull-out resistance meets the design requirements (such as a sampling ratio of ≥ 3% and no less than 3 bolts).

Dimensional verification: Use a total station to measure bolt spacing and elevation, with an allowable deviation of ± 2mm.

Operation phase maintenance

Regularly inspect the exposed parts of bolts for corrosion and promptly apply anti-corrosion paint (based on actual reports).

During equipment overhaul, check the tightness of nuts, and tighten equipment with high vibration once a year.

After extreme weather conditions such as typhoons and earthquakes, special non-destructive testing (such as ultrasonic testing) is required for the foundation bolts of important equipment.