Key Points for Installing 12kV Load Switches and a guide to Preventing Typical Errors

2025-07-27 12:46:54

Key points for preparation before installation

1.1 Environmental Adaptability verification

- Temperature and humidity control: Ensure that the installation environment temperature is within the range of -25℃ to +40℃ (special design is required for high-cold regions), and the daily average relative humidity is ≤95% to prevent condensation from causing insulation degradation.

- Altitude correction: When the altitude exceeds 1000 meters, breakdown voltage correction shall be carried out in accordance with the GB/T 11022 standard (the withstand voltage value decreases by 10% for every 1000 meters increase).

- Pollution protection: In corrosive environments such as chemical industrial zones, IP54 protection grade enclosures should be selected or anti-corrosion coatings should be added to prevent sulfides from eroding conductive components.

1.2 Equipment unpacking and acceptance

- Mechanical component inspection: Measure the deviation of the contact knife thickness ≤0.1mm, and check the spring pressure value (closing pressure ≥200N, opening pressure ≥80N).

- Insulation performance verification: Use a 2500V megohmmeter to measure the insulation resistance. The values between phases and to ground should be ≥1000MΩ (when the humidity is greater than 80%, heat and dehumidify before remeasurement).

- Arc extinguishing chamber integrity: Check that the wall thickness of the gas-producing arc extinguishing chamber is ≥8mm, the organic material has no cracks, and the nozzle channel is unobstructed without burrs.

1.3 Installation Planning

- Safety distance reservation: The bottom of the switch should be no less than 2.5 meters above the ground, and a maintenance passage of no less than 0.8 meters should be reserved on the side. The distance between the high-voltage live part and the wall should be no less than 20cm.

- Operating space design: The installation height of the operating handle is 1.0 to 1.2 meters (if it is too high, the operating torque will increase by 30%), and the rotation radius is ≥0.6 meters.

- Grounding embedded parts setting: Embed 100×100×6mm galvanized steel plates in the concrete wall. The cross-section of the grounding flat steel should be no less than 40×4mm2, and the welding length should be greater than 10cm.

Detailed instructions for core installation steps

2.1 Fixed Installation

- Verticality control: Calibrated with a laser level, the vertical deviation is ≤1mm/m. Frame distortion will cause the movement trajectory of the contact tool to shift.

- Bolt selection specification:

- Foundation fixation: 4 to 6 M12 stainless steel bolts (grade 8.8), with flat washers and spring washers for anti-loosening.

Torque requirement: Staged tightening (pre-tightening at 50Nm first → standing for 30 minutes → replenishing to 80Nm).

Vibration reduction treatment: Install rubber damping pads (thickness ≥10mm) in vibration areas (such as compressor rooms) to reduce the risk of resonance.

2.2 Busbar connection

- Pre-treatment of copper busbars: The contact surface should be mfed with Ra≤3.2μm, and 0.1mm thick conductive paste (containing copper particles) should be applied. The use of vaseline is strictly prohibited.

- Stress relief: Use "S-shaped" expansion joints or reserve temperature compensation bends (when the copper bar length is greater than 1m, reserve 1.5mm expansion allowance per meter).

- Connection sequence: First, tighten the busbar on the load side → then connect the power side → finally the grounding wire to prevent induced electric shock.

2.3 Installation of Operating Mechanism

- Rod adjustment techniques:

1. Remove the shackle to empty the mechanism

2. Manually open and close three times to confirm there is no jamming

3. Measure the gap between the crank arm and the buffer (1 to 2mm is appropriate).

- Position synchronization adjustment: Adjust the length of the pull rod through the hexagonal eccentric joint to ensure that the three-phase contact knife is out of sync by no more than 2mm (if it is too large, the arc burning time will be prolonged).

- Limit device setting: When opening the switch, the opening Angle of the knife switch should be no less than 58°, and the corresponding contact spacing should be 182±3mm (indoor type). Otherwise, the oil buffer gasket needs to be added or removed.

3. Commissioning and acceptance standards

3.1 Mechanical characteristic debugging

- Closing depth detection: After the contact blade is fully inserted into the static contact, a 3±0.5mm buffer gap should be maintained between the lower edge of the blade and the bottom of the static contact to prevent impact on the insulator.

- Contact pressure test: Apply a pressure-sensing film to the section where the knife is inserted. After closing the switch, observe the distribution of the color spots. The pressure should be ≥40N/cm2 and evenly distributed.

- Operating force verification: The operating force of the handle should be ≤200N (for CS8 type mechanism). Exceeding the limit indicates excessive friction of the transmission mechanism or abnormal pre-compression of the spring.

3.2 Electrical Performance verification

- Loop resistance measurement: Use a 100A microohmmeter, with the resistance difference between phases ≤15% (standard value: ≤80μΩ for 400A switch).

- Power frequency withstand voltage test:

Test voltage: 42kV (12kV equipment)

Duration: 1 minute

Leakage current: ≤10mA (Note humidity correction)

Partial discharge detection: At a voltage of 1.73U?, the partial discharge quantity is ≤10pC (35kV level), with a focus on monitoring the junction between the shielding cover and the insulator.

3.3 Confirmation of Linkage Function

- Fuse fit: Install with the fuse indicator facing down. The operating current of the RN type fuse should be less than the breaking capacity of the switch (for example, FKN-12 breaks 31.5kA, with a 25kA fuse).

- Mechanical interlock test: When the grounding switch is closed, the operating shaft of the Load switch is physically locked, and a force of more than 500N needs to be applied to verify reliability.

- Anti-misoperation verification: Simulate 5 incorrect operations (such as tripping under load), and all switches should be reliably locked.

4 Common Installation Errors and Preventive Measures

4.1 Installation defects of the contact system

- Misaligned contact (side strike) :

- Characteristics: One side of the blade turns red, and local carbonization of the insulator occurs.

The main cause: The static contact bracket is tilted or the lateral stress of the busbar is too large.

Solution: Loosen the static contact fixing bolts → Insert the 3mm calibration gasket → Re-align and tighten.

- Insufficient insertion depth:

- Risk: The contact resistance increases by three times, and the temperature rise exceeds the limit, which may ignite the insulator.

- Detection: The exposed part of the blade after closing should be no more than 5% of the total width.

- Adjustment: Modify the connection hole position of the connecting rod crank arm or add limit blocks.

Table: Solution for Installation Issues of 12kV Load Switch Contacts

4.2 Grounding system defects

- Series grounding:

Case: In a certain chemical plant, the frame of a switch cabinet and the operating mechanism were connected in series and grounded. During a lightning strike, a 15kV potential difference broke down the insulation.

- Specification: The switch frame, operating mechanism, and cable sheath shall be respectively connected to different points of the grounding grid with copper cables of ≥16mm2.

- False connection detection:

Apply heat-sensitive color-changing paint to the grounding Terminal

2. Pass 50% of the rated current for 1 hour

3. A temperature difference greater than 15℃ is judged as a poor contact.

4.3 Mechanism and Insulation issues

- Buffer failure:

Consequence: The tripping impact caused the epoxy pull rod to break.

- Prevention: Check the thickness of the rubber pad monthly. Replace it immediately if the wear exceeds 30%.

- Insulation fit error:

Typical error: The climbing distance was not increased in the contaminated area (the standard requires ≥20mm/kV, and in the heavily contaminated area, it needs ≥31mm/kV).

- Improvement: In the H3 dirty area, silicone rubber climbing skirts are adopted, and the distance between the umbrella skirts is reduced to 45mm.

5 Key points for operation and maintenance

5.1 Periodically maintain the project

Annual maintenance:

- Clean the insulator (wipe with anhydrous ethanol, do not use acetone)

Lubricate the rotating shaft (lithium-based molybdenum disulfide grease, grease injection volume ≤ 60% of the cavity)

- Verify the operating force (deviation from the initial value ≤20%).

- Electrical life management: Record the breaking current and the number of times. Replace the arc extinguishing chamber when the cumulative value approaches 100 times (breaking 400A).

5.2 Fault Early Warning and Handling

- Overheating disposal process:

A[Infrared temperature measurement > 90℃] --> B{Is there an unpleasant smell? }

B --> Yes C[Emergency Power Outage

B --> No D[Fastening connection point]

D --> E[Remeasurement temperature]

Has E --> F{decreased? }

F --> No C[Emergency Power Outage]

F --> is G[24-hour tracking]

- Failure to operate analysis: If the opening fails, first check whether the opening spring hook has tripped (accounting for 62% of the failure rate).

5.3 Safety Operation Specifications

- Switching operation sequence:

- Opening: First the neutral phase → the leeward side phase → the windward side phase (to prevent arc short circuit).

- Closing: Windward side phase → leeward side phase → middle phase (to balance the voltage impulse).

- Protection requirements: When operating a 12kV drop-out switch, 10kV insulating gloves and goggles must be worn, and the effective length of the insulating rod should be no less than 1.2m.

Lesson learned through blood and tears: In 2023, a substation in Zhejiang Province suffered from insufficient contact pressure (measured at 28N/cm2), which led to excessive contact resistance and caused an interphase short circuit, resulting in a loss of over 800,000 yuan. Regularly measuring the rate of change in loop resistance (a warning is issued when it exceeds 10%) can prevent such accidents.