Practical Guide for Installation of 10kV Isolation Switch

2025-07-31 13:22:30

The iron law of "three prohibitions" (violation must be reworked)

1. Do not use current beyond the nameplate

Painful case: A 630A isolation switch with an 800A load in a certain factory caused a phase to phase short circuit due to contact welding

Hardcore control:

?  Current calculation formula: Load current ≤ switch rated current × temperature coefficient × altitude coefficient

-Temperature coefficient Kt: 0.85 for 40 ℃ environment (GB/T 1985)

-Altitude coefficient Ka: 1% decrease per 100 meters per liter above 1000 meters

?  Verification Example:

800A load/altitude 1500m → switch selection required ≥ 800 ÷ (0.85 × 0.95) ≈ 990A

2. Do not ignore grounding

Fatal error: Grounding resistance>10 Ω, insulation breakdown due to counterattack voltage during lightning strike (a wind farm lost 2 million yuan)

Compliance skills:

-Grounding body selection: Galvanized flat steel ≥ 40 × 4mm 2 (corrosion zone thickened by 20%)

3. Do not omit the opening and closing signs

Blood lesson: A substation misjudged the opening state and caused arc burns during loaded operation

Error prevention design:

?  Mechanical indication and rigid linkage of contacts (rejecting soft connections)

?  Mandatory differentiation of the base color of the sign:

-Opening: Yellow background with black letters

-Closing: Red background with white letters

?  Night work requirements: Self luminous signs (LED backlight or fluorescent coating)

Five check checklist after installation (20 minute quick self check)

First check: Contact point contact (lifeline)

-Contact pressure: The clearance between the contact fingers measured by a feeler gauge is ≤ 0.05mm (630A level)

-Contact resistance: measured by a micro ohmmeter, ≤ 120 μ Ω (if exceeding the standard, the contact surface needs to be polished)

-Heat warning: stick 70 ℃ thermal sensitive test paper (if it changes color after running for 1 hour, it is unqualified)

Second check: Locking function (anti misoperation)

-Mechanical locking: When the grounding knife is closed, the main knife switch operating hole is physically locked (verified by inserting a Φ 20 pin rod)

-Electrical lockout: Simulate the closing signal of the circuit breaker and measure the output resistance of the lockout relay to be greater than 10k Ω

Third check: Insulation resistance (life symbol)

-Test conditions: humidity ≤ 70%, otherwise heating and dehumidification are required

-Qualification criteria:

Fourth check: Operating torque (anti refusal to move)

-Torque upper limit: Manual operating lever ≤ 200N · m (lubrication of the shaft is required for exceeding the limit)

-Operation trajectory: The deviation of the opening and closing angle monitored by the laser level is ≤ 1 ° (e.g. GN19-10 should be 88 °± 1 °)

Fifth check: Institutional status (extended lifespan)

-Opening in place: contact opening distance ≥ 180mm (indoor type)

-Buffer check: The sound of closing impact is dull → Check the oil buffer level (if it is insufficient, add 45 transformer oil)

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Cracking plan for rework in severely affected areas

1. Contact overheating (accounting for 60% of rework)

-Incorrect practice: Sandpaper polishing the surface of the fingers (damaging the silver plating layer)

-Correct process:

1. Anhydrous ethanol cleaning

2. Silver based conductive paste filling micro depressions

3. Contact pressure retest ≥ 40N/cm 2

2. Ground resistance virtual drop

-False standard trap: Resistance reducing agent wraps around the grounding body but does not fully integrate with the soil

-True solution:

-Excavation depth ≥ 0.8m

-Resistance reducing agent: water: soil=1:1:3 mixed backfill

-Retest in 3 days (after stable water infiltration)

3. Switching on and off at different stages

-Quick calibration:

1. Remove the linkage rod

2. Unipolar adjustment of crank arm angle (calibration of laser angle meter)

3. After reinstallation, the three-phase different periods should be ≤ 2mm

Acceptance must pass the checklist

1. Prepare three sets of documents:

-Factory test report (including records of power frequency withstand voltage of 42kV/1min)

-Installation process image (focusing on capturing contacts and grounding connection points)

-Torque wrench calibration label (within validity period)

2. Five tricky questions to deal with supervision:

-How to prove that the contact pressure meets the standard? "→ Present a photo of the pressure sensing film color spot

-How to prevent corrosion of grounding grid? "→ Display hot melt welding points+anti-corrosion asphalt coating

-How to adjust the overtravel? "→ The measured insertion depth of the plug gauge contact is ≥ 10mm

Remember: By following the "three prohibitions" and "five inspections", the acceptance rate can reach 100%. After applying this method, the rework rate of a certain provincial power transmission and transformation company decreased from 38% to 0!