**Maintenance and Operation of SF6 Circuit Breakers**
1. **General Safety Precautions**
During the operation and maintenance of SF6 circuit breakers, it is essential to follow the safety regulations outlined in DL/T 639-1997. This standard provides guidelines for safe handling, operation, and maintenance of SF6 electrical equipment. All personnel must be trained and equipped with proper protective gear to ensure their safety during all operations.
2. **Operational Inspection**
Regular inspections are critical to ensure the reliable performance of the circuit breaker. Key points to check include:
- The external insulation (porcelain sleeve) should be intact, clean, and free from damage or flashover.
- Monitor the pressure gauge or density controller to ensure it remains within the specified range. Record pressure and temperature values periodically.
- Verify that the position indicators show correct status and that the contacts are fully engaged.
- Check for any loose or missing fasteners.
- Listen for abnormal noises from the energy storage motor and the circuit breaker itself.
- Inspect the closing and tripping coils for signs of burning, smoke, or damage.
- Ensure the grounding connection of the enclosure or bracket is secure.
- Confirm that the circuit breaker housing and operating mechanism box are intact and not corroded.
- Check for any visible damage, deformation, or severe corrosion on the circuit breaker components.
3. **Routine Maintenance**
To maintain optimal performance, the following maintenance tasks should be performed regularly:
- Apply anti-corrosion treatment to rusted areas of the housing annually.
- Lubricate the circuit breaker and its moving parts every six months and perform three operational tests.
- Conduct a qualitative leak test on all sealing surfaces once every two years. No leakage above 10â»â¶ atm·cm³/s should be detected.
- Perform an SF6 gas moisture test annually. The moisture content should not exceed 300 ppm at 20°C.
- Other tests such as insulation checks and operational testing should be carried out according to relevant standards.
4. **Precautions During Maintenance**
- Never operate the circuit breaker in a vacuum state, as this can damage the arc-quenching chamber.
- Always release the stored energy in the tripping and closing springs during normal maintenance.
5. **Overhaul Technical Parameters**
When overhauling, ensure that the main technical parameters meet the specifications listed in Table 1.
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**Failure Analysis and Maintenance**
1. **Leak Detection and Repair (Density Relay Signaling)**
If the density relay signals a fault, investigate the cause immediately:
- If the relay’s action value is incorrect, adjust or replace it. Check secondary wiring for faults and correct any errors.
- If the circuit breaker itself is leaking, locate the source and perform repairs.
- If the gas pressure drops to the signaling level, refill the SF6 gas using the pressure-temperature curve to reach rated pressure. Refilling can be done while the system is live.
- In cases of rapid pressure drop or zero gauge pressure, isolate the circuit breaker immediately. Possible causes include weld defects, casting leaks, loose bolts, gas line leaks, or faulty gauges.
*Note: When dealing with serious leaks, approach the equipment from the windward side. Wear a gas mask and protective clothing, and maintain a safe distance from live parts.*
2. **Low Closing or Tripping Speed**
Several factors can lead to slow operation:
- Adjust the stroke of the closing core if it is too short.
- Avoid repeated closing operations that may overheat the coil.
- Check the auxiliary switch for poor contact or burn damage.
- Replace the closing spring if it has deformed.
- Replace a burned or damaged closing coil.
- Ensure the closing core is not stuck and adjust as needed.
- Check the sector plate and axle gap; readjust if necessary.
- Adjust the buckle joint between the sector plate and half shaft to the recommended range.
- Replace the closing locator or cam if they are deformed.
- Check for mechanical jams and perform a slow-motion or disassembly inspection.
- Verify that the sub-gate coil voltage does not exceed 30% of the rated voltage.
- Adjust the power supply if the voltage is insufficient.
- Check for open circuits in the control loop and repair as needed.
3. **Low Tripping or Opening Speed**
Similar issues may affect opening speed:
- Adjust the half shaft and sector plate alignment.
- Check the auxiliary switch for poor contact or burn damage.
- Ensure the sub-gate core is fully reset and free from obstruction.
- Replace a damaged or burned coil.
- Adjust the sub-gate circuit parameters to ensure proper voltage.
- Check for open circuits in the control loop.
- Inspect for mechanical jams and perform disassembly if necessary.
- Adjust the pre-stretching length of the opening spring.
- Replace the opening spring if it is faulty.
4. **Closing Spring Not Charging or Charging Incomplete**
- Ensure the control motor’s automatic air switch is set to the "on" position.
- Check the control circuit for errors or poor connections.
- Adjust the contactor if it has poor contact.
- Adjust the trip switch to prevent premature disconnection.
- Inspect the energy storage mechanism for jams or broken parts.
5. **Excess Moisture (Water Infiltration)**
- Replace the desiccant.
- Vacuum and dry the system, or replace the SF6 gas if necessary.
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**Dismantling and Overhaul Procedures**
1. **When to Return for Overhaul**
The circuit breaker should be returned to the manufacturer for dismantling and overhaul under the following conditions:
- After 10 years of operation, or if abnormal conditions are detected that affect safe operation.
- When the number of operations reaches the mechanical life limit.
- When the cumulative breaking current exceeds the specified value.
2. **Dismantling and Overhaul Process**
- Ensure the maintenance area is clean, dry, and well-ventilated. Provide appropriate protective gear such as gas masks, gloves, and protective clothing.
- Follow specific procedures outlined in DL/T 639-1997:
- Release SF6 gas through a NaOH solution, then vacuum the system to 133 Pa and flush with nitrogen.
- Evacuate the site for 30 minutes after opening the cover.
- Remove the desiccant and clean internal components with acetone.
- Dispose of waste materials by neutralizing them in a NaOH solution.
- Replace worn, burned, or corroded parts, including fasteners, springs, seals, and insulators.
- Clean all components with industrial alcohol and bake insulating parts at 80–100°C for 4 hours. Dry the desiccant at 500–550°C for 2 hours before reassembling.
- Apply vacuum to the system to 133 Pa and maintain it for 30 minutes. Recheck after 5 hours; the difference should not exceed 65 Pa.
- Fill the system with qualified SF6 gas to the rated pressure (20°C).
- Test for leakage using a detector with sensitivity of 10â»â¸ atm·cm³/s. Annual leakage rate should be ≤1%, and moisture content ≤150 ppm.
- After assembly, verify that all technical parameters meet factory standards and conduct mechanical and electrical tests.
- Clean and dispose of all protective equipment after work, and take a shower before leaving the site.
By following these detailed procedures, the reliability and safety of SF6 circuit breakers can be ensured, reducing the risk of failure and extending their service life.
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