How to Inspect 10kV Vacuum Circuit Breakers Properly

I. Inspection of Vacuum Circuit Breakers During Normal Operation

1. Inspection in Closed (ON) Position

• The operating mechanism should be in the closed position;

• The main shaft roller should be disengaged from the oil damper;

• The opening spring should be in a charged (stretched) energy-stored state;

• The length of the moving contact rod of the vacuum interrupter protruding below the guide plate should be approximately 4–5 mm;

• The bellows inside the vacuum interrupter should be visible (this does not apply to ceramic-tube interrupters);

• The temperature-indicating stickers on the upper and lower brackets should show no significant change.

2. Inspection of Conductive Parts

• External connection bolts on upper and lower brackets;

• Bolts fixing the vacuum interrupter to the upper bracket;

• Bolts on the lower bracket's conductive clamp.

All of the above bolts must not be loose.

3. Inspection of Transmission Components

• Three pivot shafts connecting the linkage arm and the moving end of the interrupter, including retaining clips at both ends;

• Lock nuts and jam nuts securing the pull rod to the linkage arm;

• Six M20 bolts fixing the support insulators (on the vacuum circuit breaker frame);

• Installation bolts securing the vacuum circuit breaker;

• Lock nut and jam nut connecting the mechanism main shaft to the breaker’s linkage arm;

• Welded joints on the transmission connecting rods for any cracks or fractures;

• Shaft pins on the main drive shaft for looseness or detachment.

Do not place any objects on the static frame of the vacuum circuit breaker, to prevent them from falling and damaging the vacuum interrupter.

4. Internal Inspection of Vacuum Interrupter

Check for Contact Erosion

After multiple interruptions of short-circuit currents, the contacts of the vacuum interrupter may suffer erosion due to arcing. Contact loss should not exceed 3 mm. Inspection methods include: measuring the interrupter’s contact gap and comparing it with previous results; measuring loop resistance using DC resistance method; checking for obvious changes in compression travel. If contact erosion occurs but adjustments bring parameters back within specifications, the interrupter may continue in service (subject to comprehensive assessment).

Check Vacuum Integrity of the Interrupter

Visually inspect the glass (or ceramic) envelope of the vacuum interrupter for cracks or damage; check the welded joints at both ends of the interrupter for deformation, displacement, or detachment. Disconnect the pin between the pull rod and the linkage arm, then manually pull the contact rod to check whether it automatically returns—ensuring the moving contact remains self-held in the closed position (due to external atmospheric pressure). If the holding force is weak or there is no return movement, vacuum integrity has likely decreased.

Use power-frequency withstand voltage test for qualitative verification. For example, if a 10kV vacuum circuit breaker shows insulation strength below 42 kV, this indicates reduced vacuum level and the interrupter should be replaced.

II. Inspection of Vacuum Circuit Breakers During Abnormal Operation

1. Damage to the Vacuum Chamber

If damage to the vacuum chamber is observed during patrol inspection, and grounding or short-circuit has not yet occurred, immediately report to dispatch, transfer the load to an alternate line, and disable the reclosing relay link.

2. Abnormal Vacuum Level During Operation

Vacuum circuit breakers utilize high vacuum for insulation and arc extinguishing due to its high dielectric strength. They exhibit excellent arc-quenching performance, require minimal maintenance, have long service life, support frequent operation, operate reliably, and are suitable for switching high-voltage motors, capacitor banks, and other indoor 6–35 kV equipment. Contacts are typically made of copper-chromium alloy, with rated currents up to 1000–3150 A, and rated breaking currents up to 25–40 kA. 

Full-capacity breaking capability can reach 30–50 operations. Most are equipped with electromagnetic or spring-operated mechanisms. The vacuum level in the interrupter must be maintained above 1.33 × 10⁻² Pa for reliable operation. If the vacuum level drops below this value, arc extinction cannot be guaranteed. Since field measurement of vacuum level is difficult, qualification is generally determined by passing a power-frequency withstand voltage test.During routine inspection, observe the color of the shield (screen) for abnormal changes. Pay special attention to the arc color when the breaker opens. Under normal conditions, the arc appears pale blue; if the vacuum level decreases, the arc turns orange-red—indicating the need to request shutdown, inspection, and replacement of the vacuum interrupter.

Main causes of reduced vacuum level include: poor material selection, inadequate sealing, defective metal bellows sealing, over-travel exceeding the bellows’ design range during commissioning, or excessive impact force.

Additionally, check for reduction in overtravel (i.e., measure contact wear). When cumulative wear exceeds the specified limit (4 mm), the vacuum interrupter must be replaced.

III. Common Faults and Troubleshooting of Vacuum Circuit Breakers

1. Failure to Close Electrically

• Cause: Detachment between the solenoid core and pull rod.

• Solution: Adjust the position of the solenoid core—remove the stationary core to make adjustment—so that manual closing becomes possible. At the end of closing, ensure a 1–2 mm clearance exists between the latch and the roller.

2. Closing Without Latching ("Empty Close")

• Cause: Insufficient latching distance—the latch fails to pass the toggle point.

• Solution: Turn the adjusting screw outward to ensure the latch passes the toggle point. After adjustment, tighten the screw and seal it with red paint.

3. Failure to Trip Electrically

• Excessive latching engagement. Turn the screw inward and tighten the locknut.

• Disconnected wiring in the trip coil. Reconnect and secure the terminals.

• Low operating voltage. Adjust the control voltage to the specified level.

4. Burnout of Closing or Tripping Coils

• Cause: Poor contact at auxiliary switch contacts.

• Solution: Clean the contacts with sandpaper or replace the auxiliary switch; replace the faulty closing or tripping coil as needed.