What are the common issues in SF₆ gas circuit faults and circuit breaker failure-to-operate faults?

This article categorizes faults into two main types: SF₆ gas circuit faults and circuit breaker failure-to-operate faults. Each is described below:

1.SF₆ Gas Circuit Faults

1.1 Fault Type: Low gas pressure, but density relay does not trigger alarm or lockout signal

Cause: Faulty density gauge (i.e., contact not closing)
Inspection & Handling: Calibrate actual pressure using a standard gauge. If confirmed, replace the density gauge.

1.2 Density Relay Triggers Alarm or Lockout Signal (but pressure is normal)

Cause 1: Signal crosstalk
Inspection & Handling 1: Disconnect the alarm wiring and measure the contact on the density gauge itself. If the contact is normal, resolve the signal crosstalk issue.

Cause 2: Voltage crosstalk
Inspection & Handling 2: Disconnect the alarm wiring and measure the contact on the density gauge. If the contact is normal, troubleshoot and fix the voltage crosstalk.

Cause 3: Faulty density gauge
Inspection & Handling 3: Disconnect the alarm wiring and measure the contact. If confirmed closed when it should not be, replace the density gauge.

1.3 Density Relay Triggers Alarm or Lockout Signal (pressure is low)

Cause: Leak point in the circuit breaker — such as at the charging valve, column flange surface, or sand hole in the rotating housing
Inspection & Handling: Perform lateral pressure comparison; if only one phase shows low pressure and instrument error is ruled out, conduct leak detection and repair accordingly.

1.4 Pressure Too High

Cause 1: Overcharging during gas filling
Inspection & Handling 1: Review gas replenishment records and calibrate the pressure gauge. If confirmed, release gas (pressure must not exceed 0.3 atm above rated, regardless of temperature).

Cause 2: Faulty density gauge
Inspection & Handling 2: Calibrate actual pressure with a standard gauge. If inaccurate, replace the density gauge.

Cause 3: Voltage crosstalk
Inspection & Handling 3: If pressure is normal and no motor operation signal precedes lockout, inspect the secondary circuit and correct any issues.

2.Circuit Breaker Failure-to-Operate Faults

2.1 Circuit Breaker Fails to Operate

Cause 1: Control power not energized
Inspection & Handling 1: Visually inspect relays — if all are de-energized, restore control power.

Cause 2: Remote/local switch is set to "Local" position
Inspection & Handling 2: Check for control circuit disconnection signal. Switch selector to "Remote" mode.

Cause 3: High resistance in opening/closing circuit contacts
Inspection & Handling 3: Measure total resistance of the trip/close circuit. Identify faulty component and repair or replace.

Cause 4: Damaged component in trip/close circuit
Inspection & Handling 4: Measure resistance of the trip/close circuit. Locate and replace the faulty component.

Cause 5: Loose auxiliary switch wiring
Inspection & Handling 5: Measure circuit resistance, identify loose connections, and re-terminate securely.

Cause 6: Faulty mechanism or auxiliary switch
Inspection & Handling 6: Visually inspect mechanism and auxiliary switch. Develop repair plan based on findings.

2.2 Minimum Operating Voltage Does Not Meet Standards

Cause 1: Bypassing lockout relay and auxiliary switch contacts for convenience
Inspection & Handling 1: When testing coil minimum operating voltage, the test must go through auxiliary switch S1 and lockout contact, using momentary operation. Perform test at the terminal block in the circuit breaker control cabinet.

Cause 2: Insufficient test instrument power
Inspection & Handling 2: Before testing, verify instrument reliability (e.g., check for AC or DC offset). Replace the instrument and retest.

Cause 3: Discrepancy between instrument output voltage and display reading
Inspection & Handling 3: Replace or recalibrate the test instrument.

Cause 4: Test instrument outputs AC component (waveform superposition affects low-voltage accuracy and may burn out coil or resistor; must be <10V)
Inspection & Handling 4: Before testing, use a multimeter on AC voltage range to measure AC component output. Replace the instrument if present.

Cause 5: Test instrument outputs DC component
Inspection & Handling 5: Before testing, use a multimeter on DC voltage range to measure DC component output. Replace the instrument if present.

Cause 6: Transient interference spike superimposed on output pulse, causing abnormally low minimum operating voltage
Inspection & Handling 6: Monitor output pulse with an oscilloscope. Confirm issue and replace the instrument; compare results with different testers.