What is the Insulation Resistance Test for Vacuum Circuit Breakers?

The insulation resistance test for vacuum circuit breakers is a key test for evaluating their insulation performance. The following is a detailed explanation:

1.Test Locations

Main circuit to ground: Insulation resistance between conductive parts (such as contacts and conductive rods) and the grounded housing.

Between phases (multi-pole circuit breakers): Insulation resistance between the conductive parts of each phase.

2. Test Instruments

Megohmmeter (Insulation Resistance Tester):

Voltage: Typically 1000V or 2500V DC (2500V is commonly used for 12kV circuit breakers).

Range: 0-10GΩ or higher (high resistance values require interference prevention).

Notes:

Before testing, disconnect the power supply and discharge the insulation (including parasitic capacitance).

Ambient humidity should be ≤ 80% to prevent condensation on the surface from affecting the results.

3. Test Procedure

1) Wiring:

Ground test: Connect the "L" terminal of the megohmmeter to the main circuit and the "E" terminal to the grounded housing.

Interruption test: In the open state, connect "L" to the moving contact and "E" to the static contact.

2) Measurement:

Read the stable value after 60 seconds at a constant speed (for manual megohmmeter) or in automatic mode (for absorption ratio test, record the 15s/60s ratio). 4) Recovery:

Discharge again after the test to prevent residual voltage hazards.

4. Acceptance Criteria

Test Location	Minimum Requirements (Normal Temperature	Remarks
Main Circuit to Ground	≥1000MΩ	12kV and Above Equipment
Inter-contact Gap	≥5000MΩ	Vacuum interrupter key indicators
Between Phases (Open)	≥1000MΩ	1000MΩ Multi-Pole Circuit Breakers

Abnormal Detection:

Value 50% below the standard: Moisture or contamination may be present.

Value drops sharply or approaches zero: Insulation breakdown or severe defects.

Example (12 kV vacuum circuit breaker)

Test voltage: 2500 V DC

Normal values:

Between interrupters: 10 GΩ (new interrupter chambers can reach over 100 GΩ)

To ground: 5 GΩ

Fault case: If the interrupter resistance is only 100 MΩ, the vacuum level may have deteriorated and the interrupter chamber may need to be replaced.

Insulation resistance testing is a fundamental maintenance measure for vacuum circuit breakers and should be combined with other tests (such as loop resistance and withstand voltage testing) to comprehensively assess the equipment's condition.

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