33 kV VCB (Vacuum Circuit Breaker) Megger / Insulation Resistance Test
The Megger (IR) test of a 33 kV VCB checks the insulation health of the vacuum interrupters, bushings and control circuits before commissioning or after maintenance.
Test Equipment
- 5 kV or 10 kV Megger (recommended for 33 kV)
- Proper earthing cable
- Test record sheet
Safety Precautions
VCB (Vacuum Circuit Breaker) must be OFF, racked-out AND isolated.
All control supplies removed.
Ensure proper grounding.
After each test, discharge the breaker.
IR Test Points for 33 kV VCB
1). Phase to Phase (Contacts OPEN)
Purpose
Check insulation between phases.
Connection
- Megger Line (L) → R phase
- Megger Earth (E) → Y phase
- B phase left free
Repeat
R–B, Y–B
Condition
Contacts OPEN
Test Voltage
- 5 kV (minimum)
- 10 kV (preferred, if allowed by manufacturer)
2). Phase to Earth (Contacts OPEN)
Purpose
Check insulation of interrupter to ground.
Connection
- Megger Line (L) → One phase (R)
- Megger Earth (E) → VCB body / earth
- Repeat for Y & B
Test Voltage
5–10 kV
33 kV VCB Testing with Circuit Breaker Analyzer
(ON / OFF Condition Verification)
Purpose of CBA Test
- Confirm contact position (OPEN / CLOSED).
- Measure closing time, opening time.
- Check contact travel and synchronization.
- Verify mechanical & electrical health.