IEC Type Test Items for 24kV 1250A / 20kA Vacuum Circuit Breaker

As core protection equipment in medium voltage distribution network, the 24kV 1250A 20kA vacuum circuit breaker is used for switching normal load current and clearing short-circuit faults. For international projects such as Indonesia PLN and Central Asian power grid tenders, the product must complete full type tests according to IEC 62271-1 and IEC 62271-100. All tests verify insulation performance, current carrying capacity, short-circuit interruption capacity and mechanical reliability. The full test list and standard requirements are listed below.

1. Dielectric Tests

  1. Lightning impulse withstand test (1.2/50μs): Test voltage 125kV phase-earth, 145kV across open contacts. No breakdown or flashover. Verify insulation against lightning overvoltage.
  2. Power frequency withstand test (50Hz, 1 min): 50kV for phase-earth, 60kV for open break; auxiliary circuits withstand 2kV.
  3. Partial discharge measurement: PD value within limits at 1.1 times rated phase voltage, detect hidden insulation defects.
  4. Dielectric test for auxiliary and control circuits.

2. Main Circuit Resistance Measurement & Temperature Rise Test

  • Main circuit resistance is measured before and after all type tests; resistance increase shall not exceed permitted limits.
  • Temperature rise test under rated continuous current 1250A. Temperature of contacts, vacuum interrupters and terminals cannot exceed standard limits to avoid contact ablation and insulation aging.

3. Short-time Withstand Current & Peak Withstand Current Tests

  • Rated short-time withstand current: 20kA / 3s (thermal stability). The closed breaker shall sustain short-circuit current without welding or permanent damage.
  • Rated peak withstand current: 50kA (dynamic stability). Withstand electromagnetic force without permanent mechanical deformation.

4. Short-circuit Making & Breaking Tests (Core Test)

Rated short-circuit breaking current: 20kA; standard operating sequence: O – 0.3s – CO – 3min – CO

  1. Terminal fault tests (T10, T30, T60, T100): Successfully interrupt short-circuit current under specified transient recovery voltage (TRV), no reignition.
  2. Rated short-circuit making test: Make onto 20kA fault current without contact welding.
  3. Capacitive current switching test; Class C2 certification is preferred for cable-intensive distribution networks.
  4. Out-of-phase switching test (optional, frequently required by utility tender).

5. Mechanical Operation & Mechanical Endurance Test

  • Mechanical characteristic test: Measure opening/closing time, pole synchronism, contact bounce, operating voltage range (85%~110% rated voltage). Verify interlock and position indicator function.
  • Mechanical endurance test: Class M1 (10,000 operations), Class M2 (20,000 extended operations). Mechanism shall operate smoothly after endurance test.

6. Electrical Endurance Class Verification (E1 / E2)

Class E2: Maintenance-free electrical endurance, widely required for export power projects. Vacuum interrupter can operate continuously without maintenance after multiple fault interruptions.

7. Ingress Protection Test (IEC 60529)

Indoor circuit breaker cabinet standard IP4X; optional IP54 to prevent dust and moisture ingress.

8. Optional Additional Tests (Mandatory for PLN and large overseas grid projects)

Internal arc classification (IAC) test, temperature cycling test, damp heat test, EMC test, X-ray radiation test for vacuum circuit breaker.

Market Tip

International tenders including PT PLN (Indonesia) usually demand complete IEC 62271-100 type test certificates, Class E2 electrical endurance, M2 mechanical endurance and Class C2 capacitive switching performance. The full set of test reports is essential bidding document for medium voltage switchgear projects.