IEC Test Items & Requirements for SF6 Load Break Switches

SF6 load break switches are widely used in ring main units and distribution substations. Sulfur hexafluoride gas serves as insulation and arc-quenching medium. For global export markets, SF6 load break switches shall pass full type tests according to IEC 62271-103:2021 High-voltage switchgear and controlgear – Part 103: Alternating current switches for rated voltages above 1 kV up to 52 kV, together with IEC 62271-1. All tests verify insulation performance, current carrying capacity, mechanical reliability, switching capability and SF6 tightness.

1. Dielectric Tests

  1. Lightning impulse withstand test (1.2/50 μs): applied to phase-earth, phase-phase and open break. No breakdown or flashover.
  2. Power frequency withstand test (50 Hz, 1 min): test across main insulation and isolating gap. Auxiliary circuits withstand 2 kV power frequency voltage.
  3. Partial discharge measurement: PD level shall meet limits under 1.1 times rated phase voltage.
  4. Artificial pollution test (optional for outdoor type).

2. Main Circuit Resistance Measurement & Temperature Rise Test

  • Main circuit resistance is measured before and after all type tests; resistance rise after tests must be within permitted range.
  • Temperature rise test under rated normal current. Temperature of all conductive parts shall not exceed the limits specified in IEC standard to avoid contact ablation and SF6 decomposition.

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

  • Short-time withstand current (thermal stability): withstand short-circuit current for specified duration without melting, deformation or damage.
  • Peak withstand current (dynamic stability): resist electromagnetic force during short-circuit; no permanent mechanical deformation. Important note: Load break switches are not designed to break short-circuit current, but must sustain short-circuit faults.

4. Making and Breaking Capacity Tests (Core Tests)

  1. Rated load current switching test
  2. Loop current switching test (critical for ring network application)
  3. Cable-charging current breaking test Two classes defined by IEC:
  • Class C1: limited restrike risk
  • Class C2: enhanced performance for frequent capacitive switching (widely required by overseas power utilities such as PLN Indonesia)
  1. Unloaded transformer switching test
  2. Short-circuit making test (optional upon customer demand)

5. Mechanical Tests & Mechanical Endurance Test

  • Mechanical operation test: measure opening/closing time, stroke, interlock function.
  • Mechanical endurance test: thousands of operating cycles without voltage. After endurance, mechanism and interlocks shall work normally.

6. SF6 Compartment Tightness Test (Mandatory for Gas-insulated type)

  • Gas leakage test: Annual leakage rate ≤ 0.5% at 20℃.
  • SF6 moisture measurement: excessive moisture causes corrosion inside the switch after arcing.

7. Ingress Protection Test (IEC 60529)

IP rating test for metal enclosure. Gas tank usually requires IP67, operating cabinet IP54.

8. Auxiliary and Control Circuit Tests

Coil operating voltage range test, insulation test and EMC compatibility test.

9. Optional Tests (Frequently requested by international tender)

Internal arc classification (IAC) test, low/high temperature test, damp heat cycle test, radio interference voltage test.

Market Tip

Power utilities including PLN (Indonesia), Central Asia and Middle East buyers usually require complete IEC 62271-103 type test certificates, Class C2 capacitive switching performance and SF6 tightness reports. Class C2 SF6 load break switches are preferred for urban ring network projects.