Metal Clad Switchgear Testing: Factory Tests, Site Tests & IEC 62271-200 Requirements

The Testing Framework for Metal Clad Switchgear

Metal clad switchgear is the most rigorously tested category of medium voltage equipment. The consequences of switchgear failure — equipment damage, arc flash injuries, extended power outages — demand that every design is proven by destructive type tests and every manufactured unit is verified by routine tests before leaving the factory.

This guide explains the complete testing framework for metal clad switchgear per IEC 62271-200 (the international standard) and ANSI C37.20.2 (the North American standard), covering what is tested, how it is tested, and what the results mean for engineers, buyers, and installers.

Type Tests (Design Verification)

Type tests are performed once on a representative sample of a new switchgear design to prove that the design meets all performance requirements. These tests are typically conducted at an accredited high-power test laboratory — KEMA (Netherlands), CESI (Italy), CEPRI or Xihari (China), or similar nationally recognized test centers.

1. Dielectric Tests

Dielectric tests verify that the insulation system can withstand the specified overvoltages without flashover or puncture.

Power frequency withstand voltage (1 minute):

Lightning impulse withstand voltage (1.2/50 microsecond impulse): Applied as 15 positive and 15 negative impulses at the BIL level. No more than 2 disruptive discharges are allowed across external insulation per IEC 62271-1.

Partial discharge test: Measured at 1.1x rated voltage. Apparent charge must not exceed 10 pC for gas-insulated switchgear and 20 pC for air-insulated switchgear per IEC 62271-200. This test detects insulation defects (voids, contamination, tracking) that would lead to progressive insulation failure in service.

2. Temperature Rise Test

The temperature rise test verifies that the switchgear does not overheat when carrying rated continuous current. The test is conducted by passing rated current (e.g., 1,250 A, 2,000 A, or 3,150 A) through the complete current path — bus bars, circuit breaker, cable connections, CTs — until thermal equilibrium is reached (temperature change < 1 degree C per hour).

Temperature rise limits per IEC 62271-1:

• Bare copper or copper alloy connections: 75 K above ambient (for silver or tin plated: 90 K for non-spring-loaded connections, 105 K for spring-loaded)
• Accessible surfaces: 30 K (to prevent burn injuries)
• Oil (in CT/VT): 50 K (top oil) — relevant if oil-filled CTs/VTs are installed within the switchgear

The temperature rise test is particularly important for draw-out circuit breaker contacts — the sliding or tulip-type primary contacts that mate the circuit breaker to the stationary bus connections. Poor contact pressure or worn contacts cause localized hot spots that accelerate contact degradation. NAIJI Electric's ASN3-12 uses silver-plated tulip contacts with spring loading to maintain consistent contact pressure throughout the draw-out cycle.

3. Short-Circuit Withstand Test

This test subjects the switchgear to the rated short-time withstand current (e.g., 25 kA or 40 kA for 1 or 3 seconds) to verify that:

• Bus bars and connections withstand the electromagnetic forces without deformation
• The enclosure structure maintains integrity under mechanical shock
• Temperature rise during the short circuit does not exceed the limit for the conductor material (250 degrees C for bare copper per IEC 62271-1)
• All mechanical interlocks, shutters, and grounding devices remain functional after the test

The short-circuit test also includes a making capacity test: the circuit breaker must close onto a fault at 2.5x the rated short-time current (peak asymmetric value). For a 40 kA switchgear, the making capacity test is at 100 kA peak — an enormous electromagnetic impulse.

4. Internal Arc Test (IEC 62271-200 Annex A)

The internal arc test is the most dramatic and critical test for metal clad switchgear. It simulates an internal arc fault — a rare but catastrophic event where an arc forms inside the switchgear enclosure between phases or between phase and earth.

Test setup: A thin wire is placed inside the switchgear to initiate the arc at the rated short-circuit current. The test duration is specified by the manufacturer (typically 0.1 s, 0.5 s, or 1.0 s — representing the maximum time the arc can burn before upstream protection operates).

Pass criteria:

1. No door opening: All doors, covers, and removable panels must remain closed and latched throughout the arc event and the subsequent pressure pulse
2. No fragmentation: No parts of the enclosure with mass > 60g may be ejected toward accessible areas
3. No ignition: Cotton indicators placed 300 mm from accessible surfaces (per the manufacturer's specified accessibility zones) must not ignite from hot gases
4. No perforation: The enclosure must not develop holes in accessible areas through which hot gases could directly impinge on personnel
5. Earth continuity: The enclosure must maintain earthing continuity after the test (verified by passing 500 A through the earth system)

IAC classification:

• IAC-A: Accessible sides only (front, defined by manufacturer)
• IAC-AF: Front side tested
• IAC-AFL: Front and lateral sides tested
• IAC-AFLR: Front, lateral, and rear sides tested — the highest classification, suitable for switchgear that can be approached from all sides

The internal arc test is arguably the most important safety test for metal clad switchgear. NAIJI Electric's ASN3-12 is type-tested to IAC-AFLR at 40 kA for 1 second — the most demanding internal arc classification.

5. Mechanical Endurance Test

The circuit breaker and draw-out mechanism are operated for the rated number of operations — 10,000 (Class M1) or 30,000 (Class M2) per IEC 62271-100. The test verifies that all mechanical components (springs, latches, rollers, shutter mechanisms, position indicators) function correctly throughout the rated life without adjustment or part replacement.

Routine Tests (Manufacturing Quality Verification)

Routine tests are performed on every individual switchgear panel at the factory before shipment. They verify that the specific unit has been manufactured correctly — that no wiring errors, loose connections, dimensional deviations, or material defects exist.

Mandatory routine tests per IEC 62271-200:

1. Power frequency withstand voltage: Applied at 80% of the type test level (per IEC 62271-1 revision). For 12 kV switchgear: 24 kV rms for 1 minute across all open switching devices, phase-to-phase, and phase-to-earth. No flashover or breakdown is permitted.
2. Auxiliary circuit voltage test: 2 kV rms for 1 minute on all secondary circuits (control wiring, relay circuits, CT/VT secondaries).
3. Main circuit resistance measurement: Contact resistance of all main circuit connections measured by DC injection (typically 100 A). Measured values must not exceed 120% of the type test values.
4. Mechanical operation test: 5 close-open operations of the circuit breaker and draw-out mechanism to verify correct operation, contact alignment, and interlock function.
5. Visual and dimensional inspection: Verification of nameplate data, earthing connections, interlock operation, IP rating (gasket integrity), and dimensional compliance with drawings.

NAIJI Electric additional routine tests (beyond IEC minimum):

• Partial discharge measurement at 1.1x rated voltage (10 pC limit) — more sensitive than IEC minimum requirements
• Draw-out travel measurement with dial indicator to verify primary contact engagement depth
• CT ratio and polarity verification by primary injection
• Insulation resistance measurement at 2,500 V DC (minimum 1,000 megohm)

Site Acceptance Tests (Post-Installation Verification)

After the switchgear is transported to site, installed, and connected, a site acceptance test (SAT) verifies that the equipment has survived transport undamaged and is correctly installed. The SAT should be conducted by the manufacturer's commissioning engineer or a qualified third-party commissioning agent.

Recommended SAT scope:

Phase 1 — Pre-energization checks:

• Visual inspection: transport damage, assembly correctness, bolt torques (sample check), earthing connections, labeling
• Insulation resistance: megger at 2,500 V DC or 5,000 V DC — minimum 100 megohm (derate for altitude and humidity). Test phase-to-phase, phase-to-earth, and across each open switching device
• Contact resistance: DC micro-ohm measurement of all main circuit joints — compare with factory routine test values (should not exceed 150%)
• Circuit breaker timing: measure close time, open time, and close-open time using a circuit breaker timing analyzer. Compare with manufacturer's specifications (typical 12 kV VCB: close time 45-65 ms, open time 25-40 ms)
• Mechanical interlocks: verify every interlock sequence (breaker cannot close in test position, earthing switch cannot close with breaker closed, door cannot open with earthing switch open, etc.)

Phase 2 — Protection relay commissioning:

• CT ratio verification by primary injection (if CT primary is accessible) or secondary injection with known burden
• Protection relay settings verification: confirm overcurrent pickup, time delay, earth fault pickup, and curve type match the protection coordination study
• Trip circuit test: inject current to verify the relay trips the circuit breaker at the set pickup value
• Alarm function test: verify all relay alarms (trip, lockout, battery fail, CT supervision) are correctly wired to the SCADA system

Phase 3 — Energization:

• First energization procedure: close the incomer breaker under controlled conditions with load-side breakers open. Verify correct phase rotation. Monitor for abnormal noise, vibration, or temperature.
• Load test: close feeder breakers progressively, verifying current balance, CT secondary currents, and voltage measurements at each step.

NAIJI Electric Testing & Quality Assurance

All NAIJI Electric metal clad switchgear undergoes the full IEC 62271-200 routine test sequence before shipment, with type test reports available from CEPRI (China Electric Power Research Institute) and Xihari (Xi'an High Voltage Apparatus Research Institute). Our ASN3-12 switchgear holds type test certifications for internal arc (AFLR, 40 kA, 1s), short-circuit withstand (40 kA, 4s), and temperature rise (3,150 A continuous).

For project-specific test witness arrangements, factory acceptance test (FAT) scheduling, or type test report requests, contact our quality assurance team.