Table of Contents
Introduction
Type testing of medium-voltage (MV) switchboards in NABL-accredited laboratories is a mandatory requirement for compliance with IEC 62271-200. These tests verify critical aspects such as dielectric strength, temperature rise, short-time current withstand, and internal arc classification.
However, switchboards are usually offered in multiple variants within the same product family—differing in current ratings, fault levels, or configuration. Testing every variant individually is neither cost-effective nor time-efficient.
So, what’s the way out?
The answer is Design Validation. IEC provides guidelines to validate non-tested assemblies (partially or not type tested) with reference to a type-tested assembly of the same family.
Let us first understand the recommended type tests as per IEC 62271-200 before discussing the design validation rules.
Mandatory Type Tests as per IEC 62271-200
- Dielectric tests (insulation) —
- Lightning impulse withstand and one-minute power-frequency voltage withstand voltage are applied to the assembly to verify insulation levels. For air-insulated panels, this decides the creepage and clearance between phases and phase to earth.
- Temperature rise test —
- This is also called “heat run test”. It measures the temperature rise of conductors, connections and components under rated current (and specified overloads) to verify thermal performance. It confirms the suitability of the bus bar cross-section and material (Al or Cu) for the tested current rating.
- Short-time and peak (electrodynamic) current withstand tests —
- Short-time withstand current (Ik for specified duration) and peak (making) current tests to check adequacy of busbars, connections and mechanical integrity of support insulators & structures under short circuit fault conditions. It is the test of the bus bar and its support arrangement against electrodynamic stress created during short circuit fault condition.
- Short-circuit (making/breaking) and switching tests
- Where relevant, tests for breaking capacity, making capacity and switching of capacitive/inductive currents (often performed on circuit-breakers as installed in the assembly). IEC 62271-200 requires tests of switching duties as applicable.
- Measurement of the resistance of the main circuit
- Verify main circuit resistance to check contact resistance and quality of joints.
- Mechanical operation tests —
- Operate the switching devices through many cycles, mechanical and electrical operations to verify mechanisms, interlocks and durability.
- Radio-interference voltage (RIV) / electromagnetic compatibility (EMC)
- RIV / EMI checks to verify the switchgear does not generate excessive interference whenever exposed to such radiation.
- Verification of degree of protection (IP)
- Check ingress protection against dust/water and other environmental robustness tests for outdoor/indoor versions.
- Internal arc (IAC) test
- Internal arc classification and tests to demonstrate personnel & asset protection and pressure relief performance. Panels accessibility class defined are classified AFLR, A, B, etc.
IEC/TR 62271-307:2024 — The Framework for Design Validation
Designing and validating medium-voltage (MV) switchgear is a complex task. Manufacturers must balance safety, reliability, and cost efficiency while meeting international standards.
The IEC has published IEC/TR 62271-307:2024, which guides manufacturers on extending type test validity from one configuration to others within the same product family.
It applies to:
- Metal-enclosed switchgear (IEC 62271-200)
- Solid-insulation switchgear (IEC 62271-201)
- Voltage range: above 1 kV up to 52 kV
Design Validation Rules and Practices
- Group your switchgear assemblies into families with shared designs, functional units, and components. A “validated test object”, i.e., an already type-tested assembly, serves as the reference for other variants. For example, 33kV AIS Panels can be considered as one family.
- Reference to Tested Assemblies: Non-tested switchboards must be proven equivalent to type-tested “family members” based on documented design similarities, construction methods, and critical parameters like dimensions, phase distances, and insulation.
- Design Documentation: Detailed drawings, bills of material, and assembly records must clearly show compliance with IEC requirements and equivalence to the tested configuration.
- Extension of Type Test Validity: IEC/TR 62271-307 provides guidance: if a panel in a product family has passed type tests, other members may be validated by:
- Comparison of key design parameters (refer to summary tables in IEC/TR 62271-307), including: dielectric distances, conductor size, mechanical supports, compartment arrangements, volume of high voltage compartment and the rated operational values.
- Calculations confirming performance (e.g., dielectric withstand, temperature rise, and mechanical strength).
- Evidence of Material and Technical Dependability: Materials, components, and construction techniques used must be proven to have adequate service history and suitability for intended conditions.
Key Areas for Design Validation
- Dielectric Performance: Validate insulation performance by comparing dielectric distances (creepage & clearances), insulation materials, and construction methods with those of the tested products. So if creepage and clearances are similar or higher in the same family compared to the tested assembly, then the type test can be extended to a non-tested assembly.
- Short-Time Current & Thermal Performance: Confirm mechanical and thermal withstand by calculation, referencing type-tested switchboards of similar size and rating. Here, the validation is for the withstand capability of a non-tested switchboard against electrodynamic forces during short circuit and thermal performance while operating at rated current. Suppose the design of a non-tested switchboard has a higher or equivalent cross-section of bus bars, similar or better insulators, and less or equal space between insulators. In that case, its validity can be extended to non-tested switchboards for short-circuit and thermal performance.
- Mechanical Endurance: Ensure that moving parts, interlocks, and doors are equivalent in reliability to those tested in validated assemblies.
- Internal Arc Withstand: If declaring internal arc classification, provide analysis based on enclosure design and pressure relief mechanisms proven in previously tested units.
- Partial Validation: When full equivalence cannot be shown, partial validation is acceptable with calculations and selective third-party testing.
Information and Verification
- Comparison Tables: Manufacturers must prepare tables comparing the non-tested switchboard against tested item parameters—covering dimensions, ratings, electrical clearances, and mechanical features.
- Manufacturer’s Declaration: Compliance is demonstrated by detailed engineering reports, calculation sheets, and referenced third-party test reports; manufacturers must supply all necessary documentation to end users and authorities.
- Routine Tests: Despite a lack of full type testing, routine tests (dielectric, operation, and functional safety checks) must always be performed on each manufactured unit before shipment.
These rules, when followed, allow non-tested MV switchboards to be validated for IEC 62271-200 compliance through engineering judgment, robust documentation, and linkage to type-tested designs.
Case Example: Indoor vs Outdoor Panels (IAC Test Extension)
The reference type tested assembly is indoor, but the manufacturer wants to extend the validity to the outdoor panel. This is possible. Let us understand how through the following example:
- Common Construction of Indoor & Outdoor Panels:
- The active part (i.e., busbars, VCBs, CTs, protection system) and the internal segregation of indoor and outdoor panels are identical.
- In outdoor panels, an additional weatherproof canopy/ additional front door is provided for IP protection against rain, dust, sunlight, etc. This canopy has no functional role in arc fault containment.
- Test Condition is the Same:
- Internal arc fault behavior (pressure build-up, gas venting, flame propagation) depends on the internal design of the switchgear compartments (busbar chamber, cable chamber, breaker chamber), which are the same in both indoor and outdoor panels.
- Once validated for indoor type, the safety of operators is already ensured.
- Outdoor Panel is Only Indoor Panel + Weather Canopy & additional front door:
- Since outdoor panels are essentially indoor panels fitted with a Weather Canopy at the top & additional front door, repeating the internal arc test does not add technical value. The arc is contained by the inner tested panel; the outer canopy only provides environmental protection. In some cases, the enclosure volume increases due to a 100 mm expansion of the panel width to accommodate the outer door, thereby further lowering the pressure due to IAC and making it safer.
- International Practice / Standards Alignment:
- IEC 62271-200 (for MV switchgear) allows this approach. Type test reports of IAC for indoor construction are accepted for outdoor panels of the same design, provided the arc containment path, clearances, and operator accessibility zones remain unchanged. Please refer to the guidelines in the IEC below:
Key Benefits of Design Validation
✅ Cost Savings – Eliminates redundant type tests.
✅ Time Efficiency – Faster market introduction of new variants.
✅ Compliance Assurance – IEC 62271-200 aligned.
✅ Flexibility – Supports wide product portfolios with validated safety.
Conclusion
Design validation under IEC/TR 62271-307:2024 provides a structured and globally accepted method to extend type test validity across product families. By combining engineering calculations, documentation, and reference to tested assemblies, manufacturers can ensure compliance, safety, and reliability—while saving both time and cost. For detailed design validation rules IEC 62271-307:2024 can be referred.
This approach empowers MV switchgear manufacturers to confidently expand product portfolios, adopt new insulating technologies, and maintain a competitive advantage without compromising compliance or safety.
Frequently Asked Questions (FAQs)
1. What is the difference between type testing and design validation in MV switchgear?
Type testing is performed in accredited labs to verify insulation, temperature rise, short-circuit withstand, and safety performance. Design validation extends the results of these type tests to other variants within the same product family through engineering calculations, documentation, and comparison, avoiding redundant full-scale testing.
2. Do all MV switchboards need to undergo type testing?
No. Only one representative assembly per product family must be type tested. Other non-tested variants can be validated using IEC/TR 62271-307:2024 guidelines, provided they share critical design parameters with the tested configuration.
3. Can indoor type-tested panels be considered valid for outdoor versions?
Yes. If the internal design (busbar chamber, breaker chamber, cable chamber) remains the same, and only a weather canopy or enclosure modification is added for outdoor protection, the indoor arc test results can be extended to the outdoor version.
4. What are the main benefits of design validation?
- Significant cost savings by avoiding repeated type tests
- Faster market launch of new ratings or configurations
- Assured compliance with IEC standards
- Flexibility to expand product families while maintaining safety
5. Which IEC standard should I refer to for design validation?
The key document is IEC/TR 62271-307:2024, which provides detailed rules for extending the validity of type tests to non-tested assemblies. For type test requirements themselves, refer to IEC 62271-200.
6. Are routine tests still required for non-type-tested panels?
Yes. Regardless of design validation, each manufactured switchboard must undergo routine tests (dielectric, operational, and functional checks) before delivery to ensure unit-level quality and safety.