A type test is not repeated for every variant of a switchgear assembly: IEC TR 62271-307 allows the result to be extended to another assembly of the same family if design criteria are met. It applies to metal-enclosed and solid-insulation switchgear from 1 kV to 52 kV, and calculation is only for comparison, not for extrapolation.
Short answer
A switchgear manufacturer does not test every possible combination of functions, currents and dimensions. It tests representative panels and extends their results to others of the same family through design criteria. IEC TR 62271-307, 2015 edition, is the technical report that sets those criteria for prefabricated metal-enclosed and solid-insulation switchgear from above 1 kV up to 52 kV (IEC 62271-200 and IEC 62271-201). IEC 62271-1, 2017 edition, covers the principle in its Annex J, which is informative.
For you, as a buyer or project engineer, the question is this: does the type test report I am given apply to the panel I am going to receive? This guide gives you the criteria to read it.
When a test does not need to be repeated
Annex J of IEC 62271-1 gives three situations in which a test is not repeated:
- A change in a construction detail, if the manufacturer demonstrates that it does not influence the result of that test.
- A change in the installation instructions, provided the test conditions are not invalidated by the new instructions.
- Different rated values for the same switchgear, if the new values are covered by the tests already made, for example when lower ratings are requested.
The standard adds a condition: evidence must be provided to support the extension. Saying they are similar is not enough.
Annex J also gives concrete examples:
| Test | What the result covers | Clause |
|---|---|---|
| Dielectric, non-enclosed conductors | Other arrangements with equal or greater distances to their surroundings and between conductors, if the materials and shapes of conductors and insulators are the same | J.2 |
| Short-time and peak withstand current | A test at 50 Hz or 60 Hz with a peak factor of 2.6 covers both frequencies in networks with a d.c. time constant of 45 ms or less; with a factor of 2.7 it covers any time constant | J.3 |
| Continuous current | A test on a single pole or unit covers larger arrangements if the influence between poles or units is negligible, as is usually the case in switchgear without an enclosure | J.4 |
How the technical report method works
Each panel is characterized by its design parameters. The report distinguishes component parameters, which are controlled and specified by the manufacturer of each component, from assembly parameters. For each type of test it gives a non-exhaustive list of parameters to analyse (clauses 4.1 to 4.6).
The procedure is this: each parameter of the assessed panel is compared with that of the panel already tested, applying the acceptance criterion of the corresponding table. If all the criteria are met, the test of one panel applies to the other. An example given by the report itself: the phase-to-phase distance of the assessed panel is greater than or equal to that of the tested panel.
- Panel with a type test. Design parameters known
- New panel or variant. Same family, other values or dimensions
- Parameter-by-parameter comparison. With the acceptance criterion of each table
- Additional evidence. Technical arguments, comparative calculation or specific test
- Test extended or repeated. Decision backed by the manufacturer
- Are all the extension criteria of the test met?
- Yes: The type test result applies to the variant, with the comparison documented
- No: Are there technical arguments or a comparative calculation that cover the criterion?
- Yes: It is extended with that evidence, and the manufacturer keeps it
- No: The test is repeated on the variant or on a representative panel
What each test allows
- Dielectric (4.1). They are extended from one functional unit or assembly to another of the same family with the same or a lower rated insulation level. If the test included barriers or supplementary insulation, the extension is valid only for arrangements with the same design of that insulation. The tested object must include the high-voltage connections of instrument transformers or fuses, or replicas that reproduce their field configuration.
- Temperature rise (4.2). It applies to normal currents equal to or lower than the tested one. The report asks for a one-to-one comparison of the components of a family, such as instrument transformers or fuses, by their dissipated power.
- Mechanical (4.3). The switching devices are tested according to their component standard. In the panel, the shutters, the contacts of the removable part and the interlocks and kinematic chains are assessed. The extension is made only when the tested arrangement operates under equal or more demanding conditions, and the rated number of operations is equal or lower.
- Short-time and peak withstand current (4.4). It is extended to panels with equal or lower rated currents, whether 50 Hz or 60 Hz.
- Making and breaking (4.5). The switching devices are verified according to their component standards. IEC 62271-200 states that no additional tests are needed if they were already made on the device in a panel with identical or more demanding conditions.
- Internal arc (4.6). Tests are made per compartment. Tests of compartments of different functional units can be combined to extend the result to the assembly under study, with arc current and duration equal to or lower than those tested.
What role calculations have
The technical report uses calculations and simulations only as a comparison between the result of the tested panel and that of the assessed panel, with the same parameters and criteria. They work best when the geometry is complex and a single value does not describe it, such as the distance between conductors, which changes along the path.
- Temperature: the method of IEC TR 60890 can be applied with its limitations, as can thermal networks or computational fluid dynamics.
- Electric field: finite elements or finite volumes, to compare field strengths of two designs.
- Mechanical stresses: they serve to assess the strength of individual parts or supports, but not to extend the mechanical endurance of a mechanism.
- Short circuit: forces between phases and stress on busbars and supports, and the I²t thermal effect when a lower current with a longer duration is assessed.
- Internal arc pressure: the pressure rise in a compartment, considering the opening of the pressure relief flaps.
The complete map of type tests is in type tests of switchgear. The tests that are repeated on every unit, in the factory and after assembly, are in switchgear tests in the factory and after assembly. What to ask the manufacturer when buying is explained in data to specify switchgear.
The other parts of IEC 62271 are arranged in the standards for primary equipment testing.
What not to do
- Do not accept “it is the same design” without seeing which parameters changed and which criterion they were compared against.
- Do not extend a test toward rated values more demanding than those tested.
- Do not use a simulation as a substitute for a mechanical endurance test.
- Do not forget to ask for the drawings of the report: without them nothing can be compared.
When to call us
At Tiza Group we review with you the type test reports of switchgear against the variants you are offered, and we define what evidence to ask the manufacturer for. See our primary engineering and medium-voltage switchgear testing services. Write to us and we will send you a quote.
Related guides
- Type tests of switchgear: what is tested
- Data to specify switchgear: enquiry and order
- MV switchgear tests: factory and assembly
- Medium-voltage switchgear: parts, functions and tests
- Standards for substation primary equipment testing
References
- IEC TR 62271-307, High-voltage switchgear and controlgear - Part 307: Guidance for the extension of validity of type tests of AC metal and solid-insulation enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV, 2015 edition. Clauses 1.1, 3.1 to 3.3 and 4.1 to 4.6.
- IEC 62271-1, 2017 edition, Annex J (informative), subclauses J.1 to J.4.
Frequently asked questions
Does a switchgear panel of a different width need a new type test?
Not always. If all the extension criteria of the technical report are met, the result of the tested panel applies to the other one. An example of a dielectric criterion: the phase-to-phase distance of the assessed panel must be greater than or equal to that of the tested panel. If any criterion is not met, more evidence is needed: technical arguments, calculation or simulation, or a specific test (IEC TR 62271-307, clause 3.1).
Does a calculation replace a type test?
No. The technical report accepts calculations and simulations only in a comparative sense: the result of the tested panel is compared with that of the panel under study, with the same design criteria (clause 3.3.1). For the mechanical endurance test, simulations are not recommended (clause 3.3.4).
Can a test be extended to values higher than those tested?
Not with this report. For the electric field, the text makes clear that it covers interpolation between characteristics and not extrapolation, for example toward higher field strengths (clause 3.3.3). A rated value more demanding than the tested one calls for a new test.