Every reliable medium-voltage panel is backed by two very different kinds of evidence: type tests that prove the design and routine tests that prove each unit was built correctly. This guide explains what IEC 62271-1 and IEC 62271-200 require for each, how site tests fit in, and what to look for in a test report.
Two Questions, Two Kinds of Test
Buyers of switchgear need answers to two separate questions:
- Is this design capable of its ratings? Can it withstand the rated voltage, carry the rated current, survive the rated short circuit and, if claimed, contain an internal arc? Type tests answer this.
- Was this particular unit built to that design? Are the insulation, wiring, mechanisms and connections free of manufacturing defects? Routine tests answer this.
Neither replaces the other. A brilliant design is worthless if a cubicle leaves the factory with a loose busbar bolt, and a perfectly assembled cubicle is unsafe if its design was never proven at full fault current.
Type Tests: Proving the Design
Type tests are performed on one or a few representative units of a design. Several of them are destructive or stressful enough that the tested sample is not sold afterwards. They are normally carried out or witnessed by an independent high-power and high-voltage laboratory, many of which belong to the Short-Circuit Testing Liaison (STL). The result is a type test report or certificate that applies to every unit built to the same design.
Mandatory type tests under IEC 62271-200
| Type test | What it proves |
|---|---|
| Dielectric tests (power-frequency and lightning impulse) | Insulation withstands Ud and Up, phase-to-earth, between phases and across isolating distances |
| Measurement of main circuit resistance | Reference value for later routine and site checks |
| Temperature-rise test | Rated normal current can be carried without exceeding temperature limits |
| Short-time and peak withstand current tests | Main and earthing circuits survive Ik for tk and the peak Ip |
| Making and breaking tests of switching devices | Circuit breakers, switches and earthing switches perform as rated when installed in the panel |
| Mechanical operation and interlock tests | Mechanisms, withdrawable parts and interlocks work reliably |
| Verification of IP protection | Enclosure, partitions and shutters meet their declared IP code |
| Tightness tests | Gas-filled compartments meet the specified leakage rate |
| EMC tests on auxiliary and control circuits | Secondary equipment works in the electromagnetic environment of a substation |
| Internal arc test (when IAC is claimed) | Personnel are protected as declared, for example IAC AFLR 25 kA 1 s |
Depending on the design, further type tests may apply: pressure withstand tests for gas-filled compartments, tests on insulating partitions, mechanical impact tests and weatherproofing tests for outdoor equipment. Switching devices installed in the panel also carry their own type tests, for example under IEC 62271-100 for circuit breakers and IEC 62271-103 for switches.
When a type test stops being valid
A type test covers a design, not a brand name. Changes to busbar sizes, compartment dimensions, insulating materials, switching devices or the arc venting path can invalidate it. IEC TR 62271-307 gives guidance on when an existing test can be extended to a modified design and when new tests are required. Ask the supplier to show that the offered configuration falls within the tested range.
Routine Tests: Checking Every Unit
Routine tests are carried out on every unit before it leaves the factory. They are non-destructive and are designed to detect faults in materials or assembly.
| Routine test | Purpose |
|---|---|
| Dielectric test on the main circuit (power-frequency, 1 min) | Detects insulation defects, wrong clearances and contamination |
| Dielectric test on auxiliary and control circuits | Confirms secondary wiring insulation |
| Measurement of main circuit resistance | Finds loose or poor joints; compared with the type-tested value |
| Tightness test | Confirms gas-filled compartments are sealed |
| Design and visual checks | Compliance with drawings, nameplates, labels and wiring diagrams |
| Mechanical operation tests | Every mechanism, interlock and withdrawable part operates correctly |
| Pressure tests of gas-filled compartments | Enclosure strength for pressurized designs |
| Partial discharge measurement (when agreed) | Detects voids and defects in solid insulation such as cast-resin parts |
Partial discharge testing is especially relevant for solid-insulated and cast-resin components such as embedded poles and bushings, and for instrument transformers tested under IEC 61869.
Side-by-Side Comparison
| Aspect | Type test | Routine test |
|---|---|---|
| Question answered | Can the design meet its ratings? | Was this unit built correctly? |
| Performed on | Representative samples of a design | Every unit produced |
| Frequency | Once per design, repeated after significant changes | Every time, before shipment |
| Severity | Full ratings, may be destructive | Non-destructive |
| Where | Independent laboratory or witnessed facility | Manufacturer’s test bay |
| Document | Type test report or certificate | Routine test report per serial number |
Factory Acceptance and Site Tests
Many projects add a factory acceptance test (FAT), in which the customer or a third-party inspector witnesses selected routine tests and functional checks of protection and control schemes. After delivery and installation, site tests verify that nothing was damaged in transport and that the assembled line works as a system. Typical site tests include:
- Main circuit resistance across busbar joints made on site.
- Insulation resistance and, where specified, a power-frequency or VLF test of the main circuit and cables.
- Gas density and tightness checks for gas-insulated units.
- Mechanical operation, interlock and racking checks.
- Secondary injection of protection relays and end-to-end trip tests.
- Verification of earthing connections.
Site dielectric tests are usually performed at a reduced level compared with factory values, often around 80 percent, to avoid stressing healthy insulation. Follow the manufacturer’s instructions.
How to Review a Test Report
- Match the ratings: voltage, current, short-time current, duration and IAC in the report must equal or exceed those on the offer.
- Match the configuration: panel width, busbar arrangement, switching device type and compartment layout should correspond to the tested sample.
- Check the standard edition: reports to older editions may still be accepted, but note significant differences.
- Check the laboratory: look for an accredited or independent laboratory and a signed, dated report with an identifiable sample.
- Ask for routine test reports by serial number for every unit delivered.
Frequently Asked Questions
Are type tests repeated for every order?
No. They are performed once for a design and remain valid as long as the design does not change significantly. Routine tests are repeated for every unit.
Is a partial discharge test always a routine test?
Not for every switchgear type. It is often agreed between buyer and manufacturer and is common for solid-insulated parts and instrument transformers.
What is the difference between a type test and a design verification?
For MV switchgear under IEC 62271, type testing is the method of proof. For LV assemblies under IEC 61439, “design verification” may combine testing, calculation and comparison with a tested reference design.
Can I witness routine tests?
Yes. Most manufacturers offer witnessed factory acceptance tests if they are agreed in the order.
Work with METTZ Group
METTZ Group offers a wide range of medium-voltage switchgear to suit many needs – from air-insulated distribution panels to gas- and solid-insulated units, supplied with routine test documentation for every unit. Check out our website to learn more, or contact METTZ Group today to work with a representative.
