When the site exceeds normal service, IEC 62271-1 asks the user to specify it using standardized steps: external insulation per IEC 60071-2 above 1,000 m, six temperature ranges, heavy or very heavy pollution, earthquake with an admissible damage level, and wind above 34 m/s. Internal insulation does not change with altitude.
Short answer
When a substation or a plant lies outside the normal service conditions, IEC 62271-1 (2017 edition) does not leave the subject open: clause 4.2 gives standardized steps the user must follow in the specification. They cover altitude, pollution, temperature and humidity, earthquake and vibration, wind and other parameters.
Altitude above 1,000 m
Clause 4.2.2 requires determining the external insulation level required at the site according to clause 4 of IEC 60071-2:1996. The rated insulation level of the equipment must be equal to or higher than that value. The standard gives no formula here: it refers to the insulation coordination standard.
Two clarifications from the notes of the same clause:
- Internal insulation has the same dielectric characteristics at any altitude and needs no special precautions.
- Low-voltage auxiliary and control equipment needs no precautions below 2,000 m. Above that altitude, the standard refers to IEC 60664-1.
For the parallel case in instrument transformers, see the guide on altitude and instrument transformers.
Pollution
Clause 4.2.3 reclassifies the environment when it exceeds the normal one:
- Outdoor: if air polluted by dust, smoke, corrosive gases, vapors or salt exceeds the «medium» class of IEC TS 60815-1:2008, it is classified as «heavy» or «very heavy».
- Indoor: if it exceeds the «very light» class, it is classified as «light», «medium», «heavy» or «very heavy».
Annex K of the standard (informative) defines the levels and recommends minimum creepage distances for external insulation. For indoor equipment up to 52 kV, clause 4.2.3 notes that IEC TS 62271-304 can be specified when pollution on the switchgear insulation is a concern.
Temperature and humidity
Clause 4.2.4 lists the minimum and maximum temperature ranges to specify when the site falls outside the normal range:
| Climate | Ambient temperature range |
|---|---|
| Extremely cold | −50 °C to 40 °C |
| Very cold | −40 °C to 40 °C |
| Cold | −30 °C to 40 °C |
| Cold (indoor conditions) | −25 °C to 40 °C |
| Moderate (indoor conditions) | −15 °C to 40 °C |
| Very hot | −5 °C to 55 °C |
In tropical indoor conditions, the 24 h average relative humidity can reach 98%. The note to the clause warns that in regions with frequent warm, humid winds, abrupt changes of temperature and atmospheric pressure can occur.
Vibration, earthquake and movement
Clause 4.2.5 starts from the premise that standard switchgear is designed to be mounted on substantially level structures free of excessive vibration, shock or tilt. If those conditions do not exist, the user must specify the requirements of the application.
Where earthquakes are likely, the user must specify:
- The severity level, per a relevant publication (the standard cites IEC TR 62271-300, IEC 62271-207 and IEC TS 62271-210).
- The operating requirements.
- The admissible damage level.
Other uncommon forms of vibration must also be identified, such as proximity to mine blasting or mobile applications.
Wind and other parameters
If wind above the normal service value of 34 m/s is expected, the user must specify the requirements of the application (clause 4.2.6). For other particular environmental conditions, clause 4.2.7 refers to the IEC 60721-1, IEC 60721-2 and IEC 60721-3 series.
What must be written in the specification
Clause 4.2.1 requires the user’s requirements to refer to the standardized steps of 4.2.2 to 4.2.7, provided the product standards do not give them. In practice, the equipment data sheet should state:
- The site altitude above sea level.
- The ambient temperature range from the six listed, or the expected extreme value.
- The pollution class of the site per IEC TS 60815-1, if it exceeds «very light» indoors or «medium» outdoors.
- The seismic severity level, the required operation and the admissible damage.
- The expected wind speed, if it exceeds 34 m/s.
The standard adds that the detailed classification of environmental conditions is in IEC 60721-3-3 for indoor and IEC 60721-3-4 for outdoor. Annex K describes the pollution levels in words (very light, light and medium) and gives, for each, the recommended minimum specific creepage distance in mm/kV for external insulation.
The reference conditions are in the normal service conditions for switchgear. The condensation and pollution classes in switchgear describe condensation and pollution for indoor equipment, and the rated values that depend on them, such as the rated insulation level, have guides of their own. For more on the normal service conditions of a transformer under IEC 60076-1: normal service conditions of a transformer.
To see how this fits in the rest of the IEC 62271 series, see the standards for primary equipment testing.
How it is used in a specification
- Which condition exceeds normal service?
- Altitude above 1,000 m: Determine the required external insulation with IEC 60071-2; internal does not change
- Temperature out of range: State one of the six ranges of clause 4.2.4
- Pollution: Classify it with IEC TS 60815-1 (heavy or very heavy outdoors)
- Earthquake or vibration: Specify severity, required operation and admissible damage
- Wind above 34 m/s: State the expected value for the application
When several conditions combine, each one must be written in the specification.
What not to do
- Do not apply an altitude correction to internal insulation: the standard says it does not change.
- Do not assume an extreme climate is covered by the type test of standard equipment: the temperature range that applies must be specified.
- Do not leave the earthquake undefined. Without a severity level and admissible damage, buyer and manufacturer are not talking about the same thing.
- Do not forget auxiliary equipment: the standard notes that other components, such as relays, need suitable measures to operate under those conditions.
When to call us
At Tiza Group we define the switchgear service conditions with you and verify that the specification and the type test report cover them. See our primary engineering design service. Write to us and we will quote it.
Related guides
- Normal service conditions for switchgear
- Condensation and pollution classes in indoor switchgear
- Rated insulation level of switchgear
- Altitude above 1,000 m in instrument transformers
- Creepage distance on instrument transformer insulators
- Transformer Normal Service Conditions: IEC 60076-1
References
- IEC 62271-1, High-voltage switchgear and controlgear - Part 1: Common specifications for alternating current switchgear and controlgear, 2017 edition: clauses 4.2.1 to 4.2.7 and Annex K.
- IEC 60071-2:1996, Insulation co-ordination - Part 2: Application guide, clause 4 (cited by the standard).
- IEC TS 60815-1:2008, site pollution severity classes (cited by the standard).
Frequently asked questions
What changes in switchgear or a circuit breaker installed above 1,000 m?
The external insulation changes: the withstand voltage level required at the site is determined with clause 4 of IEC 60071-2:1996, and the rated level of the equipment must be equal or higher (IEC 62271-1, clause 4.2.2). Internal insulation does not change with altitude.
Which temperature ranges does the standard propose for cold and hot climates?
Six ranges: −50 to 40 °C (extremely cold), −40 to 40 °C (very cold), −30 to 40 °C (cold), −25 to 40 °C (cold, indoor), −15 to 40 °C (moderate, indoor) and −5 to 55 °C (very hot). They are in clause 4.2.4.
Who defines the seismic level that switchgear must withstand?
The user. The standard states that where earthquakes are likely, the user must specify the severity level using a relevant publication, plus the operating requirements and the admissible damage level (clause 4.2.5).