Switchgear Specification: Enquiry and Order Data

Short answer

An incomplete enquiry produces tenders that cannot be compared. IEC 62271-1, 2017 edition, devotes its clause 10 to defining the information that must accompany an enquiry, a tender and an order for switchgear, so that the buyer enquires properly and the supplier tenders accurately. It also lets the buyer compare and evaluate the tenders of different suppliers. Clause 9 is the preliminary guide: it explains how to choose the values that are then written down. Both are informative, and Annex F presents similar information in table form.

How each value is chosen (clause 9)

• Rated values. They are chosen according to the characteristics of the system and its expected development. For almost all rated voltages there are several insulation levels, and the choice depends on exposure to fast-front and slow-front overvoltages, the type of neutral earthing and the overvoltage limiting devices. Local atmospheric and climatic conditions also count, as does use above 1,000 m altitude.
• Fault currents. The fault duty is determined by calculating the fault currents at the place where the switchgear will be installed, with IEC 60909-0 as a reference.
• Cables. For cable connection, the maximum temperature at the terminals at full continuous current must stay below the limits of the cable insulation and termination.
• Overload. The equipment can carry a current above the rated one for a short time or when the ambient allows, provided it does not exceed the maximum temperatures of Table 14. For some apparatus, such as load-break switches, that overload may exceed their switching capacity.
• Environment. The switchgear must meet at least the service conditions the user requires. If access may be affected by snow or sand build-up, greater clearances should be considered. With high humidity and condensation, switchgear designed for it is used, or the problem is prevented with ventilation, heating, dehumidifiers or thermostat-controlled resistors. With strong solar radiation a roof, forced ventilation or current derating may be needed.

What the buyer states (clause 10.2)

In addition, the buyer must state any condition that may influence the tender or the order. Examples are special mounting or installation, the location of the external high-voltage connections, pressure vessel rules and cable tests. The buyer must also say whether the function has to be maintained during or after an earthquake. If you want type test reports or other conformity assessment documents, you must request them in the enquiry.

What the manufacturer answers (clause 10.3)

The manufacturer supplies, with descriptive material and drawings:

• The rated values and characteristics the buyer asked for.
• Construction features: mass of the heaviest transport unit, overall dimensions, arrangement of external connections, future extensions, means of transport and erection, accessible sides, and the installation, operation and maintenance instructions.
• For gas or liquid systems: type of system, filling level or pressure and functional minimum, volume or mass per compartment and fluid specification.
• For the operating devices: types and rated values, operating current or power and operating times.
• The list of spare parts the user should purchase.

How to check a tender against your enquiry

With the list of clause 10 in hand, a tender is checked by groups and not all at once:

1. Rated values. Every value of the enquiry must appear in the tender, with the same name and the same unit. If one is missing, ask before comparing prices.
2. Control and auxiliaries. Compare the control supply voltage, the operating times and the auxiliary contacts available with what your control system needs.
3. Fluids. Check the type of gas or liquid, the filling pressure and the functional minimum, because they define the alarms and lockouts you will configure.
4. Dimensions and masses. Confirm that the room and the access route can take the heaviest transport unit.
5. Spare parts and manuals. The spare parts list and the installation, operation and maintenance instructions are part of what is bought.

This order lets you compare tenders from different suppliers on the same basis, which is the purpose the standard itself gives this clause.

Data that change risk and price

Some data move the design more than others, so it pays to state them from the enquiry:

• Altitude above 1,000 m. It changes the external insulation. For instrument transformers it is explained in the guide on altitude above 1,000 m.
• Fault current at the point of installation. Define Ik with a short-circuit study, not with the catalogue value that seems close. For a first estimate you can use our free short-circuit current tool.
• Neutral earthing. It changes the insulation level and the overvoltages. See isolated versus earthed neutral.
• Cables and overload. If the site requires operating above the rated current, say so: the terminal temperature and the switching capacity matter.
• Auxiliary contacts. State how many you need and what performance you require, as the guide on circuit breaker auxiliary contacts explains.
• Type test reports. Ask for them in the enquiry, not after the purchase.

The type test reports worth requesting are explained in type tests of switchgear. The routine test protocol is in the routine tests of switchgear, and the input data the user supplies at installation in switchgear installation. On the IP and IK protection degrees of the enclosure, read IP and IK protection degrees of switchgear.

To see how this fits with the rest of the IEC 62271 series, see the standards for primary equipment testing.

What not to do

• Do not ask for “a 24 kV switchgear panel” without insulation level, currents and short-circuit duration.
• Do not leave service conditions out of the enquiry because “they are normal”: confirm them in writing.
• Do not compare tenders that did not answer the same list.
• Do not accept a tender without the mass of the heaviest transport unit: it defines lifting and access.

When to call us

At Tiza Group we draw up with you the switchgear specification (rated values, service conditions, control and documents) and compare the tenders you receive. This is a remote service, available worldwide. See our primary engineering service and write to us for a quote.

Related guides

• Type tests of switchgear: what is tested
• Routine tests of switchgear in the factory
• Switchgear installation: final inspection and data
• Switchgear maintenance and failure report
• Medium-voltage switchgear: parts, functions and tests
• IP and IK Protection Degrees of Switchgear Enclosures

References

• IEC 62271-1, High-voltage switchgear and controlgear - Part 1: Common specifications for alternating current switchgear and controlgear, 2017 edition, clauses 9.1 to 9.5 and 10.1 to 10.3, and Annex F (informative).

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