Recommendations for the successful erection of medium voltage switchgear

Erection of MV switchgear

Electrical engineers working on project execution know that switchgear erection brings many challenges, no matter the voltage level. The switchgear cannot always be assembled in the factory and shipped to the site as a complete plant, so it is usually necessary to pack the equipment in its individual cubicles, ship it to the site, and eventually erect it.

Erection includes the setting in place of these cubicles, their interconnection both mechanically and electrically, and the fitting of any extra relays together with the power and control cables. The chambers may have to be filled with insulating media of different types.

Once the equipment has been erected it needs to be commissioned, which is defined as the work of testing and finally placing in service of the installed apparatus.

The focus of this technical article will be the metal-enclosed switchgear (switchgear assemblies with an external metal enclosure intended to be earthed, and complete except for external connections), and metal-clad switchgear (metal-enclosed switchgear in which components are arranged in separate compartments with metal enclosures intended to be earthed).

Table of contents:

1. Storage of MV switchgear
2. Erection:
   1. Foundations
   2. General assembly
   3. Busbar and circuit chamber assembly
   4. Cabling
   5. Earthing
   6. Oil filling
   7. Gas filling
   8. Vacuum interrupters
   9. Small wiring
3. Final inspection

1. Storage of MV switchgear

It is best to deliver the switchgear cubicles at a time convenient for their immediate erection. However, it sometimes (often) happens that the site works are delayed, in which case the switchgear must be stored carefully until it is needed.

On delivery, it is important to check that all items are present and correct in accordance with the delivery note and then to store these components carefully to ensure that no parts go astray.

If possible, arrangements should be made to keep the building temperature in excess of the dew point so that condensation on the equipment is prevented and thereby the plant is protected from corrosion.

Figure 1 – An example of medium voltage switchgear storage

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2. Erection

Before commencing erection it must be ensured that the workforce is in possession of all the drawings and instructions required to erect the equipment, which is normally provided by the manufacturer. The substation in which the switchgear is to be erected should be as clean and dry as possible and all debris should have been cleared away.

During erection particular attention should be paid to a number of points:

• Dirt and debris should be excluded from partially erected cubicles.
• All openings that are not in immediate use should be blanked off or covered by clean sheets.
• All electrical insulation should be kept clean and dry by being kept covered and, if necessary, heated.
• Materials that have been issued from stores and not yet used on erection should be stored safely and tidily.

When handling the cubicles and major components care should be taken to observe the correct lifting arrangements and to make certain that slings are attached to the manufacturer’s designated lifting points. This ensures that no parts are subjected to undue strains or sudden stresses which could result in disturbed settings or other damage.

Figure 2 – Lifting the MV cubicle from the truck

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2.1 Foundations

The successful erection and operation of the switchboard depend very largely on the accuracy of the foundations. The most useful form of fixing medium for the type of switchboard considered here is some form of proprietary channel embedded in the floor, containing captive adjustable nuts.

Less commonly nowadays, holes may be cast in the floor in which suitable foundation blots can be grouted after the switchgear has been erected carefully.