Installation And Operating Principles For Medium Voltage Switchgear

MV Switchgear Installation

The purpose of this guide book is to address the main issues concerning the installation site, provide end users with indications as to what sort of information manufacturers require, and the measures to adopt to ensure the switchgear continues to function correctly over time.

The first thing to consider is that substations are not normally sealed from the outdoor environment, thus the conditions of this latter affect conditions inside the substation to a considerable extent. The air pressure, for instance, will be the same both inside and outside the structure.

The condition of the building or room will obviously affect conditions inside the substation and should therefore be very carefully assessed.

If the materials provide a good degree of thermal insulation, the outdoor temperature changes from day to night and vice versa become less drastic. Consequently, condensation is less likely to form. However, the doors are usually made of metal and are thus excellent thermal conductors.

Depending on their position, they are able to transfer a fair amount of heat inside the substation and this gives rise to significant temperature changes.

Normal service conditions

The regulation governing medium voltage switchgear is IEC 62271-200, High-voltage switchgear and controlgear, Part 200: A.C. metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV.

Sub-clause 9.1 of IEC 62271-200 (Information to be given with enquiries, tenders and orders) specifies that enquirers requesting an offer or placing an order for metal-enclosed switchgear and controlgear, should not only provide the main electrical characteristics of the system but also the service conditions if different from standard, i.e.

• Minimum and maximum ambient air temperature;
• Unusual exposure to vapour;
• Moisture;
• Smoke/fumes;
• Explosive gases;
• Excessive dust or salt;
• Thermal radiation;
• The risk of earth tremors or other vibrations due to causes external to the equipment to be delivered.

In short, any condition deviating from the normal service conditions or affecting the satisfactory operation of the equipment.