HV switchgear (part 2)

Before tackling the problem of disconnection, this booklet recalls the fundamental problems that a designer of high-voltage HV switchgear must master and solve. These are of four types:

• to guarantee the insulation level required for the device;

• overtemperature, to ensure that the permissible temperature and component overtemperature limits are not exceeded when the device carries its rated current in continuous operation;

• contacts, to define contacts and methods of assembly such that the device is able to ensure the passage of the permanent current without excessive overheating, to withstand its short-time withstand current and to have the required closing capacity;

• leaktightness: for SF ₆ devices, the aim is to minimize leakage to the atmosphere in order to limit the impact on the environment and reduce the number of gas supplements to be supplied during the lifetime of a device; for vacuum circuit breakers, it is of course necessary to maintain a sufficient vacuum level to guarantee the assigned dielectric strength and breaking capacity performances.

Assigned device characteristics were given in the first part of this article.

The article "High-voltage alternating-current switchgear" is the subject of several fascicles:

D 4 690 Part 1: General. Classifications. Characterization

D 4 692 Part 2: Basic problems. Switching currents on and off

D 4 694 Part 3: Presentation of equipment. Type and individual tests

D 4 696 Appendices

The subjects are not independent of each other. Readers will often need to refer to other issues.

Article D 4 700 deals with the interruption of DC circuits.