Switching in Electrical Transmission and Distribution Systems

12 Reliability Studies of Switchgear

12.1 CIGRE Studies on Reliability of Switchgear

12.1.1 Reliability

Reliability of equipment is usually approached by its opposite: the probability of the occurrence of failures. The failures and failure rate can be investigated with a focus on the consequences for the power system or with a focus on the performance of the equipment itself. Looking at the power system, the network topology and the service condition play a dominant role in assessing the consequences of malfunctioning equipment. However, looking at the switchgear itself, the system approach gives more or less underweighted information. Therefore, in this chapter, the focus will be on the switchgear, especially on the circuit-breaker.

Following the definitions in the IEC standards [1], failures and defects in a circuit-breaker will be distinguished into:

• major failures (MF) – failures that cause the cessation of one or more fundamental functions of a breaker;
• minor failures (mf) – other failures; and
• defects – imperfections or inherent weakness of the state of an item, which may result in one or more failures of the device itself or of another component under the specific service, environmental, or maintenance conditions in a stated period of time.

An MF will result in an immediate change of the power-system operating conditions, requiring the back-up protective equipment to remove the fault, or it will result in mandatory removal from service within 30 minutes for non-scheduled ...