PAC System Components
Protection relays are not the only component of a fault clearing system. Even that they are responsible for detecting a fault condition, determining its cause and taking specific action to clear it or reduce its impact on the electric power system and its components, they are not the only element that requires maintenance testing in order to ensure the security of the system under different conditions.
If we analyze the components of a typical fault clearing system (see Figure 1), we can see that potential failure of each individual element may lead to failure to operate when necessary, or undesired operation under normal or borderline conditions.
Some of the components of the fault clearing system are used to create an image of the primary system parameters that are used by the relays to detect an abnormal condition. They include the instrument transformers and the wiring between them and the analog inputs of the relays.