The main task of the IEDs, which have been developed for reliable Local System Integrity Protection Schemes (SIPS) are: prevention of power system oscillations, elimination of operating conditions, which may damage or even destroy different primary equipment and secure this way the acceptable operating conditions during emergency situations. They should also secure reliable automatic restoration of power systems under changed operating conditions.
Local SIPS systems are designed on the basis of TOR 300 SIP devices installed within a number of separate cubicles, communication with each other and (mostly over PLC communications) with similar equipment in remote substations. This secures collection of information from wider area and more reliable decisions within one substation or power plant.
· elimination of out-of-step conditions based on either impedance and/or well proven oscillating current detection;
· automatic prevention of frequency decrease in power system by:
o automatic underfrequency load reduction with automatic reclosing after frequency regeneration,
o automatic connection of back-up power supply,
o additional load shedding at significantly reduced frequency,
o low frequency initiated split of power system;
· automatic prevention of frequency increase based on its value as well as on ROCOF;
· three time delayed steps of under and/or overvoltage protection;
· load shedding dependent on increase of measured current;
· local automatic preventing initiation of system oscillations:
o automatic detection of disconnected: power line, transformer, generator, etc.,
o automatic complexity analysis of detected short circuit,
o automatic load reduction under overloading conditions.