1. total absence of voltage for at least three minutes in the concerned TSO's control area, leading to the triggering of restoration plans.

2. The Burgas Airport ATC Centre (Burgas ATC Centre) is a structural unit of BULATSA providing air traffic services in the Terminal Control Area (TMA) and in the Control Zone (CTR) of Burgas Airport

3. The locking pin (20) also has at least one locking point (27, 28) which is aligned, in the releasing point thereof, with the retaining area (31) of a pin retaining lever (30) which also has a control area (32).

4. each element has an influence factor on electrical values, such as voltages, power flows, rotor angle, in the TSO's control area greater than common contingency influence thresholds, meaning that the outage of this element can significantly influence the results of the TSO's contingency analysis;