Systems interconnection and voltage stability protection schemes increase power transfer limits and prevent regional blackouts at Panama's transmission system

Panama's transmission system has geographical and infrastructure constraints that make it very susceptible to different contingencies. These contingencies have led to major blackouts that have affected loads in Panama and the Central American transmission system in recent years. ETESA – CND developed a special protection scheme that takes remedial actions to increase reliability and power transfer limits of the Central American regional system to allow for the most economical operation. Excess generation in the Panama system and Central American interconnection overload could be steady state or transient conditions caused by uncontrolled and major loss of load due to fault induced slow voltage recovery (FIDVR), events such as N-2 contingencies, load shedding schemes, by oscillations caused by failures with long clearing times, or various other reasons. This paper presents the principal challenges found during power system studies and the remedial action solutions implemented. Schemes require accurate and simultaneous measurement of the total power flow at the interconnection link composed by three transmission lines during transient conditions. Synchrophasors measurements (PMUs) and PMU high speed phasor concentration technologies (PDCs) are applied for synchronous measurement and used to make generation-shedding decisions. The proposed solution combines different schemes and logics in order to be effective for several different contingencies and operating conditions. Very fast generation-shedding actions are preferred, but pre-armed, contingency-based schemes cannot be applied for uncontrolled loss of load due to FIDVR, because there is no single location to detect contingency. The scheme needs to respond to power flow measurements after the event. Two response-based schemes are described, one uses the total power flow in the three interconnection lines to make tripping decisions during slower evolution events, while the other calculates the rate-of-change of power at the interconnection link to accelerate the protection. Generation-shedding algorithms perform a real-time selection among multiple generation plants to optimize amount to shed and automatically changes selection both after dispatch changes, and after initial operation.