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. CND (ETESA) 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. The uncontrolled and major loss of load due to fault-induced delayed voltage recovery (FIDVR), double (N-2) contingencies, load-shedding schemes, or various other reasons caused excess generation in the Panama system to flow into the Central American interconnection, driving the system to steady-state or transient overload conditions, which caused cascade events and blackouts before a new scheme was implemented.
This paper presents the challenges found during power system studies and the remedial action solutions implemented to address these challenges. System protection schemes require accurate and time-synchronized measurements of the total power flow at the interconnection link, which consists of three transmission lines during transient conditions. Phasor measurements (PMUs) and high-speed phasor data concentration technologies (PDCs) are applied for synchronous measurement and used to make generation-shedding decisions. The implemented solution combines different schemes and logics 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. Instead, 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 slow 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 the amount to shed and automatically changes selection both after dispatch changes, and after initial operation.