Static Synchronous Series Compensator (SSSC) and its Challenge for

In the case of the Santa Marta project, under steady-state conditions, SSSC devices perform as inductive series compensation, redistributing the overload of the circuit itself through the area's circuits. In the event of a fault in the compensated circuit or a neighbouring one, the SSSC is bypassed, returning the total line impedance to its original value. During protection studies and

Real Time Digital Simulation (RTDS) with hardware-in-the-loop tests of these devices, several challenges were identified with the current protection schemes of the compensated circuits in which some incorrect trips for external faults were issued. Initially, a detailed modelling of the influence area of the project associated with the Santa Marta-Termocol and Santa MartaTermoguajira’s SSSCs were carried out in the PSCAD program, considering the impedance characteristics of the protection relays installed on these lines and some adjacent lines of interest, as well as considering the respective protection settings. Through this sensitivity analysis, it was possible to identify that under certain asymmetric operating conditions such as an external fault, the Phase-Locked Loop (PLL) of the SSSC’s control and protection system

(C&P) on the healthy line compensated was able to be disconnected and produce undesired effects on the commutation of the IGBTs, executing an uncontrolled switching on/off continuously, which produced a non-sinusoidal and deformed series voltage injection with high harmonic content. As a result, the directionality of the respective protection relays was affected, altering their normal expected performance, ending in an unwanted operation of the directional comparison scheme of the non-faulted circuit and distance protection, overreaching the zone 1.

The above situation was later corroborated in the RTDS laboratory with the actual C&P of the

SSSC devices of this project. Mitigation measures such as an external command from the compensated line’s protective relays to make a quick three-phase bypass of SSSC compensations, eliminate the transient effect of asymmetric operation on SSSC devices, avoiding the undesired trip of the line.

Notwithstanding the relief actions applied, the manufacturer was advised that it was needed to take definite actions on the C&P of the SSSC devices to address the root cause, that is, to eliminate the possibility of uncontrolled voltage injection from these devices. All this detailed analysis of the technical issues mentioned above, the approaches to eradicate the unwanted trips of the healthy compensated line’s protection systems, their RTDS tests and analysis of the results, and final recommendations for this technology and the protective relays of these types of compensated lines will be presented in this work.