Experiences and recommendations for parallel operation of SSSC devices, Candelaria – Ternera 220 kV circuits case

Static Synchronous Series Compensator (SSSC) to mitigate overloading and to improve operation system flexibility. According to its manufacturer, this technology offers several advantages such as the control of power flows with various control modes such as current, injected voltage and decrease and increase of impedance. The SSSC acts as virtual impedance changing the overall line impedance and therefore the power active transfer across the line. This technology reduces the need for new lines or the expansion of transmission capacity.

Enlaza GEB is the owner and operator of a 220 kV substation in the north coast of Colombia called Candelaria, this substation is important because it allows the interconnection of the load of the Caribbean zone in the country and a thermal generation of more than 500 MW towards the national transmission system. ENLAZA GEB has installed SSSC devices in both parallel circuits Ternera – Candelaria 1 & 2 220 kV at Candelaria side to reduce the network congestion and maximize Candelaria power plant active power dispatch and to avoid the construction of a new line between both substations, that new lines was impossible to construct because both substations are located in urban zone. The SSSC at Candelaria substation operates in fixed inductive reactive impedance mode to limit the current in the Candelaria – Ternera circuits. This operation mode gives rise to deviant conditions in SSSC control and in power electronics. Therefore, we have faced many challenges in parallel operation by the interaction between SSSC devices in both normal and abnormal conditions of the power system. Since 2021 until the date, we have found situations that had not been seen at planning studies, factory and site acceptance tests, as not injection after many attempts, unbalance operations in three phase systems, misoperation of protection systems, overcurrents for not paralleling operations, among others.

This paper addresses the issues with SSSC behavior, performance evaluation of control and protection schemes response based on simulations, data gathered from relays, fault recordings and internal records. We carried out several analysis under normal and contingencies scenarios to evaluate the impact of SSSC devices in the area as near lines, in protection schemes, changes in current and voltages component sequences, these simulations were carried out with power flow and dynamic (rms) analysis in balancing and unbalancing conditions, concluding that these devices do not impact in near protection schemes and the SSSC be beneficial in system operation.

Also, we show the strategies and solutions developed in conjunction with the manufacturer to overcome the operational challenges as modification of protection schemes for the purpose of avoiding undesirable tripping operations, different starting sequences algorithms to improve, changing control setting parameters, among others.

We conclude with recommendations for further implementations like FAT and SAT specs, technical specs, considerations of protection schemes, control setting guidelines, simulation scenarios, recommendation for system operators and planning departments to consider in the parallel operation of these devices.