The static synchronous series compensator (SSSC) is a device for controlling the power flow and compensating losses in the transmission lines. A transformerless SSSC (TLSSSC) with control system was developed for a high-voltage transmission line. It is based on modular multilevel converter topology. The compensator has been successfully designed and validated using a mathematical model in MATLAB/Simulink. The next stage of the study is experimental validation of the proposed solutions for prototype of the TLSSSC. However, the compensator operates at 10 MW and the manufacturing facilities do not have the necessary power sources to conduct these tests. Therefore, this paper presents the design of the test bench and control system required for the functional verification of the TLSSSC parameters after manufacturing.<br/>