IEC 60143-4:2023 specifies the testing of thyristor controlled series capacitor (TCSC) installations used in series with transmission lines. This document also addresses issues that consider ratings for TCSC thyristor valve assemblies, capacitors, and reactors as well as TCSC control characteristics, protective features, cooling system and system operation.IEC 60143-4:2023 cancels and replaces the first edition published in 2010. This edition constitutes a technical revision.This edition includes the following significant technical changes with respect to the previous edition:a) thyristor valve testing requirements refer to IEC 62823;b) Formula (1) in Subclause 4.2 has been corrected;c) Hardware-in-the-loop (HIL) tests, Subclause 7.5.4, replaces previously specified real time protection and control system test with network simulator.