IEC 61954:2011 defines type, production and optional tests on thyristor valves used in thyristor controlled reactors (TCR), thyristor switched reactors (TSR) and thyristor switched capacitors (TSC) forming part of static VAR compensators (SVC) for power system applications. The requirements of the standard apply both to single valve units (one phase) and to multiple valve units (several phases). This edition includes the following significant technical changes with respect to the previous edition: a) Definitions of terms ' thyristor level' , ' valve section' , ' valve base electronics' and ' redundant thyristor levels' have been changed for clarification b) Conditions of testing thyristor valve sections instead of a complete thyristor valve have been defined c) The requirement has been added that if, following a type test, one thyristor level has become short-circuited, then the failed level shall be restored and this type test repeated d) The time period of increasing the initial test voltage from 50 % to 100 % during type a.c. dielectric tests on TSC, TCR or TSR valves has been set equal to approximately 10 s e) The duration of test voltage U< sub> ts2< / sub> during type a.c.-d.c. dielectric tests between TSC valve terminals and earth as well as the duration of test voltage U< sub> tvv2< / sub> during dielectric tests between TSC valves (for MVU only) has been changed from 30 min to 3 h f) The reference on the number of pulses per minute of the periodic partial discharge recorded during a.c.-d.c. dielectric tests on TSC valves and exceeding the permissible level has been deleted.