This document specifies requirements for devices for the suppression of DC magnetic bias of power transformers and convertor transformers. It includes requirements for service conditions@ structures@ testing@ packing@ transport and storage. The devices are connected to neutral points of power transformers and converter transformers to suppress DC bias current in the case an HVDC system is operated in monopole ground return mode or bipolar unbalanced mode. In the case of dedicated metallic return HVDC system@ the devices are useful to mitigate DC stray current flowing through power transformers and converter transformers during transient conditions such as DC line fault. This document applies to DC magnetic bias suppression devices for operation at frequencies of 50 Hz and 60 Hz on power systems having voltages above 110 kV.