PM078: Modification of STCP01-1Appendix D to provide a trigger phrase for controlling the power flow on a HV DC transmission line

The current range of trigger phrases do not allow the specification of load flow on the circuit, given that in HV AC transmission this value is governed by the characteristic of the network generation and demand. With HV DC transmission the flow is determined by the setting of its associated control system, hence needs to be specified by the ‘SO’ to the ‘TO'