In this study, the development of a wide-area, multi-objective cost function is explained. The cost function is designed for implementation on wide-area phasor measurement unit data. In this study, the cost function was applied to the IEEE 30 and 57 Bus models for monitoring and control purposes. Although the cost function was originally intended as a situational awareness tool that indicated system health; it has now been applied as a control metric for the operation of on-load tap changing transformers on a variety of standard IEEE test systems. The system benefits, relative to conventional local control, are quantified. The primary metrics for testing protection outcomes are maximum voltage deviation and line thermal overload. The wide-area optimisation is assessed from a voltage profile, reactive power demand, and transmission losses. The benefits of this type of wide-area control are demonstrated in a variety of situations and environments.