The next generation of smart electricity substations and grids are on the horizon. Part of the drive behind this movement is a need to improve safety and security. In parallel, software-defined networking has been proposed as a disruptive approach when deployed in these environments, presenting the opportunity to deploy novel functionality alongside existing forwarding behaviour. The benefits of software-defined networking are clear. Yet, if this technology is deployed without due care and attention, then it has the potential to reduce the safety and security of energy systems. In this paper we identify the aspects that must be considered to maintain the stringent requirements imposed by substation networks. With these as a basis, we provide recommendations for the successful deployment of software-defined networking technologies in these environments. We then demonstrate how additional functionality can be brought to the network without violating these requirements.