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Recent increases in the installation of renewable generation in the north of Scotland have triggered the requirement for major transmission system reinforcements. However due to the relatively long lead times for major transmission system reinforcements, it was identified that the installation of phase shifting transformers (PST) on the interconnected 132 kV network would maximise the utilisation of the existing transmission system and reduce the potential for generation constraints in the north due to a lack of transmission capacity at certain times of the year. This paper describes SSE's experience on commissioning the digital differential protection relays associated with these PSTs. To the author's knowledge, there is no such information available so far in the UK and it is hoped this paper will therefore serve as a good reference to the industry as well as for research purposes.