Modern electrical power grids are expected to be resilient, secure, efficient, and flexible. In terms of power grid modernisation, the IEC 61850 based communication and automation has been developed over the years to satisfy the requirements. Furthermore, the digital substation concept has emerged as one revolutionary idea that might change the future of substation automation. In PLN Indonesia, several hybrid-digital bays combining the IEC 61850 based process bus, merging unit, and conventional instrument transformer has been constructed recently. This idea promises excessive wire reduction using the digital substation concept for substation operation, control, and automation while still incorporating conventional instrument transformers, breakers, and disconnecting switches. This paper presents a comparative study of the hybrid digital bay implementation at PLN substations in Central Java from three different manufacturers. Technical and economic comparisons are delivered to exhibit benefits and drawbacks over the three designs. The future topology of the digital bay is also discussed to improve the technical design of the digital bay in Indonesia. The result shows that digital bay has brought investment cost reduction while also needs a specification standardisation to be optimally utilised.
