Process Interface Units (PIU) and its advantages for Full Digital Substations

In the context of full digital substations, which includes the capability to exchange voltage and current data in between IEDs in real time over network through Sampled Values protocol, the substations started to be segmented into process and station level, in which interface IEDs, usually responsible to digitize binary and analog data or to Interact directly with primary equipment are now positioned on the yard, cumulating advantages related to cable reduction, civil infrastructure, cost, simpler installation and safer when using fibre optic.A study based on comparison of hypothetical devices with market standard characteristics is presented to analyze quantitative and qualitative advantages for full digital substation architectures based on multiple IEDs against a single PIU as interface for primary equipment. It is also presented how PIUs can be logically modelled using the base concepts of the IEC61850 standard to segregate functions into logical devices and allowing to decouple logical and physical devices, simplifying architectural decisions for both cases.It is concluded that PIU as single interface IED has advantages as smaller footprint and cost and higher system reliability. All mentioned advantages are maximized when the substation architecture considers redundancy of devices, common for critical parts of the electrical system, pointing the use of PIUs as a tendency for modern full digital substations..