This guideline investigates the new IEEE 1547-2018 standard and other industry requirements for Time Domain System Impact Studies (TD SIS). It also identifies the benefits of these studies to ensure system reliability and to reduce interconnection costs.

BACKGROUND

The rapid increase and high penetration of Distributed Energy Resource (DER) interconnections fundamentally changed traditional distribution systems. New challenges and adverse impacts of these interconnections have resulted in extensive changes and the development of the recent IEEE 1547-2018 standard. Many new requirements are just now being implemented in the industry with much uncertainty due to lack of testing and certification listings.

Traditionally, distribution impact studies were performed using steady state software for conducting short circuit and load flow analyses, which were used to determine total project interconnection upgrade costs. However, due to new standards and an increasing penetration of DER, TD SIS are becoming a requirement to analyze impacts on transient overvoltage (TrOV), temporary overvoltage (TOV), islanding, transient stability, and other time domain concerns. While steady state analysis can predict some time domain impacts through simplified screens, it cannot accurately simulate the true effect as it is based on RMS fundamental frequency sources on an impedance model. Time domain software, such as PSCAD, utilize electromagnetic properties in the system model, and consider control algorithms of equipment in sub-cycle time intervals. This provides a more accurate and in-depth representation of system influences from the DER project.

Unlike urban distribution systems in the US, rural distribution systems are occasionally fed from subtransmission sources, have very long, lightly loaded distribution feeders, have vast land availability for more DER interconnections, and weak infrastructure to accommodate large generation injections. While the existing distribution infrastructure was adequate to serve customer load, these factors contribute to the likelihood of feeder and substation adverse impacts when interconnecting large amounts of DER. Adverse impacts such as thermal overloads, voltage rise, voltage flicker, islanding, TrOV, and TOV are more prevalent in the Area Electric Power System (EPS) in rural distribution systems. Furthermore, this typically adds more complexity to the scope of TD SIS.