Protection Challenges Under Bulk Penetration of Unconventional Sources - Detailed Study, Analysis and Implementation of Upgradation in Protection Philosophy to Suit New Power System Dynamics

Synchronous generation exhibits inherent grid-forming and grid-support features whereas unconventional generation is predominantly a grid-following technology that does not exhibit grid-support features inherently and needs to be articulated to suit power system requirements by means of connectivity standards and grid codes. With bulk penetration of unconventional generation sources, the dynamics and characteristics of modern power systems are transitioning towards systems with reduced on line synchronous inertia, reduced system strength and prolonged oscillations greatly impacting stability, power quality and protection systems.

In this context, paper comprehensively covers study and analysis of differentiating characteristics and behaviour of unconventional generation sources influencing prevailing protection practices/philosophies and their reliability.

The outcome of the analysis revealed a complete nonlinear, controlled and unpredictable response with low fault currents, which is a direct threat to the reliability of impedance-based protection, negative sequence based protection, over-voltage and O/C - E/F protection. Some real-world occurrences and a simulation case study are also discussed to validate the analysis regarding challenges to prevailing protection practices/philosophies. Based on the inferences of the occurrence analysis, this paper proposes a solution to counter the risk by upgrading the protection philosophies/practices from: i) Impedance-based to differential current based, ii)

Permissive under reach trip transfer (PUTT) / Plain permissive over reach trip transfer (POTT) to POTT with weak infeed + echo and current reversal guard, iii) Negative sequence based to zero sequence based direction detection, iv) Plain over-voltage to flexible-adaptive-coordinated over-voltage protection, v) Plain direction earth fault to carrier aided directional earth fault etc.

GETCO, being a pioneer state transmission utility in India to envisage challenges and upgrade the protection philosophy based on a detailed study and analysis, it is also referred to Grid India

(National authority for power system operation and control) to seek expert inputs and facilitate wider adoption. Also, the impact of bulk penetration of unconventional generation sources on power swing, out-of-step protection and auto-reclose are discussed as a way forward alongside the scope of further study and analysis in deriving approaches to alleviate the impact.

Overall, the initiative undertaken by GETCO to counter the reliability risk of prevailing protection practices on the pathway to seamless transition to secure and reliable RE-rich grid could be a useful reference for stakeholders in anticipating challenges to existing protection system and deriving approaches to suit the new power system dynamics.