Challenges, Operational experience and key learnings of Protection and Control of networks, integrating renewable generation sources with large grid

Voltage) / EHV (Extra High Voltage) networks, dominated by conventional generators has introduced material challenges in grid inertia, reactive power support and short-circuit ratio (SCR) with direct implications for transient and voltage stability. Field performance shows that adapting conventional, economy-grade protection and control schemes for renewable plants— characterized by extensive, repeated sub-systems (Inverters, IDTs - Inverter Duty Transformers,

MV – Medium Voltage – switchgear, cables, and grid-connected switchyards) often fails to capture complex behaviour during grid disturbances, leading to mis-operations, equipment damage and creates safety hazards. The inherently low or absent electrical inertia of solar and wind resources further reduces fault current contribution, challenging traditional overcurrent and earth-fault detection philosophies.

The behaviour and performance of discrete renewable generation sources fundamentally influence the adequacy of protection schemes, control philosophies, and overall system stability, as illustrated above.

Considering project viability, implementation schedules, technological limitations, and skill constraints, conventional cost-optimized protection and control solutions are often engineered and implemented for renewable plants. These solutions typically provide only basic functionality and do not adequately address the complex system behaviour observed under various operating and disturbance scenarios. Major reasons of challenges experienced in renewable plants:

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  Inability for fault feeding from Inverters due to low / no electrical inertia.

Ungrounded system design at Inverter level to the Transformation level limiting fault detection and sensitivity of relaying and protection.

Varying response of Inverters to abnormal grid condition parameters like under voltage, over voltage, unbalance, voltage ride through, oscillations, etc.

Large volume of installations like Inverters, Inverter Duty Transformers, LV (Low Voltage) panels, long distance, and huge cable networks and therefore variations of voltage profile, system impedance, earthing profile etc. creating non uniformity of fault detection at various locations in the same vicinity of one plant.

Actual performance of STATCOMs (Static Synchronous Compensators), VAR Generators,

VAR support system from Inverters for intended purposes of grid stability during Transients in grid are not up to the mark. This paper describes operational experience from multiple utility-scale plants and presents three detailed case studies along with mitigation.

Case studies identify root causes for recurring faults of ungrounded LV / MV configurations systems, impeding single-line-to-ground fault detection; variations in inverter ride-through behaviour; non-uniform impedance / earthing profiles and inadequate auxiliary power designs

(local battery / UPS – Uninterrupted Power Supply) which failed during disturbances and surges.

We present a mitigation framework comprising: (i) voltage-based zero-sequence (open-delta VT

– Voltage Transformer) neutral displacement detection for unearthed LV systems; (ii) sensitive, two-stage high-set overcurrent schemes with reverse blocking for MV buses; (iii) arc-flash optical sensing to capture low-current arcing; (iv) unit protections (line / cable differential) on transmission interfaces; and (v) robust tripping architectures using station batteries or breakerenergy storage, dual trip coils, and disciplined maintenance.

Results from field implementations demonstrates improved selectivity, faster isolation, and reduced collateral damage, while recommendations on earthing practices (single-end armour earthing near source, pit integrity, cable type / arrangement) address overvoltage and oscillation risks. Contributions offer a practical blueprint for protection and control in renewable-rich networks, aligning operational reliability with project viability and supporting secure growth of unconventional generation portfolios.