Intelligent Grounding Transformers for Island Grid Support

1. Project Background

Distributed photovoltaic (PV) and energy storage projects are developing rapidly across Vietnam and Southeast Asia, yet face significant challenges:

1.1 Grid Instability:

Vietnam's power grid experiences frequent fluctuations (particularly in northern industrial zones). In 2023, coal power shortages triggered large-scale blackouts, resulting in daily losses exceeding USD 5 million. Traditional PV systems lack effective neutral grounding management capabilities, making equipment vulnerable to damage and safety incidents during grid failures. This highlights the critical need for reliable grounding transformers.

1.2 Policy and Safety Compliance Pressure:

Vietnam's 2024 regulations require energy storage systems to pass Vietnam Electricity Group's (EVN) 72-hour islanding operation test and possess high/low voltage ride-through (HVRT/LVRT) capabilities. With extensive power electronics deployment, zero-sequence current and harmonic issues are prominent, often triggering protection malfunctions. High-performance grounding transformers are essential for meeting these compliance requirements.

1.3 Environmental Adaptability Requirements:

High temperature and humidity climates (annual average humidity >80%) accelerate equipment aging, demanding grounding transformers with robust anti-corrosion and moisture-proof performance. Coastal salt spray environments (air salt content >5mg/m³) further exacerbate corrosion risks, placing higher demands on the environmental adaptability of grounding transformers.

2. Solution: Intelligent Grounding Transformer System

2.1 Core Technology Design

Zigzag Connection Grounding Transformer:

Features a specialized six-winding design with rated capacity of 1250kVA, ultra-low zero-sequence impedance of 4-6Ω (versus 30Ω in conventional transformers), and short-circuit withstand capability of 25kA/2s, perfectly suited for large-scale distributed power plants.

• Harmonic Suppression Optimization: Integrated Δ-YY winding structure with LC filters achieves ≥85% suppression of 3rd/5th/7th harmonics, reducing total harmonic distortion (THD) from 12% to <5%, effectively preventing equipment damage caused by resonance. This harmonic mitigation capability represents a core safety feature of the grounding transformer.
• Environmental Adaptability Enhancement: Enclosure with IP54 protection rating; critical components treated with nano-ceramic coating, passing IEC 60068-2-52 salt spray testing (3000 hours with no corrosion). These protective measures ensure long-term reliability of grounding transformers in harsh environments.
• Thermal Management Design: Equipped with aluminum alloy heat sinks and forced air cooling system, temperature rise is controlled to ≤55K at 45°C ambient temperature. This efficient thermal management system is crucial for the safe operation of grounding transformers in tropical climates.

2.2 Intelligent Monitoring and Protection System

Integrated Sensor Module: Real-time monitoring of winding temperature, partial discharge, and insulation status; data synchronized to local SCADA and cloud platforms (such as Hoymiles S-miles Cloud) within milliseconds. Continuous monitoring significantly enhances the safety profile of the grounding transformer.

Protection Logic Coordination:

• Circuit Breaker Coordination: Automatically switches grounding mode within 10 seconds upon detecting grid voltage drop to 20%UN (meeting Vietnam's low-voltage lockout requirements)
• Arc Fault Detection (AFCI) System Integration: Cuts off fault circuits within 0.5 seconds, preventing ground faults from causing fires. This rapid protection logic integrates seamlessly with the grounding transformer.

2.3 Localized Adaptability Improvements

Grid Compliance: Supports EVN-required islanding test mode, simulating seamless transition to energy storage supply after grid interruption. The grounding transformer is a core component for passing this critical test.

Pre-installed sealing wire interfaces meet Vietnam's mandatory metering room sealing requirements.

Maintenance Convenience: Design service life ≥25 years; maintenance cycles extended to 3 years, significantly reducing O&M costs in tropical regions. The durability of the grounding transformer substantially lowers lifecycle costs.

3. Achieved Results

3.1 Enhanced Safety and Reliability

Achieves neutral grounding switching within 15ms during grid faults (surpassing Vietnam's 50ms standard), ensuring continuous operation of critical loads (such as factory production lines). The rapid fault management provided by the grounding transformer reduced equipment failure rates by 85% and completely eliminated grounding-related incidents after deployment in a 2024 Hanoi industrial zone project.

3.2 Economic Benefits and Compliance

• Reduced Penalty Risk: Meets carbon emission requirements of the "Green Industry Act," avoiding 3% annual revenue fines.
• Shortened Payback Period: Through reduced maintenance costs (35% reduction) and decreased downtime losses, IRR increased by 2-3 percentage points, shortening the payback period from 5.8 to 4.2 years.

3.3 Enhanced Grid Support Capability

Passed dynamic regulation testing: Under EVN's flexible dispatch (when grid load <75%), supports power regulation of up to 30% of installed capacity, enabling power plants to participate in the Frequency Regulation Market (FRM). The stable neutral point provided by the grounding transformer forms the foundation for this grid support functionality. In a Ho Chi Minh City pilot project, by providing reactive power support, the power plant earned an additional 12% revenue from ancillary services.