Safety Isolation in Photovoltaic Inverters
Ensuring Ground Safety in Transformerless Solar Systems.
The Rise of Transformerless Inverters
The design of transformerless inverters has become the industry standard due to its significant advantages in improving overall energy conversion efficiency and reducing weight and manufacturing costs. By eliminating the heavy isolation transformer, modern inverters are lighter and more efficient.
The Safety Challenge: Ground Isolation
However, the removal of the transformer eliminates the inherent galvanic isolation between the PV panels and the grid. This creates potential safety hazards that must be addressed by adding active safety mechanisms, specifically Isolation Resistance Testing.
Before the inverter connects to the grid and starts generation, it must perform a rigorous Ground Insulation Test to ensure there are no leakage paths that could endanger personnel or equipment.
The Role of the Isolation Relay
To perform this test accurately, the measurement circuit must be temporarily connected to the high-voltage DC bus. This requires a relay that can withstand high voltage but also provide absolute isolation when the test is complete.
MiRelay Solution: High Voltage & High Insulation
MiRelay’s fully sealed dry reed relays are optimized for this exact function. They ensure the safety performance of the inverter’s grounding system through superior isolation specifications.
Key Performance Metrics
- 4000V DC Withstand: The relay provides an insulation withstand voltage of up to 4000VDC between open contacts and between the contacts and coil, ensuring safety even during voltage spikes.
- 10TΩ Insulation Resistance: With an insulation resistance value of 10 Tera-Ohms ($10^{13} \Omega$), the relay prevents any leakage current from affecting the inverter’s operation during normal generation.
- 100GΩ Disconnect Resistance: The high disconnect resistance ensures the MOSFET sensing array is completely isolated from the ground before the inverter is enabled, preventing false readings or component damage.
Recommended Product: HVR Series
HVR High Insulation Series
The HVR series combines high voltage stand-off with ultra-high insulation resistance.
- Isolation: 4kV – 10kV
- Insulation: > 10TΩ
- Leakage: Pico-Amp range
- Life: Billions of operations