During a system commissioning, a solar technician observes that a newly installed string inverter is frequently cycling on and off, displaying a 'High Grid Voltage' error. The utility grid voltage appears stable and within normal limits at the service entrance. What is the MOST likely cause of this inverter behavior?
- AInsufficient DC voltage from the PV array.
- BA faulty internal temperature sensor within the inverter.
- CExcessive impedance on the AC circuit between the inverter and the point of interconnection.
- DOversized PV array for the inverter's capacity.
Show answer & explanationAnswer & explanation
Correct answer: C. Excessive impedance on the AC circuit between the inverter and the point of interconnection.
Excessive impedance (resistance) on the AC circuit between the inverter and the point of interconnection (e.g., main service panel) can cause a voltage rise. When the inverter attempts to push power onto the grid, this impedance causes the voltage at the inverter's output terminals to rise above the utility's acceptable limits, tripping the 'High Grid Voltage' error, even if the utility grid itself is stable.
Why the other options are wrong
- A. Insufficient DC voltage leads to 'Low DC Voltage' or 'MPPT out of range' errors, not 'High Grid Voltage'.
- B. A faulty temperature sensor would typically lead to over-temperature errors or unexpected shutdowns, not 'High Grid Voltage'.
- D. An oversized array might clip power but wouldn't directly cause a 'High Grid Voltage' error unless it's overloading the inverter causing other issues; the primary cause is typically AC impedance.
Inverter Voltage Rise
The phenomenon where the voltage at the inverter's output terminals increases above the utility's nominal voltage, typically due to impedance in the AC interconnection circuit when power is being exported.
- Caused by resistance in AC wiring, breakers, or utility infrastructure.
- Leads to 'High Grid Voltage' errors and inverter shutdowns.
- Mitigated by proper conductor sizing and minimizing circuit length.
Memory trick: High Grid Voltage? The 'AC Resistance Roadblock' is the culprit!