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In photovoltaic (PV) solar systems, there can be errors caused by problems on the grid side. Inverters are a critical operating function of a solar PV system and the grid, and are very sensitive to grid issues, and respond quickly. Grid imbalance faults, although rare, can easily affect inverters, PV systems, and sometimes even loads.
Fault Description
At start-up, the Soils inverters detect the status of the grid. If the grid phase is unbalanced, the inverter will disconnect from the grid and display the “G_PHASE” error.
<img decoding="async" loading="lazy" class="aligncenter size-full wp-image-30084" src="https://mercomindia.com/wp-content/uploads/2021/10/Figure-I.png" alt="Figure I" width="810" height="487" srcset="https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-I.png 810w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-I-300x180.png 300w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-I-768x462.png 768w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-I-650x391.png 650w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-I-624x375.png 624w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-I-600x361.png 600w" sizes="(max-width: 810px) 100vw, 810px" />
Causes of “G-PHASE” Errors
 Voltage imbalance on the grid side
‘Grid unbalanced’ is an important issue that causes this alarm for the inverter as they monitor the grid voltage in real-time. When the three-phase waveform of the grid is abnormal, the inverter will immediately provide feedback and disconnect from the grid.
<img decoding="async" loading="lazy" class="aligncenter size-full wp-image-30083" src="https://mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced.png" alt="Figure 1. Waveform diagram when the power grid is unbalanced" width="831" height="273" srcset="https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced.png 831w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced-300x99.png 300w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced-768x252.png 768w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced-650x214.png 650w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced-624x205.png 624w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-1.-Waveform-diagram-when-the-power-grid-is-unbalanced-600x197.png 600w" sizes="(max-width: 831px) 100vw, 831px" />
Figure 1. Waveform diagram when the power grid is unbalanced
Large-scale equipment used has an impact on the grid and causes the grid to be unstable.
For PV systems installed in industrial areas, inverters are more prone to alarms from the grid, such as grid overvoltage, grid unbalanced, and grid imbalance. These are all because the operation of large current equipment affects the operation of the inverter through the grid.
<img decoding="async" loading="lazy" class="aligncenter size-full wp-image-30082" src="https://mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks.jpg" alt="Figure 2. The grid problems caused by various load shocks" width="1269" height="306" srcset="https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks.jpg 1269w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks-300x72.jpg 300w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks-768x185.jpg 768w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks-650x157.jpg 650w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks-624x150.jpg 624w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-2.-The-grid-problems-caused-by-various-load-shocks-600x145.jpg 600w" sizes="(max-width: 1269px) 100vw, 1269px" />
<h6 style="text-align: center;">Figure 2. The grid problems caused by various load shocks</h6>
Solution
An oscilloscope can be used to check whether the three-phase voltage and waveform of the grid are normal. If not, the waveform can be recorded and reported to the Solis technical team for support.
Possible Inverter Related Causes
The AC cable is incorrectly connected
During the installation process, errors can be caused by cables being incorrectly connected, which causes phase to unbalance in the power injection process.
<img decoding="async" loading="lazy" class="aligncenter size-full wp-image-30081" src="https://mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error.png" alt="Figure 3. Wire sequence connection error" width="831" height="295" srcset="https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error.png 831w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error-300x106.png 300w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error-768x273.png 768w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error-650x231.png 650w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error-624x222.png 624w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-3.-Wire-sequence-connection-error-600x213.png 600w" sizes="(max-width: 831px) 100vw, 831px" />
<h6 style="text-align: center;">Figure 3. Wire sequence connection error</h6>
Solution 

Reconnect the AC cable and make sure that the wiring sequence is correct.
The AC wire used in the PV system is unsuitable
If an unsuitable cable is selected during the design process, such as an inferior AC cable made from low-grade material or small diameter, problems could arise. The system will be in contact with the metal of the cable due to the current heating effect during the long-term operation of the system. The film is deformed and blackened, and the impedance is significantly different, which will cause the three-phase voltage to appear unbalanced and cause the inverter to trigger the alarm.
<img decoding="async" loading="lazy" class="aligncenter size-full wp-image-30080" src="https://mercomindia.com/wp-content/uploads/2021/10/Figure-II.jpg" alt="Figure II" width="1269" height="422" srcset="https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-II.jpg 1269w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-II-300x100.jpg 300w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-II-768x255.jpg 768w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-II-650x216.jpg 650w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-II-624x208.jpg 624w, https://cms.mercomindia.com/wp-content/uploads/2021/10/Figure-II-600x200.jpg 600w" sizes="(max-width: 1269px) 100vw, 1269px" />
Solution 

For the correct selection of cables and specifications, refer to the manual provided with the Solis inverter, which contains detailed cable recommendations. 
The AC terminal of the inverter is in poor contact
If there is a problem with the AC terminal of the inverter, such as a loose lead wire, poor lead contact, etc., this alarm will also appear. In such cases, replace the AC terminal of the inverter.
G_PHASE error is an uncommon problem, but it will still cause system shutdown and affect power generation. So, when this fault occurs in a solar PV system, it needs to be rectified immediately to minimize system downtime.
This article is sponsored by solar inverter manufacturer <a href="https://www.ginlong.com/hi" target="_blank" rel="noopener">Ginlong Technologies</a>.
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Image Credit: Solis
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Solutions to ‘G_PHASE’ Error in Solar Inverters

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