Background
The power grid is a fragile and complex system and its operation will affect connected equipment. At the same time, the abnormal operation of connected equipment will also affect it causing what’s known as, “grid disturbance”. Grid disturbance is a relatively common type of a grid-side fault . The frequency of its occurrence is second only to the over-voltage/under-voltage of the grid; In this Solis Seminar, we will share the causes and treatment methods of such faults.
Fault Description
If the inverter is affected by the voltage distortion on the grid side during operation, the output current of the inverter will suddenly increase to 1.4 times the peak current. Simultaneously, abnormal current fluctuations will be automatically monitored 5 times within 30 seconds. If it occurs again for the sixth time, the inverter will be disconnected from the grid for the protection of the equipment and show the message “GRID INTF”.
What Can Cause the Error GRID-INTF?
PV System Issues
In the photovoltaic system, the wiring points between equipment, cables, and power grid are most prone to problems. When the “GRID-INTF” message appears, it is recommended to check the following points first:
1) Check whether the AC wiring of the grid side is satisfactory, if it is incorrectly connected, it will cause AC current fluctuations;
2) Check whether the wire diameter of the AC cable meets the standard requirements. If the wire diameter is too small, it will cause the grid voltage to fluctuate.
3) Check whether the material of the on-site AC line is satisfactory. The inverter output can be abnormal due to the use of sub-standard materials.
Grid Surge
Grid surges can be a very difficult issue to diagnose. The simplest way to start your diagnosis is to confirm whether there are large-scale electrical machinery in the owner’s electrical load or surrounding it, such as stamping machines, high-power motors, processing machine tools, etc. The switching of this type of equipment will have impact and interference on the grid, causing excessive harmonics and exceeding the tolerance range of Solis inverters. In order to protect itself, the inverter will disconnect from the grid and display the “GRID INTF” message.
Solutions
PV System Side
1) For poor AC terminal wiring of the inverter, re-tighten the AC line or replace the AC terminal(s);
2) For undersized AC wires, the AC wires need to be replaced with properly sized wires that have higher current carrying capacity.
Grid Surge
If the owner’s electrical load or surrounding areas have high-current equipment running, use an oscilloscope to test the voltage and current waveforms on the AC side of the grid. The waveform should be shared with the customer and Solis engineers. Based on the waveform, Solis engineers can evaluate and solve the problem through special software settings.
Summary
Grid interference is a common problem that can be managed through installation best practices and an understanding of onsite loads. If a solar PV system is installed with correct and compatible wiring and connection solutions this will help to prevent errors on the PV system side. Grid surges are more difficult to plan for but with a detailed survey of the site and knowledge of all equipment at the property and surrounding areas, a PV system can be designed to properly function and withstand grid surges.