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.