The solar inverter is the safety control center of PV system. Thus, during the PV system operation, the inverter condition, including the temperature and operation of interval cavity and main element, the bus voltage and the communication among chips, shall be inspected from time to time. In addition, the insulation among components and DC system, the DC voltage and current, the AC output voltage, current and frequency shall also be inspected. In case of any failure, it shall be solved in time.
People who always maintain the solar power inverter may find that inverter will not stop working immediately after the failure appears. When some failures appear, the PV inverter only gives alarm and shows red light, but it will not stop immediately. When some other failures appear, the solar inverter will stop immediately but the stop time is different. Why?
When people are ill, the illness degree will be different. Some can be cured automatically or be cured by taking medicines, like common cold. Thus, it will not affect people's normal work. However, some illnesses are serious and need to be treated in the hospital. This is also true for the solar PV inverter. The inverter failure also includes general failure and serious failure. The main goal of the whole system is to improve power generation. Thus, when some small failure appears, the system will work normally because the failure can not bring big impact. If the device stops working immediately after a failure appears, the power generation will be affected. Instead, if we choose to stop the device at night and at the cloudy day, it will not bring big impact on the power generation. If the failure will affect personnel safety, device safety, or belongs to the failure regulated by related safety regulation, the solar PV inverter shall be stopped immediately.
When the general failure appears, the device or the monitor will generate alarm by flashing red light or buzzing sound. It reminds user to handle with the failure in time but it can be delayed for a while. But the following situations shall be emphasized:
- Current leakage: The current leakage will be caused by excessively small DC and AC insulation resistance. Most manufacturers will set up two insulation resistance values, such as 100kohm and 50kohm. When it is lower than 100kohm, PV inverter will give alarm but will not stop working. Under this situation, the maintenance staff can close the site and solve the problem at night. If it is slightly lower than 100kohm, it will not cause serious impact. But if it is lower than 50kohm, it violates the safety regulation and the device shall be stopped immediately.
- Fan failure: Currently, large-size Photovoltaic inverter will use three or more fans. The solar inverter usually adopts the intelligent fan cooling system and the fan will be started when certain temperature is reached. In addition, the fan running speed will increase with the increasing of the temperature degree. Thus, if it is found that a fan is not started, it is not necessary to stop the inverter immediately. By slightly decreasing the output power, the inverter can keep working for some time. It will take some time to find the failure and solve the failure. Thus, making the inverter keep running can save some electricity fee.
- External communication failure: The external communication of solar power inverter is very important but it is not necessary at all time. Thus, the external communication failure can be solved a little later.
- Series group failure. If a series group has broken circuit or short circuit, this serious group can be removed directly, which will not affect the power generation function of other groups.
The commonness of the general failure: The general failure will not cause serious impact on personnel safety and solar PV inverter safety. The situation will not become worse immediately and can be solved a little later. But it does not mean that the general failure does not need to be solved. As long as the inverter gives alarm, users shall handle with it as soon as possible and the inverter shall be restarted after the failure is solved.
When the serious failure is detected by the solar inverter, it will start protection system and stop working immediately to prevent situation becoming worse. Specific situations are as following:
- Serious device fault: It includes excessively high temperature, over-current protection, bus voltage abnormality, delay abnormality, drive abnormality, auxiliary power source abnormality, etc. When the Photovoltaic inverter encounters hardware or software failure, it can not keep working and will stop. Solar inverter is the safety manager of the PV system. To ensure that investors can manage the power station easily, manufacturers that work with inverter.com designs many monitor tools so that investors can check the power station operation situation from the mobile App or from the computer. In case of any failure, the reminding message will be sent to the power station management staff by SMS or e-mail. In addition, the investor shall also form the habit of checking the operation data of the power station frequently so that they can discover and solve problems in time.
- Safety aspect: If the defaults like high DC voltage, low DC insulation impedance and AFCI DC arc are not handled immediately, they may cause personnel electric shock or fire accident, or they will affect the normal operation of other power grid equipment.
- Safety regulation: The faults regulated by safety regulation include the abnormal grid voltage, no mains power, abnormal grid frequency, high DC component, etc. There are many safety regulations about the solar PV inverter, most of which are the design requirements of the inverter. If any situations that violate safety regulation appear in system operation, the inverter shall be stopped immediately.The situations that violate safety regulation are mainly about the grid voltage and frequency.
Based on the national standard, the protection range of the under-voltage and over-voltage at the AC output side is the 85%-110% of the rated voltage. The solar panel inverter operation shall be stopped when it exceeds this range. The rated voltage of the single-phase grid is 230V. When the grid voltage is lower than 195.5V or is higher than 253V, principally the Photovoltaic inverter shall be stopped. The rated voltage of the three-phase grid is 400V. when the grid voltage is lower than 340V or is higher than 440V, principally, the inverter shall be stopped. If the frequency is among 49.5Hz to 50.2Hz, the PV inverter can work continuously. But if the frequency is among 48Hz and 50.2Hz, the solar inverter shall be stopped within 10 minutes. If the frequency is lower than 48Hz, the inverter shall be stopped within 0.2 seconds.