Solar PV Ground Fault Detector
PV insulation resistance Riso faults - find them quickly
Preventive and Predictive Maintenance of PV
Solar ground faults result in PV array shutdown and energy losses. Safety hazards to service technicians is also important to consider. Using the Z200 PV Analyzer solar ground faults can very quickly and safely be located and repaired.
The Z200 PV Analyzer is a new type of solar PV testing instrument capable of measuring the position of solar PV installation electrical faults. In particular the Z200 PV Analyzer is probably the fastest solution on the market for PV ground fault troubleshooting.
Solar ground fault troubleshooting
PV system ground faults occur if the insulation resistance RISO drops below a certain value of typically 2 MΩ. When this happens most string and central inverters immediately shut down operation, and the risk is thus massive energy losses, if an Earth Fault (or a PV ground fault) is not found and corrected. Also safety to persons and animals becomes an issue when a PV system is not isolated properly. Among many features, the Z200 PV Analyzer offers fast an automated PV Ground Fault analysis that leads to the exact localization of faults. In the illustration below we see the PV ground fault setup i.e. the instrument is connected at the system terminals, and from here the analysis is done automatically once the user has logged on to the instrument using an internet browser on a device that is set up for WiFi communication
Periodic solar panel Riso faults
In some cases solar panel earth faults are periodic, which means they are only present at certain times. Typically moisture in the morning will provoke solar system ground faults, and strings are down until the fault dries up in the sun. This makes PV ground fault troubleshooting difficult.
The Z200 PV Analyzer has a build in ground fault detector that can measure the position of a ground fault in a solar PV system. The ground fault detector furthermore has a timer function, which means that the analyzer may be used for monitoring also.
The user can simply set a time interval suitable for “catching” the ground fault, and hence let the instrument measure for an extended time period e.g. 24 hours. When the user returns to the instrument e.g. after 24 hours of monitoring, the results may be downloaded and the position of the fault can be read.
Solar PV systems are not maintenance free
The world-wide market for MW-scale O&M is expected to triple over th enext years. This development is driven mainly by the big markets in China, the U.S. and Japan.
Solar PV O&M means a lot of things, but basically it evolves around the following major tasks and activities
- Achive maximum system performance
- Monitor PV system performance
- Perform preventive maintenance
- Manage PV system alerts
- Audit energy production
The tasks all depend on each other, and if one task is avoided, problems tend to build up. Let us consider ground faults as an example. Firstly ground faults, or earth faults in the PV array, is what apparently takes up many field technicians time.
WHAT IS A SOLAR PV STRING GROUND FAULT?
According to the Photovoltaic Systems textbook (published by NJATC), a solar PV ground fault is “the condition of current flowing through the grounding conductor.” The cause of this very undesirable current flow is an unintentional electrical connection between a current-carrying conductor in the PV array, and the equipment grounding conductor. In other words, electric current that was supposed to flow to the inverter, or combiner box, flows directly to the ground terminal. Above a certain current threshold, the inverter shuts down entirely for obvious safety reasons.
Reduce the ground fault troubleshooting costs now!
Many ground fault tools are available on the market today. The most common feature is that the tools may help to detect, whether or not a ground fault exist in the PV system. From a maintenance-cost point of view, this is not enough. Ideally a tool should not just detect faults. It should also make it 100% clear where the fault is.
The safety requirements and details can be studied in the IEC 62446-1:2016, Photovoltaic (PV) systems – Requirements for testing, documentation and maintenance.
For the PV array owner, a ground fault has a clear consequence! The fault makes the solar inverter, or combiner box shut down completely. Production is only reestablished, if the isolation resistance (Riso) becomes sufficiently high again. Typically Riso must be minimum 2 MΩ, but a healthy PV system has an Riso value of more than 40 MΩ.
For a residential PV array, a ground fault typically takes down 2 or 3 strings. The system owner has to pay a local service provider, for hours of troubleshooting, transportation, and scaffolds. Meanwhile the faulty component is typically a cheap connector or a cable. In some cases ground faults are caused by modules with water intrusion, or by other more rare and exotic faults.
The cost associated to residential ground fault fixing is often higher than the system owner appreciates. This is especially the case, when the return on investment is considered. This is one of the reasons why some residential PV arrays are not properly maintained, and why systems can undergo irreversible damage.
For utility PV power plants, the ground fault problem is basically the same, but the scale is extended. More technicians has to be involved, transport costs become essential, and entire PV arrays will be down until the faults are found. For utility scale PV systems, a ground fault often means that 200-400 modules are not producing while the ground fault persist.
Another “time-killer” is observed when field technicians are looking for certain inverters, combiners, strings or modules. While monitoring software can often pinpoint strings or PV arrays on a circuit diagram, this is of limited help, when no one made efforts to label and map the rows of modules. And even when components are labeled, it still takes time to find the strings, because systems are huge these days – and they are only getting bigger.
A photovoltaic array is an investment that is not subject to wear. This hypothesis might have persisted for years, however this does not make it tenable: even carefully planned and executed arrays need monitoring, an occasional inspection and, at times, repairs.
Jochen Siemer, PHOTON International 2016
The above statement from Jochen Heimer seems to be confirmed by almost anyone in the modern solar industry, who has a field-oriented responsibility. A while ago, when solar energy was still a new star in the sky, it was common to hear sales pitches describing solar energy, and how “maintenance free” it was. Nowadays, the solar industry is however more mature and also consolidated in many areas.