Overvoltage: main problems in photovoltaic installations?

Photovoltaic inverters increasingly have embedded technologies and facilities for monitoring and detecting problems, with different types of alerts for each possible anomaly identified. As a result, their indications facilitate analysis by the technicians responsible for correcting the problem.

However, a greater amount of information about the system may not be an advantage if the person responsible for the analysis does not know the concepts behind each of the errors. In the equipment manuals, for example, there are lists with several error codes, as exemplified below.

In this article, we will discuss the three most common errors that reach technical , all of which indicate abnormalities in the installation and require analysis and correction in the field. Most of the errors mentioned and presented in the inverter alerts relate to a problem in the installation and not in the inverter, which only identified it.

ing that the codes vary for each manufacturer, however the concept behind the cause of the error is the same for the vast majority of alerts generated.

Table 1 – List of errors in an inverter installation and operation manual. Source: Sungrow

Among the most common errors in photovoltaic systems that reach technical are AC overvoltage, islanding and low insulation resistance, each of which will be addressed exclusively in a series of three articles, starting with this one, where we will deal with the error. overvoltage, which is without a doubt the most common demand.

The overvoltage error, when the occurrence is on the utility side (alternating voltage), represents that the inverter is measuring, at its input, a voltage value per phase greater than that configured for protection in the inverter.

All equipment of this type has a nominal operating voltage and a limit range of variation, defined by standards and resolutions of the ANEEL (National Electric Energy Agency), which regulates the sector in Brazil, as well as ABNT (Brazilian Association of Technical Standards).

According to these, every photovoltaic inverter must necessarily go into protection and shut down if the values ​​in the table below are reached:

In other words, in an electrical network with a nominal voltage of 220 V, the inverter will act to protect against overvoltage when reaching 242 V and undervoltage at 176 V. This should be uncommon, but it occurs extremely frequently in several installations in Brazil.

And what is the reason for this? There are a few reasons that can cause an overvoltage error. A less common one, and one that is simple to resolve, is when the setup was configured incorrectly. For example, let's say that the network where the system was installed is a single-phase rural 254V network, which is common in Brazil.

If the previously informed option is selected (Vnom = 220 V), the system will obviously not operate, as the nominal voltage (254 V) is already higher than the configured protection value, making it necessary to correctly adjust the protection values.

However, the most common cases do not concern this, but rather the actual increase in AC voltage that reaches the inverter, which is caused by one of the following two options: poor utility power supply or internal problems in the AC installation of the photovoltaic system.

However, before going into the details of each one, let's understand how overvoltage occurs. The voltage variation is related to the current that will be transported between the points of the installation or, in general, between the generator and the load. We can illustrate it as follows:

The point where the generator is located, in our case, represents the photovoltaic inverter. The load can be the customer's own internal consumption or, in cases where there is a surplus of generation, the additional energy is transported to the utility company, serving neighboring consumers. In both cases, when transporting energy between two points, there is a voltage variation due to the impedance or resistance existing in the section, which is obtained by Ohm's 1st Law:

ΔV=Vgenerator-Vload=Zeq*I

Where Zeq is the equivalent impedance of the circuit and I is the current flowing through it. In other words, the greater the current flowing through it, and the greater the impedance (resistance) of the circuit, the greater the voltage variation. This is why overvoltage problems are so common, especially during peak hours in the photovoltaic system – this is when we have the highest value of electric current flowing through this section.

And for the same reason, at times of lower generation or when the inverter is turned off, the measured electrical voltage is “normal”. Of course, there is no current flowing, and consequently there is no variation in electrical voltage between the points. And since it is not feasible, much less interesting, to reduce the injected current (reduce power), we have to understand why the impedance rises to the point of tripping the equipment due to overvoltage.

As previously stated, this is due to the internal electrical installation to which the inverter is connected or to the power grid of the power company itself. In the first case, the precariousness of the electrical installation may be caused by a very long section of AC cabling without the appropriate cable cross-section or some t or connection in the s that may be poorly tightened, generating high resistance (hot spot) — all of this can cause a considerable increase in voltage.

Or, something very common to happen: you (or the engineer responsible for the work) correctly sized the cable section for the inverter, checked all the connections up to the customer's internal , and everything is fine. However, what is the quality and reliability of the existing network, connecting your customer's general to the input standard? That could be the problem.

In cases where the problem is in the utility grid, it is very common to occur mainly in rural grids and end-of-line grids, with lower quality and reliability in the supply of electrical energy. Problems generally occur in older electrical grids, with less maintenance. When they suffer a high injection of current from inverters, they cannot transmit this energy over a long distance, with satisfactory quality to maintain the electrical levels required by standard.

As mentioned at the beginning, in most cases, overvoltage errors will be a problem with the installation, not with the inverter. Therefore, the first step is to identify the origin or cause of the overvoltage in the electrical grid. Many installers go straight to expanding the operating voltage range of the inverter, since the vast majority higher voltages, reaching values ​​such as 270 V, for example. However, this has some implications:

• This high voltage range will not always make the inverter work at its optimum point, reducing system efficiency;
• If there is a problem in the installation, sooner or later it can get worse and, even with the overvoltage adjustment, the error continues to occur, causing loss of performance;
• The voltage, when adjusted, will be high as a whole in the installation. Therefore, there is a risk of burning the customer's electronic equipment, which may be more sensitive to this variation;
• Current standards require overvoltage protection to operate at 10% above the nominal voltage (as previously mentioned). Any damage to the electrical network resulting from these changes may be held responsible for the consumer unit where the inverter operates outside these limits.

Therefore, we must understand the concepts that cause this increase and act to correct the problem. Initially, we must check whether the electrical project actually meets the minimum requirements, whether it is correctly dimensioned and, from there, whether the installation is in accordance with what was designed. Once this is done, one possible way to get an initial indication of the location of the problem is to measure the voltage at several points simultaneously to find out in which section the voltage is varying. For example:

In the figure above, we can see the voltage measurement being performed at 3 different points of the installation: at the photovoltaic inverter, at the customer's internal AC , where the photovoltaic system is interconnected, and finally at the utility's input standard. The measurement must be performed with the inverter running, of course, since this is when the overvoltage occurs. With this, we can have an initial diagnosis as follows:

• Voltage increase in the section between inverter and AC . Possible problem in PV installation: cables, connections, poor tightening, poor quality transformers (high impedance), etc.;
• Elevation in the AC frame section – input standard: Existing infrastructure at the customer with problems, whether of low quality, poorly dimensioned, with poor connection, etc.;
• “t” elevation at all points, that is, from the inverter to the standard, the voltage remains very close, even during the voltage elevation. Possible infrastructure problem at the dealership.

In the first two, a detailed inspection of the installation will be enough to find the problem and correct it. In the latter, it depends on a complaint being made to the energy company for reinforcement or repair of the network, as it is the only permanent solution in the case.

Let us that when issuing the access report, the concessionaire guarantees us that we can make the PV connection with the informed power and that the electrical grid will such a system. A quality analyzer installed on site for a period of time, collecting information, will be of great value in this argument with them.

Conclusion

Overvoltage should not be, but it is a common problem in photovoltaic systems installed in Brazil. Low-quality electrical grids from the concessionaires, especially in more remote locations, make it impossible or impair the generation of electrical energy by the inverters. Add to this several installation errors, poor quality of materials and equipment used, and we have the most common error in Brazilian photovoltaic systems.

To make the situation worse, in many cases the solution sought is to adjust the inverter protection parameters to their maximum limits, as simply as if we were adjusting the date and time of the equipment, without prior analysis of the problem and without understanding the risks involved in this process, without knowing the origin of the problem of rising AC voltage.

These and other reasons increasingly frequent complaints from end s (customers) dissatisfied with a product that should only bring security and savings on their energy bills.

These challenges highlight the importance of invest in solar energy training, where professionals can acquire specialized knowledge about identifying and solving problems related to the operation of photovoltaic systems. The search for suitable solutions and understanding the underlying principles are essential to ensure customer satisfaction and the efficiency of solar systems.

that economy and sustainability go hand in hand! Learn more about renewable energy in our articles about solar energy produced by our experts.