Voltage Regulation Using an Automatic On-Load Tap-Changers
In recent years, employees in the Norwegian low-voltage grid have encountered a recurring struggle. The voltage from the transformer to the consumer has been too low to properly function. However, with the introduction of solar panels, grid employees now face an issue of the opposite nature: An increasing amount of users experience voltage reaching higher levels than anticipated.
To avoid expensive fines, grid companies must adhere to governmental regulations which state that the voltage in the customer’s intake must not exceed or fall below 230V, give or take 10%. The voltage must therefore always be within 207 – 253V.
— Due to there being hundreds of meters from each substation to the customers, you will lose voltage before the electricity reaches the customer’s socket. With ENOVA support and high electricity prices, more and more solar panels are installed allowing customers to produce their own electricity. Now, the voltage level is beyond elevated, says Frode Johansen, Energy Project Manager at SafeBase.
Photo: Norsk Transformator. Left: Close up from an installation in Italy. Right: From the Måløy installation.
Alternative Solutions
Johansen is supported by Reidar Tjeldhorn in Norsk Transformator, with whom SafeBase has collaborated on several projects.
— It is the grid company’s responsibility to ensure that the voltage levels comply with regulations. There are also strict guidelines for solar electric systems; they must be automatically disconnected if the voltage exceeds the predetermined limits, which usually leaves the owners dissatisfied. Grid companies have a challenge related to whether the produced power is within the range that solar panels legally can deliver, says Tjeldhorn.
Read more: Link to the Røros cases
Potential solutions to this issue are to reinforce the network with stronger cables, to replace the entire transformer, or to move the transformer closer to the customers – all costly investments.
Automatic On-Load Tap-Changers
How do you avoid expensive investments? That is where automatic on-load tap-changers come in. The aspect of automation is key, as manual on-load tap-changers require regular service travels to the substation.
— Automatic on-load tap-changers save you both time and costs. They are installed on the transformer, in the transition from the medium- to the low-voltage network. The tap-changers have nine steps, and for each step the voltage, moving from the transformer to the customer, varies by typically 1.0 – 2.5%, depending on the predetermined limits defined by the grid company themselves.
Photo: Norsk Transformator. Taken in the neighbourhood where Føie tested Automatic On-Load Tap-Changers.
Tested at Føie
During a previous project, SafeBase and Norsk Transformator collaborated with the company Føie to test whether a neighborhood could get an even voltage with automatic on-load tap-changers as the solution.
—With the SensorHub software, supplied by SafeBase, installed in an automatic on-load tap-changer, supplied by us, Føie received data from the grid station. This data, together with data from Safebase’s smart meter management system, provided insight into the voltage quality. With an automatic on-load tap-changer, the entire neighborhood received optimal voltage, regardless of whether one neighbor produced solar energy and the other charged two electric cars, Tjeldhorn elaborates.