We can say that, basically, the difference between an autotransformer and an isolating transformer is the fact that the autotransformer has a single winding on a laminated core, while the isolating transformer has two separate windings, these being the primary winding and the secondary winding.
However, there are other aspects that are also considered: type of insulation, induction, excitation current, losses, size, cost and application. The differences can be seen in the table below.
Table 1 – Differences between autotransformer and isolating transformer
The isolation transformer is used when it is necessary to isolate the system from the electrical grid (following a recommendation from ANEEL); when we have two neutrals available (network and inverter), requiring isolated connections between them; to prevent network disturbances that could cause the inverter to disconnect; in networks that have interference from non-linear loads (harmonics), such as rural areas, end of line, among other cases; and systems with more than one inverter.
The isolating transformer has the advantages of isolating and protecting the system from the electrical network; neutrals isolated from each other; greater reliability and security of cargo protection. Regarding the disadvantages of the isolating transformer, we can mention the larger physical size, greater weight, higher cost and greater additional losses.
When we talk about an autotransformer, despite having a smaller size, lower losses and lower price, it has the disadvantage of not filtering, allowing impurities to pass straight through the network and offering greater risks of shock to the installations.
Differences between a solar transformer and a conventional transformer
Solar transformers are designed to be used in photovoltaic energy systems.
To transform solar energy into electrical energy, in addition to photovoltaic panels, a DC-AC inverter is also required and, in some cases, a photovoltaic transformer to make the inverter output compatible with the electrical grid or to provide additional protection, isolating the system photovoltaic from the electrical grid.
The isolating transformer, in addition to keeping the system safe due to its galvanic isolation, is also responsible for adjusting the electrical voltage that exists between the inverter and the electrical network, that is, without it, it is not possible to use solar energy in the sockets.
They are applied when the three-phase photovoltaic solar inverter needs to produce energy on a three-phase network, but with different voltages. For example, 380V three-phase inverter used in 220V three-phase power grid.
The use of this equipment is necessary so that the voltages are adequate. This means that the transformer or autotransformer will transform electrical energy between two circuits, raising the grid voltage level to 380 V, allowing the connection and operation of the inverter.
The opposite process also happens: when the inverter is injecting energy into the grid, the transformer will reduce the voltage to 220 V, adapting the system to the local grid. We should always consult the dealership's recommendation to use the appropriate transformer.
What differentiates a solar transformer from a conventional isolating transformer are the characteristics of its construction. The solar transformer is built and specified with the aim of serving photovoltaic systems. This change occurs in the stacking dimensions, number of turns ratio and type of wire to be used, that is, it covers the characteristics of the transformer design.
This is necessary because in solar transformers, there is a need to reduce losses and optimize no-load consumption in order to improve performance, making the system operation more efficient.
The opinions and information expressed are the sole responsibility of the author and do not necessarily represent the official position of the author. Canal Solar.
An answer
I bought a fab autotransformer with 500 VA power (127/220). UPSAI, Since my load IS around 160VA. pirem when turning it on it would get very hot and turn off. In other words, it was 500VA, but it only serves 100VA.