In the development of distributed photovoltaic power generation projects, they will be exposed to the “self-use and spare electricity online” mode. Most of their access methods are access to the low voltage side bus of distribution transformers in the plant area, and the amount of electricity generated is distributed to the busbars through the bus. The use of the load, the remaining power through the transformer reverse boost to the grid.
At this point, most homeowners have the same question: Can a step-down transformer be boosted in reverse? Is there a bad effect on the transformer?
First of all need to understand the characteristics of the transformer. A transformer is a common electrical device that can be used to convert an alternating voltage of a certain value into an alternating voltage of another value of the same frequency. A step-up transformer is a transformer that converts a low-value alternating voltage to another higher-value alternating voltage of the same frequency, and a step-down transformer converts a higher voltage at the input of the power supply to a lower ideal voltage. Used for load. The principle of the transformer is to transfer the power through electromagnetic conversion, and to play the role of electrical isolation, as shown below.
I1 (I2), U1 (U2), and W1 (W2) are currents, voltages, and turns of the primary (secondary) winding, respectively, and their relationship is U1/U2=W1/W2=I2/I1. Φ is the magnetic flux generated by electromagnetic induction. The physical entity in which it lies is the core, which is the magnetic circuit of the transformer.
Step-down transformer, the primary winding is high voltage, current is small, but because the electromagnetic induction Φ, so consider the loss, so the primary winding voltage to reserve 5% of the loss, such as 10KV voltage, the actual 10.5 KV; secondary windings are low voltage, large current, need to consider the voltage drop of the winding itself and reach the load end (electric equipment), so its voltage should also reserve about 5% of the margin, for example, generally speaking 380V voltage, in fact, the low voltage side of the transformer is 400V.
Then, if a step-down transformer is used as a step-up transformer, the low-voltage side needs to generate electromagnetic induction, and the high-voltage side as the load power supply. Both of them need to consider the corresponding losses. If they are all reserved for 5%, they can be realized, and the photovoltaic inverter can The output voltage of the transformer can be adjusted in a large range to meet the needs of voltage changes.
In other words, in principle, a step-down transformer can be used as a boost converter.
However, in the actual application process, the step-down transformer has certain differences in structure (winding three-phase connection mode, etc.) and protection part and step-up transformer, and long-term reverse use will gradually reduce the use stability of the transformer, and at the same time Affect its service life.
Moreover, the existing policies and regulatory documents generally require the use of self-utilized Internet access projects for their own use. The proportion of self-use is greater than 50% of the electricity generated, and the access capacity is not greater than 25% of the upper-level transformers. (The author WeChat public account: Photovoltaic experience network)
