“What is the difference between a double winding and a double split transformer?†The friend’s casual question asked a lot of questions. What is the relationship between the two? What is the particularity of the double-split transformer? Why are the dual-transformers used in photovoltaics? If you want to interpret these problems in a simple and plain way, you need to prepare for the next point. This opportunity is a small lesson from Xiaobian. The following opinions only represent the summary of the personal work of Xiaobian. If there is any delay, please advise.
Interpret the problem.
1, the relationship between double winding and double split
First, the winding is introduced. The general winding mainly corresponds to the voltage level. One winding of the transformer corresponds to a voltage level (for example, the main transformer ratio is 110/35, which includes 110kV and 35kV voltage levels). The general engineering uses two-winding and three-winding transformers, which contain two and three voltage levels.
Looking at the split transformer, the difference from the ordinary transformer is that it splits into several branches with equal rated capacity in its low-voltage winding. There is no electrical connection between these branches, only weak magnetic contact, and each There is a large impedance between the branches.
According to the above analysis, specifically speaking, the three-phase double-winding double-split transformer has two windings of high voltage and low voltage, and splits the low voltage winding into two parts, which are electrically disconnected from each other. The two split low pressures can be operated in parallel or separately. The three-phase three-winding transformer consists of three independent windings, which are high voltage, medium voltage and low voltage, and have obvious voltage level differences such as 110/35/10.
As for the "speciality of the double-split transformer? Why is the multi-split transformer used in photovoltaics?" These two questions are unified to answer.
2. The particularity of split transformer and its application in photovoltaic engineering
Double-split transformers are often seen in large-scale photovoltaic projects. It is almost common for people who don’t know too much about this equipment, but for designers, choosing dual splits instead of ordinary transformers has its own Deep meaning.
At present, large-scale photovoltaic power plants use 500kW as the basic power generation unit, and the mainstream inverter capacity in the market is also 500kW. The connection between the inverter and the box-type substation is a key step in the whole photovoltaic power generation system. Therefore, considering cost control, the selection technology is reasonable. The boosting scheme is necessary, and based on this, the double-split transformer gives the perfect answer.
The connection between the power generation unit and the step-up transformer mainly refers to the wiring of the inverter and the transformer. Generally, there are three ways:
Scheme 1: 500kW power generation unit and one 500kVA double winding step-up transformer to form a generator-double winding transformer unit wiring;
Option 2: Two 500kW power generation units and one 1000kVA double-winding step-up transformer to form a generator-double winding transformer expansion unit wiring;
Option 3: Two 500kW power generation units and one 1000kVA double split boost transformer to form a generator-double split transformer expansion unit wiring;
Scheme 1 corresponds to one step-up transformer for each power generation unit. Although it has the advantages of simple unit wiring structure and high reliability, compared with scheme 2 and scheme 3, its cost disadvantage is self-evident, generally applicable to power generation units. In the decentralized project, in order to reduce the line loss and reduce the cost of the wire, this type of wiring can be considered, but it is not suitable for the application of centralized photovoltaic power plants.
Both scheme 2 and scheme 3 are extended unit wiring modes, which are applicable to the application of large-scale centralized photovoltaic power plants. Compared with the two-winding transformer of scheme 2, the cost of the double-split transformer of scheme 3 is high, but the double-split transformer is realized due to structural advantages. The electrical isolation between the two inverters not only reduces the electromagnetic interference and circulation effects between the two branches, but also the AC output of the two inverters is filtered by the transformer, and the output current harmonics are small, which improves the output. The quality of power. Considering the occurrence of a short circuit condition, when a short circuit occurs in one branch, in addition to effectively limiting the short-circuit current, the voltage of the other branch can be kept at a certain level without affecting the operation of the user.
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