A friend once casually asked, “What is the difference between a double winding and a double split transformer?†That simple question actually raised several important points. What’s the relationship between the two? What makes a double-split transformer unique? Why are they commonly used in photovoltaic systems? If you want to explain these questions clearly and simply, it’s time to dive into the details. This is a brief lesson from Xiaobian. The following content is based on personal experience and understanding, and any inaccuracies are welcome for correction.
Interpreting the Question
1. The Relationship Between Double Winding and Double Split Transformers
First, let’s clarify what a "winding" means. A winding in a transformer corresponds to a specific voltage level. For example, a 110/35 kV transformer has two windings—one for 110 kV and one for 35 kV. Most transformers used in engineering are either two-winding or three-winding, meaning they handle two or three different voltage levels.
Now, a split transformer differs from a standard one. Its low-voltage winding is divided into multiple branches with equal rated capacity. These branches are electrically isolated from each other but still share a common magnetic circuit. There's a high impedance between them, which limits current flow.
So, a three-phase double-winding double-split transformer has two windings (high and low voltage) and splits the low-voltage winding into two parts that are electrically separate. These can be operated in parallel or individually. A three-winding transformer, on the other hand, has three distinct windings—high, medium, and low voltage—with clear voltage differences like 110/35/10 kV.
As for the special features of a double-split transformer and why it's used in photovoltaics, these are closely related. Let’s explore this next.
2. The Special Features of a Split Transformer and Its Use in Photovoltaics
Double-split transformers are commonly found in large-scale photovoltaic projects. While many people may not be familiar with them, for engineers and designers, choosing a double-split transformer over a regular one isn’t just a technical choice—it’s a strategic one.
In today’s photovoltaic power plants, a typical unit is 500 kW, and most inverters on the market have similar capacities. Connecting the inverter to the box-type substation is a crucial step in the system. To manage costs effectively, selecting the right boosting scheme is essential, and this is where the double-split transformer shines.
There are generally three wiring configurations for connecting the power generation unit to the step-up transformer:
Option 1: One 500 kW unit connected to a 500 kVA double-winding transformer. Option 2: Two 500 kW units connected to a 1000 kVA double-winding transformer. Option 3: Two 500 kW units connected to a 1000 kVA double-split transformer.
Option 1 offers simplicity and reliability but is more expensive per unit. It’s often used in decentralized projects where reducing line loss is key. However, it’s not ideal for large centralized solar farms.
Options 2 and 3 are better suited for large-scale photovoltaic systems. Compared to a double-winding transformer, a double-split transformer has higher initial cost, but its structural advantages provide better electrical isolation between the two branches. This reduces electromagnetic interference, circulating currents, and harmonic distortion. In case of a short circuit, the fault is limited to one branch, while the other remains stable and unaffected.
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