Foreword
With the advancement of the energy storage industry, the large-scale application of energy storage systems and photovoltaic systems imposes higher demands on power equipment. As the core device for energy conversion and transmission, the selection of transformers directly impacts system efficiency, reliability, and economic viability. Therefore, to address the differentiated requirements of energy storage and photovoltaic scenarios, it is essential to understand the technical characteristics of dual-winding transformers and split-core transformers, ultimately enabling a rational choice.
I. Principles and Differences Between Two Types of Transformers
1. Double-Winding Transformer
The double-winding transformer is the most common type in power systems. Its core structure comprises a primary winding (high-voltage side) and a secondary winding (low-voltage side), which achieve electromagnetic coupling through a common iron core.
Its operation is based on the principle of electromagnetic induction. When an AC voltage is applied to the primary winding, the alternating magnetic flux within the core induces the target voltage in the secondary winding, thereby achieving voltage level conversion of electrical energy. The windings are structurally independent and isolated, with no electrical connection between the primary and secondary sides-energy transfer occurs solely through magnetic coupling. Typical applications include power transmission in grid systems, distribution networks, and electrical energy conversion for industrial equipment.
2. Split-Winding Transformer
The split-winding transformer is a specialized transformer characterized by a single high-voltage winding and a low-voltage side divided into two independent windings (referred to as "split windings"). These two low-voltage windings are electrically independent yet magnetically coupled through the core.
The split-winding design enables the two low-voltage outputs to connect to different loads or power sources independently. Simultaneously, by adjusting the short-circuit impedance between windings, it achieves functions such as limiting short-circuit currents and enhancing power supply reliability. Its core principle leverages the magnetic coupling characteristics between split windings: maintaining energy transmission efficiency during normal operation while suppressing fault currents through high short-circuit impedance during faults.
3. Differences Between the Two
During a short circuit in a dual-winding transformer, the low impedance between windings results in high fault currents, necessitating external protection. Its single energy transmission path achieves over 95% efficiency, making it suitable for high-efficiency power transmission scenarios. It features a simple structure and low maintenance costs but has limited functionality, often used in applications with fixed power supply paths.
When a split-winding transformer experiences a winding short circuit, the other winding forms an additional impedance through magnetic coupling, effectively suppressing the short-circuit current. Although leakage flux causes losses 5%-8% higher than in double-winding transformers, this can be optimized. It supports multiple independent power supply paths, making it suitable for distributed energy integration. Their low-voltage side windings can operate independently or in parallel, supporting redundant designs. In photovoltaic applications, they enable flexible integration of diverse equipment, enhancing system reliability and flexibility.
II. Reasons for Selecting Dual-Winding Transformers in Energy Storage Systems
1. Efficient Bidirectional Energy Flow: Energy storage systems must switch between charging (power supply from grid to storage device) and discharging (power supply from storage device to grid) modes. The low-impedance characteristics of dual-winding transformers reduce energy transmission losses and enhance efficiency.
2. Compact Structural Requirements: Energy storage power stations typically adopt centralized designs. The simple structure of dual-winding transformers reduces footprint and lowers construction costs.
3. Flexible Voltage Matching: By adjusting the turns ratio between primary and secondary windings, the transformer can flexibly accommodate voltage level differences between energy storage devices (e.g., battery banks) and the grid.
III. Reasons for Selecting Dual-Split Transformers in Photovoltaic Systems
1. Multi-source Distributed Power Connection: Photovoltaic power plants are often composed of multiple photovoltaic arrays (or inverters) connected in parallel. The two low-voltage windings of a dual-split transformer can connect different arrays separately, preventing a single array failure from affecting overall power generation.
2. Short-Circuit Current Suppression Requirements: Grid-connected photovoltaic inverters may generate inrush currents. The high impedance between split windings limits inrush and fault currents, reducing the burden on grid protection devices.
3. Harmonic Suppression and Power Quality Optimization: The magnetic coupling characteristics of split windings provide partial suppression of harmonics generated by photovoltaic systems, improving grid-connected power quality.
IV. Selection Logic for Two Transformer Types
1. Efficiency and Cost
Dual-winding transformers offer efficiency advantages, typically achieving over 98.5% efficiency. Dual-split transformers, however, generally achieve 97.5%-98% efficiency due to magnetic coupling losses in the split windings. Yet in photovoltaic systems, dual-split transformers reduce overall costs by minimizing cable usage and switchgear specifications.
2. Reliability and Maintenance
Double-winding transformers feature simple structures and low maintenance costs, with annual upkeep expenses amounting to approximately 0.5%-1% of the equipment's original value. Due to their complex winding designs and support structures, split-winding transformers incur higher maintenance costs, reaching 1.5%-2% annually. However, within PV systems, the fault isolation capability of split-winding transformers minimizes downtime, yielding superior overall operational benefits.
3. Application-Specific Adaptation
Energy Storage Systems: Prioritize dual-winding transformers for their efficient bidirectional conversion and cost advantages. For large-scale centralized storage projects, deploying multiple PCS units in parallel with dual-winding transformers further reduces costs while enhancing reliability.
Photovoltaic Systems: Select transformer types based on plant scale and topology. Dual-split transformers are recommended for large centralized plants to achieve short-circuit current suppression and flexible grid integration. Dual-winding transformers can also be used in small distributed plants to balance cost and efficiency.
V. Conclusion
The fundamental difference between dual-winding transformers and dual-split transformers stems from their distinct functional purposes: the former centers on "high-efficiency energy conversion," making it suitable for scenarios with fixed pathways and a focus on transmission efficiency (energy storage systems); the latter emphasizes "multi-path power supply and fault current limiting," making it ideal for scenarios requiring distributed energy integration and reliability assurance (photovoltaic systems). In power system design, comprehensive selection based on specific application requirements-considering structural design, impedance characteristics, and reliability-is essential to achieve the optimal balance between economic benefits and technical performance.