In a photovoltaic box-type substation, how should the transformer selection be matched to the output characteristics of photovoltaic arrays with different power ratings?
Release Time : 2026-04-29
In a photovoltaic box-type substation, the transformer, as the core device connecting the photovoltaic array to the power grid, must be selected closely based on the output characteristics of the photovoltaic array to ensure efficient and stable system operation. The output power of a photovoltaic array is affected by factors such as light intensity, temperature, and shading, exhibiting nonlinear fluctuation characteristics. Especially under maximum power point tracking (MPPT) control, the output voltage and current will dynamically adjust. Therefore, transformer selection needs to comprehensively consider dimensions such as capacity matching, voltage level, cooling method, insulation performance, short-circuit impedance, protection level, and intelligent functions to adapt to the output characteristics of photovoltaic arrays with different power ratings.
Capacity matching is the foundation of transformer selection. The output power of a photovoltaic array varies with light conditions, and the transformer capacity must cover the maximum output power of the array, with a certain margin. Insufficient capacity may lead to long-term overload operation of the transformer, accelerating insulation aging and shortening equipment life; excessive capacity will increase no-load losses and reduce system efficiency. It is generally recommended that the transformer capacity be selected at 110% to 125% of the peak power of the photovoltaic array, meeting full-power requirements while also considering economic efficiency. For arrays with significant power fluctuations, multiple transformers can be connected in parallel. Redundancy enhances power supply reliability and prevents a single unit failure from causing a complete station outage.
The voltage level selection must strictly match the photovoltaic array's output voltage and grid connection requirements. The output voltage of a photovoltaic array is affected by the number of modules connected in series, while the inverter's output voltage is typically three-phase AC, requiring a transformer to step up to the grid voltage level. For example, small-scale commercial and industrial photovoltaic systems often use 380V grid connection, while large ground-mounted power stations require step-up to 10kV or higher. The high-voltage side voltage level of the transformer must match the grid connection point voltage, and the low-voltage side must be compatible with the inverter's output voltage to avoid equipment damage or grid connection failure due to voltage mismatch. Furthermore, the output voltage of photovoltaic arrays fluctuates significantly; the low-voltage side of the transformer must be designed to accommodate this range to ensure stable voltage boosting under various operating conditions.
The choice of cooling method directly affects the transformer's heat dissipation performance and operating efficiency. Photovoltaic box-type substations are often placed outdoors, and are significantly affected by ambient temperature, solar radiation intensity, and other factors, leading to prominent transformer temperature rise issues. Oil-immersed transformers use insulating oil as the cooling medium, offering excellent heat dissipation performance and making them suitable for large-capacity applications with relatively controlled operating environments. Dry-type transformers, on the other hand, use air or resin-impregnated paper as the cooling medium, eliminating the risk of oil leakage, simplifying maintenance, and making them more suitable for high-humidity, dusty, or environmentally demanding environments. In high-temperature regions, transformers with strong temperature resistance should be prioritized, or measures such as forced ventilation and increased heat dissipation area should be implemented to improve heat dissipation and prevent capacity reduction or equipment damage due to overheating.
Insulation performance is crucial for ensuring the long-term safe operation of transformers. Photovoltaic power station equipment is mostly exposed outdoors, affected by environmental factors such as ultraviolet radiation, wind, rain, and dust, which can easily cause insulation materials to age. The transformer insulation class should meet long-term operating requirements; it is generally recommended to choose insulation level H or higher, and strictly implement moisture-proof, dust-proof, and corrosion-proof designs. For example, in coastal areas with high salt spray, stainless steel shells or epoxy resin-cast insulation should be used to prevent salt spray corrosion; in dusty areas, enhanced sealing performance is necessary to reduce dust intrusion. In addition, transformer insulation design must consider the impact of lightning overvoltage and switching overvoltage. By appropriately configuring surge arresters and grounding devices, the equipment's lightning protection capability can be improved.
The selection of short-circuit impedance must balance voltage fluctuations and short-circuit current control. Excessive short-circuit impedance will lead to increased voltage drop, affecting the power quality of the photovoltaic system; insufficient impedance may cause excessive short-circuit current, increasing the burden on protection devices and even damaging equipment. During selection, the short-circuit impedance must be adjusted according to grid connection conditions and the characteristics of protection equipment to ensure that voltage fluctuations are within the allowable range while meeting the system's short-circuit current control requirements. Typically, the short-circuit impedance design of photovoltaic step-up box-type transformers is within a reasonable range, which can suppress short-circuit current, reduce voltage drop, and improve system stability.
The selection of protection level must be adapted to harsh outdoor environments. Photovoltaic box-type substations are usually installed outdoors and must be rainproof, dustproof, rustproof, and resistant to high and low temperatures. The transformer enclosure protection level generally requires IP54 or higher to ensure normal operation in environments such as sandstorms, rain, and snow. For rooftop projects, wind-resistant reinforcement designs are necessary to prevent equipment from overturning due to strong winds. In areas prone to lightning strikes, lightning protection systems are required to reduce losses. Furthermore, transformer operating noise can impact the surrounding environment. Dry-type transformers are generally quieter, while oil-immersed transformers require optimized oil circulation designs or the addition of soundproof enclosures to reduce noise and meet environmental protection requirements.
Intelligent functions are crucial for improving transformer operation and maintenance efficiency. Modern photovoltaic box-type transformers are often equipped with intelligent protection and operation monitoring systems, such as overload protection, temperature alarms, leakage detection, and oil temperature and level monitoring (for oil-immersed transformers). These systems can monitor equipment status in real time and provide early warnings of potential faults. Some high-end products support SCADA system access, enabling remote meter reading and data analysis, providing decision-making support for operation and maintenance. Intelligent upgrades can reduce the frequency of on-site inspections, lower maintenance costs, and improve overall system efficiency. For example, intelligent temperature control systems can automatically adjust fan speeds based on load conditions to optimize heat dissipation; fault diagnosis functions can quickly locate problems, shorten downtime, and ensure stable power plant operation.