‌Differences Between Power Transformers And Distribution Transformers

‌Differences Between Power Transformers and Distribution Transformers

Voltage Levels and Power Ratings:
Power transformers are primarily used in ‌transmission systems‌, operating at high voltage levels such as ‌110kV or 220kV‌ with large capacities typically ‌10,000kVA or above‌.
Distribution transformers are mainly employed in ‌distribution systems‌, operating at medium-to-low voltage levels like ‌10kV and below‌ with smaller capacities generally ‌under 2,500kVA‌.

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The differences between distribution transformers and power transformers are mainly reflected in their application scenarios and functional positioning. Distribution transformers belong to a specific category within the broader class of power transformers, dedicated to the end of the distribution system.

The common pole-mounted transformers or box-type substations seen in ordinary residential neighborhoods mostly fall under distribution transformers. Their primary task is terminal voltage conversion from 10kV to 400V. Such transformers typically have capacities ranging from 30kVA to 2500kVA. Structurally, they often feature a fully-sealed oil-immersed design with cooling fins directly exposed to the air.

 

Power transformers are mainly used for large-scale power transmission and transformation across extensive areas such as large industries, cities, and rural regions. Distribution transformers, in contrast, are primarily employed for electricity supply and distribution within smaller urban or rural areas, such as residential compounds, factories, mines, commercial buildings, and industrial workshops.

 

The concept of power transformers is broader, encompassing voltage conversion equipment used in all stages of power generation, transmission, and distribution. At the outlets of large power plants, one can find massive transformers with capacities exceeding 100 MVA. These units are responsible for stepping up the generator output voltage of 10-20kV to ultra-high voltages of 500kV and above. Transformers in UHV converter stations may even use split-type structures, where a single bushing can weigh up to 8 tons, requiring specially built anti-vibration platforms.

 

From a technical parameter perspective:

• Distribution transformers must comply with the GB20052 standard for no-load losses, incurring fixed daily losses of approximately 0.5-2.5 kW. For example, a specific 1000kVA distribution transformer model has its short-circuit impedance controlled between 4%-6% to adapt to the short-circuit current characteristics of distribution networks.
• Power transformers vary significantly based on application scenarios. A 750kV main transformer might have a short-circuit impedance reaching 14%, with windings adopting an interleaved disc structure to withstand high voltage stress.

 

Regarding operating environments:

• Distribution transformers need to withstand harsh conditions. For instance, distribution transformers inside ring main units in a coastal city might specifically use Dyn11 vector groups and be equipped with moisture-proof breathers to combat salt spray corrosion.
• Power transformer operating environments are relatively more controlled but require special considerations. For example, a 220kV main transformer supporting a wind farm in Northwest China may be configured with sand-dust filtration systems and seismic dampers.

 

Maintenance methods exhibit significant differences. Distribution transformers commonly adopt a maintenance-free design, requiring only routine temperature monitoring with infrared thermometers. For example, a dry-type distribution transformer in an industrial park operated continuously for 7 years without core inspection. Power transformer maintenance requirements are stringent; main transformers at 500kV substations must undergo oil chromatography analysis every 6 years and scheduled outage maintenance every 12 years, involving over ten specialized inspections including bushing dielectric loss tests and winding deformation detection.

 

Regarding cost, similarly-rated equipment can differ in price by tens of times. A certain 1000kVA oil-immersed distribution transformer has a market price of approximately ¥120,000, while a 220kV power transformer of equivalent capacity exceeds ¥3,000,000 in procurement cost. This disparity originates from differing insulation material grades: distribution transformers use 0.3mm standard copper wire for high-voltage windings, whereas ultra-high-voltage transformers employ transposed conductors wrapped with 4mm insulation paper.

 

Cross-functional cases exist in practical applications. The 24-pulse rectifier transformer at a Shenzhen metro station belongs to the power transformer category while simultaneously performing 1500V DC distribution functions. Such special transformers utilize a three-winding structure, achieving harmonic suppression through phase adjustment, and incorporate technical features of both transformer types.

 

Equipment selection requires primary consideration of application scenarios. Residential power distribution prioritizes S13 energy-efficient distribution transformers, whose no-load losses are 30% lower than older models. For photovoltaic plant grid-connection scenarios, double-split winding power transformers should be selected, enabling both 35kV step-up and isolation requirements between different generation units. A biopharmaceutical enterprise employs on-load tap-changing distribution transformers with ±5% voltage adjustment range to ensure power supply quality for precision instruments.