Dry-type Transformer Knowledge Sharing

I. What is a dry-type transformer? 

Dry-type transformer (Dry-type Transformer) is a kind of power transformer relying on air or other gases (e.g. nitrogen) as the cooling and insulating medium, whose core and windings are not immersed in insulating oil but are insulated by solid insulating materials (e.g. epoxy resin, Nomex paper, silicone rubber, etc.). Because of its oil-free, non-polluting characteristics, widely used in safety and environmental protection requirements of high places.

Second, the classification of dry-type transformer

Classification according to the insulation material

Epoxy resin casting type (SCB series)

The winding adopts epoxy resin vacuum casting, forming a high-strength insulation layer, moisture-proof, anti-corrosion ability, suitable for high humidity or pollution environment.

Impregnated type (SG series)

The winding is impregnated and cured several times with high-temperature-resistant insulating varnish, which is less costly, but the moisture-proof performance is slightly inferior to that of the casting type.

Classification according to cooling method

Natural air cooling (AN): Relying on natural air convection to dissipate heat.

Forced air cooling (AF): Forced heat dissipation through the addition of fans, which can enhance the short-term overload capacity (usually 40-50% capacity).

III. Core Structure and Working Principle

Structure Composition

Iron core: made of stacked silicon steel sheets to reduce hysteresis loss.

Winding: High-voltage winding and low-voltage winding, wound with copper or aluminium conductor.

Insulation material: epoxy resin, glass fibre, etc. to ensure electrical isolation.

Shell: Protection level is generally IP20 or IP23, dust cover or heat sink can be added.

Working Principle

Through the principle of electromagnetic induction to achieve voltage transformation: high-voltage side input alternating current generates alternating magnetic field, low-voltage side winding cutting magnetic line of inductance induced voltage, the voltage size is proportional to the number of turns of the winding.

Fourth, the advantages and limitations of dry-type transformer

Advantage

Safety and environmental protection: no risk of oil leakage, high fire rating (in line with UL94-V0 standard), suitable for densely populated areas (such as hospitals, shopping centres, underground).

Easy maintenance: no need to change the insulating oil regularly, low operation and maintenance costs.

Strong adaptability: resistant to humidity and dirt, can operate stably under -25°C to +40°C environment.

High efficiency and energy saving: low loss (SCB13 and above models meet Grade 1 energy efficiency), no-load loss is more than 30% lower than oil-immersed type.

Limitations

Capacity limitation: single capacity generally does not exceed 2500kVA (higher capacity requires special design).

High heat dissipation requirements: large-capacity transformers need to be forced air-cooled, increasing energy consumption.

Higher cost: the price of the same capacity than the oil-immersed transformer is about 20-30% higher.

V. Typical application scenes

Construction field: high-rise buildings, data centres, hospitals, airports power distribution system.

Industrial field: chemical plants, mines and other flammable and explosive environment.

New energy field: photovoltaic power station, wind power generation step-up transformer.

Railway transport: traction power supply system of underground and high-speed railway.

Selection and maintenance guide

Selection points

Capacity calculation: select rated capacity according to load demand (considering future expansion), avoid long-term overload.

Insulation level: Class H (temperature resistance 180°C) or Class F (155°C), prefer Class H for high temperature environment.

Protection class: IP23 for humid environment, IP20 for clean environment.

Maintenance Precautions

Regular inspection: Clean the dust every 6 months and check the windings for cracks and discolouration.

Temperature rise monitoring: temperature rise of the winding ≤ 100K (H class) during normal operation, abnormal temperature rise needs to be investigated for load or heat dissipation failure.

Preventive test: Measure insulation resistance (≥100MΩ) and DC resistance deviation (≤2%) every year.

Future development trend

Intelligent: integrated temperature sensors, local discharge monitoring module, to achieve remote status diagnosis.

Material innovation: nano insulation materials, amorphous alloy core to improve energy efficiency.

Modular design: facilitate rapid installation and expansion, reduce the complexity of operation and maintenance.