Classification of industrial transformers:

1. By number of phases:
A: Single-phase transformer: Used for single-phase loads and three-phase transformer banks, often suitable for small power, control, lighting, and small equipment.
B: Three-phase transformer: Used for voltage regulation in three-phase systems, often suitable for industrial main power sources, large power distribution, motors, and overall plant power supply.

2. By cooling method:
   A: Dry-type transformer: Air self-cooling, epoxy resin casting, indoor, factory, and machine room fireproof and dustproof.
It relies on air convection for natural cooling or adds fans for cooling, mostly used in high-rise buildings, toll stations with electricity, and small-capacity transformers for local lighting and electronic circuits.
   B: Oil-immersed transformer: Oil self-cooling, oil-air cooling, large-capacity distribution, outdoor substations.
It relies on oil as the cooling medium, such as oil self-cooling, oil-air cooling, oil-water cooling, forced oil circulation, etc.

3. By function and purpose:
A: Distribution transformer: Main power source for industrial enterprises, industrial parks, substations, responsible for high and low voltage power distribution and transmission, large capacity, strong stability.
B: Control transformer: Special for machine tools, automated production lines, control cabinets; converts high voltage to 220V/110V/36V/24V/12V, for control circuits, indicator lights, solenoid valves.
C: Isolation transformer: Complete electrical isolation, anti-interference, anti-electric shock, suppress harmonics; commonly used in precision instruments, medical equipment, laboratories, industrial precision measurement and control.
D: Auto-transformer: Single winding tap voltage regulation, can increase or decrease voltage; small size, low cost, no electrical isolation, mostly used for industrial voltage regulation, motor starting.
E: Rectifier transformer: Matching rectifier bridge, rectifier cabinet; electroplating, electrolysis, chemical industry, DC motor drive, rail transit DC power supply dedicated.
F: Inverter transformer: Special for photovoltaic, wind power, energy storage, grid-connected inverters, suitable for direct-to-indirect conversion, grid-connected power supply conditions.
G: Voltage regulating transformer: Contact-type, induction-type regulators, used for industrial experiments, equipment debugging, stable power supply.
H: Filter / Reactor transformer: Suppress harmonics, reactive power compensation, frequency conversion filtering, three-phase imbalance management, matching frequency converters, UPS, frequency conversion units.
I: Special industrial transformers, electric furnace transformers, mine explosion-proof transformers, ship transformers, high-temperature and anti-corrosion industrial transformers.

4. By winding form:
A: Double-winding transformer: Used to connect two voltage levels in the power system.
B: Three-winding transformer: Generally used in power system regional substations, connecting three voltage levels.
C: Auto-transformer: Used to connect different voltage power systems. Can also be used as a common voltage booster or voltage reducer transformer.

5. By core form:
A: Core-type transformer: Used for high-voltage power transformers.
B: Amorphous alloy transformer: Amorphous alloy core transformer uses new magnetic material, with a 80% reduction in no-load current, is an ideal distribution transformer with energy-saving effect, especially suitable for low-load areas such as rural power grids and developing regions.
C: Shell-type transformer: Used for special transformers with large current, such as electric furnace transformers, welding transformers; or for power transformers of electronic instruments and televisions, radios, etc.

6. By core structure:
A: EI type transformer: Most commonly used, low cost, versatile.
B: EE/EF/EPC/PQ/RM type: High-frequency switching power supply, industrial control adapter.
C: Ring-type transformer: Low leakage inductance, low noise, high efficiency, used in precision equipment, medical instruments.
D: C-type / CD-type transformer: Large power, high voltage resistance, used in industrial equipment, medium-frequency power supply.
E: Amorphous / nano-crystalline core transformer: Low loss, energy-saving, high frequency, dedicated to new energy.

7. By insulation and packaging form:
A: Open-type transformer: Bare winding, good heat dissipation, low cost.
B: Encapsulated sealed transformer: epoxy resin encapsulation, moisture-proof, dust-proof, shock-proof, resistant to harsh working conditions.
C: Planar transformer: PCB windings, ultra-thin and lightweight, high-density industrial control, server power supply.

8. Classified by voltage level:
A: Low-voltage industrial transformer: 1kV and below, operating frequency 50Hz/60Hz, standard industrial grid frequency; mostly used for plant power distribution, machine tool control, lighting power supply, three-phase power transformer, and is the most basic and largest category in industrial applications.
B: Medium-voltage industrial transformer: 1kV to 35kV, frequency several hundred Hz to 10kHz; suitable for induction heating, smelting furnaces, medium-frequency power supply, variable frequency speed regulation, electroplating and smelting equipment.
C: High-voltage industrial transformer: above 35kV, operating frequency 20kHz to several MHz; used for industrial switching power supply, photovoltaic inverter, energy storage converter, charging piles, industrial control power supply, high-frequency inverter equipment, with small size, high efficiency, and a significant trend towards lightweight.