Distribution Transformers: Commonly referred to as "distribution transformers," these are static electrical devices that, based on the principle of electromagnetic induction, transform three-phase AC voltage and current to transmit AC electrical energy within distribution systems. Distribution transformers typically operate in distribution networks with voltage levels ranging from 10 to 35 kV (most commonly 10 kV and below) and have capacities of up to 6300 kVA, directly supplying power to end-users.
Classification by Installation Location:
Distribution transformers can be classified by their installation location as either indoor or outdoor. Outdoor installations are further divided into pole-mounted, platform-mounted, and ground-mounted (including pre-installed) types.
Pole-Mounted Transformers: These transformers are installed on a pole structure and can be categorized into single-pole and double-pole types. For distribution transformer capacities of 30 kVA and below (including 30 kVA), single-pole transformer platforms are generally used. These platforms typically support the transformer, high-voltage drop-out fuses, and high-voltage surge arresters on a single concrete pole, with the pole slightly tilted (13°-15°) in the opposite direction of the transformer.
Double-pole transformer platforms are commonly used for transformer capacities ranging from 50 kVA to 315 kVA. These platforms consist of a primary pole and a secondary supporting pole. The primary pole houses the high-voltage drop-out fuses and the high-voltage downleads, while the secondary pole handles the secondary return leads. The double-pole transformer platform is reinforced by the single-pole transformer structure. The advantages of pole-mounted installations include minimal land use, no need for surrounding walls or barriers, and a high elevation of live parts from the ground, reducing the likelihood of accidents. The disadvantages include higher construction costs due to the extensive use of steel materials.
Platform-Mounted Transformers: Platform-mounted transformers are installed on a square platform made of bricks and stones, typically 0.5 to 1 meter high, with the transformer placed on top. This method is generally used for transformers with capacities of 315 kVA and above.
When installing platform-mounted transformers, attention should be given to the following: (1) A solid barrier or wall at least 1.8 meters high should be installed around the transformer, with the gate locked and under the supervision of a designated person. (2) The barrier or wall should provide enough safe operating distance from the transformer. (3) Warning signs such as "High Voltage Danger, No Climbing" should be posted on poles or walls to prevent people and animals from approaching. The advantages of platform-mounted installations include low construction costs and ease of maintenance and inspection. However, they require more land, and small animals can easily climb onto live parts, increasing the risk of accidents due to external forces.
Ground-Mounted Transformers: Ground-mounted transformers are directly placed on the ground, with the high-voltage downleads, drop-out fuses, and surge arresters located on the terminal pole of the line.
When installing ground-mounted transformers, attention should be given to the following: (1) Reliable barriers must be installed around the transformer, with the gate locked and under the supervision of a designated person. (2) Warning signs such as "High Voltage Danger, No Climbing" should be posted outside the barrier. (3) Since the live parts of the transformer are close to the ground, access within the barrier is only permitted after the power supply has been disconnected.
Classification by Cooling Method:
Transformers can be classified by their cooling method into oil-immersed and dry-type transformers. Oil-immersed transformers use oil as the cooling medium, including oil-immersed self-cooled, oil-immersed air-cooled, oil-immersed water-cooled, and forced oil circulation types. Dry-type transformers rely on natural air convection for cooling or may have additional fan cooling, and they are commonly used in high-rise buildings, highway toll stations, local lighting, electronic circuits, and other small-capacity transformer applications.
Oil-Immersed Transformers by Shell Type:
Non-Sealed Oil-Immersed Transformers: This type includes series such as S8, S9, and S10, and is widely used in industrial and mining enterprises, agriculture, and civil construction.
Sealed Oil-Immersed Transformers: This type includes series such as S9, S9-M, and S10-M, and is mostly used in oil and chemical industries where there is significant oil and chemical contamination.
Hermetically Sealed Oil-Immersed Transformers: This type includes series such as BS9, S9-, S10-, S11-MR, SH, and SH12-M, and can be used for distribution in various settings including industrial and mining enterprises, agriculture, and civil construction.
Dry-Type Transformers by Insulating Medium:
Encapsulated Coil Dry-Type Transformers: This type includes series such as SCB8, SC(B)9, SC(B)10, and SCR-10, and is suitable for high-rise buildings, commercial centers, airports, stations, subways, hospitals, factories, and other similar environments.
Non-Encapsulated Coil Dry-Type Transformers: This type includes series such as SG10, and is suitable for high-rise buildings, commercial centers, airports, stations, subways, petrochemical industries, and other applications.
Classification by Voltage Regulation Method:
Transformers can be classified by their voltage regulation method into on-load tap-changing transformers and off-load tap-changing transformers. Off-load tap-changing switches do not have the capability to switch taps while under load, requiring the transformer to be de-energized during tap changing. On-load tap changers, however, can switch taps while the transformer is under load.
Classification by Phase:
The number of phases can classify transformers into single-phase transformers and three-phase transformers. A single-phase transformer has both its primary and secondary windings as single-phase windings. These transformers are simple in structure, small in size, and have low losses, particularly in terms of iron losses, making them suitable for application and promotion in low-voltage distribution networks with low load density.
Three-phase transformers are used to raise or lower voltage in three-phase systems. Typically, a three-phase transformer has three primary windings, which can be connected in different configurations such as delta, wye, or zigzag. The phase difference between the three windings is 120 degrees, which is the common configuration for three-phase 380V connections. Traditional core designs for these transformers include three-phase three-leg, three-phase five-leg, and involute core types.