Introduction
Single phase pole mounted transformers are structurally simple and compact in size. They are typically installed in a hanging manner (on either single or double poles) close to the electrical load points, which shortens the low-voltage supply radius. This makes them suitable for distributed load power supply modes, and they can operate either as single phase units or as three units combined for three phase operation. Currently, they are widely used in regions such as the United States, Canada, Mexico, Southeast Asia, and South America.
HV/LV Ratings
| High Voltage Side | Low Voltage Side | Typical Application / Region | Frequency | Taps (Common) |
| 2400V | 120/240V | North/South America - light industrial, residential | 60 Hz | ±5% or ±2×2.5% |
| 4800V | 120/240V, 240/480V | North/South America - medium distribution | 60 Hz | ±5% |
| 7200V | 120/240V, 347/600V | Most common in North America - residential & commercial | 60 Hz | ±5% |
| 7620V | 120/240V, 277V | North/South America, parts of Asia | 60/50 Hz | ±2×2.5% |
| 7970V | 120/240V, 347/600V, 277V | Industrial areas, generator matching | 60 Hz | ±5% |
| 14400V | 120/240V, 240/480V | North America - suburban, longer feeders | 60 Hz | ±5% |
| 19920V | 240/480V, 277V, 347/600V | Industrial parks, large commercial, HV distribution | 60/50 Hz | ±2×2.5% or None |
Polarity
Polarity requirements vary by region. According to IEEE Std C57.12.20, single phase transformers have both additive and subtractive polarity.
This standard specifies that transformers with a capacity of ≤200kVA and high voltage ≤8660V should be made with additive polarity, while others should have subtractive polarity.
Bushings
| Bushing Type | Possible Numbers | Description / Notes |
| High Voltage (HV) | 1 (Single) | One bushing on top cover; other end grounded inside tank. |
| 2 (Double) | Both bushings on top cover. | |
| Low Voltage (LV) | 2, 3, or 4 | Usually side-mounted. Dual-voltage windings can be connected in parallel or series. |
Completely Self-Protected (CSP)
If the transformer has CSP, it includes arrester(s) and fuse(s) on the HV side, and circuit breaker(s) on the LV side. An LV arrester is optional. CSP integrates multiple protective functions, including lightning impulse protection, overload indication, LV circuit breaker tripping, and short-circuit fuse operation - to achieve comprehensive automatic protection for the transformer.
Structure
The transformer can be built with either a core-type or a shell-type structure. The core material can be amorphous alloy or silicon steel sheets, and both types employ a wound-core design with an open joint.
Core-type: A single core with two coils. The core usually has a top-opening joint, and the winding arrangement typically follows a low-high configuration.
Shell-type: A single coil with two cores. The core often features a side-opening joint, and the winding arrangement may be either low-high-low or low-high.
Oil Tank
The tank is generally made of 2-3 mm cold-rolled steel plate formed into a cylindrical shape. The cover can be connected to the cylindrical body either by a clamping band or by a pressing‑pin structure. Upper and lower lifting lugs must be welded onto the body according to standard requirements. A small air gap is reserved at the top of the tank to accommodate the thermal expansion and contraction of the transformer oil. Depending on performance requirements, radiators are fitted, which can be either corrugated fins or plate‑type radiators.
Conclusion
The design of pole mounted transformers always strikes a balance between standardized structures and customized requirements. Whether it's the choice between core-type and shell-type, or differences in bushing quantity and CSP configurations, everything ultimately serves reliable operation in specific scenarios. VKE Transformer's focus is precisely to help clients achieve this balance. We can assist you in translating project requirements into clear, feasible transformer specifications - and ensure that the final product meets expectations.