The core of a cylindrical pole-mounted transformer is based on the mutual inductance principle of electromagnetic induction, which reduces high-voltage distribution voltage to low-voltage user voltage. Its cylindrical design and pole-mounted installation determine its typical characteristics: compact outdoor design, suitable insulation and heat dissipation, and primarily single-phase operation.
I. Working Principle (Core: Three Steps of Electromagnetic Induction)
Electromagnetism: Alternating current is applied to the high-voltage side (primary winding), generating an alternating current that induces an alternating magnetic flux in the iron core. This flux is conducted along the closed magnetic circuit of the iron core.
Magnetic Coupling: The alternating magnetic flux passes through the low-voltage side (secondary winding), achieving magnetic coupling and energy transfer between the primary and secondary sides.
Electromagnetism: The magnetic flux changes over time, inducing an electromotive force in the secondary winding (Faraday's law of electromagnetic induction); when a load is connected to the secondary side, an output current is generated, completing the voltage conversion.
Key principles: Transformer ratio ≈ turns ratio (U₁/U₂ ≈ N₁/N₂), power is approximately conserved (U₁I₁ ≈ U₂I₂), transformer frequency is constant (my country's power frequency is 50Hz).
II. Core Properties (Structural and Application Dual Attributes)
(I) Structural and Electrical Properties
Phase Number and Capacity: Primarily single-phase, suitable for low-voltage 220V/three-phase unbalanced loads; capacity is mostly 50–500kVA, commonly found in 10kV distribution network step-down.
Core and Windings: The core is often a cylindrical wound core, with uniform magnetic circuit and low no-load loss; windings are mostly epoxy-cast or oil-impregnated insulation, the cylindrical structure optimizes insulation distance and mechanical strength.
Cooling and Insulation: Divided into oil-impregnated (insulating oil also serves as cooling and arc extinguishing) and dry epoxy-cast (maintenance-free, fireproof), suitable for outdoor humid and high/low temperature environments.
Efficiency and Losses: Low no-load loss (especially with wound core), low load loss, and high overall efficiency; small fault impact range and convenient maintenance.
(II) Installation and Operation Characteristics
Installation Forms: Available in single-pole (≤50kVA) and double-pole platform (>50kVA) types, small footprint, can be placed close to the load center, reducing line losses.
Protection Configuration: Standard configuration includes drop-out fuses (short circuit/overload protection) and surge arresters (lightning overvoltage protection), ensuring high safety for outdoor operation.
Environmental Adaptability: Windproof, rainproof, and condensation-proof design, protection level suitable for outdoor use; cylindrical shell facilitates uniform heat dissipation and resistance to external impacts.
III. Core Differences from Ordinary Distribution Transformers
Form: Cylindrical structure + pole-mounted installation, small size, light weight, no need for a distribution room.
Scenarios: Specifically designed for outdoor power distribution terminals, suitable for dispersed loads such as urban streets, rural areas, and streetlights. Maintenance: Oil-immersed systems require regular checks of oil level and quality, while dry systems are basically maintenance-free, resulting in lower overall operating costs.
