25 kVA electricity pole transformer - reliable rural power with 9 kV HV Arrester for surge protection and long-term safety
01 General
1.1 Project Description
A small coastal township in Atlantic Canada relies on overhead distribution lines. Feeders run long distances across open fields and along the coast. The area often experiences thunderstorms in summer and strong wind or ice in winter. Homes and small businesses receive single-phase 120/240 V power from pole transformers installed along the feeders.
The 25kVA electricity pole transformer is designed for this environment. It has a primary voltage of 12,470 GRDY/7,200 V and secondary 120/240 V, operates at 60 Hz, and features aluminium windings, a laminated steel core, ONAN cooling, and an NLTC with ±2×2.5% tap range. It is highly efficient (≥98.87%), has an impedance of 1.9% ±10%, and includes a 9 kV HV arrester for surge protection. It is used to supply a few houses or a small business safely and reliably.
Supply 3–6 houses or a small roadside business.
Be mounted on wooden poles with standard hardware.
Operate in areas with high risk of lightning strikes and switching surges.
Why the 9 kV HV Arrester Matters? The 9 kV arrester keeps the single phase electricity pole transformer safe by quickly diverting sudden voltage spikes, like lightning or switching surges, to the ground before the insulation can be damaged.
This is especially important in rural and coastal overhead networks, where a single strong surge could puncture the insulation, harm the windings, or degrade the transformer oil, leading to failures and outages. The 9 kV rating is carefully chosen to match the system voltage, ensuring the arrester activates before the transformer itself is stressed.
1.2 Technical Specification
25kVA electricity pole transformer specification and data sheet
| Delivered to | Canada |
| Year | 2025 |
| Type | Pole mounted transformer |
| Standard | CSA C2.2-06/C802.1-23 |
| Rated Power | 25KVA |
| Frequency | 60HZ |
| Phase | Single |
| Cooling Type | ONAN |
| Liquid insulant | Mineral Oil |
| Primary Voltage | 12470GRDY/7200 |
| Secondary Voltage | 120/240 V |
| Polarity | Additive |
| Vector Group | Ii6 |
| Winding Material | Aluminum |
| Impedance | 1,9%(±10%) |
| Efficiency | ≥98.87% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 85 W |
| Load Loss at Rated Voltage | 254 W |
| Accessories | 9kV HV Arrester |
1.3 Drawings
25kVA electricity pole transformer dimensions and weight details
02 Manufacturing
2.1 Core
| The transformer has a wound core made of thin steel sheets. It helps magnetic energy move easily between the primary and secondary windings, reducing energy loss. The core is strong and compact, keeping voltage stable, lowering heat and noise, and making the transformer reliable every day. |  |
2.2 Winding
 | Designed for steady performance, this transformer pairs foil LV with wire HV. Copper takes the current, aluminum lightens the weight. They work together. Heat stays managed. Losses stay low. Loads fluctuate, weather shifts, but it keeps running. Simple, effective, a quiet worker in pole-mounted distribution. |
2.3 18kV HV Arrester
| Its 9 kV HV arrester, connected from the HV bushing to ground, protects the transformer by quickly diverting lightning or switching surges before insulation or windings are damaged. With a continuous operating voltage of 7.65 kV and residual voltage below 30 kV, it matches the system voltage while handling currents up to 100 kA. Low partial discharge (<10 pC) and 308 mm creepage distance ensure safe, reliable operation in wet or coastal conditions. |  |
2.4 Final Assembly
 | After we place the core and coils into the sealed steel tank, the whole unit goes through careful welding and a solid anti-corrosion treatment so it can handle years of outdoor, coastal weather. Before and after filling it with mineral oil, we run a full vacuum-drying process to drive out any moisture or trapped air—this step really strengthens the insulation and keeps partial discharge low. With the tank filled and its ONAN cooling system ready, the transformer comes out of final assembly built for long, reliable pole-mounted service. |
03 Testing
04 Packing And Transportation
05 Electricity Pole Transformer: How They Work
A pole-mounted transformer uses electromagnetic induction to step down high-voltage electricity to a level suitable for homes and small businesses. Inside, it has two windings-primary and secondary-wrapped around a magnetic core:
• The primary winding connects to the high-voltage distribution network.
• The secondary winding connects to lower-voltage service lines that deliver 120 V or 240 V to buildings.
Voltage is reduced according to the turns ratio between the primary and secondary windings, providing safe, usable electricity for everyday devices.
