Elevated Isolating Transformer

The Elevated Isolating Transformer is a specialised variant of the standard AGL isolating transformer, optimised for above‑ground installation. Unlike buried or pit‑mounted transformers, this unit is housed in a robust, weather‑resistant enclosure (typically IP65 or higher) and equipped with mounting brackets or flanges for attachment to poles, masts, or structural supports. It is commonly used in areas where soil conditions are unsuitable for burial, where access for maintenance is required, or where the transformer must be positioned near elevated light fixtures such as obstruction lights on masts or approach lighting structures.

The transformer provides the same essential galvanic isolation between the 6.6A (or 20A) primary series circuit and the secondary fixture circuit, ensuring safety and fault containment. It is available in a range of power ratings (15W to 100W) and secondary voltages, matching the requirements of most AGL fixtures. The elevated design simplifies inspection, testing, and replacement, as the transformer is readily accessible without excavation.

The elevated isolating transformer exists for sites where burying a transformer isn't practical or safe — rocky or waterlogged ground, or locations like obstruction lights on masts and towers where the transformer needs to sit close to the fixture it feeds rather than at ground level. Without an above-ground option, these installations would either be compromised on isolation or forced into an impractical and expensive burial effort.

Mounting it above ground also directly supports maintainability: a technician can inspect, test, or swap the unit without excavation, which matters because a failed isolating transformer takes its fixture out of service, and every hour spent digging to reach it is an hour the light stays dark. Faster access means faster restoration of full lighting coverage.

The elevated isolating transformer is deployed in a variety of above‑ground scenarios, including:

• Obstruction Lighting on Masts and Towers: Powering high‑intensity obstruction lights on communication towers, chimneys, or wind turbines, where the transformer is mounted on the structure itself.
• Approach Lighting Structures: Supporting approach lighting systems (e.g., ALSF‑1, ALSF‑2) where transformers are mounted on the approach light stanchions or gantries.
• Airport Beacons and Masts: Powering rotating beacons or heliport beacons mounted on tall masts, with the transformer located at the base or on the mast.
• Apron and Gate Lighting: Where floodlights or guidance fixtures are mounted on poles, the transformer can be integrated into the pole base or mounted on the pole itself.
• Areas with High Water Table or Rock: Where direct burial is impractical due to water logging or hard rock, elevated mounting provides a viable alternative.
• Retrofit and Maintenance‑Friendly Installations: Replacing existing above‑ground transformers or upgrading systems to improve accessibility for maintenance crews.

The transformer is typically mounted using heavy‑duty brackets or clamps, with cable entries via weatherproof glands. It is designed to withstand wind loads, vibration, and temperature variations, with an operating temperature range of -40°C to +55°C.

Rather than sitting in a below-grade pit, the elevated transformer is mounted above ground using heavy-duty brackets or clamps, typically at the base of a mast, stanchion, or pole, or partway up the structure near the fixture it feeds. Cable entries use weatherproof glands to keep the enclosure sealed against wind-driven rain, and the mounting position is chosen to keep the unit accessible for maintenance from a ladder or platform rather than requiring excavation. This above-ground placement is favoured on obstruction-lit masts, approach lighting gantries, and beacon towers, and in ground conditions — high water table, shallow rock, or heavy paving — where digging a pit is impractical.

Electrically, the elevated isolating transformer operates identically to standard AGL transformers: the primary winding is connected in series with the constant‑current loop, and the secondary winding delivers the appropriate voltage to the fixture. The key differentiator lies in its mechanical design and environmental protection:

• Weatherproof Enclosure: The transformer is housed in a sealed, corrosion‑resistant enclosure (typically aluminium or stainless steel) with gasketed covers and cable glands that maintain IP65 or IP66 protection against rain, dust, and UV exposure.
• Mounting Provisions: Integrated brackets, flanges, or mounting holes allow secure attachment to poles, masts, or structural members using U‑bolts, clamps, or bolted connections.
• Thermal Management: The enclosure is designed with heat dissipation features (e.g., fins, ventilation slots with filters) to prevent overheating in direct sunlight while maintaining IP rating.
• Cable Entry: Primary and secondary cables enter through compression glands or cable connectors that maintain the enclosure's weatherproof seal while providing strain relief.
• Earthing Provision: A dedicated earthing terminal (internal or external) ensures proper grounding of the transformer casing for lightning and fault protection.

The transformer is fully compatible with standard CCR dimming profiles and meets all applicable electrical and safety standards. Its elevated design does not compromise electrical performance; efficiency and regulation remain within the same tolerances as conventional transformers.

The elevated enclosure changes the transformer's mechanical environment, not its place in the control chain. An Airfield Lighting Control and Monitoring System (ALCMS) selects the required brightness step based on prevailing RVR, ATC instruction, or pilot-controlled lighting input, and the CCR regulates the whole loop to the corresponding fixed current; the elevated transformer's primary winding carries that current exactly as a buried or handhole-mounted unit would, with no addressable identity of its own and no way to be commanded independently of the loop. Its above-ground mounting does offer one practical advantage during fault-finding: once the CCR's loop voltage monitoring flags a fault in the general area, an elevated unit's weatherproof enclosure can be visually inspected and its connections tested in place without excavation, which is why this variant is often specified on masts, gantries, or structures where field access is already straightforward.

Unlike the buried variant, the elevated transformer is not the seal itself — its windings and core sit inside a weatherproof enclosure, typically powder-coated aluminium or 304/316 stainless steel, rated IP65 or IP66 rather than the fully potted IP68 of a direct-burial unit, because the enclosure is designed to be opened for inspection and connection testing rather than sealed permanently. Gasketed covers keep the interior dry, brackets, flanges, or U-bolts provide the mounting to a pole, mast, or structural support, and vents or fins allow the winding to dissipate heat without breaking the IP seal, which a fully potted unit does not need but a serviceable enclosure does. Complete units typically weigh 3.0–6.0 kg depending on power rating and enclosure material, and internal wiring terminates at accessible terminal blocks rather than sealed splice connectors, since the enclosure itself — not the connection — is what keeps moisture out.