150W Isolating Transformer

The 150W Isolating Transformer is a high‑power isolating transformer for 6.6A AGL series circuits, sitting above the standard 45‑100W range while the 200W, 300W, and 500W variants cover the tiers above it. With a secondary rating of 150W, it is designed for demanding airfield lighting applications requiring elevated luminous intensity, without stepping up to the rarer extreme‑power tiers.

This transformer features a substantially larger core, heavier‑gauge windings than the standard 45‑100W range, and advanced thermal management to handle the extreme power dissipation. It provides the same galvanic isolation and constant‑current transfer as lower‑power variants, but is built to withstand the significant thermal and electrical stresses associated with high‑power operation. While relatively uncommon, it is indispensable for specialised applications such as very high‑intensity approach lighting systems, large‑scale obstruction lighting, and critical runway installations where maximum output is mandated.

The 150W isolating transformer exists for demanding lighting applications that need meaningfully more output than the standard 45–100W range but don't require the rare, extreme-power variants above it. It fills that gap while performing the same fundamental role as every transformer in the family: isolating a higher-power fixture from the shared series loop so it can be maintained, tested, or replaced without affecting the rest of the circuit.

The larger core and heavier windings exist to manage the additional heat that comes with higher power transfer, ensuring the transformer's reliability keeps pace with the demanding lighting systems — approach lighting, large obstruction arrays, critical runway installations — that call for a 150W rating in the first place.

The 150W isolating transformer is deployed in the most extreme AGL applications, including:

• Very High‑Intensity Approach Lighting: ALSF‑2 configurations requiring maximum luminous output for CAT III operations, with high‑power barrettes and crossbars.
• High‑Intensity Obstruction Lights: High‑intensity white flashing obstruction lights on the tallest structures (e.g., >200m) requiring up to 200,000 cd peak intensity with 150W lamps.
• Large Airport Beacons: High‑power rotating beacons and heliport beacons with 150W halogen or high‑output LED equivalents.
• Sequenced Flashing Lights: High‑intensity flashing approach lights requiring high instantaneous power.
• Multiple High‑Power Fixtures: Configurations where a single transformer powers multiple high‑intensity fixtures (e.g., two 65W fixtures or combinations of lower‑power fixtures).
• Critical CAT III Runway Lighting: Some CAT III runways use 150W transformers for edge and centreline lights where maximum intensity is mandated by operational requirements.
• Military and Specialised Airfields: Military airfields and specialised operations often require 150W transformers for enhanced visibility in combat or extreme weather conditions.

The transformer is typically installed in large handholes or pits with enhanced ventilation, given the substantial heat dissipation. It uses standard L‑823 primary connectors and heavy‑gauge secondary cabling (≥ 4mm²) to handle the increased current.

The 150W transformer requires a larger handhole or pit with enhanced ventilation to handle its substantial heat dissipation, installed adjacent to the CAT III fixture, beacon, or obstruction light it serves. The primary is spliced into the series loop with a standard L-823 connector, and secondary cabling of at least 4mm² is run to the fixture to keep voltage drop within limits at this power level. Because several such transformers may be feeding closely spaced high-intensity fixtures on a CAT III runway, pit spacing and access are planned so each unit can be tested and replaced without disturbing neighbouring transformers on the same loop.

The 150W transformer operates on the same electromagnetic induction principle as other isolating transformers, but with significant design optimisations for extreme high‑power operation. The primary winding is connected in series with the 6.6A constant‑current loop. The primary current induces a secondary voltage—typically 22.7V (for a 150W lamp at 6.6A, V = P/I = 150W/6.6A ≈ 22.7V) or 24V/48V for specialised configurations.

Specific design features for the 150W variant include:

• Extra‑Large Core Cross‑Section: The core is significantly larger than lower‑power variants to handle the high flux density and prevent saturation, especially at maximum current.
• Heavy‑Gauge Windings: Primary and secondary windings use the thickest copper wire in the product family to minimise I²R losses and prevent overheating at full load.
• Advanced Thermal Management: The encapsulation compound is specially formulated with high thermal conductivity, and the form factor often includes cooling fins, a larger surface area, or enhanced heat dissipation features.
• Optimised Turns Ratio: Designed for a secondary voltage around 23V at 6.6A, providing the required power while maintaining efficient primary‑secondary coupling.
• Regulation Performance: Maintains secondary voltage within ±5% across the full dimming range (2.8A to 6.6A), though regulation at the lowest steps may be slightly reduced due to the high power rating.
• Robust Short‑Circuit Protection: The leakage impedance limits secondary fault currents, though the extremely high power means short‑circuit conditions must be addressed immediately to prevent damage.

The 150W transformer occupies the same position in the control chain as any other isolating transformer: 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 (2.8A–6.6A, 5-step). The transformer has no addressable identity of its own — it converts whatever current the loop is carrying at that moment into roughly 22.7V on the secondary side, and cannot be commanded independently of the rest of the loop. Because this variant is typically sized to feed a parallel group of fixtures rather than one lamp, a loop fault detected upstream by the CCR's voltage monitoring can mean more on this circuit than usual: it may represent the loss of an entire fixture group rather than a single light, which is why the combined-load behaviour covered next matters as much as the fault-detection principle itself.

Sized to feed a parallel fixture group rather than a single lamp, the 150W transformer carries a proportionally larger winding than the single-fixture ratings, but the construction principle is unchanged: a laminated core wound for a 150W secondary is enclosed in a moulded shell and fully encapsulated — vacuum-impregnated and back-filled with epoxy or polyurethane resin — which gives the completed unit, typically 8.0–12.0 kg, its IP68 rating without a separate gasketed enclosure. Insulation is specified to Class H, mandatory at this size for the continuous operating temperature the winding reaches. Leads terminate in sealed L-823 splice connectors rated for burial and continuous immersion, and the base can housing the unit is sized to accommodate the additional splice connections a parallel fixture group requires.