45W Isolating Transformer

The 45W Isolating Transformer is the industry‑standard single‑phase transformer for Airfield Ground Lighting. It is the most common power rating in AGL series circuits, used to power a vast majority of runway and taxiway lighting fixtures. With a secondary power rating of 45W, it is designed to drive 45W halogen lamps (the traditional standard for runway edge lights) and is equally suitable for LED equivalents with similar power consumption.

The transformer provides essential galvanic isolation between the high‑voltage series loop (primary) and the low‑voltage lamp circuit (secondary), ensuring safety, fault containment, and the ability to remove individual fixtures without interrupting the series current. Its robust construction, fully encapsulated design, and adherence to international standards make it a reliable workhorse in airfield lighting systems worldwide.

The 45W isolating transformer exists as the default building block for the majority of runway and taxiway edge lighting worldwide, sized specifically to match the traditional 45W halogen lamp that has long been the standard fixture on these circuits. Its purpose is to isolate that fixture from the shared series loop, so any individual light can be removed, tested, or replaced without breaking the current path to every other fixture on the same circuit.

Because it's built to the same robust, fully encapsulated standard as every transformer in the family, its reliability is what lets an airfield trust a series circuit carrying dozens or hundreds of these units at once — a single weak transformer in that chain would be a single point of failure for the whole loop, which is exactly what the design is meant to avoid.

The 45W isolating transformer is the default choice for a wide range of AGL applications, including:

• Runway Edge Lights: High‑intensity edge lights on precision approach runways (CAT I, II, III) using 45W halogen or LED.
• Runway Centreline Lights: Flush‑mounted centreline lights on precision runways.
• Runway Threshold and End Lights: Green threshold lights and red end lights.
• Touchdown Zone Lights (TDZ): Flush‑mounted lights in the touchdown zone of precision runways.
• Approach Lighting Systems: Many barrette and crossbar fixtures in ALSF‑1, ALSF‑2, and other approach lighting configurations.
• Taxiway Centreline and Edge Lights: Medium‑ to high‑intensity taxiway fixtures.
• Stop Bars and Clearance Bars: Red and yellow wing bar lights at runway holding positions.

The transformer is typically installed in handholes, concrete pits, or direct‑buried enclosures adjacent to each fixture, using L‑823 primary connectors and secondary cables. Its widespread use makes it the most commonly stocked and replaced AGL transformer.

As the standard transformer for precision-runway edge, centreline, threshold, and touchdown zone fixtures, the 45W unit is installed in a handhole, concrete pit, or direct-buried enclosure immediately adjacent to the light it feeds, in line with the fixture spacing set out along the runway or taxiway. The primary side is spliced into the series loop using an L-823 connector sealed against moisture, and the secondary leads run a short distance to the fixture. Its high installation volume means the enclosure and cable route are usually designed around this transformer as the base case, with other wattages substituted into the same pit footprint where a fixture's power demand differs.

The 45W transformer operates on the principle of electromagnetic induction. The primary winding is connected in series with the 6.6A constant‑current loop. The primary current creates a magnetic flux in the core, which induces a secondary voltage—typically 6.6V (for a 45W lamp at 6.6A, V = P/I = 45W/6.6A ≈ 6.8V) or 12V/24V for other lamp configurations. The secondary is connected to the lamp or LED driver, supplying the required current and voltage.

Key performance features of the 45W design:

• Optimised Turns Ratio: Designed to deliver the correct secondary voltage at 6.6A primary current, ensuring maximum light output at full intensity.
• Low Core Loss: High‑grade silicon steel laminations minimise no‑load losses, improving efficiency across the entire dimming range (2.8A to 6.6A).
• Excellent Voltage Regulation: Maintains secondary voltage within ±5% over the full current range, ensuring consistent light output at all brightness levels.
• High Thermal Capacity: The 45W power level generates manageable heat, and the fully encapsulated design provides effective heat dissipation to the surrounding soil or concrete.
• Robust Short‑Circuit Protection: The transformer’s leakage impedance limits secondary fault currents, protecting the loop and minimising the risk of CCR tripping.

The 45W 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 6.8V, or 12V/24V for other configurations, and cannot be commanded independently of the rest of the loop. This wattage is the standard rating for a single runway or taxiway edge light, so a fault here is detected exactly as described for the isolating transformer generally: a CCR-monitored voltage rise flags increased loop impedance without distinguishing an open-circuit lamp from a failed transformer, and sectionalised field testing narrows the fault to the specific fixture position.

The 45W unit — the standard rating for a single runway or taxiway edge light — is built as a fully encapsulated, potted assembly: the primary and secondary windings around a laminated core are enclosed in a moulded outer shell, vacuum-impregnated, and back-filled with epoxy or polyurethane resin so there is no internal cavity for water to collect in. That encapsulation is what gives the unit its IP68, submersible rating; there is no separate gasket or seal to inspect or fail. Winding insulation is specified to Class F or Class H depending on the manufacturer, and the complete unit typically weighs 3.0–5.0 kg. Primary and secondary leads terminate in sealed L-823 splice connectors rated for direct burial and continuous immersion, and the transformer sits in its own base can adjacent to the fixture it feeds, secured by the surrounding backfill rather than mechanical fasteners.