Constant Current Regulator

A Constant Current Regulator (CCR) is a specialised power supply used in airfield ground lighting (AGL) systems. It converts the mains supply into a constant current output, typically 6.6 amperes, which is fed into a series circuit that powers all the lights on a particular runway, taxiway, or approach lighting system. The CCR ensures that every fixture in the loop receives the same current, so that all lights burn at the same intensity regardless of how many lights are connected or changes in the circuit impedance. This is essential for maintaining uniform brightness and safe visual guidance. Modern CCRs are available in different technologies, including thyristor (SCR), IGBT, and ferroresonant types, each offering specific advantages in efficiency, reliability, and control.

The CCR exists because the series-circuit topology used across AGL systems requires every fixture on a loop to receive exactly the same current regardless of how many fixtures are connected or how circuit impedance varies over the loop's length, a requirement that ordinary constant-voltage power distribution cannot satisfy. Without the CCR forcing a fixed current through the whole loop, some fixtures would burn brighter or dimmer than others depending on their position in the circuit, undermining the uniform-intensity visual reference that runway and taxiway lighting exists to provide in the first place. Its purpose is therefore foundational to the entire AGL power architecture: every other power-side component described elsewhere in this library — UPS, generator interface, distribution panel, monitoring systems — exists to keep the CCR itself powered, protected, and controllable, because the CCR is what actually converts raw electrical supply into the uniform current the lighting system depends on.

CCRs are installed in airfield electrical rooms or equipment shelters, typically near the runway or taxiway they serve. They are used in all AGL applications that require a series circuit, including:

• Runway Lighting: Edge lights, centreline lights, threshold lights, and touchdown zone lights.
• Taxiway Lighting: Edge lights, centreline lights, and stop bars.
• Approach Lighting: All approach lighting systems (ALSF-1, ALSF-2, MALS, etc.) that use series circuits.
• Obstruction Lighting: Some obstruction lighting systems may also use CCRs.
• Heliport Lighting: For helipad lighting circuits.

A typical airfield may have multiple CCRs, each dedicated to a specific lighting circuit (e.g., one for runway edge lights, one for centreline, one for taxiways).

CCRs are floor-mounted on a concrete plinth or wall-mounted within the electrical equipment room or shelter that serves the circuit, positioned close to the runway or taxiway to minimise the length of the high-voltage series loop. Incoming mains and control/communication cabling enter from below through a cable trench or duct, while the high-voltage output feeds the series circuit and isolating transformers via its own dedicated cable route, kept separate from mains wiring. The regulator frame is bonded to the room's earthing system, and clearance is left on the ventilated sides and front access panel per the manufacturer's cooling and maintenance requirements. A typical equipment room houses several regulators side by side, each dedicated to one lighting circuit (edge, centreline, taxiway, and so on).

The CCR takes the incoming AC mains (typically 230V or 400V) and regulates it to provide a constant current output, usually 6.6A RMS, with a high open-circuit voltage (up to several thousand volts) to drive the series circuit. The CCR uses a control loop that continuously monitors the output current and adjusts the voltage to maintain the set current despite changes in the load (e.g., due to lamp failures or temperature variations). The output current is adjustable in steps (typically 5 brightness levels: 2.8A, 3.4A, 4.1A, 5.2A, 6.6A) to provide different light intensities for various weather conditions (clear, mist, fog). The CCR includes protection features such as overcurrent, overvoltage, short-circuit, and earth fault detection. Modern CCRs often have digital control and communication interfaces for remote monitoring and integration with Airfield Lighting Control and Monitoring Systems (ALCMS).

A CCR is generally housed in a floor-standing or wall-mounted steel cabinet, powder-coated for corrosion resistance and fitted with lockable doors, ventilation louvres, and a cable gland plate at the base for incoming mains and outgoing series-circuit cabling. Internally, the cabinet is arranged in distinct sections: an input section with isolator, circuit breaker, and input filtering; a power conversion section (transformer, thyristor bridge, IGBT module, or ferroresonant core, depending on technology); an output section with current transducers and output isolation switching; and a control section housing the regulation electronics, HMI, and terminal blocks, usually on a separate sub-panel to isolate it from heat and electrical noise in the power section. Forced-air cooling with filtered fan intakes is common on higher-power units, while smaller regulators may rely on natural convection through the cabinet's louvred sides. Earthing bars, surge arrestors, and clearly labelled terminal strips are provided for the incoming supply and outgoing series circuit, and the cabinet is rated for its intended installation environment, whether an equipment room or an outdoor enclosure.