Different CCR technologies
Thyristor, saturable reactor, moving coil and switch-mode: four ways to hold one constant current in a series circuit, differing in control method, moving parts and waveform.
Every constant current regulator does the same job: it holds a fixed current in a series lighting circuit, and the selected intensity step sets that current. What differs is the power stage. A thyristor CCR fires a pair of thyristors at a chosen angle. A saturable reactor is controlled by a DC winding. A moving-coil regulator changes the coupling by moving a coil. A switch-mode regulator switches at high frequency and filters the result. Other designs, such as the ferroresonant regulator, are also widely used.
In thyristor, switch-mode and saturable-reactor designs the loop that keeps the current right is the same idea: measure the output, compare it with the step, and correct. A moving-coil regulator holds the current largely through the magnetic balance of its coil rather than electronic feedback, as the design provides. The difference shows up in the maintenance. A moving-coil type has moving parts to inspect, a thyristor type has a chopped waveform that needs a true-RMS meter, and every type has heat to manage. Terms and designs vary between makers, so check the data for the unit in front of you.
Thyristor and switch-mode regulators use electronic switching in the power stage. They have no moving power parts but need cooling and a suitable meter.
Saturable-reactor and moving-coil regulators control the current through magnetic coupling. The moving-coil type adds mechanical parts to inspect.
| Aspect | Thyristor | Saturable reactor | Moving coil | Switch-mode |
|---|---|---|---|---|
| Control method | Anti-parallel thyristors fired at a set angle in each half-cycle | A DC control current in a reactor winding changes how much the reactor passes | A secondary coil moves relative to the primary, changing the coupling | Fast switching of the supply with the pulse width varied, then filtered |
| How it holds current | A current sensor feeds the control board, which adjusts the firing angle to hold the set step | The control current is adjusted to hold the set step, as the design provides | The coil position is set for each step, as the design provides | A current sensor feeds the controller, which adjusts the pulse width to hold the set step |
| Moving parts | None in the power stage; a fan may cool it | None in the power path | Yes: the coil and its drive | None in the power stage; a fan may cool it |
| Output waveform | Chopped; measure with a true-RMS meter | Check the maker’s data for the unit | Close to the supply waveform | Filtered; check the maker’s data for the unit |
| Typical position | Common in modern CCRs | Older designs, still in service on some airfields | Older mechanical designs, still in service on some airfields | Newer solid-state designs |
| Heat and cooling | Power stage and transformer heat removed by heatsink and fan | Reactor and transformer heat; check the maker’s cooling data | Winding heat and the drive; check the maker’s cooling data | Switching devices and filter heat removed by heatsink and fan |
| Watch points | Firing and control board, thyristors, fan, filter, protection settings | Control winding, reactor condition, step accuracy | Coil drive and travel, wear, step accuracy, lubrication as the maker requires | Switching stage, filter, fan, control board, protection settings |
What to check on CCRs
Output current at each step
Measure the output at every step with a meter suited to the waveform, and compare it with the setting.
Waveform and meter
A chopped waveform needs a true-RMS meter. Check the maker’s data for the meter and method for the type in use.
Moving parts and wear
On a moving-coil type, check coil travel, drive and wear. Solid-state types have no moving power-stage parts but a fan to check.
Heat and cooling
Check fans, filters, heatsinks and ventilation. Heat is the common enemy of every regulator.
Protection and alarms
Check overcurrent and open-circuit protection, and that alarms reach the control system, as the standard requires.
Isolate before work
Never open a live series circuit. Isolate, lock out and prove the circuit dead before work.
Frequently Asked Questions
Q1What do all CCR technologies have in common?
Every constant current regulator holds a fixed current in a series lighting circuit, and the selected intensity step sets that current. They differ in how they do it: by switching the supply with thyristors, by controlling a saturable reactor, by moving a coil in a transformer, or by high-frequency switching.
Q2How does a thyristor CCR hold the current?
A pair of anti-parallel thyristors is fired at a chosen angle in each half-cycle. A later firing angle passes less of the waveform and lowers the output. A current sensor on the output feeds the control board, which adjusts the firing angle to hold the set step. The output waveform is chopped, so measure it with a true-RMS meter.
Q3What is a moving-coil CCR?
It is a constant-current transformer whose secondary coil can move relative to the primary. Moving the coil changes the coupling between them, which changes the current delivered to the circuit. It is a mechanical design, so it has moving parts that need inspection.
Q4Which technology should I choose?
That depends on the airport's circuit, the standard, the maker's data and the maintenance practice on site. Compare control method, moving parts, waveform, efficiency, size and spares, and follow the specification for the project rather than a generic rule.
Q5What limits and requirements apply?
Ratings, accuracy, protection and test limits come from the standard, such as IEC 61822 or FAA AC 150/5345-10, and from the manufacturer's data for the unit. Use the requirements for your site, and never open a live series circuit; isolate, lock out and prove the circuit dead first.
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