What is a ferroresonant CCR?
A constant current regulator that holds the loop current with a saturating transformer and a resonant capacitor — regulation built into the magnetics, not fired by thyristors.
A ferroresonant CCR uses a ferroresonant transformer: a transformer whose core partly saturates and is tuned by a resonant capacitor. A magnetic shunt in the core limits and steadies the current, so the output stays close to the set value when the supply voltage varies. The regulation is passive, built into the magnetics rather than fired by a thyristor and control board as in a thyristor CCR.
Intensity steps are made by switching taps or capacitors with contactors. The design is robust and has few electronic parts, but it is heavy and bulky, its step currents are fixed by the taps or capacitors, the output waveform may not be a clean sine unless it is filtered, the output can be sensitive to supply frequency on a generator supply, and an ageing capacitor or a worn contactor changes the current. Use a true-RMS meter, never open a live series circuit, and discharge the capacitors before working inside the unit.
- Supply. The supply feeds the primary winding through the tap or step chosen.
- Saturate. The secondary section of the core partly saturates, tuned by the resonant capacitor.
- Limit. The magnetic shunt and saturation hold the output current near the set value as the supply varies.
- Deliver. The secondary feeds the series loop with the set current.
- Select. The step selector switches taps or capacitors to give each intensity step.
- Check. Measure the current on each step with a true-RMS meter and log it against the baseline.
Frequently Asked Questions
Q1What is a ferroresonant CCR?
A constant current regulator that holds the series-circuit current with a ferroresonant transformer: a transformer whose core partly saturates and is tuned by a capacitor. The regulation is passive, so the output current stays nearly constant as the supply voltage varies, without thyristors or a control board in the power path.
Q2How is it different from a thyristor CCR?
A thyristor CCR measures the output current and fires thyristors at a chosen angle to correct it. A ferroresonant CCR gets its regulation from the magnetic design of the transformer and its capacitor. It has fewer electronic parts, but it is heavier and bulkier and gives less fine adjustment of each step current.
Q3What does the resonant capacitor do?
It is connected to the secondary side and tuned with the winding so the core saturates in a controlled way. That saturation is what holds the output steady against supply changes. If the capacitor ages or fails, the regulation is lost.
Q4How are the intensity steps set?
Typically by switching taps or capacitors with contactors, so each brightness step gives a different set current. The exact method varies by design, so check the manufacturer's manual.
Q5What should be checked on a ferroresonant CCR?
The capacitors for swelling, leakage or reduced value, the contactors and tap connections for wear and tightness, the transformer for heat and abnormal noise, and the output current on each step with a true-RMS meter, compared with the commissioning baseline.
Q6What are the main safety points?
Never open a live series circuit, since the CCR tries to hold the set current and the voltage across the break can rise to a dangerous level. Isolate and lock out the supply, prove it dead, and discharge the capacitors before working inside the unit.
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