AGL-CS-035 — CCR Output Voltage Abnormally High
The AGL Knowledge Hub | Engineering Case Study Series. A voltage-regulation investigation where progressive circuit impedance increase caused the CCR to operate near its voltage limit — from trend analysis through impedance measurement, sectional testing, thermal inspection, and targeted repairs.
Important: This is an engineering simulation created for training. It is not presented as an actual airport incident. All readings, values, dates and outcomes are illustrative, and no airport, organisation, person or manufacturer is identified or implied.
1Case Study Overview
During a routine CCR performance review, the maintenance team observed that one runway edge lighting circuit required an unusually high output voltage to maintain the selected 6.6 A current.
Although the lighting circuit remained operational, the CCR output voltage had increased from a historical operating value of 2.4 kV to 3.8 kV.
No overcurrent or undercurrent trip had occurred, but the CCR was operating close to its maximum voltage capability.
A systematic investigation identified progressive increase in circuit impedance caused by multiple deteriorated cable joints, aging cable insulation, and one partially open transformer secondary connection.
This case demonstrates that abnormally high CCR output voltage is often an early warning indicator of deteriorating field-circuit conditions.
2Learning Objectives
After completing this case study, the learner should be able to:
- Understand CCR voltage regulation principles.
- Interpret high output voltage conditions.
- Differentiate CCR voltage abnormalities from current abnormalities.
- Analyze circuit impedance increases.
- Investigate cable, connector, and transformer resistance.
- Correlate voltage trends with circuit deterioration.
- Apply preventive maintenance based on CCR voltage behavior.
3System Background
A CCR automatically adjusts output voltage to maintain constant current.
Normal regulation:
High-voltage condition:
The voltage required by the CCR is a valuable indicator of overall circuit health.
4Problem Statement
The reported condition was:
- Selected current: 6.6 A.
- Current regulation normal.
- Output voltage abnormally high.
- No circuit trip.
- All lights operational.
- Voltage increasing over several months.
Why is the CCR requiring unusually high voltage to maintain normal current?
5Initial Observations
| CCR status | Operational |
| Selected current | 6.6 A |
| Actual current | 6.6 A |
| Output voltage | 3.8 kV |
| Historical voltage | 2.4 kV |
| Light operation | Normal |
The important observation was that current remained normal while voltage increased significantly.
6Initial Engineering Hypotheses
The maintenance team considered:
CCR voltage measurement error.
Circuit length increase.
Progressive cable resistance increase.
Multiple high-resistance connections.
Transformer secondary deterioration.
7Voltage Regulation Principle
For a CCR:
With constant current:
Therefore, abnormal voltage is often an impedance problem.
8Test Equipment
The investigation used:
- CCR monitoring system.
- True-RMS multimeter.
- Clamp meter.
- Circuit impedance measurement equipment.
- 5 kV insulation resistance tester.
- Thermal imaging camera.
- Low-resistance ohmmeter.
- Approved AGL circuit test equipment.
- Airport-approved PPE.
9Investigation
Step 1: Verify CCR Performance
Testing with a calibrated load showed:
| Current regulation | Normal |
| Voltage regulation | Normal |
| Output stability | Normal |
The CCR was healthy.
Step 2: Historical Trend Review
CCR voltage records showed:
| 12 months earlier | 2.42 kV |
| 9 months earlier | 2.61 kV |
| 6 months earlier | 2.93 kV |
| 3 months earlier | 3.34 kV |
| Current | 3.82 kV |
The increase was progressive.
Step 3: Circuit Impedance Measurement
Measured impedance:
36 Ω
Historical value:
23 Ω
The circuit resistance had increased substantially.
Step 4: Sectional Resistance Testing
The circuit was divided into sections.
Results:
| CCR–S1 | Normal |
| S1–S2 | Elevated resistance |
| S2–S3 | Elevated resistance |
| S3–S4 | Elevated resistance |
Multiple degraded sections were identified.
Step 5: Thermal Inspection
Thermal imaging revealed:
- Three overheated cable joints.
- Two warm transformer secondary connectors.
- One transformer with elevated terminal temperature.
The heating pattern indicated distributed resistance increases.
Step 6: Transformer Secondary Testing
One transformer showed:
- Stable primary continuity.
- Elevated secondary resistance.
- Intermittent contact resistance.
- Moderate insulation deterioration.
The transformer contributed additional impedance.
10Root Cause
The CCR output voltage became abnormally high because multiple distributed resistance increases accumulated throughout the field circuit.
The contributing factors were:
- Deteriorated cable joints.
- Aging cable insulation.
- High-resistance connectors.
- One partially degraded transformer secondary connection.
The CCR remained operational but required progressively higher voltage to maintain the selected current.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Replaced deteriorated cable joints.
- Replaced damaged connectors.
- Replaced the degraded transformer secondary connection.
- Performed insulation resistance testing.
- Measured circuit impedance.
- Verified CCR output voltage.
- Restored the circuit.
- Updated maintenance records.
- Implemented voltage-trend monitoring.
12Post-Repair Verification
The CCR voltage returned to its normal operating range.
13Root-Cause Analysis
High CCR voltage observed
Healthy
Progressive increase
High
Distributed resistance identified
Joint and connector heating found
Progressive circuit impedance increase
Repair cable joints, connectors, and transformer connection
14Why This Case Was Important
A CCR can maintain current successfully while circuit conditions continue deteriorating.
High voltage is often the earliest measurable symptom of:
- Cable aging.
- Joint deterioration.
- Connector resistance.
- Transformer connection problems.
Voltage trending enables predictive maintenance before current regulation fails.
15Engineering Lessons
High CCR output voltage usually indicates excessive circuit impedance.
High CCR output voltage usually indicates excessive circuit impedance.
Current regulation can remain normal during early circuit deterioration.
Current regulation can remain normal during early circuit deterioration.
Distributed resistance increases are often more difficult to detect than single faults.
Distributed resistance increases are often more difficult to detect than single faults.
Voltage trending is a powerful predictive-maintenance tool.
Voltage trending is a powerful predictive-maintenance tool.
Thermal inspection helps identify high-resistance components contributing to elevated voltage.
Thermal inspection helps identify high-resistance components contributing to elevated voltage.
16Engineer's Decision Point
You observe: Selected current: 6.6 A. Actual current: 6.6 A. CCR output voltage increased from 2.4 kV to 3.8 kV. All lights operational. What should you investigate first?
17Knowledge Check
18Interview Questions
19Frequently Asked Questions
Quick answers about abnormally high CCR output voltage, based on this case study.
Q1What is AGL-CS-035?
AGL-CS-035 is an engineering training case study on a CCR output voltage that had risen abnormally high while still maintaining the selected current. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2How much had the CCR voltage increased?
Output voltage rose from a historical 2.4 kV to 3.8 kV while current stayed at the selected 6.6 A. All lights were operating and no trip had occurred, but the CCR was close to its maximum voltage capability.
Q3Why does normal current with higher voltage matter?
The important observation was that current remained normal while voltage increased significantly. That points to rising circuit impedance, and the CCR is compensating by using more voltage.
Q4What was the root cause?
Multiple distributed resistance increases accumulated through the circuit: deteriorated cable joints, ageing cable insulation, high-resistance connectors and one partially degraded transformer secondary connection.
Q5What should you investigate first?
Measure circuit impedance and inspect cable joints, connectors and transformer secondary connections. Replacing the CCR, increasing the current setting or replacing all transformers is not the right first step.
Q6How was the circuit repaired?
The team isolated the circuit and replaced deteriorated cable joints, damaged connectors and the degraded secondary connection. They tested insulation resistance, measured impedance, verified CCR output voltage, restored the circuit and implemented voltage-trend monitoring.
Q7How was the repair verified?
Output voltage returned to 2.46 kV with current at 6.6 A and circuit impedance of 23 Ω. Light operation was normal and the CCR margin was restored.
Q8Why implement voltage-trend monitoring?
The rise was gradual over several months, so tracking CCR output voltage over time can reveal developing impedance problems before the CCR reaches its limit.
Engineering & Expert Notes
Trend Output Voltage at Each Step
PredictiveA slow rise year on year shows distributed resistance growing. It is a cheap and powerful indicator.
Prioritise Joints and Connectors by Age
PlanningDistributed faults need a programme, not a single repair. Rank by age and exposure.
Look for Heat Where Voltage Is Lost
ThermalWarm connections mark where energy is being wasted. Record conditions.
Set an Action Threshold in Advance
ManagementAgree the voltage margin at which maintenance is triggered so decisions are not made under pressure.
20Case Study Conclusion
Abnormally high CCR output voltage is usually an indication of excessive circuit impedance caused by progressive deterioration of cable joints, connectors, transformer secondary connections, or cable insulation rather than CCR malfunction.
Systematic CCR verification, voltage-trend analysis, circuit impedance measurement, sectional resistance testing, thermal inspection, and targeted field repairs can accurately identify the source of the voltage increase and restore normal regulation margins.
In AGL engineering, high CCR voltage is often the circuit asking for maintenance long before it asks for repair.
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