Discharge Lamp Lighting Device Ground Fault Detection
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Solution Overview
Problem
Existing discharge lamp lighting devices have difficulty detecting ground faults, especially those with high ground fault resistance, as they rely on voltage polarity differences that may not consistently indicate a fault.
Innovation Solution
A lighting device with a controller that calculates power values for both halves of an AC voltage cycle and determines a ground fault if the difference between these values exceeds a threshold for a predetermined time, using a voltage detector and current detector to measure AC voltage and current, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage polarity difference method is used to detect ground faults, then detection capability for low resistance ground faults is improved, but detection capability for high resistance ground faults deteriorates
Solution Approach 1:
The patent changes the detection parameter from voltage polarity difference to power imbalance between half cycles. By calculating the absolute difference between power in the first half cycle and power in the second half cycle, the system can detect ground faults with high resistance that were previously undetectable, while maintaining detection accuracy for low resistance faults.
2Measurement precision
If voltage polarity difference threshold is set low to detect high resistance ground faults, then detection sensitivity is improved, but false detection rate increases
Solution Approach 1:
The patent introduces a time-based feedback mechanism where the system monitors power imbalance continuously and determines ground faults based on sustained conditions. By requiring the power difference to exceed the threshold for a predetermined time period, the system filters out transient anomalies and reduces false detections while maintaining high sensitivity for actual ground faults.
3Measurement precision
If power imbalance detection is implemented, then ground fault detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing controller perform multiple functions: it continues to control the discharge lamp operation while simultaneously detecting ground faults through power imbalance analysis. By utilizing the existing microprocessor and memory resources for dual purposes, the system achieves enhanced detection capability without adding separate dedicated hardware circuits.
Data Source
AI summary
The lighting device of one aspect according to the present disclosure calculates, based on a voltage value of an AC voltage applied to a discharge lamp and a current value of AC current flowing through the discharge lamp, a first power value defined as a value of power supplied to the discharge lamp in a first half period of the AC voltage and a second power value defined as a value of power supplied to the discharge lamp in a second half period of the AC voltage. The lighting device determines that a ground fault has occurred, when an imbalance state in which a difference between the first power value and the second power value is equal to or greater than a threshold value continues for a predetermined time period.