Q: What may happen if I don’t trace the signal fault in DC system?
A: Multiple grounds can occur on the dc system at the same time. This situation becomes critical when the combined ground resistance becomes so low that high-voltage circuit breaker control schemes are unable to open or close breakers when required or dc system circuit breakers and or fuses open due to over current resulting in de-energization of vital operating equipment.
There are some other bad consequences due to ground fault. Please click HERE for more consequences and solutions.
Q: What are the causes of DC ground fault?
A: Some common sources of low resistances to ground include:
- Moisture in conduit
- Junction boxes or switch/sensor terminations
- Wire splices soaking in water
- Degraded cable or wire insulation caused by aging
- Environmental conditions
- Wild habitat and constant abrasion from vibration
- Sharp objects piercing cable and wire insulation
- Wires that have pulled out of their terminations and touch ground or water
- Failed capacitors or semiconductor surge suppressors.
Q: What are the principles of tracing the signal fault?
A: There are 3 methods for signal tracing in circuit which is with earth fault:
1). Traditional Method: Sectionalization
Traditional ways of fault location in DC system involves sectionalization or interruption of DC branches to isolate the ground fault.
2). Current Injection
This method will inject a low-frequency AC signal and use this AC signal to locate the ground fault in the DC system.
3). Use Measurement Bridge
For online fault location, ground fault locator adopts the measurement bridge (switchable resistor) inside the signal analyzer to analyze voltage, current and grounding resistance. Then it uses signal detector to pinpoint the fault.
Q: What are the advantages of using switchable bridge (resistor) measurement?
A: It does not need injection of current signal to tested system and thus no relay tripping. It is more effective for fault location and safe to the tested circuits.
Q: How do you bypass the interference during live (online) signal tracing?
A: There is always interference caused by distributed capacitance in live (online) measurement. To bypass this interference and trace the fault faster, in firmware we use very low measurement frequency; in hardware, we use high sensitive current sensor for signal tracing.
Q: How do you avoid relay tripping during signal tracing?
A: We are using very low measurement current (lower than 5mA). This will not cause relay tripping in live signal tracing.