Guidebook for Detecting and Mitigating Low-Level DC Leakage and Fault Currents in Transit Systems (2020) / Chapter Skim
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2 Nonintrusive Injection-Based Techniques The nonintrusive active clamp approach involves injecting a high frequency signal into the power line and determining the high frequency impedance of the selected line segment. Segmentation of the line is achieved by applying a virtual blocker at each end of the chosen segment, typically at the traction power substation.
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Nonintrusive Injection-Based Techniques 3 High voltage DC bus Blocking signalBlocking signal Injected signal L i-1 L i Rail InsulatorInsulator Si-1 Si+1Si Figure 1. High frequency impedance detection for DC railway system.
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4 Guidebook for Detecting and Mitigating Low-Level DC Leakage and Fault Currents in Transit Systems 2.1 Segmentation of the DC Electric Network The maximum length of the network allowed to be monitored is as follows: • The nonintrusive injection-based sensor can measure impedances down to 2 Ω, which is equivalent to a line capacitance of 0.795 μF at 100 kHz. The recommended maximum line is 10 km, considering the transmission line modeling at high frequencies.
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Nonintrusive Injection-Based Techniques 5 Two factors must be considered in determining the maximum length of the network allowed to be monitored: 1. Electrical railway structure.
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6 Guidebook for Detecting and Mitigating Low-Level DC Leakage and Fault Currents in Transit Systems For the sensor design, the magnitude of the high frequency voltage needed to be induced on the power line is the determining factor of the design. This value, in conjunction with the desired maximum measurable line impedance, determines the minimum high frequency current level that should be detectable by the current-sensing transformer.
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Nonintrusive Injection-Based Techniques 7 Humidity. The sensor needs to comply with the EN50155 standard with the requirement of 2 × 25 hr at 40°C.
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