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DC ground fault detection

  • US 4,929,901 A
  • Filed: 07/13/1989
  • Issued: 05/29/1990
  • Est. Priority Date: 09/06/1985
  • Status: Expired due to Fees
First Claim
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1. A method of detecting low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising the steps of connecting a resistor across the DC power supply, connecting an indicator between a tapping point relative to the resistor and a ground point such that a ground leakage current in the system closes a ground circuit to activate the indicator means, periodically interrupting said circuit by opening and closing the ground circuit effectively to generate a DC pulse interrupted ground fault signal being substantially a square wave to produce proportional periodic changes in a magnetic field associated with the system while the ungrounded DC system remains substantially operational, and magnetically sensing in a location relative the DC system said magnetic field changes related to said pulse interrupted ground fault signal whereby said magnetic field changes provide the necessary signal for low level ground fault current detection, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

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