Hybrid Passive-Overcurrent Relay for Detection of Faults in Low-Voltage DC Grids

Khaled A. Saleh, Ali Hooshyar, Ehab F. El-Saadany

Research output: Contribution to journalArticlepeer-review

124 Scopus citations


Detection of high-resistance faults on meshed low-voltage dc grids poses a challenge, as such faults have very low fault current magnitudes. This paper proposes a hybrid passive-overcurrent relay to overcome this problem. The proposed relay consists of one current and one voltage transducer, as well as two passive elements: 1) an inductor; and 2) a capacitor. For bolted and relatively low-resistance faults, the relay uses a simple overcurrent function to detect the resultant high fault current magnitudes within 2 ms. On the other hand, for relatively high-resistance faults, a real-time discrete wavelet transform is used to detect the voltage transients generated by the relay passive elements in less than 5 ms. Furthermore, the proposed relay is inherently capable of identifying the type of fault. The proposed approach relies on local-bus measurements to detect and classify various types of faults with resistance up to 200 ohms. Analytical modeling proves that the proposed approach is system independent. Testing the hybrid passive-overcurrent relay on a ±750 V meshed TN-S dc grid reveals that the proposed relay is fast, sensitive, and selective under various conditions.

Original languageBritish English
Pages (from-to)1129-1138
Number of pages10
JournalIEEE Transactions on Smart Grid
Issue number3
StatePublished - May 2017


  • Discrete wavelet transform (DWT)
  • high-resistance fault
  • low-voltage dc (LVdc) grid
  • overcurrent protection


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