An innovative decaying DC component estimation algorithm for digital relaying

Yoon Sung Cho, Chul Kyun Lee, Gilsoo Jang, Heung Jae Lee

Research output: Contribution to journalArticlepeer-review

124 Citations (Scopus)


We propose a new decaying dc component estimation algorithm for digital relaying. Fault currents tend to include a dc decaying component. This component decreases the accuracy and speed of the protection relay operation. The proposed algorithm can estimate and eliminate the dc decaying component from fault current signals after one cycle from the fault instant. Also, it can be applied to a conventional discrete Fourier transform to calculate phasor quantities of fault currents in a digital protection relay. In the proposed algorithm, the dc decaying magnitude and time constant are estimated exactly by integrating fault currents during one cycle. The dc decaying component is eliminated by subtracting the dc value at each sampling instant. To verify the performance of the proposed algorithm, we performed a dc component estimation test and distance protection test using PSCAD/EMTDC. The results of the PSCAD/EMTDC simulation showed that the proposed algorithm can estimate dc components exactly from fault currents and can be applied to digital protection relays for phasor extraction.

Original languageEnglish
Pages (from-to)73-78
Number of pages6
JournalIEEE Transactions on Power Delivery
Issue number1
Publication statusPublished - 2009

Bibliographical note

Funding Information:
Manuscript received August 07, 2007; revised January 02, 2008. Current version published December 24, 2008. This work is the result of the KETEP fostering program and the KESRI Project (R-2007-2-055) funded by the Korean government (MKE). Paper no. TPWRD-00478-2007. Y. S. Cho and C. K. Lee are with the Electrotechnology R&D Center, LS Industrial Systems Co., Cheongju 361-720, Korea (e-mail:, G. Jang is with the School of Electrical Engineering, Korea University, Seoul 136-701, Korea (e-mail: H. J. Lee is with the Department of Electrical Engineering, Kwangwoon University, Seoul 139-701, Korea (e-mail: Digital Object Identifier 10.1109/TPWRD.2008.2005682


  • DC estimation
  • DC magnitude
  • DC time constant
  • Digital protection
  • Discrete Fourier transform (DFT)
  • Fault current

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering


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