Directional overcurrent relay using superconducting fault current limiter voltage and method for correcting the same

Patent metadata

Field	Value
Publication number	US-11018501-B2
Application number	US-201816199130-A
Country	US
Kind code	B2
Filing date	Nov 23, 2018
Priority date	Jul 4, 2018
Publication date	May 25, 2021
Grant date	May 25, 2021

Abstract

A directional overcurrent relay using a superconducting fault current limiter voltage as a relay element includes: a current measuring circuit measuring a current of a line connected from a system power source to a load, a voltage measuring circuit measuring a voltage at both ends of a superconducting fault current limiter connected to the line, and a correcting circuit correcting a tripping time Ttrip by using a fault current If that is the current of the line and a superconducting fault current limiter voltage VSFCL that is the voltage at both ends of the superconducting fault current limiter and the tripping time Ttrip is maintained consistently regardless of whether the superconducting fault current limiter operates or not.

First claim

What is claimed is:

1. A directional overcurrent relay using a superconducting fault current limiter voltage as a relay element, the directional overcurrent relay comprising:
a current measuring circuit measuring a current of a line connected from a system power source to a load;
a voltage measuring circuit measuring a voltage at both ends of a superconducting fault current limiter connected to the line; and
a correcting circuit correcting a tripping time T trip by using a fault current I f that is the current of the line and a superconducting fault current limiter voltage V SFCL that is the voltage at both ends of the superconducting fault current limiter, wherein the tripping time T trip is maintained consistently regardless of whether the superconducting fault current limiter operates or not,
wherein the correcting circuit is configured to calculate a characteristic variable M allowing a decreased amount of the fault current I f due to the operation of the superconducting fault current limiter to be compensated by adding an amount of the superconducting fault current limiter voltage V SFCL modified by a modification factor α to the decreased amount of the fault current I f , and configured to correct the tripping time T trip by using the characteristic variable M.

2. The directional overcurrent relay of claim 1 , wherein when a fault occurs, the correcting circuit modifies the superconducting fault current limiter voltage V SFCL by using the modification factor α that is preset by a ratio I f /I f SFCL of the current measured at the line according to whether the superconducting fault current limiter operates and an impedance Z SFCL of the superconducting fault current limiter, and calculates the characteristic variable M.

3. The directional overcurrent relay of claim 1 , wherein the correcting circuit maintains a time lever value TD and a current tap value I pickup that are preset, and corrects the tripping time T trip by controlling the characteristic variable M according to the superconducting fault current limiter voltage V SFCL .

4. The directional overcurrent relay of claim 1 , further comprising:
a trip signal transmitting circuit transmitting a trip signal to the breaker and operating a breaker that blocks the fault current I f flowing to the load when the tripping time T trip is reached.

5. A method for correcting a directional overcurrent relay that uses a superconducting fault current limiter voltage, the method comprising:
measuring a fault current I f that is a current of a line connected from a system power source to a load;
measuring a superconducting fault current limiter voltage V SFCL that is a voltage at both ends of a superconducting fault current limiter connected to the line; and
correcting a tripping time T trip by using the fault current I f and the superconducting fault current limiter voltage V SFCL , wherein the tripping time T trip is maintained consistently regardless of whether the superconducting fault current limiter operates or not,
wherein the correcting the tripping time T trip includes calculating a characteristic variable M allowing a decreased amount of the fault current I f due to the operation of the superconducting fault current limiter to be compensated by adding an amount of the superconducting fault current limiter voltage V SFCL modified by a modification factor α to the decreased amount of the fault current I f , and correcting the tripping time T trip by using the characteristic variable M.

6. The method of claim 5 , wherein
the modification factor α is preset by a ratio I f /I f SFCL of the current measured at the line according to whether the superconducting fault current limiter operates and an impedance Z SFCL of the superconducting fault current limiter.

7. The method of claim 5 , wherein in the correcting the tripping time T trip , a time lever value TD and a current tap value I pickup that are preset are maintained, and the tripping time T trip is corrected by controlling the characteristic variable M according to the superconducting fault current limiter voltage V SFCL .

8. The method of claim 5 , further comprising:
transmitting a trip signal for operating a breaker that blocks the fault current I f flowing to the load when the tripping time T trip is reached, to the breaker.

Assignees

• Foundation Soongsil Univ Industry Cooperation

Inventors

• Lim Sung Hun
• Lim Seung Taek

Classifications

• H02H9/023 Primary

  Current limitation using superconducting elements · CPC title

• Y02E40/60

  Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment · CPC title

• H02H7/001

  for superconducting apparatus, e.g. coils, lines, machines · CPC title

• H02H3/006 Primary

  Calibration or setting of parameters · CPC title

• H02H3/093 Primary

  with timing means {(in general H02H3/027; thermal delay H02H3/085; timing means for undervoltage protection H02H3/247)} · CPC title