A method for compensating for a remote line end infeed effect in a distance protection relay during determination of a distance (d) to a resistive fault on a three-phase power transmission line, where a fault current (IF) flows through the fault resistance (RF), the method comprising:
- calculating a fault loop impedance (Zrelay) by dividing a fault loop voltage (Vrelay) by a fault loop current (Irelay) measured from one end (A) of the transmission line, where the fault loop voltage (Vrelay) is composed of the respective phase voltages (Vph1, Vph2, Vph3) and the fault loop current (Irelay) is composed of the respective phase currents (Iph1, Iph2, Iph3) of those phases which are involved in the fault,
- determining a shift of the fault loop impedance (ΔZ), determining the distance to fault (d) by shifting the fault loop impedance (Zrelay) by the determined shift (ΔZ),
- determining the shift of the fault loop impedance (ΔZ) from the fault loop impedance (Zrelay), the impedance of the transmission line for the positive current sequence (Z1L) and the phase angle (γ) of a complex fault current distribution factor (kF), according to the equation
- Δ
-
-
- Z
- _
- =
- R
- relay
-
- X
- 1
-
-
- L
- -
- R
- 1
-
-
- L
-
- X
- relay
- R
- 1
-
-
- L
-
- tg
-
- (
- γ
- )
- +
- X
- 1
-
-
- L
-
- (
- 1
- -
- j
- ·
- tg
-
- (
- γ
- )
- )
- ,
- where Zrelay=Rrelay+jXrelay, Z1L=R1L+jX1L and where the fault current distribution factor (kF) is the ratio of the fault loop current (Irelay) to the fault current (IF),
- calculating the phase angle (γ) of the complex fault current distribution factor (kF),
- either from the fault loop current (Irelay) and the fault current (IF), where the fault current (IF) is determined from currents measured synchronously at both ends (A and B) of the transmission line, where
- in case of a phase-to-ground, a phase-to-phase or a three-phase-balanced fault the fault current (IF) is determined using the incremental positive sequence current components (ΔIA1, ΔIB1) of both ends (A and B) of the transmission line, or
- in case of a phase-to-phase-to-ground fault the fault current (IF) is determined using the incremental positive sequence current components (ΔIA1, ΔIB1) as well as the negative sequence current components (IA2, IB2) of both ends (A, B) of the transmission line,
- or from the fault loop current (Irelay) and the fault current (IF) for three different, predetermined line distances (di), where the fault current (IF) is determined
- in case of a phase-to-ground or a phase-to-phase fault using impedance parameters (Z1L, Z1SA, Z1SB) of the transmission line, the fault loop current (Irelay) and the negative sequence current component of the one end (A) of the transmission line (IA2), or
- in case of a three-phase or a phase-to-phase-to-ground fault using impedance parameters (Z1L, Z1SA, Z1SB) of the transmission line, the fault loop current (Irelay), the negative sequence current component of the one end (A) of the transmission line (IA2) and the incremental positive sequence current component of the one end (A) of the transmission line (ΔIA1),
- utilizing the three resulting phase angles (Γi) to determine three impedance shifts (ΔZi) and three corresponding possible distances to fault (dpi), where the one of the three possible distances to fault (dpi) which lies closest to a reference distance to fault (dref), which is calculated as the quotient of the fault loop impedance (Zrelay) and the impedance of the transmission line for the positive current sequence (Z1L), is chosen as the distance to fault (d), and
- determining the distance to fault (d) by subtracting the impedance shift (ΔZ) from the fault loop impedance (Zrelay) and dividing the result by the impedance of the transmission line for the positive current sequence (Z1L).