WO2013004359A1 - A method of selecting between faulted and healthy circuits in parallel lines using one-end measurements - Google Patents

A method of selecting between faulted and healthy circuits in parallel lines using one-end measurements Download PDF

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Publication number
WO2013004359A1
WO2013004359A1 PCT/EP2012/002715 EP2012002715W WO2013004359A1 WO 2013004359 A1 WO2013004359 A1 WO 2013004359A1 EP 2012002715 W EP2012002715 W EP 2012002715W WO 2013004359 A1 WO2013004359 A1 WO 2013004359A1
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Prior art keywords
fault
line
parallel lines
determination
phase
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PCT/EP2012/002715
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French (fr)
Inventor
Przemyslaw Balcerek
Murari Saha
Eugeniusz Rosolowski
Jan Izykowski
Piotr Pierz
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Abb Technology Ag
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Priority claimed from EP11460034A external-priority patent/EP2544322A1/en
Priority claimed from EP11460033A external-priority patent/EP2544014A1/en
Application filed by Abb Technology Ag filed Critical Abb Technology Ag
Publication of WO2013004359A1 publication Critical patent/WO2013004359A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead

Definitions

  • the present invention relates to a selection between faulted and healthy circuits in parallel lines with the use of one-end measurements in electric power lines, applicable to parallel power lines, fit for use in the power industry for overhead transmission lines.
  • SC Series compensation
  • the present practice relies on using traditional distance relays but with modified settings. Considerable shortening of the first zone reach to 30-40% instead of 85% is applied.
  • the disadvantage of this method is that it requires the use of mutual impedance which is not uniformly distributed or known.
  • the invented method does not use mutual impedance.
  • the invented method is designed to allow selection between faulted and healthy circuits in parallel lines.
  • the input signals in the method are samples of three- phase currents from both circuits of the parallel lines. Due to the applied specific kind of measurements the delivered method is considered to be a simple and important supplementation of the distance relay protection of parallel lines aimed at fast switching-off of the faulty line.
  • the invented method can be used for both series compensated and uncompensated parallel transmission lines and it is also applicable in cases where one of the parallel lines works as series compensated and the other line of the parallel lines works as uncompensated.
  • the subject of the inventive method using measurement of current signals at one end of the line in terminal A or in terminal B, processing the measuring data, determination of the pre-fault and fault current signals and the zero-sequence current signal, obtaining current phasors (IAI, IBI, Id, 2, IB2, IC2 , i » I02)
  • eciprei is the value of the positive sequence currents of the parallel lines
  • lABC2 re is the value of the positive sequence currents of the other one of the parallel lines
  • FAULT _ Ph - G ] ⁇ n) is a fault type coefficient indicating phase-to-ground faults and in the line #1
  • FAULT _ Ph - Ph x ( «) is a fault type coefficient indicating phase-to-phase fault in the line #1 or non-fault conditions
  • FAULT _ Ph - G 2 ⁇ n is a fault type coefficient indicating phase-to-ground faults and in the line #2
  • FAULT _ Ph - Ph 2 ⁇ n is a fault type coefficient indicating a phase-to-phase fault in the line #2 or non-fault conditions.
  • a computer program product comprising a computer program code which when executed on a data processor unit of a protective device carries out the steps of the method according to claim 1.
  • the subject of the inventive system having a protective device with a processor located at one end of the parallel lines and with a functional module for storing data delivered from an on-line measurement, with a calculating module for doing calculation operations and with an information module for presenting the result of the inventive method, is that the protective device has a selection module for performing the actions according to any of the method claims.
  • the protective device has a form of a protective relay.
  • the inventive method is used in a protective device having the form of a protective relay.
  • a real-time digital current signal coming from current transformers and converted in an A/D converter into a digital signal compatible with IEC 61850 standard, is transmitted by the IEC 61850 9-2 protocol or any other communication protocol.
  • the conversion of analogue phase current signals with the aid of the current instrument transformer CT's allows to obtain sampled discrete time values.
  • interconnection by means of a station communication protocol preferably compatible with the IEC 61850 standard should be regarded as conventional techniques and have therefore been omitted.
  • the present invention relates to a method for selecting between faulted and healthy circuits in parallel lines using one-end current signal measurements from both circuits of the parallel lines. Thanks to the inventive approach high reliability of identification of faulted and healthy circuits in parallel lines with the use of one-end measurements is achieved.
  • FIG. 1 shows the schematic system for selecting between faulted and healthy circuits in parallel lines with the use of one-end measurements
  • fig. 2 the inventive part of the system for selecting between faulted and healthy circuits in parallel lines with the use of one-end measurements in a protection relay
  • fig. 3 - a set of steps for the realisation of the inventive method.
  • Line #1 and Line #2 current transformers 1 are connected with a protective device 2, having a form of a protection relay, by an analogue wire link 3 or by means of a process communication bus 4 containing a Margin Unit 5.
  • the protection relay 2 with a data processing unit P comprises an A/D converter 6 and an arrangement of functional modules M1 , M2, M3, M4 where the module M1 is a buffer module for storing data delivered from an on-line measurement, the module M2 is the module of selection between faulted and healthy circuits, the module M3 is a calculating module connecting with the others modules, and the module M4 is an information module for giving the result of the inventive method.
  • the A/D converter 6 may be located in the Margin Unit 5 instead of being in the protection relay 2, which is indicated on the drawing by the dotted line.
  • the protection relay 2 comprises other modules which are essential for the proper operation of the protection relay and which are not described in the description, and not presented in the fig. 1.
  • the module M2 of the selection between faulted and healthy circuits in parallel lines, presented in fig. 2, comprises a pre-filtering block B1 for filtering digital current signals, a data analysis block B2 for processing digital current signals, and a decision block B3 for selecting between faulted and healthy circuits in the parallel lines.
  • the method according to the invention is carried out in the following steps:
  • Step S1 real-time analog current signals IALI» IBLL 'CLI» L2.
  • IBL2, lcL2 from the individual phases A, B, C from both circuit of the parallel lines Line #1 and Line #2 and optional zero sequences currents of both circuits of the parallel lines lou, IOL2 are measured in the current transformers.
  • the measured data are converted in an A/D converter to digital current signals IAI, IBI > f ci > ⁇ 2, ⁇ 2, ic2, hi, io2. and stored in the buffer module M1 of the protection relay.
  • step S2 in the pre-filtering block B1 digital current signals from individual phases ⁇ A I, ⁇ BI, ici, >A2, IB2, >C2 of both circuit of the parallel lines and zero sequences currents i, io2 are filtered using one of the known methods of half- period filtering, for example the half-period window Fourier filter method, in order to obtain the phasor value of digital current signals i, IBI, ICI, IA2, IB2, IC2 for each individual phase A, B, C of both circuits of the parallel lines , which are represented by magnitude and phase angle.
  • half- period filtering for example the half-period window Fourier filter method
  • zero sequences digital currents IOLI , OL2 of both circuits of the parallel lines are filtered in order to obtain the phasor value loi and lo2.
  • the phasor value of zero sequences digital currents loi, I02 can be calculated from the digital current signal according to the following formulas:
  • step S3 having the phasor value of digital current signals l A 1 , l B1 , IQI, IA2, IB2, l C 2, he pre-fault current Signals hlpre, leipre, lcipre, U2pre, lB2pre, Ic2pre, lo-lpre.
  • I 0 2pre, and fault current signals I F AI, IFBI, ci, IFA2, IFB2, IFC2, IFOI, IFO2 are determined using any of the known method, with the use of the fault detection time t F delivered in step 1.
  • the pre-fault current signals are determined using the one period length pre-fault current signals in the pre-filtering block B1.
  • step S4 first, having the pre-fault current signals hipre, leipre, lcipre, 2pre, lB2pre, Ic2pre, the average values of 3-phase digital current signals magnitude lABCipre, . lABC2pre, of both circuits of the parallel lines are calculated in the data analysis block B2 as:
  • STEP 5 Calculation of the difference values of the corrected fault during the fault.
  • the corrected values of current phasors/ ⁇ y , / ⁇ ⁇ / , ⁇ c ⁇ f ⁇ Aif - > ⁇ B2f - > ⁇ cif are determined assuming that fault currents from one of the line (Line #1 or Line #2) are taken as reference corrected values of current phasors according to the following formulas:
  • n- is the real consecutive number of the present digital sample processed by the relay
  • n- is the real consecutive number of the present digital sample processed by the relay.
  • the difference values of the corrected fault current , d/ ' ci , // " oi, di B 2, dici, c1 ⁇ 2 are determined in the data analysis block B2 for each of the circuits of the parallel transmission line according to the following formulas:
  • step 6 having the difference values of the corrected fault current d -i, , d/ ' ci, d/ ' oi, C di ' Q2, di ' c2, dio2, the sums of the current differences sdij, sd i, sdi 2 , sdi 0 2 are calculated in the data analysis block B2 according to the following formulas:
  • sdi x (n) sdi (n - 1)+ dz ⁇ , (n) + di m (n)+ di c (n)
  • step S7 having the sum of the current differences sdii, sdi 0 i, sdj2, sdio2 the fault f
  • FAULT _Ph - G ] (n) is a fault type coefficient indicating phase-to-ground faults and in the line #1
  • FAULT Ph - Ph ⁇ n is a fault type coefficient indicating phase-to-phase fault in the line #1 ,
  • FAULT _Ph - G 2 (n) is a fault type coefficient indicating the phase-to- ground faults and in the line #2,
  • FAULT Ph - Ph 2 (n) is a fault type coefficient indicating the phase-to- phase fault in the line #2. Next, it is checked if only one of the flags f-i or ff 2 equals one. This condition is described by the following equation:
  • the value of the flag ffi, and ff ⁇ zero or one is a conventional value and the inverse possibility of the selection is contained in the scope of the invention.
  • flags ffi, ff 2 available in each of the modules M1...M4 are transmitted to the display or to printing devices which are connected with one of the modules and which are not shown in the drawing. This information is presented to the user of the protective device 2 and is further processed in order to assure the reliable operation of the protective device 2.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The present invention is concerned with a selection between faulted and healthy circuits in parallel lines, using one-end measurements in electric power lines, applicable to parallel power lines, fit for use in the power industry for overhead transmission lines. The subject of the inventive method using measurement of current signals at one end of the line in terminal A or in terminal B, processing measuring data, determination of pre-fault and fault current signals and the zero- sequence current signal, obtaining current phasors I A1 , I B1 , I C1 , I A2 , I B2 , I C2 , I 01 , I 02 , consists in that the method further comprises the steps of: -determination of a symmetrical scaling coefficient k prefault establishing a reciprocal relation between the currents of a single line of the parallel lines, - determination of the corrected fault current phasors after scaling and calculation of current differences sum for each line sdi1, sdi01, sdl2, sdi02, - determination of fault f 1 , f i01 , f 2 , f 02 coefficients, - determination of the value of flags ff1 and ff2 having a conventional value one or zero and a selection of faulted and healthy circuits in the parallel lines.

Description

A method of selecting between faulted and healthy circuits in parallel lines using one-end measurements
The present invention relates to a selection between faulted and healthy circuits in parallel lines with the use of one-end measurements in electric power lines, applicable to parallel power lines, fit for use in the power industry for overhead transmission lines.
Series compensation (SC) is applied to worldwide EHV transmission lines where long transmission distance and large power transmission are involved. It is an effective and economic means of increasing power transmission capability, improving power system stability, reducing transmission losses, enhancing voltage control and flexible power flow control.
However, protection of such kind of line still causes problems especially for parallel lines. This is due to the fact that series capacitors shift the fault-loop impedances which results in tripping the healthy line. Additionally, the currently used algorithms aimed at identifying the fault direction maloperate in the case of inversion of voltage and current signals.
To avoid such misoperation, the present practice relies on using traditional distance relays but with modified settings. Considerable shortening of the first zone reach to 30-40% instead of 85% is applied.
An example of a current application for detecting the position of a fault on a parallel lines link is described in the US patent 4325098. This application is based on determination of the fault direction in the protection relays located at each end of the parallel lines . If both relays located in one of the circuits of the parallel lines indicate the same forward fault direction, this circuit of the parallel lines is declared to be the faulted one.
Another example of a method for fault location in the parallel transmission lines with series compensation is described in US patent 6476613. In this solution the zero sequence current measurement is used to compensate the mutual impedance effect in distance-to-fault calculation.
The disadvantage of this method is that it requires the use of mutual impedance which is not uniformly distributed or known. The invented method does not use mutual impedance.
The invented method is designed to allow selection between faulted and healthy circuits in parallel lines. The input signals in the method are samples of three- phase currents from both circuits of the parallel lines. Due to the applied specific kind of measurements the delivered method is considered to be a simple and important supplementation of the distance relay protection of parallel lines aimed at fast switching-off of the faulty line.
The invented method can be used for both series compensated and uncompensated parallel transmission lines and it is also applicable in cases where one of the parallel lines works as series compensated and the other line of the parallel lines works as uncompensated.
The subject of the inventive method using measurement of current signals at one end of the line in terminal A or in terminal B, processing the measuring data, determination of the pre-fault and fault current signals and the zero-sequence current signal, obtaining current phasors (IAI, IBI, Id, 2, IB2, IC2 , i » I02)
consists in that the method further comprises the steps of:
- determination of the symmetrical scaling coefficient kprefault establishing a reciprocal relation between the currents of the single line of the parallel lines, which is calculated in the following way: kprefault
Figure imgf000003_0001
where
eciprei is the value of the positive sequence currents of the parallel lines , lABC2 re is the value of the positive sequence currents of the other one of the parallel lines, determination of the corrected fault current phasors after scaling and calculating the current differences sum for each line (sdi1, sdi01, sdi2, sdi02), determination of fault fi, f,oi, f2, fo2 coefficients
determination of the value of flags ffi and ff2 having a conventional value of one or zero in order to carry out the selection of faulted and healthy circuits in the parallel lines when the following conditions are fulfilled:
for Line #1
Figure imgf000004_0001
for Line #2 (Circuit #2):
FA ULT _ Ph - Ph2 {n) FA ULT _ Ph - G2 (n)
Figure imgf000004_0002
where:
fihr - threshold for fault coefficients fiJioi,f2,fo2
FAULT _ Ph - G] {n) is a fault type coefficient indicating phase-to-ground faults and in the line #1
FAULT _ Ph - Phx («) is a fault type coefficient indicating phase-to-phase fault in the line #1 or non-fault conditions,
FAULT _ Ph - G2 {n) is a fault type coefficient indicating phase-to-ground faults and in the line #2, FAULT _ Ph - Ph2 {n) is a fault type coefficient indicating a phase-to-phase fault in the line #2 or non-fault conditions.
Next the selection is performed in the following actions.
First it is checked if only one of the flags ffi or ff2 equals one, and if :
ff,(n)=\ AND ff2(n)=\ then ff,(n)=0 AND ff2(n)=0, or
ff,(n)=0 AND ff2(n)=0,
it means that the outside fault of the parallel lines has been identified.
Next the relation between the value of the ffi and ff2 is checked, and if ff,(n)=l A O ff2(n)=0 , it means that internal fault within line # 1 of the parallel lines has been identified; or if ff,(n)=0 AND ff2(n)=\, it means that internal fault within line # 2 of the parallel lines has been identified.
In the embodiment of the invention the threshold for coefficients fi,fjoi, , fo2 was
Figure imgf000005_0001
A computer program product comprising a computer program code which when executed on a data processor unit of a protective device carries out the steps of the method according to claim 1.
The subject of the inventive system having a protective device with a processor located at one end of the parallel lines and with a functional module for storing data delivered from an on-line measurement, with a calculating module for doing calculation operations and with an information module for presenting the result of the inventive method, is that the protective device has a selection module for performing the actions according to any of the method claims. Preferably the protective device has a form of a protective relay.
The inventive method is used in a protective device having the form of a protective relay. A real-time digital current signal coming from current transformers and converted in an A/D converter into a digital signal compatible with IEC 61850 standard, is transmitted by the IEC 61850 9-2 protocol or any other communication protocol. The conversion of analogue phase current signals with the aid of the current instrument transformer CT's allows to obtain sampled discrete time values. In this context, interconnection by means of a station communication protocol preferably compatible with the IEC 61850 standard should be regarded as conventional techniques and have therefore been omitted.
The present invention relates to a method for selecting between faulted and healthy circuits in parallel lines using one-end current signal measurements from both circuits of the parallel lines. Thanks to the inventive approach high reliability of identification of faulted and healthy circuits in parallel lines with the use of one-end measurements is achieved.
A method of selecting between faulted and healthy circuits in parallel lines is presented in the drawing, where fig. 1 shows the schematic system for selecting between faulted and healthy circuits in parallel lines with the use of one-end measurements, fig. 2 - the inventive part of the system for selecting between faulted and healthy circuits in parallel lines with the use of one-end measurements in a protection relay, fig. 3 - a set of steps for the realisation of the inventive method.
In two parallel lines Line #1 and Line #2 current transformers 1 are connected with a protective device 2, having a form of a protection relay, by an analogue wire link 3 or by means of a process communication bus 4 containing a Margin Unit 5. The protection relay 2 with a data processing unit P comprises an A/D converter 6 and an arrangement of functional modules M1 , M2, M3, M4 where the module M1 is a buffer module for storing data delivered from an on-line measurement, the module M2 is the module of selection between faulted and healthy circuits, the module M3 is a calculating module connecting with the others modules, and the module M4 is an information module for giving the result of the inventive method. In a case where the protection relay 2 is connected by the communication bus 4, the A/D converter 6 may be located in the Margin Unit 5 instead of being in the protection relay 2, which is indicated on the drawing by the dotted line. It is obvious that the protection relay 2 comprises other modules which are essential for the proper operation of the protection relay and which are not described in the description, and not presented in the fig. 1. The module M2 of the selection between faulted and healthy circuits in parallel lines, presented in fig. 2, comprises a pre-filtering block B1 for filtering digital current signals, a data analysis block B2 for processing digital current signals, and a decision block B3 for selecting between faulted and healthy circuits in the parallel lines.
The method according to the invention is carried out in the following steps:
STEP 1 - gathering input measurements and settings
In Step S1 , real-time analog current signals IALI» IBLL 'CLI» L2. IBL2, lcL2 from the individual phases A, B, C from both circuit of the parallel lines Line #1 and Line #2 and optional zero sequences currents of both circuits of the parallel lines lou, IOL2 are measured in the current transformers. Next, the measured data are converted in an A/D converter to digital current signals IAI, IBI> fci> ΪΑ2, ΪΒ2, ic2, hi, io2. and stored in the buffer module M1 of the protection relay.
Additionally a fault type coefficient FA ULT _ Ph - Gx (ri) indicating phase-to- ground faults and in the line #1 coefficient FAULT _ Ph - Phx (n) indicating a phase-to-phase fault in the line #1 , coefficient FA ULT _ Ph - G2 (n) indicating phase-to-ground faults and in the line #2 coefficient FA ULT _ Ph - Ph2 (n) indicating a phase-to-phase fault in the line #2, and a fault detection time , are taken from other essential modules required for the proper operation of the protection relay. Also in this step a different current sum coefficient sdithr indicating a threshold value is delivered to the relay by the user. All of those coefficients are stored in the buffer module M1 of the protection relay.
If during the operation of the parallel lines, a phase-to-ground fault occurs in line #1 , then the coefficient FAULT _Ph - Gl (n) = 1 and the coefficient
FAULT _ Ph - Phx (n) - 0. If during the operation of the parallel lines a phase-to- phase fault occurs in line #1 then the coefficient FAULT _Ph - Gx («) = 0 and the coefficient FAULT _ Ph - P x {n) - \ . When a phase-to-phase-to-ground fault occurs both FAULT _ Ph - Gl (n) and FAULT _ Ph - Ph (n) are set to 1.
If during the operation of the parallel lines, a phase-to-ground fault occurs in line #2, then the coefficient FAULT _Ph - G2 (n) = 1 and the coefficient
FAULT _ Ph - Ph2 (n) - 0. If during the operation of the parallel lines a phase-to- phase fault occurs in line #1 , then the coefficient FAULT _Ph - G2 (n) = 0 and the coefficient FAULT Ph - Ph2 (n) = 1. When a phase-to-phase-to-ground fault occurs, both FAULT _ Ph - G2 {n) and FAULT _Ph - Ph2 (n) are set to 1.
STEP 2 - Filtering data
Next, in step S2 in the pre-filtering block B1 , digital current signals from individual phases \A I, \BI, ici, >A2, IB2, >C2 of both circuit of the parallel lines and zero sequences currents i, io2 are filtered using one of the known methods of half- period filtering, for example the half-period window Fourier filter method, in order to obtain the phasor value of digital current signals i, IBI, ICI, IA2, IB2, IC2 for each individual phase A, B, C of both circuits of the parallel lines , which are represented by magnitude and phase angle. Also zero sequences digital currents IOLI , OL2 of both circuits of the parallel lines are filtered in order to obtain the phasor value loi and lo2. Alternatively, if the zero sequence currents lou and IOL2 are not measured and delivered in step 1 , the phasor value of zero sequences digital currents loi, I02 can be calculated from the digital current signal according to the following formulas:
^oi = 3 + ^m + )'
Figure imgf000009_0001
where:
hi, hi, Ici> - A, B, C phasor value of digital current signals in Line #1 ,
IA2, IB2, IC2,- A, B, C phasor value of digital current signals in Line #2.
STEP 3 - Determination of pre-fault and fault current signals
In step S3, having the phasor value of digital current signals lA 1, lB1, IQI, IA2, IB2, lC2, he pre-fault current Signals hlpre, leipre, lcipre, U2pre, lB2pre, Ic2pre, lo-lpre.
I02pre, and fault current signals IFAI, IFBI, ci, IFA2, IFB2, IFC2, IFOI, IFO2 are determined using any of the known method, with the use of the fault detection time tF delivered in step 1. In the embodiment of the invention the pre-fault current signals are determined using the one period length pre-fault current signals in the pre-filtering block B1.
STEP 4 - Determination of the symmetrical scaling coefficient
In step S4, first, having the pre-fault current signals hipre, leipre, lcipre, 2pre, lB2pre, Ic2pre, the average values of 3-phase digital current signals magnitude lABCipre, . lABC2pre, of both circuits of the parallel lines are calculated in the data analysis block B2 as:
1 / ABCXpre - ~i ^ I A\ + B\ + r ci
/ 1 ABC2pre - ~1 ^ I A2 \ + B2 \ + VC Next, the symmetrical scaling coefficient kprefaull is determined according to the following formula: prefault
Figure imgf000010_0001
STEP 5 - Calculation of the difference values of the corrected fault during the fault. In the step S5 in the data analysis block B2, the corrected values of current phasors/^y , /βι/ , ^c\f ^Aif -> ^B2f -> ^cif are determined assuming that fault currents from one of the line (Line #1 or Line #2) are taken as reference corrected values of current phasors according to the following formulas:
• if the reference line is the Line # 1 then:
JAlf W = JFA\ (»)» IB\f (fl) = I FBI (4 7C1 / W = 1 FC\ («)» ^01/ M = 1 FOX M
I A2 f (n) = prefault * I FA2 (n\ I B2f (n) = ^ prefault * ^ FB2 in\ ^C2f (n) ~ prefault * I FC2 (
Figure imgf000010_0002
where: n- is the real consecutive number of the present digital sample processed by the relay
• if the reference line is the Line # 2 then
Figure imgf000010_0003
IA2f (n) = W» /02 W = 02 W
^AXf (n) = prefault * ^ FAX (n\ ^BXf (w) = 1 / ^ prefault * ^FBX (n)> ^C f (M) ~ 1 / ^ prefault *
Figure imgf000010_0004
where: n- is the real consecutive number of the present digital sample processed by the relay.
Next, having the corrected values of the current phasors IAXf ,
Figure imgf000011_0001
> Icif the pre-fault current signals lAiPre, iBipre, lcipre, ^Mpre, ^ 2pre, Ic2pre and average value of 3 phase digital current signals magnitude ecipre, . BC2pre, the difference values of the corrected fault current , d/'ci , //"oi, diB2, dici, c½ are determined in the data analysis block B2 for each of the circuits of the parallel transmission line according to the following formulas:
for Line #1 :
Figure imgf000011_0002
Figure imgf000011_0003
STEP 6 - Calculation of the current differences sum
In step 6, having the difference values of the corrected fault current d -i, , d/'ci, d/'oi, C di'Q2, di'c2, dio2, the sums of the current differences sdij, sd i, sdi2, sdi02 are calculated in the data analysis block B2 according to the following formulas:
for r=1 and for Line #1 :
sdix O) = diM O) + dim («) + diC] (n) , sdi0l (n) = di0i (n) for n=1 and for Line #2:
sdi2 («) = diA2 (n) + diB2 («) + diC2 («) ,
sdiQ2 (n) = di02 (n) for n> and for Line #1
sdix (n) = sdi (n - 1)+ dz^, (n) + dim (n)+ dic (n)
sdi0l (n) = sdi0l (n - 1) + <#01 («) for n>1 for and Line #2:
sdi2 (n) = sdi2 (n - 1) + i¾2 («) + diB2 (n)+ diC2 in)
sdi02 («) = 5i/i02 (« - 1) + di02 (n)
STEP 7
In step S7, having the sum of the current differences sdii, sdi0i, sdj2, sdio2 the fault f| , fjoi , , fo2 coefficients are calculated according to the following formulas:
- for Line #1 :
Figure imgf000012_0001
- for Line #2:
Figure imgf000012_0002
STEP 8 In the next step, having the fault , fioi, , fo2 coefficients and coefficient the FA ULT _ Ph - G, (n) indicating the phase to ground faults and in the line #1 the coefficient FAULT _Ph - Phx {n) indicating the phase-to-phase fault in the line #1 , the coefficient FAULT _Ph - G2(n) indicating the phase-to-ground faults and in the line #2 the coefficient FAULT _Ph - Ph2 (n) indicating the phase-to-phase fault in the line #2, delivered in Step 1 , flags ffi and ff2 are calculated:
for Line #1
FA ULT _ Ph - Ph (n) = 1 FAULT _ Ph - G] («) = 1
Figure imgf000013_0001
and for Line #2: FAULT _ Ph - Ph2 (n) FAULT _ Ph - G2 («)
Figure imgf000013_0002
where
fthr - the threshold for fault coefficients fifioi,f2,fo2,
FAULT _Ph - G] (n) is a fault type coefficient indicating phase-to-ground faults and in the line #1
FAULT Ph - Ph^n) is a fault type coefficient indicating phase-to-phase fault in the line #1 ,
FAULT _Ph - G2(n) is a fault type coefficient indicating the phase-to- ground faults and in the line #2,
FAULT Ph - Ph2 (n) is a fault type coefficient indicating the phase-to- phase fault in the line #2. Next, it is checked if only one of the flags f-i or ff2 equals one. This condition is described by the following equation:
Figure imgf000014_0001
or
Figure imgf000014_0002
it means that an outside fault of the parallel lines is identified;
when ff,(n)=l AND ff2(n)=0 it means that an internal fault within line # 1 of the parallel lines is identified; when fft(n)=0 AND ff2(n)=\ it means that an internal fault within line # 2 of the parallel lines has been identified.
In the embodiment of the invention, the threshold for coefficients fi,fioi, ^2, fo2 was set to (fthr = -5). This threshold is set according to the system configuration.
The value of the flag ffi, and ff∑ zero or one is a conventional value and the inverse possibility of the selection is contained in the scope of the invention.
STEP 9
In the next step S9, flags ffi, ff2 available in each of the modules M1...M4 are transmitted to the display or to printing devices which are connected with one of the modules and which are not shown in the drawing. This information is presented to the user of the protective device 2 and is further processed in order to assure the reliable operation of the protective device 2.

Claims

Claims
1. A method for selecting between faulted and healthy circuits in parallel lines, using one-end measurements, where selection functions are implemented by a protective device (2) located at one end of the parallel lines, and where the method contains: measurement of current signals at one end of the line in terminal A or in terminal B, processing of measuring data, determination of pre-fault and fault current signals and the zero-sequence current signal, obtaining current phasors lA1, lB1, lCi, 2, IB2, IC2 , i , I02,
characterised in that that the method further comprises the steps of:
• determination of a symmetrical scaling coefficient kpreja- u establishing a reciprocal relation between the currents of a single line of the parallel lines, which is calculated in the following way:
ABC\ pre
kprefault
I ABClpre
where
ecipre, is the value of the positive sequence currents of one of the parallel lines ,
BC2pre is the value of the positive sequence currents of the other one of the parallel lines,
determination of the corrected fault current phasors after scaling and calculation of current differences sum for each line sdi1, sdi01, sdi2, sdi02, determination of fault f fjoi, fo2 coefficients,
determination a the value of flags ffi and #2, having the conventional value one or zero, in order to carry out the selection between faulted and healthy circuits in parallel lines when the following conditions are fulfilled:
for Line #1 :
Figure imgf000016_0001
and for Line #2: FAULT _Ph- Ph2 («) = 1 FAULT _Ph-G2{n)=\
Figure imgf000016_0002
where f,hr - the threshold for fault coefficients fifio f2,fo2
n - is the real consecutive number of the present digital sample processed by the protective device,
FAULT Ph-G {n) is a fault type coefficient indicating phase-to-ground faults and in the line #1
FAULT _Ph~ Ph {n) is a fault type coefficient indicating a phase-to- phase fault in the line #1,
FAULT _Ph - G2(n) is a fault type coefficient indicating phase-to-ground faults and in the line #2,
FAULT _Ph- Ph2(n) is a fault type coefficient indicating a phase-to- phase fault in the line #2
and next a selection is performed in the following actions:
- first it is checked if only one of the flags ffi or ff2 equals one, and if :
ff,(n)=\ AND ff2(n)=\ then J?,(n)=0 AND ff2(n)=0, or
ff,(n)=0 AND ff2(n)= ,
it means that an outside fault of the parallel lines has been identified; - next the relation between the value of ffi and ff2 is checked, and if fft(n)=\ AND ff2(n)=0 , it means that an internal fault within line # 1 of the parallel lines has been identified;
or if
Figure imgf000017_0001
it means that an internal fault within line # 2 of the parallel lines has been identified.
• automatic presentation of the results to the user by the protective device.
2. A computer program for selecting between faulted and healthy circuits in parallel lines using one-end measurements which is loadable into and executable on a data processing unit and which computer program, when being executed, performs the steps according to one of the preceding claims.
3. A system for selecting between faulted and healthy circuits in parallel lines, using one-end measurements, having a protective device (2) with a processor (P), located at one end of the parallel lines and with a functional module (M1) for storing data delivered from an on-line measurement (M1 ), with a
calculating module (M3) for doing calculation operations and with an
information module (M4) for presenting the result of the inventive method, characterised in that the protective device (2) has a selection module (M2) for performing the actions according to any of the method claims, which is connected with the other modules (M1 , M3, M4).
4. A system according to claim 3, characterised in that the protective device (2) has a form of a protection relay.
PCT/EP2012/002715 2011-07-05 2012-06-27 A method of selecting between faulted and healthy circuits in parallel lines using one-end measurements WO2013004359A1 (en)

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