METHOD OF DISTANCE PROTECTION OF PARALLEL TRANSMISSION LINE

摘要

The present invention is concerned with a method of distance protection of parallel transmission lines applicable both to series compensated and uncompensated electric power lines, using a distance relay. The method is characterized in that a pair of flags (ff1, ff2) are calculated for indication faulted and healthy circuits in parallel lines and in the same time a flag (Internal_Fault) for indication internal or external fault in parallel lines is calculated independently. Next gathering all calculated flags (ff1, ff2, Internal_Fault) an analyze of the value of these flags are performed and depending on the values of flags (ff1, ff2, Internal_Fault) and on their reciprocal relationship, a trip permission signal from the protection relay (4) is released and sent to the alarms devices or to the line breakers, or a block signal from the protection relay (4) is generated and sent to protect parallel lines before damage.

主权项

1. A method for distance protection of parallel transmission lines comprises:
measuring current and voltages signals from the individual phases (A, B, C) from both line circuit #1 and line circuit #2 of the parallel lines and optional zero sequence currents of both line circuit #1 and line circuit #2 of the parallel lines, processing the measured signals and using a protection relay (4) calculating a coefficient FAULT_Ph-G1(n) which indicating phase-to-ground faults in the line circuit #1, a coefficient FAULT_Ph-Ph1(n) which indicating a phase-to-phase fault in the line circuit #1, a coefficient FAULT_Ph-G2(n) which indicating phase-to-ground faults in the line circuit #2, a coefficient FAULT_Ph-Ph2(n) which indicating a phase-to-phase fault in the line circuit #2, calculating a pair of a flags (ff1, ff2) for indication faulted and healthy circuits in parallel lines, where the flag (ff1) for line circuit #1 is calculated according to the following formula:ff1(n){1when{f1(n)≥fthrANDFAULT_Ph-Ph1(n)=1ORf01(n)≥fthrANDFAULT_Ph-G1(n)=1}0otherwise and where the flag (ff2) for line circuit #2 is calculated according to the following formula:ff2(n){1when{f2(n)≥fthrANDFAULT_Ph-Ph2(n)=1ORf02(n)≥fthrANDFAULT_Ph-G2(n)=1}0otherwise where:
fthr—is a threshold for fault coefficients f1, f01, f2, f02 given by user, n—is the real consecutive number of the present digital sample processed by the protective device, FAULT_Ph-G1(n) is a fault type coefficient indicating phase-to-ground faults in the line #1, FAULT_Ph-Ph1(n) 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 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, calculating a flag (Internal_Fault) for indication internal or external fault in Parallel lines in independent way according to the formula:Internal_Fault(n)={1when{sdi_max(n)sdi_min(n)>sdithrANDFAULT_Ph-Ph(n)=1ORsdi_0max(n)sdi_0min(n)>sdithrANDFAULT_Ph-G(n)=10otherwise where: sdithr—is a different current sum coefficient threshold given by the user, sdi_max(n), sdi—0max(n)—are maximum values of the sum of the current differences, sdi_min(n), sdi—0min(n)—are minimum values of the sum of the current differences, n—is the real consecutive number of the present digital sample processed by the protective device, FAULT_Ph-G1(n) is a fault type coefficient indicating phase-to-ground faults, FAULT_Ph-Ph1(n) is a fault type coefficient indicating phase-to-phase fault, gathering all calculated flags (ff1, ff2, Internal_Fault) an analyze of the reciprocal relationship between the values of these flags and when:
ff1=1 AND Internal_Fault=1 AND ff2=0 AND Internal_Fault=1,it means that fault within protected line circuit #1 has been identified and fault impedance (ZF) is calculated in the known way with using the three phase to ground loops and the multi-phase faults loops and additionally if the apparent fault impedance (ZF) is outside the relay zone operation characteristic (ZI) then a block signal from the protection relay (4) is released,ORwhen: ff1=1ANDInternal_Fault=0ORff1=0ANDInternal_Fault=1ORff2=0ANDInternal_Fault=0ORff2=0andInternal_Fault=1ORff2=1ANDInternal_Fault=1ORff2=1ANDInternal_Fault=0OR⋮ff2=1ANDInternal_Fault=0,}it means that fault outside protected line circuit #1 has been identified and a block signal from the protection relay 4 is generated,
OR when
ff1=1 AND Internal_Fault=1 AND ff2=0 AND Internal_Fault=1,it means that fault within protected line circuit #1 has been identified and fault impedance (ZF) is calculated in the known way with using the three phase to ground loops and the multi-phase faults loops and additionally if the apparent fault impedance (ZF) is within the relay zone operation characteristic (ZI) then a permission trip signal from the protection relay (4) is released, realising a trip permission signal from the protection relay (4) and sending it to the alarms devices or to the line breakers, or generating a block signal from the protection relay (4) and sending it to the users in order to protect parallel lines.