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 indicates 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 indicating 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 indicating 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-G(n) is a fault type coefficient indicating phase-to-ground faults,FAULT_Ph-Ph(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.