GB2504594A

GB2504594A - Pilot wire differential protection apparatus for multi-end circuit based on phase comparison principle

Info

Publication number: GB2504594A
Application number: GB1309864.5A
Authority: GB
Inventors: Jiankai Liu; Zhemin Yu
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2012-06-06
Filing date: 2013-06-03
Publication date: 2014-02-05
Anticipated expiration: 2033-06-03
Also published as: GB201309864D0; MY172416A; CN103474971A; GB2504594B; CN103474971B; SG195497A1

Abstract

A differential protection apparatus and method for a power transmission or distribution line including three or more connecting ends comprises three or more translay relays, respectively connected at the ends of the line. Summation transformers of the respective relays are connected to the phases and a neutral point of the line and first and second pilot wires of the respective relays are connected with each other in parallel. Respective phase comparators compare corresponding phases of voltages within the relays so as to obtain a phase difference and thereby detect a fault condition. At each of the relays, a pilots padding resistor Rpp is adjusted so that Rpp+Rw=k*Ro, wherein k is a set constant, Rw is a resistance of the pilot wire, and Ro is a linear impedance of the relay. When To<Tr or To>Tr, a value of k satisfies a condition ofÂ -n*k-1<-1< -(n*k+n)*T0/ Tr+n-1or a condition of -(n*k+n)*To/Tr+n-1<-1<-n*k-1, respectively, To and Tr being respectively the number of turns of an operating winding and the number of turns of a restraining winding in the relay and n being the number of ends of the line.

Description

PILOT WIRE DIFFERENTIAL PROTECTION APPARATUS FOR MULTI-END

CIRCUIT BASED ON PHASE COMPARISON PRINCIPLE

TECHNICAL FIELD

[0001] The present invention relates to a protection apparatus and method for power transmission and distribution lines in a middle/short distance. In particularly, the present invention relates to a pilot wire differential protection apparatus and method for multi-end circuit based on a phase comparison principle.

BACKGROUND

100021 As a protection apparatus for power transmission and distribution lines in the middle/short distance, a TRANSLAY relay manufactured, for example, by General Electric Company (GEC) in UK or similar products manufactured by other companies may be utilized to form the pilot wire differential protection apparatus. The TRANSLAY relay utilizes a phase comparator to form ajudgment element and thus has excellent properties.

[0003] Fig. 1 is a view illustrating main structure of the TRANSLAY relay Respective elements in the Fig.! are: a summation transformer 1i, a secondary winding Tt, a secondary winding Ts, an auxiliary transformer Tjj, an operating winding To, a restraining winding Tr, a non-linear resistor RVD, a linear impedance Ro, a pilots padding resistor Rpp, a phase comparator 4). Ia, lb. Ic and In arc currents in an a phase, a b phase, a c phase and a neutral point of a protected circuit end, respectively. Px and Py arc two terminals connecting with the pilot wires.

[0004] The summation transformer T1 is used for transforming three-phase cunents into a single-phase summated current. The secondary winding Tt is used for providing one phase comparison voltage. The secondary winding Ts is used for outputting the single-phase summated current at the secondary side of the summation transformer T1. An output circuit of the auxiliary transformer T11 is used for providing the other phase comparison voltage. The operating winding To is used for providing an operation current of protection. The restraining winding Tr is used for providing a restraining current of protection. A difference between the operating current and the restraining current is a protection start current. The non-linear resistor RYD is used for voltage stabilization. The linear impedance Ro is a linear impedance on a single-phase summated current loop at the secondary side. The pilots padding resistor Rpp is used for matching a total resistor in a pilot wire loop to a set value, and an aim of the matching is to perform adjustment so as to remain the total resistor unchanged, since the total resistor on the pilot wire must be fixed and preset according to a TRANSLAY pilot wire protection principle. The phase comparator I is used for comparing phases of two voltages and judging an in-zone/out-zone fault based on the phase difference between the two comparison voltages, wherein the phase comparator is an analogous phase comparator or a digital phase comparator. A protecting mechanism will be triggered when the start current is greater than a set threshold value and it is judged as the in-zone fault by the phase comparator.

[0005] However, both a wiring manner and an action equation of a current pilot wire longitudinal differential protection apparatus composed of the TRANSLAY relays arc based on a protection for the two-end circuit and therefore can only be applied to protect the two-end circuit. Unfortunately, no protection apparatus or method based on the TRANSLAY relays is proposed for the multi-end circuit in the lines of the power transmission and distribution.

[0006] In view of the above disadvantages in the prior art, the present invention proposes a pilot wire differential phase-compared apparatus and method being applicable to the multi-end circuit, which may extend a usage range of the TRANSLAY relay.

SUMMARY

[0007] An object of the present invention is to make up the disadvantages existed in the current pilot wire differential phase-compared protection apparatus and mcthod for the power transmission and distribution lines based on the TRANSLAY relay and to provide a pilot wire differential phase-compared apparatus and method for the power transmission and distribution lines based on the TRANSLAY relay, which may be applied to the multi-end circuit.

[0008] According to an aspect of the present invention, there is provided a pilot wire differential protection apparatus for a power transmission and distribution lines including three or more connecting ends, comprising: [0009] three or more TRANSLAY relays, which are sequentially connected at the corresponding connecting ends of the power transmission and distribution lines, respectively, [0010] wherein summation transformers of the respective TRANSLAY relays are connected to an a phase, a b phase, a c phase and a neutral point at the connecting ends of the corresponding protected circuits, and a pilot wire first connecting terminal and a pilot wire second connecting terminal of the respective TRANSLAY relays are connected with each other in parallel, respectively, [0011] wherein the TRANSLAY relays comprise corresponding phase comparators, respectively, for comparing corresponding phases of U1 and U11 in the respective TRANSLAY relays so as to obtain a corresponding phase difference ArgL, wherein Ui is a voltage at one side of the phase comparator, that is, a voltage at a secondary winding side of the relay, U11 is a voltage of the other side of the phase comparator, that is, a voltage at a auxiliary transformer side of the relay, and a false state of the power transmission and distribution lines is judged according to the corresponding phase differences [0012] wherein, at each of the connecting ends, a pilots padding resistor Rpp of the respective TRANSLAY relay is adjusted so that Rpp + Rw = k * R0 is satisfied at each of the ends, k is a set constant, Rw is a resistance on the pilot wire, and Ro is a linear impedance of the TRANSLAY relay, 100131 wherein a value of k satisfies a condition of _n*k_l< -l<-(ntk+n)t1)/Tr+n-1 when To<Tr, or the value of k satisfies a condition of _n*k+n)*T0!Trn_1<_1<_n*k_1 when To>Tr, To is number of turns of an operating winding in the TRANSLAY relay and Tr is number of mrns of a restraining winding in the TRANSLAY relay.

[0014] It is judged that a system of the power transmission and distribution lines is in an in-zone fault state and the pilot wire differential protection apparatus is triggered to perform protection, when at least one of the phase differences in the phase comparators of the respective TRANSLAY relays does not satisfy 900 »= Arg »= -S0° and a start current of the relay is greater than a set threshold value.

[0015] Tt is judged that the system of the power transmission and distribution lines is in a normal operation state or an out-zone fault state when all of the phase differences between the Uj and Uji in the respective TRANSLAY relays satisfy 90° »= »= -90°.

[0016] The phase comparator is an analogous phase comparator or a digital phase comparator.

[0017] According to another aspect of the present invention, there is provided a method for a pilot wire differential protection apparatus, comprising steps of: [0018] measuring phases of corresponding Uj and U11 of respective TRANSLAY relays, wherein U1 is a voltage at one side of the phase comparator, that is, a voltage at a secondary winding side of the relay, and Un is a voltage of the other side of the phase comparator, that is, a voltage at a auxiliary transformer side of the relay; [0019] comparing, by corresponding phase comparators in the TRANSLAY relays, the phases of U1 and U11 in the respective TRANSLAY relays so as to obtain a corresponding phase difference ArgL; and [0020] judging a false state of the power transmission and distribution lines according to the corrcsponding phase differences Arg-k-1-, [0021] wherein, at each of the connecting ends, a pilots padding resistor Rpp of the respective TRANSLAY relay is adjusted so that Rpp + Rw = k * R0 is satisfied at each of the ends, k is a set constant, Rw is a resistor on the pilot wire, and Ro is a linear impedance of the TRANSLAY relay, [0022] wherein a value of k satisfies a condition of

D

_n*k_1 <-I <-nHc +n)*T0/Tr+n_l when To<Tr, or the value of k satisfies a condition of _(n*k+n)*7T/Tr+n_1c_1 c-n4k-1 when To>Tr, To is number of turns of an operating winding in the TRANS LAY relay and Tr is number of turns of a restraining winding in the TRANSLAY relay.

[0023] It is judged that a system of the power transmission and distribution lines is in an in-zone fault state and the pilot wire differential protection apparatus is triggered to perform protection, when at least one of the phase differences in the phase comparators of the respective TRANS LAY relays does not satisfy 900 »= Argi »= _9Ø0 and a start current of the relay is greater than a set threshold value.

[0024] It is judged that the system of the power transmission and distribution lines is in a normal operation state or an out-zone fault state when all of the phase differences between the Uj and Uji in the respective TRANSLAY relays satisfy 900 »= »= 90°.

[0025] The phasc comparator is an analogous phase comparator or a digital phase comparator.

[0026] The pilot wire differential phase-compared apparatus and method of the present invention which are applicable to the multi-end circuit extend a usage range of the TRANSLAY relay

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will become more fully understood from the detailed description of the exemplary embodiments given hereinafter in connection with accompanying drawings. It should be understood that the described embodiments are given by way of illustration and example only, and the present invention is not limited thereto. The spirit and scope of the present invention are defined by contents stated in the accompanying claims attached. Below is a brief description for the drawings and wherein: [0028] Fig I is a diagram illustrating a main structure of the TRANSLAY relay; [0029] Fig 2 is an exemplary view illustrating a wiring in a pilot wire differential phase-compared protection apparatus applied to a three-end circuit according to a first embodiment of the present invention; 100301 Fig 3 is an equivalent circuit diagram for the pilot wire differential phase-compared protection apparatus applied to the three-end circuit according to the first embodiment of the present invention; [0031] Fig 4 is a motion trajectory of a differential protection for the pilot wire differential phasc-compared protcction apparatus applied to the thrcc-cnd circuit according to the first embodiment of the present invention; [0032] Fig S is an exemplary vicw illustrating a wiring in a pilot wirc differential phase-compared protection apparatus applied to a multi-end circuit according to a second embodiment of the present invention; [0033] Fig 6 is an equivalent circuit diagram for the pilot wire differential phase-compared protcction apparatus applied to the multi-end circuit according to the second embodiment of the present invention; [0034] Fig 7 is a motion trajectory of a differential protection for the pilot wire differential phase-compared protection apparatus applied to the multi-end circuit according to the second embodiment of the present invention.

DETAILED DESCRIPTION

[0035] The pilot wire differential phase-compared protection apparatus and method according to the present invention will be explained now with reference to the accompany drawings.

[0036] Fig 2 is an exemplary view illustrating a wiring in a pilot wire differential phase-compared protcction apparatus applied to a thrce-cnd circuit according to a first embodiment of the present invention.

[0037] Three sets of TRANSLAY relays Relayl, Relay2, Relay3 are connected at the end 1, end 2, end 3 of the power transmission and distribution lines, respectively, summation transformers T1 of the respective TRANSLAY relays Relayl, Relay2, Relay3 are connected to an a phase, a b phase, a c phase and a neutral point at the protected circuit end, and pilot wire connecting terminals Px and Py of the respective TRANSLAY relays Relay!, Relay2, Relay3 are connected with each other at nodes ji and j2 in parallel, respectively.

100381 In the above connection, configurations of each set of the TRANSLAY relays at the end 1, end 2, end 3 should be same completely. That is, all of other elements and parameters in the relays illustrated in Fig I are the same without considering errors, other than the Rpp. The connections and configurations at the three ends are same, therefore the three ends are symmetrical complctely.

100391 Thus an equivalent circuit diagram Ibr the pilot wire differential phase-compared protection apparatus applied to the three-end circuit according to the first embodiment of the present invention shown in Fig 2 may be illustrated as Fig 3. Rw is a resistance on the pilot wire in Fig 3.

[0040] At each of the ends, a resistor Rpp of the respective TRANSLAY relay is adjusted so that Rpp+Rw= k 14 is satisfied at each of the ends, k is a set constant [0041] According to the structure of the TRANSLAY relay, by making the protection at the relay Relayl end as an example, currents flowing through the To, Tr and Ro of the Relayl may be calculated as Ibllows, respectively, from Fig 3: 1, ((3_l)*11_(12+13))/(3*k+3)and ((3*k+l)*14+(12+13))/(3*k+3), wherein 1, 2 and 13 are current flowing through the To of the Relayl, current flowing through the To of the Relay2 and current flowing through the To of the Relay3, respectively.

[00421 According to a design principle of thc TRANSLAY rclay, voltages at thc windings Tt and Ts are in-phase, and voltage on the Ro is approximatively same as that on thc Ts, thercibre a voltagc at the Tt side of thc phase comparator satisfies an equation (1), wherein K1 is a calculation constant.

LOW] U1K1 *((3*k+I)*11 --(2 +13)) (1) 100441 A voltage at the T side of the phase comparator is decided by two primary windings To and Tr and satisfies an equation (2), wherein K11 is a calculation constant.

[0045] UK*(((3*k+3)*7/Tr_3+l)*J -l-(/2 +1;)) (2)

S

[0046] Given A = 2, which is a current ratio between the sum of current vectors in remote ends and the current in local end, then: [0047] 900 »= ArgL = Arg A _(_3*k_l) »= -90° (3) U11 A _(_(3*k+3)*T/Tr*3_I) [0048] Assuming a value of Ic selected suitably, that is, the value of Ic satisfies a condition of _3*k_1<_1<_(3*k+3)*I/Tr+3_1 when To<Tr, or the value of k satisfies a condition of _(3*k+3)*J!Tr+3_l<_1<_3*k_1 when To>Tr, a region corresponding to the current ratio between the sum of current vectors in remote ends and the current in local end in the equation (3) is circular on a complex plane. Fig 4 is a motion trajectory of a differential protection for the pilot wire differential phase-compared protection apparatus applied to the three-end circuit according to the first embodiment of the present invention. 12+L

[0049] When the system operates normally or has an out-zone fault, p = is -l under ideal conditions, therefore a portion inside the circle corresponding to the p1 is a restraining zone or stable zone.

[0050] Further, when the system has an in-zone fault, a portion outside the circle corresponding to the Pi is an operating zone.

100511 Thus the in-zone fault and the out-zone fault may be judged by comparing the phases of Uj and U11.

L

100521 In particularly, in an actual application, when 90° »= Arg-7---»= -90°, the UI' system operates normally or is in the out-zone fault state; if 90° »= Arg-3--»= -90° is not satisfied and a start current of the relay is greater than a set threshold value, the system is in the in-zone fault state.

100531 That is, it is judged whether the 90° »= Arg-!_!_ »= -90° is satisfied if fault occurs in the system: it is the in-zone fault if the 90° »= Arg..L »= -90° is not satisfied and the start current of the relay is greater than the set threshold value; and it is the out-zone fault if thc 90°»=A!g »=-90° is satisfied.

[00541 Above descriptions are made by taking the relay Relay I end as an example, and the phase differences between the U1 and Uu in the Relay2 and ReIay3 also can be used to make judgment. The phase differences between the U1 and U11 in the respective TRANSLAY relays Relay!, Relay2, Relay3 are independent of each other.

[0055] It is also obviously that, when the system operates normally or has the 12+13 ij+13 11+12 out-zone kilt, p1= . , P2= , . are-! under the ideal 1 2 3 conditions, therefore portions inside the circles corresponding to the respective p are the restraining zones or stable zones. Further, when the system has the in-zone fitult, portions outside the circles corresponding to the respective p are the operating zones.

[00561 It is judged that the system is in an in-zone fault state, when at least one of the phase differences between the Ui and iJu in the respective TRANSLAY relays Relay!, Relay2, Relay3 does not satisfr 90° »= »= -90° and the start current of the relay is greater than the set threshold value.

[0057] It is judged that the system is in a normal operation state or an out-zone fau!t state when all of the phase differences between the U1 and Uu in the respective TRANSLAY relays Relay!, Relay2, Relay3 satist' 90° »= Arg-»= -90°.

[0058] When the system is in the in-zone fliult state, the pilot wire differential protection apparatus (hr the three-end power transmission and distribution lines is triggered to perfbrm the protection.

[0059] Fig 5 is an exemp!ary view illustrating a wiring in a pilot wire differential phase-compared protection apparatus applied to a multi-end circuit according to a second embodiment of the present invention. to

[0060] Tn Fig 5, a plurality of scts of TRANSLAY relays Relayl, Rclay2, Relay3 Relayn are connected at the end I, end 2, end n of the power transmission and distribution lines, respectively, the summation transformers T1 of the respective TRANSLAY relays Relayl, Relay2, Relay3 Relayn are connected to an a phase, a b phase, a c phase and a neutral point at the protected circuit end, and pilot wire connecting terminals Px and Py of the respective TRANSLAY relays Relayl, Relay2, Rclay3, Rclayn arc connected with each other in parallel, respectively.

[0061] Tn the above connection, configurations of each set of the TRANSLAY relays at the end 1, end 2 end n should be same completely. That is, all of other elements and parameters in the relays illustrated in Fig I arc the same without considering errors, other than the Rpp. The connections and configurations at the plurality of ends are same, therefore the plurality of ends are symmetrical completely.

[0062] Thus an equivalent circuit diagram for the pilot wire differential phase-compared protection apparatus applied to the multi-end circuit according to the second embodiment of the present invention shown in Fig 5 may be illustrated as Fig 6.

Rw is a resistance on the pilot wire in Fig 6.

[0063] At each of the ends, a resistor Rpp of the respective TRANSLAY relay is adjusted so that Rpp + Rw = k * R0 is satisfied at each of the ends, k is a set constant, and the values of k in each of the TRANS LAY relays are identical.

100641 According to the structure of the TRANSLAY relay, by making the protection at the relay Relayl end as an example, currents flowing through the To, Tr and Ro of the Relayl may be calculated as follows, respectively, from Fig 6: Ji ((n_T)*l1 -(2 +...+1fl/(n*k+n)and ((n*k+fl*j +(12 +...+I))/(n*k+n).

[0065] According to the design principle of the TRANSLAY relay, voltages at the windings Tt and Ts are in-phase, and voltage on the Ro is approximatively same as that on the Ts, therefore a voltage at the Tt side of the phase comparator satisfies an equation (4), wherein K1 is a calculation constant.

[0066] TJ[KJ *((n*k+l)*j (2 +...+Ij) (4) [0067] A voltage at the T11 side of the phase comparator is decided by two primary windings To and Tr and satisfies an equation (5), wherein K11 is a calculation constant.

[0068] 1J1=K11 *(((n*k+n)*T0 /Tr_n+1)*11 -i-U. +...+1)) (5) [0069] Given = , which is a current ratio between the sum of current vectors in remote ends and the current in local end, then: [0070] 900 »= Arg = Arg -(-n * k -I) _900 (6) U11 _(_(n*k+n)*T iTr+n-l) [0071] Assuming a value of k selected suitably, that is, the value of k satisfies a condition of _n*k_1 <-1< _(n*k+n)*T/Tr+n_1 when To<Tr, or the value of k satisfies a condition of _(n*k+n)*T /Tr+n-1 <-1 <-nk-1 when To>Tr, a region corresponding to the current ratio between the sum of current vectors in remote ends and the current in local end in the equation (6) is circular on a complex plane, as illustrated in Fig 7.

[0072] Fig 7 is a motion trajectory of a differential protection for the pilot wire differential phase-compared protection apparatus applied to the three-end circuit according to the first embodiment of the present invention.

100731 When the system operates normally or has an out-zone fault, p1 = -/ is -1 under ideal conditions, therefore a portion inside the circle corresponding to the pi is a restraining zone or stable zone.

[0074] Further, when the system has an in-zone fault, a portion outside the circle corresponding to the p is an operating zone.

[0075] Thus the in-zone fault and the out-zone fault may be judged by comparing the phases of U1 and Uji.

[0076] In particularly, in an actual application, when 90° »= Arg-Y.. »= 90°, the system operates normally or is in the out-zone fault state; if 900 »= Arg-!J1-»= -90° is not satisfied and a start current of the relay is greater than a set threshold value, the system is in the in-zone fault state.

[0077] That is, it is judged whether the 90° »= Arg--»= -90° is satisfied if fault occurs in the system: it is the in-zone fault if the 90° »= Arg »= -90° is not satisfied and the start current of the relay is greater than the set threshold value; and it is the out-zone fault if the 90° »= Arg-2-»= -90° is satisfied.

[0078] Above descriptions are made by taking the relay Relay I end as an example, and the phase differences between the Ui and U11 in the Relay2, Relay3 Relayn also can be used to make judgment. The phase differences between the Ui and Li11 in the respective TRANSLAY relays Relayl, Relay2, Relay3, Relayn are independent of each other.

[0079] It is also obviously that, when the system operates normally or has the _______ ________ i1+1,...+1"_1 out-zone fault, p1= , are-i 2 n under the ideal conditions, therefore portions inside the circles corresponding to the respective p are the restraining zones or stable zones. Further, when the system has the in-zone fault, portions outside the circles corresponding to the respective are the operating zones.

[0080] It is judged that the system is in the in-zone fault state, when at least one of the phase differences between the U1 and U11 in the respective TRANSLAY relays Relayl, Relay2, Relay3, Relayn does not satisfy 90° »= Argi_ »= -90° and the start current of thc relay is greater than thc sct threshold value.

100811 It is judged that the system is in the normal operation state or the out-zone fault state when all of the phase differences between the Ui and U11 in the respective TRANSLAY relays Relayl, Relay2, Relay3 Relayn satisfy 90° »= Arg1-»= -90°.

[0082] When the system is in the in-zone fault state, the pilot wire differential protection apparatus for the three-end power transmission and distribution lines is triggered to perform the protection.

[0083] Thereafter will describe a method for the pilot wire differential phase-compared protection apparatus according to the first embodiment and the second embodiment of the present invention.

[0084] The pilot wire differential phase-compared protection method according to the present invention is applied to the above power transmission and distribution lines having thee-end or multi-end connection. Following description is made by taking the pilot wire differential phase-compared protection apparatus applied to the multi-end circuit according to the second embodiment of the present invention as an example.

[0085] At step 1, measuring the phases of the voltage U1 at the Tt side of the phase comparator and the voltage Vu at the T11 side of the phase comparator in the respective TRANSLAY relays Relayl, Relay2, Relay3 Relayn; [0086] at step 2, comparing the phases of U1 and Ujj in the respective TRANSLAY relays Relayl, Relay2, Relay3 Relayn so as to obtain the respective phase differences Arg---;

U

H

100871 at step 3, judging whether the phase differences between the Ui and UTT in the respective TRANSLAY relays Relayl, Relay2, Relay3 Relayn satisfy 90° »= »= _9Ø0. U11

[0088] It is judged that the system operates normally or is in the out-zone fault state when all of the phase differences between the Uj and Ujj in the respective TRANSLAY relays Relayl, Rclay2, Relay3 Relayn satisfy 900 »= Arg2i »= -90°.

100891 It is judged that the system is in the in-zone fault state, when at least one of the phase differences between the U1 and Vu in the respective TRANSLAY relays Relayl, Relay2, Relay3, Relayn does not satisfy 90° »= ArgA1-»= 9O and the start current of the relay is greater than the set threshold value.

[0090] At step 4, the pilot wire differential protection apparatus for the multi-end power transmission and distribution lines is triggered to perform protcction when the system is in the in-zone fault state.

[0091] The pilot wire differential phase-compared apparatus and method of the present invention which are applied to the multi-end circuit can judge the in-zone fault and out-zone fault in the multi-end circuit efficiently, extends an application range of the TRANSLAY protection apparatus and enhance a market value of the TRAINSLAY protection apparatus.

[0092] Although the exemplary embodiments considered in the invention has been illustrated and described, those skilled in the art may understand that many changes and amendments may be made or some elements may be replaced with other equivalences without departing from the real scope of the invention, with developments in the teclmique.

Claims

Claims: 1. A pilot wire differential protection apparatus for a power transmission and distribution lines including three or more connecting ends, comprising: three or more TRANSLAY relays (Relayl, Relay2, Relay3, Relayn), which are sequentially connected at the corresponding connecting ends (end 1, end 2, end n) of the power transmission and distribution lines, respectively, wherein summation transformers of the respective TRANSLAY relays Relay1, Relay2, Relay3 Relayn) are connected to an a phase, a b phase, a c phase and a neutral point at the connecting ends of the corresponding protected circuits, and a pilot wire first connecting terminal and a pilot wire second connecting terminal of the respective TRANS LAY relays (Relay 1, Relay2, Relay3 Relayn) are connected with each other in parallel, respectively, wherein the TRANSLAY relays comprise corresponding phase comparators, respectively, for comparing corresponding phases of Ui and U11 in the respective TRANSLAY relays (Relayl, Relay2, Relay3 Relayn) so as to obtain a corresponding phase difference ArgL, wherein Ui is a voltage at one side of the phase comparator, that is, a voltage at a secondary winding side of the relay, U11 is a voltage of the other side of the phase comparator, that is, a voltage at a auxiliary transformer side of the relay, and a false state of the power transmission and distribution lines is judged according to the corresponding phase differences Arg, wherein, at each of the connecting ends, a pilots padding resistor Rpp of the respective TRANSLAY relay is adjusted so that Rpp + Rw = Ic * R0 is satisfied at each of the ends, k is a set constant, Rw is a resistance on the pilot wire, and Ro is a linear impedance of the TRANSLAY relay, wherein a value of k satisfies a condition of _n*k_1 <-1 <-(nHc +n)*T0/Tr+n_1 when To<Tr, or the value of k satisfies a condition of _(n*k +n)*T0/Tr+n_1 <-1 <-n'k -1 when To>Tr, To is number of turns of an operating winding in the TRANSLAY relay and Tr is number of turns of a restraining winding in the TRANSLAY relay.
2. The pilot wire differential protection apparatus of claim 1, wherein, it is judged that a system of the power transmission and distribution lines is in an in-zone fault state and the pilot wire differential protection apparatus is triggered to perform protection, when at least one of the phase differences in the phase comparators of the respective TRANSLAY relays (Relay!, Relay2, Relay3 Relayn) does not satisfy 900 »= Argi_ »= _90° and a start current of the relay is greater than a set threshold value.
3. The pilot wire differential protection apparatus of claim I or 2, wherein, it is judged that the system of the power transmission and distribution lines is in a normal operation state or an out-zone fault state when all of the phase differences between the U and U11 in the respective TRANSLAY relays (Relayl, Relay2, Relay3, Relayn) satis1r 90° »= »= -90°.
4. The pilot wire differential protection apparatus of claim 1, 2 or 3 wherein, the phase comparator is an analogous phase comparator or a digital phase comparator.
5. A method of operating a pilot wire differential protection apparatus of any preceding claim, comprising steps of: measuring phases of corresponding Uj and U11 of respective TRANSLAY relays (Relayl, Relay2, Relay3 Relayn), wherein U1 is a voltage at one side of the phase comparator, that is, a voltage at a secondary winding side of the relay, and U11 is a voltage of the other side of the phase comparator, that is, a voltage at a auxiliary transformer side of the relay; comparing, by corresponding phase comparators in the TRANSLAY relays, the phases of Uj and Ujj in the respective TRANSLAY relays (Relayl, Relay2, Relay3, Rdayn) so as to obtain a corresponding phase difference and judging a false state of the power transmission and distribution lines according to the corresponding phase differences wherein, at each of the coimecting ends, a pilots padding resistor Rpp of the respective TRANSLAY relay is adjusted so that Rpp + Rw = k * R0 is satisfied at each of the ends, k is a set constant, Rw is a resistance on the pilot wire, and Ro is a linear impedance of the TRANSLAY relay, wherein a value of k satisfies a condition of _n*k_l< _1<_(n*/c +n)*T0/Tr+n_1 when To<Tr, or the value of k satisfies a condition of _(n*k +n)*I/Tr+n_1 <-1 <-nk -1 when To>Tr, To is number of turns of an operating winding in the TRANSLAY relay and Tr is number of turns of a restraining winding in the TRANSLAY relay.
6. The method for the pilot wire differential protection apparatus of claim 5, wherein, it is judged that a system of the power transmission and distribution lines is in an in-zone fault state and the pilot wire differential protection apparatus is triggered to perform protection, when at least one of the phase differences in the phase comparators of the respective TRANSLAY relays (Relay 1, Relay2, Relay3 Relayn) does not satisfy 900 »= ArgL »= _9Ø0 and a start current of the relay is greater than a set threshold value.
7. The method for the pilot wire differential protection apparatus of claim 5 or 6, wherein, it is judged that the system of the power transmission and distribution lines is in a normal operation state or an out-zone fault state when all of the phase differences between the U1 and Uu in the respective TRANSLAY relays (Relayl, Relay2, Rclay3, Relayn) satisfr 9r»=ArgJ-»=_9o0.
8. The method fbr the pilot wire differential protection apparatus of claim 5, 6 or 7 wherein, the phase comparator is an analogous phase comparator or a digital phase comparator.