CA1312941C - Protective relay with selective phase selection for double lines - Google Patents

Protective relay with selective phase selection for double lines

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Publication number
CA1312941C
CA1312941C CA000587074A CA587074A CA1312941C CA 1312941 C CA1312941 C CA 1312941C CA 000587074 A CA000587074 A CA 000587074A CA 587074 A CA587074 A CA 587074A CA 1312941 C CA1312941 C CA 1312941C
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Canada
Prior art keywords
fault
station
phase
stations
line
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CA000587074A
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French (fr)
Inventor
Sten Bergman
Stefan Ljung
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ABB AB
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Asea Brown Boveri AB
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Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/267Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for parallel lines and wires

Abstract

ABSTRACT

The invention comprises a protective relay with selective phase selection in electric power distribution systems when there are double transmission lines (M1-P1,M2-P2) between two stations (TM, TP) and where the ends of the line are connected to a common busbar system located in each station. The protective device comprises a protection unit, terminal, at both ends of each line.
All the terminals (M1, M2, P1, P2) comprise an identical basic design comprising measurement of phase quantities (17), filter-ing (18) and A/D conversion (19). Furthermore, the identical part comprises a parameter estimator (20) for Fourier series expansion of measured phase signals and generation of the respective residuals. The parameter estimator cooperates with a frequency estimator (21) and a sampling regulator (22).
Each basic design also comprises a local logic unit which, by means of a transient and steady state analysis, finds out whether an event on the network is due to a fault or a connection/dis-connection of the phase/line and the current direction at each terminal. At one of the terminals, at both stations, there is a station master unit (26) which compiles all information for the station in question, calculates the distance to a fault, etc. For final decisions as to whether a recorded fault lies between the stations, as to faulty line(s) and phase(s), all information from the two stations is compiled in a superordinate unit (29) in one of the terminals at one of the stations. (Figure 2)

Description

~ 3 ~ 2 ~

Protective relay with selective phase selection for double lines TECHNICAL FIELD

For reasons of security, extension and economy, and other reasons, sometimes double electric power transmission lines are used between two stations. In practice, each station is then provided with a busbar system to which the two lines are connected. Normally, the maximum distance bet~Jeen the connec-tion of the lines to the same busbar system amounts to 20-30 m. The supply concept, i.e. the current direction in the lines, may be different depending on the load and the supply of elec-tric power, It has been found to be difficult to make a correct phase selec-tion in the case of a fault on any phase or line in a double line system. It seems to be particularly difficult to distin-guish single-phase faults which occur at short time intervals in different phases on the two lines. The present invention entails considerably improved conditions for a proper fault judgm_nt~ Also~ only the necessary measures, for example a single-phase disconnection, need be taken.

BACKGROUND ART, THE PROBLEM

~0 As prctectlon against ~round faults on double lines, according to the state of the art distance relays are usually used, which are normally based on impedance measurement. Within the current techn~cal field these are so well-known that no further descrip_ tion of them will be made, Different embodiments are disclosed, ~5 ~or example, in U.S. Patent No, 4,636,909 (Brandt), As mentioned by way of introduction, the use of impedance based protection devices in connection with double lines entails cer-tain problems of distinguishing faults~ for example when a phase fault in different phases occurs on the lines at short time , ~

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intervals. This has proved to be particularly difficult on double line systems which comprise series capacitors. In the case of a fault according to the above, in this situation normally all the phases of a conventional distance relay trip, which is due to the fact -that they are not capable of distinguishing the situation from the case where a multi-phase fault has occurred in one of the double lines.
Tllus, all three p~lases are disconnected, even when in xeality it would have been possible to break only the faulty phase.

The impedance plane analysis can be performed both analoyically and with the aid of compu~erized programs. In an axticle by Phadke and Jihuang published in IEEE Trans. on P~S, Vol. P~S-104, No. 2, February 1985, pp. ~45-452, entitled '`A Computer Based Integrated Distance Relay for P~rallel ~ransmission Lines", a method is described which is based on impedance plane analysis of the status of the line seen rom one end. A measuring point is placed at one end of each line and tlle resul-ts are coordinated. ~owever, this may be a dangerous method since it may be difficult to analyze such cases where the fault occurs in the vicinity of the other end of the line. A method of overcoming this deficiency is provided b~ the technique described in EP 0 015 259 entitled "A method and a device for detection of the position of a fault in an electric connection". According to tllis method, a relay uni-t is used at each end and each l~ne of the protected line zone. However, also in this case there is still a need to study impedances to de-termine in what phase~s) and what line all the faults occur.

The technical basis for protection using selective phase selection in connection with double lines according to the invention is based on the technique which is described in . i.~... ~ ~

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detail in Canadian patent application ~77,446. A brief resumé o~ these applicationg will be given here.

Measured signals for phase currents and phase voltages obtained from the power network are transformed, after iltering and diyitization, into an analytical ~odel in the form of a harmonic /

( 1sin ot ~ a2cos~0t). The Fourier coefficients are determined in a parameter estimator operating with an estimation method according to the least squares method.
With the aid of the model an exact calculation can be made of the fundamental frequency of the model in a frequency estimator, the output signal of which is returned to the parameter estima-tor, SE 8703580-4 shows, for example, that the angular frequen-cy ~ for the model can be calculated with the aid of three con secutive sample values Y1, Y2, y3 of the processed signal as 0 -1 Y + Y3 ~ = h arcos ~
where h is the distance in time between the sample values.

The current parameter estimation method will be clear from the following.

The measured signals in question can, in general, be modelled by N

y~t) = aOexp(-bOt) + ~ cjsin(~j t~dj) (1) which can be transformed into y(t) - O ~(t) (2) where ~0 0 = (aO, _cobo, clcosd1, c1sind1, ... cNcosdN, cNsindN) ~3) is a parameter vector and ~t) - (1, t~ sin~Ot, cos~Ot, ... sinN~Ot, cosN~Ot) (4) is a regression vector.

Estimation of the parameters according to the least squares method entails that the value of a "loss function" VN is mini_ mized. VN can be written as .

VN(A, t) = ~ 1~2(~ , VN(,~, t_1) ~ ~2(t) (5) where A is a forgetting factor and where ~(t) is an estima-tion error function (a residual) as defined by ( 11 ) .

The minimization gives the following equation to comp~te an estimation tc ~(t), ~

~(t) = ~ p 1 (n) ~ ~ t~ T(j)] -1~ ~ t_j~ (6) The actual estimati~n is performed recursively with the aid of the following algorithm R(t)=~ R(t-1) + ~(t)~-T(t) (7) 10 R(O) = ~I (8) R(t)L(t) = ~(t) (9) y(t) - ~Ttt~1)~(t) (10) ~(t) = y(t)-y(t) (11) ~t) = ~(t-1) + L(t)~(t) (12) 1~ Here, R(t) is the covariance matrix of the regre3si~rl vector and P(t), according to the following, is the inverse thereof.
Otherwise, the following recurrence formulae will be used:

r(t) - P(t_1)~(t) t13) d(t) = ~ ~ ~ (t)r(t) (14) 20 L(t) = r(t)/d(t) (15) P(t) = (P(t-1)-r(t)LT(t))/~ (16) (O) = (1/~)~ I (17) .
.

,: ~ -2 9 .L
, ~(G) = ~0 (18) Otherwise, the same criteria as are used in the above-mentioned Swedish applications are used in this protective concept as well as regards phase selec-tion and determination of direction to a fault and as regards the possibilities of distinguishing a fault situation from a connection or disconnection of a phase and/or a line.

These criteria can be described as follows. A test whether an abrupt event has occurred is performed as a transient analysis oE suitable loss functions according to (5) by comparing the values of the functions against set threshold values. If the limit values have been exceeded, a steady state analysis is performed in order to find out whether the event is due to a fault or to a connection/disconnection of a phase and/or a line. This can be done by a study of the Fourier componen-ts before and after the event. If the result oE this analysis shows that a fault has occurred, the faulty phase can be determined by the study of the loss function of the phase voltages or by a study of the amplitude of the harmonics.

Knowledge of the direction to a fault can be obtained by finding out the current direction at the two end points, which can be done with the aid of a study of the polarity of the current residuals after the determination of a faul~.
This presupposes that measuring stations are provided on both sides of the protected line and that communication ~acilities are provided between the two ends of the line.
to determ.ine whether the fault occurs in the protected line, it i8 sufficient to study two situations, namely, whether the currents at both end points are directed away from the line or towards the line. In both of these cases the fault . .

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~.~3~ ~J ~ '~ .L

- Sa -is located on the protected line iE the signs on -the residuals are the same.

According to the present invention, there is provided a protective relay with selective phase selection in electric power distribution systems when there are double transmission lines between two stations TP, TM and where the ends of the line are connected to a common busbar station in each station, which protective relay, consisting of a protection unit at a terminal Ml,M2~Pl,P2 at both ends of the line, comprises an identical basic design arranged in each protection unit having a measuring device for measuring the current I and voltage E of the phase quantities, a filter fox higll-fre~uency filtering of the measured signals lS nnd an A/D convertor for conversion from analog to digital representation of the measured and filtered signals, ~aid digital signals being adapted to be supplied to a Fourier coeficient estimator cooperating with a fre~uency estimator and a sampling regulator, said Fourier coe~ficient estimator being adapted to generate the Fourier components ~ for a truncated model M = al sin ~ot + a2 cos ~ot of measured phase quantities and the xespective residuals ~(t), characterized in that the Fourier components estimated by the parameter estimator and the residuals are adapted to be ~upplied to a local logic unit adapted to determine whether ~n abrupt event has occurred in the power distribution system by comparing the loss functions VXnEP(t) and VXnIP(t) with the respective threshold values nE and nI according to j_l ( xn(~ VXnp~t - 1~ EP(t))2~

.._ ... .. _, xn ~`l At i~'xnP~i))2 = ~VInP(t - 1) + (~IP(t)~2 1~`
.~

~ ~t3.~ 2~ ~
5b -where xn ~(M1, M2, P1, PZ),E indicates that V-functions and residuals are based on voltage values, I indicates that the same functions are based on current values, p~(R,5,T), ~ is a forgetting factor within the range 0.9~1.0, and that, i.f the threshold values have been exceeded, the local logic unit is adapted to initialize a restart of the parameter estimator and determine whether the abrupt event derives from a conventional fault in the power distribution system by comparing a function f= ~al2 ~ a 2 with two threshold values no and ni according to no>~al2 + a2~ ~ni. and if the function lies within the threshold region, -the local logic unit is further adapted to determine the current direction at each terminal by determining whether the signals of the integrated current residuals according to WIP = wIP~t-l) + ~Ip(t) xn xn xn are greater than or smaller than zero, and that at one of the terminals M2, P2 at each station there is arranged a transmitter intended to transmit the information, obtained in the local logic unit at these terminals, to a receiver in the other terminal Ml,Pl at the same station, and that the information, thus gat~ered, for each respective station is adapted to be supplied to a master logic unit which is adapted, for each of the stations, to coordinate inEormation nbout the direction to a fault and a faulty phase or faulty phases and, with the aid of the voltage and current residuals, to obtain an indirect measure of the distance ~rom the respective station to a fault, and that in one of ~0 the master -terminals P1 there is arranged a second ~ransmitter intended to transmit the station in~ormation, collected in that terminal, -to a receiver in the master terminal Ml in the second station, and that t~le information thus gathered from both stations is adapted to be supplied , , .

- 5c -to a superordinate unit adapted to determine whether a fa~lt is located between the stations and is further adapted to allow the information from the station located nearest the fault to decide on trip signals for a faulty line and/or phase ( s ) O

BRIEF DESCRIPTION OF T~IE DRAWING
.

Figure 1 shows a combined function and action diagram for a .

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protecti~e relay according to the invention, and Figure 2 shows a preferred embodiment of a protective relay with selective phase selection for double lines~

DI~CLOSURE OF THE INVENTION

The protection concept for high resistance ground faults for double lines according to the invention will be described with reference to a combined function and action chart according to Figure 1. Between two stations TM and TP there are two parallel transmission lines, one so-called double line, connected to a busbar system in each station. One of the lines is designated M1-P1 and the other M2-P2. At each line end there is a local protection unit or terminal, designated M1 and M2 at station TM and P1 and P2 at station TP, respectively.

All the protection units comprise certain identical basic com-ponents/functions according to known technique, which are needed to implement the inv~ntion and which have roughly been described under the heading "BACKGROUND ART, THE PROBLEM". The descrip-tion of these according to Figure 1 will only comprise the pro-tection unit at terminal M1.

The function MEASUREMENT, indicated at 1, comprises measurement of all the phase currents and voltages at the measuring point, i,e. in Figure 1 at line M1-P1 at the end M1. The function FILTER A/D, at 2, comprises high frequency filtering and analog-to-digital conversion of the measured phase quantities.

The function ESTIMATION, at 3, is to be described in more detail.
lt comprises a method for estimation of the Fourier coefficients o~ the measured signals, which also includes a method for es_ timation of the frequency of the measured signals, and a samp_ ling regulator for adaptation of the sampling time so that the number of nodal points per cycle is constant. In addition to estimated values of coefficients and frequency~ this function ~:

~'~, ~ ''', ' ~3~ ~J ~

also comprises generation of the residuals ~(t) of the measured signals 7 i.e. the estimation errors.

The function FA~LT DETECT, at 4, comprises computation of a number of loss functions and local logic decisions based on the operating values obtained. This part will also be described in some more detail as applied to the current protection con-cept. As described above under ~BACKGROUND ART~, the fault detection comprises a transient and a steady state analysis.
An abrupt event in Ml can be determined if the loss functions V~ t) = ~t At-j(~6Mp(j))2 = ~V~P1(t-1) + (~P1(t))2 (19) with ~ ~(E: phase voltage, I: phase current) and ~ ~(R, S, T) exceed the set threshold values.

With x ~(M, P) and n ~(1, 2), the loss functions for all the terminals can be expressed as v~nP ( t ) = 2 At ~ ~ n ( j ) ) 2 = ,)~ v~nP( t - 1 ) ~ P ( t ) ) 2 ( 20) An abrupt event can thus be determined if, for any comblnation of the parameters p, x, n, any of the following relations is valid VxnP~t) ~E (21) VxP(t) ' qI (22) i.e. when any of the threshold values has been exceeded.

As will also have been clear from the description of the prior art~ this criterion is not sufficient to determine whether what has occurred is due to a conventional fault or if it is due to a (dis)connection of any phase(s) or line. The steady state analysis which is necessary for this can be performed as follows.

If a function f (a1~ a2) of the Fourier components a1 and a2 of the fundamental component of any of the phase voltages is lower than a set limit value, for example ~0, this indicates that the phase in the corresponding line is disconnected.
This can, for example, be determined by studying the inequality ~ ' ~o (23) So that the protective device at one therminal should not give an incorrect indication in the case o~ connection of a line, in the same way as above a steady state analysis is also required, which is also suitably based on Fourier components, expressed, for example, by the inequality ~ > ~j (24) However, it is necessary that a certain time elapses from the indication of an abrupt event until the testing according to the above relation is performed.

Now, if both the transient and the steady state analyses have shown that a fault has occurred, the direction to the fault is to be determined. This is done with the function DIRECT.DETERM. according to 5 in Figure 1. For this purpose the current directions in all protection units have to be determined. An indirect determination of the current ~5 direction can be obtained, as stated above, by studying the signs o~ the current residuals. To obtain a representative value, the polarity should be studied for a certain period of time, which can be done by a simple~ integration, for example by studying the functions WIP (~)~ W~P~t~ P(t) (25) ~or associated values of x, n and p. Depending on how the curront directions are defined and the sign of the W-:
- :. . .. ~ ~ :
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8a quantities, corresponding to the currents, it is possible, as is clear from above, to determine whether the fault is located behind, i.e. outside the zone, or located ahead, i.e. on the line side of the station.

`

, ~ 3 1 2 ~, ,t~_ As will be clear from Figure 1, the functions 1-5 are equal for all four protection ur.its. For directional determination, etc., at each station, communication between the protection units at M1 and M2 and between P1 and P2, respectively, is needed. It is then suitable to designate one of the terminals at each station as master. From Figure 1 it is clear that, in the example shown, these master functions have been assigned to terminals Ml and P1.

The functions according to 6 at terminals M2 and P2, i.e. TRANS-MIT INFO M2 and TRANSM`T I~FO P2, respectively~ comprise the transmission of data concerning the fault, the direction to the fault and residuals to RECEIVER M1 and RECEIVER P1 t respec-tively, at 7, at terminals M1 and P1, respectively. Because of the short distance between M1 and M2 and P1 and P2, respec-tively, no communication problems may arise, since optical fibretechnique offers a feasible medium for communication.

The assigned M- and P-masters are provided with the functions INFO M and INFO P, respectively, as shown at 8. These functions are supplied with the available information from M1, M2 and P1, P2, respectively, whereby opportunities are created for deter-mining the direction to a fault, the fault type and the fault distance. If, for example~ both terminals at TP, according to the criteria described above, show that it is a question of a fault lying behind (outside of the zone), the fault has occurred outside of the protected lines. On the other hand, if, for example, terminal P2 indicates a fault lying behind and termi_ nal P1 indicates a fault lying ahead, this indicates that the fault is to be found on the line P1-M1. However, the fault may be located behind terminal M1. The reverse is, of course, true for a ~ault on the line P2-M2. The corresponding reasoning and result are obtained with the M-master. As has been mentioned above~ however, for the final determination of the direction to the fault and of the phase, communication is necessary also between the two stations.

The function FAULT TYPE, shown at 9, comprises the determination of what phase or phases is/are faulty (see table 1). As pre_ ...
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viously described, this can be determined by studying the loss functions of the phase voltages or by studying the amplitude of the harmonics.

As has also been mentioned previously, it is necessary to make an approximate judgment of the fault distance to be able to see what station pair lies nearest to the fault and thus gain in-creased certainty in the final determination of the faulty phase, which can be diffic~llt when the fault is located far from one of the stations. With the function FAULT DISTANCE, shown at 10, such an approximate determination can be made with the aid of the Fourier coefficients for the currents and the voltages.

All information from the M- and P-masters is now to be put to~ether for the final decision on what measures to take with respect to the fault. For this purpose~ a superordinate unit must be provided, which in Figure 1 is shown integrated into terminal ~1. Via the function TRANSMIT INFO P, shown at 11, collected P-information is transmitted to the M_master~ which via the function RECEIVER M-P, at 12, conveys the collecte~
M- and P-information to the superordinate unit (SUPERORD. UNIT), With the aid of the directional information from both the M-and P-sides~ it can now be definitively determined, via the function FAULT WITHIN ZONE at 13, whether the fault whicn has occurred lies on the double line and possibly on which of the lines, or if it lies on both. The decision logic is based on the below table 1, where B stands for a fault lying behind or out.side and A stands for a fault lying ahead. Since for each one of the four terminals two different fault directions are available, there will be sixteen possible final alternatives.
3~ As will be clear from the table, in seven of the alternatives the fault is located outside the protected zone~ which means that at least one of the pairs has detected that the fault is located behind the nearest busbar. In three of the cases, the ~ault is located on line 1 and in three of the cases it is located on line 2. When all the terminals indicate that the fault has occurred in front of the measuring points, there is a fault on both the lines. Then three cases remain, namely, when the pairs indicate a fault on different lines. If any of these situations arises, the faulty phase is determined start-in~ from the measuring pair which is close~st to the source ofthe fault. It should be noted that this ~able is based on binary information and the direction from each of the terminals for one phase. This means that t~e superordinate unit must handle three such tables at the same timeO In this wa~J, the logic is able to determine whether faults, which occur in different phases, lie outside or within the zone.

Table _ TERMINAL M1 M2 P1 P2 ¦ DECISION
. ~ . ; _~_ . , .
CURRENT , DIRECTIO _ B A ~ B A _B _ _A B A ~

A 4 X ~ X X X OUTSIDE

E ~ _ X X _ X X

N ~l X I X X X ON LINE
A 10 X ¦ X X X M1-P1 _ ~ _ _ _ . -- __ ?5T 11 X X X X FAULT
I 1? X X X X ON LINE
V 13 _ X X~ X X _ _ ~2-P~
__ _ _ _ . .

_ . _ __ To obtain the best best conditions for a correct phase selec_ tion~ data from that side which is nearest the source of the fault shall be determining. With the function SELECT P/M at 14, the most suitable side is thus selected, based on the .. ~i, .

13 ~d~

calculation of the fault distance at 10. With the aid of these data, ~he final phase determin~tion is made with the function FINAL PHASE DETERM., at 15, by studying the current residuals or Fourier coefficients in question.

For evaluation of the final TRIP DECISION, at 16, accnrding to the following table 2 nineteen different alternatives or combina-tions a.e available to decide about.

Table 2 _ .

ALTERNATIVES CHARACTERISTICS DECISIONS/ACTIONS
. . _ , . . _ , ¦ 3 ~ SM-FAULT DESIGNATED PHASE
4 ~ TM-E`AIlLr SHOULD BE
~ 5 ~ Rp-F'~l DISCONNECTED
6 Sp-E.;UI.T
7 ~ Tp-FA'JLr ! . ..
8 ¦ RM-Rp-FAULT
9 ~ RM-Sp_FAULT DESIGNATED PHASE
RM_Tp-FAULT IN EACH LINE
20 11 SM_Rp-FAULT SHOULD BE
12 SM_Sp-FAULT DISCONNECTED
13 SM_Tp-FAULT
14 TM_Rp_FAULT
TM-Sp-FAULT
~5 16 TM-Tp-FAULT
_ ~ ~ ~

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-(Table 2 continued) _ I
ALTERNATIVES' CHARACTERISTICS ¦ DECISIO~S/ACTIONS
. , ~ ,_ .

LINE 1~2-P2 = DISCONNLCTED

ONE LINE BOTH DISCONNECT~D
SINGL~-PHASE FAULT
IN THE OTHE~
. _ . ....... . _ ~

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 2 shows a preferred embodiment of a protective relay with selective phase selection for double lines acccrding to the invention. For natural reasons, Figure 2 shows great res~mblance to the func~ion and action chart according to ~igure 1. Between the two stations TM and TP there is a double line, one of which being referred to as M1-P1 and the other being referred to as M2-P2. At each line end there is a terminal, designated ~1, M2, P1 and P2. The terminals are supplied with all the respective phase-voltages and currents, commor.l~ designated E and I. The basic design for all four terminals is the same and the reference numerals for the same parts included are therefore- the same. The measurement of the incoming phase quantities is performed, in principle: in a measuring device 17. After high-~requency filtering in filter ~5 18, the signals are converted from analog to digital represen_ tation in the A/D convertor 19. Further, each basic design comprises a Fourier parameter estimator 20 and a frequency astimator 21 according to known technique, Also included is a sampling regulator 22, the task of which, as will have been 3~ ~laar, is to ensure that the sampling time is adapted in accor_ dance with current frequency changes of the processed signals.
Since the gain vector L(t) according to 15 is calculated during the initialization, it is necessary to adapt the time between the samplings such that the number of sample points per cycle is constant. This means that the sampling regulator must be supplied with the current frequency value ~0, the estimated Fourier signal y, and the parameter estimation vector â.

.. ~. ....
~ ~ "~

~ J3 Furthermore~ the basic design comprises a local logic unit 23 which, with the aid of residuals, calculates the current loss functions, compares these with the respective threshold values set, carries out the necessary transient and steady state ana-lysis to determine whether a fault has occurred~ and at thesame time finds out the current direction at the respective terminal.

The information thus obtained at terminals M2 and P2 is trans-mitted, in principle, via transmitter 24 to receiver 25 at terminals M1 and l~2. This information~ together with corre-sponding information from M1 and P1, is led to a logic M-master and logic P-master unit 26 located at terminals M1 and P1.
Here a collected determination of the information of the M-side and the P-side as well as an approximate judgment of the fault distance from the respective station are made~ suitably by determining the impedance up to the site of the fault with the aid of the Fourier coefficients.

The collected infor~ation from the P-side is then transmitted~
in principle by some known technique~ via a transmitter 27 to a receiver 28 in the M-master unit of terminal M1. This infor-mation, together with corresponding information from the M_side, is passed to a logic superordinate unit 29, located in terminal M1. For the protective device according to the invention, this logic unit makes the final decisions as to whether the f'ault is located within the line zone in question, i.e. on any of the lines between stations TM and TP, finds out which of the P side or M-side lies nearest the fault and allows that side to be determining in connection with the decision on how to act. A
possible trip signal can thus be obtained, as well as informa_ tion about zone, line and phase.

It is, of course, of no consequence to which terminals the different master functions are referred. The transmission of`
information between the two terminals at one station and between the two stations, respectively~ can, of course, also be perfor-med using different technical media depending on the technical :
. .

~ ~ ~ 2 C !, ~
_ conditions which otherwise exist at the stations.

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., . . . :

Claims (2)

1. A protective relay with selective phase selection in electric power distribution systems when there are double transmission lines between two stations TP, TM and where the ends of the line are connected to a common busbar station in each station, which protective relay, consisting of a protection unit at a terminal M1,M2,P1,P2 at both ends of the line, comprises an identical basic design arranged in each protection unit having a measuring device for measuring the current I and voltage E of the phase quantities, a filter for high-frequency filtering of the measured signals and an A/D convertor for conversion from analog to digital representation of the measured and filtered signals, said digital signals being adapted to be supplied to a Fourier coefficient estimator cooperating with a frequency estimator and a sampling regulator, said Fourier coefficient estimator being adapted to generate the Fourier components e for a truncated model M = a1 sin .omega.0t + a2 cos .omega.0t of measured phase quantities and the respective residuals .epsilon.(t), characterized in that the Fourier components estimated by the parameter estimator and the residuals are adapted to be supplied to a local logic unit adapted to determine whether an abrupt event has occurred in the power distribution system by comparing -the loss functions VXnEP(t) and VXnIP(t) with the respective threshold values ?E and ?I according to where xn .epsilon.(M1 M2, P1, P2), E indicates that V-functions and residuals are based on voltage values, I indicates that the same functions are based on current values, p.epsilon.(R,S,T), .lambda. is a forgetting factor within the range 0.9-1.0, and that, if the threshold values have been exceeded, the local logic unit is adapted to initialize a restart of the parameter estimator and determine whether the abrupt event derives from a conventional fault in the power distribution system by comparing a function f = with two threshold values ?0 and ?i according to , and if the function lies within the threshold region, the local logic unit is further adapted to determine the current direction at each terminal by determining whether the signals of the integrated current residuals according to are greater than or smaller than zero, and that at one of the terminals M2, P2 at each station there is arranged a transmitter intended to transmit the information, obtained in the local logic unit at these terminals, to a receiver in the other terminal M1,P1 at the same station, and that the information, thus gathered, for each respective station is adapted to be supplied to a master logic unit which is adapted, for each of the stations, to coordinate information about the direction to a fault and a faulty phase or faulty phases and, with the aid of the voltage and current residuals, to obtain an indirect measure of the distance from the respective station to a fault, and that in one of the master terminals P1 there is arranged a second transmitter intended to transmit the station information, collected in that terminal, to a receiver in the master terminal M1 in the second station, and that the information thus gathered from both stations is adapted to be supplied to a superordinate unit adapted to determine whether a fault is located between the stations and is further adapted to allow the information from the station located nearest the fault to decide on trip signals for a faulty line and/or phase(s).
2. A protective relay with selective phase selection in electric power distribution systems when there are double transmission lines between two stations according to claim 1, characterized in that if the local logic unit at each terminal determines that the function lies out-side the threshold values , the trip signal is to be blocked.
CA000587074A 1987-12-29 1988-12-28 Protective relay with selective phase selection for double lines Expired - Fee Related CA1312941C (en)

Applications Claiming Priority (2)

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SE8705183-5 1987-12-29
SE8705183A SE459946B (en) 1987-12-29 1987-12-29 RELAY PROTECTION WITH SELECTIVE PHASE SELECTION FOR DOUBLE CABLES

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CA1312941C true CA1312941C (en) 1993-01-19

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US4864453A (en) 1989-09-05
EP0325786A1 (en) 1989-08-02
DE3880471T2 (en) 1993-11-04
DE3880471D1 (en) 1993-05-27
EP0325786B1 (en) 1993-04-21
SE8705183D0 (en) 1987-12-29
SE8705183L (en) 1989-06-30
SE459946B (en) 1989-08-21

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