Protective relay system provided with difference and addition filters

A protective relay system detects a first electric variable and a second electric variable of a power system to discriminate in a time series whether or not a fault portion of a line or equipment included in the power system exists within a predetermined range, so as to determine whether protection of the power system should be carried out. The system includes a digital filter for outputting a first difference electric variable data indicative of a difference between at least two sample data of plural sampling data of the first electric variable and a difference between at least two sample data of plural sample data of the second electric variable at plural sampling times of the time series. The system also includes an addition filter for outputting first and second additive electric variable data indicative of orthogonal vector data with respect to the first and second difference electric variable data. The system further includes a relay control unit for calculating controlled variables of a relay operation in the power system on the basis of the first and second difference electric variable data at a certain sampling time, so as to judge whether or not protection of the power system should be carried out.

TECHNICAL FIELD 
This invention relates to a protective relay system provided with a 
difference filter and an addition filter, and more particularly to a 
protective relay system substantially free from influence of harmonic 
components which may be included in a fault current. 
Background Art 
The main technical object of protective relay systems used for protecting 
the power system is to lessen influence of harmonic components of fault 
current and fault voltage produced at the time of system failure. 
Particularly, in recent years, since charge capacity component of the 
system in equipments or facilities such as cable (power) transmission line 
and/or phase modifying capacitor, etc. has been increased, the order of 
harmonic wave produced in the system power has tendency to increase (value 
twice or three times greater than the fundamental wave). 
For this reason, in a method of attenuating harmonic components by filter 
which has been conventionally applied, it is necessary to prolong delay 
time of the filter in order to ensure desired attenuation quantity, 
resulting in delayed operation time of the relay. In order to solve such a 
problem, there has been conventionally employed an approximation system 
such that even if any harmonic component is included in the system power, 
there essentially results no influence of the harmonic wave. 
One example of the system employed at present will be described below. 
In a transmission line 2 of FIG. 1, assuming now that voltage and current 
at point A of installation of a protective relay 1 are respectively v and 
i when transmission line impedance constants up to the fault point F are 
such that resistance is R and inductance is L, the differential equation 
of the transmission line 2 is expressed by the following equation (1) in 
the case where fault point (F) voltage is zero. By carrying out 
approximate calculation of the differential term (di/dt) of this equation 
(1), it is possible to calculate, with high accuracy, value proportional 
to inductance L without eliminating harmonic wave by using filter. 
##EQU1## 
An example of an actual method for digital operation practically applied is 
indicated below. 
EQU v.sub.m +v.sub.m-1 =R.multidot.(i.sub.m +i.sub.m-1)+L.multidot.(i.sub.m 
-i.sub.m-1) v.sub.m-1 +v.sub.m-2 =R.multidot.(i.sub.m-1 
+v.sub.m-2)+L.multidot.(i.sub.m-1 -V.sub.m-2) (2) 
When X(=.omega..sub.0 .multidot.L) is calculated from the equation (2), the 
following equation (3) is obtained. The frequency characteristic of the 
reactance value X.sub.m /X (true value) is represented by the following 
equation (4), and its characteristic is as indicated by line (a) of FIG. 
2. FIG. 2 is a graph in which frequency is taken on the abscissa and 
reactance measured value is taken on the ordinate. In this case, the line 
(a) indicates the characteristic in the case where sampling frequency is 
600 Hz, and the line (b) indicates the characteristic in the case where 
sampling frequency is 4800 Hz. 
##EQU2## 
EQU L.sub.m /L (true value)=tan (.omega..sub.0 T/2)/tan (.omega.T/2) (4) 
In this case, since i.sub.m =I.multidot.sin (.omega.t.sub.m) and v.sub.m 
=V.multidot.sin (.omega.t.sub.m +.theta.), differential approximation 
quantity "i.sub.m -i.sub.m-1 " and diffentiated quantity "v.sub.v 
+v.sub.m-1 " can be respectively expressed by the following equations (5) 
and (6). 
EQU i.sub.m -i.sub.m-1 =2I.multidot.sin 
(.omega.T/2).multidot.cos(.omega.t.sub.m -.omega.T/2) (5) 
EQU v.sub.m +v.sub.m-1 =2V.multidot.cos(.omega.T/2).multidot.sin(.omega.t.sub.m 
-.omega.T/2+.theta.) (6) 
In the above equation, T is sampling period, .omega. is angular frequency, 
and .theta. is voltage lead phase with respect to current. 
As shown in FIG. 2, it is understood that according as frequency deviates 
from that of the fundamental wave, value of L.sub.m /L (true value) 
becomes smaller than 1. This value is permitted to keep value in the 
vicinity of 1 at values approximately twice or third times greater than 
the fundamental wave if the value of (.omega.T/2) is further held down to 
lower value (the sampling period is reduced). The frequency characteristic 
when the sampling frequency is set to value eight times greater than the 
fundamental wave is shown FIG. 2(b). Namely, from a qualitative point of 
view, the relationship between the differential approximation quantity 
"i.sub.m -i.sub.m-1 " and the differentiated quantity "v.sub.m +v.sub.m-1 
" are as indicated by the following equations (7) and (8). From these 
equations, it is indicated that its approximation accuracy is improved. 
EQU sin (.omega.T/2).apprxeq..omega.T/2, cos(.omega.T/2).apprxeq.1 i.sub.m 
-i.sub.m-1 =2I.multidot.sin (.omega.T/2).multidot.cos (.omega.t.sub.m 
-.omega.T/2) .apprxeq.2I.multidot.(.omega.T/2).multidot.cos 
(.omega.t.sub.m -.omega.T/2) (7) 
EQU v.sub.m +v.sub.m-1 =2V.multidot.cos (.omega.T/2).multidot.sin 
(.multidot.t.sub.m -.omega.T/2+.theta.) .apprxeq.2V.multidot.sin 
(.omega.t.sub.m -.omega.T/2+.theta.) (8) 
Accordingly, if the sampling frequency is caused to become high (the period 
is reduced), the approximation accuracy of differentiation can be 
improved. However, the value of the equation (7) becomes very small value 
with respect to the amplitude value I, and noise error .epsilon. included 
in the sample or sampled data "i.sub.m, i.sub.m-1 " effectively becomes 
great. From a viewpoint of practical use, it is very difficult to ensure 
accuracy. 
EQU (i.sub.m -i.sub.m-1)/(.omega..sub.0 T/2) 
.apprxeq.2I.multidot.(.omega./.omega..sub.0).multidot.cos (.omega.t.sub.m 
-.omega.T/2))+.epsilon./(.omega..sub.0 T/2) (9) 
In the above equation, .epsilon. is noise error. This noise error is white 
noise, etc. produced in the analog circuit, and quantization error, etc. 
produced at the time of analog-to-digital conversion. 
When the sampling period T=i/4800 sec., and .omega..sub.0 
=2.pi..multidot.50 Hz, error of the portion ".epsilon./(.omega..sub.0 
T/2)" of the equation (9) is as indicated by the following equation (10). 
The error is amplified so that it becomes equal to value 30 times greater 
than the original value. 
EQU .epsilon./(.omega..sub.0 T/2)=96.epsilon./.pi..apprxeq.30.557.epsilon.(10) 
SUMMARY OF THE INVENTION 
This invention has been made in view of the above-mentioned circumstances, 
and its object is to provide a protective relay system in which error 
amplification by differential approximation is suppressed so that there 
results the characteristic that L.sub.m /L (true value) is unlimitedly 
equal to 1 in broad frequency band, and free from influence of harmonic 
components produced in fault voltage/fault current of the power system. 
To achieve the above-mentioned object, a protective relay system according 
to this invention is directed to a protective relay system adapted for 
detecting, in time series manner, first electric variable (quantity of 
electricity) and second electric variable of the power system to 
discriminate on the basis of changes in the respective electric variables 
in the time series whether or not fault portion (point) of line or 
equipment included in the power system exists (falls) within a 
predetermined range thus to protect the power system, the system 
comprising: digital filter means including a difference filter for 
outputting first difference electric variable data indicative of 
difference between at least two sample data of plural sample data of the 
first electric variable and second difference electric variable data 
indicative of difference between at least two sample data of plural sample 
data of the second electric variable at plural sampling times of the time 
series, and an addition filter for outputting first and second additive 
electric variable data indicative of data respectively orthogonal to the 
first and second difference electric variable data in terms of vector; and 
relay control means for calculating controlled variable of the relay 
operation in the power system on the basis of the first and second 
difference electric variable data at a certain sampling time, first and 
second additive electric variable data at the certain sampling time point, 
the first and second difference electric variable data at any other 
sampling time point and the first and second additive electric variable 
data at the other sampling time point to judge (discriminate), on the 
basis of the controlled variables, the operation as to whether or not 
protection of the power system should be carried out. 
In the above-mentioned protective relay system, the difference filter is a 
filter in which transfer function "Z.sup.-k =Z.sup.-q " (Z is Z transform 
operator and k&lt;q) is used to output voltage data v.sub.jm and current data 
i.sub.jm serving as the first and second difference electric variable data 
at certain sampling time t.sub.m and voltage data v.sub.jm-p and current 
data i.sub.jm-p at any other sampling time t.sub.m-p, and the addition 
filter is a filter in which transfer function "(1+Z.sup.-1 +Z.sup.-2 +. . 
. +Z.sup.-n) (1+Z.sup.-1)" ("n+1=k+q") is used to output voltage data 
v.sub.sm and current data i.sub.sm serving as the first and second 
additive electric variable data at the certain sampling time t.sub.m and 
voltage data v.sub.sm-p and current data i.sub.sm-p at the other sampling 
time t.sub.m-p. 
Further, in the above-mentioned protective relay system, the relay control 
means includes controlled variable calculation means for calculating relay 
controlled variable including at least one of reactance value, ohm value 
and operation/suppression quantity on the basis of the voltage data 
v.sub.jm and v.sub.jm-p and the current data i.sub.jm and i.sub.jm-p which 
are outputs of the difference filter of the digital filter means and the 
voltage data v.sub.sm and v.sub.sm-p and the current data i.sub.sm and 
i.sub.sm-p which are outputs of the addition filter; and operation 
judgment means for judging whether or not value of the relay controlled 
variable calculated by the controlled variable calculation means has a 
predetermined relationship with respect to a predetermined setting value 
and constant. These components are the fundamental configuration of the 
protective relay system according to this invention. 
In accordance with the protective relay system according to the first 
aspect of this invention, in the above-mentioned fundamental 
configuration, the controlled variable calculation means is constituted by 
reactance value calculation means for determining reactance value X.sub.m 
by the following equation (A) on the basis of the current data i.sub.jm 
and i.sub.jm-p which are outputs of the difference filter, and the voltage 
data v.sub.sm and v.sub.sm-p and the current data i.sub.sm and i.sub.sm-p 
which are outputs of the addition filter 
##EQU3## 
Moreover, the operation judgment means judges the discriminant "X.sub.m 
.ltoreq.X.sub.s " from reactance value X.sub.m and setting value X.sub.s 
determined by the reactance calculation means. 
In accordance with the protective relay system according to the second 
aspect of this invention, in the above-mentioned configuration, the 
controlled variable calculation means is constituted by 
operation/suppression quantity calculation means for calculating 
operation/suppression quantities a.sub.m and b.sub.m corresponding to 
reactance value by the following equation (B) on the basis of the current 
data i.sub.jm and i.sub.jm-p which are outputs of the difference filter 
and the voltage data v.sub.sm and v.sub.sm-p and the current data i.sub.sm 
and i.sub.sm-p which are outputs of the addition filter: 
EQU a.sub.m =-v.sub.sm .multidot.i.sub.sm-p +i.sub.sm .multidot.v.sub.sm-p 
b.sub.m =-i.sub.jm .multidot.i.sub.sm-p +i.sub.jm-p .multidot.i.sub.sm (B) 
Moreover, the operation judgment means judges discriminant "b.sub.m 
.multidot.X.sub.s -a.sub.m .gtoreq.KO" from the operation/suppression 
quantities am and bm determined by the operation/suppression quantity 
calculation means, and setting value X.sub.s and constant KO. 
In accordance with the protective relay system according to the third 
aspect of this invention, in the above-mentioned fundamental 
configuration, the controlled variable calculation means is constituted by 
ohm value calculation means for determining ohm value Rm by the following 
equation (C) on the basis of the current data i.sub.jm and i.sub.jm-p 
which are outputs of the difference filter and the voltage data v.sub.sm 
and v.sub.sm-p and the current data i.sub.sm and i.sub.sm-p which are 
outputs of the additive filter: 
##EQU4## 
Moreover, the operation judgment means judges discriminant "R.sub.m 
.ltoreq.R.sub.s " from the ohm value R.sub.m determined by the ohm value 
calculation means and setting value R.sub.s. 
In accordance with the protective relay system according to the fourth 
aspect of this invention, in the fundamental configuration, the controlled 
variable calculation means is constituted by operation/suppression 
quantity calculation means corresponding to ohm value by the following 
equation (D) on the basis of the current data i.sub.jm and i.sub.jm-p 
which are outputs of the difference filter and the voltage data v.sub.sm 
and v.sub.sm-p and the current data i.sub.sm and i.sub.sm-p which are 
outputs of the addition filter: 
EQU c.sub.m =-i.sub.jm .multidot.v.sub.sm-p +v.sub.sm .multidot.i.sub.jm-p 
b.sub.m =-i.sub.jm .multidot.i.sub.sm-p +i.sub.jm-p .multidot.i.sub.sm (D) 
Moreover, the operation judgment means judges discriminant "b.sub.m 
.multidot.R.sub.s -c.sub.m .ltoreq.Kl" from the operation/suppression 
quantity C.sub.m and b.sub.m determined by the operation/suppression 
quantity calculation means, and setting value R.sub.s and constant Kl. 
In accordance with the protective relay system according to the fifth 
aspect of this invention, in the above-mentioned configuration, the 
controlled variable calculation means is constituted by reactance value 
calculation means for determining reactance value X.sub.m by the following 
equation (A) on the basis of the current data i.sub.jm and i.sub.jm-p 
which are outputs of the difference filter, and the voltage data v.sub.sm 
and v.sub.sm-p and the current data i.sub.sm and i.sub.sm-p which are 
outputs of the addition filter 
##EQU5## 
and ohm value calculation means for determining ohm value K.sub.m by the 
following equation (C) on the basis of the current data i.sub.jm and 
i.sub.jm-p which are outputs of the difference filter and the voltage data 
v.sub.sm and v.sub.sm-p and the current data i.sub.sm and i.sub.sm-p which 
are outputs of the addition filter: 
##EQU6## 
Moreover, the operation judgment means serves to judge (discriminate) the 
discriminant (E) on the basis of the reactance value R.sub.m determined by 
the reactance value calculation means the ohm value R.sub.m determined by 
the ohm value calculation means: 
EQU (R.sub.m -R.sub.0).multidot.(R.sub.m -R.sub.F).multidot.(X.sub.m 
-X.sub.0).multidot.(X.sub.m -X.sub.f).ltoreq.0 (E) 
where 
R.sub.0 (ohmic component) is the offset mho near side setting value 
X.sub.0 (reactance component) is offset mho near side setting value 
R.sub.F (ohmic component) is the offset mho far side setting value, and 
X.sub.F (reactance component) is the offset mho far side setting value 
In accordance with the protective relay system according to the sixth 
aspect of this invention, in the above-mentioned fundamental 
configuration, the controlled variable calculation means is constituted by 
polarity voltage preparation means for preparing polarity voltage 
v.sub.pjm having a predetermined relationship with respect to the voltage 
data v.sub.jm and/or v.sub.sm on the basis of the voltage data v.sub.jm 
which is output of the differential filter and voltage data v.sub.sm which 
is output of the addition filter, and the operation judgment means serves 
to judge, whether or not the following discriminant holds, on the basis of 
voltage data v.sub.jm and current data i.sub.jm which are outputs of the 
difference filter, voltage data v.sub.sm and current data i.sub.sm which 
are outputs of the additive filter, polarity voltage v.sub.pjm which is 
output of the polarity voltage preparation means, and setting values 
R.sub.s and X.sub.s : 
EQU v.sub.pjm-p .multidot.{(R.sub.s .multidot.i.sub.sm +X.sub.s 
.multidot.i.sub.jm)-v.sub.sm } -v.sub.pjm .multidot.{(R.sub.s 
.multidot.i.sub.sm-p +X.sub.s .multidot.i.sub.jm-p)-v.sub.sm-p }.gtoreq.K2 
(F) 
In accordance with the protective relay system according the seventh aspect 
of this invention, in the above-mentioned sixth aspect, the polarity 
voltage preparation means synthesizes a voltage orthogonal in a 
fundamental wave with respect to output v.sub.sm of the addition filter in 
terms of vector to output it as the polarity voltage v.sub.pjm to the 
operation judgment means. 
In accordance with the protective relay system according to the eighth 
aspect of this invention, in the above-mentioned sixth aspect, the 
polarity voltage preparation means serves to output a voltage earlier by 
predetermined time of voltage data v.sub.jm from the difference filter at 
the sampling time point t.sub.m to the operation judgement means as the 
polarity voltage v.sub.pjm. 
In accordance with the protective relay system according to the ninth 
aspect of this invention, in the above-mentioned sixth aspect, the 
polarity voltage preparation means serves to synthesize positive phase 
voltage from output v.sub.jm of the difference filter and output v.sub.sm 
of the addition filter with three-phase voltage of the power system at the 
sampling time tm being as reference to output it as the polarity voltage 
j.sub.pjm to the operation determination means. 
In accordance with the protective relay system according to the tenth 
aspect of this invention, in the above-mentioned fundamental 
configuration, the controlled variable calculation means is composed of 
charge current compensation means for determining a predetermined electric 
variable (i.sub.sm -C.sub.s .multidot.v.sub.jm) on the basis of the 
voltage data v.sub.jm as output of the difference filter, and the current 
data i.sub.sm as output of the addition filter at the sampling time point 
t.sub.m, and setting value C.sub.s ; and transmitting/receiving means 
adapted for transmitting the predetermined electric variable (i.sub.sm 
-C.sub.s .multidot.v.sub.jm) delivered from the charge current 
compensation means to a destination electric station (B electric station) 
where the protective relay system is installed and for receiving electric 
variable (i.sub.sm -C.sub.s .multidot.v.sub.jm) B from any other 
protective relay system installed in the destination electric station (B 
electric station), and the operation judgment means serves to judges, on 
the basis of the predetermined electric variable (i.sub.sm -C.sub.s 
.multidot.v.sub.jm) delivered from the charge current compensation means 
and the predetermined electric variable (i.sub.sm -C.sub.s 
.multidot.v.sub.jm) B delivered from the transmitting/receiving means, 
whether or not the following discriminant (G) holds: 
EQU .parallel.(i.sub.sm -C.sub.s .multidot.v.sub.jm)+(i.sub.sm -C.sub.s 
.multidot.v.sub.jm)B.parallel..gtoreq.ka.multidot.{.parallel.i.sub.sm 
-C.sub.s .multidot.v.sub.jm .parallel.+.parallel.(i.sub.sm -C.sub.s 
.multidot.v.sub.jm)B.parallel.}+kb (G) 
where 
.parallel.am.parallel. is quantity proportional to amplitude value of a.c. 
electric variable a at the time point of t.sub.m, 
ka is No. ratio suppression digits (absolute number), and 
kb is minimum sensitively current. 
The fundamental operation of the protective relay system constructed as 
above will be described below. 
When sample data of current i=I.multidot.sin(.omega.t) is inputted to the 
digital filter means, processing as described below is carried out. 
Initially, by allowing such sample data to be passed through the digital 
filter of the first stage (1+Z.sup.-1 +Z.sup.-2 +. . . +Z.sup.-n), current 
i'.sub.sm at time point tm is obtained. 
##EQU7## 
Further, by allowing such sampling data to be passed through digital filter 
of the succeeding stage (1+Z.sup.-1), current i'.sub.sm at the time point 
t.sub.m is as indicated by the following equation. 
##EQU8## 
Also with respect to the voltage, expansion can be similarly made. When the 
current i=I.multidot.sin(.omega.t) is caused to be passed through the 
difference filter, current i.sub.jm at time point tm is as indicated by 
following equation (14). 
##EQU9## 
Also with respect to the voltage, expansion can be similarly made. In this 
case, if the equations (12) and (13) have the relationship that they are 
orthogonal to each other in terms of vector, k+q=n+1 holds. 
Moreover, if value as close as to 1 is selected in the fundamental wave so 
that quantity which determines magnitudes of the right side of the 
equation (14) does not become .vertline.sin((q-k).omega.T/2.vertline.&lt;&lt;1, 
performance of the frequency characteristic can be ensured in the state 
where noise error is not amplified. For example, let consider the case 
where k=0 and q=n+1. At this time, the equation (14) is expressed as 
follows. 
EQU i.sub.jm =2I.multidot.sin ((n+1).omega.T/2).multidot.cos (.omega.t.sub.m 
-(n+1).omega.T/2) (15) 
Further, substitution of the relationship of the equation (15) and the 
equation (13) into the equation gives the following equation. 
##EQU10## 
Accordingly, if n is caused to be sufficiently greater value, influence of 
noise error on the current data of the equation (15) can be lessened, and 
the frequency characteristic performance with respect to the fundamental 
wave of X.sub.m can satisfy the characteristic of FIG. 2. X.sub.m /X 
(value in terms of the fundamental wave)=tan (.omega..sub.0 T/2)/tan 
(.omega.T/2). 
As described above, in accordance with this invention, even if harmonic 
components are superimposed on fault current/voltage produced at the times 
of failure of the power system, input data is caused to be passed through 
predetermined digital filters of which characteristics are orthogonal to 
each other in terms of vector in a broad frequency band, thereby making it 
possible to approximately solve, with high accuracy, a predetermined 
differential equation. Thus, high accuracy protective relay system can be 
realized.

BEST MODE FOR CARRYING OUT INVENTION 
Preferred embodiments of a protective relay system according to this 
invention will now be described in detail with reference to the attached 
drawings. 
Prior to description of the embodiments of the protective relay system 
according to this invention, the fundamental concept of this invention 
will now be described with reference to FIG. 3. 
FIG. 3 is a block diagram showing the entirety of a power system provided 
in the protective relay system. In FIG. 3, the protective relay system 1 
is connected to a transmission line 2 comprising an a.c. power supply 3, a 
potential transformer (PT) 4 and a current transformer (CT) 5. The 
potential transformer 4 is voltage transformer used for measuring high 
voltage to measure voltage at a certain point of the transmission line 2. 
The current transformer 5 is an instrument transformer to measure a 
current at a certain point of the transmission line 2. The voltage and the 
current are the above-described first and second electric variables. 
The protective relay system 1 comprises analog processing means 10 for 
processing analog data relating to voltage and current measured at plural 
sampling points continuous in time series manner, and digital protective 
relay means 15 for carrying out protective relay operation on the basis of 
digital data obtained by allowing the analog data to undergo 
analog-digital conversion. 
The analog processing means 10 comprises a voltage sample-hold circuit 11 
for detecting, every predetermined sampling time, voltage at a certain 
point of the transmission line 2 measured by the potential transformer 4, 
a current sample-hold circuit 12 for detecting, every sampling time, 
current at a certain point of the transmission line 2 measured by the 
current transformer 5, a multiplexer 13 for multiplexing or selecting 
voltage data and current data of time series respectively outputted from 
the voltage sample-hold circuit 11 and the current sample-hold circuit 12 
to output them, and an analog-to-digital converter 14 for converting 
voltage data and current data delivered from the multiplexer 13 from 
analog signal to digital signal to deliver it to the digital protective 
relay system 15. 
The digital protective relay system 15 comprises a memory 16 for 
temporarily storing respective digital data relating to voltage and 
current delivered from the analog/digital converter 14 of the analog 
processing means 10, digital filter means 20 for allowing voltage and 
current digital data as first and second electric variables delivered from 
the memory 16 to respectively undergo filtering (processing) to obtain 
output necessary for control, and relay control means 30 for determining 
controlled variable of the relay operation on the basis of plural outputs 
from the digital filter means 20. 
The digital filter means 20 comprises a difference filter 21 for outputting 
first difference electric variable data which is difference between at 
least two sample data of plural sample data with respect to voltage as the 
first electric variable and second difference electric variable data which 
is difference between at least two sample data of plural data as the 
second electric variable at plural sampling times of the time series, and 
an addition filter 22 for outputting first and second additive electric 
variable data which are data respectively orthogonal to the first and 
second difference electric variable data in terms of vector. In more 
practical sense, the differential filter 21 is a filter in which transfer 
function "Z.sup.-k -Z.sup.-q " (Z is Z transform operator, and k&lt;q) is 
used to output voltage data v.sub.jm and current data i.sub.jm which serve 
as the first and second difference electric variable data at a certain 
sampling time t.sub.m, and voltage data v.sub.jm-p and current data 
i.sub.jm-p at any other sampling time t.sub.m-p. Moreover, the addition 
filter 22 is a filter in which transfer function "(1+Z.sup.-1 +Z.sup.-2 +. 
. . +Z.sup.-n) (1+Z.sup.-1)" ("n+1=k+q") is used to output voltage data 
v.sub.sm and current data i.sub.sm serving as the first and second 
additive electric variable data at the certain sampling time t.sub.m, and 
voltage data v.sub.sm-p and current data i.sub.sm-p at the other sampling 
time point t.sub.m-p. 
Further, the relay control means 30 comprises controlled variable 
calculation means 31 for calculating relay controlled variable including 
at least one of reactance value, ohm value, operation/suppression quantity 
on the basis of the voltage data v.sub.jm and V.sub.jm-p and the current 
data i.sub.jm and i.sub.jm-p outputs of the difference filter of the 
digital filter means, and the voltage data v.sub.sm and v.sub.sm-p and the 
current data i.sub.sm and i.sub.sm-p which are outputs of the addition 
filter, and operation judgment means 32 for judging whether or not the 
value of the relay controlled variable calculated by the controlled 
variable calculating means has a predetermined relationship with respect 
to predetermined setting value and constant. By such a configuration, the 
relay control means calculates controlled variable of the relay operation 
in the power system on the basis of the first and second difference 
electric variable data at a certain sampling time, first and second 
additive electric variable data at the certain sampling time, first and 
second difference electric variable data at any other sampling time, and 
first and second additive electric variable data at the other sampling 
time to judge, on the basis of the controlled variable, the operation as 
to whether or not protection of the power system should be carried out, 
thus making it possible to control the relay operation of the power 
system. 
The gist of this invention resides in that there is used digital filter 
means comprising difference filter 21 using the transfer function 
"(Z.sup.-k -Z.sup.-q)" and addition filter 22 operative while correlating 
with the operational action of the difference filter 21, and using the 
transfer function "(1+Z.sup.-1 +Z.sup.-2 +. . . +Z.sup.-n) (1+Z.sup.-1)". 
The first to ninth embodiments (first to tenth aspects) are characterized 
in that the kinds of controlled variables calculated by using respective 
outputs of the filters 21, 22 constituting the digital filter means are 
respectively different in various manners. 
Explanation will now be given in detail in connection with digital 
protective relay means by different configurations caused to corresponding 
to different kinds of controlled variables, e.g., reactance value, ohm 
value, respective operation/suppression quantities, polarity voltage, and 
charge current compensation quantity, etc. 
FIG. 4 is a block diagram of the first embodiment for explaining the 
protective relay system according to the first aspect of this invention 
This invention is characterized in that a measure is taken such that even 
if the sampling period is reduced, noise error included in data of 
differential quantity is not amplified, thereby making it possible to 
ensure performance of the frequency characteristic indicated by the 
equation (14). In FIG. 4, reference numeral 21 denotes a digital 
difference filter for extracting predetermined frequency components of 
voltage and current of power system (not shown) subject to protection, and 
reference numeral 22 denotes a digital addition filter for extracting 
voltage and current orthogonal to output data of the difference filter 21 
in terms of vector even with respect to all frequency components. 
Moreover, reference numeral 31 denotes reactance value calculation means 
for calculating reactance, and reference numeral 41 denotes operation 
judgment means for judgment of operation. 
Sample values v.sub.m, i.sub.m at time t.sub.m of voltage v and current i 
of the power system are inputted to the addition filter 22 of FIG. 4 to 
allow them to be passed through a filter having transfer function 
(1+Z.sup.-1 +Z.sup.-2 +. . . +Z.sup.-n) (1+Z.sup.-1) (Z indicates Z 
transform operator) to thereby obtain voltage v.sub.sm, current i.sub.sm. 
Further, the sample values v.sub.m, i.sub.m are inputted to the difference 
filter 21 to allow them to be passed through a filter having transfer 
function (Z.sup.-k -Z.sup.-q) (d+q=n+1; k&lt;q) to thereby voltage v.sub.jm, 
current i.sub.jm. 
The reactance value calculation means 31 calculates reactance value X.sub.m 
on the basis of the following equation (11) from voltage v.sub.sm and 
current i.sub.sm obtained at the addition filter 22 and voltage v.sub.jm 
and current i.sub.jm obtained at the differential filter at time t.sub.m, 
and voltage v.sub.sm-p, current i.sub.sm-p obtained from the addition 
filter 22 and voltage v.sub.jm-p and current i.sub.jm-p obtained from the 
differential filter 21 at time t.sub.m-p. Further, the operation judgment 
means 41 judges, from the reactance value X.sub.m obtained at the 
reactance value calculation means 31 and setting value X.sub.s, whether or 
not X.sub.m .ltoreq.X.sub.s hold to conduct judgment of operation such 
that if the above relationship holds, the protective relay is in operative 
state, while it does not hold, the it is inoperative state. 
##EQU11## 
Functions of respective digital filters are represented by using Z 
transform operator in a manner as indicated by the following equation. It 
is to be noted that since orthogonal relationship is described in detail 
in the Disclosure of the Invention, explanation thereof is omitted here 
(there holds the relationship that the addition filter 22 is lag by 90 
degrees with respect to the difference filter 21). 
(1+Z.sup.-1 +Z.sup.-2 +. . . +Z.sup.-n) (1+Z.sup.-1) 
(Z.sup.-k -Z.sup.-q) (In this case, k+q=n+1) 
Further, in the case where setting is made such that k=0, q=n+1 in the 
difference filter 21, the transfer function of the addition filter 22 may 
be caused to be (1+Z.sup.-1 +Z.sup.-2 +. . . +Z.sup.-n) (1-Z.sup.-1), 
(=1-Z.sup.-n-1). Moreover, it is apparent that this configuration and the 
configuration of the addition filter 22 can be realized by divisional 
configuration consisting of three digital filters. Namely, input voltage 
and current are caused to be first passed through the first filter of the 
following equation to input its output to two filters, i.e., a second 
filter and a third filter, thus making it possible to obtain an output 
equivalent to the differential filter and the additive filter 22. 
First filter: (1+Z.sup.-1 +Z.sup.-2 +. . . +A.sup.-n) 
Second filter: (1+Z.sup.-1) 
Third filter: (1-Z.sup.-1) 
The reactance value calculation means 31 of FIG. 4 is means for calculating 
reactance value from the protective relay installation point up to fault 
point of the transmission line of FIG. 1 by the equation (11). When input 
voltage and current of the differential filter 21 and the addition filter 
22 are expressed as i=I.multidot.sin (.omega.t), v=V.multidot.sin 
(.omega.t+.theta.), the equation (11) can be represented by the equation 
(16). 
The operation judgment means 41 makes a correction as indicated by X.sub.m 
.ltoreq.X.sub.s /tan (.omega..sub.0 .multidot.T/2) by X.sub.m calculated 
at the reactance value calculation means 31, setting value X.sub.s and 
constant tan (.omega..sub.0 T/2) at the fundamental wave determined in 
advance to judge whether or not the protective relay is operative. It is 
to be noted that, in the description of the gist of this invention, 
description of plural collating operations of the operation judgments is 
omitted here. 
The protective relay system of the second embodiment corresponding to the 
second aspect will now be described. 
FIG. 5 is a block diagram showing the configuration of the protective relay 
system according to the second embodiment of this invention. 
In the second embodiment, in place of the reactance value calculation means 
41 of FIG. 4, reactance value operation/suppression quantity calculation 
means 42 for calculating the following equation (17) is applied. 
EQU a.sub.m =-v.sub.sm .multidot.i.sub.sm-p +i.sub.sm .multidot.v.sub.sm-p 
b.sub.m =-i.sub.jm .multidot.i.sub.sm-p +i.sub.sm-p .multidot.i.sub.sm ( 
17) 
When current input and voltage input of the digital filter 20 consisting of 
difference filter 21 and addition filter 22 of FIG. 4 are respectively 
expressed as i=I.multidot.sin (.omega.t), v=V.multidot.sin 
(.omega.t+.theta.), the above equation is represented by the following 
equation (18). 
EQU a.sub.m =4.multidot.I.multidot.v.multidot.{(sin ((n+1).omega.T/2)) /tan 
(.omega.T/2)}.sup.2 .multidot.sin (.theta.).multidot.sin (p.omega.T) 
EQU b.sub.m =4.multidot.I.sup.2 .multidot.{sin((n+1).omega.T/2)}.sup.2 
/tan(.omega.t/2).multidot.sin(p.omega.T) (18) 
The operation judgment means 42 is of a structure to make a correction of 
reactance setting value X.sub.s such that "X.sub.s .rarw.X.sub.s /tan 
(.omega..sub.0 T/2)" to carry out judgement of operation on the basis of 
discriminant expressed as "b.sub.m .multidot.X.sub.a -a.sub.m .gtoreq.KO" 
(KO is sensitivity constant). The protective relay of the second 
embodiment is protective relay having reactance characteristic similar to 
FIG. 4, and differs from the system disclosed in the first embodiment of 
FIG. 4 only in the technique for realization. The reactance characteristic 
diagram is shown in FIG. 6. 
FIG. 7 is a block diagram showing the configuration of the protective relay 
system according to the third embodiment corresponding to the third 
aspect. 
In the third embodiment, ohm value calculation means 33 for calculating the 
equation (c) is applied as the controlled variable calculation means 30. 
In accordance with this equation, when current and voltage inputs of the 
digital filter 20 consisting of difference filter 21 and addition filter 
22 of FIG. 4 are respectively expressed as i=I.multidot.sin (.omega.t) and 
v=V.multidot.sin (.omega.t+.theta.), -i.sub.jm .multidot.v.sub.sm-p 
+v.sub.sm .multidot.i.sub.jm-p =4.multidot.I. 
.multidot.V.multidot.{sin((n+1).omega.T/2)}.sup.2 /t an 
(.omega.T/2).multidot.cos (.theta.).multidot.sin (P.omega.T). Further, 
from the relationship of the equation (18), the following equation is 
obtained: 
EQU R.sub.m =(I/V) cos(.theta.) (19) 
The operation judgment means 43 is of a structure to judge the relationship 
in, magnitude between the ohm value calculated by the equation (19) and 
the setting value R.sub.s to judge the protective relay to be operative 
when "R.sub.m .ltoreq.R.sub.s " holds. 
FIG. 8 is a block diagram showing the configuration of the protective relay 
system according to the fourth embodiment corresponding to the fourth 
aspect of this invention. In the fourth embodiment, ohm value 
operation/suppression quantity calculation means 34 for calculating the 
equation (D) is applied as the controlled variable calculation means 30. 
In the fourth embodiment, when current and voltage inputs of digital filter 
20 consisting of differential filter 21 and addition filter 22 of FIG. 3 
are respectively expressed as i=I.multidot.sin (.omega.t) and 
v=V.multidot.sin (.omega.t+.theta.), c.sub.m =i.sub.jm 
.multidot.v.sub.sm-p +v.sub.sm .multidot.i.sub.jm-p 
=4.multidot.I.multidot.v.multidot.{sin ((n+1).omega.T/2) }.sup.2 /tan 
(.omega.T/2).multidot.cos(.theta.).multidot.sin (P.omega.T). Additionally, 
b.sub.m is the same variable as that in the second embodiment shown in 
FIG. 5. 
The operation judgment means 44 is of a structure to carry out operation 
judgment on the basis of b.sub.m .multidot.R.sub.s -c.sub.m .gtoreq.k1 
from ohm setting value Rs, sensitivity constant K1 and outputs c.sub.m, 
b.sub.m of the operation/suppression quantity calculation means 34. The 
protective relay of this embodiment is a protective relay having ohm 
characteristic in a manner similar to FIG. 5, and differs from the system 
disclosed in the second embodiment only in the technique for realization. 
The ohm characteristic diagram is shown in FIG. 9. 
FIG. 10 is a block diagram showing the configuration of the protective 
relay system according to the fifth embodiment corresponding to the fifth 
aspect of this invention. The protective relay of the fifth embodiment is 
combination of the protective relays which have been already described. 
Namely, this system comprises controlled variable calculation means 30 
including reactance value calculation means 31 for carrying out an 
operation described below, 
##EQU12## 
which is equivalent to that of the reactance value calculation means 31 in 
the protective relay system of the first embodiment shown in FIG. 4, and 
ohm value calculation means 33 in the third embodiment shown in FIG. 7. 
Accordingly, output to the operation judgment means 45 of the controlled 
variable calculation means 30 is reactance value X.sub.m and ohm value 
R.sub.m. 
The operation judgment means 45 judges whether or not the protective relay 
is operative, on the basis of discriminant "(R.sub.m 
-R.sub.0).multidot.(R.sub.m -R.sub.F)+(X.sub.m -X.sub.0).multidot.(X.sub.m 
-X.sub.F).ltoreq.0" from output Xm of a reactance value calculating means 
31A and output Rm of ohm value calculation means 33. In this case, 
R.sub.0, X.sub.0 and R.sub.s, X.sub.s are as indicated below. 
offset mho: 
near side setting value (R.sub.0 (ohm component) X.sub.0 (reactance 
component)). 
far side setting value (R.sub.F (ohm component) , X.sub.F (reactance 
component)). 
The protective relay of the fifth embodiment is protective relay having 
offset mho characteristic. The offset mho characteristic diagram is shown 
in FIG. 11. 
The sixth to eighth embodiment of this invention will now be described. 
These three embodiments respectively correspond to the seventh to ninth 
aspects, and are conceptually included within the sixth aspect as the 
higher rank concept. 
Accordingly, the controlled variable calculation means is comprised of 
polarity voltage preparation means for preparing polarity voltage 
v.sub.pjm having a predetermined relationship with respect to these 
voltage data v.sub.jm and/or v.sub.sm on the basis of the voltage data 
v.sub.jm which is output of the difference filter and voltage data 
v.sub.sm which is output of the addition filter. The predetermined 
relationship is somewhat different in the sixth to eighth embodiments. 
Moreover, the operation judgment means judges whether or not the following 
discriminant (F) holds, on the basis of voltage data v.sub.jm and current 
data i.sub.jm which are outputs of the difference filter, voltage data vsm 
and current data i.sub.sm which are outputs of the additive filter, 
polarity voltage v.sub.pjm which is output of the polarity voltage 
preparation means, and setting values R.sub.s and X.sub.s. 
EQU v.sub.pjm-p .multidot.{(R.sub.s .multidot.i.sub.sm +X.sub.s 
.multidot.i.sub.jm)-v.sub.sm }-v.sub.pjm .multidot.{R.sub.s 
.multidot.i.sub.sm-p +x.sub.s .multidot.i.sub.jm-p)-v.sub.sm-p }.gtoreq.K2 
(F) 
FIG. 12 is a block diagram showing the configuration of the protective 
relay system according to the sixth embodiment corresponding to the 
seventh aspect. The protective relay of the sixth embodiment is 
combination of the protective relay already described. The polarity 
voltage preparation means 36 extracts voltage variable v.sub.pjm 
orthogonal to output vsm of the addition filter in terms of vector as 
controlled variable calculation means 30. The operation judgment means 46 
judges, on the basis of the following equation, whether or not, whether or 
not the protective relay is operative. (R.sub.s, X.sub.s) are setting 
values of the ohm component and the reactance component. It is necessary 
to use X.sub.s after undergone correction of X.sub.s .rarw.X.sub.s 
/tan(.omega..sub.0 T/2) . In the following equation (F), the electric 
variable of the portion of (R.sub.s .multidot.i.sub.sm +X.sub.s 
.multidot.i.sub.m) leads by magnitude of (R.sub.2.sup.2 
+X.sub.s.sup.2).sup.1/2 and phase .phi.=tan.sup.-1 (X.sub.s /R.sub.s) with 
the current i.sub.sm being as reference. The relationship thereof is shown 
in FIG. 13. 
EQU v.sub.pjm-p .multidot.((R.sub.s .multidot.i.sub.sm +X.sub.s 
.multidot.i.sub.jm)-v.sub.sm) -v.sub.pjm .multidot.((R.sub.s 
.multidot.i.sub.sm-p +X.sub.s .multidot.i.sub.jm-p)-v.sub.sm-p).gtoreq.K2 
(F) 
When i=I.multidot.sin (.omega.t) and v=V.multidot.sin (.omega.t+.theta.) 
are respectively substituted for input current and input voltage of the 
difference filter 21 and the addition filter 22 of the embodiment, the 
following equation is provided. 
EQU V.sub.pj .multidot.{(R.sub.s .multidot.I.sub.s .multidot.cos 
(.theta.)+X.sub.s /tan (.theta..sub.0 T/2).multidot.I.sub.j .multidot.sin 
(.theta.))-V.sub.s }.multidot.sin (p.omega.T).gtoreq.K2 
In this case, I.sub.s, V.sub.s and I.sub.j are expressed as follows. 
I.sub.s =2I.multidot.sin((n+1).omega.T/2)/tan(.omega.T/2) 
V.sub.s =2V.multidot.sin((n+1).omega.T/2)/tan(.omega.T/2) 
I.sub.j =2I.multidot.sin((n+1).omega.T/2) 
When the above-mentioned equation is represented by the following 
relational expression is provided. 
##EQU13## 
The above-mentioned equation eventually the equation of the principle of 
operation of the mho characteristic. The mho characteristic is shown in 
FIG. 14. 
FIG. 15 is a block diagram showing the configuration of the protective 
relay system according to the seventh embodiment corresponding to the 
eighth aspect of this invention. In FIG. 15, operation judgment means 47 
is provided in place of the operation judgment means 46 shown in FIG. 12. 
In this embodiment, memory voltage earlier by predetermined cycle (data 
earlier by N samples) of voltage v.sub.jm orthogonal to the voltage 
v.sub.sm is caused to be polarity voltage. Namely, 
##EQU14## 
Others are similar to those of FIG. 12. 
FIG. 16 is a block diagram showing the configuration of the protective 
relay system according to the tenth embodiment corresponding to the ninth 
aspect. In FIG. 16, operation judgment means 48 is provided in place of 
the operation judgment means 46 shown in FIG. 12. In this embodiment, as 
voltage v.sub.pjm orthogonal to the voltage vsm, if that voltage is 
voltage for detection of short circuit, e.g., in the case of AB phase, 
positive phase voltage having AB phase as reference is extracted (A, B, C 
represent respective phases of three-phase a.c. electric variable). The 
voltage v.sub.pjm can be extracted by v.sub.pjm (AB)=3.sup.1/2 
.multidot.v.sub.sm (c)+v.sub.jm (AB) . 
Moreover, if positive phase voltage is voltage for grounding, the positive 
phase voltage having A phase as reference can be calculated by v.sub.pjm 
(A)=3.sup.1/2 v.sub.jm (A)-v.sub.jm (BC) . In addition to the method in 
which predetermined (required) voltage vector is synthesized from two 
electric variables orthogonal to each other, a method in which the 
sampling time series is shifted by 90 degrees may be applied. 
FIG. 17 is a block diagram showing the configuration of the protective 
relay system according to the ninth embodiment corresponding to the tenth 
aspect of this invention. Charge current compensation means 35 makes a 
correction of setting value C.sub.s such that C.sub.s .rarw.C.sub.s 
/tan(.omega..sub.0 T/2) to calculate i.sub.sm -C.sub.s .multidot.v.sub.jm 
from output ism of the additive filter 22 and output v.sub.jm of the 
differential filter 21. The C.sub.s .multidot.v.sub.jm is compensation 
component of current produced by the charge capacity C.sub.s. The electric 
variable "(i.sub.sm -C.sub.s .multidot.v.sub.jm)B" for the destination 
electric station B is received by transmitting/receiving means 39, and the 
electric variable of the terminal for source of transmission is 
transmitted to the B electric station. 
The operation judgment means 49 carries out operation judgment on the basis 
of the following equation from vector sum current of current obtained by 
compensating charge current of the terminal for source of transmission 
provided by the charge current compensation means 35 and current obtained 
by compensating charge current of the destination electric station B 
terminal, i.e., scalar sum current of amplitude value of differential 
current and amplitude of current obtained by compensating charge currents 
of respective terminals. This equation is the operation principle equation 
of the ratio differential relay system well known as the transmission line 
differential protective relay 
EQU .parallel.(i.sub.sm C.sub.s .multidot.v.sub.jm)+(i.sub.sm -C.sub.s 
.multidot.v.sub.jm B.parallel..gtoreq.ka.multidot.{.parallel.i.sub.sm 
-C.sub.s .multidot.v.sub.jm .parallel.+.parallel.i.sub.sm -C.sub.s 
.multidot.v.sub.jm)B.parallel.}+kb 
where 
.parallel.a.parallel. indicates quantity proportional to amplitude value of 
a.c. electric variable a at time point of tm 
Ka is No. of ratio suppression digits (absolute number), and 
Kb is minimum sensitivity current. 
The physical meaning of the charge current compensation of this equation 
will be described below with reference to the transmission line of FIG. 
18. The well known transmission equation is indicated at the 
transmitting/receiving terminal. 
forward wave: i.sub.DF (t)=i.sub.s (t-.tau.)+e.sub.s (t-.tau.)/z +i.sub.R 
(t+.tau.)-e.sub.R (t+.tau.)/z 
backward wave: i.sub.DB (t)=i.sub.s (t-.tau.)+e.sub.s (t-.tau.)/z +i.sub.R 
(t+.tau.)-e.sub.R (t+.tau.)/z 
differential current: i.sub.DD (t)=(i.sub.DF (t)+i.sub.DB (t))/2 
where suffix s is transmission terminal, 
R is charge terminal, 
Z is serge impedance=(L/C).sup.1/2 
.tau. is propagation time=1.multidot.(LC).sup.1/2 
Implementation of Taylor expansion approximation to the differential 
current i.sub.DD (t) under the condition of (.tau..apprxeq.0) gives: 
##EQU15## 
If differential current is extracted only by current vector sum current 
(is(t)+iR(t)) of the transmitting/receiving terminal, the previously 
described charge current component would be error current, leading to 
lowering of sensitivity of the differential relay. Accordingly, such error 
current is compensated so that only the fault current component can be 
extracted. It is apparent as previously described that this invention can 
be applied to the time differential equation of the above-mentioned 
equation. In addition, it is omitted that the meaning of the ratio 
differential system is described here. 
INDUSTRIAL APPLICABILITY 
In accordance with the protective relay system according to this invention, 
even if harmonic components are superimposed on fault current or fault 
voltage produced at the time of occurrence of failure of the power system, 
an approach is employed to approximate, with higher accuracy, a 
predetermined time differential equation by predetermined digital filters 
of which characteristics are orthogonal to each other in terms of vector 
in a broad frequency band. Accordingly, there is provided protective relay 
system of high accuracy free from influence of noise error in failure of 
the system. Thus, this protective relay system can be widely applied to 
power system including various power equipments, particularly equipments 
such as cable transmission line, phase modifying capacitor and the like.