Method of distance protection of parallel transmission line
View Patent ↗The present invention is concerned with a method of distance protection of parallel transmission lines applicable both to series compensated and uncompensated electric power lines, using a distance relay. The method is characterized in that a pair of flags (ff 1 , ff 2 ) are calculated for indication faulted and healthy circuits in parallel lines and in the same time a flag (Internal_Fault) for indication internal or external fault in parallel lines is calculated independently. Next gathering all calculated flags (ff 1 , ff 2 , Internal_Fault) an analyze of the value of these flags are performed and depending on the values of flags (ff 1 , ff 2 , Internal_Fault) and on their reciprocal relationship, a trip permission signal from the protection relay ( 4 ) is released and sent to the alarms devices or to the line breakers, or a block signal from the protection relay ( 4 ) is generated and sent to protect parallel lines before damage.
1. A method for distance protection of parallel transmission lines comprises:
measuring current and voltages signals from the individual phases (A, B, C) from both line circuit # 1 and line circuit # 2 of the parallel lines and optional zero sequence currents of both line circuit # 1 and line circuit # 2 of the parallel lines,
processing the measured signals and using a protection relay ( 4 ) calculating a coefficient FAULT_Ph-G 1 (n) which indicates phase-to-ground faults in the line circuit # 1 , a coefficient FAULT_Ph-Ph 1 (n) which indicating a phase-to-phase fault in the line circuit # 1 , a coefficient FAULT_Ph-G 2 (n) which indicating phase-to-ground faults in the line circuit # 2 , a coefficient FAULT_Ph-Ph 2 (n) which indicating a phase-to-phase fault in the line circuit # 2 ,
calculating a pair of a flags (ff 1 , ff 2 ) for indicating faulted and healthy circuits in parallel lines, where the flag (ff 1 ) for line circuit # 1 is calculated according to the following formula:
ff
1
(
n
)
{
1
when
{
f
1
(
n
)
≥
f
thr
AND
FAULT_Ph
-
Ph
1
(
n
)
=
1
OR
f
01
(
n
)
≥
f
thr
AND
FAULT_Ph
-
G
1
(
n
)
=
1
}
0
otherwise
and where the flag (ff 2 ) for line circuit # 2 is calculated according to the following formula:
ff
2
(
n
)
{
1
when
{
f
2
(
n
)
≥
f
thr
AND
FAULT_Ph
-
Ph
2
(
n
)
=
1
OR
f
02
(
n
)
≥
f
thr
AND
FAULT_Ph
-
G
2
(
n
)
=
1
}
0
otherwise
where:
f thr —is a threshold for fault coefficients f 1 , f 01 , f 2 , f 02 given by user,
n—is the real consecutive number of the present digital sample processed by the protective device,
FAULT_Ph-G 1 (n) is a fault type coefficient indicating phase-to-ground faults in the line # 1 ,
FAULT_Ph-Ph 1 (n) is a fault type coefficient indicating phase-to-phase fault in the line # 1 or non-fault conditions,
FAULT_Ph-G 2 (n) is a fault type coefficient indicating phase-to-ground faults in the line # 2 ,
FAULT_Ph-Ph 2 (n) is a fault type coefficient indicating a phase-to-phase fault in the line # 2 or non-fault conditions,
calculating a flag (Internal_Fault) for indicating internal or external fault in parallel lines in independent way according to the formula:
Internal_Fault
(
n
)
=
{
1
when
{
sdi_max
(
n
)
sdi_min
(
n
)
>
sdi
thr
AND
FAULT_Ph
-
Ph
(
n
)
=
1
OR
sdi_
0
max
(
n
)
sdi_
0
min
(
n
)
>
sdi
thr
AND
FAULT_Ph
-
G
(
n
)
=
1
0
otherwise
where:
sdi thr —is a different current sum coefficient threshold given by the user,
sdi_max(n), sdi_ 0 max(n)—are maximum values of the sum of the current differences,
sdi_min(n), sdi_ 0 min(n)—are minimum values of the sum of the current differences,
n—is the real consecutive number of the present digital sample processed by the protective device,
FAULT_Ph-G(n) is a fault type coefficient indicating phase-to-ground faults,
FAULT_Ph-Ph(n) is a fault type coefficient indicating phase-to-phase fault,
gathering all calculated flags (ff 1 , ff 2 , Internal_Fault) an analyze of the reciprocal relationship between the values of these flags and when:
ff 1 =1 AND Internal_Fault=1 AND ff 2 =0 AND Internal_Fault=1,
it means that fault within protected line circuit # 1 has been identified and fault impedance (Z F ) is calculated in the known way with using the three phase to ground loops and the multi-phase faults loops and additionally if the apparent fault impedance (Z F ) is outside the relay zone operation characteristic (Z I ) then a block signal from the protection relay ( 4 ) is released,
OR
when:
ff
1
=
1
AND
Internal_Fault
=
0
OR
ff
1
=
0
AND
Internal_Fault
=
1
OR
ff
2
=
0
AND
Internal_Fault
=
0
OR
ff
2
=
0
and
Internal_Fault
=
1
OR
ff
2
=
1
AND
Internal_Fault
=
1
OR
ff
2
=
1
AND
Internal_Fault
=
0
OR
⋮
ff
2
=
1
AND
Internal_Fault
=
0
,
}
it means that fault outside protected line circuit # 1 has been identified and a block signal from the protection relay 4 is generated,
OR
when
ff 1 =1 AND Internal_Fault=1 AND ff 2 =0 AND Internal_Fault=1,
it means that fault within protected line circuit # 1 has been identified and fault impedance (Z F ) is calculated in the known way with using the three phase to ground loops and the multi-phase faults loops and additionally if the apparent fault impedance (Z F ) is within the relay zone operation characteristic (Z I ) then a permission trip signal from the protection relay ( 4 ) is released,
realising a trip permission signal from the protection relay ( 4 ) and sending it to the alarms devices or to the line breakers, or generating a block signal from the protection relay ( 4 ) and sending it to the users in order to protect parallel lines.