Title: Plausibility checking of current transformers in substations
Abstract: The invention relates to a method, a computer program and a device (20) for the plausibility checking of current transformers (7) in an electrical switchgear assembly (1) and to a switchgear assembly (1) having such a device (20). According to the invention, zones (1a, 1b, 1c) bounded by current transformers (7) and possibly by open switches (3-5) are detected for an instantaneous topology of the switchgear (1), in each zone (1a, 1b, 1c) the signed current measurement signals are added and in the case of significant deviations of the current sum from zero, all current transformers (7) of the associated zone (1a, 1b, 1c) are identified as being problematic. Exemplary embodiments relate to, among other things: a warning counter (2e) for problematic current transformers (7); in the case of a defective current transformer (7), an operation with calculated currents or an automatic combining of zones (1a, 1b, 1c); and coordinating the plausibility test with switching actions. Advantages are, among other things: the method is independent of the complexity and operating state of the switchgear (1); dynamic topology tracking; high information content of the plausibility test; and access to current measuring values already available in the substation control system (2).
Patent Number: 6,870,719 Issued on 03/22/2005 to Wimmer, et al.
| Inventors:
|
Wimmer; Wolfgang (Rietheim, CH);
Schutter; Jan (Nussbaumen, CH)
|
| Assignee:
|
ABB Schweiz AG (Baden, CH)
|
| Appl. No.:
|
388522 |
| Filed:
|
March 17, 2003 |
Foreign Application Priority Data
| Current U.S. Class: |
361/36; 361/35; 700/292; 700/295; 700/297; 324/500; 324/512 |
| Intern'l Class: |
G01R 019//00; G01R 031//02 |
| Field of Search: |
700/292,295,297
361/35,36
|
References Cited [Referenced By]
U.S. Patent Documents
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|
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|
| 4237512 | Dec., 1980 | Forford | 361/87.
|
| 4402028 | Aug., 1983 | Udren | 367/36.
|
| 4631622 | Dec., 1986 | Howell | 361/45.
|
| 4661877 | Apr., 1987 | Usui | 361/36.
|
| 4871971 | Oct., 1989 | Jeerings et al. | 324/509.
|
| 5170308 | Dec., 1992 | Inagaki et al. | 361/36.
|
| 5241443 | Aug., 1993 | Efantis | 361/36.
|
| 5245498 | Sep., 1993 | Uchida et al. | 361/47.
|
| 5408176 | Apr., 1995 | Blatt | 324/107.
|
| 5428549 | Jun., 1995 | Chen | 702/59.
|
| 5455776 | Oct., 1995 | Novosel | 702/59.
|
| 5469051 | Nov., 1995 | Yarmchuk | 324/158.
|
| 5566041 | Oct., 1996 | Rumfield | 361/115.
|
| 5600526 | Feb., 1997 | Russell et al. | 361/65.
|
| 5661664 | Aug., 1997 | Novosel et al. | 700/293.
|
| 6453248 | Sep., 2002 | Hart et al. | 702/58.
|
| Foreign Patent Documents |
| 4142471 | Jul., 1992 | DE.
| |
| 1074849 | Feb., 2001 | EP.
| |
Primary Examiner: Picard; Leo
Assistant Examiner: Masinick; Michael D.
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis, L.L.P.
Claims
What is claimed is:
1. A method for the plausibility checking of current transformers in an
electrical switchgear, the switchgear being controlled by a control system
and measurement signals from current transformers arranged at at least two
different measuring points being processed by the control system, wherein,
for testing the plausibility checking of the current transformers,
an instantaneous topology of the switchgear is detected by the institution
control system based on existing electrical connections of primary devices
and based on instantaneous positions of switches,
based on the instantaneous topology, at least one zone of the switchgear is
identified, which zone represents a conductively connected area which is
bounded by at least one current transformer,
in the zone, the measurement signals of the current transformers are
detected with a current-direction-dependent sign and are added to form a
current sum of the zone, and
if there is a current sum which is not equal to zero within a permissible
current transformer measuring accuracy, all current transformers of the
associated zone are identified as being problematic.
2. The method as claimed in claim 1, wherein
in each test for the presence of a current sum not equal to zero, a warning
counter for the current transformers identified as being problematic in
the associated zone is incremented,
in each zone, the same number of tests for the presence of a current sum
not equal to zero is performed, and
current transformers having a higher warning count than other current
transformers, particularly having a highest warning count, are identified
as being defective.
3. The method as claimed in claim 1, wherein
there is at least one zone having a number of current transformers, and
the warning counters of the current transformers of this zone are reset to
zero if a current sum equal to zero is measured in the zone and a
measurement signal not equal to zero is measured by at least two current
transformers of the zone.
4. The method as claimed in claim 1, wherein, in a zone having exactly one
current transformer, the current transformer is identified as being
defective if its measurement signal is repeatedly not equal to zero.
5. The method as claimed in claim 1, wherein
each current transformer of the switchgear is divided into at least one
zone, and
in an overall test of the switchgear exactly one test for the presence of a
current sum not equal to zero is performed in each zone.
6. The method as claimed in claim 1, wherein
the identification of the zones is based on starting from a busbar of the
switch gear assembly and searching out all current transformers
conductively connected thereto and/or
two zones of the switchgear are identified which are adjacent to one
another and which adjoin one another via a common current transformer and
if the common current transformer fails or if the common current
transformer is detected as being defective, the two zones are
automatically combined to form a single zone.
7. The method as claimed in claim 1, wherein, when exactly one current
transformer fails in one zone, a current measurement signal to be detected
by this current transformer is calculated from the remaining current
measurement signals of the zone, assuming that the current sum is equal to
zero.
8. The method as claimed in claim 1, wherein the plausibility check of the
current transformers is performed separately for each phase or alternately
for different phases.
9. The method of claim 8, wherein the plausibility check of the current
transformers is performed in a cyclically alternating fashion.
10. The method as claimed in claim 1, wherein
in the operating state, tests for the presence of a current sum not equal
to zero and, particularly, overall tests of the switchgear are repeated
periodically and/or after switching actions, and/or
the plausibility check of the current transformers is carried out
regardless of any switching actions and is repeated in the case of
inconsistencies of the measurement signals caused by switching actions or
the plausibility check of the current transformers is only carried out or
evaluated if a previous check for instantaneous switching actions has had
a negative result.
11. The method as claimed in claim 1, wherein in the operating state of the
switchgear, an asynchronism of the measurement signals of a zone is
measured or estimated and, the greater the asynchronism, the greater the
permitted current transformer inaccuracy to be selected.
12. The method as claimed in claim 1, wherein results of the plausibility
check are represented in the form of a list of the current transformers
with their zone allocation, as statistics of the frequency with which each
current transformer has been identified as being problematic.
13. The method of claim 12 wherein results of the plausibility check are
represented as graphical information in a single-pole diagram of the
switchgear.
14. The method of claim 13 wherein the graphical information includes
colors.
15. The method as claimed in claim 1, wherein
the current transformers are measuring-type current transformers and/or
the measurement signals are effective current measurement values of the
current transformers and/or
the current-direction-dependent sign is determined from a phase angle
between voltage and current of a phase or between currents of different
phases.
16. A computer program for the plausibility checking of current
transformers in an electrical switchgear, which can be loaded and executed
on a data processing unit of a control system of the switchgear, wherein
the computer program, when executed, executes the steps of the method as
claimed in claim 1.
17. The method of claim 1, wherein the electrical switch gear assembly is a
high-voltage or medium-voltage switch gear assembly.
18. The method of claim 1, wherein the zone represents a conductively
connected area which is bounded by open switches.
19. The method of claim 1, wherein the plausibility check of the current
transformers is performed for average values of at least two phases.
20. The method of claim 19, wherein the plausibility check of the current
transformers is performed for average values of all phases.
21. A device for the plausibility checking of current transformers in an
electrical switchgear, the device comprising:
means for detecting an instantaneous topology of the switchgear based on
the the existing electrical connections of primary devices and based on
the instantaneous positions of switches,
means for detecting at least one zone of the switchgear, which zone
represents a conductively connected area which is bounded by at least one
current transformer,
means for detecting the measurement signals of the current transformers in
the zone with a current-direction-dependent sign and for adding the
measurement signals to form a current sum of the zone, and
means for checking the current sum for a value of zero within a permitted
current transformer measurement accuracy and for marking the current
transformers of the zone as being problematic if the current sum is not
equal to zero.
22. The device as claimed in claim 21, wherein
there is a warning counter for carrying out the method, and/or
there are means for carrying out the method.
23. The device of claim 21, wherein zone represents a conductively
connected area which is bounded by open switches.
Description
FIELD OF THE INVENTION
The invention relates to the field of system control technology, in
particular to the substation control technology for high, medium or low
voltage switchgear assemblies.
BACKGROUND OF THE INVENTION
A power supply network comprises substations or electrical switchgears, in
particular high or medium voltage switchgears which are controlled by a
distributed substation control system. The substations comprise primary or
field devices, e.g. switches, drives, generators, transformers, voltage
and current transformers. The control system has, for example, field
control devices and a control station which are connected to one another
by means of various communication buses and bus couplers. The field
control devices control, monitor and protect the field devices of the
system.
Current transformers in electrical substations measure the system currents
at predetermined measuring points of the switchgear with a certain
measurement inaccuracy. The measuring points are typically located at all
incoming and outgoing lines and possibly also within the system, e.g. for
the busbar protection. The current measurement values are filtered, scaled
to primary current values of the system, digitized, if necessary, and
detected as current measurement signals by the control system. For
communication purposes, additional rate-of-change filtering can be
provided which e.g. comprises temporal averaging by integration or an
algorithm for deciding about updating or retaining and transmitting or not
transmitting the current measurement value. The current measurement
signals are used for protective functions, for monitoring the substation,
for calculating performance data for operating purposes or for consumption
billing and for the representation on a display. Both the measurement
values detected by the current transformer and the parameters of the
filtering and scaling, i.e. the so-called parametrisation of the
measurement values can have errors. Primary errors in the current
transformer itself are produced e.g. by defective parts or material
fatigue. Errors in the parametrisation or in the power calculation can be
caused in the electronics by external influences, aging, drift, errors by
the operating personnel or the like. Errors in the transmission of
measurement values or measurement signals can occur in the device and
function chain from the current transformer to the screen display or power
system control center.
For protection purposes, it is known to monitor the current transformers by
means of local plausibility tests at an isolated point of the facility.
During the phase balance supervision test, all three phase currents and
the neutral current are measured at one point in the line and deviations
from an assumed maximum asymmetry between the phases are detected. During
the comparison test of current and voltage values, coarse inconsistencies
between voltage and current values can be discovered at the measuring
point. These local plausibility tests related to a single measuring point
are very coarse and only permit a yes/no decision, whether a current
transformer is operating or not. Wrong scaling or a loss of accuracy, in
contrast, cannot be detected, particularly since the tests in the
protective device are performed, as a rule, with relative values to the
nominal voltage.
In differential protection for transformers, the currents of the
high-voltage end and the low-voltage end are measured, provided with a
scaling factor given by the transformation ratio of the transformer and
compared with one another. This makes it possible to detect and correct
scaling errors for the differential protection.
Such tests are performed in protective devices for protective current
transformers. In general, such algorithms cannot be used in control
devices for measuring-type current transformers, because, as a rule,
transducers are used for digitizing the current measurement values and
these supply, instead of the instantaneous values needed, time-averaged
RMS or effective values of the current, the voltage or the power, the
frequency or the phase angle.
SUMMARY OF THE INVENTION
It is an object of the present invention to specify a method, a computer
program, a device and a switchgear with such a device for the improved and
simplified monitoring of current transformers in electrical switchgears.
In a first aspect, an exemplary embodiment of invention includes a method
for the plausibility checking of current transformers in an electrical
switchgear, in particular a high-voltage or medium-voltage switchgear, the
switchgear being controlled by a control system and measuring signals from
current transformers arranged at at least two different measuring points
being processed by the control system, the following steps being performed
for the plausibility testing of the current transformers: (i) recording an
instantaneous topology of the switchgear by the control system on the
basis of the existing electrical connections of primary devices and of
instantaneous positions of switches; (ii) based on the instantaneous
topology, identifying at least one zone of the switchgear, which zone
represents a conductively connected area which is bounded by at least one
current transformer and possibly by open switches; (iii) detecting the
measuring signals of the current transformers in the zone with a
current-direction-dependent sign and adding the measurement signals to
form a current sum of the zone; and (iv) testing the current sum for a
value zero within a permissible current transformer measurement accuracy
and marking the current transformers of the zone as problematic, if the
current sum is not equal to zero.
Thus, each zone represents a current node, the current sum of which is
ideally zero. Open switches can be assigned a current measuring value of
zero since they correspond to current transformers with a nominal current
of zero. The test of the current sum for deviations from the ideal value
of zero represents a simple, efficient method for checking, by means of a
relative comparison of the current transformers of a zone, their scaling
within permissible measurement signal deviations. The method requires
little computing effort and no additional measuring expenditure in the
current transformers. In particular, it is not necessary to know or
estimate a correct or absolute current value. The identification of
current transformers as problematic represents a first warning or alarm
stage and signals that further monitoring of the current transformers of
this zone is required. The method is independent of the configuration or
the network arrangement of the primary devices of the switchgear and, in
particular, independent of the complexity of their networking and,
therefore, can be implemented for any desired arrangements without
significant adaptations. The method is also independent from the
instantaneous operating state of the switchgear and, in particular, can
also be performed with fluctuating current values. Tracking the topology
is done dynamically, i.e. the topology or the division into zones is
updated continuously or on demand. In particular, it can change due to
switching actions. It is also advantageous that measuring signals of the
current transformers already available in the control system can be
accessed. The method is also compatible with conventional local
plausibility tests for current transformers. Going beyond these, however,
it allows slight deviations or errors in the scaling of current
transformers to be detected. More severe faults or defects on the primary
side of current transformers can also be detected.
A preferred exemplary embodiment comprises the following features: in each
zone, the same number of tests for the presence of a current sum not equal
to zero is performed; in each test for the presence of a current sum not
equal to zero, a warning counter for the current transformers identified
as being problematic in this zone is incremented; and, finally, current
transformers having a higher warning count than other current
transformers, particularly having a highest warning count, are identified
as being defective. This is because, if a defective current transformer
belongs to two or more zones, its warning counter is incremented with each
formation of a current sum in its zones, whereas the other warning
counters are only incremented by one unit. The higher or highest warning
count is, therefore, a reliable measure for detecting the defective
current transformer.
An exemplary embodiment wherein at least one zone includes a number of
current transformers, and wherein the warning counters of the current
transformers of this zone are reset to zero if a current sum equal to zero
is measured in the zone and a measurement signal not equal to zero is
measured on at least two current transformers of the zone, has the
advantage that the warning signal of a current transformer which is
arranged within the switch gear assembly and is not defective can be reset
to zero immediately in dependence on the order of the formation of sums in
the zones and the current transformer can be detected as intact.
An exemplary embodiment wherein, in a zone having one and only one current
transformer, the current transformer is identified as being defective if
its measurement signal is repeatedly not equal to zero, has the advantage
that zones with one and only one current transformer can be monitored in a
very simple and reliable manner.
An exemplary embodiment wherein each current transformer of the switch gear
assembly is divided into at least one zone, and wherein in an overall test
of the switch gear assembly one and only one test for the presence of a
current sum not equal to zero is performed in each zone, has the advantage
that the current transformers of the entire switch gear assembly can be
checked by exemplary methods according to the invention.
An exemplary embodiment wherein the identification of the zones is based on
a busbar of the switch gear assembly and all current transformers
conductively connected thereto are searched out, and/or wherein two zones
of the switch gear assembly are identified which are adjacent to one
another and which adjoin one another via a common current transformer and
if the common current transformer fails or if the common current
transformer is detected as being defective, the two zones are
automatically combined to form a single zone, has the advantage of
particularly simple zone detection and fast combining of zones in the case
of defective current transformers.
An exemplary embodiment wherein, when exactly one current transformer fails
in one zone, a current measurement signal to be detected by this current
transformer is calculated from the remaining current measurement signals
of the zone, assuming that the current sum is equal to zero, has the
advantage that it is possible to operate the switch gear assembly with
calculated currents.
In other aspects, exemplary embodiments of the invention relate to a
computer program for the plausibility checking of current transformers,
the method steps being implemented by a program code, furthermore to a
device for carrying out the method and to a switch gear assembly
comprising the device.
Further statements, advantages and applications of the invention will be
apparent from the description now following and the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a shows a single-pole diagram in a first topological state defined by
switch positions,
FIG. 1b shows the single-pole diagram in a second topological state.
In the figures, identical parts are provided with the same reference
symbols.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1a and 1b show a single-pole scheme of an electrical high-voltage
switchgear assembly 1. A control system 2 of the switchgear 1 is shown
diagrammatically and without the connections to the primary devices 3-9
and without reference to its spatial arrangement. 1a, 1b, 1c designate
topological sections or current areas or zones 1a, 1b, 1c which result
from the instantaneously assumed position of circuit breakers 3, isolators
4 and earthing isolators 5. The busbars are designated by 6, the current
transformers by 7, the voltage transformers by 8 and the outgoing lines or
outgoers by 9.
In FIG. 1a, a first instantaneous topology with a first, second and third
zone 1a, 1b and 1c is shown. The first zone 1a comprises a first current
transformer 7 at the left-hand outgoing line 9 and a second current
transformer 7 in the coupling part between the busbars 6. The adjoining
zone 1b contains the second current transformer 7 and the third and fourth
current transformer 7 at the right-hand outgoing line 9. The other
adjoining zone 1c contains the first current transformer 7. All current
transformers 7 are arranged at spatially separate positions 7a. According
to an exemplary embodiment of the invention, the measurement signals of
the current transformer 7 are detected separately with a
current-direction-dependent sign in each zone 1a, 1b, 1c to be monitored
and are added to form a current sum of the respective zone 1a, b, 1c and,
if a current sum which is not equal to zero within a permissible current
transformer measurement accuracy is present, all current transformers 7 of
the respective associated zone 1a, 1b, 1c are identified as being
problematic. The current sum is checked for zero within a permissible
measurement error or on the basis of measurement inaccuracies of the
current transformer 7 which are allowed and normally known a priori. If
the current sums deviate from zero by typically more than the measurement
inaccuracy, at least one current transformer 7 is presumably defective.
The transition from FIG. 1a to FIG. 1b occurs in that the substation
control system 2, by tracing the topology, detects which positions of the
switches 3-5 are instantaneously current. FIG. 1b shows a second
topological operating state of the switchgear 1 in which zone 1a contains
the first and fourth current transformer 7, zone 1b contains the second
and third current transformer 7 and the new zone 1c contains the second
current transformer 7. Adjacent zones, i.e. zones with a common current
transformer 7, are zones 1a, 1b and 1a, 1c in FIG. 1a but not 1b, 1c and
zones 1b, 1c in FIG. 1b. In the coupling part, there is also a line area
which is not divided into zones and which is exclusively bounded by open
switches 3 and isolators 4.
Thus, in the method, the current transformer measurement signals detected
at various measuring points 7a within each zone 1a, 1b, 1c are compared
with one another for consistency in that, when their current sum deviates
from the ideal value of zero by more than a predetermined difference
value, the current transformers 7 of the associated zone 1a, 1b, 1c are
marked as being problematic. The difference value is typically greater
than or equal to the measurement inaccuracy of the transformers 7.
In an advantageous embodiment, in each test of a zone 1a, 1b, 1c for the
presence of a current sum not equal to zero, a warning counter 2e is
incremented for the current transformers 7 graded as being problematic. If
the zones 1a, 1b, 1c to be monitored are tested with the same incidence,
current transformers 7 having a higher or having the highest warning count
can be marked as being defective.
A higher or highest warning count is a reliable measure of defective
current transformers 7: if in a zone 1c having exactly one current
transformer 7, this transformer is defective, its warning counter 2e is
incremented and all other warning counters 2e remain at zero. If the
defective current counter 7 is a member in two adjacent zones 1a, 1b; 1a,
1c (FIG. 1a) or 1b, 1c (FIG. 1b), its warning counter 2e is incremented to
twice the value of the intact current transformers 7 of these zones. If
the defective current counter 7 is a member in a disjoint zone 1a (FIG.
1b) which does not overlap other zones 1b, 1c (FIG. 1b) and thus does not
have a common current transformer 7, the warning counters 2e of all
current transformers 7 of this zone 1a are uniformly incremented and the
defective current transformer 7 can only be detected if another topology
or zone division exists on the basis of switching actions. To provide
identification, suitable switching actions can be carried out
intentionally, if necessary, as long as these switching actions are
compatible with the other requirements for the operation of the
substations. In the text which follows, further exemplary embodiments are
specified.
If there is at least one zone 1a, 1b having a plurality of current
transformers 7, the warning counters 2e of the current transformers 7 of
this zone 1a, 1b are reset to zero, if in the zone 1a, 1b a current sum
equal to zero and by at least two current transformers 7 of the zone 1a,
1b a measurement signal not equal to zero is measured. In a zone 1a, 1b,
1c having exactly one current transformer 7, the current transformer 7 is
identified as being defective, if its measuring signal is repeatedly not
equal to zero.
Advantageously, each current transformer 7 of the switchgear 1 is divided
into at least one zone 1a, 1b, 1c and in an overall test of the switchgear
1, exactly one test for the presence of a current sum not equal to zero is
performed in each zone 1a, 1b, 1c. For simple identification of the zones
one starts from a busbar 6 of the switchgear 1 and looks for all current
transformers 7 conductively connected thereto.
If two zones 1a, 1b; 1b, 1c of the switchgear 1 are adjacent to one another
and thus adjoin one another via a common current transformer 7, the two
zones 1a, 1b; 1b, 1c can be automatically combined to form a single zone
in the case of a failure of the common current transformer 7 or when the
common current transformer 7 is detected as being defective.
In the case of a failure of exactly one current transformer 7 in a zone 1a,
1b, 1c, a current measuring signal to be detected from this current
transformer 7 can be calculated from the remaining current measuring
signals of the zone 1a, 1b, 1c, assuming a current sum equal to zero. The
calculated current value can be used like a measured current measuring
signal for monitoring operation or for billing.
The plausibility test of the current transformer 7 can be performed
separately for each phase or alternately for various phases, in
particularly cyclically alternately, or for average values of at least two
phases, particularly all phases. In the operating state of the switchgear
1, tests for the presence of a current sum not equal to zero and, in
particular, overall tests of the switchgear 1 can be repeated periodically
and/or after switching actions, i.e. after each change in the
instantaneous topology. The plausibility test of the current transformers
7 can be carried out regardless of any switching actions and can be
repeated when inconsistencies of the measurement signals caused by
switching actions occur. As an alternative, the plausibility test of the
current transformers 7 is only carried out or evaluated when a previous
checking for instantaneous switching actions has proven to be negative.
The plausibility test can also be carried out when current transformers 7
are taken into operation, to provide early detection of inconsistencies in
their measurement value parametrisation.
An asynchronism of the measurement signals of a zone 1a, 1b, 1c can be
measured or estimated and the greater the asynchronism, the greater the
permitted current transformer inaccuracy which can be selected.
The results of the plausibility test can be represented in the form of a
list of the current transformers 7 with their zone allocation, as
statistics of the frequency with which each current transformer 7 has been
identified as being problematic and/or as graphical, particularly colored
information in a single-pole diagram of the switchgear 1. Preferably, the
current transformers 7 are measuring-type current transformers 7, the
measuring signals are effective current measurement values of the current
transformers 7, in particular RMS values, and/or the
current-direction-dependent sign is determined from a phase angle between
voltage and current of a phase, between currents of different phases or in
other ways.
In another aspect, an exemplary embodiment of the invention relates to a
computer program product for the plausibility checking of voltage
transformers 8 in an electrical switchgear 1, comprising a
computer-readable medium and computer-readable program code means which,
when executed on a data processing means of a control system 2 of the
electrical switchgear 1 cause the data processing means to execute the
method described above. Furthermore, a computer program for the
plausibility checking of current transformers 7 in an electrical
switchgear 1, which can be loaded and executed on a data processing unit
of a control system 2 of the switchgear 1 is claimed, wherein the computer
program, when executed, executes the steps of the method represented
above.
In a further aspect, an exemplary embodiment of the invention relates to a
device 20 for carrying out the method for the plausibility checking of
current transformer 7. The device comprises means 2a for recording the
instantaneous switchgear topology, means 2b for detecting at least one
switchgear zone 1a, 1b, 1c, defined as conductive area 1a, 1b, 1c bounded
by at least one current transformer 7 and possibly open switches 3-5,
means 2c for detecting the measuring signals of the current transformers 7
in the zone 1a, 1b, 1c with a current-direction-dependent sign and for
adding the measuring signals to form a current sum of the zone 1a, 1b, 1c,
and means 2d for testing the current sum for a value of zero within a
permitted current transformer measurement accuracy and for marking the
current transformers 7 of the zone 1a, 1b, 1c as problematic if the
current sum is not equal to zero. Preferably, the device 20 comprises a
warning counter 2e for monitoring the frequency with which a current
transformer 7 is identified as being problematic, and/or means 2f for
carrying out the method represented above.
The device 20 can be a station monitoring device 20, which can be connected
to the substation control system 2, or it can be integrated in an
operating interface of the control system 2. Furthermore, all device means
2a-2f mentioned can be implemented in hardware and/or software.
Exemplary embodiments of the invention also extend to an electrical
switchgear 1 which comprises such a device 20.
LIST OF REFERENCE SYMBOLS
Electrical switchgear
1a, 1b, 1c Sections of the topology, zones
2 control system
20 Device for the plausibility checking
2a Means for topology recording
2b Means for detecting a zone
2c Means for measurement signal detection
2d Means for current sum testing
2e Warning counter
2f Execution means
3 Circuit breaker
4 Isolator
5 Earthing isolator
6 Busbar
7 Current transformer
7a Measuring point of a current transformer
8 Voltage transformer
9 Outgoing lines.
*
