Title of Invention

DEVICE FOR MONITORING THE LEAKAGE CURRENT OF A SURGE ARRESTER

Abstract The invention relates to a device for supervising a leakage current of a lighting arrester (1) and to an measuring element (7) for detecting a leakage current in a leakage current circuit (3). A filter assembly (8) filters said leakage current in order to extract a third harmonic oscillation which is evaluated by an evaluation circuit (6) with respect to the quantity thereof. Said evaluation circuit (12, 24) delivers at least one warning signal to a display device (13,14,15, 25). In a preferred embodiment, three display devices (13,14,15) operating as a signaling light are provided. A power supply for the used circuits (5,6) is obtainable by means of a transformer (16) which extracts a necessary auxiliary zero-potential energy contained in the leakage current and with the aid of a main power supply unit (19) connected to said transformer (16).
Full Text Description
Device for monitoring the leakage current of a surge arrester
The invention relates to a device for monitoring the leakage
current of a surge arrester in accordance with the
precharacterizing clause of the main claim.
Surge arresters for electrical power transmission systems are
extremely reliable devices. However, it is often nevertheless
desirable to monitor the operating state of the arrester. This
is particularly the case when the devices are subject to
unusually stringent requirements, for example owing to the
design or environmental conditions, or are installed at
particularly significant points in the system, such as at
machine transformers or strategically important substations. In
this case, the user would wish to be able to use monitoring
devices to identify in good time whether the arrester is
capable of reliably arresting surges having the specified power
content at any time or whether the arrester has been damaged or
is at risk of failure. In addition to the established method of
introducing a monitoring spark gap in series with the arrester,
in the case of which witness marks on the polished electrodes
of the spark gap are evaluated, and in addition to the method
of using surge counters which register the occurrence of an
arresting process above a specific amplitude, methods involving
the measurement of leakage currents are known in particular in
the case of modern metal-oxide arresters. In the case of metal-
oxide arresters, the active part is not DC-isolated from the
power supply system but is connected permanently to the
voltage. The electrical properties of the active part are thus
reflected, at any point in time in the leakage current through
the arrester. So-called total leakage current measurement is
known, in the case of which the peak value for the total
leakage current is usually evaluated, use being made

of the fact that an increasing resistive component is
superimposed on the normally predominantly capacitive leakage
current

as the temperature of the active part increases or as the
voltage applied to said active part increases, and this
increasing resistive component increases the total leakage
current. Various influencing variables which are included in
the total leakage current may, however, result in erroneous
interpretations, and only a low degree of information quality
can be achieved with this method.
The Patent Abstract of Japan JP 11307226 A has disclosed a
monitoring device for a surge arrester. The monitoring device
is supplied from an external power supply device. The voltage
produced by this external power supply device is synchronized
with the system voltage of the surge arrester in order to
ensure monitoring of the surge arrester.
Furthermore, the Patent Abstract of Japan JP 2003037932 A has
disclosed a surge arrester which has a device which monitors
the ageing of the arrester. Leakage-current monitoring detects
the leakage current of the surge arrester. In addition, the
number of arresting processes of the surge arrester is
monitored. When a predetermined number of arresting processes
has been reached, correspondingly differently colored light
signals are output.
Patent Abstracts of Japan JP 09145759 A and JP 2000321318 A
have each disclosed apparatuses for monitoring a surge
arrester. For monitoring purposes, the leakage current of an
arrester is monitored and evaluated in a computer unit. For
this purpose, a Fourier transformation is carried out, for
example. The result of the analysis is represented in each case
on a display device.
The Patent Abstract of Japan JP 03001476 A has disclosed a
monitoring device for inspecting a surge arrester. An
instrument transformer is inserted into the ground current path

of a surge arrester. In this case, the ground connection forms
the primary winding. The instrument transformer is fed

an inspection current from an external AC voltage source.
The Patent Abstract of Japan JP 08017552 A has disclosed a
device for monitoring a leakage current of a surge arrester.
The leakage current of the surge arrester is monitored by means
of a detection device. A resistive component is calculated from
the measured leakage current by means of a computation unit.
This resistive component of the leakage current is used to
diagnose the state of the surge arrester.
The zinc oxide material used, for example, for metal-oxide
arresters has a conductance which is nonlinear as a function of
the voltage and leads to the formation of a third harmonic
component in the resistive leakage current of the arrester when
a sinusoidal voltage is applied. If the resistive component of
the leakage current is increased, for example by means of
degradation, this results in a shift to the range of altered
nonlinearity of the characteristic and thus in a further rise
in the third harmonic component content. Methods are therefore
known in which analysis of the third harmonic of the leakage
current is carried out. For this purpose, the leakage current
is generally output via a measuring element and passed via a
filter arrangement, by means of which the third harmonic
component is filtered out and is evaluated in terms of its
amplitude. However, at present this method has the disadvantage
that the available devices are costly and require a high degree
of experience for correctly measuring and interpreting the
measured values. In addition, these devices require auxiliary
power for their voltage supply and are therefore generally not
used for continuous long-term monitoring on arresters.
The invention is therefore based on the object of providing a
device for monitoring the leakage current of a surge arrester
using the third harmonic

of the leakage current, in the case of which no auxiliary power
is required for the supply of the components and the
measurement results can be evaluated in a simple manner, and
which can be produced in a cost-effective manner, with the
result that continuous long-term monitoring of the surge
arrester is possible.
This object is achieved according to the invention by the
characterizing features of the main claim in conjunction with
the features of the precharacterizing clause.
As a result of the fact that the filter arrangement is
connected to an evaluation circuit for the third harmonic,
which, if appropriate, outputs at least one warning signal to a
display apparatus which is connected to the evaluation circuit,
and the fact that a transformer is connected in the arrester
circuit, via which transformer the power for a voltage supply
to the filter arrangement and the evaluation circuit can be
output, no auxiliary power is required for the electronic
components, i.e. the latter are fed the leakage current, and no
user-dependent erroneous interpretation is possible and only
low demands are placed on the qualifications of the user since
the result of the monitoring is displayed. Furthermore, the
device can be produced from standard electronic components, as
a result of which it is cost-effective. The device can
therefore be installed permanently at the arrester for
continuous monitoring purposes.
The measures specified in the dependent claims make
advantageous developments and improvements possible. A
measuring resistor can advantageously be used as the measuring
element, but the use of a current-compensated coil arrangement
comprising a current compensator is also possible.
An active bandpass filter having a frequency of 150 Hz can be
used as the filter arrangement, and a microprocessor can be

used as the evaluation circuit. In one simplified embodiment,
the microprocessor

can be replaced by a single discrete or integrated threshold
value switch.
In one advantageous embodiment, the display apparatus has one
or more light-emitting diodes, in which case only one light-
emitting diode can be provided for the simplified version with
the threshold value switch, which light-emitting diode displays
the instance of a predetermined threshold value being exceeded.
However, three light-emitting diodes with the colors of a
traffic light are particularly advantageously connected to the
microprocessor and display the fault-free, the critical and the
faulty operating modes. It is particularly advantageous to
connect a coil arrangement having a toroidal core and two
windings, which are wound around the toroidal core and whose
connections are passed to the outside, into the arrester
circuit, since, in the critical case, i.e. when the evaluation
circuit outputs a warning signal, an external measuring device
can be connected which can carry out a more accurate
measurement and evaluation of the operating state.
Exemplary embodiments of the invention are illustrated in the
drawing and will be explained in more detail in the description
below. In the drawing:

figure 1 shows one circuitry refinement of the monitoring
device according to the invention,
figure 2 shows a further embodiment of the checking circuit
used in figure 1 for the third harmonic, and
figure 3 shows a further embodiment of the evaluation circuit
used in figure 1 with a display.
The device for monitoring the leakage current illustrated in
figure 1 has a metal-oxide arrester 1 having a protection spark

gap 2 for arrester currents and the actual leakage current path
3. In addition to the arrester 1,

the device comprises three switching units, a voltage supply
unit 4, a checking circuit 5 for the third harmonic and an
evaluation unit 6. The checking circuit 5 has a measuring
resistor 7, which is connected into the leakage current path 3,
and an active bandpass filter 8 having a mid-frequency of
150 Hz. In addition, a coil arrangement 9 is arranged in the
leakage circuit 3, said coil arrangement 9 having a toroidal
core 10 and two coils 11 wound around the toroidal core, the
connections of the coils being passed to the outside for
connection to an external measuring device.
The evaluation unit 6 essentially comprises a microprocessor
circuit 12 and three light-emitting diodes 13, 14, 15, which,
in the exemplary embodiment, are selected to be the colors of a
traffic light, namely green, amber and red. Of course other
light sources can in principle also be used, in which case, if
appropriate, one or more audible display elements are also
conceivable in place of the visual display elements.
The voltage supply unit 4 comprises a transformer 16, whose
primary winding 17 is connected into the leakage current path
3, and whose secondary winding 18 is connected to a switched
mode power supply 19 having a rectification circuit and a
filter circuit. The bandpass filter 8 and the microprocessor
circuit 12 are connected to the outputs of the switched mode
power supply 19 for their voltage supply. The auxiliary power
is output, floating, from the leakage current flowing in the
leakage current path 3 via the transformer 16, the secondary
coil 18 providing the switched mode power supply 19 with an
alternating current. The switched mode power supply carries out
rectification and filtering and makes a positive and a negative
DC voltage having a corresponding zero potential available at
its output.

During operation of the arrester 1, the leakage current is
checked by the measuring resistor 7 and passed on to the active
bandpass filter 8, which filters out the third harmonic

from the checked leakage current. The microprocessor circuit 12
evaluates the third harmonic on the basis of the magnitude of
its peak value and drives the LEDs 13 to 15. For this purpose,
the microprocessor circuit 12 contains three threshold values,
in which case, in the event of a peak value below a first
threshold value, normal operation is indicated by a green LED
13, in the event of a peak value above the first threshold
value but below the second threshold value, the critical range
is indicated by an amber LED 14, and, in the event of a peak
value above the second threshold value, faulty operation is
indicated by a red LED.
As has already been explained above, the coil arrangement 9,
which can be connected as a current-compensated coil, is used
merely as an additional sensor for an external measuring device
for precise, compensated measurement of the third harmonic, if,
for example, the amber LED 14 blinks.
Figure 2 illustrates a further embodiment of a checking circuit
5, which can be used in place of the checking circuit shown in
figure 1, i.e. the measuring resistor 7 shown in figure 1 is
replaced by a current-compensated coil arrangement, which has a
toroidal core 20 having two coils 21, 22 and a current
compensator 23 connected to the connections of the coils 21,
22. In this case, the total magnetic field of the coil
arrangement is brought to zero by means of a reverse current,
with the result that the measured voltage is available at the
output of the current compensator 23. The active bandpass
filter 8 in turn filters out the third harmonic.
Figure 3 illustrates one variant of the evaluation unit 6, in
the case of which the microprocessor circuit 12 is replaced by
a single threshold value switch 24, which has only one
threshold value for the display of the critical operating
range. In this exemplary embodiment, there is only one LED 25,
which can illuminate or blink amber, for example.

The coil arrangement 9 can also be provided in all of the
exemplary embodiments.

WE CLAIM:
1. A device for monitoring the leakage current of a surge
arrester having a measuring element for the purpose of checking
the leakage current flowing in the arrester circuit and a
filter arrangement for the purpose of filtering out the third
harmonic from the leakage current, which is a measure of the
operating state of the arrester, the filter arrangement (8)
being connected to an evaluation circuit (12, 24) for the third
harmonic,
characterized
in that, if appropriate, at least one warning signal is output
to a display apparatus (13, 14, 15, 25) which is connected to
the evaluation circuit, and in that a transformer (16) is
connected into the arrester circuit (3), via which transformer
(16) the power for a voltage supply to the filter arrangement
(8) and the evaluation circuit (12, 24) can be output.
2. The device as claimed in claim 1, characterized are that
the primary winding (17) of the transformer (16) is in the
arrester circuit (3), and the secondary winding (18) is
connected to a rectifier circuit (19), which is connected to
the filter arrangement (8) and the evaluation circuit (12, 24).
wherein
3. The device as claimed in claim 1 or claim 2, characterised
in that the measuring element is a measuring resistor (7).
wherein
4. The device as claimed in claim 1 or claim 2, characterized
in that the measuring element is a current-compensated coil
arrangement comprising a current compensator (23), the current
compensator (23) being connected to the filter arrangement (8)
and the rectifier circuit.

5. The .device as claimed in one of claims 1 to 4,
wherein
characterized—in—that the filter arrangement comprises an
active bandpass filter (8).
6. The .device as claimed in one of claims 1 to 5,
wherein
characterized in that the evaluation circuit comprises a
microprocessor circuit (12), which evaluates the peak values of
the third harmonic and outputs at least one warning signal.
7. The device as claimed in one of claims 1 to 5,
characterized in that the evaluation circuit is a threshold
value circuit (24), which outputs a warning signal when a
threshold value is exceeded.
8. The device as claimed in one of claims 1 to 7,
wherein
characterized in that the display apparatus is of the visual or
audible type.
9. The device as claimed in one of claims 1 to 8,
wherein
characterized in that the display apparatus has at least one
LED (13, 14, 15, 25) .
10. The device as claimed in one of claims 1 to 9,
wherein
characterized in that the display apparatus comprises a
plurality of LEDs (13, 14, 15), and in that the evaluation
circuit (12) drives different light-emitting diodes on the
basis of the magnitude of the peak values.
11. The device as claimed in one of claims 1 to 10,
charactcriged in that a coil arrangement (9), which is provided
with a toroidal core (10) and two coils (11) wound around the
toroidal core, is connected in the arrester circuit (3), the
connections of the coils being passed to the outside for
connection to an external measuring device in the event of the
presence of a warning signal.

The invention relates to a device for supervising a leakage current of a lighting
arrester (1) and to an measuring element (7) for detecting a leakage current in a
leakage current circuit (3). A filter assembly (8) filters said leakage current in order
to extract a third harmonic oscillation which is evaluated by an evaluation circuit (6)
with respect to the quantity thereof. Said evaluation circuit (12, 24) delivers at least
one warning signal to a display device (13,14,15, 25). In a preferred embodiment,
three display devices (13,14,15) operating as a signaling light are provided. A
power supply for the used circuits (5,6) is obtainable by means of a transformer
(16) which extracts a necessary auxiliary zero-potential energy contained in the
leakage current and with the aid of a main power supply unit (19) connected to said
transformer (16).

Documents:

587-KOLNP-2006-CORRESPONDENCE 1.1.pdf

587-KOLNP-2006-FORM 27-1.1.pdf

587-KOLNP-2006-FORM 27.pdf

587-KOLNP-2006-FORM-27.pdf

587-kolnp-2006-granted-abstract.pdf

587-kolnp-2006-granted-claims.pdf

587-kolnp-2006-granted-correspondence.pdf

587-kolnp-2006-granted-description (complete).pdf

587-kolnp-2006-granted-drawings.pdf

587-kolnp-2006-granted-examination report.pdf

587-kolnp-2006-granted-form 1.pdf

587-kolnp-2006-granted-form 18.pdf

587-kolnp-2006-granted-form 2.pdf

587-kolnp-2006-granted-form 3.pdf

587-kolnp-2006-granted-form 5.pdf

587-kolnp-2006-granted-gpa.pdf

587-kolnp-2006-granted-reply to examination report.pdf

587-kolnp-2006-granted-specification.pdf

587-kolnp-2006-granted-translated copy of priority document.pdf

587-KOLNP-2006-PA.pdf


Patent Number 227607
Indian Patent Application Number 587/KOLNP/2006
PG Journal Number 03/2009
Publication Date 16-Jan-2009
Grant Date 14-Jan-2009
Date of Filing 13-Mar-2006
Name of Patentee SIEMENS AKTIENGESELLSCHAFT
Applicant Address WITTELSBACHERPLATZ 2, 80333 MUNCHEN
Inventors:
# Inventor's Name Inventor's Address
1 HAIKO SCHILLERT EICHENHOF 6 15831 MAHLOW
2 MATTHIAS SCHUBERT DYROTZER STR 7D 13583 BERLIN
3 KAI STEINFELD HUTTENSTR. 30 10553 BERLIN
PCT International Classification Number H01T 15/00,H01C 7/12
PCT International Application Number PCT/DE2004/002123
PCT International Filing date 2004-09-16
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 103 45 858.8 2003-09-25 Germany