Apparatus and method for diagnosis of power appliances

A power appliance diagnosis apparatus includes a plurality of detectors provided on outer surfaces of gas-insulated casings of a power appliance for detecting the state of an insulating function and/or a current conduction function of the power appliance, a switch for time-divisionally taking in detection signals of the plurality of detectors, a frequency analyzer for performing frequency analysis on the detection signals taken in by the switch, and a controller for performing switching control of the switch.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus and a method for diagnosis of 
power appliances, and, particularly, relates to a diagnosis apparatus and 
a diagnosis method which are suitable for diagnosing insulation, abnormal 
current conduction, and foreign matter mixing in gas-insulated power 
appliances. 
In recent years, a demand for reliability of supply and for improvement in 
quality in environment of utilization of electric power has become greater 
with the advance of a highly information-oriented society and with the 
increase of dependency on electric power in the human living environment. 
With this demand, maintenance techniques for preventing accidents in 
operating equipment in an electric power station and for taking 
measurement in the event of accidents have been desired. For example, in a 
power appliance of a gas-insulated switchgear constituting one equipment 
in an electric power station, it is necessary to monitor functions 
thereof, such as an insulating function, a current-conduction function and 
the like. A method for detecting abnormality in the functions, that is, 
abnormality such as partial electric discharge, foreign matter mixing and 
the like, is described in Hitachi Review, Vol. 70, No. 3, August, 1988, 
pages 105 to 112. 
In such a conventional technique, means for detection of partial discharge, 
detection of abnormal current conduction, and detection of foreign matter 
mixing in a power appliance is constituted by separately provided 
individual detection systems. In the case where there are many places to 
be detected, therefore, the number of detectors is increased so that the 
number of local panels for housing those detectors is increased. There 
arises therefore a problem in that not only cost becomes high but 
reliability is lowered because of use of a large number of detectors. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to solve the problems in 
the conventional technique. 
It is another object of the present invention to provide an inexpensive and 
accurate diagnosis apparatus and a method therefor. 
To attain the foregoing objects, according to an aspect of the present 
invention, the diagnosis apparatus for a power appliance comprises a 
plurality of detectors provided on the outer surface of a gas-insulated 
casing of the power appliance and for detecting the state of an insulating 
function and/or a current-conduction function of the power appliance; a 
switch for taking in detection signals from the plurality of detectors in 
time division; a frequency analyzer for performing frequency analysis on 
the detection signals taken into the switch; and a controller for 
controlling switching operation of the switch. 
According to the present invention, the controller may be arranged so as to 
perform switching control on both the switch and the frequency analyzer so 
that the state of the power appliance is diagnosed by analysis means based 
on a value of frequency analysis obtained by the frequency analyzer and 
outputs the result of diagnosis. 
According to the present invention, the apparatus may be provided for two 
systems of two-phase similar portions within one and the same circuit or 
of similar portions in different circuits in a substation. 
According to another aspect of the present invention, the diagnosis method 
comprises the steps of detecting the state of an insulating function 
and/or a current-conduction function of the power appliance by means of a 
plurality of detectors provided on a casing of the power appliance; taking 
in detection signals from the plurality of detectors by means of a 
time-divisionally controlled switch; performing frequency analysis on the 
detection signals by means of a frequency analyzer; and diagnosing a value 
of the frequency analysis by means of the diagnosis apparatus to thereby 
diagnose the state of the power appliance. 
The state of an insulating function and/or a current-conduction function of 
the power appliance is detected by the plurality of detectors provided on 
the casing of the power appliance. The detection signals are successively 
fed to the frequency analyzer through the switch which is 
time-divisionally controlled by the controller. The frequency analyzer 
performs frequency analysis on the respective detection signals and 
outputs a value of frequency analysis. In the case where the value of 
frequency analysis has components within a frequency band of from the 
order of tens of MHz to the order of hundreds of MHz, it is considered 
that partial electric discharge has occurred. In the case where the value 
has components within a frequency band of from the order of tens of Hz to 
the order of thousands of Hz, it is considered that abnormal current 
conduction has occurred. In the case where the value has components within 
a frequency band of from the order of tens of KHz to the order of hundreds 
of KHz, it is considered that mixing of foreign matter has occurred. The 
aforementioned method is useful for an off-line measurement on regular 
interval inspection. 
Further, the controller may be designed so as to perform time-divisional 
switching control on the switch and also perform changing control on the 
frequency analyzer so as to cope with a frequency band detected by one of 
the detectors selected by the switch. This method is useful for always 
monitoring the result of diagnosis on line. 
Other features and advantages of the present invention will be apparent 
from the following description taken in connection with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention will be described with 
reference to the accompanying drawings. 
FIG. 1 illustrates an embodiment of the present invention. In this 
embodiment, the present invention is applied to a gas-insulated 
opening/closing apparatus. The gas-insulated switchgear 1 has a plurality 
of grounded casings 2 housing therein various types of switches and 
current conduction appliances, and insulating spacers 3 for separating the 
casings 2. Electromagnetic wave detectors 10 for detecting partial 
electric discharge produced in the casings 2, vibration detectors 20 for 
detecting abnormal current conduction in the inside of the casings 2 based 
on the vibration of the casings 2 and vibration detectors 30 for detecting 
the motion of foreign matter in the casings 2 are attached on the outer 
surfaces of the casings 2, respectively. The partial electric discharge 
decomposes insulating gas within the casings 2 to lower the insulating 
function of the power appliance. The partial electric discharge appears in 
the form of frequency components within a frequency band of from the order 
of tens of MHz to the order of hundreds of MHz. Similarly, the abnormal 
current conduction decomposes insulating gas within the casings 2 because 
of local heating caused by contact failure to lower the insulating 
function of the power appliance. The abnormal current conduction appears 
in the form of frequency components within a band of from the order of 
tens of Hz to the order of thousands of Hz. The foreign matter mixing 
produces partial electric discharge to thereby lower the insulating 
function of the power appliance in the same manner as described above. The 
foreign matter mixing appears in the form of frequency components within a 
band of from the order of tens of KHz to the order of hundreds of KHz. The 
electromagnetic wave detectors 10 and 10 for detecting partial electric 
discharge are connected to fixed contacts S.sub.11 and S.sub.12 of a 
switch 40 through transmission cables 11 and 12, respectively. The 
vibration detectors 20 and 20 for detecting abnormal current conduction 
are connected to fixed contacts S.sub.21 and S.sub.22 of the switch 40 
through transmission cables 21 and 22, respectively. The vibration 
detectors 30 and 30 for detecting the motion of foreign matter are 
connected to fixed contacts S.sub.31 and S.sub.32 of the switch 40 through 
transmission cables 31 and 32, respectively. The fixed contacts S.sub.11, 
S.sub.12, S.sub.21, S.sub.22, S.sub.31 and S.sub.32 of the switch 40 are 
arranged one by one successively counterclockwise with respect to a 
movable contact 41 of the switch 40. The movable contact 41 of the switch 
40 is connected to a frequency analyzer 50 through a transmission cable 
42. The switch 40 is controlled by a controller 72 operated based on an 
instruction issued from a central processing unit (CPU) 70, so that the 
movable contact 41 is time-divisionally counterclockwise switched. The 
frequency analyzer 50 is controlled by a controller 71 operated based on 
an instruction issued from the CPU 70, so that the frequency band thereof 
is changed corresponding to the detector selected by the switch 40. The 
frequency analyzer 50 successively performs frequency analysis of 
detection signals from the detectors. An AD converter 60 is connected to 
the output of the frequency analyzer 60. The frequency-analyzed signal 
from the AD converter 60 is processed by the CPU 70. The switch 40, the 
frequency analyzer 50, the AD converter 60, the CPU 70 and the controllers 
71 and 72 are provided on a local panel 4 provided in the vicinity of the 
power appliance. The local panel 4 and a central panel 5 provided in a 
building of a transformer substation are connected to each other through 
an electro-optic converter 73, an optical transmission cable 80 and an 
opto-electric converter 91. The central panel 5 has a CPU 90 for 
processing the received signal, and a cathode ray tube (CRT) 92 and a 
printer 93 used for indicating the results of processing, that is, the 
results of diagnosis. 
The operation of the aforementioned embodiment of the present invention 
will be described hereunder. 
The switch 40 selects the movable contact 41 under the control of the 
controller 72 to turn the movable contact 41 successively to the fixed 
contacts S.sub.11, S.sub.12, S.sub.21, S.sub.22, S.sub.31, S.sub.32, in 
that order. The frequency analyzer 50 selects the frequency detection band 
under the control of the controller 71 to determine the frequency band 
corresponding to the contact selection in the switch 40. In short, in the 
case where the movable contact 41 of the switch 40 is connected to either 
one of the fixed contacts S.sub.11 and S.sub.12, the frequency detection 
band of the frequency analyzer 50 is set in a component detection band of 
from the order of tens of MHz to the order of hundreds of MHz for the 
purpose of detecting partial electric discharge. In the case where the 
movable contact 41 of the switch 40 is connected to either one of the 
fixed contacts S.sub.21 and S.sub.22, the frequency detection band of the 
frequency analyzer 50 is set in a component detection band of from the 
order of tens of Hz to the order of thousands of Hz for the purpose of 
detecting abnormal current conduction. In the case where the movable 
contact 41 of the switch 40 is connected to either one of the fixed 
contacts S.sub.31 and S.sub.32, the frequency detection band of the 
frequency analyzer 50 is set in a component detection band of from the 
order of tens of KHz to the order of hundreds of KHz for the purpose of 
detecting the motion of foreign matter. The switching operation for the 
switch 40 and the frequency analyzer 50 is performed in a period of the 
order of seconds or minutes. Detection of partial electric discharge, 
detection of abnormal current conduction and detection of foreign matter, 
which are necessary for diagnosis of abnormality of the power appliance, 
can be carried out by using the connection-sequence-controlled switch 40 
and the detection-frequency-band-controlled frequency analyzer 50 in 
combination. More in detail, the detection signals detected by the 
detectors 10, 20 and 30 are fed to the frequency analyzer 50 through the 
switch 40 which is subjected to time-divisional switching control. The 
frequency analyzer 50 carries out frequency analysis on the detection 
signals supplied thereto. The detection signals thus frequency-analyzed 
are fed to the CPU 70 through the AD converter 60. In the CPU 70, 
diagnosis of abnormality is made. The result of diagnosis is transmitted 
to the central panel 5 serving as a man-machine interface and then 
displayed on the CRT 92 and the printer 93. 
As described above, according to the present invention, a plurality of 
time-divisionally supplied detection signals which exhibit partial 
discharge, abnormal current conduction, foreign matter mixing and the like 
in the power appliance can be analyzed by a common frequency analyzer to 
decide diagnosis of abnormality. Accordingly, the number of local panels 
can be reduced to thereby attain reduction both in size and in cost. 
According to this embodiment, diagnosis of abnormality can be monitored on 
line. 
FIG. 2 illustrates another embodiment of the present invention. In FIG. 2, 
items the same as or equivalent to those in FIG. 1 are referenced 
correspondingly. In this embodiment, the detection signals from the 
detectors 10, 20 and 30 are successively selected through the switch 40 
under the control of the controller 72 so as to be fed to the frequency 
analyzer 50'. In the frequency analyzer 50', the detection signals are 
successively frequency-analyzed and then recorded. 
According to this embodiment, a plurality of time-divisionally supplied 
detection signals in the power appliance can be analyzed by a common 
frequency analyzer. As a result, the number of local panels can be reduced 
because the number of frequency analyzers can be reduced to one. 
Accordingly, reduction both in size and in cost can be attained. According 
to this embodiment, off-line monitoring effective for regular interval 
inspection in the site or local place can be made. 
FIG. 3 illustrates a further embodiment of the present invention. In FIG. 
3, items the same as or equivalent to those in FIGS. 1 and 2 are 
referenced correspondingly. In this embodiment, the detection signals from 
the detectors 10, 20 and 30 are led to the local panel 4 through the 
transmission cables 11, 21 and 31. The results of diagnosis are 
transmitted to the central panel 5 through the transmission cable 80 so 
that diagnosis of abnormality can be monitored at all times. Further, 
transmission cables 15, 25 and 35 branched from the transmission cables 
11, 21 and 31 are connected to the switch 40. The output of the switch 40 
is connected to the frequency analyzer 50, so that diagnosis can be 
monitored also in inspection of the power appliance. In this embodiment, 
the local panel 4 and the central panel 5 are constructed in the same 
manner as in FIG. 1, so that a detailed description thereof will be 
omitted. 
In such a configuration of this embodiment as described above, primary 
diagnosis can be carried out through on-line monitoring in the system of 
the local panel 4 and the central panel 5. In the case where a sign of 
abnormality is detected by the primary diagnosis, the switch 43 is closed 
so that a highly accurate diagnosis can be made through off-line 
monitoring. 
According to this embodiment, not only reduction both in size and in cost 
can be attained in the same manner as in the aforementioned embodiment, 
but a highly accurate diagnosis can be made. 
FIG. 4 illustrates a still further embodiment of the present invention. In 
FIG. 4, items the same as or equivalent to those in FIG. 1 are referenced 
correspondingly. In this embodiment, two systems of abnormality diagnosis 
apparatuses A and B are provided. Specifically, diagnosis of two systems 
of two-phase similar portions within one and the same circuit or of 
similar portions in different circuits in a substation is carried out in 
the same order and judged by the CPU 70. 
By such a configuration in this embodiment as described above, diagnosis is 
carried out on two systems of similar portions which come into 
substantially the same condition to thereby make it possible to attain an 
improvement in diagnostic accuracy. This is because, in the case where a 
certain abnormality occurs in a gas-insulated switch gear or the like, the 
probability that the same abnormality occurs at the same time in a 
plurality of portions can be considered to be very low. 
According to this embodiment, not only reduction both in size and in cost 
can be attained but diagnostic accuracy for two systems of similar 
portions can be improved. 
Although this embodiment has shown the case where diagnosis is made based 
on comparison therebetween, it is a matter of course that the present 
invention is not limited to the specific embodiment. For example, 
diagnosis may be made in the order of the system A, the system B, the 
system A, .... Alternatively, upon occurrence of an abnormal system, only 
the system in which abnormality has occurred may be diagnosed exclusively 
diagnostic accuracy can be improved. 
According to the apparatus of the present invention, diagnosis of a power 
appliance in working condition can be carried out through one and the same 
frequency analyzer. Accordingly, reduction both in size and cost of the 
apparatus can be attained. 
According to the method of the present invention, inexpensive and accurate 
diagnosis of a power appliance in working condition can be carried out.