CA2058473A1 - Method and apparatus for checking the state of electrical insulation of an electrically conducting work - Google Patents
Method and apparatus for checking the state of electrical insulation of an electrically conducting workInfo
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- CA2058473A1 CA2058473A1 CA002058473A CA2058473A CA2058473A1 CA 2058473 A1 CA2058473 A1 CA 2058473A1 CA 002058473 A CA002058473 A CA 002058473A CA 2058473 A CA2058473 A CA 2058473A CA 2058473 A1 CA2058473 A1 CA 2058473A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
- G01N17/02—Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement
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- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
- Prevention Of Electric Corrosion (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
- Gas-Insulated Switchgears (AREA)
- Measurement Of Resistance Or Impedance (AREA)
- Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
Abstract
METHOD AND APPARATUS FOR CHECKING THE STATE OF
ELECTRICAL INSULATION OF AN ELECTRICALLY
CONDUCTING WORK
ABSTRACT
The invention relates to the checking of the state of electrical insulation of a conducting work (1) placed in an electrolytic medium (3) and connected to a reference electrode (11) in contact with this same medium.
The proposed apparatus comprises means (15) of measuring the voltage between the work and the electrode, a generator (7) for establishing a DC current between the work and the anode piece, a clock (9) for interrupting and reestablishing the circulation of the said current and triggering measurements of this current and of the said voltage, processing means for calculating, for each current intensity, the potential difference between the said voltages measured without and with current circula-tion, and for calculating the ratio between this poten-tial difference and the corresponding measured intensity of the said current, and means of displaying the calcu-lated ratio.
The invention applies to the field of the catho-dic protection of buried works.
ELECTRICAL INSULATION OF AN ELECTRICALLY
CONDUCTING WORK
ABSTRACT
The invention relates to the checking of the state of electrical insulation of a conducting work (1) placed in an electrolytic medium (3) and connected to a reference electrode (11) in contact with this same medium.
The proposed apparatus comprises means (15) of measuring the voltage between the work and the electrode, a generator (7) for establishing a DC current between the work and the anode piece, a clock (9) for interrupting and reestablishing the circulation of the said current and triggering measurements of this current and of the said voltage, processing means for calculating, for each current intensity, the potential difference between the said voltages measured without and with current circula-tion, and for calculating the ratio between this poten-tial difference and the corresponding measured intensity of the said current, and means of displaying the calcu-lated ratio.
The invention applies to the field of the catho-dic protection of buried works.
Description
2 ~ 7 3 The invention relates to a method and an ap-paratus for checking the state of electrical insulation of an electrically condl~cting work placed in an electro-lytic medium and connected by a network of electrical conductors, on the one hand to a counter-electrode placed in the abovementioned electrolytic medium and, on the other hand, to a reference electrode which is in contact with this same electrolytic medium, a voltage existing na~urally between this electrode and the said work.
During trials undertaken within the context of the invention, the electrically conducting work consisted of a buried gas conduit made of a metallic material. The prime usefulness of the method which is the s~bject of the invention consisted in checking the quality of the placement of this pipe which was in this particular case covered with an electrically in~ulating coating forming a passive protection intended to remove the pipe from the electrolytic environment of the ground.
Experience having shown that placements in particular of such buried pipes are not always perfect and that furthermore the coatings for passive protection are not always entirely effective, thought was con-sequently given to the problem of checking the state of electrical insulation of these works, once the latter are in place in their medium.
Now, ~uch checking in practice encounters a certain number of difficultie~ relating in particular to the variable nature over time of the parameters to be meaRured, these variations possibly in particular being induced by poorly insulated DC in~tallations (railway traction, electrolysis plant, etc).
Problems of measurement error~ also arose due to the phenomena of polarisation of the works, these polari-sations changing over time and as a function of the electxical change in particular of the worX, of the counter-electrode and of the disturbances which may, nearby, cross the electrolytic medium.
After lengthy studies, the Applicant succeeded in developing a truly reliable and effective method making 2~8~73 it possible to check the state of electrical insulation of a conducting work, this metho~ being characterised in particular in that:
a) the voltage between the work and the reference S electrode is sensed at least once and recorded, b) ah impos0d circulation of current who5~ intensity which is sensed and recorded ,is established in the conducting network, between the work and the counter-electrode, c! the voltage between the work and the reference electrode, current circulating, is sensed at least once and recorded anew, d) the difference ~U between the voltages recor-ded in a) and c) is calculated and recorded without and with imposed current circulation respectively, e) the said imposed current circulation is inter-rupted and steps a), b), c) and d) are repeated a given number of times whilst varying, during step b), the intensity of the imposed current, f) the change is next deduced therefrom in the said voltage difference QU as a function of the intensity I o~ current established in the network, which change is linear o~ the form ~U = AI (A = constant) from I = 0 up to a specified value of intensity of this current, 25 g) the slope A is calculated, h) and the state of eleotrical insulation of the woxk is deduced therefrom by identifying the said slope with the electrical re~istance of this work.
In this way, through rapid capture of the mea-sured or sensed potentials, it will be possible to obtain quantities approximating the actual values existing on site.
Moreover, by limiting oYer t.ime, through rigorous monitorinq, the settling periods of the imposed currents, it will be possible to undertake series of trials of r~asonable duration by repeating the measurements a large number of times and by statistically processing them so as to detect and negate in particular the disturbing presence of the stray curren~s.
2~8~73 With this aim, a complementary characteristic of this invention moreover provides that, the voltages between the work and the counter-electrode being disturbed by electrical sources generating frequencies S which modify over time the voltages to be measured, these said frequencies are eliminated by filtering ~uring the abovementioned steps a) and/or c) when the said frequencies are beyond a predetermined threshold and/or correspond to known frequencies identified as disturbing.
As will be seen below in the description which will follow, and still in order to meet this problem of electrical disturbances, provision has also been made in the invention to preferably statistically process the measurements so as to take into consideration only values judged to be consistent and reasonable, as explained in particular in Claims 3, 4 and 7 attached.
Apart from such a checking method, the subject of the invention is also an apparatus intended to check the state of electrical insulation of the chosen work.
In accordance with tha invention, this apparatus is characterised in particular in that it comprises:
- means of measuring the voltage between the reference electrode and the work, - a generator for generating a current Z5 between the work and the counter-electrode, - means of measuring thi~ current, - a clock for interrupting and establishing sequentially the circulation of the current Lmposed by the generator between the work and the counter-electrode, and triggering measuremants of the said current and of the said voltage, - means of processing the measure-ments made in order to calculate, for each intensity of current, the difference ~U between the voltages measured without and with circulation o~ said current, and in order to calculate also the ratio A between the difference in the abovementioned vol~ages (~U) and the said corresponding intensity of current, - and means of displaying the calculated ratio A.
20~8~3 Other characteristics and advantages of the invention will emerge further from the following descrip-tion made with reference to the attached drawings in which:
- Figure 1 represents a general configurational diagram of a circui-t permitting implementation of the me~hod of the invention, - Figure 2 is a block diagram representing in more detail the processing and dis~lay unit of the apparatus of the invention, - Figure 3 presents an illustrative curve of a possible change, with respect to a work, in the potential difference U as a function of the Lmposed current I, - Figures 4a, 4b present two curves which can be obtained with the voltage-measuring means used by the apparatus of the invention, in the absence of a filter permitting elimination of the interference frequencies (Figure 4b) and in the case where such a filter is used (Figure 4a).
- And Figures 5a and 5b present curves of the change over time of current and voltage signals respectively.
If referencs is made to the drawings, there is seen firstly in Figure 1 a metal pipe 1 constituting in this example the electrically conducting work whose state of insulation it is desired to check. This pipe 1 is buried withln an elec~rolytic medium constituted here by the ground 3. In this ground i~ also buried a counter-electrode 5 connected to the pipe by an electrical network in which a current will be made to circulate.
Under the action of such a current, the piece 5 generally behaves like an anode serving to inject the current into the ground. In practice, the piece 5 may take the form of a crosspiece or even a metal stake made of for example steel. Hence it will be po~sible to promote a cathodic reaction in the region of the work, whilst transferring the natural oxidation reaction to the anode 5, de~enera-tion of which is accepted a priori (it will however be noted that sometLmes for the protection of certain 2~847~
metals, such as certain stainless s~eels or aluminium alloys, which can be passivated in the electrolyte, it may be appropriate to make the ~counter-electrode~ play the role of cathode, then making an "anodic protective~
current circulate).
To ensure the intended circulation of the current in the network, use is made of a current generator 7 mounted in series in the network and able to deliver a ~c~shn~cr direct current to the piece 5~ ad~nt~g~o~si~
For the purposes of monitoring, with this genera-tor 7 have been associated in series a clock 9 making it possible to interrupt and reestablish sequentially the circulation of the current imposed by the generator 7 and to control the triggering of the measuring means 15 and 17 presented below. The clock 9 may consist for example of a generator of low-frequency signals forming an interrupter with adjustable pulse times, for example from l ms to 1 s.
In the field of the protection of metal works placed in an electrolytic environment, it is known that the potential difference between the work and the elec-trolyte is representative of the electrical state of this work.
In actual fact, thi~ potential difference is usually measured between the metal of ~he work and a reference electrode in contact with the electrolyte but situated some distance from the metal surface of the work. This is why there have been represented, at 11, such an electrode placed on the ground and connected up to the abovementioned electrical network, at 13, a conductor connecting the negative terminal 7a of the generator 7 and, at la, the metal structure of the pipe 1.
As known per se, a metal electrode immersed in an electrolyte can be regarded a~ a half~cell. Now, only the potential difference of a cell can be measured. In the present case, this cell will therefore consist of the electrochemical chain comprising the metal work to be studied and the reference electrode which, in regard to 2 ~ 7 ~
practice, is usually of the Cu/CuSO4,Ag/AgCl type or else in calomel (Hg/HgCl-KCl), whose respective potentials are known.
To measure the potential gradient between the pipe 1 and the electrode 11, provision has of course been made for a Yoltage-measuring sensor schematised at 15 in Figure 1 and conn~cted up between the electrode and the point 13 of the network. This first measuring means could consist of an oscilloscope with memory, with an associa-ted printer.
Given that in the invention the recording of theintensity of the currents which may circulate in the network is to be taken into consideration, a second measuring means 17 has been provided. To this end, the use could be envisaged of an oscilloscope connected up in parallel across the terminals of a resistor 19 placed in series between the positive output 9a of the clock 9 and the piece or outlet 5. Hence, by correctly choosing the value of the resistor 19, a direct reading of the current circulating in the network could be made on the measuring apparatus 17.
In order to process these voltage and current measurements, the apparatu~es 15 and 17 have been con-nected to a capturing, processing and viewing unit 21, a more detailed illustration o~ which is presented in Figure 2.
In this figure is ~ound firstly the terminal la of the pipe, the connection terminal of the outlet 5, as well as the connec~ion ter~inal of the electrode 11. The current qenerator 7, the clock 9 and the resistor 19 have also been represented schematically. Finally, there are the two means 15 and 17 for measuring respectively the ~oltag~ U between the pipe and the electrode and, on the other hand, the current I between this same pipe and the piece 5.
During the trials carried ou~, it wa apparent that the voltages read between the work and the anode piece were sometimes greatly disturbed by electrical sources generating disturbing frequencies in the 2~8~7~
electrolytic medium 3. Provision was therefore made for the possibility of adding at the output of the measuring apparatus 1~ a filter 23 of the low-pass filter type possibly with a rejector making it possible thereby to eliminate by filtering the sensed ~requencies having values situated beyond a predetermined threshold and/or corresponding to frequencies identified as particularly disturbing. During the tests carried out, it had for example been chosen to eliminate frequencies above 5 ~z.
For the sake of clarity, in Figures 4a and 4b have been illustrated the shape of the signals obtained without filter (Figure 4b) and with filter (Figure 4a), from the voltage-capturing apparatus 15.
In Figure 4a, one can immediately observe the beneficial effect of the filter which, without especially deforming the signals, makes possible a smoothing benefi-cial to the quality of the measurements.
As has certainly been understood from the above, an Lmportant aspect of the invention lies in fact in the manner in which the readings sensed and captured by the two, voltage and current, measuring means 15 and 17 are processed.
In Figure 2 ha~ been schematised with the block 25 the processing unit used and which contains essen-tially a microprocessor 27, programmable memories 29,proce~sing programs 31 and a calculator 32.
O~ course, a viewing unit 33 has been added to the proces~ing unit. This viewing unit could take the form of for example a printer or a computer screen linked with a keyboard 35 itself connected to ~he processing unit 25 for programming and control, via the control unit 24, of the operations which will now be presented.
As has been stated, the aLm of the apparatus just presented is to permit automatic checking of the state of electrical insulation of a conducting work.
For this purpose, it will therefore be sought to establish rigorously the relationship existing between the pipe l/electrode 11 voltage U and the current I
circulating in the installed electrical network.
20~8d7~
Choosing to take such a relationship into con-sideration is explained by the fact that, whatever the work and its environment, the characteristics obtained have the particular feature of being linear and of the type ~U = AI with (A = constant), from the origin I = O
up to a certain value of current (see Figure 3). It is in fact the slope A (that is to say, as understood, the resistancq of the work) which will enable the operator in possession of this information to analyse the state of electrical insulation of the work.
To accomplish this analysis, the rate imposed by the clock 9 will firstly be suitably adjusted, so that for example the generator 7 establishes an imposed current I in the network for about 0.5 to 1 second, with exposure times to zero imposed current of the order of for example 8 to 10 seconds.
In Figures 5a and 5b respectively have been represented two examples of signals recorded, for current and voltage. It will be noted that the duration of the in;ections of current made by the generator 7 is repre-sented by the interval T3 - T1, whereas the interval between two injections is seen to correspond to T5 - T3.
To understand the functioning of the system, we firstly take up position at the time origin. Up to time T1, the generator 7 will deliver no current. During this interval, the voltage between the work 1 and the elec-trode 11 will then be sensed and recorded, preferably several times. At time Tl, a constant-value square-wave current of specified intensity will be established in the network. The ~ensor 17 will then sense and record the intensity of this current. Following the settling tLme for the filter 23 (T2 - T1), the voltage between the work and the electrode will then be sensed and recorded anew, preferably several tLmes. This takes place up to time T3 which marks the end of the square-wave current injection.
The processing unit 25 will then calculate and record in memory the difference ~U between the voltages recorded previously, without and with circulation of imposed current I.
2~ 7 ~
Of course, during this time, new work/electrode voltage measurements have been sensed and recorded by the oscilloscope 15, current cut, until the clock 9 commands a new square-wave current for the generator 7 and until a new measurement of voltage and of current is taken into consideration for a new calculation of the difference in the potentials AU.
Thus, as t.he measurements proceed, the processing unit 25 will be able to supply to the viewing unit 33 the change, as a function of the intensity I of the imposed current, in the difference in the pipe/electrode poten-tials ~U with and without circulation of this imposed current.
This change being, as indicated above, linear and of the form ~U = AI (A = constant) from I = 0 up to a specified value of intensity, the calculator 32 will be able to calculate the slope A and thus supply the unit 33 with the value of this slope A which can be identified with the electrical resistance of the work.
Having presented the general principle of the measurements made, the various improvements which may be added in order to guarante~ the reliability of the measurements will now be described briefly.
Firstly, within the current established and current cut time intervals (T3 - T2 and T5 - T4 in Figure 5b), it will in practice be preferred to sense and record several voltage values, uniformly staggered over time, of the work/electrode gradients.
Next, it was seen to be preferable to complement these staggered measurements with two tests carried out, advantageously in combin tion, current cut and current established.
For this purpose, provision has been made to compare with one another the voltage readings made during the interval T3 - T2 and then the interval T5 - T4. If these values lie within a predetermined range, and evidence a steady potential, the following steps of the method are undertaken. If on the other hand one at least of the said values does not lie within this range, no `` 2~3~73 voltage value is recorded and a new cycle of measurements and of generation of new square-wave currents is renawed a few moments later, by repeating the comparison step above.
Hence, it will be po~sible to avoid taking into consideration disturbed readings, during the steady states of the system with and without imposed current.
However electrical disturbances may also inter-vene during the transient phases of voltage drop or rise (T2 - Tl or T4 - T3 in Figure 5b). To remedy this pro-blem, provision has been made to repea~ several tLmes the steps of measuring and capturing pipe/electrode voltages with and without imposed current, for the same intensity of generated current, so as to thereby engender the calcula~ion of several potential gradients ~U calculated from constant square-wave currents. During this calcula-tion of ~U, the processing unit 25 will then statisti-cally process these values of potentials and will record values only if the latter converge to an average value.
It will be observed that these various precau-tions appertain to the capturing and processing of the measurements of potential. As f 2r as the checXing of the measurements of current is concerned, a monitoring loop has been envisaged7 schematised by the line 37 in Figure 2 and intended to monitor the intensity values actually supplied by the current generator 7.
More precisely, provision has been made to record fir~tly the intensity of the square-wave currents con-trolled by the operator and introduced into the memory units 29 of the machine. After having ~ensed, with the measuring means 17, the intensity of current supplied periodically by the generator 7, the processing unit 25 and more particularly the calculator 32 will compare the controlled recorded intensity and the sensed intensity.
If the deviation between these two intensities lies within a predetermined range the sensed intensity will then be recorded. Otherwise, provision may be made for an alarm signal such that it may be displayed on the viewing unit 33, thus enabling the operator to act.
During trials undertaken within the context of the invention, the electrically conducting work consisted of a buried gas conduit made of a metallic material. The prime usefulness of the method which is the s~bject of the invention consisted in checking the quality of the placement of this pipe which was in this particular case covered with an electrically in~ulating coating forming a passive protection intended to remove the pipe from the electrolytic environment of the ground.
Experience having shown that placements in particular of such buried pipes are not always perfect and that furthermore the coatings for passive protection are not always entirely effective, thought was con-sequently given to the problem of checking the state of electrical insulation of these works, once the latter are in place in their medium.
Now, ~uch checking in practice encounters a certain number of difficultie~ relating in particular to the variable nature over time of the parameters to be meaRured, these variations possibly in particular being induced by poorly insulated DC in~tallations (railway traction, electrolysis plant, etc).
Problems of measurement error~ also arose due to the phenomena of polarisation of the works, these polari-sations changing over time and as a function of the electxical change in particular of the worX, of the counter-electrode and of the disturbances which may, nearby, cross the electrolytic medium.
After lengthy studies, the Applicant succeeded in developing a truly reliable and effective method making 2~8~73 it possible to check the state of electrical insulation of a conducting work, this metho~ being characterised in particular in that:
a) the voltage between the work and the reference S electrode is sensed at least once and recorded, b) ah impos0d circulation of current who5~ intensity which is sensed and recorded ,is established in the conducting network, between the work and the counter-electrode, c! the voltage between the work and the reference electrode, current circulating, is sensed at least once and recorded anew, d) the difference ~U between the voltages recor-ded in a) and c) is calculated and recorded without and with imposed current circulation respectively, e) the said imposed current circulation is inter-rupted and steps a), b), c) and d) are repeated a given number of times whilst varying, during step b), the intensity of the imposed current, f) the change is next deduced therefrom in the said voltage difference QU as a function of the intensity I o~ current established in the network, which change is linear o~ the form ~U = AI (A = constant) from I = 0 up to a specified value of intensity of this current, 25 g) the slope A is calculated, h) and the state of eleotrical insulation of the woxk is deduced therefrom by identifying the said slope with the electrical re~istance of this work.
In this way, through rapid capture of the mea-sured or sensed potentials, it will be possible to obtain quantities approximating the actual values existing on site.
Moreover, by limiting oYer t.ime, through rigorous monitorinq, the settling periods of the imposed currents, it will be possible to undertake series of trials of r~asonable duration by repeating the measurements a large number of times and by statistically processing them so as to detect and negate in particular the disturbing presence of the stray curren~s.
2~8~73 With this aim, a complementary characteristic of this invention moreover provides that, the voltages between the work and the counter-electrode being disturbed by electrical sources generating frequencies S which modify over time the voltages to be measured, these said frequencies are eliminated by filtering ~uring the abovementioned steps a) and/or c) when the said frequencies are beyond a predetermined threshold and/or correspond to known frequencies identified as disturbing.
As will be seen below in the description which will follow, and still in order to meet this problem of electrical disturbances, provision has also been made in the invention to preferably statistically process the measurements so as to take into consideration only values judged to be consistent and reasonable, as explained in particular in Claims 3, 4 and 7 attached.
Apart from such a checking method, the subject of the invention is also an apparatus intended to check the state of electrical insulation of the chosen work.
In accordance with tha invention, this apparatus is characterised in particular in that it comprises:
- means of measuring the voltage between the reference electrode and the work, - a generator for generating a current Z5 between the work and the counter-electrode, - means of measuring thi~ current, - a clock for interrupting and establishing sequentially the circulation of the current Lmposed by the generator between the work and the counter-electrode, and triggering measuremants of the said current and of the said voltage, - means of processing the measure-ments made in order to calculate, for each intensity of current, the difference ~U between the voltages measured without and with circulation o~ said current, and in order to calculate also the ratio A between the difference in the abovementioned vol~ages (~U) and the said corresponding intensity of current, - and means of displaying the calculated ratio A.
20~8~3 Other characteristics and advantages of the invention will emerge further from the following descrip-tion made with reference to the attached drawings in which:
- Figure 1 represents a general configurational diagram of a circui-t permitting implementation of the me~hod of the invention, - Figure 2 is a block diagram representing in more detail the processing and dis~lay unit of the apparatus of the invention, - Figure 3 presents an illustrative curve of a possible change, with respect to a work, in the potential difference U as a function of the Lmposed current I, - Figures 4a, 4b present two curves which can be obtained with the voltage-measuring means used by the apparatus of the invention, in the absence of a filter permitting elimination of the interference frequencies (Figure 4b) and in the case where such a filter is used (Figure 4a).
- And Figures 5a and 5b present curves of the change over time of current and voltage signals respectively.
If referencs is made to the drawings, there is seen firstly in Figure 1 a metal pipe 1 constituting in this example the electrically conducting work whose state of insulation it is desired to check. This pipe 1 is buried withln an elec~rolytic medium constituted here by the ground 3. In this ground i~ also buried a counter-electrode 5 connected to the pipe by an electrical network in which a current will be made to circulate.
Under the action of such a current, the piece 5 generally behaves like an anode serving to inject the current into the ground. In practice, the piece 5 may take the form of a crosspiece or even a metal stake made of for example steel. Hence it will be po~sible to promote a cathodic reaction in the region of the work, whilst transferring the natural oxidation reaction to the anode 5, de~enera-tion of which is accepted a priori (it will however be noted that sometLmes for the protection of certain 2~847~
metals, such as certain stainless s~eels or aluminium alloys, which can be passivated in the electrolyte, it may be appropriate to make the ~counter-electrode~ play the role of cathode, then making an "anodic protective~
current circulate).
To ensure the intended circulation of the current in the network, use is made of a current generator 7 mounted in series in the network and able to deliver a ~c~shn~cr direct current to the piece 5~ ad~nt~g~o~si~
For the purposes of monitoring, with this genera-tor 7 have been associated in series a clock 9 making it possible to interrupt and reestablish sequentially the circulation of the current imposed by the generator 7 and to control the triggering of the measuring means 15 and 17 presented below. The clock 9 may consist for example of a generator of low-frequency signals forming an interrupter with adjustable pulse times, for example from l ms to 1 s.
In the field of the protection of metal works placed in an electrolytic environment, it is known that the potential difference between the work and the elec-trolyte is representative of the electrical state of this work.
In actual fact, thi~ potential difference is usually measured between the metal of ~he work and a reference electrode in contact with the electrolyte but situated some distance from the metal surface of the work. This is why there have been represented, at 11, such an electrode placed on the ground and connected up to the abovementioned electrical network, at 13, a conductor connecting the negative terminal 7a of the generator 7 and, at la, the metal structure of the pipe 1.
As known per se, a metal electrode immersed in an electrolyte can be regarded a~ a half~cell. Now, only the potential difference of a cell can be measured. In the present case, this cell will therefore consist of the electrochemical chain comprising the metal work to be studied and the reference electrode which, in regard to 2 ~ 7 ~
practice, is usually of the Cu/CuSO4,Ag/AgCl type or else in calomel (Hg/HgCl-KCl), whose respective potentials are known.
To measure the potential gradient between the pipe 1 and the electrode 11, provision has of course been made for a Yoltage-measuring sensor schematised at 15 in Figure 1 and conn~cted up between the electrode and the point 13 of the network. This first measuring means could consist of an oscilloscope with memory, with an associa-ted printer.
Given that in the invention the recording of theintensity of the currents which may circulate in the network is to be taken into consideration, a second measuring means 17 has been provided. To this end, the use could be envisaged of an oscilloscope connected up in parallel across the terminals of a resistor 19 placed in series between the positive output 9a of the clock 9 and the piece or outlet 5. Hence, by correctly choosing the value of the resistor 19, a direct reading of the current circulating in the network could be made on the measuring apparatus 17.
In order to process these voltage and current measurements, the apparatu~es 15 and 17 have been con-nected to a capturing, processing and viewing unit 21, a more detailed illustration o~ which is presented in Figure 2.
In this figure is ~ound firstly the terminal la of the pipe, the connection terminal of the outlet 5, as well as the connec~ion ter~inal of the electrode 11. The current qenerator 7, the clock 9 and the resistor 19 have also been represented schematically. Finally, there are the two means 15 and 17 for measuring respectively the ~oltag~ U between the pipe and the electrode and, on the other hand, the current I between this same pipe and the piece 5.
During the trials carried ou~, it wa apparent that the voltages read between the work and the anode piece were sometimes greatly disturbed by electrical sources generating disturbing frequencies in the 2~8~7~
electrolytic medium 3. Provision was therefore made for the possibility of adding at the output of the measuring apparatus 1~ a filter 23 of the low-pass filter type possibly with a rejector making it possible thereby to eliminate by filtering the sensed ~requencies having values situated beyond a predetermined threshold and/or corresponding to frequencies identified as particularly disturbing. During the tests carried out, it had for example been chosen to eliminate frequencies above 5 ~z.
For the sake of clarity, in Figures 4a and 4b have been illustrated the shape of the signals obtained without filter (Figure 4b) and with filter (Figure 4a), from the voltage-capturing apparatus 15.
In Figure 4a, one can immediately observe the beneficial effect of the filter which, without especially deforming the signals, makes possible a smoothing benefi-cial to the quality of the measurements.
As has certainly been understood from the above, an Lmportant aspect of the invention lies in fact in the manner in which the readings sensed and captured by the two, voltage and current, measuring means 15 and 17 are processed.
In Figure 2 ha~ been schematised with the block 25 the processing unit used and which contains essen-tially a microprocessor 27, programmable memories 29,proce~sing programs 31 and a calculator 32.
O~ course, a viewing unit 33 has been added to the proces~ing unit. This viewing unit could take the form of for example a printer or a computer screen linked with a keyboard 35 itself connected to ~he processing unit 25 for programming and control, via the control unit 24, of the operations which will now be presented.
As has been stated, the aLm of the apparatus just presented is to permit automatic checking of the state of electrical insulation of a conducting work.
For this purpose, it will therefore be sought to establish rigorously the relationship existing between the pipe l/electrode 11 voltage U and the current I
circulating in the installed electrical network.
20~8d7~
Choosing to take such a relationship into con-sideration is explained by the fact that, whatever the work and its environment, the characteristics obtained have the particular feature of being linear and of the type ~U = AI with (A = constant), from the origin I = O
up to a certain value of current (see Figure 3). It is in fact the slope A (that is to say, as understood, the resistancq of the work) which will enable the operator in possession of this information to analyse the state of electrical insulation of the work.
To accomplish this analysis, the rate imposed by the clock 9 will firstly be suitably adjusted, so that for example the generator 7 establishes an imposed current I in the network for about 0.5 to 1 second, with exposure times to zero imposed current of the order of for example 8 to 10 seconds.
In Figures 5a and 5b respectively have been represented two examples of signals recorded, for current and voltage. It will be noted that the duration of the in;ections of current made by the generator 7 is repre-sented by the interval T3 - T1, whereas the interval between two injections is seen to correspond to T5 - T3.
To understand the functioning of the system, we firstly take up position at the time origin. Up to time T1, the generator 7 will deliver no current. During this interval, the voltage between the work 1 and the elec-trode 11 will then be sensed and recorded, preferably several times. At time Tl, a constant-value square-wave current of specified intensity will be established in the network. The ~ensor 17 will then sense and record the intensity of this current. Following the settling tLme for the filter 23 (T2 - T1), the voltage between the work and the electrode will then be sensed and recorded anew, preferably several tLmes. This takes place up to time T3 which marks the end of the square-wave current injection.
The processing unit 25 will then calculate and record in memory the difference ~U between the voltages recorded previously, without and with circulation of imposed current I.
2~ 7 ~
Of course, during this time, new work/electrode voltage measurements have been sensed and recorded by the oscilloscope 15, current cut, until the clock 9 commands a new square-wave current for the generator 7 and until a new measurement of voltage and of current is taken into consideration for a new calculation of the difference in the potentials AU.
Thus, as t.he measurements proceed, the processing unit 25 will be able to supply to the viewing unit 33 the change, as a function of the intensity I of the imposed current, in the difference in the pipe/electrode poten-tials ~U with and without circulation of this imposed current.
This change being, as indicated above, linear and of the form ~U = AI (A = constant) from I = 0 up to a specified value of intensity, the calculator 32 will be able to calculate the slope A and thus supply the unit 33 with the value of this slope A which can be identified with the electrical resistance of the work.
Having presented the general principle of the measurements made, the various improvements which may be added in order to guarante~ the reliability of the measurements will now be described briefly.
Firstly, within the current established and current cut time intervals (T3 - T2 and T5 - T4 in Figure 5b), it will in practice be preferred to sense and record several voltage values, uniformly staggered over time, of the work/electrode gradients.
Next, it was seen to be preferable to complement these staggered measurements with two tests carried out, advantageously in combin tion, current cut and current established.
For this purpose, provision has been made to compare with one another the voltage readings made during the interval T3 - T2 and then the interval T5 - T4. If these values lie within a predetermined range, and evidence a steady potential, the following steps of the method are undertaken. If on the other hand one at least of the said values does not lie within this range, no `` 2~3~73 voltage value is recorded and a new cycle of measurements and of generation of new square-wave currents is renawed a few moments later, by repeating the comparison step above.
Hence, it will be po~sible to avoid taking into consideration disturbed readings, during the steady states of the system with and without imposed current.
However electrical disturbances may also inter-vene during the transient phases of voltage drop or rise (T2 - Tl or T4 - T3 in Figure 5b). To remedy this pro-blem, provision has been made to repea~ several tLmes the steps of measuring and capturing pipe/electrode voltages with and without imposed current, for the same intensity of generated current, so as to thereby engender the calcula~ion of several potential gradients ~U calculated from constant square-wave currents. During this calcula-tion of ~U, the processing unit 25 will then statisti-cally process these values of potentials and will record values only if the latter converge to an average value.
It will be observed that these various precau-tions appertain to the capturing and processing of the measurements of potential. As f 2r as the checXing of the measurements of current is concerned, a monitoring loop has been envisaged7 schematised by the line 37 in Figure 2 and intended to monitor the intensity values actually supplied by the current generator 7.
More precisely, provision has been made to record fir~tly the intensity of the square-wave currents con-trolled by the operator and introduced into the memory units 29 of the machine. After having ~ensed, with the measuring means 17, the intensity of current supplied periodically by the generator 7, the processing unit 25 and more particularly the calculator 32 will compare the controlled recorded intensity and the sensed intensity.
If the deviation between these two intensities lies within a predetermined range the sensed intensity will then be recorded. Otherwise, provision may be made for an alarm signal such that it may be displayed on the viewing unit 33, thus enabling the operator to act.
Claims (10)
1. Method for checking the state of electrical insulation of an electrically conducting work placed in an electrolytic medium and connected by a network of electrical conductors, to a counter-electrode (5) placed in the said electrolytic medium and, to a reference electrode (11) in contact with this same electrolytic medium, wherein:
a) the voltage between the work (1) and the reference electrode is sensed at least once and recorded, b) a circulation of current whose intensity is sensed and recor-ded, is established in the said network, between the work and the counter-electrode(5), c) the voltage between the work and the electrode (11), current circulating, is sensed at least once and recorded anew, d) the difference .DELTA.U between the voltages recor-ded in a) and c) is calculated and recorded without and with said current circulation respectively, e) said current circulation is inter-rupted and steps a), b), c) and d) are repeated a given number of times whilst varying, during step b), the intensity of said current, f) the change is next deduced therefrom in said difference .DELTA.U as a function of the intensity I of the current established in the network, which change is linear of the form .DELTA.U = AI (A = constant) from I = 0 up to a specified value of said intensity, g) the slope A is calculated, h) and the state of electrical insulation of the work (1) is deduced therefrom by identifying said slope with the electrical resistance of the work.
a) the voltage between the work (1) and the reference electrode is sensed at least once and recorded, b) a circulation of current whose intensity is sensed and recor-ded, is established in the said network, between the work and the counter-electrode(5), c) the voltage between the work and the electrode (11), current circulating, is sensed at least once and recorded anew, d) the difference .DELTA.U between the voltages recor-ded in a) and c) is calculated and recorded without and with said current circulation respectively, e) said current circulation is inter-rupted and steps a), b), c) and d) are repeated a given number of times whilst varying, during step b), the intensity of said current, f) the change is next deduced therefrom in said difference .DELTA.U as a function of the intensity I of the current established in the network, which change is linear of the form .DELTA.U = AI (A = constant) from I = 0 up to a specified value of said intensity, g) the slope A is calculated, h) and the state of electrical insulation of the work (1) is deduced therefrom by identifying said slope with the electrical resistance of the work.
2. Method according to Claim 1, wherein the voltage between the work (1) and the counter-electrode (5) being disturbed by electrical sources generating, in said electrolytic medium (3), disturb-ing frequencies which modify said voltage over time, these said disturbing frequencies are eliminated through filtering during steps a) and/or c) when the said frequencies are beyond a predetermined threshold.
3. Method according to Claim 1 or Claim 2, charac-terised in that:
- during step a) several values of voltages between the work and the reference electrode (11) are sensed successively, - these values are compared with one another, - if these values lie within a predetermined range, they are recorded and the following steps of the method are undertaken, - if, by contrast, one at least of the said values does not lie within the said range, no value is recorded and the various steps above are repeated.
- during step a) several values of voltages between the work and the reference electrode (11) are sensed successively, - these values are compared with one another, - if these values lie within a predetermined range, they are recorded and the following steps of the method are undertaken, - if, by contrast, one at least of the said values does not lie within the said range, no value is recorded and the various steps above are repeated.
4. Method according to any one of Claims 1 to 3, characterised in that:
- during step c), several values of voltage between the work and the reference electrode (11) are sensed, staggered over time, - these values are compared with one another, - if these values lie within a predetermined range, they are recorded and the following steps of the method are undertaken, - if, by contrast, one at least of the said values does not lie within the said range, no values are recorded and the next step d) is not performed.
- during step c), several values of voltage between the work and the reference electrode (11) are sensed, staggered over time, - these values are compared with one another, - if these values lie within a predetermined range, they are recorded and the following steps of the method are undertaken, - if, by contrast, one at least of the said values does not lie within the said range, no values are recorded and the next step d) is not performed.
5. Method according to Claim 1 or Claim 2, charac-terised in that during steps a) and c), several values of voltage between the work and the reference electrode (11) are sensed successively and recorded.
6. Method according to Claim 3 and Claim 4, charac-terised in that, when the said values of voltages between the work (1) and the reference electrode (11) sensed during steps a) and c) without and with imposed current circulation lie within the said predetermined ranges of values, the difference(s) in potentials .DELTA.U is/are calculated, during step d), through the difference in the arithmetic averages of the said values recorded without and with imposed current.
7. Method according to any one of the preceding claims, characterised in that:
- steps a), b), c) and d) are repeated several times whilst keeping each time during step b) the same intensity of imposed current, so as to obtain during step d) several potential differences .DELTA.U calculated from this same current intensity, - and, during this step d), the said calculated values of the potential differences .DELTA.V are statistically processed and, if these values converge to an average value, this average value is recorded.
- steps a), b), c) and d) are repeated several times whilst keeping each time during step b) the same intensity of imposed current, so as to obtain during step d) several potential differences .DELTA.U calculated from this same current intensity, - and, during this step d), the said calculated values of the potential differences .DELTA.V are statistically processed and, if these values converge to an average value, this average value is recorded.
8. Method according to any one of the preceding claims, characterised in that during step b), - in order to establish the imposed current in the network, use is made of a current generator (7) which is controlled so as to deliver the said specified intensity, - this controlled specified intensity is recorded, - after having sensed at a location in the said network the current intensity circulating, - the controlled recorded intensity and the sensed intensity are compared, and - if the deviation between these two intensities lies within a predetermined range, the sensed intensity is recorded.
9. Apparatus for checking the state of electrical insulation of an electrically conducting work (1) placed in an electrolytic medium (3) and connected by a network of electrical conductors, on the one hand to a counter-electrode (5) placed in the said electrolytic medium and, on the other hand to a reference electrode (11) in contact with this same medium, characterised in that it comprises:
- voltage-measuring means (15) connected up to the network between the work (1) and the reference electrode (11), - a current generator (7) for establishing an imposed current circulation between the work (1) and the counter-electrode (S), - means of measuring this current (17, 19), - a clock (9) for interrupting and reestablishing sequentially the circulation of the said imposed current and triggering measurements of the said current and of the said voltage, in the absence of and then with cir-culation of this imposed current, - means (25, 32) of processing the measurements made, these processing means comprising calculation means (32) for calculating, for each given imposed current intensity:
a) the difference .DELTA.U between the said voltages measured without and with circulation of imposed current, b) the ratio A between the difference .DELTA.U in the said voltages and the corresponding measured intensity of the imposed current, - and means (33) of displaying the calculated ratio A.
- voltage-measuring means (15) connected up to the network between the work (1) and the reference electrode (11), - a current generator (7) for establishing an imposed current circulation between the work (1) and the counter-electrode (S), - means of measuring this current (17, 19), - a clock (9) for interrupting and reestablishing sequentially the circulation of the said imposed current and triggering measurements of the said current and of the said voltage, in the absence of and then with cir-culation of this imposed current, - means (25, 32) of processing the measurements made, these processing means comprising calculation means (32) for calculating, for each given imposed current intensity:
a) the difference .DELTA.U between the said voltages measured without and with circulation of imposed current, b) the ratio A between the difference .DELTA.U in the said voltages and the corresponding measured intensity of the imposed current, - and means (33) of displaying the calculated ratio A.
10. Apparatus according to Claim 9, characterised in that it comprises, furthermore, associated with these said voltage-measuring means, a low-pass filter (23) eliminating the disturbing frequencies of the measured voltage signals, above a specified threshold, said current generator consisting in a DC current generator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9016343A FR2671192A1 (en) | 1990-12-27 | 1990-12-27 | METHOD AND APPARATUS FOR VERIFYING THE ELECTRICAL ISOLATION STATE OF AN ELECTRICALLY CONDUCTIVE WORK. |
| FR9016343 | 1990-12-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2058473A1 true CA2058473A1 (en) | 1992-06-28 |
Family
ID=9403725
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002058473A Abandoned CA2058473A1 (en) | 1990-12-27 | 1991-12-27 | Method and apparatus for checking the state of electrical insulation of an electrically conducting work |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0494012B1 (en) |
| AT (1) | ATE158412T1 (en) |
| CA (1) | CA2058473A1 (en) |
| DE (1) | DE69127685T2 (en) |
| DK (1) | DK0494012T3 (en) |
| ES (1) | ES2106067T3 (en) |
| FR (1) | FR2671192A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2703458B1 (en) * | 1993-03-31 | 1995-05-24 | Gaz De France | Method and device for measuring the real electrochemical potential of a building element in an electrolyte such as a pipe buried in the ground, cathodically protected against corrosion. |
| JP3058844B2 (en) * | 1997-06-03 | 2000-07-04 | 東京瓦斯株式会社 | Method and apparatus for determining state of cathodic protection using steel probe |
| DE19755417C2 (en) * | 1997-12-12 | 1999-11-04 | Fraunhofer Ges Forschung | Evaluation circuit for determining complex impedances, device for measuring complex impedances and use of the device |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4099117A (en) * | 1976-04-26 | 1978-07-04 | Dick Gaut | Method and apparatus for measuring the quality of insulation on a buried pipeline and the quantity of metal oxide present at breaks in the insulation |
| US4511844A (en) * | 1982-12-10 | 1985-04-16 | Panhandle Eastern Pipe Line Company | E-Log I field computer |
| US4721957A (en) * | 1984-06-06 | 1988-01-26 | Trw Inc. | Ground shift compensated parameter measurement system |
| US4755267A (en) * | 1986-06-03 | 1988-07-05 | Pennwalt Corporation | Methods and apparatus for protecting metal structures |
| US4823072A (en) * | 1986-09-04 | 1989-04-18 | Walcott Kenneth J | Measurement of the polarized potential of buried pipeline having impressed current cathodic protection |
| IT215064Z2 (en) * | 1988-10-14 | 1990-07-30 | Il Gas S P A Soc It | EQUIPMENT FOR INSULATION CONTROL AND CATHODIC PROTECTION OF UNDERGROUND METAL PIPES |
| IT1230366B (en) * | 1989-08-01 | 1991-10-18 | Eniricerche Spa | PROCEDURE FOR THE CONTINUOUS CHECK OF THE INTEGRITY OF THE PROTECTIVE COATING OF UNDERGROUND METAL STRUCTURES AND DEVICES FOR ITS REALIZATION. |
-
1990
- 1990-12-27 FR FR9016343A patent/FR2671192A1/en active Granted
-
1991
- 1991-12-20 DE DE69127685T patent/DE69127685T2/en not_active Expired - Fee Related
- 1991-12-20 DK DK91403503.5T patent/DK0494012T3/en active
- 1991-12-20 EP EP91403503A patent/EP0494012B1/en not_active Expired - Lifetime
- 1991-12-20 AT AT91403503T patent/ATE158412T1/en not_active IP Right Cessation
- 1991-12-20 ES ES91403503T patent/ES2106067T3/en not_active Expired - Lifetime
- 1991-12-27 CA CA002058473A patent/CA2058473A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DK0494012T3 (en) | 1997-10-13 |
| FR2671192A1 (en) | 1992-07-03 |
| DE69127685D1 (en) | 1997-10-23 |
| EP0494012B1 (en) | 1997-09-17 |
| ES2106067T3 (en) | 1997-11-01 |
| DE69127685T2 (en) | 1998-01-15 |
| EP0494012A1 (en) | 1992-07-08 |
| FR2671192B1 (en) | 1993-02-26 |
| ATE158412T1 (en) | 1997-10-15 |
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| Date | Code | Title | Description |
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