HK40013664B - Method and apparatus for monitoring the loss factor of capacitor bushings - Google Patents

Description

The invention relates to a method and device for monitoring capacitor conduction for a three-phase AC network.

Electrical equipment for AC networks, such as power transformers and throttles, is usually connected to the mains power lines of the AC network by means of capacitor lines. As failure or failure of these capacitor lines can have serious consequences, such as damage or destruction of the electrical equipment and resulting power supply outages, it is known to monitor characteristics of the capacitor lines, such as capacities and loss factors in operation. Known loss factor monitoring techniques can significantly affect various influencing factors, such as the temperature variations associated with the high-capacity conductors or the temperature variations in operation, and make monitoring of the relevant characteristics more difficult.

DE 10 2004 027 349 A1 describes a method for determining the loss factor of an insulation of a high voltage line. The high voltage line has insert controls for an electric field, with an external clamping at the potential of a first inlet and at least one internal clamping connected to a clamping at the potential of the first inlet in the cross section further inward. The external clamping is connected to ground potential via a controllable reference capacitor. A test between the internal clamping and the external clamping results in a voltage drop, a steady voltage drop at a reference capacitor and a phase shift of the voltage and the voltage drop. The resulting voltage drop is obtained by means of a differential of the voltage drop between the reference capacitor and the voltage drop, or by taking into account the speed of the test. The resulting voltage drop between the reference capacitor and the reference capacitor can be calculated as the difference between the current and the voltage drop.

DE 100 37 432 A1 describes a method for monitoring a capacitor line loaded with an electrical operating voltage, where a voltage divider is formed with an electrically conductive insert, and at least one measurement value of an electrical measurement quantity is recorded and stored with a measuring device connected to the insert and with ground potential. After recording at least one measurement value, the impedance between the measuring device and the ground potential is changed and at least one signal value of a measuring signal then being formed is recorded and stored with the measuring device and the ground potential, with the time interval between the time of recording one measurement value and the time of recording a signal indicating that a change in the operating voltage can occur between the two measuring points, if necessary.

WO 2015/071253 A1 describes a method for monitoring capacitor conductivity of a three-phase AC network, determining and monitoring the upstream and downstream capacities of each capacitor conductor.

In this context, the invention proposes the subject matter of the independent claims.

The invention allows for better monitoring of capacitor conductivity. The invention proposes, in a first aspect, a method for monitoring capacitor conductivity for an AC network as described in claim 1.

The proposed method uses the characteristics and measurements of adjacent capacitor lines of the same power transformer for the actual monitoring, compensating for external influences such as temperature changes on the loss factor changes of the capacitor line, and avoiding that when monitoring a capacitor line that is connected to its associated mains line, variations in the mains voltage at a mains line are transmitted to the external mains voltage by the capacitor line connected to the respective mains line, thus at least partially compensating for measurement voltages in the load voltage detection and providing a better measurement of the condition of the conduit.

The loss factor for each capacitor line is determined according to claim 1 and is normally in the range of 0.005% to 1% for capacitor lines in the high voltage range.

Each capacitor line may be configured in any way desired, for example, with a top and a bottom capacity, for example, the top capacity may be configured as the capacity of a capacitor formed by the respective coating and conductor, and the usual values for top capacities are in the range of 200 to 600 pF.

The subcapacitance may be, for example, the capacity of a parallel circuit comprising a measuring device, for example, capable of detecting and/or measuring a load voltage, and a capacitor, the above-mentioned capacitor being formed from the respective outermost layer and mass potential or from the respective outermost layer and an electrically conductive flange attached to the outer surface of the respective capacitor conduit and adjacent to the mass potential. The subcapacitors are usually between 1 and 5 μF, but may have other values as required, for example between 0,1 μF and 50 μF or between 0,2 μF and 20 μF or between 0,5 μF and 10 μF.

The measurement of the mains voltage and the generation of the mains voltage indicators can be carried out by any means, for example by means of a capacitor voltage divider.

The voltage measured at the undercapacity by a measuring device between the outermost layer of the capacitor conduit and the mass potential is called the load voltage.

In the case of a three-phase AC network, the term neighbourhood is defined with respect to a predetermined direction of rotation of the corresponding pointer system, for example such that the second phase B is adjacent to the first phase A, the third phase C to the second phase B and the first phase A to the third phase C.

The tolerance value may be calculated in any way as required, for example as a percentage of a corresponding value from the data sheet of a capacitor line or derived from experience; the tolerance values may be chosen uniformly for all capacitor lines or individually for each capacitor line, if necessary.

The monitoring signal may be generated in any way, as appropriate, such as an acoustic and/or optical and/or electrical signal.

The reference voltage shall be the reference voltage of the power-generating module.

It may be provided that the first line is connected to a first parallel capacitor line;the second line is connected to a second parallel capacitor line;the third line is connected to a third parallel capacitor line;each of these parallel capacitor lines comprises a conductor connected to the associated line and an electrically conductive layer surrounding it;for each of these phases, the first and second reference voltages are a first and second coating voltage, which are located at the first and second time points respectively between the load and mass potential of the respective parallel capacitor line.

For example, these parallel capacitor lines are available to connect, in addition to a first electrical device connected to the three phases via the three capacitor lines, a second electrical device, also referred to here as a parallel device, parallel to the first device to the three phases.

It may be provided that the reference voltage is a constant voltage for each of the phases, for which a corresponding constant voltage gauge is prescribed, and that the size of each constant voltage gauge is equal to a nominal voltage of the AC network, and that the phase angles of the first and second constant voltage gauges are 0° for the first phase, 120° for the second phase, and 240° for the third phase.

It is envisaged that: the change in the loss factor of the first capacitor run according to the following formula with The second capacitor run-through loss factor change is calculated as follows: with The loss factor change of the third capacitor line is calculated as follows: with wherein Ra ((t1), Rb ((t1), Rc ((t1) are the first reference voltage gauges of the first, second and third phases; and Va ((t1), Vb ((t1), Vc ((t1) are the first coating voltage gauges of the first, second and third phases; and Ra ((t2), Rb ((t2), Rc ((t2) are the second reference voltage gauges of the first, second and third phases; and Va (t2), Vb ((t2), Vc ((t2) are the second coating voltage gauges of the first, second and third phases.

It may be provided that tolerances DA > 0, DB > 0, DC > 0 are determined for the loss factor comparisons and if the loss factor comparisons show that If the test is not performed, a monitoring signal is generated indicating that the capacitor lines are in the correct condition and, if not, a monitoring signal is generated indicating that at least one capacitor line is not in the correct condition.

It may be provided that tolerances DA > 0, DB > 0, DC > 0 are determined for the loss factor comparisons and If the loss factor comparisons show that If the test is performed on a single capacitor, the test shall be performed on a single capacitor with a capacity of at least 10 m3/h. If the test is performed on a single capacitor, the test shall be performed on a single capacitor with a capacity of at least 10 m3/h. If the test is performed in the same way, a monitoring signal is generated indicating that either the first capacitor line is not in the correct condition or the other two capacitor lines are not in the correct condition and have an identical fault.

Each of these tolerances DA, DB, DC may be determined by any means necessary and may be set, for example, to a value of 0,0001, or 0,0002, or 0,0005, or 0,001, or 0,002, or 0,005, or 0,01 or 0,02, or 0,05; each of these tolerances and at least one of the other tolerances may be equal or different.

Alternatively, a monitoring signal may be generated to indicate that either all three capacitor lines are not in the correct condition or two capacitor lines are not in the correct condition and do not have an identical fault.

It may be provided that any tolerance depends on the age of the respective capacitor conduit antiton.

It may also be provided that, at a predetermined third date after the second date, for each of these stages: the reference voltage and a corresponding third reference voltage gauge or complex voltage reference value are determined;the load voltage is recorded and a corresponding third load voltage gauge or complex voltage value is determined;the second reference voltage gauge is replaced by the third reference voltage gauge and the second load voltage gauge by the third load voltage gauge; The calculation and comparison of the loss factor change shall be repeated for each of these capacitor run-throughs; a monitoring signal is generated depending on the results of these loss factor comparisons.

The second reference voltage gauge and the first reference voltage gauge may be replaced by the second reference voltage gauge and the first reference voltage gauge by the second voltage gauge before each replacement of the second reference voltage gauge and the load gauge.

It may also be provided that at least at a later date after the second date, for each of these stages, for a reference voltage, a corresponding later reference voltage indicator or complex network voltage value is determined;the load voltage is recorded and a corresponding later reference voltage indicator or complex load voltage value is determined;for each of these capacitor runs, the calculation of the loss factor change is dependent on the respective later reference voltage indicators and complex load voltage indicators in addition.

It may also be provided that at least at a later date after the second date, for each of these stages, the reference voltage is measured at a reference voltage and the reference voltage at the reference voltage level is measured at the reference voltage level; for each of these capacitor lines, a loss factor change is calculated depending on the respective first, second and subsequent reference voltage gauges and load gauges, and the first, second and subsequent reference voltage gauges and load gauges of the respective adjacent capacitor line;the loss factor change is compared to a tolerance; a monitoring signal is generated depending on the results of these loss factor comparisons.

It may also be provided that the loss factor change of the first capacitor run-through is as follows: with is calculated; and/or the loss factor change of the second capacitor runway according to the following formula with The loss factor change of the third capacitor line is calculated as follows: with wherein > 2 is the number of times; t1, t2 is the first and second time and t3, ..., tn is the later time; ga, gbi, gci i-te are weighting factors for the first, second and third capacitor run.

It may also be provided that each weighting factor is dependent on the age of the antiton at the time of the given weighting factor; and/or The following paragraphs shall apply:

It may continue to be provided that: between the determination of the first reference voltage gauge and the determination of the first coating voltage gauge the values of the first reference voltage gauges are compared,the first load gauges are determined if these values are compared and show that they do not differ by more than a predetermined amount; and/or between the determination of the second reference voltage indicator and the determination of the second load voltage indicator the second reference voltage gauge shall be compared with each other,the second load gauge shall be determined if these comparisons show that the difference between these two values is no more than a predetermined value.

This comparison of the values of the reference voltage gauges allows the determination of a time when the actual monitoring, namely the comparison of the loss factor changes of the capacitor lines and the generation of the monitoring signal, is particularly advantageous or favourable, since it is not then made difficult, impeded or even impossible by reference voltages which differ from each other beyond the predetermined level, thus making it possible to make a better statement on the condition of the capacitor lines independently of variations in the voltages in the AC network and of measurement tolerances when recording the load voltages.

For example, the reference voltages allow for the detection of time changes in voltage conditions, also known as asymmetries, and thus at least partially compensate for the corresponding deviations in the load voltages applied to the capacitor lines, thus ensuring reliable monitoring of the capacitor lines, taking into account and evaluating the deviations and disturbances of the voltages in the AC network.

The reference voltage gauge shall be measured at a frequency of at least one second.

It may continue to be provided that: any comparison shall be made in such a way that: The test is performed on the following test conditions: The measurement of the voltage of the reference voltage shall be performed in accordance with the following formula:

Each of these tolerances RAB, RBC, RCA may be determined by any means necessary, for example, by a value equal to or different from 0,1% or 0,2% or 0,5% or 1% or 2% or 3% or 4% or 5% or 7% or 10% or 15% or 20% or 25% or 30% or 40% or 50% of the nominal value of the respective reference voltage Rae, Rbe, Rce.

It may continue to be provided that: between the determination of the first reference voltage gauge and the determination of the first coating voltage gauge the phase angles of the first reference voltage gauges are compared with each other;the determination of the first coating voltage gauges shall be carried out if these angle comparisons show that these phase angles do not differ from each other by more than a predetermined amount;between the determination of the second reference voltage gauge and the determination of the second coating voltage gauge; the phase angles of the second reference voltage gauge are compared,the second coating voltage gauge shall be determined if these angle comparisons show that these phase angles do not differ from each other by more than a predetermined amount.

This comparison of the phase angles of the reference voltage gauges allows the determination of a time when the actual monitoring, namely the comparison of the loss factor changes of the capacitor lines and the generation of the monitoring signal, is particularly advantageous or favourable, since it is not then made difficult, impeded or even impossible by phase conditions which differ beyond the predetermined range.

It may continue to be provided that: each angular comparison shall be made in such a way that The test is performed on the following samples: Each of these tolerances PAB, PBC, PCA may be determined by any means necessary and set, for example, to a value equal to or less than 0,1% or 0,2% or 0,5% or 1% or 2% or 4% or 5% or 7% or 10% or 15% or 20% of the standard value of the respective phase shift. Each of these tolerances may be at least one of the other tolerances.

It may also be provided that each coating stress indicator is determined by measuring the coating stresses at least twice and that these measured coating stresses are averaged and/or filtered.

It may also be provided that a moving average is derived for the means; and/or a weighted average is derived for the means, in particular by determining a weighting factor for each measured value that depends on the age of that measured value.

The invention proposes, in a second aspect, a device for monitoring capacitor conduction for an AC network as described in claim 17, and furthermore it may be envisaged that each of these transformers is designed as a capacitive voltage converter or an inductive voltage converter or a resistive voltage converter.

It may also be provided that the measuring device includes at least one measuring capacitor or measuring hunter.

The terms and conditions of the invention shall be such that they are not subject to any limitation or restriction.

The following illustrations explain the embodiments of the invention in more detail. The individual features resulting from the embodiments are not, however, limited to the individual embodiments but may be combined and/or combined with the individual features described above and/or with individual features of other embodiments. The details in the drawings are intended to be illustrative only and not to be interpreted in a restrictive manner. The references in the claims are not intended to limit the scope of the invention in any way but merely to refer to the embodiments shown in the drawings. Figure 1 - an embodiment of a device for monitoring capacitor conductivity for a three-phase AC network;Figure 2 - a part of the device of Figure 1;Figure 3 - a replacement circuit consisting of a sub-voltage capacitor and a super-voltage capacitor;Figure 4 - a flow diagram of an embodiment of a process for monitoring capacitor conductivity for a three-phase AC network;Figure 5 - another embodiment of a device for monitoring capacitor conductivity for a three-phase AC network;

The embodiments described below in the specifications of Fig. 1 to Fig. 4 refer to an embodiment in which the respective reference voltage indices Ra (tj), Rb (tj), Rc (tj) are determined from the respective mains voltages Ua (tj), Ub (tj), Uc (tj).

Furthermore, it is assumed that the small angle approximation can be used for the calculation of the loss factor change in the following statements due to the small angle approximation.

In Fig. 1 an embodiment of a device 1 for monitoring capacitor conduction 2a, 2b, 2c for a three-phase AC network is shown schematically. The capacitor conduction 2a, 2b, 2c in this embodiment belong to a transformer not shown here, which is an example of a high voltage transformer. Such capacitor conduction 2a, 2b, 2c is used, for example, at high voltages in the range of only a few kV to some 1000 kV. The AC network is an example of a high voltage network. Each of the three conductor conductors 2a, 2b, 2c of the three connected conductors A, B, C, and C, is arranged on a layer of 4, 5 or more conductors, each of which is surrounded by an external layer of 3 and 5a, which is surrounded by an external layer of 5 and 5a, which is surrounded by an external layer of 3 and 5c.

The device 1 shall have an evaluation device 8 and, for each phase A, B, C, a measurement device 7 and a measurement adapter 6 connected to layer 3 of the capacitor line 2a, 2b, 2c of the respective phase. The evaluation device 8 shall be connected to each measurement device 7 to determine the load voltage gauges Va, Vb, Vc for phases A, B, C, forming a common evaluation device 8 for all measurement devices 7.

The load voltage indicators Va, Vb, Vc are electrical voltage indicators, each measured at a sub-voltage capacitor KU1, KU2, KU3 of the respective phases A, B, C, described below and shown in Fig. 3. In this embodiment, the device 1 also has a voltage converter 9a, 9b, 9c for each phase A, B, C, which is connected to the respective mains line 5a, 5b, 5c to capture a second electrical measurement for the respective phase A, B, C. These second measurement values are electrical voltage indicators, which are measured between the respective mains outputs 5a, 5b, 5c and Ub 13 respectively, and all the mains voltages are measured as 9a, 9b, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c, 9c,

The device 1 shall allow the evaluation device 8 to take into account asymmetries and/or variations of the mains voltage gauges Ua, Ub, Uc on mains lines 5a, 5b, 5c when monitoring capacitor lines 2a, 2b, 2c.

Figure 2 shows in more detail a first part of the apparatus 1 which is associated with a first phase A. This first part corresponds to a second part of the apparatus 1 corresponding to a second phase B and a third part corresponding to a third phase C, so that the statements and explanations on the first part are also applicable by analogy to these two other parts.

The first capacitor line 2a, which is assigned to the first phase A, has an insulating body 11 through which the conductor 4 is insulated. This contacts at its upper end the mains line 5a, which is assigned to its capacitor line 2a, and at its lower end a high-voltage transformer winding not shown here. In the insulating body 11 the electrically conductive surfaces are inserted, which are only indicated here by the outermost layer 3 and electrically form a series of capacitors. This upper circuit shows the capacitors, each coated by two adjacent capacitors, and a conductor, which is not coated by the coated capacitor 4a, and is formed by an internal circuit corresponding to the outermost layer 2a. This circuit forms a series of capacitors between the KO2 and KO3 conductor, each of which is coated by two adjacent capacitors.

At the capacitor line 2a, an electrically conductive flange 12 is placed adjacent to the ground potential or mass potential 13 and this flange 12 is used to attach and/or secure the capacitor line 2a. The outermost layer 3 forms a corresponding external capacitor KA1, KA2, KA3 with the flange 12 and mass potential 13 as a replacement circuit for each capacitor line 2a, 2b, 2c.

The measuring adapter 6 penetrates the insulation body 11 and establishes an electrically conductive connection to the outermost layer 3. In this embodiment, each measuring device 7 has a measuring capacitor KM1, KM2, KM3 connected to mass potential 13.

The measuring device 8 is electrically conductive, connected via the voltage converter 9a to the mains line 5a. In this embodiment, the voltage converter 9a is designed as a capacitive voltage converter and has a capacitive voltage divider comprising two capacitors K1, K2 connected in series and two coils or windings W1, W2 connected as a transformer for inductive galvanic separation.

In Fig. 3 for the first phase A, a replacement circuit from the respective sub-voltage capacitor KU1 and the respective super-voltage capacitor KO1 is schematically shown. A parallel circuit containing the respective measuring capacitor KM1 and the external capacitor KA1 forms the sub-voltage capacitor KU1 with the undercapacity C1. This undercapacity C1a can therefore be easily calculated from the measuring capacitor KM1's capacity CM1 and the external capacitor KA1's capacity CA1 CM1 using the known capacitor series circuit formula. If necessary, the parallel circuit can be used instead of the measuring capacitor KM1 to measure the entire unit and then 7/ 8a additional instructions, so that the measuring capacitor C1a must be calculated depending on the measuring capacitor's capacity, the direction of the measuring capacitor 7,1a and the capacity of the measuring capacitor KM1a.

The load voltage V1a is located at the downstream capacitor KU1 and is applied at the connection line or connection point between the downstream capacitor KU1 and the upstream capacitor KO1 and is related to mass potential 13.

In Fig. 4 a schematic diagram of an embodiment of a process for monitoring capacitor conduction 2a, 2b, 2c for a three-phase AC network is shown.

In this embodiment, the procedure has the following steps, which are explained by reference to the device 1 and Figure 1-3, Step 101: Start of the procedure.

Step 102: Recording of initial mains voltages Ua ((t1), Ub ((t1), Uc ((t1) and initial overhead voltages Va ((t1), Vb ((t1), Vc ((t1) for time t1 for each of phases A, B, C.

Step 103: Determination of initial mains voltage readings Ua (t1), Ub (t1), Uc (t1) from the recorded mains voltages Ua (t1), Ub (t1), Uc (t1) and comparison of the mains voltage readings Ua (t1), Ub (t1), Uc (t1) at time t1 with each other.

The power supply voltage indicators Uae, Ube, Uce are used in this embodiment for comparison with each other, and the sums and/or peak values and/or amplitudes of the power supply indicators can also be used for comparison.

It is also provided that the tolerance values RAB > 0, RBC > 0, RCA > 0 are determined for the comparison and the comparison is made in such a way as to check whether Uae - Ubeubos ≤ RAB and Ubeubos ≤ RBC and Uueubos ≤ RCA are valid.

If yes, this means that the comparison of the network voltage indicators LJa(t1), Ub(t1), Uc(t1) between them shows that the network voltage indicators do not differ from each other more than a predetermined measure RAB, RBC, RCA.

If no, this means that the first network voltage indices Ua(t1), Ub(t1), Uc(t1) are compared and the first network voltage indices RAB, RBC, RCA differ by more than a predetermined measure.

Step 104: A warning signal is generated to indicate a short circuit in the power grid and/or too strong or excessive asymmetry of the mains voltages Ua, Ub, Uc.

Step 105: Determine the phase angle φa, φb, φc of the first mains voltage gauge Ua(t1), Ub(t1), Uc(t1) at time t1, where cpa is the phase angle of the mains voltage gauge Ua(t1), φb is the phase angle of the mains voltage gauge Ub(t1) and cpc is the phase angle of the mains voltage gauge Uc(t1).

Step 106: Comparison of the phase angles φa, φb, φc of the first mains voltage indicators Ua (t1), Ub (t1), Uc (t1) with each other. For comparison of the phase angles of the first mains voltage indicators with each other, it is intended that the tolerance values PAB > 0, PBC > 0, PCA > 0 are determined as the measure for the angle comparison. The size comparison is made in such a way that it is checked whether PCa - φb ≤ PAB and ≤ PAB and ≤ PBC and ≤ PBC apply.

If yes, this means that the phase angle comparison shows that the phase angles of the first mains voltage gauges φa, φb, φc do not differ from each other by more than a predetermined measure PAB, PBC, PCA.

If no, this means that the phase angle comparison shows that the phase angles of the first mains voltages φa, φb, φc differ from each other by more than a predetermined measure PAB, PBC, PCA.

Step 107: Determine from first coating stress indicators Va ((t1), Vb ((t1), Vc ((t1) for time t1 the coating stresses Va ((t1) Vb ((t1), Vc ((t1) measured in step 102 between the respective coating 3 and mass potential 13 at time t1.

Step 108: Determine and archive the phase shift θab, θbc, θac between the load voltage indicators Va ((t1), Vb ((t1), Vc ((t1) at the predetermined time t1 according to the following formulae wherein Ua (tj), Ub (tj), Uc (tj) are the first mains voltage indicators of the first, second and third phases at time j; Va (tj), V (b) (tj), V (c) (tj) are the first load indicators of the first, second and third phases at time j.

Step 109: Recording secondary mains voltages Ua(t2), Ub(t2), Uc(t2) and secondary load voltages Va(t2), Vb(t2), Vc(t2) and determination of secondary mains voltage indicators Ua(t2), Ub(t2), Uc(t2) for a time t2 after time t1, using the mains voltages Ua(t2), Ub(t2), Uc(t2) recorded at time t2 for each of phases A, B, C.

Step 110: Comparison of the mains voltage indicators Ua ((t2), Ub ((t2) Uc ((t2) at time t2 with each other.

The comparison of the mains voltage gauges at time t2 shall be carried out in the same way as the comparison of the first mains voltage gauges at time t1 from step 103. If the mains voltage gauges Ua(t2), Ub(t2), Uc(t2) differ more than one predetermined measure RAB, RBC, RCA, step 104 shall be performed, otherwise step 111 shall be continued.

Step 111: Determine the phase angle φa, φb, φc of the second mains voltage gauge Ua ((t2), Ub ((t2), Uc ((t2) at time t2 where cpa is the phase angle of the mains voltage gauge Ua ((t2), cpb is the phase angle of the mains voltage gauge Ub ((t2) and cpc is the phase angle of the mains voltage gauge Uc ((t2).

Step 112: Comparison of the phase angles φa ((t2), φb ((t2), φc ((t2) of the second mains voltage gauge Ua ((t2), Ub ((t2), Uc ((t2) at time t2 by analogy to step 106.

If the phase angles of the second mains voltage gauge deviate from each other by more than a predetermined measure PAB, PBC, PCA, step 104b is performed, otherwise step 113 is continued.

Step 104b: A warning signal is generated to indicate a short circuit in the power grid and/or an overly strong or excessive asymmetry of the mains voltages Ua, Ub, Uc. The step 109 is then jumped if necessary.

Step 113: A second coating voltage gauge Va ((t2), Vb ((t2), Vc ((t2) is obtained for time t2 from a measured coating voltage between the respective coating 3 and mass potential 13 at time t2.

The consensus transmissions from the load voltage gauges Va ((t2), Vb ((t2), Vc ((t2) are determined and archived according to the following formulae.

Any measurements from possible previous process runs recorded between a time t1 and a time t2 are not taken into account in this embodiment.

Step 114a: In this embodiment, for each capacitor line 2a, 2b, 2c, a loss factor change ΔDa, ΔDb, ΔDc is calculated depending on the phase shift θab (tj), θbc (tj), θac (tj) between adjacent capacitor lines as previously determined at different times, according to the following formula. ΔDa (t2) thus describes the loss factor change of the capacitor line 2a at time t2 compared to time t1. ΔDb (t2) describes the loss factor change of the capacitor line 2b at time t2 compared to time t1. ΔDc (t2) describes the loss factor change of the capacitor line 2c at time t2 compared to time t1.

In this embodiment, the loss factor change of capacitor runs 2a, 2b, 2c is also determined for subsequent times t3, t4,...tn after time t2 with reference to the first time t1.

Step 115: For each capacitor run, the loss factor changes of capacitor run 2a, 2b, 2c identified in step 114a are compared. This embodiment provides for the determination of tolerances DA > 0, DB > 0, DC > 0 for the loss factor change of the respective capacitor run and the comparison is made in such a way as to check whether: If this is the case, step 116 is performed. If not, step 117 is performed.

Step 116: A monitoring signal is generated to indicate that the capacitor conduits 2a, 2b, 2c are in proper condition, and then the jump to step 109 is made.

Step 117: The loss factor comparison is also carried out in such a way as to check whether a first case is applicable or in the second case or in a third case

If one of the three cases above occurs, a jump to step 118 is made.

Step 118: Depending on the loss comparison from step 117, a monitoring signal is generated.

If the first case has occurred in step 117, the monitoring signal shall indicate that either the second capacitor line 2b is not in the correct condition or the other two capacitor lines 2a, 2c are not in the correct condition and have an equivalent fault.

If the second case has occurred in step 117, the monitoring signal shall indicate that either the third capacitor line 2c is not in the correct condition or the other two capacitor lines 2b, 2a are not in the correct condition and have an equivalent fault.

If the third case has occurred in step 117, the monitoring signal shall indicate that either the first capacitor line 2a is not in the correct condition or the other two capacitor lines 2c, 2b are not in the correct condition and have an equivalent fault.

Step 119: If none of the above three cases occurs, a monitoring signal is generated indicating that either all three capacitor lines 2a, 2b, 2c are not in the correct condition or two capacitor lines are not in the correct condition and do not have an equivalent error.

Alternative embodiments 114b, 114c of step 114a are described below.

In contrast to step 114a, in step 114b the loss factor change of the respective capacitor line for measurements at time t3, t4,... tn after time t2 can also be determined from the previous measurement, as is the case for a time t3 after time t2 as shown by the following formulae:

In another alternative embodiment, a variety of measurements between an initial time t1 and a later time tn can also be used in step 114c to determine the loss factor change of the respective capacitor conductor.

The loss factor change of a first capacitor run 2a is thus: with

The loss factor change of a second capacitor runway 2b is determined by: with

The loss factor change of a third capacitor runway 2c is determined by: with

Whereas n > 2 is the number of times;gai, gbi, gci i t are weighting factors for the first, second and third capacitor conduction.

The weighting factors may depend on the age of the capacitor conduit or the location of installation, statistical or probabilistic methods or other empirical data.

Steps 102, 109 can be performed, for example, by the voltage converters 9a, 9b, 9c, the measuring adapters 6, the measuring devices 7 and the evaluation device 8, which thus form means designed to detect the mains and load voltages at different points Ua, Ub, Uc, Va, Vb, Vc, Ua.

Steps 103, 105, 106, 110, 111, 112 can be performed, for example, by the voltage converters 9a, 9b, 9c and the measuring device 8, which thus form means designed to detect and compare the mains voltage indicators at different times.

For example, steps 104a, 104b, 116, 118, 119 can be performed by the evaluation device 8, which thus forms means designed to generate a monitoring signal that depends on the results of the comparison of the network voltages, phase states and loss factor changes.

Steps 107, 108, 113, 114a, 114b, 114c can be performed, for example, by the measuring device 8 and the measuring adapter 6 and the measuring device 7, which thus form means designed to detect and compare the coating stress indicators at different times.

Steps 115, 117 can be performed, for example, by the evaluation device 8, which thus forms means designed to compare the change in the loss factor of the respective capacitor conduit with each other.

It is advantageous to run steps 103/105 and/or 110/112 in parallel.

Figure 5 shows another embodiment of a device for monitoring capacitor conduction for a three-phase AC network. Unlike the previous embodiments, the reference voltage indicator Ra (tj), R (tj), R (tj) is used here to compare the loss factor changes not by a voltage divider 9a, 9b, 9c on the respective power lines 5a, 5b, 5c, but by a group of parallel capacitor conductors 2a`, 2b', 2c' on a second high voltage transformer (not shown). The parallel capacitor conductors 2a, 2b, 2c' are connected to the same power line as the 5a, 5b, 5c, 5c, 2c, 2c, 2c, 2c.

As shown in Figure 2, each parallel capacitor line 2a`, 2b' 2c' is equipped with a measuring device consisting of a measuring adapter 6 and a measuring device 7. The measuring device 8 is electrically connected to the parallel capacitor lines 2a`, 2b', 2c' via the respective measuring device 7 and the respective measuring adapter 6. This connection determines the load indicators Va`, Vb`, Vc` of the parallel capacitor lines.

For the process sequence, in this alternative embodiment, the load voltage gauges Va`(tj), Vb'(tj), Vc'(tj) are used as the reference voltage gauges Ra(tj), Rb(tj) Rc(tj).

The phase angles φa, φb, φc are replaced by the phase angles φa', φb', φc' of the load-voltage gauge Va`, Vb' Vc` in the process sequence shown in Figure 5.

The test shall be carried out on the basis of the data provided by the manufacturer and shall be carried out in accordance with the requirements of the relevant harmonised standards.

In another embodiment, constant voltages for which corresponding constant voltage indicators are predetermined may also be used as reference voltages.

The size of each constant voltage indicator shall in this case preferably correspond to the rated voltage of the AC network.

The phase angles φa, φb, φc are set at 0°, 120°, 240° in this embodiment constantly according to the procedure described in the instructions in Figure 5.

The following shall be added:

1 device2a, 2b, 2cccondenser conductor2a`, 2b', 2c'parallel condenser conductor3Belag4conductor5a, 5b, 5cNetwork line6Measurement adapter7Measuring device7'surge protection8Assessment device9a, 9b, 9cVolt converters11Isolation body12FΔFlank13MK potentialK1, K2KcondensatorsW1, W2WicketingA, B, C, CM, second, third phase KORa, Rb, KOR, KOc upper voltage thresholdj), Rb, 5cNetwork line6Measurement adapter7Measuring device7'surge protection8Assessment device9a, 9b, 9cVolt converters11Isolation body12FΔFlank13MK potentialK1, K2KcondensatorsW1, W2WicketingA, B, C, CM, CM, second, third phase KORa, Rb, KOc KORa, KOc upper voltage thresholdj), Rb, Rj, Rc, Rc, Rj) Reference voltage capacitance at the time of transmission, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj, Tj,

Claims (17)

1. Method of monitoring capacitor bushings (2a, 2b, 2c) for an alternating current mains, wherein

   - the alternating current mains has a first, second and third phase (A, B, C) and comprises

   • a first mains line (5a), with which the first phase (A) and a first capacitor bushing (2a) are associated and at which a first mains voltage is present,

   • a second mains line (5b), with which the second phase (B) and a second capacitor bushing (2b) are associated and at which a second mains voltage is present,

   • a third mains line (5c), with which the third phase (C) and a third capacitor bushing (2c) are associated and at which a third mains voltage is present;

   - each of these capacitor bushings (2a, 2b, 2c) comprises

   • a conductor (4) connected with the associated mains line (5a, 5b, 5c);

   • an electrically conductive foil (3) surrounding this conductor (4);

   - at a predetermined first instant (t1), for each of these phases (A, B, C)

   • a corresponding first reference voltage phasor (Ra(t1), Rb(t1), Rc(t1)) is determined for a first reference voltage;

   • a foil voltage present between the respective foil (3) and ground potential (13) is detected and a corresponding first foil voltage phasor (Va(t1), Vb(t1), Vc(t1)) is determined;

   - at a predetermined second instant (t2) lying after the first instant (t1), for each of these phases (A, B, C)

   • a corresponding second reference voltage phasor (Ra(t1), Rb(t1), Rc(t1)) is determined for a second reference voltage;

   • the foil voltage is detected and a corresponding second foil voltage phasor (Va(t2), Vb(t2), Vc(t2)) is determined;

   characterised in that

   - for each of these capacitor bushings (2a, 2b, 2c)

   • a loss factor change (ΔDa, ΔDb, ΔDc) is calculated in dependence on the respective first and second reference voltage phasors and foil voltage phasors as well as on the first and second reference voltage phasors and foil voltage phasors of the respectively adjacent capacitive bushing (2b, 2c, 2a);

   - the loss factor change of the first capacitor bushing (2a) is calculated in accordance with the following equation wherein and/or

   - the loss factor change of the second capacitor bushing (2b) is calculated in accordance with the following equation wherein and/or

   - the loss factor change of the third capacitor bushing (2c) is calculated in accordance with the following equation wherein wherein;

   - Ra(t1), Rb(t1), Rc(t1) are the first reference voltage phasors of the first, second and third phase;

   - Va(t1), Vb(t1), Vc(t1) are the first foil voltage phasors of the first, second and third phase;

   - Ra(t2), Rb(t2), Rc(t2) are the second reference voltage phasors of the first, second and third phase;

   - Va(t2), Vb(t2), Vc(t2) are the second foil voltage phasors of the first, second and third phase.

   • the loss factor change is compared with a tolerance value (DA, DB, DC);

   - a monitoring signal is generated in dependence on the results of these loss factor comparisons.
2. Method according to the preceding claim, wherein

   - each reference voltage is the respective mains voltage (Ua(t1), Ua(t2), Ub(t1), Ub(t2), Uc(t1), Uc(t2)).
3. Method according to claim 1, wherein

   - a first parallel capacitor bushing (2a') is associated with the first mains line (5a);

   - a second parallel capacitor bushing (2b') is associated with the second mains line (5b);

   - a third parallel capacitor bushing (2c') is associated with the third mains line (5c);

   - each of these parallel capacitor bushings (2a', 2b', 2c') comprises

   • a conductor (4) connected with the associated mains line (5a, 5b, 5c),

   • an electrically conductive foil (3) surrounding this conductor (4);

   - for each of these phases (A, B, C)

   • the first and second reference voltages are first and second foil voltages (Va'(t1), Vb'(t1), Vc'(t1), Va'(t2), Vb'(t2), Vc'(t2)) respectively present at the first instant and the second instant between the foil (3) and ground potential (13) of the respective parallel capacitor bushing.
4. Method according to claim 1 or one of the preceding claims, wherein

   - for each of these phases (A, B,C)

   • the reference voltage is a constant voltage for which a corresponding constant voltage phasor is predetermined.
5. Method according to the preceding claim, wherein

   - the magnitude of each constant voltage phasor is equal to a rated voltage value of the alternating current mains;

   - for the first phase (A) the phase angle of the first and second constant voltage phasors (Ra(t1), Ra(t2)) is 0°;

   - for the second phase (B) the phase angle of the first and second constant voltage phasors (Rb(t1), Rb(t2)) is 120°;

   - for the third phase (C) the phase angle of the first and second constant voltage phasors (Rc(t1), Rc(t2)) is 240°.
6. Method according to any one of the preceding claims, wherein

   - tolerance values DA > 0, DB > 0, DC > 0 are determined for the loss factor comparisons;

   - if the loss factor comparisons have the result that then a monitoring signal is generated which indicates that the capacitor bushings (2a, 2b, 2c) are in a state of proper order.
7. Method according to any one of the preceding claims, wherein

   - tolerance values DA > 0, DB > 0, DC > 0 are determined for the loss factor comparisons;

   - if the loss factor comparisons have the result that then a monitoring signal is generated which indicates that either the second capacitor bushing (2b) is not in a state of proper order or the two other capacitor bushings (2a, 2c) are not in a state of proper order and have a fault of the same kind;

   - if the loss factor comparisons have the result that then a monitoring signal is generated which indicates that either the third capacitor bushing (2c) is not in a state of proper order or the two other capacitor bushings (2b, 2a) are not in a state of proper order and have a fault of the same kind;

   - if the loss factor comparisons have the result that then a monitoring signal is generated which indicates that either the first capacitorbushing (2a) is not in a state of proper order or the two other capacitor bushings (2c, 2b) are not in a state of proper order and have a fault of the same kind.
8. Method according to the preceding claim, wherein

   - otherwise a monitoring signal is generated which indicates that either all three capacitor bushings (2a, 2b, 2c) are not in a state of proper order or two capacitor bushings are not in a state of proper order and do not have a fault of the same kind.
9. Method according to any one of the preceding claims, wherein

   - at a predetermined third instant (t3) lying after the second instant (t2), for each of these phases (A, B, C)

   • a corresponding third reference voltage phasor Ra(t3), Rb(t3), Rc(t3) is determined for a reference voltage;

   • the foil voltage is detected and a corresponding third foil voltage phasor Va(t3), Vb(t3), Vc(t3) is determined;

   • the second reference voltage phasor is replaced by the third reference voltage phasor and the second foil voltage phasor is replaced by the third foil voltage phasor;

   - for each of these capacitor bushings (2a, 2b, 2c)

   • the calculation and comparison of the loss factor change (ΔDa, ΔDb, ΔDc) are repeated;

   - a monitoring signal is generated in dependence on the results of these loss factor comparisons.
10. Method according to the preceding claim, wherein

    - before each replacement of the second reference voltage phasor and foil voltage phasor

    • the first reference voltage phasor is replaced by the second reference voltage phasor and the first foil voltage phasor is replaced by the second foil voltage phasor.
11. Method according to any one of the preceding claims, wherein

    - at at least one predetermined later instant (tn) lying after the second instant (t2), for each of these phases (A, B, C)

    • a corresponding later reference voltage phasor (Ra(tn), Rb(tn), Rc(tn)) isdetermined for a reference voltage;

    • the foil voltage is detected and a corresponding later foil voltage phasor (Va(tn), Vb(tn), Vc(tn)) is determined;

    - for each of these capacitor bushings (2a, 2b, 2c)

    • the calculation of the loss factor change (ΔDa, ΔDb, ΔDc) additionally depends on the respective later mains voltage phasors and foil voltage phasors.
12. Method according to any one of the preceding claims, wherein

    - at at least one predetermined later instant (tn) lying after the second instant (t2), for each of these phases (A, B, C)

    • a later reference voltage phasor (Ra(tn), Rb(tn), Rc(tn)) is determined;

    • the foil voltage is detected and a corresponding later foil voltage phasor (Va(tn), Vb(tn), Vc(tn)) is determined;

    - for each of these capacitor bushings (2a, 2b, 2c)

    • a loss factor change (ΔDa, ΔDb, ΔDc) is calculated in dependence on the respective first, second and later reference voltage phasors and foil voltage phasors as well as on the first, second and later reference voltage phasors and foil voltage phasors of the respectively adjacent capacitor bushing (2b, 2c, 2a);

    • the loss factor change is compared with a tolerance value (DA, DB, DC);

    - a monitoring signal is generated in dependence on the results of these loss factor comparisons.
13. Method according to one of the two preceding claims, wherein

    - the loss factor change of the first capacitor bushing (2a) is calculated in accordance with the following equation wherein and/or

    - the loss factor change of the second capacitor bushing (2b) is calculated in accordance with the following equation wherein and/or

    - the loss factor change of the third capacitor bushing (2c) is calculated in accordance with the following equation wherein wherein;

    - n > 2 is the number of the instants;

    - t1, t2 are the first and second instants and t3, ..., tn are the later instants;

    - gai, gbi, gci are ith weighting factors for the first, second and third capacitor bushings.
14. Method according to the preceding claim, wherein

    - each weighting factor antitonically depends on the age of the respective instant; and/or

    - there applies for the weighting factors
15. Method according to any one of the preceding claims, wherein

    - between determination of the first reference voltage phasors and determination of the first foil voltage phasors

    • the magnitudes of the first reference voltage phasors are compared with one another,

    • determination of the first foil voltage phasors is carried out if these magnitude comparisons have the result that these magnitudes do not differ from one another by more than a predetermined amount;

    and/or

    - between determination of the second reference voltage phasors and determination of the second foil voltage phasors

    • the magnitudes of the second reference voltage phasors are compared with one another,

    • determination of the second foil voltage phasors is carried out if these magnitude comparisons have the result that these magnitudes do not differ from one another by more than a predetermined amount.
16. Method according to any one of the preceding claims, wherein

    - between determination of the first reference voltage phasors and determination of the first foil voltage phasors

    • the phase angles of the first reference voltage phasors are compared with one another,

    • determination of the first foil voltage phasors is carried out if these angle comparisons have the result that these phase angles do not differ from one another by more than a predetermined amount;

    - between determination of the second reference voltage phasors and determination of the second foil voltage phasors

    • the phase angles of the second reference voltage phasors are compared with one another,

    • determination of the second foil voltage phasors is carried out if these angle comparisons have the result that these phase angles do not differ from one another by more than a predetermined amount.
17. Device (1) for monitoring capacitor bushings (2a, 2b, 2c) for an alternating current mains, wherein

    - the alternating current mains has a first, second and third phase (A, B, C) and comprises

    • a first mains line (5a), with which the first phase (A) and a first capacitor bushing (2a) are associated and at which a first mains voltage is present,

    • a second mains line (5b), with which the second phase (B) and a second capacitor bushing (2b) are associated and at which a second mains voltage is present,

    • a third mains line (5c), with which the third phase (C) and a third capacitor bushing (2c) are associated and at which a third mains voltage is present;

    - each of these capacitor bushings (2a, 2b, 2c) comprises

    • a conductor (4) connected with the associated mains line (5a, 5b, 5c);

    • an electrically conductive foil (3) surrounding this conductor (4);

    - the device comprises:

    • a first voltage converter (9a) which can be connected with the first mains line (5a);

    • a second voltage converter (9b) which can be connected with the second mains line (5b);

    • a third voltage converter (9c) which can be connected with the third mains line (5c);

    • a first measuring adapter (6a) which can be connected with the foil (3) of the first capacitor bushing (2a);

    • a second measuring adapter (6b) which can be connected with the foil (3) of the second capacitor bushing (2b);

    • a third measuring adapter (6c) which can be connected with the foil (3) of the third capacitor bushing (2c);

    • a measuring device (7) coupled to the measuring adapters (6a, 6b, 6c);

    • an evaluating device (8) coupled to the voltage converters (9a, 9b, 9c) and the measuring device (7);

    - each of these voltage converters (9a, 9b, 9c) for the respective phase (A, B, C) can detect the mains voltage;

    - the measuring device (7) for each of these phases (A, B, C) can detect, with the help of the respective measuring adapter (6a, 6b, 6c), a foil voltage present between the respective foil (3) and ground potential (13);

    - the evaluating device (8) is so constructed that at a predetermined first instant (t1), for each of these phases (A, B, C) it

    • can detect the mains voltage with the help of the respective voltage converter (9a, 9b, 9c) and can determine a corresponding first mains voltage phasor (Ua(t1), Ub(t1), Uc(t1));

    • can detect the foil voltage with the help of the measuring device (7) and can determine a corresponding first foil voltage phasor (Va(t1), Vb(t1), Vc(t1));

    - the evaluating device (8) is so constructed that at a predetermined second instant (t2) lying after the first instant (t1), for each of these phases (A, B, C) it

    • can detect the mains voltage with the help of the respective voltage converter (9a, 9b, 9c) and can determine a corresponding second mains voltage phasor (Ua(t2), Ub(t2), Uc(t2));

    • can detect the foil voltage with the help of the measuring device (7) and can determine a corresponding second foil voltage phasor (Va(t2), Vb(t2), Vc(t2));

    characterised in that

    - the evaluating device (8) is so constructed that for each of these capacitor bushings (2a, 2b, 2c) it

    • can calculate a loss factor change (ΔDa, ΔDb, ΔDc) in dependence on the respective first and second mains voltage phasors and foil voltage phasors as well as on the first and second mains voltage phasors and foil voltage phasors of the respectively adjacent capacitor bushing (2b, 2c, 2a);

    • can compare the loss factor change with a tolerance value (DA,DB, DC);

    - the evaluating device (8) is so constructed that it can generate a monitoring signal in dependence on the results of these loss factor comparisons; wherein

    - the loss factor change of the first capacitor bushing (2a) is calculated in accordance with the following equation wherein and/or

    - the loss factor change of the second capacitor bushing (2b) is calculated in accordance with the following equation wherein and/or

    - the loss factor change of the third capacitor bushing (2c) is calculated in accordance with the following equation wherein wherein;

    - Ra(t1), Rb(t1), Rc(t1) are the first reference voltage phasors of the first, second and third phase;

    - Va(t1), Vb(t1), Vc(t1) are the first foil voltage phasors of the first, second and third phase;

    - Ra(t2), Rb(t2), Rc(t2) are the second reference voltage phasors of the first, second and third phase;

    - Va(t2), Vb(t2), Vc(t2) are the second foil voltage phasors of the first, second and third phase.