JP2004138491A - Degradation diagnostic method and degradation diagnostic device of cv cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a degradation diagnostic method and a degradation diagnostic device of a CV cable capable of conducting precise insulation diagnosis by using a residual charge measuring method. <P>SOLUTION: This device is provided with residual charge measuring devices 2-7 for earthing after energizing the CV cable by a direct-current voltage, discharging the charge accumulated by energization by the direct-current voltage by being energized by an alternating-current voltage changing in a step shape thereafter, and outputting a signal showing a plurality of residual charge quantities, and a processing device 8 for calculating the center of gravity of a distribution of the plurality of residual charge quantities based on the signal showing the plurality of residual charge quantities outputted from the residual charge measuring devices, and outputting the alternating-current voltage corresponding to the calculated center of gravity as a signal showing a degradation index. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for diagnosing deterioration of a CV cable, and more particularly to a technique for non-destructively diagnosing residual performance of an insulator of a CV cable deteriorated by water tree by measuring a residual charge amount.
[0002]
[Prior art]
Conventionally, as an underground power transmission cable, a CV cable (Cross-linked polyethylene insulated polyvinyl chloride sealed cable) having excellent electrical characteristics and ease of work has been used. Since the CV cable is used in an environment where water exists, a phenomenon called water tree occurs in the insulator, and insulation deterioration occurs.
[0003]
Therefore, a residual charge measurement method is being studied as a technique for diagnosing the occurrence of water trees. In this residual charge measurement method, a DC voltage is applied to a CV cable, and then grounded to remove the DC application, and subsequently an AC voltage is applied, and the resulting DC current component is detected. The amount of residual charge is calculated by integrating the current signal obtained by this detection. This residual charge measurement method has a good correlation with the degree of water tree deterioration and breakdown voltage, and is attracting attention as a CV cable deterioration diagnosis method.
[0004]
The mechanism of the generation of residual charges in the water-tree-degraded insulator is disclosed in, for example, JP-A-2001-349922. In other words, when water trees are present in the insulator, space charge is accumulated at the interface between the water tree portion and a healthy insulator due to DC power application. When the DC charge is removed by grounding after the DC charge is applied, space charges remain inside the insulator, and the space charges start moving due to the electric field and eventually disappear.
[0005]
When the ground charge (short circuit) is maintained, the direct current (reverse absorption current) that decays exponentially with time flows to the ground circuit. Further, when the ground is opened, the DC voltage (residual voltage) recovers between the opened electrodes so as to saturate to a certain value with time. The generation of the reverse absorption current and the residual voltage is caused by the response delay of the space charge inside the insulator to the sudden change of the ground after the DC application.
[0006]
The residual charge recovered after the grounding of the DC power application can be used to determine insulation deterioration due to water trees. However, since the time required for the movement and disappearance of the space charge is extremely long, the recovery time of the residual charge observed in the measurement circuit becomes extremely slow. If the measurement time is short, a large signal cannot be obtained. However, when the AC voltage is applied, the moving speed of the space charge existing in the water tree deterioration part is increased, and the residual charge caused by the water tree deterioration can be realized in a short time. This is the reason why residual charge measurement is performed using AC charging.
[0007]
In this residual charge measurement method, the residual charge amount generally obtained by residual charge measurement is average information generated from the entire cable. Therefore, whether a part of the cable is extremely deteriorated or slight deterioration is considered. Cannot be determined. Therefore, it is difficult to make a deterioration diagnosis between long cables or samples having different lengths.
[0008]
In order to solve such a problem, for example, in Patent Document 1, in the above-described residual charge measurement method, an alternating voltage having a predetermined power application pattern is applied stepwise a plurality of times, and the residual charge is measured. CV cable deterioration diagnosis method that diagnoses the degree of insulation deterioration by estimating the AC breakdown voltage level of the cable from the highest AC voltage value and evaluates the degree of water tree deterioration between long cables or cables of different lengths. Is disclosed.
[0009]
According to this deterioration diagnosis method, the residual charge amount distribution can be obtained by measuring the residual charge while applying power by repeating step-up and step-down a plurality of times by setting the maximum voltage from a low voltage to an operating voltage by step boosting. The residual charge component emitted at higher AC voltages reflects a long water tree that has the greatest effect on insulation performance. Therefore, by examining the residual charge amount distribution and using up to which AC charging voltage the residual charge was detected as a deterioration index, it is possible to estimate how long water trees are generated in the insulator. It is possible to evaluate the residual performance.
[0010]
[Patent Document 1]
JP-A-2001-349922
[0011]
[Problems to be solved by the invention]
However, in this conventional deterioration diagnosis method, the highest AC application voltage from which the residual charges are released is used as the deterioration index, and therefore, as shown in, for example, types 1 to 3 in FIG. even if different, the degradation index if the best Affairs Division electrostatic voltage residual charge is released the same (V ₅ in FIG. ₄₎ is the same, the determination result of such residual performance is the same.
[0012]
On the other hand, one having a distribution in which a large amount of residual charge is released at a low AC charging voltage as shown in type 3 in FIG. It is more likely that a longer water tree has occurred in the latter, and as a result, the latter may have lower insulation performance. Therefore, when the highest AC charging voltage at which the residual charges are released is used as the deterioration index, the deterioration diagnosis is not sufficient.
[0013]
FIG. 5 shows the breakdown field strength obtained as a result of the breakdown test for the emission field strength of the residual charges based on the highest AC application voltage obtained by the above method. It can be seen from FIG. 5 that even when the emission field strength is the same, a large variation occurs in the breakdown field strength.
[0014]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a CV cable deterioration diagnosis method and a deterioration diagnosis apparatus capable of accurately performing insulation diagnosis using a residual charge measurement method. Is to do.
[0015]
[Means for Solving the Problems]
The present invention is configured to perform insulation diagnosis using a deterioration index in consideration of the shape of the residual charge amount distribution.
[0016]
That is, in order to achieve the above object, the method for diagnosing deterioration of a CV cable according to the present invention includes the steps of applying a DC voltage to a CV cable, grounding the cable, and then applying an AC voltage to apply the DC voltage. In the residual charge measurement method of measuring the amount of residual charge by discharging the accumulated charge, a plurality of residual charge amounts are measured by applying power while changing the AC voltage in a step-like manner, and the obtained plurality of residual charge amounts are measured. Is characterized by using the AC voltage corresponding to the calculated center of gravity as a deterioration index. In this case, the center of gravity may be a weighted average of a plurality of residual charge amounts.
[0017]
According to this method of diagnosing deterioration of a CV cable, in a distribution where a large amount of residual charge is obtained at a low AC charging voltage, the center of gravity is on the low AC voltage side. Therefore, even if the highest AC charging voltage from which residual charges are released by using this deterioration diagnosis method is the same, the AC voltage side having a higher center of gravity is determined to have a higher degree of deterioration. That is, it is possible to obtain a diagnosis result that accurately reflects the state of deterioration.
[0018]
Further, in order to achieve the above object, the deterioration diagnosis device for a CV cable according to the present invention applies a DC voltage to the CV cable, grounds the CV cable, and then applies a stepwise changing AC voltage to the CV cable. A residual charge measuring device that outputs a signal representing a plurality of residual charge amounts by discharging charges accumulated by applying a voltage; and a plurality of signals based on the plurality of residual charge amount signals output from the residual charge measuring device. And a processing unit that calculates the center of gravity of the distribution of the residual charge amount and outputs an AC voltage corresponding to the calculated center of gravity as a signal indicating a deterioration index. In this case, the processing device can calculate the center of gravity by obtaining a weighted average of the plurality of residual charge amounts.
[0019]
According to the CV cable deterioration diagnosis apparatus, the same operation and effect as those of the above-described CV cable deterioration diagnosis method can be obtained.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0021]
FIG. 1 is a block diagram showing a configuration of a CV cable deterioration diagnosis device according to an embodiment of the present invention. The CV cable deterioration diagnosis device is roughly composed of a residual charge measuring device and a processing device. The residual charge measuring device includes a changeover switch 2, a DC charging device 3, an AC charging transformer 4, a voltage adjusting device 5, a residual charge detecting device 6, and a low-pass filter 7. The processing device is constituted by a personal computer (PC) 8.
[0022]
The changeover switch 2 is a switch that can switch the connection of the common terminal T to three contacts 2a, 2b, and 2c. The test cable 1 is connected to a common terminal T of the changeover switch 2. The contact 2 a of the changeover switch 2 is connected to the DC power application device 3. The DC power supply device 3 generates a DC voltage _VDC . The contact 2b of the changeover switch 2 is grounded via the protection resistor R. The contact 2 c of the changeover switch 2 is connected to one terminal U of the secondary winding of the AC power transformer 4.
[0023]
The AC charging transformer 4 transforms the AC voltage supplied from the voltage regulator 5 and outputs the transformed voltage from the secondary winding. One terminal U of the secondary winding of the AC charging transformer 4 is connected to the contact 2c of the changeover switch 2 as described above, and the other terminal V is connected to the input terminal of the voltage regulator 5 as described above. . The primary winding of the AC power transformer 4 is connected to the voltage regulator 5.
[0024]
The input terminal of the voltage regulator 5 is connected to an AC power supply, and the output terminal is connected to the primary winding of the AC power transformer 4. The voltage regulator 5 changes the AC voltage from the AC power supply and supplies the AC voltage to the AC power transformer 4. Thus, it is possible to change the output voltage of the secondary side of the AC Division electric transformer 4 from zero to a predetermined voltage V _AC.
[0025]
The residual charge detection device 6 is provided between the AC charging transformer 4 and the ground. That is, one terminal of the residual charge detection device 6 is connected to the terminal V of the AC charging transformer 4, and the other terminal is grounded. The residual charge detection device 6 includes a switch SW connected in parallel between the two terminals for short-circuiting the two terminals, a capacitor Cd for AC bypass, and a detection resistor Rd. The residual charge detection device 6 sends a signal generated between the two terminals to a low-pass filter 7.
[0026]
The low-pass filter 7 allows the DC component of the signal input from the residual charge detection device 6 to pass therethrough, amplifies it by an amplifier circuit (not shown), and sends the signal to the personal computer 8 as a signal representing the residual charge amount.
[0027]
The personal computer 8 corresponds to the processing device of the present invention. The personal computer 8 calculates a center of gravity of a residual charge distribution described later based on the received signal indicating the residual charge and generates a deterioration index.
[0028]
Next, the operation of the thus configured CV cable deterioration diagnosis apparatus according to the embodiment will be described. First, the operation of measuring the residual charge amount in the residual charge measuring device of the CV cable deterioration diagnosis device will be described with reference to the power application pattern shown in FIG.
[0029]
First, the common terminal T of the changeover switch 2 is connected to the contact 2a, and the DC voltage _VDC from the DC power supply device 3 is applied to the test cable 1 for a predetermined time. Next, the connection of the common terminal T of the changeover switch 2 is switched to the contact 2b. As a result, the test cable 1 is grounded via the protection resistor R for the time t1 (grounding time t1). Next, the connection of the common terminal T of the changeover switch 2 is switched to the contact 2c. As a result, the test cable 1 is connected to the AC charging transformer 4, and the residual charge measurement is enabled.
[0030]
In this state, the voltage adjusting device 5 is adjusted, and the AC charging voltage is applied from the secondary side of the AC charging transformer 4 to V ₁ → V ₂ → V ₃ → V ₄ → ... (V ₁ <V ₂ < V ₃ <V ₄ <...) Are output in a stepwise manner. At the same time, the residual charge amount is detected by the residual charge detection device 6 for each of the AC application voltages V ₁ , V ₂ , V ₃ , V ₄ ,... In the respective steps, and is sent to the personal computer 8 as a signal representing the residual charge amount. Sent.
[0031]
The personal computer 8 calculates the center of gravity of the distribution as a parameter representing the shape of the residual charge distribution from the signal representing the residual charge transmitted from the residual charge measuring device. Assuming that the residual charge amounts obtained by applying the AC charging voltages V ₁ , V ₂ , V ₃ , V ₄ ,... Are Q ₁ , Q ₂ , Q ₃ , Q ₄ ,. The center-of-gravity voltage Va in the residual charge amount distribution is given by the following equation for calculating a weighted average.
[0032]
_{Va = (V 1 · Q 1} + V 2 · Q 2 + V 3 · Q 3 + V 4 · Q 4 + ···) / (Q 1 + Q 2 + Q 3 + Q 4 + ···)
In a distribution in which a large amount of residual charge is obtained at a low AC application voltage, the center of gravity is on the low AC voltage side. By using this method, even if the highest AC charging voltage from which the residual charges are released is the same, it is determined that the AC voltage side having a higher center of gravity has a higher degree of deterioration. For example, in the example shown in FIG. 4, the degree of deterioration is determined to be higher in the order of type 1, type 2, and type 3.
[0033]
FIG. 3 is a graph showing the residual charge amount distribution obtained by repeatedly applying the voltage step-up and step-down multiple times from a low AC voltage to a high AC voltage in the sample showing the same residual charge emission electric field strength in FIG. This figure shows the relationship between the electric field strength at the center of gravity corresponding to the AC applied voltage at the center of gravity and the breakdown electric field strength. An increase in the electric field intensity at the center of gravity indicates that the residual charge distribution is a distribution from a high AC voltage.
[0034]
As described above, even for samples in which the breakdown electric field strength is different and the emission electric field strength is the same, it is possible to perform the deterioration diagnosis more accurately and calculate the remaining performance by classifying the specimen by the electric field strength of the center of gravity. It can be confirmed that the electric field intensity at the center of gravity is effective as a deterioration index.
[0035]
As described above, in the conventional degradation diagnosis method, when the highest AC charging voltage from which the residual charges are released is the same, the determination result of the degree of degradation is the same, but the degradation diagnosis according to this embodiment is performed. If the method is used, it is possible to classify the degree of deterioration based on the distribution shape of the residual charge amount, so that accurate deterioration diagnosis can be performed.
[0036]
【The invention's effect】
As described above in detail, according to the present invention, the characteristic of the shape of the residual charge distribution is used as a diagnostic indicator of deterioration, so that the insulation diagnosis can be accurately performed using the residual charge measurement method. A method and a degradation diagnosis device can be provided.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a CV cable deterioration diagnosis device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a power application pattern for explaining the operation of the CV cable deterioration diagnosis device according to the embodiment of the present invention.
FIG. 3 is a diagram showing a relationship between a centroid electric field strength and a breakdown electric field strength obtained by the CV cable deterioration diagnosis apparatus according to the embodiment of the present invention.
FIG. 4 is a diagram for explaining a conventional deterioration diagnosis method.
FIG. 5 is a diagram showing a relationship between a residual electric field emission field strength and a breakdown electric field strength obtained by a conventional deterioration diagnosis method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Test cable 2 Changeover switch 3 DC charging device 4 AC charging transformer 5 Voltage regulator 6 Residual charge detection device 7 Low-pass filter 8 Personal computer

Claims (4)

A residual charge measuring method for measuring a residual charge amount by applying a DC voltage to a CV cable, grounding the AC voltage, and thereafter applying an AC voltage to release charges accumulated by applying the DC voltage.
Applying power while changing the AC voltage stepwise to measure a plurality of residual charge amounts,
Calculate the center of gravity of the distribution of the obtained plurality of residual charges,
A method of diagnosing deterioration of a CV cable, wherein an AC voltage corresponding to the calculated center of gravity is used as a deterioration index. 2. The method according to claim 1, wherein the center of gravity is a weighted average of the plurality of residual charges. After applying a DC voltage to the CV cable, the CV cable is grounded, and thereafter, an AC voltage that changes in a stepwise manner is applied, thereby discharging charges accumulated by applying the DC voltage to represent a plurality of residual charge amounts. A residual charge measuring device for outputting a signal,
Calculating a center of gravity of the distribution of the plurality of residual charges based on signals indicating a plurality of residual charges output from the residual charge measuring device, and converting the AC voltage corresponding to the calculated center of gravity to a signal indicating a deterioration index; A processing device that outputs as
A deterioration diagnostic device for a CV cable, comprising: The CV cable deterioration diagnosis apparatus according to claim 3, wherein the processing device calculates the center of gravity by obtaining a weighted average of the plurality of residual charge amounts.

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