JP2001153913A - Method for diagnosing insulation deterioration of cv cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating a region section where a water tree deteriorates locally, and evaluating the degree of its deterioration, by solving such problem that the quantity of measured charge by a residual charge measuring method heretofore in use is an average quantity of the whole of a cable, and that it is difficult to judge whether the cable deteriorates locally or uniformly and slightly. SOLUTION: When insulation deterioration of the CV cable is diagnosed by residual charge measurement, the first reflected wave measurement to be performed by inputting pulselike voltage from one end of the cable and measuring its reflected wave is performed before applying DC voltage, and the second reflected wave measurement similar to the first measurement is performed after the application of the DC voltage, and the third reflected wave measurement similar to the above-mentioned measurement is performed after the first application of AC voltage. On the basis of the measured reflected wave information, the region of generation of a locally deteriorated water tree is detected. Besides, the degree of deterioration of the region of generation of this water tree is evaluated, on the basis of the quantity of residual charge measured when the AC voltage is applied, and the region of generation of the deteriorated water tree found by the method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating insulation deterioration of a CV cable, in particular, a section of a water tree where a local tree is extremely deteriorated, and evaluating the degree of deterioration.

[0002]

2. Description of the Related Art When a CV cable is used for a long time under wet conditions, water trees may be generated in a cable insulator. Since the water tree causes the insulation performance to deteriorate, it is necessary to diagnose and grasp the insulation deterioration state of the CV cable for stable power supply.

Many methods have been proposed for diagnosing the water tree deterioration.

[0004] There is a residual charge measurement as a method of diagnosing insulation deterioration capable of detecting water tree deterioration of a CV cable. The conventional method of measuring residual charge is to apply a DC voltage, then ground and remove the DC applied voltage, and then apply a single AC applied voltage, and then generate the resulting DC current component. The residual electric charge is calculated by detecting and integrating the obtained current signal.

[0005]

The residual charge measurement method described above has a good correlation with the degree of water tree deterioration and breakdown voltage, and is attracting attention as an insulation deterioration diagnosis method. The total charge detected from the entire cable is to be evaluated, and the measured amount is the average amount of the entire cable, and it is determined whether the deterioration is extremely local or extremely slight There is a problem that you can not. On the other hand, the most influential on the insulation performance is extremely deteriorated water trees, which need to be accurately detected.

[0006]

According to the method of diagnosing deterioration of insulation of a CV cable according to the present invention, a DC voltage is applied to a CV cable, then grounded, an AC voltage Va is applied, and then an AC voltage Vb (Vb > Va) and measuring the residual charge at the time of applying each AC voltage to diagnose insulation deterioration, wherein a pulsed voltage is input from one end of the cable and reflected before the DC voltage is applied. A first reflected wave measurement for measuring a wave; a second reflected wave measurement for measuring the reflected wave while inputting the pulsed voltage from one end of the cable after applying the DC voltage; and applying the AC voltage Va. After the power is supplied, the pulsed voltage is input from one end of the cable and a third reflected wave measurement for measuring the reflected wave is performed, and the reflection measured by the first, second, and third reflected wave measurements is performed. Based on the information, and detecting the extreme degradation water tree generation region.

[0007] Further, the degree of deterioration of the water tree generation area is evaluated based on the measured residual charge amount at the time of applying the AC voltage and the deteriorated water tree generation area obtained by the above method. I do.

According to the present invention, when water tree is generated in the CV cable, the impedance of the water tree generation area changes as compared with that of the cable due to the water tree. When a pulsed voltage is input, a reflected wave is generated at a place where an impedance change occurs.

[0009] When DC power is applied as a pre-application in the residual charge measurement, polarization occurs inside the water tree, and electric charges are accumulated inside the water tree. Due to this charge accumulation, the resistance of the water tree section changes as compared with the case where no charge is accumulated. That is, due to the presence of the water tree in which the charge accumulation has occurred in the CV cable, the cable impedance changes at that point as compared to before the DC voltage is applied. At this time, when a pulsed voltage is input from one end of the cable, a reflected wave different from the reflected wave before the power application is generated.

On the other hand, in the residual charge measurement, a certain voltage V
Even when Vb (Vb> Va) is applied after a is applied, a residual charge signal is also detected. The residual charge detected at this time is due to the extremely deteriorated water tree region. Therefore, after applying Va, the impedance of the water tree deterioration region caused by the residual charge generated by Va returns to the impedance before DC application. On the other hand,
At this time, since the electric charge remains only at the location where the extreme deterioration has occurred, the impedance in this region remains the same. Therefore, before applying Va and V
After applying a, a pulsed voltage is input, and the reflected wave is compared between the two to detect a region where the charge to be released at the AC voltage of Vb is accumulated (extremely deteriorated region). Becomes possible. That is, it is possible to detect an extremely deteriorated region locally.

Further, by measuring the amount of charge released at the AC voltage of Vb, and decreasing the amount of charge in the region obtained above,
The degree of deterioration of this region can be evaluated.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram of the residual charge measuring circuit according to the present invention. In FIG. 3, first, the changeover switch 5 is connected to the contact 5a side, and the DC voltage VDC from the DC power supply device 2 is applied to the test CV cable 1 for a predetermined time. Thereafter, the changeover switch 5 is switched to the contact 5b, and the test CV cable 1 is grounded. Next, the changeover switch 5 is switched to the contact 5c to be connected to the test transformer 3 for AC power application, thereby establishing a circuit state in which measurement of residual charge and AC power application are possible. An induction voltage regulator 4 is connected to the primary winding side of the test transformer 3 so that the output voltage on the secondary side of the test transformer 3 is changed from zero to VAC.
Change by. The low-voltage terminal V of the test transformer 3
The residual charge measuring device 6 is connected between the shielding layer of the test CV cable 1 and ground.

The CV cable insulation deterioration diagnosis of the present invention is performed using the above-described residual charge measuring circuit.

First, a first reflected wave measurement before DC voltage application is performed.

In FIG. 1, when water tree is generated in the CV cable 1, the impedance of the water tree generation area changes (Z0 → Za, Zb) compared to the impedance of the cable due to the water tree. When a pulsed voltage is input from one end of the cable, reflected waves A, B, and C are generated at impedance change points A, B, and C. This reflected wave can be observed at the input end.
Since the propagation speed of the pulsed voltage in the cable is a known value, the distance Ld to the region where moisture is mixed can be specified by the time difference td between the input end of the input wave and the input end of the reflected wave. That is, assuming that the propagation speed of the pulse voltage in the cable is cp, Ld = ｄ × td × cp.

Next, a second reflected wave measurement is performed. When a pulsed voltage (same as above) is input from one end of the cable after DC power application, a reflected wave A ^* , a reflected wave B ^* , and a reflected wave C ^* are generated as shown in FIG. This reflected wave is different from the reflected wave before the DC application, that is, due to the presence of the water tree in which the charge accumulation occurs in the CV cable, the cable impedance is lower at that point than before the DC voltage is applied. It is because it changes at.

Next, a third reflected wave measurement is performed. In the residual charge measurement, the application of the DC voltage is followed by the application of the AC voltage twice in the application pattern shown in FIG. After the first voltage Va is applied, when the same pulsed voltage is input from one end of the cable, as shown in FIG.
A reflected wave A, a reflected wave B ^* , and a reflected wave C ^* are generated. This reflected wave A is the reflected wave A at the time of the first reflected wave measurement before DC power application. That is, after the application of the voltage Va, the slight impedance of the water tree deterioration region caused by the residual charge generated by the DC application returns to the impedance Za before the application of the DC voltage. On the other hand, at this time, since the electric charge remains only in the place where extreme deterioration has occurred, the impedance in this region remains Zb ^* .

Therefore, before applying the voltage Va and after applying the voltage Va, a pulse-like voltage is input from one end of the cable, and the reflected waves are compared with each other to be emitted at the second applied voltage Vb. It is possible to detect a region where the electric charge is accumulated (extremely deteriorated region).

Further, the section distance of the locally water-tree-deteriorated region obtained by the above-mentioned reflected wave measurement, the residual charge amount Q1 measured during the first AC power application, and the second AC power application. Based on the measured residual charge amount Q2, it is possible to evaluate the degree of deterioration for each region section.

[0020]

As described above, according to the method for diagnosing insulation deterioration of a CV cable according to the present invention, it is possible to accurately evaluate an area in which water tree is locally deteriorated, including its section distance. Thereby, the water tree deterioration diagnosis of the CV cable can be accurately performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of an insulation deterioration diagnosis method according to the present invention.

FIG. 2 is an explanatory view showing a power application method in residual charge measurement according to the present invention.

FIG. 3 is a circuit diagram for performing a residual charge measurement according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 CV cable 2 DC charging device 3 AC charging transformer 4 Induction voltage regulator 5 Changeover switch 6 Residual charge measuring device

Claims (2)

[Claims] An AC voltage Va is applied to a CV cable after applying a DC voltage to the CV cable, and then an AC voltage Vb (Vb> Va) is applied to the CV cable. In the method for diagnosing insulation deterioration by measuring electric charge, a first reflected wave measurement for inputting a pulsed voltage from one end of a cable and measuring a reflected wave thereof before applying the DC voltage; After the charging, the pulsed voltage is inputted from one end of the cable and the second reflected wave measurement for measuring the reflected wave thereof. After applying the AC voltage Va, the pulsed voltage is inputted from one end of the cable and Performing a third reflected wave measurement for measuring the reflected wave, and detecting an extremely deteriorated water tree generation region based on the reflected wave information measured in the first, second, and third reflected wave measurements. CV insulation degradation diagnosis method of the cable characterized by. 2. A method for diagnosing deterioration of insulation by measuring residual charge according to claim 1, wherein the amount of residual charge measured when the AC voltage is applied and the deterioration obtained from the method according to claim 1. A method of diagnosing insulation deterioration of a CV cable, comprising: evaluating a degree of deterioration of the deteriorated water tree generation area based on the water tree generation area.