JP2015184250A - Online deterioration diagnosis device and method of power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately diagnose insulation deterioration due to water tree while a power cable to be diagnosed is kept in an online state.SOLUTION: An online deterioration diagnosis device of a power cable comprises current detection means for detecting leakage current Ie flowing in a ground line of a shield conductor of a power cable, reference signal generation means for generating a reference signal, phase adjustment means for adjusting a phase θ of the reference signal, and specific frequency component extraction means for accepting inputs of the reference signal generated by the reference signal generation means and the leakage current Ie detected by the current detection means and outputting an absolute value |I| having the same frequency component as the reference signal, of the leakage current Ie.

Description

  The present invention relates to an on-line deterioration diagnosis device for a power cable and an on-line deterioration diagnosis method for a power cable that diagnose deterioration of the power cable having a cross-linked polyethylene as an insulator online.

  Conventionally, when a power cable (CV cable, also internationally called XLPE cable) equipped with cross-linked polyethylene as an insulator is laid in an environment with moisture such as a factory or a building, water is applied to the insulator of the power cable. It is known that deterioration called a tree occurs.

  Water trees are mainly caused by wet crosslinking in the process of producing cross-linked polyethylene at the beginning of the development of power cables equipped with cross-linked polyethylene. In recent years, dry-crosslinking has overcome deterioration caused by water trees. Has been said to have been. However, it has been clarified that even a power cable manufactured by dry crosslinking begins to deteriorate due to a water tree after several decades have passed since the start of use. Therefore, there is a need for a technique for diagnosing deterioration of an insulator caused by a water tree.

  There are a residual charge method and a reverse absorption current method for diagnosing power tree water tree degradation in a state where the power is turned off and the power cable is off-line.

  However, in such a method, it is necessary to perform a construction in which the equipment is blacked out and the power cable is disconnected from the electric circuit for diagnosis, and the cost and time required for the diagnosis become enormous. Also, power cables connected to facilities such as GIS cannot be easily disconnected and cannot diagnose water tree degradation.

  Japanese Patent Application Laid-Open No. 2004-228561 measures a dielectric loss of an insulator of a power cable to be diagnosed and compares the measured dielectric loss with a dielectric loss of an insulator of a normal power cable to diagnose the deterioration of the power cable. Is disclosed. Specifically, in Patent Document 1, when measuring the dielectric loss of an insulator of a power cable to be diagnosed, an AC voltage is used as a signal source, and a current flowing through the power cable to be diagnosed is detected as a measurement signal. A reverse addition signal that is 90 ° out of phase with respect to the voltage is generated and added to the measurement signal, and the AC voltage is input to the specific frequency component extraction means using the reference signal, and the output of the specific frequency component extraction means is minimized. The magnitude of the inverse addition signal is adjusted so that the dielectric loss is calculated from the magnitude of the output.

  In Patent Document 2, an AC voltage fundamental wave of a harmonic component contained in a loss current obtained by applying an AC voltage of at least two kinds of voltage values to a power cable and applying the AC voltage and the AC voltage to the power cable. A method for diagnosing power cable degradation using the degree of change in the superimposed phase of harmonic components included in the loss current when at least two types of AC voltages are applied is measured. Yes.

Japanese Patent No. 2535292 Japanese Patent Laid-Open No. 11-6854

  In the method of Patent Document 1, a detection resistor is connected to a power cable to be diagnosed, and a current flowing through the detection resistor is used as a measurement signal. Therefore, when connecting the detection resistor to the power cable to be diagnosed, the power cable must be off-line. In the method disclosed in Patent Document 1, an AC voltage applied to a power cable to be diagnosed is input to a specific frequency component extracting unit as a reference voltage. However, since an online power cable is loaded with a high voltage of several thousand volts, an online AC voltage cannot be used as a reference voltage as it is. Therefore, in the method of Patent Document 1, it is necessary to take the power cable off-line and use a small AC voltage for diagnosis as a reference voltage at the time of diagnosis, and it is impossible to perform online diagnosis of the power cable.

  The method of Patent Document 2 must apply at least two or more types of AC voltages to the power cable, and cannot be applied to online deterioration diagnosis of a power cable to which a constant voltage is applied. In the method of Patent Document 2, an AC voltage is applied to a sample (insulator of a power cable) and a standard capacitor, and a component advanced by 90 ° from the power supply voltage phase is removed from the current flowing through the sample by a bridge circuit. Current is detected. However, in the bridge circuit, it is not possible to accurately separate the component and the loss current that are advanced by 90 ° from the power supply voltage phase having greatly different current values.

  The present invention has been made for such a problem, and an object of the present invention is to provide an on-line deterioration diagnosis device for an electric power cable and an on-line deterioration diagnosis method for an electric power cable that can accurately diagnose on-line deterioration of an electric power cable. To do.

In order to achieve the above object, the present invention has the following features.
[1] current detection means for detecting a leakage current Ie flowing through the ground line of the shield conductor of the power cable;
A reference signal generating means for generating a reference signal;
Phase adjusting means for adjusting the phase θ of the reference signal;
The reference frequency generated by the reference signal generation means and the leakage current Ie detected by the current detection means are input, and the specific frequency that outputs the absolute value | I | of the same frequency component as the reference signal in the leakage current Ie Component extraction means;
An on-line degradation diagnosis device for power cables having
[2] The on-line deterioration diagnosis device for a power cable according to [1], including a control device that extracts a loss current Ir from a leakage current Ie including a charging current Ic and a loss current Ir.
[3] The control device
The reference signal generating means is used to set the frequency of the reference signal to the same frequency as the fundamental wave component of the current flowing in the power cable, and the phase adjusting means is used to extract the phase θ of the reference signal from the specific frequency component extracting means. Is adjusted to a phase θc at which the absolute value | I |
The phase θ of the reference signal is adjusted to a phase θr delayed by 90 ° from the phase θc, and the deterioration diagnosis of the power cable is performed based on the absolute value | Ir | output from the specific frequency component extraction means at this time [2] The online degradation diagnosis device for power cables as described in 1.
[4] The power cable online deterioration diagnosis device according to [3], wherein the control device performs power cable deterioration diagnosis based on a relationship between | Ir | and | Ic |.
[5] The on-line deterioration diagnosis device for a power cable according to any one of [1] to [4], wherein the current detection means is a detachable through-type measuring AC device.
[6] Detect the leakage current Ie flowing through the ground line of the shield conductor of the power cable,
The reference signal and the detected leakage current Ie are input, and the absolute value output from the specific frequency component extraction means that outputs the absolute value | I | of the current component of the same frequency component as the reference signal in the leakage current Ie. The phase θ of the reference signal is adjusted to the phase θc so that I | becomes maximum | Ic |
The phase θ of the reference signal is adjusted to the phase θr delayed by 90 ° from the phase θc, and the power cable is diagnosed for deterioration based on the absolute value | Ir | output from the specific frequency component extraction means at this time. Online degradation diagnosis method.
[7] The power cable online deterioration diagnosis method according to [6], wherein the power cable deterioration diagnosis is performed based on a relationship between | Ir | and | Ic |.

  According to the power cable deterioration diagnosis device and the power cable deterioration diagnosis method according to the present invention, it is possible to accurately diagnose insulation deterioration due to a water tree while the power cable to be diagnosed is in an online state.

It is a figure which shows the structure of the power cable used as a diagnostic object. It is a figure which shows the mechanism in which water tree degradation generate | occur | produces. It is a figure which shows the structure of the online degradation diagnosis apparatus of the power cable which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the principle of the present invention will be described.

  FIG. 1 is a diagram illustrating a configuration of a power cable to be diagnosed. On the outer periphery of the conductor 1, an insulator 2, a shielding conductor 3, and a covering material 4 are provided in this order. The insulator 2 is made of cross-linked polyethylene. The insulator 2 is deteriorated by a water tree. The shield conductor 3 is grounded. The current flowing through the ground line is referred to as a leakage current Ie. A high voltage such as several thousand volts is loaded on the conductor 1 of the power cable configured as described above.

  FIG. 2 is a diagram illustrating a mechanism in which water tree deterioration occurs. If the power cable is laid in an underground environment such as underground, water penetrates into the insulator 2. When water penetrates into the insulator 2, a cavity 5 of about several μm is generated in the insulator 2.

  The cavity 5 grows in a dendritic shape over time. This dendritic cavity is called a water tree 6. As this deterioration progresses, for example, dielectric breakdown occurs approximately 30 years after the start of use.

  The present invention proposes an on-line deterioration diagnosis device and an on-line deterioration diagnosis method for a power cable that can diagnose the degree of deterioration caused by a water tree in this manner online with a high voltage applied to the power cable.

  The leakage current Ie flowing through the shielding conductor 3 can be expressed as a combined current of a current Ic leaked from the capacitance component (hereinafter, charging current Ic) and a current Ir leaked from the resistance component (hereinafter referred to as loss current Ir). The charging current Ic flows with a 90 ° phase advance with respect to the voltage of the conductor 1, and the loss current Ir flows with the same phase as the voltage of the conductor 1.

Ie = Ic + Ir
It can be considered that the insulator 2 is sandwiched between the conductor 1 and the shield conductor 3, and a kind of capacitor is formed by the conductor 1, the shield conductor 3, and the insulator 2. The charging current Ic flows through this capacitor due to the voltage of the conductor 1. Therefore, the main component of the leakage current Ie is the charging current Ic.

  It is known that the loss current Ir increases when the insulator 2 of the power cable is deteriorated by the water tree. This loss current Ir has non-linearity. Therefore, it is possible to diagnose the deterioration of the power cable by extracting the component of the loss current Ir from the leakage current Ie flowing through the ground line. However, the magnitude of the loss current Ir is 1/100 or less of the charging current Ic, and the loss current Ir must be accurately extracted from the leakage current Ie.

  In the embodiment according to the present invention, a charging current Ic, which is a main component, is removed from the leakage current Ie and a minute loss current Ir is extracted using the following apparatus.

  FIG. 3 is a diagram showing a configuration of the power cable online deterioration diagnosis device according to the embodiment of the present invention.

  The power cable online deterioration diagnosis apparatus includes a current detection unit 11, a specific frequency component extraction unit 12, a reference signal generation unit 13, and a phase adjustment unit 14. In FIG. 3, the conductor 1 constituting the power cable is indicated by a solid line, and the shielding conductor 3 is indicated by a dotted line.

  The current detection means 11 is attached to the ground line of the power cable to be diagnosed and detects the leakage current Ie. As the current detection means 11, a detachable through-type AC current transformer can be used.

  The specific frequency component extraction unit 12 receives the leakage current Ie detected by the current detection unit 11 and the reference signal from the reference signal generation unit 13. The specific frequency component extraction unit 12 outputs the absolute value | I | of the current having the same frequency component as the frequency of the reference signal included in the input leakage current Ie. As the specific frequency component extraction means 12, a lock-in amplifier can be used.

  The reference signal generator 13 generates a reference signal having an arbitrary frequency. A phase adjustment unit 14 is connected to the reference signal generation unit 13. The phase adjusting unit 14 adjusts the phase θ of the reference signal.

  Next, an on-line degradation diagnosis method for power cables using the apparatus configured as described above will be described.

  The current detection means 11 is attached to the ground line of the power cable to be diagnosed, and the apparatus shown in FIG. 3 is set on the power cable.

  The reference signal generator 13 sets the frequency of the reference signal to be output to the same frequency as that of the power system to which the power cable to be diagnosed is connected (step 1). For example, if the frequency of the power system to which the power cable to be diagnosed is connected is 60 Hz, the frequency of the reference signal is adjusted to 60 Hz.

  As a result, the specific frequency component extraction unit 12 outputs the absolute value | I | of the current having the same frequency component as the frequency of the fundamental component of the power cable, which is included in the leakage current Ie.

  In this state, the phase θ of the phase adjusting unit 14 is adjusted so that the absolute value | I | output from the specific frequency component extracting unit 12 becomes maximum. Since the main component of the leakage current Ie is the charging current Ic as described above, the phase of the charging current Ic and the specific frequency component are adjusted by adjusting the phase θ so that the absolute value | I | The phase of the signal output from the extracting means 12 is matched (step 2). The absolute value | I | of the frequency component output from the specific frequency component extraction unit 12 after the phase adjustment and the phase θ of the phase adjustment unit 14 at that time are defined as an absolute value | Ic | and a phase θc.

  The phase adjusting means 14 is operated to adjust the phase θ of the reference signal to a phase delayed by 90 ° from the phase θc (step 3). At this time, the absolute value | I | output from the specific frequency component extracting unit 12 and the phase θ of the phase adjusting unit 14 at that time are defined as an absolute value | Ir | and a phase θr. The absolute value | Ir | and the phase θr correspond to the loss current Ir. Then, based on the absolute value | Ir |, the deterioration diagnosis of the power cable is performed (step 4).

  For example, in step 4, | Ir | / | Ic | is calculated. Then, | Ir | / | Ic | is compared with a preset threshold value. If | Ir | / | Ic | is larger than this threshold value, the insulator 2 of the power cable to be diagnosed Judge that water tree has deteriorated.

  Specifically, according to IEEE Std 400-2001, when | Ir | / | Ic | is 0.4% or more, it is necessary to be careful, and when 1.0%, it can be determined that an abnormality due to a water tree has occurred. Has been.

  Such measurement and determination of the power cable are performed for each of the three-phase cables to diagnose the power cable.

  In the above description, the deterioration due to the water tree is determined based on the calculated | Ir | / | Ic |. However, | Ic | may not be used for diagnosis. For example, the deterioration due to the water tree may be determined by comparing the absolute value | Ir | with a threshold value determined by the current value flowing through the power cable. Even when | Ic | is used for diagnosis, the power cable may be diagnosed using any value as long as it is based on the relationship between | Ir | and | Ic |.

  As described above, in the present embodiment, by using the specific frequency component extracting unit 12, the charging current Ic is accurately extracted from the leakage current Ie, and as a result, the loss current Ir can be detected with high accuracy. Therefore, the influence of noise (charging current Ic) superimposed on the loss current Ir when the power cable is online can be accurately removed.

  In addition, the leakage current Ir that flows with a 90 ° phase delay with respect to the charging current Ic is measured with reference to the charging current Ic that is the largest current component of the leakage current Ie, and therefore flows in the conductor 1 of the power cable. Without measuring the voltage signal, the deterioration diagnosis of the power cable can be performed only by measuring the leakage current Ie flowing through the ground line. Therefore, there is no need to power out the power cable, and the power cable can be diagnosed in an online state.

  Further, in the present embodiment, by using a detachable through-type measuring current transformer as the current detection means 11, diagnosis can be performed safely without opening the circuit.

  In addition, you may comprise so that the process of step 1-step 4 may be performed artificially, a computer (control apparatus) is provided in an online degradation diagnosis apparatus, and arbitrary processes of step 1-step 5 are performed by a computer. You may comprise so that it may carry out automatically.

  In the above description, the power cable online deterioration diagnosis device and the deterioration diagnosis method have been described. However, the power cable online deterioration diagnosis method may be configured as a program that is executed by a computer.

DESCRIPTION OF SYMBOLS 1 Conductor 2 Insulator 3 Shielding conductor 4 Cover material 5 Cavity 6 Water tree 11 Current detection means 12 Specific frequency component extraction means 13 Reference signal generation means 14 Phase adjustment means

Claims (7)

Current detection means for detecting a leakage current Ie flowing in the ground line of the shield conductor of the power cable;
A reference signal generating means for generating a reference signal;
Phase adjusting means for adjusting the phase θ of the reference signal;
The reference signal generated by the reference signal generation means and the leakage current Ie detected by the current detection means are input, and the absolute value | I | of the current having the same frequency component as the reference signal is output from the leakage current Ie. Specific frequency component extraction means;
An on-line degradation diagnosis device for power cables having   The on-line deterioration diagnosis device for a power cable according to claim 1, further comprising a control device that extracts a loss current Ir from a leakage current Ie composed of a charging current Ic and a loss current Ir. The control device
The reference signal generating means is used to set the frequency of the reference signal to the same frequency as the fundamental wave component of the current flowing in the power cable, and the phase adjusting means is used to extract the phase θ of the reference signal from the specific frequency component extracting means. Is adjusted to a phase θc at which the absolute value | I |
The phase θ of the reference signal is adjusted to a phase θr delayed by 90 ° from the phase θc, and the deterioration diagnosis of the power cable is performed based on the absolute value | Ir | output from the specific frequency component extracting means at this time. The online degradation diagnosis device for power cables as described in 1.   4. The on-line deterioration diagnosis device for a power cable according to claim 3, wherein the control device performs deterioration diagnosis of the power cable based on a relationship between | Ir | and | Ic |.   The on-line degradation diagnosis device for a power cable according to any one of claims 1 to 4, wherein the current detection means is a detachable through-type measuring AC device. Detect the leakage current Ie flowing through the grounding wire of the shield conductor of the power cable
The reference signal and the detected leakage current Ie are input, and the absolute value output from the specific frequency component extraction means that outputs the absolute value | I | of the current component of the same frequency component as the reference signal in the leakage current Ie. The phase θ of the reference signal is adjusted to the phase θc so that I | becomes maximum | Ic |
The phase θ of the reference signal is adjusted to the phase θr delayed by 90 ° from the phase θc, and the power cable is diagnosed for deterioration based on the absolute value | Ir | output from the specific frequency component extraction means at this time. Online degradation diagnosis method.   The power cable online deterioration diagnosis method according to claim 6, wherein the power cable deterioration diagnosis is performed based on a relationship between | Ir | and | Ic |.

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