JP2007046908A - Insulation deterioration diagnostic method and insulation deterioration diagnostic system of power cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose a deterioration in insulation of a cable having large thickness insulation, capable of easily applying the same, even in a narrow site. <P>SOLUTION: The insulation deterioration diagnostic system 100 diagnoses deteroration in the cable 20 under measurement by impressing voltages with a selector switch 140 upon their drop with the AC voltage held for a prescribed time, after raising to a prescribed value after the DC voltage has been impressed and grounded, and by measuring the remaining charges constrained in the insulator 22 with the short circuit switch 145 and detection circuit C<SB>d</SB>, at AC voltage impression, with the remaining charge. A fixed time interval for impressing the AC voltage is set from the remaining charge value measured under the AC voltage impression satisfies the function that decays with a fixed time constant, and represents the error charges included in the remaining charges. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an insulation deterioration diagnosis method for a power cable, and more particularly to an insulation deterioration diagnosis method and an insulation deterioration diagnosis apparatus for diagnosing insulation deterioration of a power cable caused by a water tree.

  As one of the major insulation deterioration phenomena that determine the withstand voltage life characteristics of rubber and plastic power cables such as cross-linked polyethylene insulated power cables (hereinafter referred to as CV (Cross-linked polyethylene insulated polyvinyl-chloride sheathed cable) cables) There is tree degradation.

  This water tree degradation is caused by the concentration of electric fields such as voids, foreign matter, and protrusions in the insulator when an AC voltage is applied to rubber / plastic power cables over a long period of time in an environment where water exists. Moisture is accumulated in the part, and a minute water void group is formed, which is a phenomenon that occurs in the electric field direction.

  As the water tree grows, this water tree lowers the breakdown voltage and eventually causes a breakdown of the power cable during operation. For this reason, in the insulation deterioration diagnosis of power cables such as CV cables, it is an important issue to detect water tree deterioration with high reliability.

  Therefore, the residual charge method has been developed as an effective method for detecting water tree deterioration of power cables such as CV cables. The procedure of the residual charge method will be described with reference to FIG. In the residual charge method, first, a DC voltage is applied to the cable insulator as shown in FIG. 5A, and then the electrodes of the insulator are short-circuited and grounded as shown in FIG. 5B. Then, as shown in FIG. 3C, an AC voltage or the like is applied to the insulator, and a DC component appearing at this time is detected as a deterioration signal due to the water tree.

  In the residual charge method, space charges are accumulated in the insulator by applying a direct current voltage or the like to the power cable. Next, the conductor and shielding charge (not shown) due to the DC applied voltage are removed by short-circuiting and grounding between the electrodes of the insulator. During this time, the space charge of the deteriorated portion, that is, the charge restrained in the insulator (space charge in the water tree, etc.) partially remains without disappearing. After that, due to the application of AC voltage, the charge (space charge in the water tree, etc.) constrained in the insulator is quickly released and released, and the charge or DC current accompanying the transfer of charge is a degradation signal. As detected by the detector.

  When this residual charge method is applied to a local laid line such as a power cable, it is known that the charge generated from other than the water tree accumulated at the interface of the connection part causes a decrease in reliability as an error factor. ing.

  As a countermeasure, for example, there is a cable insulation deterioration diagnosis method described in Patent Document 1. In the method of Patent Document 1, the residual charge originated from highly harmful water trees (long water trees or water trees with high internal conductivity) is caused by other factors (small water trees, connection interface, etc.). This is based on the knowledge that the response speed to AC charging is very fast compared to the residual charge of origin, and the response is completed in a few seconds.

  That is, the charge response due to the degradation is fast, the charge due to the error factor is slow, and only the residual charge component (degradation signal) that has a fast response is extracted.

  Specifically, as shown in FIG. 6, the insulation deterioration diagnosis method of Patent Document 1 firstly has an AC voltage from zero to a predetermined value that is equal to or greater than the relaxation time of the residual charge generated from the deteriorated portion, and The voltage is boosted for a time shorter than the relaxation time of the residual charge unrelated to deterioration (about 5 seconds) and then lowered to zero without holding the voltage. taking measurement. In addition, the fall time from the step-up of the AC voltage to 0 is about 12 to 13 seconds.

This operation is repeated three times in succession, and the increase in the residual charge due to the first AC charging is ΔQ ₁ , the increase in the residual charge due to the second AC charging is ΔQ ₂ , and the third AC Let ΔQ _{3 be} the increase in residual charge due to the applied voltage. The uses charge minus _{ΔQ 2 × (ΔQ 2 / ΔQ} 3) from _{ΔQ 1 Q 0 = ΔQ 1 -ΔQ} 2 × a (ΔQ ₂ / ΔQ ₃₎ the deterioration determination amount.

By this method, only charges with a quick response to AC charging can be extracted, and the reliability of diagnosis is greatly improved.
Japanese Patent Laid-Open No. 11-148959

  By the way, the response of the residual charge to the AC voltage application becomes slower as the insulation thickness is larger under the same voltage application condition for a fixed length of water tree. For example, in a 22 kv class (insulation thickness 6-8 mm) cable, the response speed of residual charges generated from harmful water trees to the AC voltage used for ground is about several seconds, but 66 kv class (insulation thickness 9-14 mm). In this case, it is about 1.5 to 2 times slower.

  In the conventional method shown in Patent Document 1, for example, the insulation deterioration diagnosis of a cable with a small insulation thickness such as a 22 kv class cable can be performed, but the insulation deterioration diagnosis of a cable with a large insulation thickness such as a 66 kv class cable is performed. The detection sensitivity may be reduced.

  In other words, when the insulation deterioration diagnosis of a cable having a large insulation thickness is performed using a conventional method, the response of the cable having a small insulation thickness such as a 22 kv class cable is as shown by B portion in the residual charge graph shown in FIG. The reaction is fast and the reaction is completed in the first short-time voltage application. On the other hand, in the case of a cable with a large insulation thickness such as a 66 kv class cable, as shown in part A in the residual charge graph of FIG. May be detected in the second short-time power application.

Using this result, if the deterioration signal is calculated by Q ₀ = ΔQ ₁ −ΔQ ₂ × (ΔQ ₂ / ΔQ ₃ ), the calculated deterioration signal Q ₀ becomes a smaller value than the actual deterioration signal Qs. As a result, the detection sensitivity may be lowered.

  In order to cope with this, it is conceivable to increase the AC applied voltage value in order to effectively discharge the electric charge constrained in the insulator that causes the measurement.

  However, as the AC voltage to be applied is increased, the AC transformer used for measurement becomes larger and the diagnostic equipment becomes larger, which makes it difficult to apply to narrow sites.

  Therefore, there is a demand for a method that can accurately perform insulation deterioration diagnosis even for a power cable such as a CV cable having a large insulation thickness, and that can be applied even in a narrow field.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is capable of performing an insulation deterioration diagnosis of a cable having a large insulation thickness, and can be easily applied to a narrow site, and an insulation deterioration diagnosis method and an insulation deterioration diagnosis apparatus for a power cable. The purpose is to provide.

  The method for diagnosing deterioration of a power cable according to the present invention is a power cable in which a DC voltage is applied to a power cable and then grounded, and after the grounding, an AC voltage is applied to the power cable and a residual charge of the power cable is measured. In the insulation deterioration diagnosis method, after the grounding, the AC voltage is boosted to a specified value with respect to the power cable, and then held for a certain period of time to reduce the voltage and apply the voltage. After performing the residual charge measurement step of measuring the residual charge of the power cable generated by the application of the DC voltage under the applied voltage, and the AC voltage application step and the residual charge measurement step in order several times, A deterioration diagnosis step of diagnosing the deterioration of the power cable using the residual charge measured in the residual charge measurement step, and the fixed time in the AC voltage application step The residual charge value measured under the AC voltage division electrodeposition is to be set based on the time that satisfies the exponential function representing an error charge contained in the residual charge.

  According to this method, after DC power is applied to the power cable, the AC voltage is boosted to a specified value, then held for a certain period of time to decrease the voltage, and the DC voltage is applied under this AC voltage. The process of measuring the residual charge of the power cable caused by electricity is repeated a plurality of times. The fixed time at this time is set based on the time when the residual charge value measured under the AC voltage application satisfies the exponential function representing the error charge contained in the residual charge, and thus is measured under the AC voltage application. The residual charge is not saturated. For this reason, in addition to the deterioration charge of the power cable having a quick response at the time of measurement, the error charge having a slow response can be surely included in the residual charge measured under the application of the AC voltage. Therefore, it is possible to accurately diagnose insulation deterioration by deterioration diagnosis using a plurality of measured residual charges.

  According to the present invention, even when a cable having a large insulation thickness is used, it is possible to perform insulation deterioration diagnosis by sufficiently applying an AC voltage to an insulating portion, and when performing AC voltage application. In addition, since it is not necessary to increase the AC voltage, no equipment for applying a large AC voltage is required, and the present invention can be easily applied even in a narrow field.

  The essence of the present invention is that a DC voltage is applied to a power cable, and then grounded, and then, after AC voltage is boosted a plurality of times to measure residual charges, the AC voltage is boosted, and then at a specified voltage. The alternating current short-time voltage application is performed by holding the voltage for a certain time and stepping down, and the deterioration signal is calculated using the detection signal detected at this time.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments to which an insulation deterioration diagnosis method for power cables according to the present invention is applied will be described in detail below with reference to the drawings.

FIG. 1 is a diagram illustrating a configuration of an insulation deterioration diagnosis device 100 and a measurement target cable 20 according to an embodiment of the present invention. In FIG. 1, an insulation deterioration diagnosis apparatus 100 includes a DC power supply 110, a ground resistor 120, an AC voltage generator (transformer or the like) 130, a variable voltage regulator 132, and an AC voltage switch 134. The switch 140, the short circuit switch 145, a detection circuit (detection capacitor) _Cd, and a control unit 160 are provided.

  The measurement target cable 20 includes a conductor 21, an insulator 22 that covers the periphery of the conductor 21, a metal shielding layer 23 that covers the periphery of the insulator 22, and the like. In the measurement target cable 20 shown in FIG. 1, an electrostatic capacity is formed between the conductor 21 and the metal shielding layer 23. Further, a lead wire from the changeover switch 140 is connected to the end portion 24 of the measurement target cable 20.

The DC power supply 110 has a positive electrode side grounded and a negative electrode side connected to the contact 140a of the changeover switch 140, and outputs a DC voltage _Vdc . In this case, the DC voltage V _dc of the DC power supply 110 is negative, but there is no problem even if it is positive.

One end of the ground resistor (R _G ) 120 is grounded, and the other end is connected to the contact 140 b of the changeover switch 140.

The AC voltage applying voltage generator 130 is connected to the contact point 140c of the changeover switch 140, and outputs the AC voltage _Vac .

  In this AC applied voltage regulator 130, one end of the primary coil is connected to the variable voltage regulator 132, and the other end of the primary coil is grounded. A voltage from an AC power source is input to the primary coil via the variable voltage regulator 132.

Further, in the AC voltage applying voltage generator 130, one end of the secondary coil is connected to the contact 140 c of the changeover switch 140 and is connected to the measurement target cable 20 via the changeover switch 140. The other end of the secondary coil is connected to a grounding unit, and a detection circuit _Cd is connected in series with the grounding unit.

The alternating voltage applied voltage regulator 130 thus connected boosts the alternating voltage input via the variable voltage regulator 132 to generate an alternating voltage V _ac and output it to the measurement target cable 20. That is, the AC voltage V _ac is applied to the measurement target cable 20.

The variable voltage regulator 132 varies the voltage input from the AC power source when the AC voltage application switch is ON and outputs the variable voltage to the AC voltage application voltage generator 130. That is, the variable voltage regulator 132 adjusts the level of the AC voltage V _ac applied to the measurement target cable 20.

Here, the variable voltage regulator 132 is controlled by the control unit 160. That is, the level of the AC voltage V _ac applied to the measurement target cable 20 is adjusted by the control signal from the control unit 160.

  The AC power application switch 134 is supplied with a voltage from the upstream AC power supply to the variable voltage regulator 132 connected downstream by closing the contact. The AC power application switch 134 is controlled by the control unit 160 to open and close.

  The changeover switch 140 includes three contact points 140a to 140c and a movable piece 140d connected to the end portion 24 of the measurement target cable 20 on the downstream side.

The changeover switch 140 connects the movable piece 140d to the contact 140a when the DC voltage _Vdc is applied to the measurement target cable 20, and connects the movable piece 140d to the contact 140b when the measurement target cable 20 is grounded. Further, the changeover switch 140 connects the movable piece 140d to the contact 140c when the AC voltage _Vac is applied to the measurement target cable 20.

By switching the movable piece 140d of the changeover switch 140 in this way, in the insulation deterioration diagnosis device 100, the DC voltage V _dc is applied to the terminal portion 24 of the measurement target cable 20, grounded, and the AC voltage V _ac is applied. It is possible to charge electricity.

The detection circuit C _d is used to detect the residual charge of the insulator 22 of the cable 20 to be measured. The detection circuit C _d is connected in parallel to the DC voltage component V _d (t between terminals of the detection circuit C _{d in} parallel. ) And a short-circuit switch 145 are connected to each other. Incidentally, the short-circuit switch 145 short-circuits the detecting circuit C _d by closing its contacts.

The DC voltage component V _d (t) between the terminals of the detection circuit C _d is detected by the DC voltmeter 153 as residual charge information of the measurement target cable 20. This residual charge information Q (t) is represented by C _d × V _d (t).

DC voltmeter 153 outputs the residual charge information based on the inter-terminal DC voltage component of the detected detection circuit C _d to the control unit 160.

  The control unit 160 controls the variable voltage regulator 132, the AC voltage application switch 134, and the like to apply an AC voltage to the cable 20 to be measured, an AC voltage application time, an AC voltage holding time, and a voltage value. Control the timing of AC power application.

  In addition, the control unit 160 uses the detection signal input from the DC voltmeter 153 to extract only the deterioration signal from the residual charges of the measurement target cable 20.

  In addition, according to the specification of the measurement target cable 20, after applying a DC voltage to the measurement target cable 20 and grounding, the AC application in which an AC voltage is applied for a predetermined time with a specified voltage is called AC short-time application. Here, the control unit 160 performs AC short-time power application for applying power while holding a predetermined AC voltage for a certain period of time at predetermined intervals. The operation control of the variable voltage regulator 132 and the AC power application switch 134 may be performed by a device other than the control unit 160. In addition, in the insulation deterioration diagnosis device 100, the control unit 160 may perform operation control of the changeover switch 140, the short-circuit switch 145, and the like.

  The AC short-time power application controlled by the control unit 160 is performed on the basis that the response time of the residual charge of the measurement target cable 20 that responds when an AC voltage is applied differs depending on the generation source.

  Specifically, the charge response due to deterioration (detected as a deterioration signal) is fast, and the charge response due to an error factor (detection as an error signal) is slow.

  Based on the relationship between the charge due to the deterioration and the response time of the charge due to the error factor, the control unit 160 applies the DC voltage to the measurement target cable 20 after grounding (specifically, the insulator of the measurement target cable 20). 22), the short-time application of the AC voltage, which is a feature of the present insulation deterioration diagnosis method, is performed a plurality of times, here three times, and in each case, the insulation deterioration diagnosis is performed using the detected residual charges.

  Next, the measurement procedure of the measurement target cable 20 in the insulation deterioration diagnosis apparatus 100 of FIG. 1 will be described.

FIG. 2 is a diagram showing an example of an embodiment of the method for diagnosing deterioration of a power cable according to the present invention, and is a timing chart showing an AC power application procedure to a measurement target cable and a measured DC voltage. In FIG. 2, a graph G1 shows an AC voltage V _ac to be applied, a graph G3 is a deterioration signal, a graph G6 is an error signal, and a graph G7 is a detection signal (deterioration signal and error detected during AC application). It is a graph which shows (addition of a signal) as a residual charge (Q (t)). In FIG. 2, t ₁ , t ₂ , and t ₃ are AC application times, Qs is a deterioration signal, ΔQ _{E1 to} ΔQ _E3 are error signals that are slower in response than the deterioration signal, and ΔQ _{1 to} ΔQ ₃ are detected. A signal (residual charge), Δt indicates a voltage holding time.

In the insulation deterioration diagnosis method of the present embodiment, a DC voltage is applied to the cable 20 to be measured and then grounded. After the grounding, AC short-time application is performed a plurality of times at a predetermined timing, here three times. In the method of calculating the residual charge of the cable 20 to be measured, that is, the degradation signal Qs, using the charges (ΔQ _{1 to} ΔQ ₃ ) detected as the detection signal, the AC voltage is boosted to a specified value, and then for a certain time. It is characterized by holding the voltage.

  In this insulation degradation diagnosis method, in order to complete all the responses in the first short-time voltage application for charges that are slightly delayed in response to alternating current, in each short-time voltage application, the voltage is increased to the specified voltage, Hold for a certain time and step down at the same speed as boost.

  That is, an AC voltage applying process in which a DC voltage is applied to the measurement target cable 20 and grounded, and then the AC voltage is boosted to a specified value, then held down for a certain period of time and then applied, and AC is applied. Under voltage application, the residual charge measurement process for measuring the residual charge of the measurement target cable 20 caused by the previous DC voltage application, the AC voltage application process, and the residual charge measurement process are repeated several times in order. And a deterioration diagnosis step of diagnosing deterioration of the measurement target cable 20 using the residual charge measured in the residual charge measurement step. The predetermined time in the AC voltage application step indicates an exponential function indicating an error charge included in the residual charge, in this case, the error charge included in the residual charge. It is set based on the time satisfying the function that decays with a constant time constant τ. In the deterioration diagnosis step, the charge detected as the deterioration signal is used in the residual charge measurement step that is performed a plurality of times in the AC voltage application step, and the detection charge that is repeatedly detected from the first detection charge thereafter. The deterioration signal of the measurement target cable 20, that is, the deterioration charge is used for insulation deterioration diagnosis.

  FIG. 3 is a conceptual diagram illustrating a method for diagnosing insulation deterioration of a power cable according to the present invention. Graphs G1 and G2 in FIG. 3 are graphs showing effective values of the AC voltage to be applied, and graph G1 is an AC voltage application in the insulation deterioration diagnosis device 100 that is held for a certain period of time after the AC application voltage is increased and then reduced. The effective value of is shown. The graph G2 shows the effective value of AC voltage charging when the AC voltage is increased immediately after the AC voltage is increased in the conventional method.

  Further, in FIG. 3, graphs G <b> 3 and G <b> 4 are graphs showing deterioration signals detected by the AC voltage application shown in graphs G <b> 1 and G <b> 2. In FIG. 3, a graph G3 shows a state in which the charges in the water tree are completely reacted when the voltage is held for a certain period of time after the AC voltage is increased and the voltage is decreased. Graph G4 shows a state in which the charge in the water tree has not reacted when the voltage is reduced immediately after the AC voltage is increased. FIG. 3 shows the superiority of the response of the degradation signal in the first AC short-time power application process by the insulation degradation diagnosis apparatus of the present embodiment as compared with the process in the conventional insulation degradation diagnosis method. Yes.

  As shown in FIG. 3, in the insulation deterioration diagnosis apparatus 100 of the present embodiment, the voltage holding time under AC short-time charging is the total time from boosting to step-down of AC short-time charging from the water tree. It is set so as to be long with respect to the response time of the charge to be generated and sufficiently short with respect to the response time of the charge generated due to an error factor other than the water tree. By applying this power application method, it is possible to completely react the charge that could not be reacted by the method of reducing the pressure immediately after the pressure increase by the first AC power application.

  When performing the insulation deterioration diagnosis method using the insulation deterioration diagnosis apparatus 100, based on the conceptual diagram of FIG. 3, the control unit 160 sets the short-time power application time t, the AC voltage holding time Δt, and the regulation in the AC short-time power application. The voltage value Vh and the AC short-time voltage application timing are set.

First, the procedure up to performing AC charging will be described with reference to FIG. The short-circuit switch 145 is short-circuited to the ground state, the movable piece 140 d of the changeover switch 140 is connected to the contact 140 a, and the DC voltage V _dc of the DC power supply 110 is applied to the terminal end 24 of the measurement target cable 20. Next, the short circuit state of the short circuit switch 145 is maintained, the movable piece 140d of the changeover switch 140 is switched from the contact point 140a to the contact point 140b, the terminal end 24 of the measurement target cable 20 is grounded, and the direct current applied to the measurement target cable 20 is applied. Remove the applied voltage.

Next, as shown in a graph G1 in FIG. 2, the insulation deterioration diagnosis apparatus 100 performs short-time AC short-time charging, which is applied at a predetermined timing while holding the AC voltage at a specified value for a certain time (Δt). It is performed between the time charging times t ₁ , t ₂ and t ₃ , respectively.

Specifically, the short-circuit switch 145 is opened, the movable piece 140d of the changeover switch 140 is switched from the contact point 140b to the contact point 140c, and the AC voltage _Vac of the AC voltage _applying voltage device 130 is applied to the terminal end 24 of the measurement target cable 20. By applying power, the first AC power is applied for a short time.

  Specifically, after performing DC voltage application and grounding on the measurement target cable 20, the control unit 160 controls the variable voltage regulator 132 and the AC application switch 134 to define the AC voltage. After the voltage is raised to the voltage, the voltage is held for a certain time Δt, and the voltage is stepped down at the same speed as the voltage boosting to perform the first short-time voltage application.

At this time, the electric charge discharged from the insulator 22 to be measured cable 20 is stored between the terminals of the detection circuit C _d. Thus charge that is discharged from the insulator 22 to be measured cable 20 is detected by the DC voltmeter 153 as inter-terminal DC voltage component of the detection circuit C _d, constrained within the insulator 22 to be measured cable 20 remaining Measured as charge ΔQ ₁ . In particular, the electric charge stored between the terminals of the detection circuit C _d is detected as a Delta] Q ₁ by the DC voltmeter 153 is outputted to the control unit 160.

After the end of the first short-time process, the controller 160 performs the second AC short-time power application in the same manner as the first time with a predetermined interval. The time charge stored in the detection circuit C _d, is detected as Delta] Q ₂ by the DC voltmeter 153 is outputted to the control unit 160. After the end of the second short-time process, the control unit 160 performs the third AC short-time power application in the same manner as the first time and the second time with a predetermined interval. At this time the charge stored in the detection circuit C _d is detected as a Delta] Q ₃ by DC voltmeter 153 is outputted to the control unit 160.

The detected charges ΔQ ₁ , ΔQ ₂ , and ΔQ ₃ are detected signals obtained by adding a deterioration signal and an error signal, in other words, a deterioration signal indicating a quick response deterioration charge and a slow response error charge. The error signal needs to be removed in order to accurately calculate the deterioration signal.

In the control unit 160, these charges ΔQ _{1 to} ΔQ ₃ are substituted into an expression of Qs≈Q ₀ = ΔQ ₁ −ΔQ ₂ × (ΔQ ₂ / Q ₃ ), and a deterioration signal (charge component with quick response) Q ₀ ≈ Qs is calculated.

The residual charge (Q (t)) including charges ΔQ ₁ , ΔQ ₂ , and ΔQ ₃ detected via the DC voltmeter 153 is generally a constant time constant indicating an error charge as shown in FIG. A function that decays with τ, for example, an exponential function f (t) = − A · {1−exp (−t / τ)} (where A> 0)
It can be approximated to FIG. 4 shows an exponential function representing an error signal for defining the voltage holding time of AC charging in AC short-time charging. Note that f (t) is not limited to the exponential function described above, and may be any function as long as it is a function that decays with a constant time constant τ indicating an error charge.

Here, the relationship of ΔQ _E1 / ΔQ _E2 ≈ΔQ _E2 / ΔQ _E3 is established by making the voltage holding time Δt during the AC short-time power application all the same during the first to third short-time power application. . As a result, the approximate expression Qs≈Q ₀ = ΔQ ₁ −ΔQ ₂ × (ΔQ ₂ / ΔQ ₃ ) can be applied as it is as the residual charge Q (t) to eliminate the influence of the error charge.

Further, Q (t) is saturated due to the finite charge. Therefore, in the range of t> t _Qf , Q (t) and f (t) do not match. Therefore, the total (t ₁ + t ₂ + t ₃ ) of the alternating current short-time charging time in the present embodiment is made smaller than the time t _{Qf at} which Q (t) = f (t) is established in FIG. Δt is set.

That is, when performing the insulation deterioration diagnosis method using the insulation deterioration diagnosis device 100, the control unit 160 equalizes each of the AC short-time power application times t ₁ , t ₂ , and t ₃ (t ₁ = t ₂ = t ₃ ) and the total alternating current short-time charging time t ₁ + t ₂ + t ₃ is smaller than t _{Qf at} f (t), that is, a time when Q (t) = f (t) is satisfied. Thus, AC short-time voltage application is performed on the measurement target cable 20.

  According to the present embodiment, power is applied three times for a short time on the measurement target cable 20 after direct current application and grounding. In order to complete all responses in the first short-time voltage application for error charges whose response to alternating current is slightly slower than the degraded charge when performing the first AC short-time voltage application, In time charging, after boosting to a specified voltage, the voltage is held for a certain period of time and then stepped down at the same speed as boosting.

The voltage holding time Δt in the short-time power application is longer than the total time t from the step-up to the step-down of the short-time power application, that is, the short-time power application time is longer than the response time of charges generated from the water tree, and It is set so as to be sufficiently short with respect to the response time of charges generated due to error factors other than from the water tree. The holding time Δt can be derived by setting the total short-time power application time t ₁ + t ₂ + t ₃ to a time smaller than the time t _{Qf at} which Q (t) = f (t) is established. The holding time Δt can be about 5 to 10 seconds.

Therefore, the charge that has not been fully reacted in the method of stepping down immediately after boosting is completely reacted by the first AC charging, and the detection signal ΔQ ₁ obtained by the first AC charging is ΔQ ₂ , ΔQ _3. In addition, the deterioration signal Qs of the measurement target cable 20 can be detected and the deterioration state can be diagnosed by being used in the equation of Qs≈Q ₀ = ΔQ ₁ −ΔQ ₂ × (ΔQ ₂ / ΔQ ₃ ).

  According to this insulation degradation diagnosis method, when the response of the residual charge that responds during AC charging is slow, for example, a cable with a large insulation thickness such as a 66 kv class cable is smaller than a cable with a small insulation thickness such as a 22 kv class. Even when the insulation deterioration diagnosis is performed, it is possible to effectively release the electric charges restrained in the insulator that causes the measurement without increasing the AC voltage to be applied.

Therefore, the insulation deterioration diagnosis of the power cable having a large insulation thickness can be performed accurately.
Further, it is possible to easily apply to a narrow field while keeping the diagnostic equipment compact without increasing the size of an AC voltage applying voltage device (for example, an AC transformer) used for measurement.

Note that in the insulation degradation diagnosis method using the insulation deterioration diagnostic device 100 when, first AC short charge by resulting residual charge (detection signal) Delta] Q ₁ is not suitably detected, the control unit 160, an AC short The voltage holding time Δt and the AC voltage applying times t ₁ , t ₂ , and t ₃ in time _charging may be variable within a range where t ₁ + t ₂ + t ₃ is smaller than t _Qf .

  Moreover, although the case where the residual electric charge restrained in the insulator of the measurement object cable 20 is measured by detecting the DC voltage between the terminals of the detection circuit has been described in the above embodiment, the present invention is limited to the configuration of the detection circuit. Instead, the residual charge may be measured using a detection means having another configuration.

  According to a first aspect of the present invention, there is provided a method for diagnosing deterioration of a power cable by grounding a power cable after applying a DC voltage, applying an AC voltage to the power cable after the grounding, and remaining the power cable. In the method of diagnosing deterioration of power cable for measuring electric charge, after the grounding, the AC voltage is boosted to a specified value for the power cable, and then the AC voltage is applied by holding the voltage for a predetermined time to reduce the voltage. And a residual charge measuring step for measuring the residual charge of the power cable generated by the application of the DC voltage under the application of the AC voltage, and the AC voltage applying step and the residual charge measuring step are sequentially repeated a plurality of times. A deterioration diagnosis step of diagnosing the deterioration of the power cable using the residual charge measured in the residual charge measurement step, and the AC voltage application step It said predetermined time kicking was as residual charge value measured under the AC voltage division electrodeposition is set based on the time that satisfies the exponential function representing an error charge contained in the residual charge.

  According to this method, after DC power is applied to the power cable, the AC voltage is boosted to a specified value, then held for a certain period of time to decrease the voltage, and the DC voltage is applied under this AC voltage. The process of measuring the residual charge of the power cable caused by electricity is repeated a plurality of times. The fixed time at this time is set based on the time when the residual charge value measured under the AC voltage application satisfies the exponential function representing the error charge contained in the residual charge, and thus is measured under the AC voltage application. The residual charge is not saturated. For this reason, in addition to the deterioration charge of the power cable having a quick response at the time of measurement, the error charge having a slow response can be surely included in the residual charge measured under the application of the AC voltage. Therefore, it is possible to accurately diagnose insulation deterioration by using the plurality of measured residual charges for deterioration diagnosis.

  Therefore, even with a cable having a large insulation thickness, it is possible to perform insulation deterioration diagnosis by sufficiently applying an AC voltage to the insulation part, and when AC voltage is applied, the AC voltage Therefore, it is not necessary to install a large AC voltage, and it can be easily applied even in a narrow field.

  The method for diagnosing deterioration of a power cable according to a second aspect of the present invention is the method for diagnosing deterioration of power cable according to the above method, wherein the total charge time of the alternating voltage voltage application step that is repeatedly performed a plurality of times is the residual charge The function indicating the error charge included in is set to be smaller than the time for the residual charge to be satisfied.

  According to this method, with respect to the power cable, for a certain period of time during which the AC voltage is held in the applied state, the total of the AC voltage application time that is repeatedly performed is measured under the AC voltage application. Since the time for which the residual charge satisfies the function indicating the error charge included in the residual charge is smaller than the time for which the residual charge is satisfied, the residual charge measured under AC voltage application is accurately measured without being saturated.

  The insulation degradation diagnosis method for a power cable according to a third aspect of the present invention is the above method, wherein the residual charge measured in the residual charge measurement step is Q (t), and the error charge included in the residual charge is calculated. The exponential function shown is a function f (t) = − A · {1−exp (−t / τ)} (where A> 0) that attenuates with a constant time constant τ, and the predetermined time is performed a plurality of times. Are set to be the same time and the total of the charging time of the AC voltage charging process repeatedly performed a plurality of times is smaller than the time when Q (t) = f (t) is satisfied. I made it.

According to this method, since the time change ratio of the error charge contained in the residual charge and the time change ratio of the residual charge are approximated under AC voltage application, the residual charge Q (t) is used to determine the residual charge. In the case of extracting the deteriorated charge Qs contained in the conventional method, Qs≈Q ₀ = ΔQ ₁ −ΔQ ₂ × (ΔQ ₂ / Q ₃ ) of the conventional method can be used.

  An insulation degradation diagnosis apparatus for a power cable according to a fourth aspect of the present invention grounds a DC voltage after applying a DC voltage to the power cable, applies an AC voltage to the power cable after the grounding, and causes the power cable to remain. An insulation degradation diagnosis apparatus for a power cable for measuring electric charge, wherein after the grounding, the AC voltage is boosted to a specified value, and the AC voltage is charged by holding the voltage for a certain period of time. An electrical unit, a residual charge measuring unit for measuring a residual charge of the power cable generated by applying the DC voltage under the application of the AC voltage, and controlling the AC voltage applying unit and the residual charge measuring unit. A plurality of the AC power applied to the power cable, and a controller for diagnosing deterioration of the power cable using residual charges measured under the AC voltage applied, Serial control unit, the predetermined time in the AC voltage Division conductive portion, the residual charge is a configuration that is set based on the time to meet the exponential function indicating the error charges contained in the residual charge.

  According to this configuration, after direct current is applied to the power cable, the alternating voltage is boosted to a specified value, then held for a certain period of time to lower the voltage, and the direct current voltage is applied under the alternating voltage. The measurement of the residual charge of the power cable caused by electricity is repeated a plurality of times. The fixed time at this time is set based on the time when the residual charge value measured under the AC voltage application satisfies the exponential function representing the error charge contained in the residual charge, and thus is measured under the AC voltage application. The residual charge is not saturated. For this reason, in addition to the deterioration charge of the power cable having a quick response at the time of measurement, the error charge having a slow response can be surely included in the residual charge measured under the application of the AC voltage. Therefore, it is possible to accurately diagnose insulation deterioration by using the plurality of measured residual charges for deterioration diagnosis.

  Therefore, even with a cable having a large insulation thickness, it is possible to perform insulation deterioration diagnosis by sufficiently applying an AC voltage to the insulation part, and when AC voltage is applied, the AC voltage Therefore, it is not necessary to install a large AC voltage, and it can be easily applied even in a narrow field.

  The insulation degradation diagnosis method for power cables according to the present invention can accurately perform insulation degradation diagnosis even for a power cable having a large insulation thickness, and is particularly useful when applied to insulation degradation diagnosis of a line in a narrow field. It is.

The figure which shows the structure of the power cable which is an insulation degradation diagnostic apparatus and measurement object which concern on one embodiment of this invention The figure which shows an example of the embodiment of the insulation degradation diagnosis method of the power cable which concerns on this invention Conceptual diagram for explaining a method for diagnosing insulation deterioration of a power cable according to the present invention The figure which shows the exponential function showing the error signal for prescribing the voltage holding time of the AC charging in the AC short-time charging As a procedure of the conventional residual charge method, (a) is a diagram showing an applied state of a DC voltage, (b) is a diagram showing a grounded state, and (c) is a diagram showing an applied state of an AC voltage. The figure which shows an example of the insulation degradation diagnosis method of the conventional cable using the residual charge method of FIG. The figure which shows the response of the residual charge when the conventional residual charge method is used for the power cable with a large insulation thickness

Explanation of symbols

20 Measurement object cable 21 Conductor 22 Insulator 23 Metal shielding layer 24 Termination part 100 Insulation degradation diagnostic device 110 DC power supply 120 Grounding resistance 130 AC charging voltage transformer (transformer)
132 variable voltage regulator 134 AC power switch 140 changeover switch 145 short circuit switch 153 DC voltmeter 160 control unit C _d detection circuit V _ac AC voltage applied V _dc DC voltage V _d (t) detection voltage

Claims (4)

In the method for diagnosing deterioration of power cable, the power cable is grounded after applying a DC voltage, and the AC voltage is applied to the power cable after the grounding to measure the residual charge of the power cable.
After the grounding, the AC voltage is boosted to a specified value for the power cable, and then the AC voltage is applied by holding the voltage for a certain period of time to reduce the voltage.
A residual charge measuring step of measuring a residual charge of the power cable caused by the application of the DC voltage under the application of the AC voltage;
A deterioration diagnosis step of diagnosing the deterioration of the power cable using the residual charge measured in the residual charge measurement step after the AC voltage application step and the residual charge measurement step are repeated a plurality of times in order. ,
The predetermined time in the AC voltage application step is set based on a time when a residual charge value measured under the AC voltage application satisfies an exponential function representing an error charge included in the residual charge. Insulation degradation diagnosis method for power cables.   The predetermined time is set so that the total charging time of the AC voltage charging process performed a plurality of times is smaller than the time for which the residual charge satisfies the function indicating the error charge included in the residual charge. The insulation deterioration diagnosis method for a power cable according to claim 1, wherein:   The residual charge measured in the residual charge measurement step is Q (t), and an exponential function indicating an error charge included in the residual charge is a function f (t) = − that decays with a constant time constant τ. A · {1-exp (−t / τ)} (where A> 0), and the predetermined time that is performed a plurality of times is the same time and the AC voltage applying step that is performed a plurality of times. 2. The method for diagnosing deterioration of a power cable according to claim 1, wherein the total charging time is set to be smaller than a time when Q (t) = f (t) is established. A power cable insulation grounding device that measures a residual charge of the power cable by applying a DC voltage to the power cable and then grounding the power cable, and then applying an AC voltage to the power cable after the grounding,
After the grounding, the AC voltage is boosted to a specified value for the power cable, and then held for a certain period of time to reduce the voltage and apply an AC voltage.
A residual charge measuring unit for measuring a residual charge of the power cable generated by the application of the DC voltage under the application of the AC voltage;
The AC cable applying unit and the residual charge measuring unit are controlled to perform a plurality of AC applying operations on the power cable, and using the residual charges respectively measured under the AC voltage applying, the power cable And a controller for diagnosing deterioration of
The control unit sets the predetermined time in the AC voltage application unit based on a time until the residual charge satisfies an exponential function indicating an error charge included in the residual charge. Insulation degradation diagnostic equipment.

Images