JPH0862280A - Diagnosis of insulation degradation of power cable - Google Patents
Diagnosis of insulation degradation of power cableInfo
- Publication number
- JPH0862280A JPH0862280A JP19948794A JP19948794A JPH0862280A JP H0862280 A JPH0862280 A JP H0862280A JP 19948794 A JP19948794 A JP 19948794A JP 19948794 A JP19948794 A JP 19948794A JP H0862280 A JPH0862280 A JP H0862280A
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- Prior art keywords
- voltage
- time
- charge
- measurement
- residual charge
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- Testing Relating To Insulation (AREA)
Abstract
Description
【0001】[0001]
【産業上の利用分野】本発明は、CVケーブル等の電力
ケーブルの絶縁劣化診断方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing insulation deterioration of power cables such as CV cables.
【0002】[0002]
【従来の技術】CVケーブル等のゴム・プラスチック電
力ケーブルに対して、水が存在する環境下で長期間に亘
って交流電圧を課電していると、絶縁体中のボイド、異
物、突起等の電界集中部に水分が蓄積され、微小な水ボ
イド集団が形成されて、これが電界方向に成長する水ト
リー劣化が発生する。この水トリーは、その成長ととも
に絶縁破壊電圧を低下させ、最終的には運転中の電力ケ
ーブルの絶縁破壊事故の原因になる。現在のCVケーブ
ル等の電力ケーブルの絶縁劣化診断においては、この水
トリー劣化を信頼性高く検出する方法の開発が重要な課
題になっている。2. Description of the Related Art When an AC voltage is applied to a rubber / plastic power cable such as a CV cable in an environment where water is present for a long period of time, voids, foreign matters, protrusions, etc. in an insulator are generated. Moisture is accumulated in the electric field concentrated portion of the above, a minute water void group is formed, and this causes water tree deterioration in which the water void grows in the electric field direction. This water tree lowers the breakdown voltage as it grows, and eventually causes a breakdown of the power cable during operation. In the current diagnosis of insulation deterioration of power cables such as CV cables, the development of a method for reliably detecting this water tree deterioration has become an important issue.
【0003】この水トリー劣化を診断する方法として
は、現在までに種々の方法が研究されてきている。これ
らの方法の中に、直流電圧課電後の接地期間中の誘電吸
収に係わる現象を測定する方法がある。一般に、誘電率
と導電率の異なる複数の材料からなる複合誘電体に直流
電圧を印加すると、異種材料の界面に空間電荷が蓄積さ
れる。直流課電終了後に接地(電極間を短絡)して直流
印加電圧を取り除くと、この空間電荷は自己の形成する
空間電荷電界によって移動を開始し、最終的には再結合
等によって消滅する。この直流課電後の接地回路には、
幾何容量や瞬時分極に基づく瞬時放電電流が減衰した後
にも、この空間電荷の移動・消滅に伴って時間とともに
減衰する直流電流が流れる。この電流は吸収電流あるい
は逆吸収電流と称され、また、この接地回路に流れる吸
収電流の源になる電荷を残留電荷と称している。即ち、
直流課電中に発生した空間電荷の中で、接地期間中に絶
縁体中を移動、消滅する成分が残留電荷に相当する。As a method for diagnosing this water tree deterioration, various methods have been studied so far. Among these methods, there is a method of measuring a phenomenon related to dielectric absorption during a grounding period after applying a DC voltage. Generally, when a DC voltage is applied to a composite dielectric made of a plurality of materials having different permittivities and electric conductivities, space charges are accumulated at the interface between different materials. When the DC applied voltage is removed by grounding (short-circuiting the electrodes) after the DC voltage is applied, the space charge starts to move by the space charge electric field formed by itself, and finally disappears by recombination and the like. In the ground circuit after this DC charging,
Even after the instantaneous discharge current based on the geometrical capacity and the instantaneous polarization is attenuated, a direct current flows that decays with time as the space charge moves and disappears. This current is called an absorption current or a reverse absorption current, and the electric charge that becomes the source of the absorption current flowing in this ground circuit is called the residual charge. That is,
Of the space charges generated during DC charging, the components that move and disappear in the insulator during the grounding period correspond to residual charges.
【0004】接地期間中の空間電荷の移動方向と移動速
度は、空間電荷電界の方向とその大きさ、並びに電荷の
移動度等によって決定される。一般的には、複合誘電体
材料の界面に形成された空間電荷に基づく直流電圧課電
接地後の吸収電流は直流課電時の電流とは逆極性にな
る。但し、直流印加電界が高くて、電極からの電荷注入
等による空間電荷が形成されていた場合等には、直流課
電時の電流と同極性の吸収電流が観察される場合もあ
る。The moving direction and moving speed of the space charge during the grounding period are determined by the direction and magnitude of the space charge electric field, the mobility of the charge, and the like. Generally, the absorption current after DC voltage charging and grounding due to the space charge formed at the interface of the composite dielectric material has a polarity opposite to that of the current when DC voltage is applied. However, when the DC applied electric field is high and space charges are formed due to charge injection from the electrodes, etc., an absorption current of the same polarity as the current during DC charging may be observed.
【0005】水トリー劣化CVケーブル絶縁体の場合に
は、導電率が極めて小さな架橋ポリエチレン(XLP
E)中に導電率の大きい微小水ボイド集団が形成される
ので、上述の複合誘電体的な特性があり、また、劣化の
進展とともに、水トリー発生個数が増加し、さらに、個
々の水トリー部分の体積や長さも増加するので、直流課
電中に発生する空間電荷は劣化の進展とともに増大す
る。従って、直流課電接地後の吸収電流や残留電荷を劣
化診断の判定信号として利用することができるが、吸収
電流は時間とともに減衰する等の劣化信号として取扱い
難い特性があるので、一般的には、吸収電流を時間積分
して残留電荷に換算した値が劣化診断の判定量に用いら
れている。In the case of water tree-degraded CV cable insulation, cross-linked polyethylene (XLP
Since a group of minute water voids having a large conductivity is formed in E), it has the above-mentioned properties of a composite dielectric, and the number of water trees generated increases with the progress of deterioration. Since the volume and the length of the part also increase, the space charge generated during the direct current charging increases with the progress of deterioration. Therefore, it is possible to use the absorption current and residual charge after grounding the DC voltage as a judgment signal for deterioration diagnosis.However, since the absorption current has a characteristic that it is difficult to handle as a deterioration signal such as decay with time, it is generally used. A value obtained by integrating the absorption current with time and converting it into a residual charge is used as a determination amount for deterioration diagnosis.
【0006】CVケーブルの水トリー劣化診断に用いら
れる直流課電接地後の残留電荷の測定方法としては、
「逆吸収電流測定」と「残留電圧測定」が知られてい
る。「逆吸収電流測定」では、接地回路に流れる吸収電
流を連続測定して、その時間積分から残留電荷を算出す
る。「残留電圧測定」では、一旦接地した回路を再び開
放して電極間に高インピーダンスの電圧計を挿入し、時
間の経過とともに回復してくる電圧(残留電圧と称す
る)を測定する。この残留電圧に試料の静電容量を乗ず
ると、残留電荷に相当する電荷が測定される。As a method of measuring the residual charge after grounding the DC voltage used for diagnosing the water tree deterioration of the CV cable,
"Reverse absorption current measurement" and "residual voltage measurement" are known. In the "reverse absorption current measurement", the absorption current flowing in the ground circuit is continuously measured, and the residual charge is calculated from the time integration. In the "residual voltage measurement", the circuit that has been once grounded is opened again, a high-impedance voltmeter is inserted between the electrodes, and the voltage (called residual voltage) that recovers over time is measured. When this residual voltage is multiplied by the capacitance of the sample, the charge corresponding to the residual charge is measured.
【0007】「逆吸収電流測定」では時間とともに減衰
する電流を測定しているので、この電流の時間特性を正
確に測定するには、電流の減衰時定数よりも遙かに早い
応答を有する測定回路が必要になる。もしも、電流検出
抵抗を不用意に大きくすると、試料の静電容量と検出抵
抗で決定される測定の時定数が大きくなり、測定開始後
の短時間側での電荷測定結果が実際の値よりも小さく検
出されてしまう。吸収電流が劣化診断に使用されない原
因のひとつは、電流の大きさがこのような測定回路条件
に依存するからである。Since the "reverse absorption current measurement" measures a current that decays with time, in order to accurately measure the time characteristic of this current, a measurement having a response much faster than the decay time constant of the current. A circuit is needed. If the current detection resistance is carelessly increased, the measurement time constant determined by the capacitance of the sample and the detection resistance becomes large, and the charge measurement result on the short time side after the start of measurement is higher than the actual value. It will be detected small. One of the reasons why the absorbed current is not used for deterioration diagnosis is that the magnitude of the current depends on such measurement circuit conditions.
【0008】一方、「残留電圧測定」では、測定回路か
らの電荷の漏洩が問題になる。通常は、1013Ω以上
程度の高入力インピーダンスのエレクトロメータ等を用
いて測定を行なうが、試料の静電容量が小さいと電荷の
漏洩が無視できなくなり、長時間測定には不向きであ
る。ところで、直流課電後に外部電界を取り除いた状態
下での水トリー劣化CVケーブル中の空間電荷の移動・
消滅には長時間を要する。本発明者らの水トリー劣化C
Vケーブルに対する経験では、直流前課電後の室温状態
で1カ月間接地していても、なおも残留電荷が観測され
た場合もある。従って、せいぜい10分間程度の実用的
な測定時間範囲内で検出される残留電荷は実際に蓄積さ
れていた空間電荷のごく一部であり、また、検出信号に
は水トリー劣化部以外の類似現象による残留電荷等が含
まれていること等から、「逆吸収電流測定」や「残留電
圧測定」によるCVケーブルの水トリー劣化診断を難し
くしている。On the other hand, in the "residual voltage measurement", leakage of charges from the measuring circuit becomes a problem. Usually, the measurement is performed using an electrometer or the like having a high input impedance of about 1013 Ω or more, but if the capacitance of the sample is small, leakage of charges cannot be ignored, and it is not suitable for long-time measurement. By the way, the movement of space charge in the water tree deterioration CV cable under the condition that the external electric field is removed after the direct current application.
It takes a long time to disappear. Our Water Tree Degradation C
In the experience with V cables, residual charges may still be observed even after being grounded for one month at room temperature after direct current application. Therefore, the residual charge detected within a practical measurement time range of about 10 minutes at most is a small part of the space charge actually accumulated, and the detection signal shows similar phenomena other than the water tree deterioration part. Since the residual charge and the like due to the above are included, it is difficult to diagnose deterioration of the water tree of the CV cable by "reverse absorption current measurement" or "residual voltage measurement".
【0009】上述の問題を解決する方法としては、直流
課電接地後に交流電界を印加して、この交流課電状態下
で吸収電流を測定し、これを時間積分して残留電荷を検
出する方法が提案されている。提案者らはこの方法を
「残留電荷測定」と称しているが、正確には、直流課電
接地後の交流課電下での吸収電流測定による残留電荷検
出である(特公平5−28350号公報参照)。As a method for solving the above-mentioned problem, an AC electric field is applied after the DC voltage is grounded, an absorption current is measured under this AC voltage application state, and this is integrated over time to detect a residual charge. Is proposed. Proponents call this method "residual charge measurement", but to be precise, it is residual charge detection by measuring the absorption current under AC voltage after DC voltage grounding (Japanese Patent Publication No. 28350/1993). See the bulletin).
【0010】前述のように、直流課電接地後の空間電荷
の移動速度は、絶縁体内部の電界の大きさに依存するの
で、外部から大きな電界を印加すれば電荷の移動速度が
早くなり、短時間で大きな吸収電流を測定することが可
能になる。接地時の空間電荷の移動を速めるための印加
電界として直流を用いると、この直流課電による電流と
測定すべき吸収電流との区別が難しくなるので、上記
「残留電荷測定」では交流電界を印加して、この時の検
出電流から交流成分を除去して吸収電流を検出してい
る。As described above, since the moving speed of the space charge after the DC voltage grounding depends on the magnitude of the electric field inside the insulator, the moving speed of the charge becomes faster if a large electric field is applied from the outside, It becomes possible to measure a large absorption current in a short time. If a direct current is used as the applied electric field to accelerate the movement of the space charge at the time of grounding, it becomes difficult to distinguish the current due to this direct current application and the absorption current to be measured. Then, the absorption current is detected by removing the AC component from the detection current at this time.
【0011】なお、この「残留電荷測定」では、直流課
電接地後の通常の交流課電を行なわない場合の吸収電流
と区別するために、この吸収電流が十分に減衰した後に
交流電圧を印加し、交流課電期間中の吸収電流を所定時
間連続測定して、これを時間積分して得た残留電荷の大
きさ、即ち、交流課電下での最終測定時刻の残留電荷の
大きさを劣化診断の判定量に用いている。In this "residual charge measurement", an AC voltage is applied after the absorption current is sufficiently attenuated in order to distinguish it from the absorption current when normal AC voltage application is not performed after DC voltage application grounding. However, the magnitude of the residual charge obtained by continuously measuring the absorption current during the AC voltage application for a predetermined time and integrating it over time, that is, the magnitude of the residual charge at the final measurement time under AC voltage application, It is used as a judgment amount for deterioration diagnosis.
【0012】[0012]
【発明が解決しようとする課題】上述の直流課電接地後
に交流電圧を印加する「残留電荷測定」では、従来の交
流課電を用いない「逆吸収電流測定」の場合と同様に、
測定完了時間での残留電荷の大きさによって劣化診断を
行っている。ところが、単なる劣化信号の大きさのみを
用いる劣化診断においては、例えば、劣化が著しい場合
のみに劣化信号が発生する等の、個々の水トリーから発
生する劣化信号の大きさが劣化状態によって著しく異な
る特性がない限り、信頼性の高い劣化診断は行えない。
残留電荷は軽微な水トリー劣化状態によっても僅かなが
らも発生するので、例えば、多数個の軽微劣化の発生と
少数の極度劣化の発生との区別は困難であり、交流課電
によってもこの本質的な問題を解決することはできな
い。In the above-mentioned "residual charge measurement" in which an AC voltage is applied after the DC voltage is grounded, as in the case of the "reverse absorption current measurement" which does not use the conventional AC voltage,
Deterioration diagnosis is performed based on the magnitude of the residual charge at the time of completion of measurement. However, in the degradation diagnosis using only the magnitude of the degradation signal, the magnitude of the degradation signal generated from each water tree is significantly different depending on the degradation state, for example, the degradation signal is generated only when the degradation is significant. Unless there is a characteristic, reliable deterioration diagnosis cannot be performed.
Since the residual charge is slightly generated depending on a slight water tree deterioration state, it is difficult to distinguish between the occurrence of a large number of slight deteriorations and the occurrence of a small number of extreme deteriorations. Can not solve the problem.
【0013】ところで、直流課電接地後の空間電荷の移
動、消滅の時間特性は、絶縁体の導電率と誘電率等に依
存する。従って、検出される残留電荷の時間特性も水ト
リー劣化診断の判定材料になり得る。本発明の目的は、
上述の問題点を解決するために、劣化診断の判定信号と
して残留電荷の大きさのみを利用するのではなく、直流
課電接地後の交流課電時に現れる残留電荷の時間特性に
着目し、これによって残留電荷の発生源となる水トリー
劣化部の有害性を判断して、信頼性の高い電力ケーブル
の絶縁劣化診断を行おうとするものである。By the way, the time characteristics of the movement and disappearance of the space charge after the DC voltage grounding depends on the conductivity and the dielectric constant of the insulator. Therefore, the time characteristic of the detected residual charge can also be used as a criterion for the water tree deterioration diagnosis. The purpose of the present invention is to
In order to solve the above-mentioned problems, not only the magnitude of the residual charge is used as a determination signal for deterioration diagnosis, but attention is paid to the time characteristic of the residual charge that appears when AC is applied after grounding by applying DC. The purpose is to judge the harmfulness of the water tree deteriorated part, which is the source of the residual charge, and to perform a highly reliable insulation deterioration diagnosis of the power cable.
【0014】[0014]
【課題を解決するための手段】本発明に係わる電力ケー
ブルの絶縁劣化診断方法は、「残留電荷測定」と同様
に、試料ケーブルに直流電圧VDCを印加した後に接地し
て、さらにその後に交流電圧VACを試料に印加した場合
の残留電荷を測定するものであるが、交流課電開始時刻
をt=0、交流電圧が零から所定の値VACに昇圧した時
刻をt=t1 、その後のVACを保持して測定を完了した
時刻をt=t2 とすると、時刻t=0からt=t1 まで
に現れる残留電荷の大きさQ(t1 )と、時刻t=t1
からt=t2 までの測定期間中の残留電荷の変化分ΔQ
/Q(t1 )={Q(t2 )−Q(t1 )}/Q(t1
)によって電力ケーブルの絶縁劣化診断を行うことを
特徴としている。A method for diagnosing insulation deterioration of a power cable according to the present invention is similar to the "residual charge measurement" in that a DC voltage VDC is applied to a sample cable and then grounded, and then an AC voltage is applied. The residual charge when VAC is applied to the sample is measured. The AC charging start time is t = 0, the time when the AC voltage is boosted from zero to a predetermined value VAC is t = t1, and the subsequent VAC is Assuming that the time at which the measurement is held and completed is t = t2, the magnitude Q (t1) of the residual charge appearing from time t = 0 to t = t1 and the time t = t1.
Change ΔQ of residual charge during the measurement period from t to t = t2
/ Q (t1) = {Q (t2) -Q (t1)} / Q (t1
), The insulation deterioration diagnosis of the power cable is performed.
【0015】また、本発明に係わる電力ケーブルの絶縁
劣化診断では交流課電中の残留電荷の時間特性を正確に
測定する必要があるので、残留電荷の測定に対しては、
直流課電後に一旦接地した回路を再び開放して、電極間
に測定期間中の電荷の漏洩を無視できる放電時定数を有
する直流電圧測定回路を挿入し、その電位差から残留電
荷を直接的に連続測定する。Further, in the insulation deterioration diagnosis of the power cable according to the present invention, since it is necessary to accurately measure the time characteristic of the residual charge during AC charging, the residual charge is measured as follows.
After DC voltage application, open the circuit that was once grounded again, insert a DC voltage measurement circuit with a discharge time constant that can ignore the leakage of charge during the measurement period, and connect the residual charge directly from the potential difference. taking measurement.
【0016】即ち、従来の「残留電荷測定」では、交流
課電によって得られる吸収電荷の大きさのみを問題にし
ているので、交流課電開始時刻t=0からVACを保持し
て、測定を完了する時刻t=t2 までの吸収電流ia
(t)を連続測定し、t=0からt=t2 までの電流を
時間積分した残留電荷の大きさ数1を劣化診断に用いて
いる。That is, in the conventional "residual charge measurement", since only the magnitude of the absorbed charge obtained by the AC voltage application is a problem, VAC is held from the AC voltage application start time t = 0 to perform the measurement. Absorption current ia until completion time t = t2
(T) is continuously measured, and the magnitude number 1 of the residual charge obtained by time-integrating the current from t = 0 to t = t2 is used for the deterioration diagnosis.
【0017】[0017]
【数1】 [Equation 1]
【0018】しかし、本発明に係わる電力ケーブルの絶
縁劣化診断方法では、残留電荷の大きさQ(t2 )を電
圧昇圧完了時刻までに現れる吸収電荷Q(t1 )と、そ
の後の交流印加電圧を一定値に保持した期間中の残留電
荷の変化分ΔQとに分離し{Q(t2 )=Q(t1 )+
ΔQ}、Q(t1 )の大きさから電力ケーブルの劣化状
況の概略を診断し、さらに、Q(t1 )やQ(t2 )等
の残留電荷の大きさだけでは判別できない信号発生源の
劣化状況をΔQで代表される残留電荷の時間変化特性か
ら判定しようとするものである。However, in the method for diagnosing insulation deterioration of a power cable according to the present invention, the magnitude Q (t2) of the residual charge and the absorbed charge Q (t1) appearing by the time when the voltage boosting is completed and the alternating voltage applied thereafter are constant. The residual charge change ΔQ during the period held at the value is separated into {Q (t2) = Q (t1) +
ΔQ}, Q (t1) magnitude is used to diagnose the outline of the power cable deterioration status, and the deterioration status of the signal source that cannot be identified only by the magnitude of residual charge such as Q (t1) and Q (t2). Is to be determined from the time change characteristics of the residual charge represented by ΔQ.
【0019】ところで、このような交流電圧課電下での
残留電荷の時間変化特性による劣化診断を行う場合に
は、真の時間特性を正確に測定する必要がある。残留電
荷の測定は、原理的には静電容量Cx に充電されている
電荷Qx を測定することとほぼ同じものである。前述の
吸収電荷測定による残留電荷検出手法は電荷Qx を直接
的に測定するものではなくて、電極間を短絡してこれを
放電させた場合の電流を測定し、その時間積分から電荷
を検出する。従って、放電回路に挿入する検出抵抗が零
に近ければ特に問題は生じないが、実際にはある有限の
大きさの検出抵抗Rs を挿入する必要があるので、試料
の静電容量をCx とすると、τ=Cx Rs なる放電時定
数、即ち、電流検出に対する測定の応答遅れが生じる。By the way, in the case of performing the deterioration diagnosis based on the time change characteristic of the residual electric charge under such AC voltage application, it is necessary to accurately measure the true time characteristic. In principle, the measurement of the residual charge is almost the same as the measurement of the charge Qx charged in the electrostatic capacitance Cx. The above-mentioned residual charge detection method by measuring the absorbed charge does not directly measure the charge Qx, but measures the current when the electrodes are short-circuited to discharge this, and the charge is detected from the time integration. . Therefore, if the detection resistance to be inserted into the discharge circuit is close to zero, no particular problem will occur, but since it is actually necessary to insert a detection resistance Rs of a certain finite size, let Cx be the capacitance of the sample. , Τ = CxRs, that is, a discharge time constant, that is, a response delay of measurement to current detection occurs.
【0020】ところで、交流課電下で直流課電接地後の
吸収電流を測定する場合には、測定回路に加わる交流電
圧を低減するために大容量のコンデンサCs を測定回路
と並列に接続する必要があるが、これを吸収電流測定回
路としてみた場合には、Csは試料の静電容量Cx と並
列に接続された状態になるので、電荷の放電時定数はτ
=(Cx +Cs )Rs となり、測定の応答時定数がCs
によって増大する。By the way, in the case of measuring the absorption current after the DC voltage is grounded under the AC voltage, it is necessary to connect a large capacity capacitor Cs in parallel with the measurement circuit in order to reduce the AC voltage applied to the measurement circuit. However, when this is viewed as an absorption current measuring circuit, Cs is in a state of being connected in parallel with the capacitance Cx of the sample, so the discharge time constant of the charge is τ.
= (Cx + Cs) Rs, and the response time constant of measurement is Cs
Is increased by
【0021】例えば、電流検出抵抗Rs を10kΩ、試
料の静電容量Cx を0.1μF、並列コンデンサCs を
200μFとした場合にはτは約2秒となる。この時、
Cxに充電されていた電荷Qx によって放電回路に流れ
る電流はix (t)=Qx /{τ×exp(−t/
τ)}であり、これを時間積分して得られる電荷はQ
(t)=Qx {1−exp(−t/τ)}となるので、
測定電荷Q(t)が真の電荷Qx と等しくなるためには
t=10秒程度の遅れが生じてしまう。また、実際の直
流電流測定回路には交流電流除去用のローパスフィルタ
等が加わるために、応答遅れはさらに増加する。一方、
応答時間を短くするために検出抵抗Rs を低減しようと
すると検出信号Vs (t)=Rs ・ix (t)が小さく
なるので、微小な電流測定が難しくなる。For example, when the current detection resistor Rs is 10 kΩ, the capacitance Cx of the sample is 0.1 μF, and the parallel capacitor Cs is 200 μF, τ is about 2 seconds. This time,
The current flowing in the discharge circuit due to the charge Qx charged in Cx is ix (t) = Qx / {τ × exp (-t /
τ)}, and the charge obtained by integrating this over time is Q
Since (t) = Qx {1-exp (-t / τ)},
Since the measured charge Q (t) becomes equal to the true charge Qx, there is a delay of about t = 10 seconds. Moreover, since a low-pass filter for removing an alternating current is added to the actual direct current measuring circuit, the response delay further increases. on the other hand,
If an attempt is made to reduce the detection resistance Rs in order to shorten the response time, the detection signal Vs (t) = Rs.ix (t) becomes small, which makes it difficult to measure a minute current.
【0022】一方、「残留電圧測定」による残留電荷測
定では、静電容量に充電されている電荷を電極間電位差
として直接的に検出するので、原理的には応答遅れが全
く生じない。例えば、上記の吸収電流測定と同様に静電
容量Cx に充電されている電荷Qx を測定する場合を例
に挙げると、測定回路と並列に大容量のコンデンサCs
が接続されている場合でも、電荷Qx は電位差Vs =Q
x /(Cx +Cs )として応答遅れなく測定される。即
ち、測定された電位差Vs に試料と並列コンデンサの静
電容量の和Cx +Cs を乗じれば、測定時刻での残留電
荷が算出される。On the other hand, in the residual charge measurement by "residual voltage measurement", the charge charged in the electrostatic capacitance is directly detected as the potential difference between the electrodes, so that in principle no response delay occurs. For example, when the charge Qx charged in the electrostatic capacitance Cx is measured as in the absorption current measurement described above, a large-capacity capacitor Cs is connected in parallel with the measurement circuit.
Even if the two are connected, the charge Qx has a potential difference Vs = Q.
It is measured as x / (Cx + Cs) without a response delay. That is, the residual charge at the measurement time is calculated by multiplying the measured potential difference Vs by the sum Cx + Cs of the electrostatic capacitances of the sample and the parallel capacitor.
【0023】ここで、「残留電圧測定」による残留電荷
測定では、検出される電圧信号Vsの大きさはCs が存
在しない場合に比べてCx /(Cx +Cs )に減少する
問題があるが、前述の吸収電流測定の応答送れ時間を算
出した測定回路条件に当てはめてみると、電荷Qx が1
00nCとすると、吸収電流測定による検出電流信号の
大きさは、測定開始後1秒で0.30mV(=30n
A)、また10秒で3.4μV(=0.34nA)であ
るのに対して「残留電圧測定」では0.5mVが測定さ
れることになり、検出感度からみても「残留電圧測定」
による残留電荷検出手法が全く問題ないことが分かる。Here, in the residual charge measurement by "residual voltage measurement", there is a problem that the magnitude of the detected voltage signal Vs is reduced to Cx / (Cx + Cs) as compared with the case where Cs does not exist. Applying to the measurement circuit condition that calculated the response sending time of the absorption current measurement, the charge Qx is 1
If the value is 00 nC, the magnitude of the detected current signal by the absorption current measurement is 0.30 mV (= 30 n
A), while it is 3.4 μV (= 0.34 nA) in 10 seconds, 0.5 mV will be measured in “residual voltage measurement”, which is “residual voltage measurement” in terms of detection sensitivity.
It can be seen that there is no problem in the residual charge detection method by.
【0024】「残留電圧測定」手法の最大の問題点は、
測定中の電荷の漏洩にあるが、電流測定の場合とは逆
に、測定回路の放電時定数τを測定時間に比べて十分大
きい値に設定しておけば、この電荷漏洩による測定誤差
は無視できる。例えば、残留電荷の連続測定時間を1分
とすると、約500分以上程度の時定数を選択すれば、
測定開始直後に発生した残留電荷の99.8%以上は1
分後の測定完了時刻まで漏洩することなく測定回路に残
留する。The biggest problem of the "residual voltage measurement" method is that
Although there is a charge leakage during measurement, contrary to the case of current measurement, if the discharge time constant τ of the measurement circuit is set to a value that is sufficiently larger than the measurement time, the measurement error due to this charge leakage will be ignored. it can. For example, assuming that the continuous measurement time of the residual charge is 1 minute, if a time constant of about 500 minutes or more is selected,
99.8% or more of the residual charge generated immediately after the start of measurement is 1
After a minute, it remains in the measurement circuit without leaking until the measurement completion time.
【0025】ここで、測定回路の放電時定数τはRs
(Cx +Cs )で表されるので、並列に存在する大容量
のコンデンサCs は電荷の漏洩を押える役割を果たす。
即ち、電圧検出感度に問題ない範囲では、Cs の増大は
電荷測定上有利に働く。例えば、試料の静電容量Cx が
0.1μFで並列コンデンサCs が無い場合にはτ=5
00分を確保するためには3×1011Ωもの抵抗Rs
が必要であるが、200μFの並列コンデンサCs が存
在すると、抵抗Rs は150MΩ程度ですむ。この程度
の測定系の放電抵抗の確保は容易であり、また、電極端
部の表面からの電荷漏洩等も容易に防止することができ
る。なお、従来の「残留電圧測定」による水トリー劣化
診断では、この測定回路の静電容量と漏洩抵抗からなる
放電時定数を考慮することなく10分程度の長時間測定
を行っていたために、測定回路あるいは電極端部からの
電荷漏洩が測定誤差になっていた。Here, the discharge time constant τ of the measuring circuit is Rs
Since it is represented by (Cx + Cs), the large-capacity capacitor Cs existing in parallel plays a role of suppressing the leakage of charges.
That is, the increase in Cs has an advantage in charge measurement in the range where there is no problem in the voltage detection sensitivity. For example, if the capacitance Cx of the sample is 0.1 μF and there is no parallel capacitor Cs, then τ = 5
To secure 00 minutes, a resistance Rs of 3 × 10 11Ω
However, if the parallel capacitor Cs of 200 μF exists, the resistance Rs is about 150 MΩ. It is easy to secure the discharge resistance of the measurement system to this extent, and it is also possible to easily prevent charge leakage from the surface of the electrode end. In the conventional water tree deterioration diagnosis by "residual voltage measurement", the measurement was performed for a long time of about 10 minutes without considering the discharge time constant consisting of the capacitance and the leakage resistance of this measurement circuit. The charge leakage from the circuit or the electrode end was a measurement error.
【0026】以上までに示したように、本発明に係わる
電力ケーブルの絶縁劣化診断方法は、劣化診断の判定信
号として直流課電接地後の交流課電時に現れる残留電荷
の時間特性を利用し、また、その残留電荷測定において
は、従来の「残留電荷測定」で用いられていた電流測定
手法を用いずに、高入力抵抗による電圧測定を行うこと
を特徴としている。As described above, the method for diagnosing insulation deterioration of a power cable according to the present invention utilizes the time characteristic of the residual charge that appears when AC power is applied after grounding DC power, as a determination signal for deterioration diagnosis. Further, the residual charge measurement is characterized by performing voltage measurement with a high input resistance without using the current measuring method used in the conventional “residual charge measurement”.
【0027】[0027]
【作用】本発明に係わる電力ケーブルの絶縁劣化診断方
法における劣化信号の発生原理を、以下に図に従って説
明する。図1(A)は、直流課電時に形成される空間電
荷のモデル図である。水トリー劣化絶縁体に負極性直流
電圧−VDCが印加されると、電荷の移動の容易な水トリ
ー部分と、これに直列に存在する電荷の移動し難い健全
部絶縁体の界面に空間電荷が蓄積される。劣化部を含む
試料の静電容量をCx として、接地側電極を基準点とす
ると、この直流課電時の状態では、電荷数2が試料の課
電側電極上に存在し、また、絶縁体中には空間電荷QS
(t)=QSDC が存在する。直流課電状態下では、この
空間電荷は水トリー部分の電界を緩和するように作用す
るので、図では、接地電極側から発生する水トリー部の
先端に正の空間電荷+QS (t)=+QSDC が蓄積され
ている場合を示している。The principle of generation of a deterioration signal in the method for diagnosing insulation deterioration of a power cable according to the present invention will be described below with reference to the drawings. FIG. 1 (A) is a model diagram of space charges formed when direct current is applied. When a negative DC voltage −VDC is applied to the water-tree deteriorated insulator, space charges are generated at the interface between the water-tree portion where the charge easily moves and the healthy portion insulator in which the electric charge is hard to move. Accumulated. Assuming that the capacitance of the sample including the deteriorated part is Cx and the ground side electrode is the reference point, the number of charges of 2 is present on the voltage side electrode of the sample in this state during DC voltage application, and the insulator Space charge QS
(T) = QSDC exists. Since the space charge acts so as to relax the electric field in the water tree portion under the direct current applied state, in the figure, positive space charge + QS (t) = + QSDC at the tip of the water tree portion generated from the ground electrode side. Shows the case where is accumulated.
【0028】[0028]
【数2】 [Equation 2]
【0029】図1(B)は、直流課電側電極を接地(電
極間を短絡)して、印加していた直流電圧を除去した状
態を示すものである。この時、直流課電中に存在してい
た電極上の電荷−QDCは瞬時に放電されるが、絶縁体中
に正の空間電荷+QS (t)が存在していると、電極間
が短絡されても電極上の電荷は完全に零にはならず、接
地側電極を基準点にとると、課電側電極上には−Q1
(t)なる負の電荷が誘導される。FIG. 1B shows a state in which the DC voltage application side electrodes are grounded (the electrodes are short-circuited) and the applied DC voltage is removed. At this time, the electric charge -QDC on the electrodes that was present during DC charging is instantly discharged, but if a positive space charge + QS (t) is present in the insulator, the electrodes are short-circuited. However, the charge on the electrode does not become completely zero, and when the ground side electrode is taken as the reference point, -Q1 appears on the charging side electrode.
A negative charge of (t) is induced.
【0030】これは、電極間の電位差を常に零とするた
めには、空間電荷によって生じる電極間電位差を打ち消
す電荷が電極上に誘導される必要があるからであり、こ
の誘導電荷−Q1 (t)は、絶縁体中の空間電荷+QS
(t)と逆の極性になり、また、その大きさは、絶縁体
中の空間電荷+QS (t)の大きさと、これが絶縁体中
に存在する位置に依存する。即ち、図では省略している
が、空間電荷+QS (t)による誘導電荷は課電側電極
上の−Q1 (t)のみならず接地電極側にも現れてお
り、これを−Q2 (t)とすると、−{Q1 (t)+Q
2 (t)}の大きさが+QS (t)の大きさに等しく、
かつ、電極間に存在するQS (t)の位置によって両電
極上に誘導される電荷の割合が変化する。This is because in order to make the potential difference between the electrodes always zero, it is necessary to induce charges on the electrodes to cancel the potential difference between the electrodes caused by the space charge. This induced charge -Q1 (t ) Is the space charge in the insulator + QS
The polarity is opposite to that of (t), and its magnitude depends on the magnitude of the space charge + QS (t) in the insulator and the position where it exists in the insulator. That is, although not shown in the figure, the induced charge due to the space charge + QS (t) appears not only at -Q1 (t) on the charging side electrode but also at the ground electrode side, and this is -Q2 (t). Then,-{Q1 (t) + Q
2 (t)} is equal to + QS (t),
In addition, the ratio of charges induced on both electrodes changes depending on the position of QS (t) existing between the electrodes.
【0031】接地と同時に絶縁体中の空間電荷+QS
(t)=+QSDC は空間電荷電界や密度拡散によって移
動を開始する。いま、密度拡散による電荷の移動を無視
すると、空間電荷の重心が存在する場所を境にして空間
電荷電界の方向が逆転するので、空間電荷は直流課電側
電極と接地側電極のいずれの方向にも移動する成分が含
まれるが、導電率が大きい水トリー側(この図では接地
電極側)へ移動する電荷が圧倒的に多くなる。即ち、殆
どの空間電荷+QS (t)=+QSDC は直流課電時とは
逆方向の接地電極側に移動し、これとともに、電極上の
誘導電荷−Q1 (t)は時間経過とともに減少する。従
って、この接地回路には直流課電時とは逆方向の吸収電
流Ia (t)が流れる。Space charge + QS in the insulator at the same time as grounding
(T) = + QSDC starts moving due to space charge electric field or density diffusion. Now, ignoring the movement of charges due to density diffusion, the direction of the space charge electric field is reversed at the place where the center of gravity of the space charge exists, so the space charge is either in the direction of the DC voltage application side electrode or the ground side electrode. Also contains a component that moves, but the amount of electric charge that moves to the water tree side (the ground electrode side in this figure) having a large conductivity is overwhelmingly large. That is, most of the space charge + QS (t) = + QSDC moves to the side of the ground electrode in the direction opposite to that at the time of direct current application, and the induced charge -Q1 (t) on the electrode decreases with time. Therefore, the absorption current Ia (t) flows in the direction opposite to that at the time of direct current application in the ground circuit.
【0032】図1(C)は、図1(B)の直流課電接地
後に、再び接地を開放した状態を示すものである。接地
開放後は直流課電側電極上に電荷を供給する回路が断た
れるので、この直流課電側電極上の電荷−Q1 (t)は
接地開放時刻に存在していた誘導電荷−Q10の一定値に
保たれ、空間電荷QS (t)の移動、消滅等には全く依
存しなくなる。従って、この接地開放状態での直流課電
側電極の直流電位VS(t)は、課電側電極上の−Q10
と絶縁体中の空間電荷+QS (t)によって決定され、
−Q10による負の電位成分を−V0 とし、また+QS
(t)による正の電位成分を+VS+(t)とすると、直
流課電側電極の直流電位はVS (t)=−V0 +VS+
(t)になる。FIG. 1C shows a state in which the grounding is opened again after the DC voltage grounding of FIG. 1B. After the ground is opened, the circuit that supplies the electric charge to the DC voltage application side electrode is cut off. Therefore, the charge -Q1 (t) on this DC voltage application side electrode is equal to the induced charge -Q10 existing at the time when the ground is opened. It is maintained at a constant value and becomes completely independent of the movement and disappearance of the space charge QS (t). Therefore, the DC potential VS (t) of the DC voltage application side electrode in the ground open state is -Q10 on the voltage application side electrode.
And the space charge in the insulator + QS (t),
The negative potential component due to -Q10 is -V0, and + QS
If the positive potential component due to (t) is + VS + (t), the DC potential of the DC voltage application side electrode is VS (t) =-VO + VS +
(T).
【0033】この課電側電極上の電荷−Q10は、接地開
放時の空間電荷+QS (t)によって直流電位差を零に
するように誘導されていたものであるから、接地開放直
後の直流電位差VS (t)は零である。ところが図1
(B)の場合と同様にして、時間経過とともに空間電荷
+QS (t)が水トリー劣化部を経由して接地電極側に
移動して行くので、+QS (t)による電位成分+VS+
(t)は時間とともに減少し、結果、課電側電極の直流
電位VS (t)は接地開放直後の零から直流課電時と同
極性の負の電圧が徐々に回復して来る。The charge -Q10 on the voltage-applying side electrode is induced by the space charge + QS (t) when the ground is opened so that the DC potential difference becomes zero, and therefore the DC potential difference VS immediately after the ground is opened. (T) is zero. However, Figure 1
As in the case of (B), the space charge + QS (t) moves to the ground electrode side via the water tree deterioration portion with the passage of time, so the potential component + VS + due to + QS (t)
(T) decreases with time, and as a result, the DC potential VS (t) of the voltage-applying side electrode gradually recovers from zero immediately after the ground is opened to a negative voltage having the same polarity as when DC power is applied.
【0034】最終的に全ての空間電荷QS (t)が電極
までに移動し消滅した場合には、直流課電側電極上の電
荷−Q1 (t)=−Q10のみが残る。電荷−Q10は接地
開放時の空間電荷の大きさQS (t)に比例した値であ
り、また、直流電位VS (t)が零からある一定の−V
0 なる値まで回復して来る現象は、空間電荷の移動消滅
過程そのものを忠実に反映している。この直流電位VS
(t)が残留電圧と称されるものである。When all the space charges QS (t) finally move to the electrodes and disappear, only the charges -Q1 (t) =-Q10 on the DC voltage application side electrode remain. The charge -Q10 is a value proportional to the size QS (t) of the space charge when the ground is opened, and the DC potential VS (t) is from zero to a certain -V.
The phenomenon of recovering to the value of 0 faithfully reflects the process of space charge migration. This DC potential VS
(T) is called residual voltage.
【0035】ところで、水トリー劣化部とは並列に健全
絶縁体などの静電容量が存在するので、直流電位VS
(t)は劣化部の空間電荷が形成成する電位よりも遙か
に小さくなる。従って、電極間が開放されてはいるが、
近似的には電極間が接地されている状態と大差ないの
で、このVS (t)に試料の静電容量Cx を乗じた値
が、電極間を接地した場合に流れる吸収電流ia (t)
を積分した場合の試料の残留電荷Q(t)とほぼ等しく
なる。By the way, since a capacitance such as a sound insulator exists in parallel with the water tree deterioration portion, the DC potential VS
(T) is much smaller than the potential formed by the space charge in the deteriorated portion. Therefore, although the electrodes are open,
Approximately, there is no great difference from the state where the electrodes are grounded, so the value obtained by multiplying VS (t) by the capacitance Cx of the sample is the absorption current ia (t) that flows when the electrodes are grounded.
Is almost equal to the residual charge Q (t) of the sample when is integrated.
【0036】次に、図1(C)の状態で、電極間に交流
電界が印加された場合の空間電荷QS (t)の挙動につ
いて述べる。空間電荷電界による空間電荷QS (t)の
移動速度よりも遙かに速く正負に変化する交流電界を印
加すると、絶縁体中での空間電荷の直流的な存在位置
(重心)は交流電界によって変化しないので、空間電荷
QS (t)の移動方向は前述の空間電荷電界のみが存在
していた場合と変わらない。しかしながら、交流電界
は、電荷がトラップされていたエネルギー障壁を実効的
に低減して、電荷の移動度を増大させるので、空間電荷
の移動速度を速める効果がある。Next, the behavior of the space charge QS (t) when an AC electric field is applied between the electrodes in the state of FIG. 1C will be described. When an AC electric field that changes positively and negatively much faster than the moving speed of the space charge QS (t) due to the space charge electric field is applied, the direct current position (center of gravity) of the space charge in the insulator changes depending on the AC electric field. Therefore, the moving direction of the space charge QS (t) is the same as that in the case where only the space charge electric field exists. However, the AC electric field effectively reduces the energy barrier in which the charges are trapped and increases the mobility of the charges, and therefore has the effect of increasing the moving speed of the space charges.
【0037】従って、図1(C)の状態で電極上の電荷
Q1 (t)を放電する事なく電極間に交流電界を印加し
た場合には、空間電荷QS (t)の移動速度が速まるの
で、結果、観測される直流電位VS (t)は交流電界を
加えなかった場合よりも一定値V0 =Q10/Cx に到達
する時刻が速まる。これによって、交流電界を加えなか
った場合よりも短時間で大きな残留電荷Q(t)=VS
(t)・Cx を観測することができるので、他の誤差要
因の影響を大幅に低減することが可能になる。Therefore, when an AC electric field is applied between the electrodes without discharging the charge Q1 (t) on the electrodes in the state of FIG. 1C, the moving speed of the space charge QS (t) increases. As a result, the observed DC potential VS (t) reaches a constant value V0 = Q10 / Cx faster than when the AC electric field is not applied. As a result, a large residual charge Q (t) = VS in a shorter time than when the AC electric field is not applied.
Since (t) · Cx can be observed, the influence of other error factors can be significantly reduced.
【0038】このように、残留電荷Q(t)の時間特性
は、絶縁体中の空間電荷の移動、消滅特性によるもので
あり、この時間変化は水トリー劣化部の導電率と誘導率
などに依存する。交流電界を加えた場合、電荷が捕獲さ
れていたエネルギー障壁が下げられることなどによって
実効的な電荷の移動度が増し、導電率が増大する。劣化
の進行している劣化部ほど交流電界による導電率の増加
効果が増大すると考えると、劣化が著しい水トリーほど
直流電位VS (t)が回復して来る時間が速くなると考
えることが出来る。この様に考えると、直流課電接地後
に交流電界を印加した場合の残留電荷の時間特性として
は、劣化が著しくなるほど残留電荷が一定値に飽和する
までの時間が短くなる可能性がある。As described above, the time characteristic of the residual charge Q (t) is due to the movement and extinction characteristic of the space charge in the insulator, and this time change depends on the conductivity and the inductivity of the water tree deteriorated portion. Dependent. When an AC electric field is applied, the effective charge mobility is increased by lowering the energy barrier where the charges are captured, and the conductivity is increased. Considering that the effect of increasing the conductivity due to the AC electric field increases in the deteriorated portion where the deterioration progresses, it can be considered that the time when the DC potential VS (t) recovers becomes faster as the water tree deteriorates significantly. Considering this, as the time characteristics of the residual charge when an AC electric field is applied after the DC voltage is grounded, the time until the residual charge saturates to a constant value may become shorter as the deterioration becomes more remarkable.
【0039】図2は交流電界を印加した場合の残留電荷
の時間特性と試料の劣化状況との関係の推定を示したも
のであり、残留電荷が回復して来る時間が遅い(a)の
場合は試料の劣化進行状況が小さく、以下、回復して来
る時間が速くなる(a)から(c)の順に水トリー劣化
が著しくなると考えることが出来る。ところで、前述の
残留電荷の極性に関する説明では、接地開放後の空間電
荷の移動方向によって観測される電荷の極性が決定され
ることを述べ、通常の水トリー劣化の場合には直流印加
電圧と同極性の残留電荷が観測されることを説明した
が、劣化が著しく進展した場合には、水トリー内部を経
由する電荷の移動が完了した後にも、これと逆方向の健
全絶縁体部分中をゆっくりと移動する電荷が残される場
合も想定される。即ち、直流課電中において、水トリー
劣化部が著しく劣化していると、これと直列に存在する
健全部絶縁体に加わる直流電界が著しく増大して、空間
電荷の一部が健全部絶縁体側深くまで注入されたり、あ
るいは健全部絶縁体側の電極からホモ電荷が注入され
て、前述までの考察とは逆方向の電荷の移動の可能性が
ある。従って、図2の(d)に示すように、劣化が著し
い場合には、残留電荷が最大値を示した後に減衰し、場
合によっては電荷の極性が逆転するような時間特性が現
れる可能性もある。FIG. 2 shows the estimation of the relationship between the time characteristic of the residual charge and the deterioration state of the sample when an AC electric field is applied. In the case where the residual charge recovers slowly (a). It can be considered that the state of deterioration of the sample is small, and that the water tree deterioration is remarkable in the order of (a) to (c) where the recovery time is short. By the way, in the above explanation of the polarity of the residual charge, it is stated that the polarity of the observed charge is determined by the movement direction of the space charge after the ground is opened. It was explained that a polar residual charge was observed, but when the deterioration progressed significantly, even after the transfer of the charge through the inside of the water tree was completed, the charge slowly moved in the opposite direction in the healthy insulator part. It is also assumed that the charge that moves with is left. That is, if the water tree deteriorated portion is remarkably deteriorated during DC power application, the DC electric field applied to the sound portion insulator existing in series with the water tree portion is remarkably increased, and a part of the space charge is on the sound portion insulator side. There is a possibility that charges may move in the opposite direction to the above consideration due to deep injection or homo injection from the electrode on the insulator side of the sound part. Therefore, as shown in (d) of FIG. 2, when the deterioration is significant, there is a possibility that a residual charge shows a maximum value and then decays, and in some cases, a time characteristic such that the polarity of the charge is reversed. is there.
【0040】[0040]
【実施例】以下に、本発明を図示の実施例に基づいて詳
細に説明する。図3は本発明に係わる電力ケーブルの絶
縁劣化診断の測定回路である。図において、1は静電容
量がCx なる試料ケーブルであり、2は直流課電用電源
である。3は交流課電用電源であり、この交流課電用電
源と直列に静電容量がCS なるコンデンサ4が接続され
ている。5は残留電荷を測定するための入力抵抗の大き
な直流電圧計であり、この直流電圧計5はコンデンサ4
と並列に接続されている。SW1 は試料に直流を印加し
た後に接地して更にその後に交流電圧を印加するための
切り替えスイッチである。また、SW2 はコンデンサ4
を短絡するためのスイッチであり、このスイッチSW2
は測定回路を短絡、開放する役割を果たしている。8は
測定中の試料破壊時などに発生する異常電圧から測定回
路を保護するためのギャップアレスタである。DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the illustrated embodiments. FIG. 3 shows a measuring circuit for diagnosing insulation deterioration of a power cable according to the present invention. In the figure, 1 is a sample cable having a capacitance of Cx, and 2 is a DC power supply. Reference numeral 3 denotes an AC power supply for power supply, and a capacitor 4 having a capacitance of CS is connected in series with this AC power supply for power supply. 5 is a DC voltmeter with a large input resistance for measuring the residual charge. This DC voltmeter 5 is a capacitor 4
And are connected in parallel. SW1 is a changeover switch for applying a direct current to the sample, grounding it, and then applying an alternating voltage thereto. SW2 is the capacitor 4
This switch SW2 is for short-circuiting
Plays the role of shorting and opening the measuring circuit. Reference numeral 8 is a gap arrester for protecting the measurement circuit from an abnormal voltage generated when the sample is broken during measurement.
【0041】コンデンサ4の静電容量CS の大きさとし
ては、後述の操作によって試料に交流電圧VACを印加し
た場合に、直流電圧計5に加わる交流電圧Cx VAC/
(Cx+CS )が許容入力電圧以下になる値に選定され
ており、また、直流電圧計5の入力抵抗Rは、τ=(C
x +CS )Rで表される測定回路の放電磁定数τが電圧
測定時間の約500倍以上の値になるように選定されて
いる。The magnitude of the electrostatic capacity CS of the capacitor 4 is such that when the AC voltage VAC is applied to the sample by the operation described later, the AC voltage Cx VAC /
(Cx + CS) is selected to be a value below the allowable input voltage, and the input resistance R of the DC voltmeter 5 is τ = (C
The electromagnetic radiation constant τ of the measuring circuit represented by x + CS) R is selected to be a value about 500 times the voltage measuring time or more.
【0042】図3にて、まずスイッチSW2 を短絡した
状態で、時刻t=t01時に切り替えスイッチSW1 をa
側に接続して、直流課電用電源2から直流電圧−VDCを
試料1に印加する。直流−VDCを所定時間試料1に印加
した後の時刻t=t02に、切り替えスイッチSW1 をb
側に切り換えて、直流−VDCを抵抗R0 を介して放電さ
せる。この抵抗R0 は直流放電時の異常電圧発生を阻止
する目的のものである。In FIG. 3, first, with the switch SW2 short-circuited, the changeover switch SW1 is turned on at time t = t01.
, And a DC voltage −VDC is applied to the sample 1 from the DC power supply 2 for power supply. At time t = t02 after applying DC-VDC to the sample 1 for a predetermined time, the changeover switch SW1 is turned on.
Switching to the side, DC-VDC is discharged through the resistor R0. The resistor R0 is for the purpose of preventing abnormal voltage generation during DC discharge.
【0043】直流電圧−VDCが完全に放電された後の時
刻t=t03に切り替えスイッチSW1 をc側に切り換え
て、試料1に交流電圧を印加できる状態にする。この状
態下では、交流課電用電源3の内部インピ−ダンスの直
流抵抗がほぼ零に近いので、直流回路として見た場合に
は、試料1は大容量のコンデンサ4と並列に接続された
状態になり、また、測定回路の短絡スイッチSW2 が短
絡されているので試料1は接地された状態にある。At time t = t03 after the DC voltage -VDC is completely discharged, the changeover switch SW1 is changed over to the c side so that the AC voltage can be applied to the sample 1. In this state, the DC resistance of the internal impedance of the AC power supply 3 is close to zero, so that when viewed as a DC circuit, the sample 1 is connected in parallel with the large-capacity capacitor 4. In addition, since the short-circuit switch SW2 of the measuring circuit is short-circuited, the sample 1 is grounded.
【0044】次に、直流課電後の接地時刻t=t02から
所定時間経過した時刻t=t04に、測定回路の短絡スイ
ッチSW2 を開放する。この状態では、直流回路として
見ると、試料1は大容量のコンデンサ4と並列に接続さ
れた状態で電極間は開放されている。従って、スイッチ
SW2 を開放した時刻t=t04以後には、静電容量がC
S のコンデンサ4には直流電圧VS (t)が時間経過と
ともに回復してくるので、この電圧を直流電圧計5で測
定すればVS (t)×(CS +Cx )として残留電荷を
求めることが出来る。Next, at a time t = t04 after a lapse of a predetermined time from the grounding time t = t02 after the DC voltage application, the short circuit switch SW2 of the measuring circuit is opened. In this state, when viewed as a DC circuit, the sample 1 is connected in parallel with the large-capacity capacitor 4 and the electrodes are open. Therefore, after the time t = t04 when the switch SW2 is opened, the electrostatic capacitance becomes C
Since the DC voltage VS (t) recovers to the S capacitor 4 with the passage of time, if this voltage is measured by the DC voltmeter 5, the residual charge can be obtained as VS (t) × (CS + Cx).
【0045】上記の測定状態において、短絡スイッチS
W2 を開放した時刻t=t04から所定時間か経過した時
刻t=0 に、交流課電用電源3を用いて、試料1に交流
電圧を印加する。交流電圧の印加方法としては、時刻t
=0 から時刻t=t1 までのt1 時間中に交流電圧を零
から規定のVACまで昇圧して、その後時刻t=t1 から
t=t2 の(t2 −t1 )時間にわたってVACを保持し
た後に再び電圧を零に降圧する。In the above measurement state, the short-circuit switch S
At a time t = 0 when a predetermined time has elapsed from the time t = t04 when W2 is opened, an AC voltage is applied to the sample 1 using the AC power supply 3 for electric power supply. As the method of applying the AC voltage, time t
= 0 to time t = t1 during t1 time, the AC voltage is boosted from zero to the specified VAC, and then VAC is held for a time (t2-t1) from time t = t1 to t = t2 and then the voltage is restored again. Step down to zero.
【0046】図4は、図3の回路において上述の操作を
行なった場合の試料ケーブル1に対する印加電圧Vx と
測定される直流電圧VS (t)を示す模式図である。時
刻t=t04からt=0 までの交流課電を行なわない状態
下では、静電容量がCS のコンデンサ4の電極間には大
きな時定数を有する直流電圧VS (t)=Vs0(t)が
徐々に回復してくる。その後、時刻t=0 からt=t1
までの短時間に交流電圧を零からVACまでに昇圧する
と、直流電圧VS (t)は飛躍的に増大する。その後交
流電圧をVACに保持しているt=t1 からt=t2 の期
間では、VS (t)の変化特性は試料ケーブル1の劣化
状況によって様相が異なり、図2で説明したように、劣
化が著しくなるほどVS (t)の変化割合ΔVS /VS
(t1 )={VS (t2 )−VS (t1 )}/VS (t
1 )が小さくなり、劣化が極端な場合にはΔVS が負、
すなわちVS (t)が減少に転ずることもある。FIG. 4 is a schematic diagram showing the applied voltage Vx to the sample cable 1 and the DC voltage VS (t) measured when the above-mentioned operation is performed in the circuit of FIG. Under the condition that the AC voltage is not applied from time t = t04 to t = 0, the DC voltage VS (t) = Vs0 (t) having a large time constant is applied between the electrodes of the capacitor 4 having the capacitance CS. It gradually recovers. After that, from time t = 0 to t = t1
If the AC voltage is boosted from zero to VAC in a short time, the DC voltage VS (t) increases dramatically. After that, during the period from t = t1 to t = t2 in which the AC voltage is held at VAC, the change characteristic of VS (t) varies depending on the deterioration state of the sample cable 1, and as shown in FIG. As it becomes more remarkable, the change rate of VS (t) ΔVS / VS
(T1) = {VS (t2) -VS (t1)} / VS (t
1) becomes small and ΔVS is negative when the deterioration is extreme,
That is, VS (t) may start to decrease.
【0047】ところで、交流課電時に測定される直流電
圧VS (t)には、交流課電を行なわない場合に回復し
て来る電圧成分VS0(t)が含まれている。この電圧成
分VS0(t)には劣化部絶縁体が発生する劣化信号も含
まれているが、その殆どは、絶縁体の劣化状況とは無関
係な、例えば、試料ケーブル1の終端部表面に蓄積した
空間電荷などに原因している成分の可能性が強い。即
ち、交流課電時のコンデンサ4の電極間電圧VS (t)
の測定結果中に交流課電を行なわない場合の電圧成分V
S0(t)が含まれていると劣化診断の誤差要因になるの
で、測定結果VS(t)からこの電圧成分VS0(t)を
除去する必要がある。By the way, the DC voltage VS (t) measured during AC voltage application includes a voltage component VS0 (t) which is recovered when AC voltage is not applied. This voltage component VS0 (t) includes a deterioration signal generated by the deteriorated insulator, but most of it is irrelevant to the deterioration condition of the insulator, for example, accumulated on the end surface of the sample cable 1. There is a strong possibility that it is a component that is caused by the space charge. That is, the voltage VS (t) between the electrodes of the capacitor 4 when the AC voltage is applied.
Voltage component V when AC voltage is not applied during the measurement result of
If S0 (t) is included, it becomes an error factor in the deterioration diagnosis, so it is necessary to remove this voltage component VS0 (t) from the measurement result VS (t).
【0048】そこで、本発明に係わる絶縁劣化診断にお
いては、時刻t=t04からt=0 までの期間とt=t2
以降の交流課電を行なわない状態下で測定したコンデン
サCS の直流電圧VS (t)=VS0(t)の時間変化特
性からt=0 からt=t2 でのVS0(t)を推定して、
交流課電中の測定値VS (t)からこのVS0(t)を減
じた値を劣化診断に用いる。即ち、交流電圧をVACまで
昇圧した時刻t=t1での真の測定結果をVS1=VS
(t1 )−VS0(t1 )とし、また、交流電圧をVACな
る一定値に保持していた最終の測定時刻t=t2 での真
の測定結果をVS2=VS (t2 )−VS0(t2 )とし
て、これらの値から交流課電によって増大した残留電荷
Q(t1 )=VS1×(CS +Cx )と、Q(t2 )=V
S2×(CS +Cx )を求め、Q(t1 )の大きさと、Δ
(t)/Q(t1 )={Q(t2 )−Q(t1 )}/Q
(t1 )の値からケーブルの劣化状況を診断する。な
お、試料ケーブル1の電極長をノーマライズする必要を
考慮して、交流電圧昇圧直後の残留電荷Q(t1 )は、
試料ケーブル1の静電容量で割ったQ(t1 )/Cx
[V]として劣化判定に用いる。Therefore, in the insulation deterioration diagnosis according to the present invention, the period from time t = t04 to t = 0 and t = t2.
Estimating VS0 (t) from t = 0 to t = t2 from the time change characteristic of the DC voltage VS (t) = VS0 (t) of the capacitor CS measured under the condition that the alternating current is not applied thereafter,
A value obtained by subtracting VS0 (t) from the measured value VS (t) during AC power supply is used for deterioration diagnosis. That is, the true measurement result at time t = t1 when the AC voltage is boosted to VAC is VS1 = VS
(T1) -VS0 (t1), and the true measurement result at the final measurement time t = t2, when the AC voltage was held at a constant value of VAC, was VS2 = VS (t2) -VS0 (t2). , The residual charge Q (t1) = VS1 × (CS + Cx) increased by AC charging from these values, and Q (t2) = V
S2 × (CS + Cx) is calculated, and the magnitude of Q (t1) and Δ
(T) / Q (t1) = {Q (t2) -Q (t1)} / Q
The deterioration condition of the cable is diagnosed from the value of (t1). In consideration of the need to normalize the electrode length of the sample cable 1, the residual charge Q (t1) immediately after boosting the AC voltage is
Q (t1) / Cx divided by the capacitance of sample cable 1
It is used for deterioration determination as [V].
【0049】表1は、上記の測定方法を用いて水トリー
劣化した22kVCVケーブルと6.6kVCVケーブ
ルの残留電荷を測定した結果例を示すものである。試料
1から試料8は内部半導電層が押出し構造の22kVC
Vケーブルであり、試料9と試料10は半導電層がテー
プ構造の6.6kVCVケーブルである。なお、試料1
は殆ど劣化していない試料であり、試料10には電極間
を橋絡寸前までに進展した著しい劣化状態の水トリーが
存在している。Table 1 shows an example of the results of measuring the residual charges of the 22 kVCV cable and the 6.6 kVCV cable which have been deteriorated by the water tree using the above-mentioned measuring method. Samples 1 to 8 are 22 kVC in which the internal semiconductive layer has an extruded structure.
The V cables, and Samples 9 and 10 are 6.6 kVCV cables in which the semiconductive layer has a tape structure. Sample 1
Is a sample that is not substantially deteriorated, and in sample 10, there is a water tree in a significantly deteriorated state that has developed between the electrodes just before the bridging.
【0050】[0050]
【表1】 [Table 1]
【0051】表1に示されるように、交流電圧昇圧直後
に観測される残留電荷の大きさQ(t1 )は交流破壊電
圧の低下とともに増大する傾向が認められ、概ね、劣化
の進行とともに残留電荷が増大する傾向を示している。
しかしながら、必ずしも残留電荷が大きい場合でも破壊
電圧の低下が顕著でない場合や、逆に、残留電荷が小さ
い場合でも破壊電圧が顕著に低下している場合が認めら
れる。この原因は、主として、試料ケーブル中に存在す
る水トリーの発生個数の違い等による。As shown in Table 1, the magnitude Q (t1) of the residual charge observed immediately after boosting the AC voltage tends to increase as the AC breakdown voltage decreases. Shows an increasing tendency.
However, it is recognized that the breakdown voltage does not always decrease remarkably even when the residual charge is large, or conversely, the breakdown voltage significantly decreases even when the residual charge is small. This is mainly due to the difference in the number of water trees existing in the sample cable.
【0052】一方、{Q(t2 )−Q(t1 )}/Q
(t1 )で表した交流課電下での残留電荷の時間特性は
試料の破壊電圧の低下に対して極めて良好な相関性を示
しており、破壊電圧の低下とともに{Q(t2 )−Q
(t1 )}/Q(t1 )が減少し、著しい劣化状態の試
料10の場合には、{Q(t2 )−Q(t1 )}/Q
(t1 )が負の値まで変化している。即ち、交流課電下
での残留電荷の時間変化特性は、試料の劣化状況を的確
に表しており、この特性を利用すれば信頼性の高い水ト
リー劣化診断が可能となる。On the other hand, {Q (t2) -Q (t1)} / Q
The time characteristic of the residual charge under AC voltage application, which is represented by (t1), shows a very good correlation with the decrease of the breakdown voltage of the sample. As the breakdown voltage decreases, {Q (t2) -Q
(T1)} / Q (t1) decreases, and in the case of the sample 10 in a significantly deteriorated state, {Q (t2) -Q (t1)} / Q
(T1) has changed to a negative value. That is, the time-varying characteristic of the residual charge under AC voltage accurately represents the deterioration state of the sample, and by using this characteristic, highly reliable water tree deterioration diagnosis can be performed.
【0053】従来の吸収電流測定から残留電荷を求める
「残留電荷測定」では、時刻t2 での残留電荷Q(t2
)に相当する量を劣化判定に用いているが、表1に示
す結果では、{Q(t2 )−Q(t1 )}/Q(t1 )
が大きいほど劣化は進展していないことを示しているの
で、Q(t2 )の大きさによる劣化診断はQ(t1 )の
大きさによる劣化診断よりも診断精度が悪いことを示し
ている。従って、本発明に係わる劣化診断では、残留電
荷の大きさに基づく劣化判定としては、交流課電開始後
の早い時刻が好ましいと考えてQ(t1 )を採用してい
る。In the "residual charge measurement" in which the residual charge is obtained from the conventional absorption current measurement, the residual charge Q (t2 at time t2
) Is used for deterioration determination, the results shown in Table 1 show that {Q (t2) -Q (t1)} / Q (t1).
The larger the value, the more the deterioration has not progressed, which means that the deterioration diagnosis based on the size of Q (t2) is worse than the deterioration diagnosis based on the size of Q (t1). Therefore, in the deterioration diagnosis according to the present invention, Q (t1) is adopted as the deterioration judgment based on the magnitude of the residual charge because it is preferable that the time is short after the start of the AC voltage application.
【0054】なお、本詳細説明においては直流課電電圧
VDCを負極性としたが、正極性であっても何等問題な
い。また、図3の測定回路例では、交流課電用電源3と
接地の間に直流電圧測定回路(コンデンサ4、直流電圧
計5)を挿入する例を示したが、これを試料ケーブル1
と接地の間に挿入する回路に変更しても観測される電圧
の極性が見かけ上逆転するだけであって本質的には全く
問題ない。In this detailed description, the DC applied voltage VDC has a negative polarity, but it does not matter if it has a positive polarity. Further, in the measurement circuit example of FIG. 3, an example in which a DC voltage measurement circuit (capacitor 4, DC voltmeter 5) is inserted between the AC power supply 3 for power supply and the ground is shown.
Even if the circuit inserted between the ground and the ground is changed, the polarity of the observed voltage is only apparently reversed and there is essentially no problem.
【0055】[0055]
【発明の効果】以上に説明したように、請求項1に係わ
る電力ケーブルの絶縁劣化診断方法は、直流課電接地後
に交流電圧を課電した場合の残留電荷の時間特性を正確
に測定し、この残留電荷の時間変化割合を劣化診断の判
定信号に用いることによって、従来の一定時刻経過時点
での残留電荷の大きさのみを利用した劣化診断では判定
が不可能であった少数の極度劣化をも検出可能な信頼性
の高い電力ケーブルの水トリー劣化診断を達成すること
ができる。As described above, the method for diagnosing insulation deterioration of a power cable according to claim 1 accurately measures the time characteristic of the residual charge when an AC voltage is applied after the DC voltage is grounded. By using the time change rate of the residual charge as the determination signal for the deterioration diagnosis, a small number of extreme deteriorations that could not be determined by the conventional deterioration diagnosis using only the magnitude of the residual charge at a certain time elapsed time can be performed. It is also possible to achieve reliable and reliable water tree deterioration diagnosis of power cables.
【0056】また、請求項2に係わる直流課電接地後の
交流課電下での残留電荷の検出方法としては、直流的に
電極間を開放した状態で試料ケーブルの電極間の直流電
圧を電荷の漏洩を無視し得る時間範囲内で測定し、これ
によって、従来の接地回路に流れる吸収電流測定で残留
電荷を検出する方法では問題となる測定回路の応答遅れ
を大幅に解消し、交流課電下での残留電荷の時間特性を
正確に検出することを可能にすることができる。Further, as a method of detecting the residual charge under the AC voltage application after the DC voltage application and grounding according to claim 2, the DC voltage between the electrodes of the sample cable is charged with the DC voltage between the electrodes being opened. The leakage of electric current is measured within a time range that can be ignored, and this significantly eliminates the response delay of the measuring circuit, which is a problem with the conventional method for detecting residual charge by measuring the absorption current flowing in the ground circuit, and AC It can be possible to accurately detect the time characteristic of the residual charge under.
【図1】直流課電後の残留電荷と吸収電流発生に関する
説明図である。FIG. 1 is an explanatory diagram regarding generation of a residual charge and an absorption current after a DC voltage is applied.
【図2】交流電界を印加した場合の直流課電による残留
電荷の時間特性の説明図である。FIG. 2 is an explanatory diagram of a time characteristic of a residual charge due to DC voltage application when an AC electric field is applied.
【図3】直流課電接地後に交流課電下で残留電荷を測定
するための測定回路図である。FIG. 3 is a measurement circuit diagram for measuring residual charge under AC voltage application after DC voltage application grounding.
【図4】試料への電圧印加手順と測定される直流電圧を
示す模式的に示すタイムチャートである。FIG. 4 is a time chart schematically showing a procedure of applying a voltage to a sample and a measured DC voltage.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 坂本 中 埼玉県熊谷市新堀1008番地 三菱電線工業 株式会社熊谷製作所内 (72)発明者 中川 雅善 埼玉県熊谷市新堀1008番地 三菱電線工業 株式会社熊谷製作所内 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inaka Sakamoto 1008 Shinbori, Kumagaya, Saitama Prefecture Mitsubishi Cable Industries, Ltd. Kumagaya Manufacturing Co., Ltd. (72) Inventor Masayoshi Nakagawa 1008, Shinbori, Kumagaya, Saitama Mitsubishi Cable Industries, Ltd. Within
Claims (2)
し、その後に交流電圧を課電した状態で直流課電によっ
て生じた残留電荷を測定することにより電力ケーブルの
絶縁劣化を診断する方法において、交流電圧課電下で残
留電荷の時間特性を測定し、該残留電荷の時間変化割合
によって電力ケーブルの絶縁劣化の程度を診断すること
を特徴とする電力ケーブルの絶縁劣化診断方法。1. A method of diagnosing insulation deterioration of a power cable by grounding after applying a DC voltage to the power cable and then measuring the residual charge generated by the DC voltage in the state of applying an AC voltage. A method for diagnosing insulation deterioration of a power cable, which comprises measuring a time characteristic of a residual charge under application of an AC voltage and diagnosing a degree of insulation deterioration of the power cable based on a time change rate of the residual charge.
測定回路の放電時定数よりも著しく短い時間範囲内で試
料ケーブルの電極間の直流電圧を測定する請求項1に記
載の電力ケーブルの絶縁劣化診断方法。2. In a state in which the electrodes are opened in a DC circuit,
The method of diagnosing insulation deterioration of a power cable according to claim 1, wherein the DC voltage between the electrodes of the sample cable is measured within a time range significantly shorter than the discharge time constant of the measurement circuit.
Priority Applications (1)
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JP19948794A JP3184712B2 (en) | 1994-08-24 | 1994-08-24 | Diagnosis method for insulation deterioration of power cable |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP19948794A JP3184712B2 (en) | 1994-08-24 | 1994-08-24 | Diagnosis method for insulation deterioration of power cable |
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JPH0862280A true JPH0862280A (en) | 1996-03-08 |
JP3184712B2 JP3184712B2 (en) | 2001-07-09 |
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JP19948794A Expired - Lifetime JP3184712B2 (en) | 1994-08-24 | 1994-08-24 | Diagnosis method for insulation deterioration of power cable |
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JP2006337226A (en) * | 2005-06-03 | 2006-12-14 | Furukawa Electric Co Ltd:The | Residual charge measuring method for cv cable |
CN111707910A (en) * | 2020-05-28 | 2020-09-25 | 广州广华智电科技有限公司 | Porcelain insulator internal insulation detection method and porcelain insulator detection circuit |
CN115372747A (en) * | 2022-09-14 | 2022-11-22 | 国网江苏省电力有限公司电力科学研究院 | Cable aging degradation state detection method and aging monitoring device |
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-
1994
- 1994-08-24 JP JP19948794A patent/JP3184712B2/en not_active Expired - Lifetime
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JP2006337226A (en) * | 2005-06-03 | 2006-12-14 | Furukawa Electric Co Ltd:The | Residual charge measuring method for cv cable |
JP4676255B2 (en) * | 2005-06-03 | 2011-04-27 | 古河電気工業株式会社 | CV cable residual charge measurement method |
CN111707910A (en) * | 2020-05-28 | 2020-09-25 | 广州广华智电科技有限公司 | Porcelain insulator internal insulation detection method and porcelain insulator detection circuit |
CN111707910B (en) * | 2020-05-28 | 2024-04-19 | 广州广华智电科技有限公司 | Porcelain insulator inner insulation detection method and porcelain insulator detection circuit |
CN115372747A (en) * | 2022-09-14 | 2022-11-22 | 国网江苏省电力有限公司电力科学研究院 | Cable aging degradation state detection method and aging monitoring device |
CN115856456A (en) * | 2023-02-27 | 2023-03-28 | 国网山东省电力公司广饶县供电公司 | Cable charge test data transmission method |
CN115856456B (en) * | 2023-02-27 | 2023-06-23 | 国网山东省电力公司广饶县供电公司 | Cable charge test data transmission method |
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