JP3431390B2 - Cable insulation diagnosis method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a cable insulation diagnosis method capable of accurately measuring the state of insulation deterioration of a power cable. 2. Description of the Related Art Conventionally, a pulsation detecting method for measuring a deterioration state of insulation of a power cable by measuring a minute current flowing through a ground wire of a metal shielding layer of a cable when a test voltage such as an AC high voltage is applied. However, this detection method is a measurement taking into account the insulation abnormality of the shielding layer. Therefore, even if an abnormality is found, it is very difficult to distinguish whether the cable insulation layer is deteriorated or the shield layer is defective. An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a cable insulation diagnosis method capable of distinguishing between cable insulation deterioration and shielding layer defects for diagnosis. According to the present invention, there is provided a cable insulation diagnosis method for injecting a random noise signal into a conductor of a power cable to which a fundamental wave is applied. The signal corresponding to the random noise signal is extracted by removing the fundamental wave from the signal obtained through the insulating layer of the cable and the metal shielding layer, and a coherence function and a transfer function are calculated based on the signal to obtain a signal. It is characterized by diagnosing the insulation deterioration state of the power cable by evaluating the obtained coherence function and transfer function. [0006] In the method for diagnosing insulation of a cable having the above structure, a random noise signal is injected into a conductor of the cable.
Diagnosis is performed by obtaining a coherence function and a transfer function from a signal corresponding to a random noise signal obtained via an insulating layer and a metal shielding layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a circuit configuration diagram for implementing the present invention. The output from the test reference AC power supply 1 is connected to the conductor 3a of the power cable 3 to be measured via the transformer 2, and the output of the random noise generator 4 for generating a Gaussian noise signal is connected to the low voltage side of the transformer 2. I do. On the other hand, the detection circuit 5 is connected to the metal shielding layer 3b of the cable 3, and the output of the detection circuit 5 is connected to the data collection circuit 6, and the data collection circuit 6 has an arithmetic circuit 7 such as a computer.
Connect. At the time of measurement, a fundamental wave is generated from an AC reference power supply 1 via a transformer 2 and is, for example, 50 Hz, 6 Hz.
An AC voltage of 600 V is applied to the conductor 3a. Further, for example, a Gaussian noise signal of several V between 0 and 50 Hz obtained by selecting the output from the random noise generator 4 is superimposed on this AC voltage. [0009] From the conductor 3a to the insulating layer 3c, the metal shielding layer 3b
Is input to the detection circuit 5, the detection circuit 5 removes a fundamental wave from the AC reference power supply 1 by a filter or the like, amplifies a signal corresponding to the obtained Gaussian noise signal as necessary, The data is collected by the collection circuit 6 and stored in a time-dependent manner. At the same time or at another time, the data is used by the arithmetic circuit 7 to determine a coherence function and a transfer function for a frequency of, for example, 0.1 to 20 Hz. The coherence function and the transfer function include information on how the Gaussian noise signal is transmitted from the conductor 3a of the cable 3 through the insulating layer 3c and the shielding layer 3b. From this, the insulation state of the cable 3 can be diagnosed. In addition, other basic statistics (standard deviation,
Calculations such as skewness and kurtosis), Crewbag identification information criterion, power spectral density, and wavelet transform were attempted, but no significant difference was obtained as much as the coherence function and transfer function. 2A to 2A are coherence functions,
(b) shows the transfer function. FIG. 2 shows a case where both the insulating layer 3c and the shielding layer 3b are normal, the coherence function is 0.5 to 0.7 at 0.5 to 15 Hz, the transfer function has a peak at 1.0 Hz, and It has a beautiful mountain shape of about 4. In this case, since linear transmission depending on the capacitance between the conductor 3a and the metal shielding layer 3b can be expected, the coherence function appears with a substantially constant correlation,
The characteristics of the preceding filter appear in the transfer function. FIG. 3 shows a case in which the insulating layer 3c is normal, but is grounded in the shielding layer 3b, and the transfer function is jagged. Since the noise signal caused by the grounding of the shielding layer 3b affects the low frequency range, this appears in the coherence function. FIG. 4 shows the case where the insulating layer 3c is deteriorated and the shielding layer 3b is normal, and the coherence function is 10 to 20.
The output is rapidly attenuated at Hz. A noise signal due to the deterioration appears in a high frequency region, and this appears in a coherence function. In addition, the transfer function is affected by the filter, and has a smaller shape. FIG. 5 shows that the insulating layer 3c has deteriorated and the shielding layer 3c has been deteriorated.
b also shows the case where it is grounded. The coherence function is reduced over the entire target frequency range, and the transfer function is also reduced in shape. The following table shows these criteria. Coherence function Transfer function Insulating layer normal, shielding layer normal 0.5 to 15 Hz Peak at 1.0 Hz 0.5 or more 0.4 or more Insulating layer normal, shielding layer deterioration 5 to 15 Hz Peak at 1.0 Hz 0.5 0.4 or more Insulation layer deterioration, shielding layer normal 1 to 10 Hz 0.5 to 1.0 Hz peak 10 to 15 Hz 0.2 or less 0.2 or less Insulation layer deterioration, shielding layer deterioration 0.5 to 15 Hz 1.0 Hz In this embodiment, the test reference AC power supply 1 is used as a fundamental wave in the test, but an actual commercial power supply can be used as it is. As described above, according to the cable insulation diagnosis method of the present invention, a random noise signal is injected into a conductor, and a coherence function and a transfer function are obtained from a signal obtained from a shielding layer. Diagnosis of insulation deterioration state from the combination of.

[Brief description of the drawings] FIG. 1 is a circuit configuration diagram of a measurement system. FIG. 2 is a waveform diagram after signal processing. FIG. 3 is a waveform diagram after signal processing. FIG. 4 is a waveform diagram after signal processing. FIG. 5 is a waveform chart after signal processing. [Explanation of symbols] 1 Reference AC power supply for testing 2 transformer 3 cable 3a conductor 3b Metal shielding layer 3c insulating layer 4 Random noise generator 5 Detection circuit 6 Data collection circuit 7 Operation circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mihaku Tsunoda 1008 Niibori, Kumagaya-shi, Saitama Mitsubishi Cable Industry Co., Ltd. (72) Inventor Shigeto Nakamura 1008 Niibori, Kumagaya-shi, Saitama Mitsubishi Cable Industries Inside Kumagaya Works Co., Ltd. (72) Inventor Yujiro Mud 1008 Shinbori, Kumagaya City, Saitama Prefecture Mitsubishi Cable Works Co., Ltd. Kumagaya Works Co., Ltd. (56) References JP-A-59-69813 (JP, A) JP-A-63-135876 (JP, A) JP-A-2-226022 (JP, A) JP-A-2-22633 (JP, A) JP-A-6-174579 (JP, A) JP-A-6-129701 (JP, A) ( 58) Surveyed field (Int.Cl. ⁷ , DB name) G01R 27/18 G01R 31/12

Claims (1)

(57) [Claim 1] A random noise signal is injected into a conductor of a power cable in a state where a fundamental wave is applied, and a random noise signal is injected from a signal obtained through an insulating layer and a metal shielding layer of the cable. A signal corresponding to the random noise signal is extracted by removing the fundamental wave, a coherence function and a transfer function are calculated based on the signal, and the obtained coherence function and transfer function are evaluated. A method for diagnosing insulation of a cable, comprising diagnosing an insulation deterioration state.