SU1486934A1 - Method for continuous testing of insulation dielectric strength of cable articles - Google Patents

Description

The invention relates to electrical engineering and can be used to create devices for continuous monitoring of the electrical strength of cable products during their rewinding.

The purpose of the invention is to increase the reliability of the test results.

. The drawing shows a device that implements the proposed method.

The device contains a high voltage source 1, one of the terminals of which is connected to the electrode 2, along which the test cable product 4 is moved by means of the rewind mechanism 3, and the other with the cable product under test, an inductive sensor 5 placed near

electrode 2 and performing together with a capacitor (without position designation) the functions of a low-pass filter. The output of the inductive sensor 5 is connected to the input of the registration unit 6.

Method for continuous testing of the electrical strength of the insulation of cable products is as follows.

From the high voltage source 1 between the cable product under test 4 and the electrode 2, along which the product 4 is moved by means of the mechanism 3, a high alternating voltage of 503000 Hz is applied. A magnetic field arises around the cable product under test 4, which is captured by sensor 5

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and converted to an electrical signal. The components of this signal, the frequency of which is lower than the natural frequency of oscillations of the current in the elec- trode circuit, the cable product being tested, are filtered out, and the resulting filtered signal is fed to the recording unit 6.

When the test voltage is supplied to the product 4 with intact insulation, a leakage current appears through the insulation, the value of which is determined by the internal resistance of the high-voltage source 1 and the partial capacitance. In addition, due to the nonlinear nature of the dependence of the leakage current on the voltage on the test electrode, due to the presence of a corona discharge near the 20 electrode and distortions in the form of the applied voltage, interference current occurs in a wide frequency range.

With a significant amount of fluctuations in the thickness of the insulation, permissible under the 25 conditions of cable production, the interference current can reach values commensurate with the current value during insulation breakdown. However, when the breakdown? insulation due to the energy stored in the parasitic capacitance, appears · an alternating current of resonant frequency, the value of which is mainly limited by the reactance of the high voltage source 1 and parasitic capacitance

stew. The oscillation frequency of this current during insulation breakdown is lower, the greater the parasitic capacitance (that is, the thicker the insulation), and is in the frequency range 100-300 kHz and higher. In this frequency range, the high-frequency components of the noise arising from the corona discharge and distortions in the form of a test voltage are many times smaller than the resonant component during breakdown, which makes it possible to fix insulation breakdowns with increased reliability.

In order to obtain the minimum value of the high-frequency component of interference in the measured signal, in the proposed method, the breakdown is fixed at the frequencies arising from the breakdown of samples of cable products. In order to take into account the entire spectrum of the useful signal, a sample with the largest possible thickness is used for breakdown, which corresponds to the lowest frequency of the resonant current.

Thus, the proposed method allows to significantly increase the reliability of insulation dielectric strength tests due to the fact that in the frequency range, starting from the resonant frequency in the circuit formed by the electrode and the product under test, the ratio of the useful signal to interference is much higher than at low hours.

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Claims (2)

METHOD OF CONTINUOUS TESTING OF ELECTRICAL STRENGTH OF ISOLATION OF CABLE PRODUCTS, which consists in 2 Applying an alternating test voltage between the cable product being tested and the electrode along which the cable under test is moved. filter components whose frequency is lower than their own; the frequency of oscillation of the current in the circuit electrode - the cable product under test, according to the nature of the change in the resulting ot-. § the filtered signal determines the presence of breakdown in the cable product.