RU2515360C2 - Method for testing of contact joint state in electric circuits - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is referred to the field of electric machine engineering and can be used for manufacture of process test systems related to operation of contact joints in electric circuits in industry and transport. The method lies in that current pulse with DC component is supplied to a deenergised contact joint, then current signals and voltage drop of this current at contact joint terminals are recorded, current and voltage curves are transformed into Fourier series, active and reactive resistance is determined for the contact joint for each harmonics of current and voltage. Harmonics related to the current source are subtracted from voltage drop spectrum. State of the contact joint is assessed against remaining harmonics of voltage spectrum by means of harmonic comparing with specific defects of the contact joint, active and reactive resistance values of harmonics are compared with the reference values for this type of the contact joint.

EFFECT: providing control for dynamics of development of contact joint deterioration process.

Description

The present invention relates to the field of electrical engineering, in particular to the creation of high-quality process control systems associated with the operation of electrical circuits.

In the energy sector, in industry and in transport, a large number of types of contact joints are used in the electrical circuits of stationary and moving objects. The work of the contact joint during operation starts from the normal mode, when the contact can be characterized by a linear electric element with active resistance. Electrical contact depends on parameters such as the resistivity of the material (or materials), contact area, contact pressure, temperature, oxide films and other factors associated with operating conditions. Moreover, in contact compounds, their operational properties deteriorate, even to the point of their destruction, associated with phenomena such as increased heating, oxidation, arcing, electric arc formation, and metal spatter [1]. The contact joint in the stage of structural deviations from the norm is a rather complex nonlinear electrical element, characterized in the general case not only by one electrical parameter (active resistance), but also by other parameters that more fully determine the contact joint in this state. In practice, there are several ways to control the electrical state of contact compounds, which actually allow you to measure or evaluate the active resistance of a contact when a small DC current is passed through it. The numerical value of the contact resistance obtained in this way is compared with its acceptable value [2].

The processes of aging of a contact joint can occur at different speeds, therefore, existing control methods with a single procedure for measuring the active resistance of a contact joint practically do not allow to assess the dynamics of the process of destruction of a contact joint and do not provide information on the causes of a change in contact resistance.

The proposed method for monitoring the state of contact connections of electrical circuits is developed on the basis of the theory of harmonic analysis [3, 4], on the results of the patent [5] and solves these problems.

The method allows to obtain the frequency spectra of the current flowing through the contact connection, and the voltage drop across it from this current, to determine its total complex resistance for each harmonic separately, to evaluate the state of the contact connection by the active and reactive components of the total complex harmonic resistance, and also to obtain information about the possibility of arcing and the formation of an electric arc during operation of the contact joint.

The method boils down to the implementation of the following procedures. The contact connection of the electric circuit is de-energized. Any form of current pulse (containing a constant component), such as a rectangular pulse, is applied to the terminals of the contact connection, for example, the input current and voltage signals at the terminals of the contact connection are taken, the current and voltage curves are expanded in a Fourier series. In this case, the Fourier expansion terms of a rectangular current pulse will contain odd harmonics and a constant current component. A linear electrical equivalent circuit of the contact connection is adopted, in this case the same harmonics will be present in the recorded voltage waveform as in the current spectrum, plus the constant voltage component. Further, according to Ohm's law, the values of the module of the total complex resistance of the contact connection for each harmonic separately of the current and voltage are found, and the active resistance of the contact connection is determined by the constant components of current and voltage using the formulas:

Z _k = U _mk / I _mk and R ₀ = U ₀ / I ₀ ,

where Z _k is the modulus of the total complex resistance Z _k = R _k + JX _{k of the} kth harmonic (j is the imaginary unit); R ₀ is the active resistance; U _mk and I _mk are the amplitude values of the kth harmonic of voltage and current, respectively; U ₀ I _0, and - a number of DC components of voltage and current, respectively, Fourier, R _k - k-resistance of the harmonics, X _k - reactance k-harmonic component. The total complex resistance Z _k = R _k + jX _k characterizing the contact compound can be inductive X _k > 0, capacitive (X _{k <} 0) or active (X _k = 0), which determine the physical properties of the studied contact compound in addition to the common resistance R ₀ . If the values of the modules of the total complex resistances of the contact connection of the k-th harmonics Z _k practically coincide with the active resistance R ₀ , then the reactance at the total complex harmonic resistance will be zero X _k = 0, then the active resistances of the harmonics are taken equal to the active resistance r ₀ (R _k = R ₀ ), which is taken as the active resistance of the contact compound R ₀ . If the values of the modules of the total complex resistances of the contact connection of the k-th harmonics are greater than the resistance value found for the constant components of the current and voltage Z _k > R ₀ , then the values of the reactance of the k-th harmonics are calculated by the formula:

, $$X_k=\sqrt{}(Z_k^2-R_0^2)$$

,

where the sign is determined by the following rule. If the current curve is more sinusoidal than the voltage curve, then the voltage harmonic coefficient will be greater than the current harmonic coefficient K _ГU > K _ГI , then the total complex resistance is inductive (X _k > 0). If the current curve is more non-sinusoidal than the voltage curve, then the voltage harmonic coefficient will be less than the current harmonic coefficient K _ГU <K _ГI , then the total complex resistance is capacitive (X _k <0).

Based on the found values of active and reactance, depending on the type of contact connection, an assessment is made of its further operation. The appearance in the voltage spectrum of harmonics frequencies different from the harmonics of the input current indicates that the contact connection is a nonlinear element. In this case, in the contact joint during its operation, electromagnetic processes such as sparking, the formation of an electric arc, a semiconductor effect and other effects can occur. In this case, the harmonics associated with the current source are subtracted from the voltage spectrum, and the state of the contact joint is estimated from the remaining harmonics of the voltage spectrum part [5]. In fact, the very fact of the appearance of such harmonics indicates its malfunction, and from the design features of the contact connection, the reason for their occurrence arises.

Practical implementation of the proposed method is carried out using a generator of rectangular (or other types) of current pulses, the signal of which is supplied to a de-energized contact connection. With the help of modern digital equipment, current and voltage signals at the contact connection are removed and processed, the current and voltage curves are expanded in a Fourier series. The active and reactive resistances of the contact compound are found, a part of the voltage spectrum characterizing the contact compound as a nonlinear element is obtained, then the state of the contact compound is estimated from the obtained data by comparing them with the reference data for this type of contact compound. The proposed method for monitoring the state of contact connections of electrical circuits can be implemented in real time in stationary and field conditions, the required number of harmonics is used to analyze the operability of the contact connection, the current pulse parameters are selected by the operator depending on the required accuracy for this type contact compound.

Literature

1. General information about electrical contacts. Internet resource: http://elektrokontakty.ru/

2. Methods for monitoring the state of contact joints during the operation of electrical networks. Internet resource: http://electricalschool.info/main/ekspluat/200-sposoby-kontrolja-stojanija.html.

3. Goldman S. Harmonic analysis, modulation and noise. - M: Publishing house of foreign literature, 1951. - 408 p.

4. Zeveke G.V. et al. Fundamentals of circuit theory. - M .: Energoatomizdat, 1989 .-- 528 p.

5. Pat. No. 2319586 Russian Federation, RU 2319586 C2, IPC V23K 9/10 (2006.01). A method of monitoring and controlling the process of electric welding. / Stepanov A.P., Milovanov A.I., Chernyak S.S., Salomatov V.N., Lopatin M.V., Butakov V.F., Stepanov M.A.,; applicant and patentee Irkut. state unt-t paths communicated. - No. 2005136650/02, declared 11.24.2005, publ. 03/20/2008, Bull. No. 8.

Claims (1)

A method for monitoring the state of contact joints of electric circuits, taking into account the state of the contact joint according to the spectrum of a current pulse having a constant component and transmitted through the contact joint, and the spectrum of voltage drop across the contact joint from this current, characterized in that the state of the contact joint is judged by the analysis of current spectra and voltage drops by calculating the active and reactance of their harmonics; the harmonics associated with the current source are subtracted from the voltage drop spectrum, and the state of the contact joint is estimated from the remaining harmonics of the voltage spectrum part by comparing the remaining harmonics with the characteristic faults of the contact joint and comparing the active and reactive resistances of the harmonics with the reference ones for this type of contact joint.