RU2536795C1 - High-voltage diagnostic method against partial discharge parameters - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is used invention relates to high-voltage engineering, in particular, to diagnostics of high-voltage equipment against parameters of electric noise induced by partial discharges. The invention concept is as follows: an electromagnetic field of partial discharges in insulation is sensed by inductive and capacitance transducers, which output signals are filtered, amplified and multiplied one by the other. Depending on the product sign informative signals are generated; the first signal is proportional to the valid average apparent charge of the partial discharges while the second signal is proportional to the valid average time of current impulses induced by the partial discharges. By means of the first signal there corrected is the speed of changing the intensity of the electric field in insulation, thus providing the frequency stabilisation of the current average value of an apparent charge by the partial discharges. By means of the second signal dependency is defined of the current pulse time resultant from the partial discharges on voltage at high-frequency input of the controlled equipment.

EFFECT: reducing the measurement error, increasing selectivity and reliability of diagnostics.

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Description

The present invention relates to high voltage technology and can be used to diagnose high-voltage equipment by the parameters of electrical noise caused by partial discharges (PD).

Known methods for diagnosing and testing insulation by measuring the characteristics of partial discharges using inductive and capacitive sensors (R.E. James et al. Application of a capacitive Network Winding Representation to the Location Partial Discharges in Transformers / Electric Engineering Transaction, Vol. EE-13 , N2, 1977. P.95-103; Patent RU 2207581 C2, 04.17.2001, IPC G01R 31/08, 31/11), consisting in the fact that partial discharges are recorded using inductive or capacitive sensors, the output signals of which are filtered and amplify, thus forming a signal that carries information about electrical noise caused by PD in isolation diagnosed high-voltage equipment. A common disadvantage of these methods is the low reliability of the diagnosis, due to the influence of electric discharges that occur outside the diagnosed equipment.

A known method of controlling partial discharges in an electric power transformer (Eurasian Patent Office 000019 B1, 12/30/1997, IPC G01R 31/02, 31/34). The method consists in the fact that, at the operating voltage at the high-voltage input, electric noise from partial discharges of the power transformer is sensed by inductive and capacitive sensors, the output signals of which are filtered, amplified and multiplied one by one, and, in accordance with the sign of the product, they form a signal that carries information about partial discharges in the transformer tank.

The method does not provide the required selectivity of the discharges inside and outside the high-voltage equipment, has insufficient reliability and does not possess the necessary visualization of the presentation of the control results. These shortcomings are largely due to a wide range of apparent charges of partial discharges in the insulation of the transformer. As a result, at certain values of the electric field strength, the current average value of the apparent PD charges in the damaged insulation is so high that it goes beyond the dynamic ranges of sensors that filter, amplify and multiply the components of the measuring instruments. Because of this, there is a distortion of the parameters of partial discharges, the appearance of a false polarity of the product of the signals of inductive and capacitive sensors is possible. The likelihood of saturation of the amplifying components as a result of overlapping PDs arising in different areas of the diagnosed equipment on top of each other increases. This leads to a temporary shift in the transition of their output voltages through the zero level and may cause an incorrect determination of the polarity of the product of the signals of the inductive and capacitive sensors. As a result, the required level of selectivity to the perception of discharges inside and outside the diagnosed high-voltage equipment is not provided. In addition, when using the known method for recording the characteristics of the Czech Republic using digital recorders widely used in the diagnosis of high-voltage equipment (Mikheev G.M. Digital diagnostics of high-voltage equipment. - Publishing House "Dodeka - XXI", 2008. - 304 p.), to ensure the visibility of the control results, there is a difficult to eliminate contradiction between the speed and accuracy of registration. These disadvantages significantly reduce the efficiency of diagnostics of high-voltage equipment using electrical noise caused by partial discharges.

The purpose of the invention is to increase the reliability and visibility of the results of electro-noise diagnostics of high-voltage equipment by providing high selectivity of electrical noise caused by PD inside and outside the equipment, reducing errors in measuring PD parameters and presenting diagnostic results in the form of dependences of the duration of current pulses caused by partial discharges on voltage at the high voltage input of the diagnosed equipment.

This goal is achieved by the fact that the electromagnetic field of partial discharges is perceived at the high-voltage input of the power transformer by inductive and capacitive sensors, the output signals of which are filtered, amplified and multiplied by one another and, in accordance with the sign of the product, form informative signals, the first of which is proportional to the current average value of the apparent of partial discharges, and the second to the current average value of the duration of current pulses caused by partial discharges, using the first They adjust the rate of change of the electric field strength in the insulation, providing stabilization of the current average value of the apparent charge of partial discharges, and using the second one, determine the dependence of the duration of current pulses caused by partial discharges on the voltage at the high-voltage input of the diagnosed equipment.

When diagnosing the proposed method, the electric field in the insulation of high-voltage equipment is changed in accordance with the current average value of the apparent charge of partial discharges, reducing the rate of change of tension with increasing current average value of the apparent charge and increasing with decreasing it. Thus, the diagnostics are carried out in the mode of stabilization of the current value of the apparent PD charge at a level corresponding to the minimum measurement error of the PD parameters, while determining the current average values of the amplitude of the current pulses caused by partial discharges.

Figure 1 presents a block diagram of a device that implements the proposed method for the diagnosis of high-voltage equipment. It shows part of tank 1 and input 2 of the diagnosed high-voltage apparatus with inductive 3 and capacitive 4 PD sensors placed on it, connected to the inputs of signal processing unit 5, the first output of which is connected to input Y of digital recorder 6, and the second output is connected to the first input subtractor 7, and the second input of the subtractor is connected to the output of a rectangular voltage source 8, and the output to the input of the integrator 9. The output of the integrator 9 is fed to the input X of the digital register ator 6 and to the primary winding of step-up transformer 10, the voltage from which is supplied to input 2.

Figure 2 presents the structural diagram of the signal processing unit 5, which includes amplifier-filtering components 11 and 12, to the inputs a and b of which the inductive 3 and capacitive 4 PD sensors are connected, and the outputs are connected to the inputs of the multiplier 13, the output of the latter connected to the control input of the switching unit 14, the signal input of which is connected to the output of the amplifier-filtering component 11, and the output is connected to the averaging RC circuit 15 and to a series-connected amplitude pulse modulator 16, averaging RC circuit 17 and the inverse value calculator 18.

The device operates as follows. The signals of electric discharges are received by inductive and capacitive sensors 3 and 4, reduced to the same level and freed from interference by passing through the filter-amplifying components 11 and 12, and then multiplied by the device 13. The output signal of this device, the polarity of which is determined by the place where the discharge occurred (t ie inside or outside the diagnosed high-voltage equipment), controls the operation of the switching unit 14, providing further passage of current pulses corresponding to the PD only inside the diagnosed equipment blowing

$$i_{hR}(t)=d{Q}_{hR}(t)/dt,\left(\mathrm{one}\right)$$

where Q _cr (t) is the apparent charge of the Czech Republic.

Coming to the input of the averaging RC circuit 15, these pulses cause voltage at its output

$$u_{\mathrm{one}}(t)=\frac{k_{\mathrm{one}}}{\Delta \tau }{\displaystyle \sum _{k=\mathrm{one}}^{\Delta N}{\displaystyle \underset{t_k}{\overset{t_k+{\tau }_k}{\int }}{i}_{hR}(t)dt=k_{\mathrm{one}}{\overline{Q}}_{hR}\Delta N/\Delta \tau \left(2\right)}}$$

where k ₁ is the coefficient of proportionality; Δτ is the averaging interval of the RC circuits 15 and 17; ΔN is the number of PD in the averaging interval; t _to and t _to - respectively, the time of occurrence and the duration of the k-th PD; Q _HR - the average value in the interval Δτ of the apparent charge of the PD. The amplitude modulator 16 generates from pulses of complex shape (1) corresponding to the PD, unipolar rectangular current pulses of the same amplitude, but of a stable duration τ ₀ . The current average value of this pulse signal is allocated by the averaging circuit 17, the output of which acts voltage

$$u_2(t)=k_2{I}_{\mathrm{from}\mathrm{<figure-callout\; id="0"\; label="R\; \tau "\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">R\; </figure-callout>}}{\tau }_{}{}_0\Delta N/\Delta \tau ,\left(3\right)$$

where k ₂ is the coefficient of proportionality; I _cf is the current average value of the amplitude of the current pulses (1).

On the subtractor 7, a voltage difference is generated and fed to the input of the integrator 9, one of which, alternating with an amplitude U ₀ = const, comes from a rectangular voltage source 8, and the other, u ₁ (t), from the averaging RC circuit 15. The output of the integrator is voltage

$$u_3(t)=\frac{k_3}{\tau }{\displaystyle \underset{0}{\overset{t}{\int }}[U_0-u_{\mathrm{one}}(t)]dt\left(\mathrm{four}\right)}$$

where k ₃ is the coefficient of proportionality; τ is the integration constant. This voltage is applied to the input X of the digital recorder 6 and to the primary winding of the step-up transformer 10.

Given that

du ₃ (t) / dt = [dQ _cp (t) / dt] × [du ₃ (t) / dQ _cp (t)] = i _cp (t) / C,

where C is the equivalent capacitance of the PD current circuit, we differentiate (4). As a result, we get

U ₀ -u ₁ (t) = τi _чр (t) / k ₃ C.

Thus, if k ₃ is large enough, which is easily achieved when the integrator is based on a modern operational amplifier, then

U ₀ ≈u ₁ (t),

those. due to negative feedback, taking into account (2), the stabilization mode of the current average value of the apparent charge of partial discharges is implemented

k ₁ Q _cp ΔN / Δτ = k ₁ I _cf τ _cf ΔN / Δτ = U ₀ ,

where τ _cf is the current average over the averaging interval Δτ is the value of the duration of the current pulses caused by partial discharges.

In this case, the expression

I _cf = ΔτU ₀ / ΔNk ₁ τ _cf

after substituting it into (3), we obtain

u ₂ (t) = k ₂ τ ₀ U ₀ / k ₁ τ _cf = k ₄ / τ _cf

where k ₄ = const.

The signal u ₂ (t) is converted by the inverse value calculator 18 to a voltage proportional to the current average value of the current pulse duration caused by partial discharges

u ₄ (t) = τ _cf / k ₄ .

This voltage is supplied to the input Y of the digital recorder 6, to the input X of which from the output of the integrator 9 a voltage is proportional to the voltage at the input 2 of the diagnosed high-voltage apparatus. Thus, the dependence of the current average values of the duration of the current pulses caused by partial discharges on the applied voltage τ _cf = f (U) is provided. Registration is performed in the mode of stabilization of the current value of the apparent PD charge at a level corresponding to the minimum measurement error of the PD parameters. This level is determined by the transmission coefficient in the control circuit, including the diagnosed isolation, as well as elements 2, 3, 4, 5, 9, and 10 (Fig. 1). The selection criterion for this level is the absence of changes in the recorded dependences τ _cf = f (U) with a decrease in the modulus of this coefficient, for example, by reducing the gain in components 11 and 12 (Fig. 2).

Analysis of the insulation state of high-voltage equipment is carried out according to the graph of the dependence τ _cf = f (U). Figure 3 presents typical dependency graphs τ _cf = f (U) obtained by the proposed method on a laboratory high-voltage transformer with low quality insulation, close to critical. The amplitude of the test voltage for curve 1 is 50%, and for the curve 2-120% of the nominal operating amplitude. The initial sections of the curves (oac for curve 1) correspond to the initial increase in the electric field strength from zero to a positive amplitude value after applying the test voltage, and closed loop-shaped contours (curve 1: obcdoefgo and curve 2: obcdoefgo) correspond to a cyclic change in tension. The region of decrease in τ _cf values observed on curve 2 at points c 'and f' with increasing voltage indicates a breakdown of the main part of local insulation defects. The informative parameters of the curves are the area bounded by them; the maximum value of τ _sr and the corresponding voltage (coordinates of the point c '); the value of τ _cf corresponding to the amplitude of the voltage (coordinates of the point d '), as well as the slopes of the tangents drawn to the curves at the characteristic points (initial, maximum, etc.).

Figure 4 presents the graphs of the dependences τ _cf = f (U) obtained in accordance with the proposed method in the diagnosis of one of the phases of the autotransformer ATDCTN-200000/110/6. Curve 1 corresponds to serviceable, and curve 2 - defective insulation. Processing the results of direct measurements of the parameters of these dependences with multiple (n = 25) observations shows that the measurement error corresponding to a confidence level of 95%, due to the stabilization mode according to the proposed method, decreases from 30-40% (without stabilization of the current average value of the apparent charge of partial discharges) up to 8-10% (with stabilization). The experimental results have good visibility, indicate the informativeness of the dependences τ _cf = f (U) and the high reliability of the proposed method for the diagnosis of high-voltage equipment.

Claims (1)

A method for diagnosing high-voltage equipment by the parameters of partial discharges, which consists in the fact that the electromagnetic field of partial discharges in isolation is perceived by inductive and capacitive sensors, the output signals of which are filtered, amplified and multiplied one by one and, in accordance with the sign of the product, form informative signals, characterized in that that the first of these signals is proportional to the current average value of the apparent charge of partial discharges, and the second to the current average value of the pulse duration The current caused by partial discharges, using the first signal, corrects the rate of change of the electric field in the insulation, stabilizing the current average value of the apparent charge of partial discharges, and using the second one determines the dependence of the duration of current pulses caused by partial discharges on the voltage at the high-voltage input of the diagnosed equipment.

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