WO2015120827A1

WO2015120827A1 - Method and device for measuring dielectric parameters of the isolation of high voltage appliances

Info

Publication number: WO2015120827A1
Application number: PCT/DE2014/000060
Authority: WO
Inventors: Michael Rösner
Original assignee: Michael Rösner
Priority date: 2014-02-17
Filing date: 2014-02-17
Publication date: 2015-08-20
Also published as: DE112014006374A5

Abstract

The invention relates to a device (100) for measuring the dielectric loss factor (ΤΑΝδ) of high voltage appliances (MO), comprising the following components: a first detection unit (110) for detecting an electrical field strength at a first measuring point (M1) on the high voltage side of the high voltage appliance (MO), wherein the first detection unit (110) forms first sample values of a first time signal profile of a first measured variable (Us) that is proportional to the acquired field strength, depending on a time reference specified by a first timer (115); a second detection unit (120) for detecting an electrical voltage at a second measuring point (M2) on an earth-side measuring connection of the high voltage appliance (MO), wherein the second detection unit (120) forms second sample values of a second time signal profile of a second measured variable (UM) that is proportional to the acquired voltage, in accordance with the time reference; and an evaluation unit (123) that compares the second sample values of the second measured variable (UM) with the first sample values of the first measured variable (Us), in order to determine the phase angle (δ) of a phase shift occurring between the signal time profiles, and which evaluation unit applies the tangent function to the phase angle (δ) to determine the dielectric loss factor (ΤΑΝδ). The device can also detect Delta-C1.

Description

Method and device for measuring dielectric characteristics of the insulation of high-voltage devices

The invention relates to a method and a device for measuring the dielectric characteristics of the insulation of high-voltage devices, such. High-voltage bushings in electrical power plants and the like, in particular for measuring the dielectric loss factor (ΤΑΝδ) and / or the temporal change of the dielectric longitudinal capacity (delta-C1).

The measurement of the dielectric loss factor, the so-called tangent delta (ΤΑΝδ), the isolation of high voltage equipment is an important diagnostic tool to assess the operating state of a high voltage device. Likewise, the temporal change of the dielectric longitudinal capacitance is of interest in order to assess the integrity of the insulation, in particular the capacitive field control.

The dielectric loss factor is a measure of the quality of the insulation. The higher it is, the worse the isolation. The failure of the insulation often announces itself by an increase of the electrical loss factor. Since the active components of the currents in the dielectric are caused by mechanisms which only occur at higher voltages (eg partial discharges and / or non-linear behavior of the residual conductivities), it is important to include the object to be measured or the device itself during the offline measurement To load a high voltage, which is in the order of the operating voltage, thus obtaining realistic measurement results.

The dielectric longitudinal capacitance or its temporal change is a parameter in order to determine the integrity of the insulation, in particular of the capacitive field control. The dielectric longitudinal capacitance (also C1

CONFIRMATION COPY Capacity) is usually measured before delivery of the device and regularly as part of the maintenance and it is checked whether there have been changes over time. An increase in the longitudinal capacity would be an indication of a partial breakdown in the insulation. A typical application is, for example, the measurement of the time change of the C1 capacitance on capacitor feedthroughs of power transformers.

As far as the other parameter, the dielectric loss factor, is concerned, it is usually carried out in the context of an offline measurement before the device is delivered or during its standstill period (for example maintenance interval). A typical application is, for example, the measurement of ΤΑΝδ on capacitor feedthroughs of power transformers. The classical measuring method used for this purpose is the alignment of a so-called Schering measuring bridge and is illustrated here with reference to FIG. 1:

The principle of the conventional ΤΑΝδ measurement illustrated in FIG. 1 requires a high-precision, low-loss high-voltage capacitance on the high-voltage side HS, the so-called normal capacitance CN and on the low-voltage or ground side ES the so-called Schering measuring bridge SMB. If the balance is established, ie the bridge current becomes zero, the known (sought) quantities C1 and R1 are determined from the known sizes of the measuring bridge and the normal capacitance C _N , from which finally the electrical loss factor TAN δ can be calculated. The schematic representation of FIG. 1 shows the basic structure of this known measuring method. In practice, the exact determination of the loss factor is still somewhat more complex than shown in FIG. 1, since in particular earth leakage capacitances which falsify the result must also be compensated in the measurement.

The classical method of determining the loss factor using the Schering bridge requires the use of a standard capacity, which is quite expensive to purchase. Therefore, this known measuring method for economic reasons, virtually only during the downtime of the respective High voltage device possible (offline measurement) and a continuous use (in online operation) of the normal capacity C _N is in fact excluded from the practical application. Because of the often very long periods between downtime and because of the importance of knowing the dielectric loss factor to assess the state of the isolation, it is desirable to find an improved and less costly method of measuring the dielectric loss factor online. The same applies to the characteristic of the dielectric longitudinal capacitance or its temporal change.

In the article "Mobile Test System for Isolation Diagnosis of Electrical Equipment" by T. Strehl and A. Engelmann, published in the journal "ETZ", Issue No. 18, 2003, a method is proposed in which a reference measurement at high voltage level using a reference capacitance is required. The determination of the loss angle is done by measuring the phase shift between the signals of a measuring branch and those of a comparison branch. The data is transmitted in real time by means of fiber optic transmission of the measured values into a digital signal processor; Thus, the phase shift of the signals can be determined in real time. Although this method is basically suitable for on-line measurement, it is rather not suitable for economic reasons, since a high-voltage standard capacitance is also required here.

DE 10 2008 004 804 A1 describes a method of an error in a capacitor bushing, wherein in particular the delta C1 value is determined. The method is primarily suitable for multi-phase transformers.

Above all, EP 1 039 304 A2 deals with the measurement of measured quantities, namely input voltages at a high-voltage bushing, and enables an efficient measurement of peak value and effective value of the considered input voltage. Measuring the electrical loss factor, the longitudinal capacity, as well as their temporal change, are not treated there however.

The object of the invention is to propose methods and devices for measuring the above-mentioned characteristics of the insulation, in particular the dielectric loss factor and / or the longitudinal capacity or its change, in order to overcome the disadvantages mentioned and to an efficient online measurement of the dielectric characteristics enable.

The object is achieved by methods with the features of the independent method claims and by devices with the characteristics of the independent device claims.

Accordingly, a method for measuring the dielectric loss factor of the insulation of high-voltage equipment is proposed, which comprises the following steps.

- detecting an electric field strength at a first measuring point on the high voltage side of the high voltage device;

- Forming first samples of a first temporal waveform of a proportional to the detected field strength first measured variable in dependence on a time reference, which is predetermined by a first timer;

- Detecting an electrical voltage at a second measuring point on the ground side or at a local measuring terminal of the high voltage device;

- Forming second samples of a second temporal waveform of a voltage proportional to the detected second measured variable in dependence on the time reference;

Comparing the second samples of the second measured variable with the first samples of the first measured variable to determine the phase angle of a phase shift occurring between the signal time profiles; and Apply the tangent function to the phase angle to determine the dielectric loss factor.

The device according to the invention, which is suitable for carrying out the method for measuring the dielectric loss factor, has the following components or units:

a first detection unit for detecting the electric field strength at the first measurement point, said detection unit forming the first time waveform of the corresponding first measurement quantity (e.g., measurement voltage at the head of a capacitor conduction) in response to the time reference; a second detecting unit for detecting the electric voltage at the second measuring point, this detecting unit forming the second time waveform of the corresponding second measured quantity (e.g., measuring voltage at the earth-side measuring terminal of the capacitor feed-through) in response to the same time reference (a common time base); and

an evaluation unit which compares the signal time characteristic of the second measured variable with the signal time characteristic of the first measured variable or the corresponding sampling values in order to determine the phase angle of a phase shift occurring between the signal time profiles; where the tangent function is applied to finally determine the dielectric loss factor.

Furthermore, a method for measuring a change in the dielectric longitudinal capacitance of the electrical insulation of high-voltage devices is carried out with in principle the same initial steps as follows:

- detecting the electric field strength at the first measuring point on the high voltage side of the high voltage device;

- forming the first samples of the first temporal signal interval of the first measured variable proportional to the detected field strength as a function of the time reference predetermined by the first timer;

Detecting the electrical voltage at the second measuring point at the ground-side measuring terminal of the high-voltage device; and Forming the second samples of the second temporal

Waveform of the second measured variable proportional to the detected voltage as a function of the time reference.

Subsequently, the following steps (variant of the first method) are carried out:

Comparing the second samples of the second measured variable with the first samples of the first measured variable to determine an amplitude ratio of the measured quantities; and

- Monitoring the amplitude ratio to its temporal

Change (i.e., determination of the desired capacitance change Delta-C1).

The device according to the invention is likewise used to carry out this method, wherein the evaluation unit compares the second samples of the second measured variable with the first samples of the first measured variable to determine the amplitude ratio of the measured quantities and monitors the amplitude ratio for its temporal change.

The invention therefore proposes to measure the electrical field strength prevailing there at the first measuring point and to measure the electrical voltage applied there at the second measuring point in order to determine the said characteristic quantities (ΤΑΝδ and / or delta C1) by evaluating the measured variables.

This ensures that cost-effective components enable a reliable online measurement of ΤΑΝδ and Delta-C1. In particular, it is not necessary in the invention to use a normal capacity, a fiber optic Ü transmission link and a digital signal processor with high computing power. The invention is particularly suitable for measuring ΤΑΝδ and delta-C1 on larger high-voltage equipment, where the measuring points are relatively far apart, such as on capacitor bushings for high-voltage transformers and like. The invention can be used in both single-phase and multi-phase high voltage devices.

Advantageous embodiments of the invention will become apparent from the dependent claims.

In the following, the invention will be described in more detail by means of exemplary embodiments and with reference to the enclosed figures:

Fig. 1 illustrates the initial situation of the invention, namely

Principle of a conventional measuring method for determining the ΤΑΝδ and the longitudinal capacitance C1 with the aid of a Schering measuring bridge.

Fig. 2 shows the structure of a device according to the invention for measuring the electrical loss factor on a high voltage device in the form of a capacitor implementation.

FIG. 3 shows the temporal signal course of the measured variables, as well as their

Phase shift from which the ΤΑΝδ results.

FIG. 4 shows a schematic flow diagram for one of the

Device according to FIG. 2, carried out according to the invention method for measuring the electrical loss factor and / or the DeltaCL

In contrast to the prior art according to FIG. 1, in which a Schering measuring bridge SMB and a normal capacitance C _N are used, according to the invention a device 100 for realizing the dielectric characteristics, in particular the loss factor ΤΑΝδ and / or the Longitudinal capacity or its change provided. The device comprises at least two spatially spaced units, namely a first detection unit 110 and a second detection unit 120. The first detection unit 110 is arranged on the high-voltage side HS of a high-voltage device MO, which represents the measurement object. namely at the head of a capacitor bushing KD. The first detection unit 1 10 measures there at a first measurement point M1 by means of a. Field sensor 1 1 1 there the prevailing electric field strength or as a measured variable a corresponding first measurement voltage US.

The second detection unit 120 is located at the ground-side measuring terminal or measuring point Mll of the capacitor bushing KD and detects there a voltage or the corresponding measured variable, that is, the falling over a measuring capacitance 121 second measuring voltage UM. The detection units contain signal amplifiers 1 12 and 122 for amplifying the measurement voltages and contain evaluation units 1 13 and 123, respectively, in order to evaluate the measured variables, as described below.

Each detection unit 1 10 and 120 also contains a timer 5 or 125, which generates a time reference corresponding to an (external) trigger signal TR, in order to obtain the measurement in both detection units on a uniform time base, so that the measured data obtained with respect

Time courses of the measuring voltages Us and UM) can finally be compared with each other. The measurements or the timers are synchronized to an external trigger signal, e.g. derived from a time base signal or a GPS signal.

In order to achieve a sufficient accuracy of the desired measurement, in particular the ΤΑΝΔ measurement, the most accurate time base is needed. The accuracy of, for example, a trigger generated by a GPS receiver is sufficient with ~ 300 ns inaccuracy. In a 50 Hz system, good measurement results can be achieved eg with a sampling rate of about 500 kSamples / s and a memory depth of eg 10000 values. The evaluation can be carried out asynchronously in a central evaluation unit or else in an evaluation unit integrated in the device 100. For this purpose, the first detection unit 110 contains a transmission module 1 14, here for example a bidirectional radio module (eg based on ZigBee), the data DAT over the first time waveform of the first measured variable or the first one

Measuring voltage Us, in particular related to the time reference

Amplitude values sent to the evaluation unit 123, which then compares this data DAT with second data with respect to the second temporal waveform of the second measured variable (measuring voltage UM). For receiving the data DAT, the second detection unit 120 includes a suitable radio module 124, here e.g. also ZigBee radio module.

The evaluation unit 123 for calculating the ΤΑΝδ or the delta C1 on the basis of the data obtained here is integrated into the second detection unit 120, but may also be provided in an external computer or PC. The evaluation units are e.g. realized by microcontroller units, short MCUs.

In contrast to known methods in which a reference or normal capacity (see C _N in FIG. 1) with well-known and time-stable characteristics (capacitance and dielectric loss factor) is constantly needed, the present invention uses an E-field sensor 1 11, which measures the time course of the electric field strength which occurs at the top of the feedthrough MO or on the connected line.

The measurement of the electric field strength at high voltage level has the advantage that the partial capacitance at which most of the high voltage drops, remains stable, because the field space between field plate and earth consists of air and thus is not subject to long-term changes.

The external trigger signal TR can be generated not only by a GPS time reference, but also by, for example, an external radio signal (transmitted through air), an optical signal (transmitted through air or optical fiber), or other highly accurate time base (eg also by an internal clock). With the help of the time base, the Measured values, which are detected on the high-voltage side HS and on the earth side ES, are brought into coincidence with one another in terms of time (see Fig. 3), in particular to determine the phase shift d. But also the amplitude values for the determination of the longitudinal capacity must correlate temporally with respect to each other.

After saving the measuring signal UM and after receiving the

Data DAT of the measurement signal Us from the detection unit 10, the two signals are compared with each other (see Fig. 3). The comparison is that the phase shift of the two signals is determined to each other. This can e.g. with the help of an autocorrelation function. Likewise, it can be detected by quotient formation of the amplitude values and monitoring of the temporal change, whether and how the longitudinal capacitance has possibly changed.

The described device 100 or the system is particularly suitable for the on-line measurement of the characteristics, e.g. ΤΑΝδ and / or delta-C1 suitable. After installing the system, the system will be calibrated. This can be done with the aid of the test protocol of the execution or an offline measurement within the scope of service work. The ΤΑΝδ determined after commissioning is compared with the value determined offline and the error is determined. The error may e.g. The result of this is that the measured field strength is to a small extent also determined by the voltages of the neighboring phases (crosstalk) and thus a phase error occurs. Since this error is geometrically conditioned, it will not change unless changes in the geometry are made (e.g., adding shielding capsules, other HS equipment, etc.). In case of such a change, the system must be recalibrated. With each later measured change in the phase angle δ, the desired phase angle or its tangent (ΤΑΝδ) can thus be determined.

The invention is also very well suited for applications in voltage transformers, in gas-insulated switchgear, etc.

Claims

claims

1. Method (10) for measuring the dielectric loss factor (ΤΑΝδ) of the electrical insulation of high-voltage devices (MO) with the following steps:

Detecting (step 1 a) an electric field strength at a first measuring point (M1) on the high voltage side of the

High voltage device (MO);

- Forming (step 1 1 b) of first samples of a first temporal

Signal curve of a first measured variable (Us) proportional to the detected field strength as a function of a time reference, which is predetermined by a first timer (115);

Detecting (step 12a) an electrical voltage at a second measuring point (M2) at a ground - side measuring flange of the

High voltage device (MO);

- forming (step 12b) second samples of a second time waveform of a second measurand (UM) proportional to the detected voltage as a function of the time reference;

Comparing (step 13a) the second samples of the second

Measured variable (UM) with the first samples of the first measurand

(Us) to determine the phase angle (δ) of a phase shift occurring between the signal timings; and

- applying (step 13b) the tangent function to the phase angle (δ) to determine the dielectric loss factor (ΤΑΝδ).

The method (10) of claim 1, wherein detecting (step 11a) the electric field strength and forming the first samples is performed by a first detection unit (110) having a first timer (115);

wherein the sensing (step 12a) of the electrical voltage and forming the second samples is performed by a second detection unit (120) spatially spaced from the first one

Detection unit (110) is arranged and a second timer (125) having; and wherein the first and second timers (1 15, 25) are synchronized to an external trigger signal to produce the same time reference (TR) in the first and second detection units (0, 120).

Method (10) according to claim 2, wherein the external trigger signal is transmitted to the first and second timers (1 15, 125) optically or by radio.

The method (10) of claim 3, wherein as the external trigger signal (TR) is obtained from a time base signal or a GPS signal.

The method (10) according to any one of claims 2-4, wherein first data (DAT) containing the first samples with respect to the time reference is sent from the first detection unit (110) to the second detection unit (20) or a central measurement data acquisition unit to compare with second data containing the second samples with respect to the time reference.

Device (100) for measuring the dielectric loss factor (ΤΑΝδ) of high-voltage devices (MO) with the following components:

a first detection unit (110) for detecting an electric field strength at a first measuring point (M1) on the high-voltage side of the high-voltage device (MO), wherein the first detection unit (110) first samples a first time waveform of a first measured variable proportional to the detected field strength In us

Dependency of a time reference formed by a first timer (1 15) is given;

a second detection unit (120) for detecting an electrical voltage at a second measuring point (M2) at a ground-side measuring terminal of the high-voltage device (MO), wherein the second detection unit (120) second samples of a second time waveform of a second measured variable proportional to the detected voltage ( UM) depending on the time reference; and

an evaluation unit (123), the second samples of the second Measured variable (UM) with the first scores of the first measurand (Us) compares to the phase angle (δ) of a between the

Determine signal time courses occurring phase shift; and applying the tangent function to the phase angle (δ) to determine the dielectric loss factor (ΤΑΝδ).

The apparatus (100) of claim 6, wherein the first detection unit (110) for detecting the electric field strength and for forming the first samples comprises a first timer (15); and wherein the second detection unit (120) is spatially spaced from the first

Detection unit (1 10) is arranged and for detecting the electrical voltage and for forming the second samples a second

Timer (125), wherein for generating the same time reference (TR) in the first and second detection unit (1 10, 120) of the first and the second timer (1 15, 125) to an external trigger signal

are synchronized.

8. The device (10) according to claim 7, wherein the first timer (1 15) and the second timer (125) each have a time base signal receiver, in particular a GPS receiver, to the external

Trigger signal from a time base signal or a GPS signal to form.

The apparatus (10) of claim 7, wherein the second timer (125) comprises a time signal transmitter, and the first timer (15) comprises a time signal receiver having a timing signal synchronous with the trigger signal second timer (125) receives.

10. Device (100) according to one of claims 6 - 9, wherein the first

Detection unit (1 10) has a transmission module (1 14), the first data (DAT), which contains the first samples with respect to the time reference, to the evaluation unit (123) or to a central

Measurement data acquisition unit sends the first data with second Data comparing the second samples with respect to the time reference is compared. The device (100) according to claim 10, wherein the evaluation unit (123) is integrated in the second detection unit (120), and wherein the second detection unit (120) has a reception module (124) which is connected to the evaluation unit (123) and receiving the first data (DAT) from the transmitting module (1 4) of the first detecting unit (10).

Method (10 *) for measuring a change in the dielectric

Longitudinal capacitance (C1) of the electrical insulation of.

High voltage equipment (MO) with the following steps:

Detecting (step 1 1 a) an electric field strength at a first

Measuring point (M1) on the high voltage side of the

High voltage device (MO);

Forming (step 1 1 b) first samples of a first time waveform of a first measured quantity (Us) proportional to the detected field strength as a function of a time reference predetermined by a first timer (15);

Detecting (step 12a) an electrical voltage at a second measuring point (M2) at a ground-side measuring terminal of the

High voltage device (MO);

Forming (step 12b) second samples of a second time waveform of a second measurand (UM) proportional to the sensed voltage versus time reference;

Comparing (step 13a ^* ) the second samples of the second

Measured variable (UM) with the first samples of the first measurand

(Us) to determine an amplitude ratio of the measured quantities (Us, U _M ); and

Monitoring the amplitude ratio (step 13b ^* ) for its temporal change (delta-C1).

13. Device (100) for measuring a change in the dielectric

Longitudinal capacity (C1) of high voltage equipment (MO) with the following components:

a first detection unit (110) for detecting an electric field strength at a first measurement point (M1) on the high-voltage side of the high-voltage device (MO), wherein the first detection unit (110) first samples a first time waveform of a first measured variable proportional to the detected field strength In us

Dependency of a time reference given by a first timer (115);

a second detection unit (120) for detecting an electrical voltage at a second measuring point (M2) at a ground-side measuring terminal of the high-voltage device (MO), wherein the second detection unit (20) second samples of a second time waveform of a second measured variable proportional to the detected voltage (UM) forms depending on the time reference; and

an evaluation unit (123), the second samples of the second

Measured variable (UM) with the first scores of the first measured variable (Us) compares to determine an amplitude ratio of the measured quantities (Us, UM) and to monitor the amplitude ratio to its temporal change (delta-C1) out.