CH643363A5 - Capacitive ac voltage divider. - Google Patents

Description

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8) Voltage divider according to claim 6 and 7, thereby

1) Capacitive AC voltage divider, in particular for indicates that the input of the DC blocking film medium or high voltages is connected with a voltage that can be connected directly to the output of the buffer amplifier (V2) and a reference voltage between a priter (Fl).

circuit of at least two capacitors, one of which 5

serves as a measuring capacitor (C2), of which as a secondary

The invention relates to a capacitive alternating voltage, and with a leak impedance (Rl) connected via the measuring capacitor divider according to the preamble of patent claim 1 to discharge the io A similar voltage divider is from the published DC voltage component, as well as with a “Bulletin Scientifique AIM” circuit from June 1973, pages order (Fl, D, Bl), which the measurement signal for deriving 154 to 155 known.

If the measurement signal derived from the measurement capacitor is routed, characterized in that the measurement signal and for monitoring the Pri-der derived DC voltage component of a compensating voltage is used for the voltage divider, then such a DC voltage sation device (VI, C3, R2-R4, SI, S2) are fed via the measuring capacitor to this monitoring function, which impair or even destroy the DC voltage present in the measuring signal. Compensated for existing components. Such a DC voltage can be distance relays

2) Voltage divider according to claim 1, characterized in that they do not respond quickly enough in time or speak that the compensation device incorrectly indicates a compensation 20; The localization of a ground fault capacitor (C3) with a parallel or phase short circuit becomes difficult or even impossible. Leakage impedance (R2), which has a common connection A DC voltage can be connected, for example, to a reference voltage at the measuring con, and a capacitor occur when a primary AC voltage line disconnects a switch arrangement (S 1, S2) for supplying a device in an instant is when the wave of the given further reference voltage (Vrefl, Vref2) on the other 2s AC voltage has no zero crossing. The voltage then remaining on the common connection of the compensation capacitor leads to a restator (C3) with the leakage impedance (R2) connected in parallel, which also acts as the DC voltage component, whereby the switch arrangement (SI, S2) is seen by one of the and which DC voltage can be controlled via the capacitor connected to the primary variable of the DC voltage component and which results in the value of the further reference voltage and 30 in the measuring capacitor. If, when the switch arrangement is switched on, there is such a DC voltage on the measuring capacitor that the voltage on the compensation capacitor would return after a few periods and the DC voltage component in the measurement signal compensates. immediately afterwards a short circuit would occur, furthermore a differential amplifier (VI), one rend of which the DC voltage has not yet been derived, the input would then receive the measurement signal and the other input the voltage would only apply a voltage to the compensation capacitor after a few periods ( C3) have a zero crossing to which a distance relay is applied and whose output signal speaks with respect to the DC voltage. However, this boils down to the fact that the relay component is compensated too late and that a DC voltage reacts. Overvoltages on the primary change-blocking filter (F1), a comparison circuit (D) and a DC voltage line can also result in switching 40 comprising residual charges and DC voltages in the logic decision circuit (B1) on the measuring capacitor.

tion arrangement is supplied. For correct operation of distance relays, an un-

3) Voltage divider according to claim 2, characterized in falsified reproduction of the changes in the primary voltage that the compensation capacitor (C3) and the essential. In the known voltage divider, an associated leakage impedance (R2), the same time constant as leakage impedance, is therefore connected in parallel to the measuring capacitor, so that the measuring capacitor (C2) is connected in parallel with the 45 that the DC voltage disappears sufficiently quickly.

Form the leakage impedance (Rl). The use of a leakage impedance prevents in the

4) Voltage divider according to claim 2 or 3, thereby the occurrence of an inadmissible delay when indicating that the switch arrangement is formed from several parts of protective devices, inter alia in the case of the pre-allel switches S1, S2), each of which on one of the conditions explained below, but such a change of predetermined reference voltage (Vrefl, Vref2) has the harmful effect that the measurement signal is counter-applied. phase shifted above the primary AC voltage

5) Voltage divider according to claim 2 or 3, thereby. As a result, the protective device, in turn, indicates that the further reference voltage (Vrefl, VreQ) responds with a delay, for example in the case of a short circuit, is equal to the derived DC voltage component. in the primary AC circuit. Except for a phase shift

6) Voltage divider according to one of claims 2 to 5, since the shift signal has the measurement signal as a result of the leakage impedance, characterized by the fact that compensation phenomena occur between the measurement capacitor, as a result of which an accurate loading (C2) and the differential amplifier (VI) drove a buffer amplifier Protection system for the primary AC voltage is inserted (V2) (Fig. 3). is disturbed how easy it is to see.

The disadvantages mentioned above are avoided by

7) Voltage divider according to one of Claims 2 to 6, so that a capacitive AC voltage divider according to the characteristic is characterized in that the one input of the list of part of claim 1.

DC circuit (D) via the DC blocking filter In the inventive capacitive AC voltage

(Fl) the pure AC voltage divider screened out from the measurement signal becomes the DC voltage component in the measurement

supply signal and the other input, the signal, i.e. the charge on the measuring capacitor, is actually supplied with a broadband, complete measurement signal and is discharged via a leakage impedance which is used for this effect.

that the switch arrangement (S 1, S2) is for the compensation, but first the DC voltage component caused in the measurement signal by this capacitor (C3) by the output signal of a logic charge is immediately

Decision circuit (Bl) can be actuated. bar compensated and remains until the load disappears.

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compensated. The term “immediately after the two patent applications mentioned above” used here means within a short time compared to the gene, while the bandwidth for the intended purpose lasts for a period which is 20 ms at 50 Hz. is sufficiently wide.

In a preferred embodiment of the invention In the case of a preferred embodiment of the invention, the compensation device consists of a voltage divider according to the compensation, the undesired ion capacitor and a leak detection on the measuring capacitor lying parallel to it are not within a short distance, their common connection is connected to the reference span time by short-circuiting this capacitor with the help of a device; furthermore, a switch for supplying a switch is eliminated; on the contrary, the further reference voltage to the other common DC voltage component is provided on the capacitor with the compensation capacitor being closed with the leakage impedance lying parallel to it, for example, with an equally high voltage, whereby this or opposite potential is compensated by controlling both switches by a signal derived from the true DC voltage in a differential amplifier and the value of the two.

The reference voltage and the point in time for switching on. The invention should now be selected in detail with the aid of the enclosed switch in such a way that the voltage on the cable is explained in the drawings, which illustrate some embodiments of the capacitor as examples of the DC voltage component. Show it:

Measurement signal quickly compensated; 1 is a first embodiment of a capacitive

Input of a differential amplifier supplied, at whose alternating voltage divider according to the invention together their input, the voltage at the compensation capacitor with the associated control device;

2, while the output signal of the control device form of the capacitive AC voltage according to the invention, which is compensated with regard to the DC voltage.

tion is fed. If one considers absolute values, the voltage divider and the voltage at the compensation capacitor can be the same as in FIG. 3, a preferred embodiment in which a true DC component is added to the measuring capacitor of the second differential amplifier.

be made. The differential amplifier can then have an amplification factor of 1 for 25, as in the known arrangement and the arrangements, both signals. according to the aforementioned patent applications of the

It should be noted that in the Dutch rin lies between the primary voltage Vp and a reference

Patent applications No. 7 711 655 and 7 802 969 the same voltage a capacitive AC voltage divider with the

A capacitive AC voltage divider with a series connection of capacitors C1 and C2 and an additional capacitor is proposed with the aid of 30 leakage impedance R1 connected in parallel. The value of these two separate signals are generated, namely a leakage impedance Rl is chosen so large that the phase error narrow-band fundamental wave signal, which therefore neglects the true signal at the connection point of Cl uad C2

AC component corresponds, and a broadband. sig or is easily compatible for the AC voltage frequency

signal that can also be used to compensate for the DC voltage component.

holds. Both can serve as a control signal, while the last one can be used on the assumption that the phase correction is omitted as a measurement signal for monitoring or protection purposes. The control signals cause capacitors C1 and C2 in this embodiment to cause the control device to have DC components next to an amplifier V], which here eliminates a differential amplifier that may be present in the wideband signal, and then the signal may appear immediately as the measurement. The signal B, which is open in these two patent applications, at the input 2 of a comparison circuit D. The method described, two more or less independent channel signals from the amplifier V, is also fed to a parallel channel with the aid of a high-voltage capacitor to obtain voltage blocking filter F1 and appears after the th, difficulties can in certain cases look at the first input 1 of the comparison circuit D as a narrow band of crosstalk or the practical feasibility of the fundamental wave signal A. Who in the comparison circuit D encounter. Although the two signals can be compared with one another by suitable selection of the capacitances, in order to achieve a high degree of independence between the two of the DC components in the broadband signals mentioned in the measurement, the signal B still has to be determined.

Need for a capacitive AC voltage divider. In this case, a compensation device with which complete independence can be achieved contains the aforementioned differential amplifier V], a compensation. This independence can be achieved with the aid of a 50 capacitor C3 with a double voltage divider connected in parallel with it, as is also stated in the leakage impedance R2 and a number of additional patent applications, but R3 and R4 and switches S1 and S2.

practical concerns arise, in particular also, the one connection point of the compensation condenser - if the measuring capacitor has a considerable capacitance: sator C3 with the leakage impedance R2 is connected to a reference voltage - then problems arise with the general preference, which in This example also uses earthed semiconductor switches because the switch can be. The other connection point is at the second stream becoming too big. This is the case, for example, when the input of the differential amplifier V,. The two resistors R3 and R4 are also to be brought up to date on this other obsolete CVT measuring device. A large additional capacitor is to be connected, each of which must be inserted via the switch S1, so that an additional one -60 or S2 connected to different connecting lines. In practice, it is then more advantageous to use a fixed leakage impedance at the additional reference voltages Vrefl or. Are led out. The switches S1 and S2 can be actuated by the one property of the capacitive output signal of the comparison circuit D according to the invention, the AC voltage divider is now both a simplified one, which can be regarded as a signal which depends on the practical practicality and also a full size of the DC voltage component is the independence of the two signals mentioned above. The Ge is determined by the comparison circuit D. This speed of the control of the DC voltage component according to the invention is first fed to a logical voltage divider which is at least equal to that of the best decision-making circuit B1, which has a number

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of outputs. At each of these exits it appears generally the same. After determining a DC signal corresponding to a predetermined size and voltage component in the broadband signal, the larity of the DC component and one of these switches S1 are closed, C3 being able to quickly switch on the differential output signals, switches S1 and S2, ie the voltage Output voltage of the comparison circuit, whereupon the further reference voltage Vrefl or Vrcf2, the shift D, is charged. The DC voltage connection point of the compensation capacitor C3 with that in the broadband measurement signal is then compensated, and S1 leakage impedance R2 is fed, which is opened again with the difference. The capacitors C2 and C3 will be more strongly connected to Vi. Unload on the compensation condenser at the same speed.

As a result, capacitor C3 is subjected to such a large DC voltage when capacitor C3 builds by closing one of the capacitors present on capacitor C2. The structure of switch SI, S2 loaded to the associated reference voltage, this compensation voltage depends on the value of the resistance, and then transition phenomena occur. These are spaced by R3 and R4, and these values are used in this process.

view and according to the desired compensation - but also via the differential amplifier V2 the pure change

speed selected. The same applies to the size of the voltage signal A which reaches input 1 of the tension voltages Vrefl and Vref2. is comparison circuit D via the DC blocking filter

When the DC voltages are supplied to the capacitors C2 F1. This disadvantage can be avoided by and C3 have become the same, then the output addition of a second differential amplifier V2 and the signal of the differential amplifier V, that is to say the desired measurement branching of the summation point exclusively to the signal, no longer contains a DC voltage component. The two branches of the broadband signal, which is fed to the input 2 of the inputs 1 and 2 of the comparison circuit D, the equalization circuit D. In this case, the th signals now only consist of the pure alternating differential amplifier V2 as a buffer amplifier. By the voltage signal. Therefore, the comparison circuit D quickly charges C3-related compensation processes no longer detects a DC component, so that they then only occur in the latter signal and are not reopened in switches Sì and / or S2. the other input of the comparison circuit D via the

It has already been shown above that the signal supplied via the 25 blocking filter F1. Therefore this signal is

Compensation capacitor C3 has a leakage impedance R2 before a more accurate narrowband fundamental wave signal than seen in. The leakage impedance Rl across the measuring capacitor - the earlier versions in which after filtering in gate C2 has such a large value that the cut-off frequency

could occur sufficiently far below the frequency of the alternating processes to be measured in signal A if the band voltage is so that the introduced phase and amplitude widths of the DC blocking filter Fl are not particularly small. This results in a small one.

large time constant. Therefore C2 slowly discharges via In the embodiment according to FIG. 1 as well as at R1, so that the DC voltage component at the connection. the other embodiments, the gain factor

point of Cl and C2 gradually decreases. Tor of the differential amplifier VI 1.

The capacitor C3 can have the leakage impedance 35. It goes without saying that the charging circuits for R2 discharge, which is preferably dimensioned such that the capacitor C3, which in this case is switched by switches S1 and S2, is as large as the time constant R2, C3 Rl, or the resistors R3 and R4 are illustrated, is much-C2. After charging from C3 to the correct compensation compartment, as is the case in the input voltage, no further corrections to the Dutch patent applications already mentioned are in principle necessary anymore, because C2, like C3, is routed through its 40.

associated leakage impedances R1 and R2 along similar lines. The significant advantages of the arrangement runs according to the invention are discharged. In the case of unequal time constants, the operating characteristics, that is to say the ar- corrections after some time, which maintain an initial operating speed, are at least the same as in the case of compensation. In the embodiment according to FIG. 2, only one voltage divider is used, for example according to FIG. 7 the Dutch patent switch S1, which is the capacitor C3 via application 7 711 655. In addition, a chip-resistor R3 can supply a reference voltage. In this voltage divider according to the invention, however, the reference voltage is added to a pre-case, the difference between the existing voltage divider is added without the wideband measurement signal B, i.e. the signal with the pure substantial changes in the voltage divider as such an AC voltage component and the DC voltage - 50 would be necessary, on the other hand considerable component and the component supplied by the DC blocking filter, for example in the case of the voltage divider after the Fl, i.e. the pure AC voltage Dutch patent application 7 711 655 required component A. This means that Vref and the by Are.

DC circuit D derived DC component

C.

1 sheet of drawings