DE2531203C3 - Method and device for the detection of short circuits on lines - Google Patents

Description

= A- ■ (»,"

bit) = k - (- u, "t- R _n ij.

with a measurement voltage u ", and a measurement current /", or variables derived therefrom, with a resistance factor R _w and a freely definable proportionality factor k and that the mutual phase position of at least one frequency component each of the opposing traveling wave signals [a (t), b (t) J is monitored as a variable characterizing the line state.

2. The method according to claim 1, characterized in that the measurement voltage (u _m ) or the traveling wave signals [a (t), b (t)] are summed up with a correction signal [sk (0J ) proportional to this measurement voltage (u _m ), in such a way that that the frequency components to be evaluated of the two corrected traveling wave signals obtained in this way are in phase opposition for a predetermined amount of the line input impedance which is lower than the set resistance factor (R _v ).

3. The method according to claim 1 or 2, characterized in that two opposing traveling wave signals [a (t), b (t)] are multiplied with each other and that the product signal thus obtained is used as the mutual phase position of the opposing traveling wave signals characterizing monitoring variable.

4. The method according to claims 2 and 3, characterized in that the correction signal corresponds to a fraction of the measurement voltage (u, ") , which is given by the ratio of the difference between the resistance factor (R _w ) and the minimum amount of the line input impedance to the latter itself .

5. The method according to claim 3, characterized in that the product signal [a (t), b (t)] is superimposed with a correction signal dependent on the magnitude of the measurement voltage (u _m ) in the same direction.

6. The method according to claim 5, characterized in that the product signal [a (t), b (t)] 'is additively superimposed with a correction signal / sArYi ^ proportional to the square of the measuring voltage (u _m ).

7. The method according to any one of claims 1 to 6, characterized in that a with amount and fio Sign of the amount or the direction of the mutual phase position of the opposing traveling wave signals assigned signal and an integration with subsequent limit value monitoring is fed. (>?

8. Device for carrying out the method according to claim 1, characterized in that a measuring voltage channel connected to a voltage measuring device (2a) and a measuring current channel connected to a current measuring device (2b) and containing a constant factor multiplier (3) are connected in parallel to an addition circuit (4) ) and ai a subtraction circuit (5) connected sin <and that the outputs of these two circuits (4 5) are ruled out to a phase angle detector (Ph) .

9. Device according to claim 8, characterized in that a correction constant voltage multiplier (3; or 3b) is connected to the measuring voltage channel.

10. Device according to claim 8 or 9, characterized in that the outputs of the addition circuit (4) and the subtraction circuit (5) ar the inputs of a function multiplier (6 are connected.

11. Device according to claim 10, characterized characterized in that an amount function generator (15) with the output-side is connected to the measuring voltage channel Constant factor multiplier (16) is connected and that the outputs of this multiplier (16) unc of the function multiplier (6) are connected to a summing circuit (7, 17).

12. The device according to claim 10 or 11, characterized in that on the function multiplier (6) a respective one polarity of the product signal formed from the traveling wave signals [a (t), b (t) J [p (t)] ™ ndeslens partially suppressing circuit (12) is connected.

13. Device according to one of claims 8 to 10, characterized in that the output of the Function multiplier (6) to an integrator (8; with at least one subsequent threshold value switch (13,14) is connected.

The invention relates to a method for the detection of short circuits on lines that have a Voltages and currents containing alternating components are operated by detecting the Time curve of voltage and current at a measurement location in the form of measurement voltages and measurement currents, The subject matter of the invention also includes a device for carrying out such a method,

The detection of short circuits on lines is a prerequisite for subsequent protective measures and thus provides a stimulus for fault location or fault location localization to a sufficiently limited one Line section is an essential part of a line or network protection system With regard to the very different possibilities of fault location or fault location localization and furthermore the identification of the type of defect (selection) following the defect detection, the latter forms an independent one technical problem that is generally also solved with its own circuitry.

Usually, the error detection takes place z. B. with the help of the minimum impedance method and the like Relays, as they are known from "Brown, Boveri Mitteilungen", Volume 53, No. 11/12, p. 788, Such methods are based on the comparison of current and voltage, so they speak for you Short circuit characterizing current increase with simultaneous, more or less strong lowering of the Line voltage at the measuring location. That known as

ngegebene method uses a Gleichnch- _U ng measuring voltage and current signals associated with, as well as a difference formation of the rectified signals, the zero crossings of the differential signal to determine the integration intervals of a subsequent integration with a fixed Anstiegsgeschwinjigkeit. The respective amplitude of the time intervals achieved is thus a function of the ratio of measuring voltage and measuring current, so that a certain limit value of the time integrals can be assigned to the ratio prevailing in the short circuit and the normal state or fault state of the line can be inferred from falling below or exceeding this limit value .

With the comparatively fast excitation process ι and excitation devices of a known type, including the example mentioned, can be used for detection times reach, the further reduction of which should be sought in the interest of rapid protective measures., is. Task of The invention is therefore to provide an error detection method or a corresponding device with which such a reduction in the detection time is attainable. The inventive solution to this problem is characterized in a method of type mentioned at the beginning by the features specified in the characterizing part of claim 1, while the associated device is characterized in claim 8.

According to this, the present detection method is based on the formation and evaluation of opposing traveling wave signals, ie signals formed at the measuring location whose time course corresponds to that of opposing traveling cells on the line - viewed at the measuring location. The resistance factor R _w , which determines the ratio of the signal component dependent on the measurement voltage to the signal component dependent on the measurement current, can be set within comparatively wide limits, but in the interest of the reliability of detection of short circuits that appear minimally at the measurement location, i.e. of short circuits with the maximum possible arc or fault resistance at the maximum distance from the measuring location, generally a certain minimum value of this resistance factor must be observed.

As this resistance factor approaches, it corresponds to the wave resistance of the line Value result especially traveling wave signals, the opposing traveling waves of only due to attenuation decreasing amplitude, but otherwise constant profile along the line and of more defined Correspond to the speed of propagation. For certain additional fault determination operations, such as B. Distance or direction determination, such special traveling wave signals or an approach to be appropriate to this. For the purposes of the present defect detection and especially with low content of the measurement signals on transient spectral components in addition to the generally dominant network frequency component however, there are comparatively large deviations of the resistance factor from the characteristic impedance permitted by the management.

Furthermore, the traveling wave signals formed in the present method with regard to the mutual phase position monitored at least one of their spectral components, preferably the network frequency component. This relative phase position experiences a sudden change in the event of a short circuit on the line Modification. In normal operation, the usual AC lines for power transmission are the dominant ones Mains frequency components of the traveling wave signals moving in opposite directions are essentially out of phase with one another, while in the event of a short circuit they become approximately in phase. There is therefore the possibility of a continuous monitoring of the mutual phase position of the network frequency components or others suitable frequency components of the traveling wave signals, the exceeding of a phase change of a specified minimum size according to the interference level to be taken into account as a detection criterion can be used. Compared to the usual method with amplitude comparison, which is generally is only possible once within a half cycle, the ongoing phase monitoring results in a significantly reduced detection time that does not affect the period duration of the frequency component under consideration is bound. This advantage also applies in the event that the phase monitoring with an integration and Limit value monitoring of the time integral is connected, because it is then in turn on an undelayed Start of integration as a result of the ongoing phase monitoring and on one of the period duration independent integration time arrives.

The invention is further based on the embodiment illustrated in the drawings explained. Herein shows

F i g. 1 shows the basic circuit diagram of an error detection circuit according to the invention,

F i g. 2A shows a time diagram of the measuring voltage u _m and the measuring current / _m over the time at which a short circuit occurs,

F i g. 2B shows the time course of the associated traveling wave signals a (t), b (t) \ md

F i g. 3 shows the time curve of a product signal p (t) formed from the two traveling wave signals and a detection signal d (t) obtained therefrom by one-way rectification and integration.

In Fig. 1 is a line extending in the direction χ, for example consisting of a conductor 1 above ground, with a measuring station 2 at a measuring location χ = 0 and with an assumed short circuit at the fault location χ = ζ . The measuring station 2 comprises a voltage converter 2a with the measuring voltage u " as the output signal and a current converter 2b with a measuring current /""as the output signal. Measurement voltage and measurement current can ζ. B. in the form of signals with the dimension of a voltage. The measured current is multiplied in a constant factor multiplier 3 by a resistance factor R _w , the amount of which corresponds to at least that of the maximum line input impedance (maximum arc resistance + maximum line impedance) in the event of a fault, and then together with the measuring span; voltage fed in parallel to a first summing amplifier 4 and a first subtracting amplifier 5. Two opposing traveling wave signals appear at the outputs of these amplifiers (both can still be multiplied by a freely selectable scale factor):

«(F) = u," -I- R _x , - i ", / Mf) - -U _n + KL-

_ς ie signals with a time course which can be assigned to the time sale occurring at measuring location x = 0 of traveling waves moving in opposite directions on the line. It should be noted that in mind "

present invention of this assignment with various modifications of the original measurement signals, d. H. Measurement voltage and measurement current, is compatible, especially one with a higher harmonic content appropriate filtering to emphasize a frequency component or with a limitation or a similar transformation of the measurement signals, through which the phase relationships of the opposing traveling wave signals are not significantly disturbed.

In the example, the practical assumption is made, that the traveling wave signals not only before the short circuit, but also afterwards one of the network frequency have corresponding, dominant frequency components, so that a special input filtering is not required.

The opposing traveling wave signals are fed through a second summing or subtracting amplifier 4 'or 5' - these are used for correction purposes to be explained - in the form of corrected traveling wave signals a '(t) and b' (t) to a phase detector Ph , which is customary, for example , at the output of which a detection signal d (t) , which is basically already suitable for short-circuit monitoring, is available. The traveling wave signals are also available at outputs A, B for other error protection purposes, such as for determining the error direction or error distance.

Furthermore, in FIG. 1 shows a special phase monitoring circuit - also following the outputs of 4 ', 5' - shown. The traveling wave signals are fed to a function multiplier 6, the output of which feeds a corresponding product signal p (t) to an integrator 8 with an amplifier 9 and a negative feedback capacitor 10. The product signal p (t) can in itself already be used as a measure of the mutual phase position of the two traveling wave signals and thus in principle as a detection signal. The subsequent integration causes a suppression of interfering harmonics and thus enables a comparatively sensitive limit value monitoring by means of a threshold value switch 13 set to a correspondingly low limit value The rate of rise of the time integral has a greater response delay. The output of this second threshold value switch can accordingly be used to check the first, less delayed and more sensitive error detection.

The network frequency components of the opposing Wanderwcl'ensignale are in the range of normal operating conditions essentially in phase opposition, provided that the amount of the line input impedance does not fall below that of the resistance factor R _w , after the occurrence of a short circuit, however, essentially in phase. The product signal p (t) is then negative in the first case and positive in the second case. Because of the generally small phase differences between line voltage and line current in the normal operating state, the product signal p (t) is briefly negative. In order to obtain a defined signal level in normal operation, a diode 12, essentially acting as a half-wave rectifier, can therefore be provided at the input of the integrator according to FIG

Limited amount. Such a polarized suppression element can in principle also be used at the output of the integrator or - as shown in the example - parallel to the negative feedback branch of the integrator to be ordered.

A discharge resistor 1 'takes care of the reset of the integrator to a neutral initial state after the failure of an error-indicating product signal. If necessary, a discharge switching device can also be used instead, which is more obvious Way is to be operated after fault detection.

For line input impedances that may occur in error-free operation, the magnitude of which is below that of the resistance factor R _w , the product signal p (t) becomes weakly positive even without the occurrence of an error. Naturally, this is preferred for comparatively large settings, e.g. B. in the range of the characteristic impedance of the line resistance factors R _w to. To correct the signal conditions for extreme load conditions in error-free operation in order to avoid false pretenses, there are various possibilities, which are shown in FIG. 1 are indicated.

For this purpose, a correction signal si <(t) can be tapped from a constant factor multiplier connected to the measuring voltage channel in the form of a potentiometer 36 and superimposed on the original traveling wave signals via the aforementioned amplifier 4 'or 5' with the polarity determined by the sign of the amplifier inputs shown . This is how the corrected traveling wave signals result

a U) = uj \ + K) + R _w ■ / ", /" O = -uj \ + K) + R _w -i _m .

Here, the correction factor K on the potentiometer 36 z. B. according to the relationship

with the resistance factor R " and a specified minimum amount /?""" of the line input impedance in the error-free state. The following then applies to the corrected product signal:

PU) = -1, J ₁ (I + K) ¹ + Ri- i ² _m .

so The term in u, " is increased accordingly in such a way that suitable sign ratios are given for the entire intended load range.

If necessary, this correction can also be carried out in the voltage measuring channel before the summing and subtracting

This is done here for the formation of the wall wave signal be, for example with the dashed line in Fig. 1 indicated constant factor multiplier 3a, which, however, as an amplifier with a gain factor (1 + / ^ must act.

ι «. Another alternative is indicated in FIG. 1 with the circuit between points C and I , namely in the form of a carrier to which the measuring voltage is applied, ie a squaring amplifier 15 with subsequent

(.s constant factor multiplier in the form of a Potcntio meters 16. There is a correction signal here

S. IfI

K ■ ■ ic

with the correction factor

K '=

This correction signal is generated by means of summing resistors 7 and 17 are additively superimposed on the product signal and, with the specified setting of the Correction factor also results in the intended uniqueness of the sign ratios. The last described embodiment requires a multiplier instead of simple summing elements, but leaves the original traveling wave signals, e.g. for a different error direction or error distance determination, unaffected

For the in the F i g. 2A, 2B and 3 illustrated The following applies:

At the point in time ίο, the measuring current / _{m shows} a strong increase over the previous curve, while the measuring voltage u _m experiences a much smaller change and essentially only contains more harmonics. Such a voltage and current curve corresponds to practical conditions for line short circuits not too close to the measurement location. Before and after the short circuit, the mains frequency component is in any case dominant in the current and voltage, so that, for example, no special input filtering is required.

The course of the opposing traveling wave signals φ) and b (t) before and after the short circuit is indicated in FIG. 2B measured proportions. The comparatively small deviation from exact antiphase of the opposing traveling wave signals results in a brief, periodic change to the positive range for the time course of the product signal p (t) shown in FIG. This phenomenon is compensated for by the corrective measures explained, which are no longer shown here. After a short circuit, the product signal, conversely, has a largely positive course with only a brief periodic changeover into the negative range, which, moreover, can no longer be effective for error detection. That also in

The integral detection signal d (t) shown in FIG. 3 remains for the intervals with a negative product signal before the occurrence of a short circuit as a result of the ifi F i g. 1, the suppression circuit explained practically to 0, the short-term positive sections of the integrand signal becoming ineffective after a short time at the output of the integrator due to the decaying time behavior due to the discharge resistance 11, even without a special correction.
From (0, the integral detection signal dft rises) im

essentially monotonously, so that when a first limit value S \ is exceeded at time t \ the first threshold value switch is triggered, and when a second limit value Si is exceeded at time h, the second threshold value switch is triggered.

It can be seen here that the time delay between to and the respective triggering is not fundamentally, but only due to the integration time constant of the integrator, i.e. essentially due to the intended filter effect with regard to higher-frequency interference signals Both limit values are possible directly by the product signal at times t \ and t { with an even lower delay, essentially only caused by the time course of the signals essentially only depends on the interference signal conditions.

For this purpose 3 sheets of drawings

709 647/32

Claims (1)

Patent claims: 1. Method for the detection of short circuits on lines which ithaltenden with an alternating component Operate voltages and currents by recording the time course of voltage and current at a measurement location in the form of measurement voltages and measurement currents, characterized in that that traveling wave signals from measurement voltage and measurement current or variables derived therefrom the form