JP2003116216A - Method of protecting power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective method for a power cable which can surely perform quick detection without accompanying complexity. SOLUTION: A current value ik and a voltage value uk for protecting the power cable 1 are measured. All values within a measuring window are analyzed using an adaptability estimator, and they are converted into an impedance value Z. If the impedance value is not an allowable value, the power cable 1 is cut off. When an alarm signal W is issued, each window is positioned so that the starting point accords with the time of the alarm signal, and/or each measuring window is shortened.

Description

Detailed Description of the Invention

[0001]

The invention relates to a method for protecting a power line in the event of a short circuit, as described in the preamble to claim 1. This method is used to shut off the power line when a short circuit occurs, that is, when the impedance to ground or another phase becomes unacceptably low. In this case, the term power line includes in particular busbars, high-current power lines, power transmission lines or other power transmission components.

[0002]

Prior art methods for protecting power lines use adaptive estimators that measure the impedance between the power line and ground or another phase from multiple points of measurement of current and voltage values. . In this case, the adaptive estimator is adapted to measure the current and voltage at a number of data points within the time measurement window and use their profile to calculate the real and imaginary parts of the impedance. The adaptive estimator checks whether the impedance value is within the forbidden region called the tripping region. If it is in the prohibited area, the power line is cut off. For example, when a bus is protected using a method called a distance protection method, a signal comparison method, and a backward interlock method, it is possible to realize a detection time in the range of 40 to 60 microseconds which depends on a device and a failure.

[0003]

SUMMARY OF THE INVENTION It is an object of the invention to provide a method of the aforesaid type which makes it possible to ensure rapid detection without complexity.

[0004]

This object is achieved by the method according to claim 1. That is, according to the present invention, an alarm signal obtained from a general indicator of the occurrence of a short circuit is generated. When the alarm signal is issued, the measurement window is restarted and / or shortened and the first estimate of impedance is quickly generated. This allows a quick response to short circuit conditions.

An alarm signal is generated when a radio frequency signal on the power line that exceeds a predetermined threshold is detected. This signal is generated by a leader, a current pulse typically of duration of a few hundred nanoseconds and magnitude of a few amps. Furthermore, the alarm signal can be generated according to other criteria such as whether or not the continuous measured values are equal to or more than the sudden change value of the predetermined width, or whether the model used by the estimator shows a contradiction in the measured values. Since the alarm signal gives information about the presence of a short circuit, it is also possible to take into account the decision whether or not to break the circuit breaker.

[0006]

The details, advantages and applications of the invention will be apparent from the claims and the following description. FIG. 1 shows one embodiment of a protection circuit 13 according to the present invention. The purpose of this circuit is to monitor the power line 1. For this purpose, three sensors 2, 3, 4 are provided on the power line.

The capacitively coupled radio frequency sensor 2 (referred to as PD sensor or partial discharge sensor) is connected to the processing circuit 5 and detects a sudden signal above a predetermined threshold in the KHz or MHz band. Generally, this signal causes a sudden change in the impedance Z of the power line. When this signal is generated, the alarm signal W is generated. The radio frequency sensor may be in the form of a partial discharge sensor and may also serve that role.

Voltage sensor 3 connected to processing circuit 6
Measures the voltage of the power line 1 and generates corresponding voltage values u _k (k = 1, 2, ...) At regular time intervals. The current sensor 4 connected to the processing circuit 7 measures the current of the power line 1 and outputs the corresponding current value i at regular time intervals.
generate _k (k = 1, 2, ...). The measuring points for the voltage value u _k and the current value i _k are supplied to the estimator 8 together with the alarm signal W. Estimator 8, continuous current value i of a predetermined number n generated in the measuring window ₁ · · · i _n and the voltage value u ₁
... The estimated value of the impedance value Z of the power line 1 is determined using u _n . _{Z = f (i 1 ··· i} n, u 1 ··· u n) n represents the duration of the measurement window. Z is a complex number. Suitable functions f are known to those skilled in the art.

Illustratively, the function f is such that all n measurement points in the measurement window are included in the result Z with the same weighting, or the weighting is reduced over time from the origin of the measurement points. It may be in the form. Iterative and inductive estimation methods are also known. For example, inductive minimum 2
In multiplication (RLS), the value of n is theoretically infinite, but past measurement points have little effect on the result. The expression "duration of the measurement window" is also used herein for these methods.
The duration in this case corresponds to the characteristic time which diminishes the influence of the individual measuring points on the result. For example, 5
0% change in value is at least 10% more in Z
May be defined as the number of measurement points that cause the change of

The estimator 8 uses the function f to make successive measurements.
Estimated value Z of impedance Z with respect to a constant window₁,
Z₂, But they overlap.
In some cases. Impedance value Z_iIs the same as the alarm signal W
Similarly, it is supplied to the switch control device 9. Switch control device
For example, comparing with the predetermined area in the complex plane
Impedance value Z_iTo analyze. This is
It is shown in FIG. In this case, two regions in the complex plane
Area is shown and tripping area 10 is not acceptable
Cover the area of high impedance value and the operating area 11 is normal
Covers a range of impedance values. Switch control
The device 9 has a number of consecutive impedance values Z _iIs a bird
When it detects that it is in the tapping area, the switch signal S
To cause the circuit breaker 12 to cut off the power line 1.

Various methods exist for analyzing the locus of the impedance value Z _i of the diagram shown in FIG. For example,
Pattern recognition techniques can be used to analyze it and distinguish between typical and unacceptable patterns of impedance value motion. Circuits based on neural networks are particularly suitable for evaluating such patterns. Further, the switch control device 9
An input / output terminal T (TRIP) is provided, and the switch control device 9 can exchange detailed contents about each state with another protection circuit 13 via the input / output terminal T, but with the central monitoring point. You can also do it.

The alarm signal W is used to quickly identify an unacceptable impedance value Z. As mentioned above,
The alarm signal W represents a radio frequency disturbance signal on the power line 1,
This signal characteristically occurs when the impedance changes suddenly, such as during a short circuit. Upon detection of the alarm signal W, the estimator 8 makes the following measurements either alternatively or in combination.

A: Position the measurement window so that the start of the measurement window essentially coincides with the time of the alarm signal W. Illustratively, the measurement window begins at the same time as the first measured current value i _k and voltage value u _k after the occurrence of the alarm signal W. In this method, essentially, only the current value and the voltage value within the measurement window are the current value and the voltage value related to the short circuit condition, and as a result, the impedance Z based on the measured value after the alarm signal is generated is promptly determined. To be guaranteed.

B: The duration n of the measurement window is shorter than the time during normal operation. Although this adversely affects the measurement accuracy, it makes it possible to obtain initial results quickly. If this method is an inference method in which the influence of relatively old measurement points on the result is continuously reduced, the attenuation rate for that can be increased, or the weight of older measurement points can be reduced. In an inductive manner, for example, the iterative process may be reinitialized for this purpose.

These methods are shown schematically in FIG. In this figure, Z1, Z2, Z3 ... Represent individual measurement windows and impedance values determined from them. As shown, the alarm signal W occurs within the measurement window associated with Z3. Measurement window 3
Terminates in an appropriate manner and a new shortened measurement window Z4 is started to quickly obtain valid results.
For example, the subsequent measurement windows Z5 to Z7 gradually become longer until the normal state is reached again.

The alarm signal W is also supplied to the switch controller 9. This takes into consideration that the generation of the alarm signal indicates a short circuit, and the switch control device 9 uses this information to generate the switch signal S, that is, the switch signal S is not only the impedance Z but also the alarm signal W. Also depends on. Furthermore, as explained below, the switch signal S also depends on the value supplied via the input terminal T. This can be expressed by the following equation. S = s (Z, W, T) Here, s represents the "non-acceptable standard", and impedance Z or impedance value Zi, input T, and alarm signal W
Is a function of.

That is, for example, when an alarm signal is generated,
The circuit breaker 12 can be interrupted after only a few unacceptable impedance values Z _k have occurred, due to the indication of a short circuit. If the alarm signal is not generated, the circuit breaker 1 will be used until a larger number of unacceptable impedance values are generated.
I can't shut off 2. That is, after the generation of one alarm signal W, the unacceptable criterion s is more quickly satisfied than in the case without the alarm signal.

FIG. 4 shows one embodiment of the input / output T. In this case, the respective protection circuits 13a and 13b monitor both ends of the power line 1. The protection circuits 13a and 13b are
Data is exchanged via the input / output terminal T. When a short circuit occurs in the vicinity of the first protection circuit 13a, the protection circuit 13a measures a very low impedance value and thus immediately responds to the short circuit. However, the short circuit is relatively far from the second protection circuit 13b, and the impedance value reaching it is not as low as the impedance value of the first protection circuit 13a, and the second protection circuit 13b does not immediately respond. However, the second protection circuit 13b is connected to the first protection circuit 1 via the input / output terminal T.
Information of occurrence of short circuit is received from 3a. As a result, the circuit breaker 12 can be immediately shut off. A configuration corresponding to that shown in FIG. 4 can be used to monitor the busbar. In that case,
Two or more protection circuits 13 generally interact.

In the exemplary embodiment described above, the alarm signal W is generated only when a radio frequency signal of a particular intensity is detected. Besides, it is also necessary to generate the alarm signal W when the duration of the radio frequency signal is longer than a predetermined threshold value. However, the current value i _k as shown by the broken line in FIG. 1
It is also possible to generate the alarm signal W on the basis of the voltage value u _k . For this purpose, for example, the difference between successive current values and voltage values is compared with the maximum sudden change value Δi _max and the maximum sudden change value Δu _max , respectively. Note that Δi _k = | i _k −i _k−1 | Δu _k = | u _k −u _k−1 |. When one or both of the differences are larger than the respective abrupt change values, the abruptly changing current value and voltage value also indicate a short circuit, so that the alarm signal W is generated.

Further, for example, the latest impedance value Z
It is also possible to find inconsistencies in the measured values, for example in the estimator 8, by multiplying by the current value and comparing the result with the next voltage value. A significant difference between the measured values and such a model also indicates that a short circuit has occurred.

The protection circuit 13, in particular the components of the estimator 8, the switch controller 9 and the processing circuit 5 for the alarm signal, are in the form of hardware or software, or a combination of both. It may be in the form of an independent unit or in the form of one common functional block.

[Brief description of drawings]

FIG. 1 shows a block diagram of a protection circuit.

FIG. 2 shows a complex plan view of impedance values.

FIG. 3 shows the position and duration of the measurement window before and after the alarm signal is generated.

FIG. 4 shows a power line with protection circuits at both ends.

[Explanation of symbols]

1 Power Line 2 Radio Frequency Sensor 3 Voltage Sensor 4 Current Sensor 5 Processing Circuit for Alarm Signal 6 Processing Circuit for Voltage Sensor 7 Processing Circuit for Current Sensor 8 Estimator 9 Switch Controller 10 Tripping Area 11 Operating Area 12 Circuit breaker 13 Protective circuit 13a Protective circuit 13b Protective circuit i _k Current value n Measurement window duration s Unacceptable reference S Switch signal T Communication path to other protective circuit u _k Voltage value W Warning signal Z Impedance Z _i Impedance value

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Walter Ruegg             Swiss Tseher-5304 Endinge             N'Zonmat Strasse 7 (72) Inventor Klaus-Dieter Wertmann             Switzerland Tsecher-5405 Baden-de             Ttwil im Zerkweg 26 (72) Inventor Lutz Niemeyer             Switzerland Tseher-5242 Bill Hugh             Nenweg 11 (72) Inventor Ralph Dieter Peach             Federal Republic of Germany Day-01936 Over             Richtenau Königsbrucker             Truss 51 F term (reference) 5G058 EE01 EF02 EG13

Claims (7)

[Claims] 1. An adaptive estimator (8) is used for each of a number of
Measurement point (i_k, U_k)
To impedance value (Z_i), Especially when short circuit
A method for protecting a power line (1), comprising:
Dance value (Z _i) Satisfies the unacceptability criterion (s)
In the method adapted to cut off the power line 1, A radio frequency signal exceeding a predetermined threshold is on the power line (1)
An alarm signal (W) is generated only when
When the alarm signal W is generated, each measurement window
C) The start of the measurement window is essentially the same as the alarm signal.
Positioned to coincide with the occurrence of (W), and / or
When the warning signal (W) is generated,
The fixed window is shortened compared to normal operation
How to characterize. 2. The measurement points (i _k , u _k ) each include one current value (i _k ) and one voltage value (u _k ) for the power line (1). The method according to Item 1. 3. A method according to any one of the preceding claims, characterized in that the number of consecutive impedance values (Z _i ) is analyzed to detect a short circuit. 4. The unacceptable criterion (s) depends on the alarm signal (W), and after the alarm signal is generated, the acceptable or unacceptable criterion is satisfied more quickly than when there is no alarm signal. Method according to any one of the preceding claims, characterized in that 5. The at least two protection circuits (13a, 13b) on the power line (1) are connected to the measuring point (i _k ,
u _k ), and the alarm signal W is generated, and the two protection circuits provide data to determine whether one of the protection circuits has detected a short circuit. Method according to any one of the preceding claims, characterized in that the other protection circuit is also switched off, likewise interrupting the power line. 6. The alarm signal W according to claim 1, wherein the alarm signal W is generated when a radio frequency signal having a duration exceeding a predetermined duration threshold is detected on the power line (1). The method according to item 1. 7. The alarm signal W is generated when the alarm signal W is larger than a sudden change value (Δi _max , Δu _max ) of a predetermined width of the continuous measurement points. The method described in.