CN110308364B - Short-circuit current rapid discrimination method and discrimination system - Google Patents
Short-circuit current rapid discrimination method and discrimination system Download PDFInfo
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- CN110308364B CN110308364B CN201910575122.6A CN201910575122A CN110308364B CN 110308364 B CN110308364 B CN 110308364B CN 201910575122 A CN201910575122 A CN 201910575122A CN 110308364 B CN110308364 B CN 110308364B
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Abstract
The invention discloses a short-circuit current rapid judging method and a judging system based on the combination of a current instantaneous value and a current change rate, which comprises the following steps: collecting and obtaining current to be distinguished; calculating the absolute value of the current instantaneous value of the current to be distinguished and the absolute value of the current change rate; when the following two criteria are met simultaneously, the current to be judged is judged to be short-circuit current: the current instantaneous value criterion expression is as follows: | I (t) | ≧ α · | ISL, |; the current change rate criterion expression is as follows:
wherein I (t) is the instantaneous value of the current to be determined, ISFor setting instantaneous value of current, DzdSetting a current change rate setting value, wherein alpha is a current instantaneous value setting adjustment coefficient, and beta is a current change rate setting adjustment coefficient; take alpha<1 and beta<1. The invention is little affected by fault phase angle, and can ensure that the fault detection time is always within the required range.
Description
Technical Field
The invention belongs to the technical field of relay protection and fault processing of power systems, and particularly relates to a short-circuit current rapid judging method and a short-circuit current rapid judging system.
Background
With the maturity of the fast switch adopting the fast eddy current driving technology, a simple and practical solution is provided for solving the problems of sensitive load off-line caused by overlarge short-circuit current and voltage sag; in addition to fast switching with a fast operating speed, the short-circuit fault detection used should also be carried out in milliseconds.
The traditional fault detection method generally adopts a Fourier method, and even if the semi-wave Fourier method is adopted, the judgment can be carried out only after data is acquired for at least 10ms, so that the requirement of quick identification cannot be met.
The existing rapid discrimination method generally detects faults based on current instantaneous values or current change rates, and the reliability is not high enough. In practical application, the detection time performance of the basic criterion is greatly reduced because the absolute value of the non-periodic component of the short-circuit current is reduced due to a fault phase angle and the short-circuit loop is inductive, so that the short-circuit current cannot break suddenly.
In summary, an improved method for fast determining a short circuit current based on the combination of a current instantaneous value and a change rate is needed.
Disclosure of Invention
The present invention provides a method and a system for fast determining a short-circuit current based on the combination of a current instantaneous value and a current change rate, so as to solve the above-mentioned problems.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention discloses a short-circuit current rapid judging method based on combination of a current instantaneous value and a current change rate, which comprises the following steps of:
the relay protection device acquires and obtains current to be distinguished;
calculating the absolute value of the current instantaneous value of the current to be distinguished and the absolute value of the current change rate; when the following two criteria are met simultaneously, the current to be judged is judged to be short-circuit current:
the current instantaneous value criterion expression is as follows: | I (t) | ≧ α · | IS|；
The current change rate criterion expression is as follows:
wherein I (t) is the instantaneous value of the current to be determined, ISFor setting instantaneous value of current, DzdSetting a current change rate setting value, wherein alpha is a current instantaneous value setting adjustment coefficient, and beta is a current change rate setting adjustment coefficient; take alpha<1 and beta<1。
A further development of the invention consists in that, assuming values of α and β of 1, ISAnd DzdAccording to the minimum short-circuit current effective value I in the protection range of the relay protection devicezdAnd an upper desired recognition time limit tdAnd (4) setting.
The invention has the further improvement that the value boundary expression of the current instantaneous value setting adjustment coefficient alpha is as follows:
wherein, ILmaxIs the maximum load current iL(t) peak value.
The invention has the further improvement that the value boundary expression of the current change rate setting adjustment coefficient beta is as follows:
wherein D isLmaxIs the maximum rate of change of the maximum load current.
The invention is further improved in that the step of optimizing the values of α and β comprises:
s1, traversing the combination of alpha and beta by an exhaustion method based on numerical simulation to obtain the condition that the short-circuit fault detection time is less than or equal to tdThe required value ranges of alpha and beta;
and S2, selecting the values of alpha and beta far away from the minimum value point in the value range of alpha and beta obtained in the step S1, ensuring that the adjusted setting value is more than or equal to 1.5 times of the maximum load current, and obtaining the optimized values of alpha and beta.
The invention discloses a short-circuit current rapid judging system based on combination of a current instantaneous value and a current change rate, and a short-circuit current rapid judging method based on the invention comprises the following steps:
the acquisition module is used for acquiring current to be distinguished in the power system;
the judging module is used for calculating the absolute value of the current instantaneous value of the current to be judged and the absolute value of the current change rate; when the following two criteria are met simultaneously, the current to be judged is judged to be short-circuit current:
the current instantaneous value criterion expression is as follows: | I (t) | ≧ α · | IS|；
The current change rate criterion expression is as follows:
wherein I (t) is the instantaneous value of the current to be determined, ISFor setting instantaneous value of current, DzdSetting a current change rate setting value, wherein alpha is a current instantaneous value setting adjustment coefficient, and beta is a current change rate setting adjustment coefficient; take alpha<1 and beta<1。
Compared with the prior art, the invention has the following beneficial effects:
compared with the judging method based on the combination of the instantaneous value of the current and the change rate of the current, the method for quickly judging the short-circuit current has higher reliability; and conventional current transients andcompared with the conventional method for judging the combination of the current change rates, the conventional method has the defects that the system impedance and the feeder line impedance at the upstream of the fault point are inductive, and the current before and after the fault cannot change suddenly, so that the fault judgment condition cannot be met in 1/4 periods where the fault occurs because a certain criterion is not met, the fault can be detected only in the next 1/4 periods and even the next 1/4 periods, and the fault detection time is seriously influenced. The invention is little affected by fault phase angle, and can ensure that the fault detection time is always within the required range. In the invention, since IzdWith the load current I in normal operationLA large gap is left, and in order to ensure that the fault rapid identification criterion does not malfunction during the normal operation of the system, the instantaneous value setting value alpha I of the criterion current is improvedSI is greater than the maximum load current iL(t) peak value ILmaxSo as not to intersect the maximum load current curve, i.e. alpha IS|>ILmax. The setting value of the current change rate is larger than the maximum change rate D of the maximum load currentLmaxI.e. beta | Dzd|>DLmax. The invention mainly obtains the improvement of the detection time performance of the rapid identification method by reducing two setting values to different degrees, thereby taking alpha<1 and beta<1。
The judging system of the invention is based on the judging method of the invention, and can realize the quick judgment of the short-circuit current based on the combination of the current instantaneous value and the current change rate.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below; it is obvious that the drawings in the following description are some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a schematic diagram of a method for rapidly determining a short-circuit current;
fig. 2 is a schematic diagram of the value range of the adjustment coefficient in which the fault detection time is not greater than the upper limit of the expected identification time.
Detailed Description
In order to make the purpose, technical effect and technical solution of the embodiments of the present invention clearer, the following clearly and completely describes the technical solution of the embodiments of the present invention with reference to the drawings in the embodiments of the present invention; it is to be understood that the described embodiments are only some of the embodiments of the present invention. Other embodiments, which can be derived by one of ordinary skill in the art from the disclosed embodiments without inventive faculty, are intended to be within the scope of the invention.
The embodiment of the invention provides a short-circuit current rapid judging method based on combination of a current instantaneous value and a current change rate, which comprises the following steps:
(1) when the instantaneous value of the current obtained by real-time sampling simultaneously meets the following two criteria, the current can be judged to be a short-circuit current:
criterion of instantaneous value of current: | I (t) | ≧ α · | IS|
Criterion of current change rate:
in the criterion, ISFor setting instantaneous value of current, DzdFor the current change rate setting, α is a current instantaneous value setting adjustment coefficient, and β is a current change rate setting adjustment coefficient.
(2)ISAnd DzdIs determined according to the effective value I of the minimum short-circuit current of the system without considering the adjustment coefficient, i.e. assuming that the values of alpha and beta are 1zdAnd an upper desired recognition time limit tdAnd (4) setting.
(3) Setting of adjustment coefficients α and β:
firstly, the value boundary of the adjustment coefficients alpha and beta is determined. Due to IzdWith the load current I in normal operationLA large gap is left, and in order to ensure that the fault rapid identification criterion does not malfunction during the normal operation of the system, the instantaneous value setting value alpha I of the criterion current is improvedSI is greater than the maximum load current iL(t) peak value ILmaxThereby corresponding to the maximum load currentThe curves do not intersect, i.e. α | IS|>ILmax. The setting value of the current change rate is larger than the maximum change rate D of the maximum load currentLmaxI.e. beta | Dzd|>DLmax. The invention mainly obtains the improvement of the detection time performance of the rapid discrimination method by reducing two setting values to different degrees, thereby taking alpha<1 and beta<1. The value boundary of the current instantaneous value setting adjustment coefficient alpha and the current change rate setting adjustment coefficient beta is:
preferably, in order to obtain optimized values of alpha and beta, traversing the combination of alpha and beta by an exhaustion method based on numerical simulation in the boundary range, and firstly obtaining the condition that the short-circuit fault detection time is not more than tdAnd selecting the values of alpha and beta far away from the minimum point in the required value range of alpha and beta to ensure that the adjusted setting value is far greater than the maximum load current.
Compared with the traditional discrimination method combining the instantaneous value of the current and the change rate of the current, the improved method provided by the invention has higher reliability, is less influenced by a fault phase angle and can ensure that the fault detection time is always in a required range.
Comparative examples of the invention:
FIG. 1 shows a schematic diagram of an improved method for rapidly determining a short-circuit current based on a combination of a current instantaneous value and a current change rate, curve i1(t) the waveform is greater than the minimum effective value I of the short-circuit current expected to be identified at each momentzdCorresponding instantaneous current waveform izd(t), it should be a failure. According to the short-circuit current rapid identification criterion, at t1At the same time, satisfyTwo criteria, so that a fault can be correctly discriminated.
Curve i2(t) is less than I at each instantzdCorresponding instantaneous current waveform izd(t), should be in a non-short-circuit fault state. According to the short-circuit current rapid identification criterion, at t2At this time, although the instantaneous value criterion is satisfied, the change rate criterion is not satisfied, and therefore, it can be correctly determined as a non-failure state.
Since both the system impedance and the feeder impedance upstream of the fault point are inductive, the current cannot jump before and after the fault, i.e. the current detected after the fault cannot be measured from i in fig. 12(t) immediate mutation to i1(t), it may happen that a certain criterion is not satisfied, and the fault determination condition cannot be satisfied in 1/4 cycles where the fault occurs, but the fault may be detected only after the next 1/4 cycle or even the next 1/4 cycle, which seriously affects the fault detection time.
In order to solve the problem, the improved method for quickly judging the short-circuit current based on the combination of the instantaneous value and the change rate introduces an adjustment coefficient concept, and for the setting of the adjustment coefficients alpha and beta:
due to IzdWith the load current I in normal operationLA large gap is left, and in order to ensure that the fault rapid identification criterion does not malfunction during the normal operation of the system, the instantaneous value setting value alpha I of the criterion current is improvedSI is greater than the maximum load current iL(t) peak value ILmaxSo as not to intersect the maximum load current curve, i.e. alpha IS|>ILmax. The setting value of the current change rate is larger than the maximum change rate D of the maximum load currentLmaxI.e. beta | Dzd|>DLmax. The invention mainly obtains the improvement of the detection time performance of the rapid discrimination method by reducing two setting values to different degrees, thereby taking alpha<1 and beta<1。
The value boundary of the current instantaneous value setting adjustment coefficient alpha and the current change rate setting adjustment coefficient beta is as follows:
in order to obtain optimized values of alpha and beta, traversing the combination of alpha and beta by adopting an exhaustion method based on numerical simulation, and firstly obtaining the condition that the short-circuit fault detection time is not more than tdThe required values for α and β are shown in fig. 2 as shaded areas. In order to ensure that the adjusted setting value is far larger than the maximum load current, and thus the action reliability of the adjustment is ensured, the values of alpha and beta far away from the minimum value point P are selected in the value range.
In the invention, the criterion of combining the improved current instantaneous value and the change rate after the setting scheme is adopted, so that the short-circuit fault current can be identified in expected time under various fault phase angles.
In summary, the invention discloses an improved short-circuit current rapid discrimination method based on combination of instantaneous values and change rates, which takes the current instantaneous values and the change rate characteristics obtained by real-time sampling as short-circuit current detection criteria that are simultaneously larger than the setting values, introduces the concept of current instantaneous values and change rate setting value adjustment coefficients, and performs traversal optimization selection on the combination of the adjustment coefficients based on numerical simulation results and by adopting an exhaustion method to realize rapid and reliable identification of short-circuit current. Compared with a judging method based on a current instantaneous value or a current change rate, the method has higher reliability, is less influenced by a fault phase angle compared with the traditional judging method combining the current instantaneous value and the current change rate, and can ensure that the short-circuit current detection time under any fault phase angle does not exceed 1/4 power frequency cycles all the time.
The invention provides a short-circuit current rapid judging system based on combination of a current instantaneous value and a current change rate, and a short-circuit current rapid judging method based on the invention comprises the following steps:
the acquisition module is used for acquiring current to be distinguished in the power system;
the judging module is used for calculating the absolute value of the current instantaneous value of the current to be judged and the absolute value of the current change rate; when the following two criteria are met simultaneously, the current to be judged is judged to be short-circuit current:
the current instantaneous value criterion expression is as follows: | I (t) | ≧ α · | IS|；
The current change rate criterion expression is as follows:
wherein I (t) is the instantaneous value of the current to be determined, ISFor setting instantaneous value of current, DzdSetting a current change rate setting value, wherein alpha is a current instantaneous value setting adjustment coefficient, and beta is a current change rate setting adjustment coefficient; take alpha<1 and beta<1。
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can make modifications and equivalents to the embodiments of the present invention without departing from the spirit and scope of the present invention, which is set forth in the claims of the present application.
Claims (3)
1. A short-circuit current rapid discrimination method is characterized by comprising the following steps:
the relay protection device acquires and obtains current to be distinguished;
calculating the absolute value of the current instantaneous value of the current to be distinguished and the absolute value of the current change rate; when the following two criteria are met simultaneously, the current to be judged is judged to be short-circuit current:
the current instantaneous value criterion expression is as follows: | I (t) | ≧ α · | IS|；
The current change rate criterion expression is as follows:
wherein i (t) is the current transient to be determinedValue of (I)SFor setting instantaneous value of current, DzdSetting a current change rate setting value, wherein alpha is a current instantaneous value setting adjustment coefficient, and beta is a current change rate setting adjustment coefficient; take alpha<1 and beta<1；
Wherein, the value boundary expression of the current instantaneous value setting adjustment coefficient alpha is as follows:
wherein, ILmaxIs the maximum load current iL(t) peak value;
the value boundary expression of the current change rate setting adjustment coefficient beta is as follows:
wherein D isLmaxIs the maximum rate of change of the maximum load current;
the step of optimizing the values of alpha and beta comprises:
s1, traversing the combination of alpha and beta by an exhaustion method based on numerical simulation to obtain the condition that the short-circuit fault detection time is less than or equal to tdThe required value ranges of alpha and beta;
and S2, selecting the values of alpha and beta far away from the minimum value point in the value range of alpha and beta obtained in the step S1, ensuring that the adjusted setting value is more than or equal to 1.5 times of the maximum load current, and obtaining the optimized values of alpha and beta.
2. The method for rapidly determining a short-circuit current according to claim 1,
assuming that the values of α and β are 1, ISAnd DzdAccording to the minimum short-circuit current effective value I in the protection range of the relay protection devicezdAnd an upper desired recognition time limit tdAnd (4) setting.
3. A short-circuit current rapid discrimination system based on the short-circuit current rapid discrimination method of claim 1 or 2, comprising:
the acquisition module is used for acquiring current to be distinguished in the power system;
the judging module is used for calculating the absolute value of the current instantaneous value of the current to be judged and the absolute value of the current change rate; when the following two criteria are met simultaneously, the current to be judged is judged to be short-circuit current:
the current instantaneous value criterion expression is as follows: | I (t) | ≧ α · | IS|；
The current change rate criterion expression is as follows:
wherein I (t) is the instantaneous value of the current to be determined, ISFor setting instantaneous value of current, DzdSetting a current change rate setting value, wherein alpha is a current instantaneous value setting adjustment coefficient, and beta is a current change rate setting adjustment coefficient; take alpha<1 and beta<1。
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