CN110824388A - 4PT wiring polarity discrimination method for small current grounding system - Google Patents
4PT wiring polarity discrimination method for small current grounding system Download PDFInfo
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Abstract
The invention discloses a 4PT wiring polarity distinguishing method of a small current grounding system, which comprises the steps of firstly, taking the electric quantity change characteristics of the small current grounding system during single-phase grounding, adopting a sequence component method to decompose and obtain the positive sequence, negative sequence and zero sequence voltage components of a fault point in a 4PT wiring mode when the system has single-phase grounding fault, further respectively calculating the voltage values of each point on a first side, a second side and a third side, and finally obtaining a whole set of theoretical analysis values of voltage when the 4PT is correctly and wrongly connected; secondly, a single-phase grounding test method of a simulated small-current grounding system is adopted, fault voltage is loaded, voltages of all points of a secondary winding and a tertiary winding are measured, and correctness of a 4PT wiring mode is verified by comparing with a theoretical calculation value. The test process of the experimental design part of the invention is simple, accords with the field measurement condition, and is beneficial to the popularization of the invention.
Description
Technical Field
The invention belongs to the technical field of power system relay protection, and particularly relates to a 4PT wiring polarity judgment method for a small current grounding system.
Background
A neutral point ungrounded mode is generally adopted in a 3-35 kV system in China, and the aim is that when single-phase ground faults occur, the line voltages of the system are still symmetrical, and the system can continuously run for a period of time under the load. The voltage transformer has certain inductance, and the line has certain capacitance to the ground, line interphase and compensation capacitor, so when single-phase ground fault occurs, the combination of the capacitance and the inductance may form a series of oscillation loops with different self-oscillation frequencies, and resonance phenomenon is generated together with an external power supply, so that the voltage transformer in the system has serious resonance overvoltage and inrush current, accidents such as voltage transformer burnout in operation, frequent burnout of a high-voltage fuse, explosion of one-phase or two-phase current-limiting resistor and the like are caused, and small economic loss is caused.
In order to prevent PT from ferromagnetic resonance, electric power engineering technicians put forward a plurality of resonance elimination measures in production practice, and document [5] analyzes several common resonance elimination principles and indicates that a 4PT connection mode can increase zero-sequence impedance and can ensure that zero-sequence voltage generated when a system is grounded in a single phase is mainly added to a zero-sequence voltage transformer, so that the resonance elimination effect is obvious. However, the 4PT wiring mode is complex, and the characteristic different from the conventional wiring mode is shown when a fault occurs, in order to deeply understand the wiring mode, a large amount of research work is done by researchers, the document [1] analyzes the abnormal phenomenon of the harmonic measurement result in the 4PT wiring mode, the document [2] simplifies and analyzes the unbalanced voltage appearing in the 4PT wiring mode, the document [3] mainly analyzes the common harmonic elimination principle at present and provides the attention during operation, the document [4] analyzes the mechanism of preventing ferromagnetic resonance voltage from occurring in the 4PT wiring, and the related research work is greatly beneficial to deeply understanding the 4PT wiring mode.
Reference documents:
[1] influence of 4PT wiring of a voltage transformer on harmonic measurement results [ J ]. power system and automation science report thereof, 2014 (4). The power system is a new generation of double-Yin, Liqinlong, Danishenquqing, Liushu Ming.
[2] Li lei, rochow wave, king rock, fountan money,. study on the basis of 10kV distribution network PT frequent fault simulation and improvement measures [ J ]. protection and control of electric power system, 2014, (14).
[3] The method comprises the steps of (1) analyzing a voltage distortion phenomenon of the improved 4PT connection mode voltage transformer and (J) of a transformer, 2013.
[4] Yellow tiger, liu jia,. 4PT wiring mode secondary voltage unbalance phenomenon discussion [ J ]. high and new technology enterprises in china, 2011, (8).
[5] Wangshi xu, wangkun, coupled with bin, discussion of the harmonic elimination problem of the low current grounding system 4PT [ J ]. huazhong power, 2010, (5).
4PT mode of connection uses more and more at the transformer substation, but because installation unit debugging level is limited, can 'T verify zero sequence voltage transformer T0 secondary connection correctly with conventional voltage transformer detection method, design department's design drawing also often leaks the polarity end of marking 4PT secondary connection, leads to often taking place 4PT polarity and connects the wrong condition. In addition, when the system normally operates, the three-phase voltage is balanced, and even if the secondary winding of the T0 is reversed, no voltage exists on the T0, so that the wiring error cannot be timely found. At present, the method of comparing drawings and checking polarity is adopted for checking whether 4PT wiring is correct or not, once a drawing is wrong, an installer can easily connect wrong wires, 4PT wiring error conditions occur for many times in a power system, so that when single-phase earth faults occur, a worker on duty cannot correctly judge the fault conditions, and therefore a method for verifying the 4PT wiring correctness needs to be found out urgently, and the installer and an inspection and acceptance staff can use the method for reference.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for judging the 4PT wiring polarity of a small-current grounding system, and avoiding the 4PT wiring error.
In order to solve the technical problems, the invention adopts the following technical scheme: a method for judging 4PT wiring polarity of a small current grounding system,
firstly, the electric quantity change characteristics of a small current grounding system during single-phase grounding are taken, the positive sequence voltage component, the negative sequence voltage component and the zero sequence voltage component of a fault point in a 4PT wiring mode when the system has single-phase grounding fault are obtained through decomposition by a sequence component method, voltage values of points on the first side, the second side and the third side are further respectively calculated, and finally a whole set of theoretical analysis values of voltage when 4PT is correctly wired and wrongly wired are obtained;
secondly, a single-phase grounding test method of a simulated small-current grounding system is adopted, fault voltage is loaded, voltages of all points of a secondary winding and a tertiary winding are measured, and correctness of a 4PT wiring mode is verified by comparing with a theoretical calculation value.
By adopting the technical scheme, the invention has the following beneficial effects:
firstly, the voltages of all points of a secondary winding and a tertiary winding under the conditions of correct 4PT wiring polarity and error under the condition of single-phase grounding fault of a small-current grounding system are obtained through theoretical analysis, and the voltage calculation method has universality and can be used as a voltage theoretical reference value under the 4PT wiring mode;
secondly, measuring the voltages of all points of the 4PT secondary winding and the tertiary winding by using the fault voltage under the condition of loading the single-phase grounding of the low-current grounding system, and directly verifying the correctness of the 4PT wiring polarity by comparing with a theoretical reference value of the voltage.
Finally, the test process of the experimental design part of the invention is simple, accords with the field measurement condition, and is beneficial to the popularization of the invention.
The following detailed description of the present invention will be provided in conjunction with the accompanying drawings.
Drawings
The invention is further described with reference to the accompanying drawings and the detailed description below:
FIG. 1 is a circuit diagram of 4PT connection mode;
FIG. 2 is a schematic diagram of the primary winding connections;
FIG. 3 is a schematic diagram of the protection, measurement, and metering winding connections;
FIG. 4 is a schematic diagram of open delta winding connections;
fig. 5 is a primary side a-phase fault vector diagram.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to inhibit ferromagnetic resonance, a voltage transformer in a small current grounding system usually adopts a 4PT wiring mode, but because the wiring mode is complex, wiring errors are easy to occur, and particularly when the polarity of a zero-sequence PT secondary winding is reversed, the phenomenon of failure analysis is difficult to analyze or even misjudgment is caused for field operation maintainers. The invention provides a polarity discrimination method of 'theoretical analysis + experimental design', which comprises the steps of mathematically deeply analyzing the voltage change condition of each point of a 4PT connection line when a system has a single-phase earth fault, obtaining test data through experimental design and fault simulation, verifying the rationality of the experimental design through comparison of theoretical data and the test data, and providing an effective inspection method for discriminating whether the polarity of the 4PT connection line is correct.
The invention is divided into two steps of theoretical calculation and experimental design, and the specific implementation mode is as follows:
when single-phase earth fault occurs in small current, the fault voltage is decomposed into symmetrical positive sequence, negative sequence and zero sequence voltages by using a sequence component method, and further voltage values of each point of each side winding can be calculated through a 4PT connection mode and a transformation ratio.
When the system has asymmetric faults, the fault quantity is decomposed into symmetric sequence components, the asymmetric fault analysis is converted into symmetric network calculation, and a sequence component calculation formula is as follows:
wherein, U+、U-、U0Respectively positive, negative and zero sequence voltages, UA、UB、UCRespectively, A, B, C phase voltages, respectively,
when single-phase earth faults occur in a small current grounding system, the fault phase voltage is reduced to 0, the non-fault phase voltage is increased to the line voltage, positive sequence, negative sequence and zero sequence voltages can be calculated and obtained through a sequence component calculation formula, and support is provided for theoretical calculation of voltages on all sides under the known 4PT connection mode and transformation ratio condition.
A single-phase grounding test method of a simulated small-current grounding system is adopted, and according to the characteristics that when a single-phase grounding fault occurs, the phase voltage value of the fault is reduced to 0, and the phase voltage value of the non-fault is increased to a line voltage, the fault voltage meeting the relation is loaded, the voltage values of all points of a 4PT secondary winding and a tertiary winding are measured, and the correctness of the 4PT wiring polarity is verified by comparing with a theoretical calculation value.
1. Calculating positive sequence, negative sequence and zero sequence voltages of fault points
And calculating positive sequence, negative sequence and zero sequence voltages at the fault point according to a sequence component method.
The positive sequence voltage is:
the negative sequence voltage is:
the zero sequence voltage is:
2. calculating the voltage of each point
The primary winding is connected as shown in figure 2, when the A phase of the system is grounded, as shown in figure 5, the voltage of the A phase is reduced to 0V, and the voltage of the B, C two phases is increased to the line voltage which is 10 ∠ -150 kV and 10 ∠ 150-150 kV respectively.
Further, the voltage U of the 4PT at the point O can be calculatedON. If A, B, C positive sequence, negative sequence and zero sequence impedances of the zero phase voltage transformer are equal respectively
The voltage at point O is:
the voltage at the point A is:
UAO＝UA-UO＝0-(-4.33)＝4.33kV (6)
the voltage at the point B is:
UBO＝UB-UO＝10∠-150°-(-4.33)＝6.6∠-131°kV (7)
the voltage at point C is:
UCO＝UC-UO＝10∠150°-(-4.33)＝6.6∠131°kV (8)
3. clear 4PT connection form and transformation ratio relation
The 4PT connection adopts a method of connecting the conventional PT in series with the zero-phase PT, wherein the transformation ratio of A, B, C phase voltage transformation is respectively
The transformation ratio of the zero sequence PT is
4. Voltage of each point of secondary winding and tertiary winding when 4PT wiring is correct
The wiring of the secondary winding is as shown in figure 3, and the voltage value of each secondary point is calculated according to the transformation ratio relation and the wiring mode of the voltage transformer.
The voltage at point O is:
the voltage at the point A is:
the voltage at the point B is:
the voltage at point C is:
and the wiring of the tertiary winding is as shown in figure 4, and the voltage values of the points of the three times are calculated according to the transformation ratio relation and the wiring mode of the voltage transformer.
The voltage at point S (point C) is:
the voltage at point B is:
the voltage at point a is:
the voltage at point L is:
5. voltage of each point of secondary winding and tertiary winding when 4PT wiring error occurs
The voltage signature at 4PT polarity wiring error was analyzed. The wiring of the secondary winding is as shown in figure 3, and the voltage value of each secondary point is calculated according to the transformation ratio relation and the wiring mode of the voltage transformer.
The voltage at point O is:
the voltage at the point A is:
the voltage at the point B is:
the voltage at point C is:
and the wiring of the tertiary winding is as shown in figure 4, and the voltage values of the points of the three times are calculated according to the transformation ratio relation and the wiring mode of the voltage transformer.
The voltage at point S (point C) is:
the voltage at point B is:
the voltage at point a is:
the voltage at point L is:
6. 4PT polarity test
The method comprises the steps of firstly disconnecting all secondary loads of 4PT by adopting a test method for simulating single-phase faults, using a relay protection tester to simulate a system for applying voltage to a high-voltage primary winding of a voltage transformer to generate A-phase grounding faults, adding 100 ∠ -150 degrees V to the A-phase, adding 100 ∠ 150 degrees V to the C-phase, measuring the secondary voltage of each point, and obtaining test data shown in table 1.
| I mother PT | II mother PT | III mother PT | |
| AO (two times) | 0.424 | 0.390 | 0.354 |
| BO (second) | 0.566 | 0.640 | 0.674 |
| CO (Secondary) | 0.676 | 0.676 | 0.713 |
| ON (twice) | 0.422 | 0.390 | 0.352 |
| AN (second) | 0 | 0 | 0.001 |
| BN (second) | 0.959 | 0.998 | 0.995 |
| CN (second) | 0.960 | 0.998 | 0.994 |
| L-C (three times) | 0.281 | 0.330 | 0.407 |
| A-C (three times) | 0.496 | 0.547 | 0.598 |
| B-C (three times) | 0.385 | 0.377 | 0.407 |
| C-N (three times) | 0.740 | 0.696 | 0.610 |
| L-A (three times) | 0.241 | 0.228 | 0.200 |
| A-B (three times) | 0.324 | 0.358 | 0.383 |
| B-C (three times) | 0.386 | 0.375 | 0.407 |
| L-N (three times) | 0.959 | 0.997 | 0.991 |
TABLE 1
The data in table 1 is compared with theoretical analysis data (because the primary rated voltage is 10kV during theoretical analysis and the applied voltage is 100V during test, the theoretical analysis data needs to be divided by 100), the error between the test data and the theoretical analysis data is within 5%, and the correctness of the polarity discrimination method is verified.
While the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that the invention is not limited thereto, and may be embodied in other forms without departing from the spirit or essential characteristics thereof. Any modification which does not depart from the functional and structural principles of the present invention is intended to be included within the scope of the claims.
Claims (7)
1. A4 PT wiring polarity discrimination method for a small current grounding system is characterized by comprising the following steps:
firstly, the electric quantity change characteristics of a small current grounding system during single-phase grounding are taken, the positive sequence voltage component, the negative sequence voltage component and the zero sequence voltage component of a fault point in a 4PT wiring mode when the system has single-phase grounding fault are obtained through decomposition by a sequence component method, voltage values of points on the first side, the second side and the third side are further respectively calculated, and finally a whole set of theoretical analysis values of voltage when 4PT is correctly wired and wrongly wired are obtained;
secondly, a single-phase grounding test method of a simulated small-current grounding system is adopted, fault voltage is loaded, voltages of all points of a secondary winding and a tertiary winding are measured, and correctness of a 4PT wiring mode is verified by comparing with a theoretical calculation value.
2. The method for judging 4PT wiring polarity of a small-current grounding system according to claim 1, characterized in that: when the system has asymmetric faults, the fault quantity is decomposed into symmetric sequence components, the asymmetric fault analysis is converted into symmetric network calculation, and a sequence component calculation formula is as follows:
wherein, U+、U-、U0Respectively positive, negative and zero sequence voltages, UA、UB、UCRespectively, A, B, C phase voltages, respectively,
when a single-phase earth fault occurs in the small-current earth system, the fault phase voltage is reduced to 0, the non-fault phase voltage is increased to the line voltage, and then the positive sequence voltage, the negative sequence voltage and the zero sequence voltage can be obtained through calculation of a sequence component calculation formula.
3. The method for judging 4PT wiring polarity of the small-current grounding system according to claim 2, characterized in that: calculating positive sequence, negative sequence and zero sequence voltages at fault points according to a sequence component method:
the positive sequence voltage is:
the negative sequence voltage is:
the zero sequence voltage is:
4. the method for judging 4PT wiring polarity of the small-current grounding system according to claim 2, characterized in that: calculating the voltage of each point for one time:
when the A phase of the system is grounded, the voltage of the A phase is reduced to 0V, the voltage of the B, C two phase is increased to the line voltage which is respectively 10 ∠ -150 degrees kV and 10 ∠ 150 degrees kV, and the voltage U of 4PT at the O point can be calculatedONIf A, B, C positive sequence, negative sequence and zero sequence impedances of zero phase voltage transformer are equal respectively
The voltage at point O is:
the voltage at the point A is:
UAO＝UA-UO＝0-(-4.33)＝4.33kV (6)
the voltage at the point B is:
UBO＝UB-UO＝10∠-150°-(-4.33)＝6.6∠-131°kV (7)
the voltage at point C is:
UCO＝UC-UO＝10∠150°-(-4.33)＝6.6∠131°kV (8)。
5. the 4PT terminal of claim 4 for a low current grounding systemA method for discriminating between characteristics, comprising: the 4PT connection mode and the transformation ratio relation are defined, the 4PT connection adopts a method of connecting the conventional PT in series with the zero-phase PT, wherein the transformation ratios of A, B, C phase voltage transformation are respectively
The transformation ratio of the zero sequence PT is
6. The method for judging 4PT wiring polarity of a small-current grounding system according to claim 5, characterized in that: voltage of each point of the secondary winding and the tertiary winding when the 4PT is correctly wired:
and calculating the voltage value of each secondary point according to the transformation ratio relation and the wiring mode of the voltage transformer:
the voltage at point O is:
the voltage at the point A is:
the voltage at the point B is:
the voltage at point C is:
calculating the voltage values of the points three times according to the transformation ratio relation and the wiring mode of the voltage transformer:
the voltage at point S (point C) is:
the voltage at point B is:
the voltage at point a is:
the voltage at point L is:
7. the method for judging 4PT wiring polarity of a small-current grounding system according to claim 5, characterized in that: voltage of each point of the secondary winding and the tertiary winding when 4PT wiring is wrong:
and calculating the voltage value of each secondary point according to the transformation ratio relation and the wiring mode of the voltage transformer:
the voltage at point O is:
the voltage at the point A is:
the voltage at the point B is:
the voltage at point C is:
calculating the voltage values of the points three times according to the transformation ratio relation and the wiring mode of the voltage transformer:
the voltage at point S is:
the voltage at point B is:
the voltage at point a is:
the voltage at point L is:
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| CN114236432A (en) * | 2021-12-17 | 2022-03-25 | 中国十七冶集团有限公司 | Method for rapidly checking wiring correctness of voltage transformer by using relay protection tester |
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