CN116093965A - Medium-voltage distribution network voltage clamping device and clamping method - Google Patents
Medium-voltage distribution network voltage clamping device and clamping method Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention discloses a medium-voltage distribution network voltage clamping device and a clamping method, which relate to the technical field of distribution network voltage optimal control and have the technical scheme that: the additional capacitor is connected with an additional capacitor in parallel on an edge-phase line of the medium-voltage distribution network to form a capacitor branch; the fault detection module is connected with the medium-voltage distribution network and is used for detecting whether a single-phase grounding fault occurs in the medium-voltage distribution network or not; the voltage clamping module is connected with the additional capacitor module and the fault detection module and is used for adjusting the size of the correlation coefficient to clamp the three-phase voltage of the medium-voltage distribution network by adjusting the size of the additional capacitor on the capacitor branch when the fault detection module detects that the medium-voltage distribution network has single-phase earth fault. The invention realizes the optimal control of the voltage levels of the middle phase and the two side phases of the medium-voltage distribution network, thereby reducing the probability of deterioration event generated after the arcing of the ground fault phase.
Description
Technical Field
The invention relates to the technical field of distribution network voltage optimization control, in particular to a medium-voltage distribution network voltage clamping device and a clamping method.
Background
Most of mountain fire events caused by power faults are caused by single-phase grounding faults, and related technologies mainly focus on improving the single-phase grounding fault handling capability so as to identify faults in early stages of fault development, thereby preventing adverse and harm of mountain fire caused by power lines.
Aiming at the problems, on the basis of a large number of single-phase ground fault scenes, the situation that the single-phase ground fault occurs mainly in two side phases of A, C is found through in-depth observation, and the fault scenes occurring in the middle phase (namely B phase) are relatively few. By combining the general range and the conditions of the air breakdown voltage, if the voltage of the side phase can be properly controlled, the possibility that the single-phase grounding fault point is started and a harsher mountain fire event is caused by a short-term temperature rise effect after the single-phase grounding fault point is started can be greatly reduced. In addition, on the premise of reducing the side phase voltage, the voltage quality requirement of low-voltage side power supply is also required to be ensured, namely the voltage of the medium-voltage distribution network line is required to be ensured to be similar to the voltage level of the original medium-voltage distribution network.
Therefore, when single-phase earth faults occur on the basis of ensuring the constant power supply quality of low-voltage distribution users or in the medium-voltage distribution network, how to optimize the voltage levels of the phases and the two side phases in the three-phase transmission line of the medium-voltage distribution network can play a vital role in restraining the single-phase earth faults or relieving the single-phase earth faults from deteriorating to uncontrolled events after the single-phase earth faults occur.
Disclosure of Invention
The invention aims to solve the problem of optimizing voltage grades of a phase and two side phases in a three-phase transmission line of a medium-voltage distribution network, and provides a medium-voltage distribution network voltage clamping device and a clamping method.
The technical aim of the invention is realized by the following technical scheme:
in a first aspect of the present application, a medium voltage distribution network voltage clamping device is provided, applied to a medium voltage distribution network, the device includes:
the additional capacitor is connected with the side phase line of the medium-voltage distribution network in parallel to form a capacitor branch, wherein the additional capacitor is equal to the correlation coefficient multiplied by the capacitance to ground of the three-phase line;
the fault detection module is connected with the medium-voltage distribution network and is used for detecting whether a single-phase grounding fault occurs in the medium-voltage distribution network or not;
and the voltage clamping module is connected with the additional capacitor module and the fault detection module and is used for adjusting the size of the correlation coefficient to clamp the three-phase voltage of the medium-voltage distribution network by adjusting the size of the additional capacitor on the capacitor branch when the fault detection module detects that the medium-voltage distribution network has single-phase grounding fault.
In one embodiment, the system further comprises a single-phase isolation transformer and a transformer area transformer;
the unidirectional isolation transformer is connected with a three-phase line of the medium-voltage distribution network in a star connection or delta connection mode;
the transformer is connected with the three-phase circuit in a star connection or delta connection mode.
In a second aspect of the present application, there is provided a medium voltage distribution network voltage clamping method applied to a medium voltage distribution network voltage clamping device according to the first aspect of the present application, the method comprising:
according to a unidirectional asymmetric operation mode of the medium-voltage distribution network connected with the single-phase isolation transformer, a first equivalent circuit of three-phase line voltage of the medium-voltage distribution network is constructed, wherein the first equivalent circuit is formed by connecting a B-phase circuit and a side-phase circuit in series;
obtaining a second equivalent circuit of three-phase line voltage after forming a capacitor branch according to the capacitor branch and the first equivalent circuit, wherein the side phase circuit is an A phase circuit and a C phase circuit, and the A phase circuit is connected with the C phase circuit in parallel;
establishing a voltage control model between three-phase line voltage of the medium-voltage distribution network after being connected to the medium-voltage distribution network through the single-phase isolation transformer and line voltage of the medium-voltage distribution network before being connected to the medium-voltage distribution network through the single-phase isolation transformer according to the second equivalent circuit;
when a single-phase earth fault of the medium-voltage distribution network is detected, the three-phase voltage of the medium-voltage distribution network is clamped by adjusting the size of the correlation coefficient to control the size of the three-phase voltage of the voltage control model.
In one embodiment, a voltage distribution model of the medium-voltage distribution network under the conditions of the capacitance to ground parameter and the resistance to ground parameter is constructed according to the capacitance to ground parameter and the resistance to ground parameter of the first equivalent circuit.
In one embodiment, the expression of the voltage distribution model is:
In one embodiment, the expression of the voltage control model is:
In one embodiment, when a single-phase earth fault of the medium-voltage distribution network is detected, the magnitude of the three-phase voltage of the voltage control model is controlled by adjusting the magnitude of the correlation coefficient, and the three-phase voltage of the medium-voltage distribution network is clamped specifically as follows:
when detecting that the medium-voltage distribution network has single-phase earth faults, controlling the voltage control model to adjust the magnitude of the side phase voltage by adjusting the magnitude of the correlation coefficient.
In one embodiment, when a single-phase earth fault of the medium-voltage distribution network is not detected, setting a target voltage of the side-phase line, calculating the magnitude of a correlation coefficient according to a voltage control model, and calculating the magnitude of an additional capacitor connected in parallel to the side-phase line according to the magnitude of the correlation coefficient.
In one embodiment, the line voltage U of the medium voltage distribution network before the medium voltage distribution network is connected through the single-phase isolation transformer L - L ＝U B -U A In the formula, U A 、U B The voltage is the voltage of the original power distribution network A relative to the ground and the voltage of the original power distribution network B relative to the ground before single-phase isolation transformation access.
In one embodiment, the determining a connection mode of the single-phase isolation transformer according to a unidirectional asymmetric operation mode of the single-phase isolation transformer of the medium-voltage distribution network specifically includes:
when the secondary winding of the main transformer is star-shaped, and the primary winding of the transformer in the transformer area is star-shaped, determining that the primary winding of the single-phase isolation transformer is star-shaped and the secondary winding is star-shaped;
when the secondary winding of the main transformer is star-shaped wiring and the primary winding of the transformer in the transformer area is delta-shaped wiring, determining that the primary winding of the single-phase isolation transformer is star-shaped wiring and the secondary winding is delta-shaped wiring;
when the secondary winding of the main transformer is in a triangular wiring mode and the primary winding of the transformer in the transformer area is in a star wiring mode, determining that the primary winding of the single-phase isolation transformer is in the triangular wiring mode and the secondary winding is in the star wiring mode;
when the secondary winding of the main transformer is in a triangular wiring mode and the primary winding of the transformer in the transformer area is in a triangular wiring mode, the primary winding of the single-phase isolation transformer is determined to be in the triangular wiring mode and the secondary winding is determined to be in the triangular wiring mode.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the voltage clamping device for the medium-voltage distribution network, the additional capacitor is connected in parallel to the grounding capacitor of the three-phase line to form a capacitor branch, and the relationship between the grounding capacitor of the three-phase line and the additional capacitor is determined, so that the theoretical association relationship between the additional capacitor and the side phase voltage is analyzed, the side phase voltage is controlled, and the voltage grades of the medium phase and the two side phases of the medium-voltage distribution network are optimally controlled on the premise of ensuring the quality requirement of low-voltage power supply voltage or under the condition that the medium-voltage distribution network suffers from single-phase grounding faults, so that the occurrence probability of single-phase grounding faults of the medium-voltage distribution network is effectively restrained or the probability of deterioration events generated after single-phase grounding faults are arcing is reduced.
2. According to the voltage clamping method of the medium-voltage distribution network, according to the unidirectional asymmetric operation mode of the medium-voltage distribution network after being connected into the single-phase isolation transformer, a first equivalent circuit is built by combining a medium-voltage distribution network power transmission line, the voltage level of a side phase is controlled, an additional capacitor is introduced to form a capacitor branch to adjust the capacitance to the ground of different phases of the power transmission line, a second equivalent circuit is obtained by combining the capacitor branch on the basis of the first equivalent circuit, a voltage control model capable of adjusting the voltage of the side phase is built on the basis of the second equivalent circuit, the size of the three-phase voltage in the voltage control model is adjusted by adjusting the size of a correlation coefficient, the size of the side phase voltage connected into the single-phase isolation transformer is changed, under the premise of ensuring the quality requirement of the low-voltage power supply voltage or under the condition that the medium-voltage distribution network has single-phase earth faults, the voltage grades of the medium-phase and the two side phases of the medium-voltage distribution network are optimally controlled, so that the occurrence probability of single-phase earth faults of the medium-voltage distribution network is effectively suppressed or the probability of occurrence of deterioration events after single-phase earth faults are suppressed is reduced.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention. In the drawings:
fig. 1 is a schematic block diagram of a voltage clamping device for a medium-voltage distribution network according to an embodiment of the present application;
fig. 2 is a circuit diagram of a first equivalent circuit of a medium voltage distribution network system under consideration of natural distribution according to an embodiment of the present application;
fig. 3 is a schematic flow chart of a method for clamping a voltage of a medium-voltage distribution network according to an embodiment of the present application.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.
It should be appreciated that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
Based on a large number of single-phase ground fault scenes, the situation that the unidirectional ground fault occurs mainly in two side phases of A, C is found through deep observation, and the fault scenes occurring in the middle phase (namely the B phase) are relatively few. By combining the general range and the conditions of the air breakdown voltage, if the voltage of the side phase can be properly controlled, the possibility that the single-phase grounding fault point is started and a harsher mountain fire event is caused by a short-term temperature rise effect after the single-phase grounding fault point is started can be greatly reduced. In addition, on the premise of reducing the side phase voltage, the voltage quality requirement of low-voltage side power supply is also required to be ensured, namely the voltage of the medium-voltage distribution network line is required to be ensured to be similar to the voltage level of the original medium-voltage distribution network.
On the basis of ensuring the constant power supply quality of low-voltage distribution users, how to optimize the voltage levels of the phases and the two side phases in the three-phase transmission line of the medium-voltage distribution network has a critical effect on suppressing the occurrence of the ground fault or relieving the occurrence of the fault and then deteriorating to an uncontrolled event. In summary, the embodiment of the application provides a voltage clamping device for a medium-voltage distribution network, which is applied to the medium-voltage distribution network for 10kV power transmission, and by connecting an additional capacitor in parallel to a grounding capacitor of a three-phase line to form a capacitor branch and determining the relationship between the grounding capacitor of the three-phase line and the additional capacitor, the theoretical association relationship between the additional capacitor and the magnitude of the side phase voltage is analyzed, so that the magnitude of the side phase voltage is controlled, and the optimal control of the voltage levels of a middle phase and two side phases of the medium-voltage distribution network is realized on the premise of ensuring the quality requirement of low-voltage power supply voltage or under the condition that the medium-voltage distribution network has single-phase grounding faults, thereby effectively suppressing the occurrence probability of single-phase grounding faults of the medium-voltage distribution network or reducing the probability of occurrence of deterioration events after arcing of single-phase grounding faults.
Referring to fig. 1, fig. 1 is a schematic block diagram of a voltage clamping device for a medium voltage distribution network, provided in an embodiment of the present application, and the device, as shown in fig. 1, includes:
the additional capacitor is connected with the side phase line of the medium-voltage distribution network in parallel to form a capacitor branch, wherein the additional capacitor is equal to the correlation coefficient multiplied by the capacitance to ground of the three-phase line;
the fault detection module is connected with the medium-voltage distribution network and is used for detecting whether a single-phase grounding fault occurs in the medium-voltage distribution network or not;
and the voltage clamping module is connected with the additional capacitor module and the fault detection module and is used for adjusting the size of the correlation coefficient to clamp the three-phase voltage of the medium-voltage distribution network by adjusting the size of the additional capacitor on the capacitor branch when the fault detection module detects that the medium-voltage distribution network has single-phase grounding fault.
In summary, according to the voltage clamping device for the medium-voltage distribution network provided by the embodiment, the additional capacitor is connected in parallel to the grounding capacitor of the three-phase line to form a capacitor branch, and the relationship between the grounding capacitor and the additional capacitor of the three-phase line is determined, so that the theoretical association relationship between the additional capacitor and the voltage of the side phase is analyzed, the voltage of the side phase is controlled, and the optimization control of the voltage levels of the medium phase and the two side phases of the medium-voltage distribution network is realized on the premise of ensuring the quality requirement of the low-voltage power supply voltage or under the condition that the medium-voltage distribution network suffers from single-phase grounding faults, so that the occurrence probability of single-phase grounding faults of the medium-voltage distribution network is effectively suppressed or the probability of deterioration events generated after the single-phase grounding faults are arcing is reduced.
In this embodiment, the fault detection module belongs to a conventional technical means in the art, that is, a method for detecting whether a ground fault occurs in the medium-voltage distribution network is a very mature prior art, so that no unnecessary explanation is made, and the side phase voltage of the medium-voltage distribution network is clamped only by means of the detection result.
In one embodiment, as shown in fig. 1, further comprising a single-phase isolation transformer and a transformer of the transformer area;
the unidirectional isolation transformer is connected with a three-phase line of the medium-voltage distribution network in a star connection or delta connection mode;
the transformer is connected with the three-phase circuit in a star connection or delta connection mode.
In this embodiment, the manner in which the single-phase isolation transformer and the transformer in the transformer area are connected to the distribution network is common knowledge of those skilled in the art, so that redundant explanation is not made here.
In one embodiment, on the basis of ensuring the constant power supply quality of low-voltage distribution users, how to optimize the voltage levels of the phases and the two side phases in the three-phase transmission line of the medium-voltage distribution network plays a vital role in suppressing the occurrence of a ground fault or relieving the occurrence of a fault and then deteriorating to an uncontrolled event. In summary, the embodiment of the application provides a voltage clamping method of a medium-voltage distribution network, which is applied to the medium-voltage distribution network of 10kV power transmission and is used for constructing a first equivalent circuit by combining a medium-voltage distribution network power transmission line according to a unidirectional asymmetric operation mode of the medium-voltage distribution network after the medium-voltage distribution network is connected with a single-phase isolation transformer, further taking the voltage level of a side phase as a target, introducing an additional capacitor to form a capacitor branch to adjust the grounding capacitance of different phases of the power transmission line, combining the capacitor branch on the basis of the first equivalent circuit to obtain a second equivalent circuit, establishing a voltage control model capable of adjusting the voltage of the side phase on the basis of the second equivalent circuit, adjusting the voltage of the three-phase in the voltage control model by adjusting the size of a correlation coefficient, changing the voltage of the side phase connected with the single-phase isolation transformer, and realizing optimal control of the voltage levels of the middle phase and two side phases of the medium-voltage distribution network on the premise of ensuring the quality requirement of low-voltage power supply voltage or under the condition that the medium-voltage distribution network generates single-phase grounding faults, thereby effectively suppressing the occurrence probability of single-phase grounding faults of the medium-voltage distribution network or reducing occurrence probability of single-phase ground faults and occurrence probability after occurrence of deterioration events.
The voltage clamping method for a medium voltage distribution network provided in the present application will be explained in detail with reference to fig. 1 and 3, and fig. 3 is a schematic flow chart of the voltage clamping method for a medium voltage distribution network provided in an embodiment of the present application, as shown in fig. 3, and the method includes the following steps:
s310, constructing a first equivalent circuit of three-phase line voltage of the medium-voltage distribution network according to a unidirectional asymmetric operation mode of the medium-voltage distribution network connected with the single-phase isolation transformer, wherein the first equivalent circuit is formed by connecting a B-phase circuit and an edge-phase circuit in series.
In this embodiment, please refer to fig. 1, fig. 2 is a power transmission line structure diagram of a medium voltage power distribution network provided in this embodiment, and the parameters in fig. 1 have the following meanings:
represents the neutral point offset voltage g L Represents damping resistance, L L Represents arc suppression coil g B Represents leakage conductance of phase B, C B Represents the capacitance of B relative to ground g A Represents leakage conductance of phase A, C A Represent the capacitance of A relative to ground, g C Represents C phase leakage conductance, C C Representing the C-phase capacitance to ground. The single-phase asymmetric operation mode based on single-phase transformer isolation is a single-phase isolation transformer isolation scheme based on zero sequence blocking.
The single-phase isolation transformer isolation scheme based on zero sequence blocking adopts a single-phase isolation transformer with the same voltage level, namely 10kV/10kV isolation, but the zero sequence loop is not connected on a 10kV feed line of a power distribution network for the first time. The technical scheme comprises 3 steps:
1. acquiring a wiring group of a transformer substation main transformer corresponding to a 10kV feeder line hung on the same transformer substation, and judging whether a primary winding is Yn and a secondary winding is Y-shaped or whether the primary winding is Yn and the secondary winding is delta-shaped;
2. for each 10kV feeder, acquiring the wiring group of a transformer at the load side area of the feeder, and judging whether the primary winding is Y and the secondary winding is Yn or the primary winding is delta and the secondary winding is Yn;
3. according to the homotypic relation between the main transformer wiring group of the transformer station and the feeder load side wiring group, selecting the wiring group of the single-phase isolation transformer, namely: i) When the primary winding of the transformer station main transformer secondary winding is Y and the primary winding of the load side transformer station area transformer is Y, selecting the primary and secondary winding wiring groups of the single-phase isolation transformer to be Y, Y respectively; ii) when the primary winding of the transformer station main transformer secondary winding is Y and the primary winding of the load side transformer station area transformer is delta, selecting the primary winding and secondary winding wiring groups of the single-phase isolation transformer to be Y and delta respectively; iii) When the primary winding of the transformer station main transformer secondary winding is delta and the primary winding of the load side transformer station area transformer is Y, selecting the primary and secondary winding wiring groups of the single-phase isolation transformer to be delta and Y respectively; and iv) when the primary winding and the secondary winding of the transformer station main transformer are delta and the primary winding of the load side transformer area is delta, selecting the wiring groups of the primary winding and the secondary winding of the single-phase isolation transformer to be delta and delta respectively.
Referring to fig. 2, fig. 2 is a circuit diagram of a first equivalent circuit of a 10kV medium voltage distribution network under natural distribution, where the first equivalent circuit is formed by connecting a B-phase circuit and a B-phase circuit in series, the B-phase circuit is formed by connecting a B-phase leakage conductance and a B-phase capacitance to ground in parallel, the B-phase leakage conductance is equal to the inverse of the B-phase leakage resistance, the a-phase and the C-phase of the B-phase circuit are identical, parameters in fig. 3 have the following meanings, and g B Represents leakage conductance of phase B, C B Represents the capacitance of B relative to ground g A Represents leakage conductance of phase A, C A Represent the capacitance of A relative to ground, g C Represents C phase leakage conductance, C C And C represents the capacitance to ground, so redundant explanation is not made.
S320, obtaining a second equivalent circuit of three-phase line voltage after forming a capacitor branch according to the capacitor branch and the first equivalent circuit, wherein the side-phase circuit is an A-phase circuit and a C-phase circuit, and the A-phase circuit is connected with the C-phase circuit in parallel; .
In this embodiment, referring to fig. 1 and 2, on the basis of the first equivalent circuit shown in fig. 2, a capacitor branch is connected in parallel to the a phase and the C phase, so as to form a circuit diagram of the second equivalent circuit shown in fig. 1, and according to the common general knowledge in the art, the second equivalent circuit based on fig. 1 can reversely deduce that the capacitor branch is connected in parallel to the ground capacitor of the a phase or the C phase on the power transmission line.
And S330, establishing a voltage control model between three-phase line voltage of the medium-voltage distribution network after being connected to the medium-voltage distribution network through the single-phase isolation transformer and line voltage of the medium-voltage distribution network before being connected to the medium-voltage distribution network through the single-phase isolation transformer according to the second equivalent circuit.
In the present embodiment, the purpose of constructing a side-phase lineThe control relationship between the reference voltage and the additional capacitor is that a capacitor branch (A phase or C phase) is connected in parallel to the side phase, as shown in FIG. 1, the additional capacitor C Delta Suppose C Delta =αc, α is a correlation coefficient. Under the action of the additional capacitor, the voltages of the system A, B and the C phases are redistributed, and a voltage control model between the three-phase line voltage of the medium-voltage distribution network after being connected to the medium-voltage distribution network through the single-phase isolation transformer and the line voltage of the medium-voltage distribution network before being connected to the medium-voltage distribution network through the single-phase isolation transformer is established according to the second equivalent circuit. The voltage control model is expressed as follows:
And S340, when the single-phase earth fault of the medium-voltage distribution network is detected, adjusting the size of the correlation coefficient to control the size of the three-phase voltage of the voltage control model, and clamping the three-phase voltage of the medium-voltage distribution network.
In the present embodiment, the flow is C Delta Let =αc, see C Delta Increasing the additional capacitance corresponds to increasing the correlation coefficient α, so that the line voltages obtained by the formulas (8) - (10) in the above embodiment are changed, and the change of the voltage control model is changed, so that the line voltage of the middle phase is pulled up, the voltage of the edge phase is reduced, the voltage levels of the middle phase and the two edge phases are optimally controlled, and the probability of occurrence of a deterioration event after the arcing of the ground fault phase is reduced.
In summary, according to the voltage clamping method for the medium-voltage distribution network provided by the embodiment, according to the unidirectional asymmetric operation mode of the medium-voltage distribution network after being connected to the single-phase isolation transformer, a first equivalent circuit is built in combination with the medium-voltage distribution network power transmission line, the voltage level of the side phases is further controlled to be the target, additional capacitors are introduced to form capacitor branches to adjust the grounding capacitance of different phases of the power transmission line, a second equivalent circuit is obtained by combining the capacitor branches on the basis of the first equivalent circuit, a voltage control model capable of adjusting the side phase voltages is built on the basis of the second equivalent circuit, the size of the three-phase voltages in the voltage control model is adjusted by adjusting the size of the correlation coefficients, the size of the side phase voltages connected to the single-phase isolation transformer is changed, and on the premise of ensuring the quality requirement of the low-voltage power supply voltage or under the condition that the medium-voltage distribution network has single-phase grounding faults, the voltage grades of the medium-voltage distribution network and the two side phases are optimally controlled, so that the occurrence probability of single-phase grounding faults of the medium-voltage distribution network is effectively suppressed or the probability of occurrence of deterioration events after the single-phase grounding faults are reduced.
In one embodiment, a voltage distribution model of the medium-voltage distribution network under the conditions of the capacitance to ground parameter and the resistance to ground parameter is built according to the capacitance to ground parameter and the resistance to ground parameter of the first equivalent circuit.
In this embodiment, as shown in fig. 2, a voltage distribution model of A, C side phase and B phase voltages under natural distribution is constructed. The voltage distribution model satisfies the following formulas (1) - (4), as follows:
U L-L ＝U B -U A (1)；
in U L-L Representing line voltage of the medium-voltage distribution network before being connected into the medium-voltage distribution network through the single-phase isolation transformer;
and U C 1 The voltages of the phase A, the phase B and the phase C are respectively obtained after the single-phase isolation transformer is connected into the medium-voltage distribution network; r is R A 、R B And R is C A, B and C, respectively, relative leakage resistances, where R A ＝R B ＝R C ；C A 、C B And C C Capacitance to ground for phase A, phase B and phase C, respectively, where C A ＝C B ＝C C The method comprises the steps of carrying out a first treatment on the surface of the w is an operator and w=2pi f, f=50 Hz,// represents the parallel calculation of the circuit.
In distribution network overhead lines, the leakage resistance tends to be much smaller than the capacitive reactance to ground, so there is a simplified term following "≡in equations (2) - (4). In fact, consider further C A ＝C B ＝C C =c, C is a constant, and equation (2) -equation (4) can be further simplified to equation (5) -equation (7) as follows
Combining the formulas (5) and (7), and considering the line voltage U of the single-phase isolation transformer after the single-phase isolation transformer is connected into the medium-voltage distribution network L-L =10kv, then
And->
The same is 3.33kV, and the two groups of voltages represent the natural distribution of the system voltage under the action of the capacitance to ground.
In one embodiment, when a single-phase earth fault of the medium-voltage distribution network is detected, the magnitude of the three-phase voltage of the voltage control model is controlled by adjusting the magnitude of the correlation coefficient, and the three-phase voltage of the medium-voltage distribution network is clamped specifically as follows:
when detecting that the medium-voltage distribution network has single-phase earth faults, controlling the voltage control model to adjust the magnitude of the side phase voltage by adjusting the magnitude of the correlation coefficient.
Specifically, the method for detecting a single-phase earth fault is the prior art, and no redundant explanation is made here, and based on table 1 in the above embodiment, it is known that increasing the correlation coefficient can reduce the side phase voltage, so in this embodiment, when a single-phase earth fault is detected, increasing the correlation coefficient control voltage control model reduces the line voltage of the side phase line of the medium-voltage distribution network, so that the possibility of an arcing event at the single-phase earth fault point can be greatly reduced, and thus the possibility of a mountain fire event caused by the earth fault can be prevented, and referring to the formulas (8) - (10), the magnitude of the correlation coefficient α between the additional capacitance and the capacitance parameter of the medium-voltage distribution network system to the earth can be known, and the parameter magnitude of the additional capacitance can also be obtained through conversion. I.e. if control
When the voltage is below 3.33kV under natural distribution, such as 2kV, the alpha=2 can be calculated by combining the formula (9), and the additional capacitance is calculatedThe size is twice the capacitance of the system A relative to the ground; if control is required +.>
At 1kV, then, it can be calculated by combining equation (9) that α=7, i.e., the additional capacitance is 7 times the capacitance of the system a to ground.
Specifically, here, the side phase A is taken as an example, and combined with
A table of the relationship between the magnitude of the additional capacitance parameter and the magnitude of the side phase voltage may be formed as shown in table 1 below. Although the side phase voltage can be clamped and the low-voltage power supply quality is ensured to be unchanged, the middle phase voltage needs to be raised, so that the method can realize that the size of the additional capacitor is adjusted to control the size distribution of the three-phase voltage, and the size of the related coefficient needs to be controlled to determine the proper additional capacitor.
TABLE 1 relationship between additional capacitance parameters and three-phase voltages
In one embodiment, when a single-phase earth fault of the medium-voltage distribution network is not detected, setting a target voltage of the side-phase line, calculating the magnitude of a correlation coefficient according to a voltage control model, and calculating the magnitude of an additional capacitor connected in parallel to the side-phase line according to the magnitude of the correlation coefficient.
In this embodiment, when a single-phase ground fault is not detected, that is, the target voltage of the phase-to-edge line is set in consideration of the condition that the power supply quality of the low-voltage distribution user is unchanged, so as to reduce the occurrence probability of the single-phase ground fault, and the magnitude of the correlation coefficient is calculated by the voltage control model, so that the magnitude of the additional capacitor connected in parallel to the phase-to-edge line is determined.
In one embodiment, the line voltage U of the medium voltage distribution network before the medium voltage distribution network is connected through the single-phase isolation transformer L - L ＝U B -U A In the formula, U A 、U B The voltage is the voltage of the original power distribution network A relative to the ground and the voltage of the original power distribution network B relative to the ground before single-phase isolation transformation access.
In this embodiment, the line voltage U of the medium-voltage distribution network is not connected to the medium-voltage distribution network via the single-phase isolation transformer L-L ＝U B -U A This is prior art and is not explained in any way.
In one embodiment, the determining a connection mode of the single-phase isolation transformer according to a unidirectional asymmetric operation mode of the single-phase isolation transformer of the medium-voltage distribution network specifically includes:
when the secondary winding of the main transformer is Y-shaped wiring and the primary winding of the transformer in the transformer area is Y-shaped wiring, determining that the primary winding of the single-phase isolation transformer is Y-shaped wiring and the secondary winding is Y-shaped wiring;
when the secondary winding of the main transformer is Y-shaped wiring and the primary winding of the transformer in the transformer area is delta-shaped wiring, determining that the primary winding of the single-phase isolation transformer is Y-shaped wiring and the secondary winding is delta-shaped wiring;
when the secondary winding of the main transformer is delta-shaped wiring and the primary winding of the transformer in the transformer area is Y-shaped wiring, determining that the primary winding of the single-phase isolation transformer is delta-shaped wiring and the secondary winding is Y-shaped wiring;
when the secondary winding of the main transformer is delta-shaped wiring and the primary winding of the transformer in the transformer area is delta-shaped wiring, the primary winding of the single-phase isolation transformer is delta-shaped wiring and the secondary winding is delta-shaped wiring.
In this embodiment, the step S110 of the above embodiment has been explained in detail for the wire category, so redundant description is not needed in this embodiment.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. A medium voltage distribution network voltage clamping device, characterized in that is applied to medium voltage distribution network, and the device includes:
the additional capacitor is connected with the side phase line of the medium-voltage distribution network in parallel to form a capacitor branch, wherein the additional capacitor is equal to the correlation coefficient multiplied by the capacitance to ground of the three-phase line;
the fault detection module is connected with the medium-voltage distribution network and is used for detecting whether a single-phase grounding fault occurs in the medium-voltage distribution network or not;
and the voltage clamping module is connected with the additional capacitor module and the fault detection module and is used for adjusting the size of the correlation coefficient to clamp the three-phase voltage of the medium-voltage distribution network by adjusting the size of the additional capacitor on the capacitor branch when the fault detection module detects that the medium-voltage distribution network has single-phase grounding fault.
2. The voltage clamping device for the medium-voltage distribution network is characterized by further comprising a single-phase isolation transformer and a transformer in a transformer area;
the unidirectional isolation transformer is connected with a three-phase line of the medium-voltage distribution network in a star connection or delta connection mode;
the transformer is connected with the three-phase circuit in a star connection or delta connection mode.
3. A medium voltage distribution network voltage clamping method applied to a medium voltage distribution network voltage clamping device as claimed in any one of claims 1-2, wherein the method comprises:
according to a unidirectional asymmetric operation mode of the medium-voltage distribution network connected with the single-phase isolation transformer, a first equivalent circuit of three-phase line voltage of the medium-voltage distribution network is constructed, wherein the first equivalent circuit is formed by connecting a B-phase circuit and a side-phase circuit in series;
obtaining a second equivalent circuit of three-phase line voltage after forming the capacitor branch according to the capacitor branch and the first equivalent circuit, wherein the side phase circuit is an A phase circuit and a C phase circuit, and the A phase circuit is connected with the C phase circuit in parallel;
establishing a voltage control model between three-phase line voltage of the medium-voltage distribution network after being connected to the medium-voltage distribution network through the single-phase isolation transformer and line voltage of the medium-voltage distribution network before being connected to the medium-voltage distribution network through the single-phase isolation transformer according to the second equivalent circuit;
when a single-phase earth fault of the medium-voltage distribution network is detected, the three-phase voltage of the medium-voltage distribution network is clamped by adjusting the size of the correlation coefficient to control the size of the three-phase voltage of the voltage control model.
4. The method for clamping voltage of a medium voltage distribution network according to claim 1, wherein a voltage distribution model of the medium voltage distribution network under the conditions of the capacitance to ground parameter and the resistance to ground parameter is constructed according to the capacitance to ground parameter and the resistance to ground parameter of the first equivalent circuit.
5. The method for voltage clamping a medium voltage distribution network according to claim 4, wherein the expression of the voltage distribution model is:
6. The method for clamping a voltage of a medium voltage distribution network according to claim 1, wherein the expression of the voltage control model is:
7. The method for clamping voltage of a medium voltage distribution network according to claim 6, wherein when a single-phase earth fault of the medium voltage distribution network is detected, the magnitude of the three-phase voltage of the voltage control model is controlled by adjusting the magnitude of a correlation coefficient, and the method is specifically as follows:
when detecting that the medium-voltage distribution network has single-phase earth faults, controlling the voltage control model to adjust the magnitude of the side phase voltage by adjusting the magnitude of the correlation coefficient.
8. The method for clamping voltage on a medium voltage distribution network according to claim 7, wherein when no single-phase earth fault is detected in the medium voltage distribution network, a target voltage of the side-phase line is set, a correlation coefficient is calculated according to a voltage control model, and an additional capacitor connected in parallel to the side-phase line is calculated according to the correlation coefficient.
9. A method for clamping a voltage of a medium voltage distribution network according to claim 5 or 6, wherein the line voltage U of the medium voltage distribution network before the single-phase isolation transformer is connected to the medium voltage distribution network L-L ＝U B -U A In the formula, U A 、U B The voltage is the voltage of the original power distribution network A relative to the ground and the voltage of the original power distribution network B relative to the ground before single-phase isolation transformation access.
10. A method for clamping a voltage of a medium-voltage distribution network according to claim 3, wherein the determining a wiring mode of the single-phase isolation transformer according to a unidirectional asymmetric operation mode of the single-phase isolation transformer of the medium-voltage distribution network specifically comprises:
when the secondary winding of the main transformer is star-shaped, and the primary winding of the transformer in the transformer area is star-shaped, determining that the primary winding of the single-phase isolation transformer is star-shaped and the secondary winding is star-shaped;
when the secondary winding of the main transformer is star-shaped wiring and the primary winding of the transformer in the transformer area is delta-shaped wiring, determining that the primary winding of the single-phase isolation transformer is star-shaped wiring and the secondary winding is delta-shaped wiring;
when the secondary winding of the main transformer is in a triangular wiring mode and the primary winding of the transformer in the transformer area is in a star wiring mode, determining that the primary winding of the single-phase isolation transformer is in the triangular wiring mode and the secondary winding is in the star wiring mode;
when the secondary winding of the main transformer is in a triangular wiring mode and the primary winding of the transformer in the transformer area is in a triangular wiring mode, the primary winding of the single-phase isolation transformer is determined to be in the triangular wiring mode and the secondary winding is determined to be in the triangular wiring mode.
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