DETERMINING METHOD AND APPARATUS FOR WORKING VOLTAGE OF ISOLATED NEUTRAL SYSTEM

Abstract

A determining method and apparatus for a neutral system working voltage includes a power system having three phase wires and three capacitor banks. Each bank has one terminal connected to one phase wire, and the other terminals form a neutral point. A phase voltage of each phase wire is periodically sampled, obtaining sampling value groups of real-time phase voltages. Each phase voltage group includes a sampling value of a phase voltage of each phase wire by measuring each phase wire. Unbalance rates between the banks are based on the groups of sampling values. The unbalance rate is a ratio between capacitances of every two phase wires. The isolated neutral system working voltage is based on the unbalance rates. The unbalance rates between banks are based on the sampling values measured in real time. The working voltage is based on the unbalance rates, permitting subsequent operations to be accurately performed.

Claims

1-12. (canceled)

13. A determining method for a working voltage of an isolated neutral system, the determining method comprising: providing a power system including three phase wires and three capacitor banks, one terminal of each capacitor bank being connected to one phase wire, respective other terminals of the capacitor banks being connected to one another to form a neutral point, and each capacitor bank including a plurality of capacitors; periodically sampling a phase voltage of each phase wire, to obtain a plurality of groups of sampling values of real-time phase voltages, each group of sampling values of real-time phase voltages including sampling value of a phase voltage of each phase wire obtained by simultaneously measuring each phase wire; determining unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages, the unbalance rates being a ratio between capacitance values of every two phase wires; and determining the working voltage of the isolated neutral system based on the unbalance rates.

14. The determining method according to claim 13, which further comprises carrying out the step of determining the unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages by: determining unbalance rates K.sub.AB and K.sub.AC between the capacitor banks based on a formula as follows: $R={\left(X^{}X\right)}^{-1}{X}^{}Y$ $\mathrm{wherein}X=\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ .Math.& .Math.\\ x_{1n}& x_{2n}\end{array}\right],Y=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ .Math.\\ y_n\end{array}\right],R=\left[\begin{array}{c}{K}_{\mathrm{AB}}\\ K_{\mathrm{AC}}\end{array}\right],$ x.sub.1n denotes a value of x.sub.1 obtained in an n.sup.th measurement, x.sub.2n denotes a value of x.sub.2 obtained in the n.sup.th measurement, y.sub.n denotes a value of y obtained in the n.sup.th measurement, x.sub.1=(V.sub.X?V.sub.B), x.sub.2=(V.sub.X?V.sub.C), y=V.sub.A?V.sub.X, V.sub.X denotes a sampling value of a zero sequence voltage of the neutral point, V.sub.A denotes a sampling value of a phase voltage of a phase-A wire, V.sub.B denotes a sampling value of a phase voltage of a phase-B wire, V.sub.C denotes a sampling value of a phase voltage of a phase-C wire, $K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{\mathrm{AC}}=\frac{C_C}{C_A},$ C.sub.A denotes a capacitance value of the phase-A wire, C.sub.B denotes a capacitance value of the phase-B wire, and C.sub.C denotes a capacitance value of the phase-C wire.

15. The determining method according to claim 14, which further comprises providing the working voltage as: $\frac{1}{3}.Math.V_X\left(1+K_{\mathrm{AB}}+K_{\mathrm{AC}}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{\mathrm{AC}}\right).Math.,\mathrm{and}$ $V_0=\left(V_A+V_B+V_C\right)/3.$

16. The determining method according to claim 13, which further comprises providing a number of the groups of sampling values of real-time phase voltages ranging from 2 to 10.

17. The determining method according to claim 13, which further comprises after the step of determining the working voltage of the isolated neutral system based on the unbalance rates: upon identifying that a fault occurs in the isolated neutral system, determining, based on the working voltage, whether the fault is an internal fault, an internal fault indicating that a fault occurs in a capacitor in the capacitor bank; and carrying out the step of determining, based on the working voltage, whether the fault is an internal fault by including a determination that the fault is an internal fault if a value of the working voltage is greater than or equal to a preset threshold.

18. A determining apparatus for a working voltage of an isolated neutral system, the determining apparatus comprising: a power system including three phase wires and three capacitor banks having terminals, one respective terminal of each capacitor bank being connected to one respective phase wire and another terminal of said capacitor banks being connected together to form a neutral point, each capacitor bank including a plurality of capacitors; a sampling unit configured to periodically sample a phase voltage of each phase wire, to obtain a plurality of groups of sampling values of real-time phase voltages, each group of sampling values of real-time phase voltages including a sampling value of a phase voltage of each phase wire obtained by simultaneously measuring each phase wire; a first determining unit configured to determine unbalance rates between said capacitor banks based on the plurality of groups of sampling values of real-time phase voltages, the unbalance rate being a ratio between capacitance values of every two phase wires; and a second determining unit configured to determine the working voltage of the isolated neutral system based on the unbalance rates.

19. The determining apparatus according to claim 18, wherein said first determining unit is specifically configured to: determine unbalance rates K.sub.AB and K.sub.AC between said capacitor banks based on a formula as follows: $R={\left(X^{}X\right)}^{-1}{X}^{}Y$ $\mathrm{wherein}X=\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ .Math.& .Math.\\ x_{1n}& x_{2n}\end{array}\right],Y=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ .Math.\\ y_n\end{array}\right],R=\left[\begin{array}{c}{K}_{\mathrm{AB}}\\ K_{\mathrm{AC}}\end{array}\right],$ x.sub.1n denotes a value of x.sub.1 obtained in an n.sup.th measurement, x.sub.2n denotes a value of x.sub.2 obtained in the n.sup.th measurement, y.sub.n denotes a value of y obtained in the n.sup.th measurement, x.sub.1=(V.sub.X?V.sub.B), x.sub.2=(V.sub.X?V.sub.C), y=V.sub.A?V.sub.X, V.sub.X denotes a sampling value of a zero sequence voltage of said neutral point, V.sub.A denotes a sampling value of a phase voltage of a phase-A wire, V.sub.B denotes a sampling value of a phase voltage of a phase-B wire, V.sub.C denotes a sampling value of a phase voltage of a phase-C wire, $K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{\mathrm{AC}}=\frac{C_C}{C_A},$ C.sub.A denotes a capacitance value of said phase-A wire, C.sub.B denotes a capacitance value of said phase-B wire, and C.sub.C denotes a capacitance value of said phase-C wire.

20. The determining apparatus according to claim 19, wherein the working voltage is $\frac{1}{3}.Math.V_X\left(1+K_{\mathrm{AB}}+K_{\mathrm{AC}}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{\mathrm{AC}}\right).Math.,\mathrm{and}$ $V_0=\left(V_A+V_B+V_C\right)/3.$

21. The determining apparatus according to claim 18, wherein a number of the groups of sampling values of real-time phase voltages ranges from 2 to 10.

22. The determining apparatus according to claim 18, which further comprises: a third determining unit configured to determine, based on the working voltage, upon an identification that a fault occurs in the isolated neutral system, whether the fault is an internal fault, an internal fault indicating that a fault occurs in a capacitor in the capacitor bank; and the determination of whether the fault is an internal fault, based on the working voltage, includes determining that the fault is an internal fault if a value of the working voltage is greater than or equal to a preset threshold.

23. A determining apparatus for a working voltage of an isolated neutral system, the determining apparatus comprising: a power system including three phase wires and three capacitor banks having terminals, one respective terminal of each capacitor bank being connected to one respective phase wire and another terminal of said capacitor banks being connected together to form a neutral point, each capacitor bank including a plurality of capacitors; at least one memory configured to store instructions; and at least one processor configured to perform, according to the instructions stored in the memory, the determining method for a working voltage of the isolated neutral system according to claim 13.

24. A non-transitory readable storage medium storing machine-readable instructions that, when executed by a machine, cause the machine to perform the determining method for the working voltage of an isolated neutral system according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other features and advantages of the present invention will be more apparent to those of ordinary skill in the art from the detailed description of preferred embodiments of the present invention with reference to the accompanying drawings, in which:

[0033] FIG. 1 is a schematic structural diagram of an isolated neutral system according to an embodiment of the present invention;

[0034] FIG. 2 is a schematic flowchart of a determining method for a working voltage of an isolated neutral system according to another embodiment of the present invention;

[0035] FIG. 3 is a schematic flowchart of a determining method for a working voltage of an isolated neutral system according to still another embodiment of the present invention;

[0036] FIG. 4A is a schematic structural diagram of a determining apparatus for a working voltage of an isolated neutral system according to an embodiment of the present invention; and

[0037] FIG. 4B is a schematic structural diagram of a determining apparatus for a working voltage of an isolated neutral system according to another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0038] In order to make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be described in further detail by way of embodiments hereinafter. Faults occurring in an isolated neutral system may be classified as an internal fault and an external fault. The internal fault indicates that a fault such as an earth fault or a capacitor breakdown occurs in a capacitor bank of the isolated neutral system. The external fault indicates that a fault does not occur in a capacitor, but occurs in a device beyond the protection of a relay protection apparatus corresponding to the capacitor bank. When the external fault occurs, the relay protection apparatus corresponding to the capacitor bank should not perform an action. Whether the relay protection apparatus should perform an action may be determined by determining whether a working voltage exceeds a preset threshold. If the working voltage is greater than or equal to the preset threshold, protection should be activated. If the working voltage is less than the preset threshold, no action should be performed. Therefore, accuracy of the working voltage plays a key role. The inventor found that the working voltage is related to a ratio between capacitor banks, and based on this, the inventor provides a method for determining a ratio between capacitor banks, to obtain an accurate working voltage.

Embodiment 1

[0039] This embodiment provides a determining method for a working voltage of an isolated neutral system, and the method is performed by a determining apparatus for a working voltage of an isolated neutral system. The apparatus may be integrated into a relay protection apparatus, or may be independently disposed.

[0040] FIG. 2 is a schematic flowchart of the determining method for a working voltage of an isolated neutral system according to this embodiment. The determining method for a working voltage of an isolated neutral system includes the following steps.

[0041] In step 201, a phase voltage of each phase wire is periodically sampled, to obtain a plurality of groups of sampling values of real-time phase voltages, where each group of sampling values of real-time phase voltages includes a sampling value of a phase voltage of each phase wire that is obtained by simultaneously measuring each phase wire.

[0042] A phase voltage of each phase wire is continuously sampled periodically, and a period may be set according to actual requirements, for example, may be set to one millisecond. In addition, each phase wire is simultaneously sampled. Specifically, a sampling value of a phase voltage may be obtained by using a voltage sensor.

[0043] The number of groups of sampling values of real-time phase voltages may range from 2 to 10. In this way, enough data can be provided to accurately determine the working voltage subsequently and the working voltage can be determined as quickly as possible.

[0044] In step 202, unbalance rates between the capacitor banks are determined based on the plurality of groups of sampling values of real-time phase voltages, where the unbalance rate is a ratio between capacitance values of every two phase wires.

[0045] Due to process errors or other factors, a capacitance value of each capacitor bank may not be equal, and it is very difficult to measure a capacitance value of each capacitor in each capacitor bank. The inventor uses a manner of determining a ratio between capacitance values of the capacitor banks based on a sampling value of a real-time phase voltage to determine the working voltage with higher accuracy.

[0046] For example, unbalance rates K.sub.AB and K.sub.AC between the capacitor banks are determined based on the following formula:

[00007]$R={\left(X^{}X\right)}^{-1}{X}^{}Y$$\mathrm{where}X=\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ .Math.& .Math.\\ x_{1n}& x_{2n}\end{array}\right],Y=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ .Math.\\ y_n\end{array}\right],R=\left[\begin{array}{c}{K}_{\mathrm{AB}}\\ K_{AC}\end{array}\right],$ [0047] x.sub.1n denotes a value of x.sub.1 obtained in the n.sup.th measurement, x.sub.2n denotes a value of x.sub.2 obtained in the n.sup.th measurement, y.sub.n denotes a value of y obtained in the n.sup.th measurement, x.sub.1=(V.sub.X?V.sub.B), x.sub.2=(V.sub.X?V.sub.C), y=V.sub.A?V.sub.X, V.sub.X denotes a sampling value of a zero sequence voltage of the neutral point, V.sub.A denotes a sampling value of a phase voltage of a phase-A wire, V.sub.B denotes a sampling value of a phase voltage of a phase-B wire, V.sub.C denotes a sampling value of a phase voltage of a phase-C wire,

[00008]$K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{AC}=\frac{C_C}{C_A},$

C.sub.A denotes a capacitance value of the phase-A wire, C.sub.B denotes a capacitance value of the phase-B wire, and C.sub.C denotes a capacitance value of the phase-C wire.

[0048] In step 203, the working voltage of the isolated neutral system is determined based on the unbalance rate.

[0049] The working voltage may be defined according to requirements, for example, may be configured based on a corresponding relay protection apparatus. In the present invention, the working voltage is, for example,

[00009]$.Math.V_X\left(1+K_{\mathrm{AB}}+K_{AC}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{\mathrm{AC}}\right).Math.,\mathrm{where}$$V_0=\left(V_A+V_B+V_C\right)/3,K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{AC}=\frac{C_C}{C_A},$

C.sub.A denotes a capacitance value of the phase-A wire, C.sub.B denotes a capacitance value of the phase-B wire, and C.sub.C denotes a capacitance value of the phase-C wire.

[0050] Optionally, after step 203, the determining method further includes: returning to perform step 201, and periodically repeating the foregoing steps, to continuously determine a sampling value of a phase voltage. In this embodiment, working personnel may trigger step 201 according to actual requirements, or steps 201 to 203 may be periodically performed by the apparatus to automatically determine the working voltage.

[0051] Optionally, after step 203, the determining method further includes: if it is identified that a fault occurs in the isolated neutral system, determining, based on the working voltage, whether the fault is an internal fault, where the internal fault indicates that a fault occurs in a capacitor in the capacitor bank. If it is determined that the fault is an internal fault, a relay protection apparatus corresponding to the capacitor bank should perform an action to clear the fault. If it is determined that the fault is a non-internal fault, that is, it is determined that the fault is an external fault, the relay protection apparatus corresponding to the capacitor bank should not perform an action. As an exemplary description, if a value of the working voltage is less than a preset threshold, it is determined that the fault is an external fault. If the value of the working voltage is greater than or equal to the preset threshold, it is determined that the fault is an internal fault. The preset threshold herein may be determined according to actual requirements, and details are not repeated herein.

[0052] In this embodiment, the unbalance rates between the capacitor banks are obtained based on the sampling values of the phase voltages measured in real time, and the working voltage is accurately determined based on the unbalance rates, so that subsequent operations can be accurately performed.

Embodiment 2

[0053] This embodiment further supplements the descriptions of the determining method for a working voltage of an isolated neutral system in Embodiment 1. FIG. 3 is a schematic flowchart of the determining method for a working voltage of an isolated neutral system according to this embodiment. The determining method for a working voltage of an isolated neutral system includes the following steps.

[0054] In step 301, when it is determined that a fault occurs in a capacitor bank, a phase voltage of each phase wire is periodically sampled, to obtain a plurality of groups of sampling values of real-time phase voltages, where each group of sampling values of real-time phase voltages includes a sampling value of a phase voltage of each phase wire that is obtained by simultaneously measuring each phase wire.

[0055] Specific operations of step 301 are consistent with those of step 201, and details are not repeated herein. Herein, the number of groups of sampling values of real-time phase voltages may range from 2 to 10, and the number of 5 groups may be specifically selected.

[0056] In step 302, unbalance rates K.sub.AB and K.sub.AC between the capacitor banks are determined based on the following formula:

[00010]$R={\left(X^{}X\right)}^{-1}{X}^{}Y$$\mathrm{where}X=\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ .Math.& .Math.\\ x_{1n}& x_{2n}\end{array}\right],Y=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ .Math.\\ y_n\end{array}\right],R=\left[\begin{array}{c}{K}_{\mathrm{AB}}\\ K_{AC}\end{array}\right],$

x.sub.1n denotes a value of x.sub.1 obtained in the n.sup.th measurement, x.sub.2n denotes a value of x.sub.2 obtained in the n.sup.th measurement, y.sub.n denotes a value of y obtained in the n.sup.th measurement, x.sub.1=(V.sub.X?V.sub.B), x.sub.2=(V.sub.X?V.sub.C), y=V.sub.A?V.sub.X, V.sub.X denotes a sampling value of a zero sequence voltage of the neutral point of the isolated neutral system, V.sub.A denotes a sampling value of a phase voltage of a phase-A wire, V.sub.B denotes a sampling value of a phase voltage of a phase-B wire, V.sub.C denotes a sampling value of a phase voltage of a phase-C wire,

[00011]$K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{AC}=\frac{C_C}{C_A},$

C.sub.A denotes a capacitance value of the phase-A wire, C.sub.B denotes a capacitance value of the phase-B wire, and C.sub.C denotes a capacitance value of the phase-C wire.

[0057] This is because, for the isolated neutral system whose capacitor bank is not faulty, that is, for the isolated neutral system where sampling values of phase voltages of the three phase wires are equal, a sum of currents of the three phase wires is 0, that is:

[00012]$\begin{array}{cc}{I}_A+I_B+I_C=j?C_A\left(V_A-V_X\right)+j?C_B\left(V_B-V_X\right)+j?C_C\left(V_C-V_X\right)=0& \left(1.1\right)\end{array}$

where I.sub.A denotes a current of the phase-A wire, I.sub.B denotes a current of the phase-B wire, I.sub.C denotes a current of the phase-C wire, V.sub.A denotes a sampling value of a phase voltage of the phase-A wire, V.sub.B denotes a sampling value of a phase voltage of the phase-B wire, V.sub.C denotes a sampling value of a phase voltage of the phase-C wire, V.sub.X denotes a sampling value of a zero sequence voltage of the neutral point of the isolated neutral system, C.sub.A denotes a capacitance value of the phase-A wire, C.sub.B denotes a capacitance value of the phase-B wire, C.sub.C denotes a capacitance value of the phase-C wire, j denotes the imaginary number symbol, and ? denotes an angular frequency of the isolated neutral system.

[0058] The inventor found, through creative efforts, that after the foregoing formula is divided by j?C.sub.A, the foregoing formula (1.1) is rewritten into the following formula (1.2):

[00013]$\begin{array}{cc}{V}_X\left(1+\frac{C_B+C_C}{C_A}\right)-3V_0+V_B\left(1-\frac{C_B}{C_A}\right)+V_C\left(1-\frac{C_C}{C_A}\right)=0& \left(1.2\right)\end{array}$

Assuming that

[00014]$K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{AC}=\frac{C_C}{C_A},\mathrm{and}3V_0=\left(V_A+V_B+V_C\right),$

foregoing formula (1.2) is rewritten into the following formula (1.3):

[00015]$\begin{array}{cc}{V}_X\left(1+K_{\mathrm{AB}}+K_{AC}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{AC}\right)=0& \left(1.3\right)\end{array}$

It is assumed that

[00016]$\mathrm{Vop}=\frac{1}{3}.Math.\mathrm{Vx}\left(1+K_{\mathrm{AB}}+K_{AC}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{AC}\right).Math.,$

where Vop denotes the working voltage.

[0059] To calculate K.sub.AB and K.sub.AC, Vop=0, that is, |Vx(1+K.sub.AB+K.sub.AC)?3V.sub.0+V.sub.B(1?K.sub.AB)+V.sub.C(1?K.sub.AC)|=0. In this way, the foregoing formula (1.3) is rewritten into the following formula (1.4):

[00017]$\begin{array}{cc}{K}_{AB}\left(V_X-V_B\right)+K_{AC}\left(V_X-V_C\right)=3V_0-\left(V_X+V_B+V_C\right)& \left(1.4\right)\end{array}$

[0060] Assuming that x.sub.1=(V.sub.X?V.sub.B), x.sub.2=(V.sub.X?V.sub.C), y=3V.sub.0?(V.sub.X+V.sub.B+V.sub.C)=V.sub.A?V.sub.X, a=K.sub.AB, and b=K.sub.AC, the foregoing formula (1.4) is rewritten into ax.sub.1+bx.sub.2=y. According to this formula, assuming that a value of x.sub.1 obtained in the first measurement is x.sub.11 and x.sub.21, a value of x.sub.1 obtained in the second measurement is x.sub.12 and x.sub.22, and by analogy, after a total of five measurements, the following formulas are obtained:

[00018]${\mathrm{ax}}_{11}={\mathrm{bx}}_{21}=y_1$${\mathrm{ax}}_{12}+{\mathrm{bx}}_{22}=y_2$${\mathrm{ax}}_{13}+{\mathrm{bx}}_{23}=y_3$${\mathrm{ax}}_{14}+{\mathrm{bx}}_{24}=y_4$${\mathrm{ax}}_{15}+{\mathrm{bx}}_{25}=y_5$

[0061] The foregoing formulas are rewritten into the following matrix formula (1.5):

[00019]$\begin{array}{cc}\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ x_{14}& x_{24}\\ x_{15}& x_{25}\end{array}\right].Math.\left[\begin{array}{c}a\\ b\end{array}\right]=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ y_4\\ y_5\end{array}\right]& \left(1.5\right)\end{array}$$\mathrm{where}X=\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ .Math.& .Math.\\ x_{1n}& x_{2n}\end{array}\right],Y=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ .Math.\\ y_n\end{array}\right],\mathrm{and}R=\left[\begin{array}{c}{K}_{\mathrm{AB}}\\ K_{\mathrm{AC}}\end{array}\right].$

[0062] In other words, the matrix formula (1.5) is XR=Y.

[0063] According to the least square method, the following formula (1.6) is obtained according to the matrix formula (1.5):

[00020]$\begin{array}{cc}R={\left(X^{}X\right)}^{-1}{X}^{}Y& \left(1.6\right)\end{array}$

where X denotes a transposed matrix of the matrix X, (XX).sup.?1 denotes an inverse of XX, and a calculation method thereof belongs to the prior art, and will not be repeated herein. Since a corresponding error may occur in each measurement, a value of R may be finally obtained according to the foregoing matrix formula, and K.sub.AB and K.sub.AC are further obtained. After the unbalance rates K.sub.AB and K.sub.AC are put into the foregoing matrix formula (1.5), an accurate value of can be obtained.

[0064] The following description is provided by using three measurements as an example.

[00021]${\mathrm{ax}}_{11}+{\mathrm{bx}}_{21}=y_1$${\mathrm{ax}}_{12}+{\mathrm{bx}}_{22}=y_2$${\mathrm{ax}}_{13}+{\mathrm{bx}}_{23}=y_3$

[0065] The foregoing formulas are rewritten into the following formula: XR=Y.

[0066] Since values in the matrices X and Y may be obtained through measurement, a value of R may be determined according to the following formula, that is, R=(XX).sup.?1 X Y.

[00022]$X^{}X=\left[\begin{array}{ccc}{x}_{11}& x_{12}& x_{13}\\ x_{21}& x_{22}& x_{23}\end{array}\right]\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\end{array}\right]=\left[\begin{array}{cc}{x}_{11}^2+x_{12}^2+x_{13}^2& x_{11}{x}_{21}+x_{12}{x}_{22}+x_{13}{x}_{23}\\ x_{11}{x}_{21}+x_{12}{x}_{22}+x_{13}{x}_{23}& x_{21}^2+x_{22}^2+x_{23}^2\end{array}\right]$

[0067] Assuming that

[00023]${\left(X^{}X\right)}^{-1}={\left(\left[\begin{array}{cc}P& Q\\ Q& L\end{array}\right]\right)}^{-1}=\frac{1}{\mathrm{PL}-Q^2}\left[\begin{array}{cc}L& -Q\\ -Q& P\end{array}\right]$$X^{}Y=\left[\begin{array}{ccc}{x}_{11}& x_{12}& x_{13}\\ x_{21}& x_{22}& x_{23}\end{array}\right]\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\end{array}\right]=\left[\begin{array}{c}{x}_{11}{y}_1+x_{12}{y}_2+x_{13}{y}_3\\ x_{21}{y}_1+x_{22}{y}_2+x_{23}{y}_3\end{array}\right]=\left[\begin{array}{c}M\\ N\end{array}\right]$$R=\frac{1}{\mathrm{PL}-Q^2}\left[\begin{array}{cc}L& -Q\\ -Q& P\end{array}\right]\left[\begin{array}{c}M\\ N\end{array}\right]=\frac{1}{\mathrm{PL}-Q^2}\left[\begin{array}{c}\mathrm{LM}-\mathrm{QN}\\ \mathrm{PN}-\mathrm{QM}\end{array}\right]$$\mathrm{where}P=x_{11}^2+x_{12}^2+x_{13}^2$$L=x_{21}^2+x_{22}^2+x_{23}^2$$Q=x_{11}{x}_{21}+x_{12}{x}_{22}+x_{13}{x}_{23}$$M=x_{11}{y}_1+x_{12}{y}_2+x_{13}{y}_3$$N=x_{21}{y}_1+x_{22}{y}_2+x_{23}{y}_3$$K_{\mathrm{AB}}=\frac{\mathrm{LM}-\mathrm{QN}}{\mathrm{PL}-Q^2}$$K_{\mathrm{AC}}=\frac{\mathrm{PN}-\mathrm{QM}}{\mathrm{PL}-Q^2}$

[0068] Since the foregoing variables can be directly obtained through measurement, corresponding values of unbalance rates K.sub.AB and K.sub.AC can be calculated. In step 303, the working voltage of the isolated neutral system is determined based on the unbalance rates.

[0069] Values in both steps 301 and 302 are determined when no fault occurs in the isolated neutral system, and the working voltage of the isolated neutral system may be subsequently determined in real time based on the unbalance rates that are obtained when no fault occurs, for example, the working voltage may be determined based on the following formula:

[00024]$\frac{1}{3}.Math.V_X\left(1+K_{\mathrm{AB}}+K_{\mathrm{AC}}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{\mathrm{AC}}\right).Math..$

[0070] In step 304, whether the working voltage is greater than or equal to a preset threshold is determined, and if it is determined that the working voltage is greater than or equal to the preset threshold, it is determined that an internal fault occurs in the isolated neutral system.

[0071] If the working voltage is still 0 or less than the preset threshold, this indicates that no internal fault occurs. If the working voltage is greater than or equal to the preset threshold, this indicates that the internal fault occurs, and a corresponding relay protection apparatus is required to perform an action to eliminate the fault. The preset threshold is, for example, 0.5 V. If the working voltage is less than the preset threshold, this indicates that an external fault occurs.

[0072] In this way, whether the internal fault or the external fault occurs may be determined based on the accurate working voltage, to avoid a false action of the relay protection apparatus. When a fault, for example, a breakdown, occurs in a capacitor in a capacitor bank, a capacitance value of a corresponding phase wire is not equal to capacitance values of the other two phase wires, causing a voltage of the corresponding phase wire to be unequal to voltages of the other two phase wires.

[0073] According to this embodiment, an actual working voltage can be determined by determining the unbalance rates between the capacitor banks. In this way, the working voltage may be continuously monitored to determine whether a fault occurs in a capacitor in a capacitor bank, and further determine whether a corresponding relay protection apparatus is required to perform an action.

Embodiment 3

[0074] This embodiment provides a determining apparatus for a working voltage of an isolated neutral system. A power system includes three phase wires and three capacitor banks. One terminal of each capacitor bank is connected to one phase wire, and the respective other terminals of the capacitor banks are connected to one another to form a neutral point. Each capacitor bank includes a plurality of capacitors, that is, each capacitor bank is composed of a plurality of capacitors connected in series and in parallel.

[0075] FIG. 4A is a schematic structural diagram of a determining apparatus for a working voltage of an isolated neutral system according to this embodiment. The determining apparatus for a working voltage of an isolated neutral system includes a sampling unit 401, a first determining unit 402, and a second determining unit 403.

[0076] The sampling unit 401 is configured to periodically sample a phase voltage of each phase wire, to obtain a plurality of groups of sampling values of real-time phase voltages, where each group of sampling values of real-time phase voltages includes a sampling value of a phase voltage of each phase wire that is obtained by simultaneously measuring each phase wire. The first determining unit 402 is configured to determine unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages, where the unbalance rate is a ratio between capacitance values of every two phase wires. The second determining unit 403 is configured to determine a working voltage of the isolated neutral system based on the unbalance rates.

[0077] Optionally, the first determining unit 402 is specifically configured to: determine unbalance rates K.sub.AB and K.sub.AC between the capacitor banks based on the following formula:

[00025]$R={\left(X^{}X\right)}^{-1}{X}^{}Y$$\mathrm{where}X=\left[\begin{array}{cc}{x}_{11}& x_{21}\\ x_{12}& x_{22}\\ x_{13}& x_{23}\\ .Math.& .Math.\\ x_{1n}& x_{2n}\end{array}\right],Y=\left[\begin{array}{c}{y}_1\\ y_2\\ y_3\\ .Math.\\ y_n\end{array}\right],R=\left[\begin{array}{c}{K}_{\mathrm{AB}}\\ K_{\mathrm{AC}}\end{array}\right],$

x.sub.1n denotes a value of x.sub.1 obtained in the n.sup.th measurement, x.sub.2n denotes a value of 2 obtained in the n.sup.th measurement, y.sub.n denotes a value of y obtained in the n.sup.th measurement, x.sub.1=(V.sub.X?V.sub.B), x.sub.2=(V.sub.X?V.sub.C), y=V.sub.A?V.sub.X, V.sub.X denotes a sampling value of a zero sequence voltage of the neutral point, V.sub.A denotes a sampling value of a phase voltage of a phase-A wire, V.sub.B denotes a sampling value of a phase voltage of a phase-B wire, V.sub.C denotes a sampling value of a phase voltage of a phase-C wire,

[00026]$K_{\mathrm{AB}}=\frac{C_B}{C_A},K_{\mathrm{AC}}=\frac{C_C}{C_A},$

C.sub.A denotes a capacitance value of the phase-A wire, C.sub.B denotes a capacitance value of the phase-B wire, and C.sub.C denotes a capacitance value of the phase-C wire.

[0078] Optionally, the working voltage is

[00027]$\frac{1}{3}.Math.V_X\left(1+K_{\mathrm{AB}}+K_{\mathrm{AC}}\right)-3V_0+V_B\left(1-K_{\mathrm{AB}}\right)+V_C\left(1-K_{\mathrm{AC}}\right).Math.,\mathrm{and}$$V_0=\left(V_A+V_B+V_C\right)/3.$

[0079] Optionally, the number of groups of sampling values of real-time phase voltages ranges from 2 to 10.

[0080] Optionally, as shown in FIG. 4B, the determining apparatus further includes a third determining unit 404, which is configured to: if it is identified that a fault occurs in the isolated neutral system, determine, based on the working voltage, whether the fault is an internal fault, where the internal fault indicates that a fault occurs in a capacitor in the capacitor bank.

[0081] The step of determining, based on the working voltage, whether the fault is an internal fault includes: [0082] if a value of the working voltage is greater than or equal to a preset threshold, determining that the fault is an internal fault.

[0083] A working method of each unit in this embodiment is the same as that in the foregoing embodiment, and will not be repeated herein.

[0084] According to the determining apparatus for a working voltage of an isolated neutral system, the unbalance rates between the capacitor banks are obtained based on the sampling values of the phase voltages measured in real time, and the working voltage is accurately determined based on the unbalance rates, so that subsequent operations can be accurately performed.

[0085] The present invention further provides a determining apparatus for a working voltage of an isolated neutral system. A power system includes three phase wires and three capacitor banks. One terminal of each capacitor bank is connected to one phase wire, and the respective other terminals of the capacitor banks are connected to one another to form a neutral point. Each capacitor bank includes a plurality of capacitors connected in series and/or in parallel. The determining apparatus includes at least one memory and at least one processor. The memory is configured to store instructions. The processor is configured to perform, according to the instructions stored in the memory, the determining method for a working voltage of an isolated neutral system according to any one of the foregoing embodiments. An embodiment of the present invention further provides a readable storage medium. The readable storage medium stores machine-readable instructions that, when executed by a machine, cause the machine to perform the determining method for a working voltage of an isolated neutral system according to any of the foregoing embodiments.

[0086] The readable storage medium stores the machine-readable instructions that, when executed by a processor, cause the processor to execute any of the foregoing methods. Specifically, a system or an apparatus with a readable storage medium may be provided, software program code for implementing the functions of any one of the foregoing embodiments is stored in the readable storage medium, and a computer or a processor of the system or apparatus is caused to read and execute the machine-readable instructions stored in the readable storage medium.

[0087] In this condition, the program code itself read from the readable storage medium may implement the functions of any one of the foregoing embodiments, and therefore machine-readable code and the readable storage medium storing the machine-readable code constitute a part of the present invention.

[0088] The embodiments of the readable storage medium include a floppy disk, a hard disk, a magnetic optical disc, an optical disc (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW and DVD+RW), a magnetic tape, a non-volatile memory card and a ROM. Optionally, the program code may be downloaded from a server computer or a cloud via a communication network.

[0089] It should be understood by those skilled in the art that various variations and modifications may be made to the embodiments disclosed above without departing from the essence of the present invention. Therefore, the protection scope of the present invention shall be limited by the appended claims.

[0090] It should be noted that not all the steps and units in the flows and structural diagrams of the system described above are necessary, and some steps or units may be omitted according to practical requirements. The execution order of the various steps is not fixed and may be adjusted according to requirements. A structure of the apparatus described in the foregoing embodiments may be a physical structure, or may be a logical structure. In other words, some units may be implemented by the same physical entity, or some units may be implemented separately by a plurality of physical entities, or may be implemented together by some components in a plurality of independent devices.

[0091] In the foregoing embodiments, a hardware unit may be implemented mechanically or electrically. For example, a hardware unit or a processor may include a permanent dedicated circuit or logic (such as a dedicated processor, FPGA or ASIC) to accomplish a corresponding operation. The hardware unit or processor may also include a programmable logic or circuit (such as a general-purpose processor or another programmable processor), and may be set temporarily by software to accomplish a corresponding operation. The specific implementation (mechanical manner, or a dedicated permanent circuit, or a temporarily set circuit) may be determined in consideration of cost and time.

[0092] The above description is merely illustrative of the preferred embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, and the like made within the spirit and principles of the present invention shall fall within the protection scope of the present invention.