CN1180271C - Apparatus and method for positioning parallel double electricity transmission line - Google Patents

Abstract

A method and an apparatus for a trouble-location on a transmission line of a concurrent double line are provided. The method includes the steps of: converting a three-phase voltage and current signal on the transmission line to a small signal; collecting and storing the converted voltage and current value as data; comparing the data with predetermined reference data to determine the trouble of the transmission line as well as trouble types; separating and obtaining the voltage and current data after and before the trouble responding the comparing step; performing trouble location algorithm for the obtained data based on a predetermined starting mode to get a current distribution factor, and caculating the trouble distance and trouble information at the trouble point by utilizing the current distribution factor.

Description

Parallel double-power-line fault positioning device and method

Technical Field

The present invention relates to a power transmission line fault locating apparatus and method, and more particularly, to an apparatus and method capable of locating a fault point on a parallel (parallel) dual power line by using voltage and current information and a self-terminal current distribution coefficient when a ground fault and a short circuit occur on the parallel dual power line.

Background

As power consumption continues to increase, power transmission line systems become more diverse, more complex, and subject to ultra-high voltage power transmission. Furthermore, a fast and correct localization of the fault becomes more important in terms of stable power supply, since the reliability of the power supply system can be enhanced by fast isolation of the faulty system from the normal system, emergency recovery, etc. Thus, the electric power company runs some power line fault locating devices, which are installed in order to correctly locate faults occurring on the power line.

In the case of a single-phase or multi-phase earth fault and a short circuit, such a fault locating device utilizes the voltage and current after/before the fault measured by the substation on the side of the self end in which the fault locating device is installed, or simultaneously utilizes the voltage and current after/before the fault measured by the substation on the side of the other end, in order to calculate the fault distance from the installation point and accordingly indicate fault point information according to the calculation result.

In this regard, general methods of locating a fault point are divided into the following two groups.

In the first group of methods, voltage and current signals are received from the own-end-side substation, and in the second group of methods, voltage and current information is received from the own-end-side substation and the other-end-side substation of the power transmission line connected to the own end.

In a first set of methods that utilize voltage and current information from the self-terminal to locate a fault point, the self-terminal power supply (power impedance) impedance is utilized in one case, while it is otherwise not utilized in other cases. In this regard, in the case of using the power supply impedance, the power supply impedance viewed from the self end may not always be constant, so that an erroneous result may be obtained, and the set value of the variable power supply impedance may not always be corrected. Therefore, in all conventional positioning devices, the supply impedance of the self-terminal has not been used up to now. In other words, the subsequent fault location methods that no longer use the source impedance of their own terminal have a problem in that, although these methods compensate for the fault resistance and the load, it is impossible to obtain a correct location result due to the sensitivity of the phase angle.

In a second set of methods for obtaining voltage and current information from the other end side, the ratio of the voltage and current of the own end to the other end side is compared for fault localization. According to these methods, although it is advantageous that the fault can be located more correctly, additional communication equipment and lines are provided to obtain post/pre fault data on the voltage and current values of the other end. Considering the distance between substations, which is typically 10-100 km, it is difficult to install communication equipment and lines to ensure additional communication paths for fault location between the two ends. Therefore, a fault locating method for obtaining voltage and current data on the other end side is difficult to adopt.

Therefore, the conventional fault locating device using only self-side information has a problem in that an error may be generated in fault locating. These errors are due to the combination of fault resistance and load current effects (reactance effects), zero phase components, the interplay of zero phase sequence impedance, the effects of atmospheric resistance, which are difficult to obtain in objective systems.

The power line system of an electric power company is composed of a three-phase single power line system, a three-phase parallel dual-output electric line system, and a multi-terminal system in which almost all power line systems operate as a three-phase parallel dual-output electric line system. When a single-phase/multi-phase earth fault occurs in a three-phase parallel dual-input electric wire system during operation, a zero-phase impedance is generated according to a zero-phase-sequence current on a non-fault line or on an adjacent line in a parallel dual-input electric wire in which a fault has occurred, so that a fault point can be correctly located only when a fault zero-phase-sequence current signal is input from the adjacent line in the parallel dual-input electric wire. However, until now, electric power companies have not been able to additionally obtain a zero-phase-sequence current of an adjacent line in a parallel dual-power-line operation, and therefore, there is a need for a fault locating apparatus and method in which the influence of the zero-phase impedance of the adjacent line due to the zero-phase-sequence current can be prevented without receiving the zero-phase-sequence current from the other-end side.

Disclosure of Invention

The present invention has been made to solve the above-mentioned problems of the related art, and therefore it is an object of the present invention to provide a fault location apparatus and method for a parallel dual-input electric wire, which can correctly locate a fault point by receiving a voltage or a current at its own terminal without receiving a zero-phase-sequence current of an adjacent line for parallel power transmission when locating the fault point in a three-phase parallel dual-input electric wire system.

Another object of the present invention is to provide a method for obtaining a current distribution coefficient that can estimate fault currents and zero phase sequence currents of a non-faulty line and an adjacent line, which are important variables for correct fault location in case of a fault in a parallel dual power line; and a fault location device and method of parallel dual-transmission line, wherein the current distribution coefficient can be used to provide fault location algorithm, and the voltage and current information of self end can be used for correct fault location, and the influence of background system impedance change and fault point resistance can be eliminated.

In order to achieve the above object of the present invention, there is provided a method for locating a fault of a parallel dual power line, comprising the steps of: converting three-phase voltage and current signal values on the power transmission line into small signals; collecting and storing the converted voltage and current values as data; comparing the stored voltage and current data with preset reference data to judge faults and fault types on the power transmission line; separating and acquiring voltage and current data after and before a fault if the power line has a fault in response to the comparing step; executing a fault positioning algorithm according to the acquired data according to a preset starting mode to obtain a current distribution coefficient, and calculating fault distance and fault information of a fault point by using the current distribution coefficient; and storing the calculated fault distance and information and transmitting the stored fault distance and information to the outside.

Preferably, the separating and acquiring step uses separating and acquiring 30 cycles of pre-fault voltage and current data of the transmission line and 60 cycles of post-fault voltage and current data; and decomposing the current distribution coefficients into zero, positive and negative phase sequence current distribution coefficients such that the voltage and current are processed in each of the balancing circuits and used in a fault location algorithm to locate a fault point according to the parallel dual input line fault type.

Drawings

Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

fig. 1 is a block diagram for illustrating a fault locating device for parallel dual power lines disposed on one power line according to the present invention;

FIG. 2 is a block diagram of a fault locating device according to the present invention;

FIG. 3 is a detailed block diagram of the master control unit according to the present invention;

FIG. 4 is a flow chart for describing a fault location method according to the present invention;

fig. 5A is a detailed flow chart of a fault location algorithm in the event of a ground fault on one power line according to the present invention;

fig. 5B is a detailed flow chart of the fault location algorithm in the event of a three-phase earth fault/short on two power lines according to the present invention;

FIGS. 6A-6B are schematic circuit diagrams for illustrating impedance changes before and after a fault on parallel twin power lines according to the present invention;

FIGS. 7A to 7C are schematic circuit diagrams for deriving power distribution coefficients due to zero, positive and negative phase sequences in accordance with the present invention;

fig. 8 is a schematic circuit diagram illustrating a system for a power line ground fault on parallel dual power lines in accordance with the present invention;

FIG. 9 is a schematic circuit diagram illustrating a system for use in the event of a three-phase short circuit between power lines on parallel twin power lines in accordance with the present invention; and

fig. 10 is a schematic circuit diagram for illustrating a system when two transmission line ground short circuits and three-phase short circuits occur on a parallel dual transmission line according to the present invention.

Detailed Description

Fig. 1 is a block diagram for illustrating a fault locating device for parallel dual power lines disposed on one power line according to the present invention.

Referring to fig. 1, voltage and current signals from a main voltage transformer C and a main current transformer B on the transmission line are applied to a fault location device E, and the transmission line fault and the fault distance are measured according to a corresponding fault location algorithm. Furthermore, a digital signal indicating a fault is supplied from the protective relay D1 to the fault location device E and calculated from information before and after the fault of the corresponding transmission line. In this connection, the fault distance refers to a distance from the installation point of the main current transformer to the fault point P.

The protection relay D1 is applied with voltage and current signals from the main voltage transformer C and the main current transformer B, rapidly detects a fault on the power line based on the applied voltage and current signals, and controls the power line breaker a to protect the power line from the fault.

FIG. 2 is a block diagram of a fault locating device according to the present invention;

referring to fig. 2, the fault locating device includes: an auxiliary voltage transformer 100, an auxiliary current transformer 120, a data collecting unit 200, a data storage unit 280, a main control unit 300, an I/O unit 400, a storage unit 600, and a correction and display unit 500.

The data aggregation unit 200 includes: a signal conditioning unit 220, a low pass filter 240, and an a/D conversion unit 260.

The auxiliary voltage transformer 100 is supplied with three-phase voltages by a main voltage transformer C installed in the power system, and the auxiliary voltage transformer 100 converts the three-phase voltages into signals of smaller voltages to be transmitted to a data collecting unit 200 to be described later.

The auxiliary current transformer 120 is supplied with three-phase current from the main current transformer B installed in the power supply line, and the auxiliary current transformer 120 converts the three-phase current into a signal of smaller current to transmit to the data collecting unit 200 to be described later.

The data gathering unit 200 adjusts the signal of smaller voltage transmitted from the auxiliary voltage transformer 100 and the signal of smaller current transmitted from the auxiliary current transformer 120 using the signal adjusting unit 220 to supply them to a low pass filter 240 to be described later.

The low pass filter 240 removes high frequency components from the supplied voltage and current signals through a filtering operation and transmits to the a/D conversion unit 260. The a/D conversion unit 260 digitizes and supplies the input voltage and current signals to the data storage unit 280. The data storage unit 280 stores the voltage and current digital signals supplied from the a/D conversion unit 260 and supplies the signals to the main control unit 300.

The main control unit 300 determines whether the power transmission line has a fault by using the digitized three-phase voltage and current data from the data storage unit 280, and obtains a current distribution coefficient by separating and obtaining voltage and current information after/before the fault to calculate a fault distance when the fault occurs. The operation of the main control unit 300 with respect to calculating the current distribution coefficient and the fault distance will be described in detail with reference to fig. 3.

The I/O unit 400 is provided with fault indication information on the power line from the protective relay D1, and the I/O unit 400 notifies the main control unit 300 whether a fault has occurred on the power line. The I/O unit 400 also receives information corresponding to a fault on the power line detected by the relay from the protective relay D1, which protective relay D1 actuates the power line breaker a, and notifies from the outside that the fault distance is calculated by judging the fault point. The storage unit 600 stores the failure information and the failure distance data discriminated by the main control unit 300. The correction and display unit 500 corrects information that can be used as a reference when determining various faults on the power transmission line, and externally displays the fault distance and information.

FIG. 3 is a detailed block diagram of the master control unit according to the present invention.

Referring to fig. 3, the main control unit 300 includes: a data collection and storage unit 310, a reference setting unit 315, a failure judgment unit 320, a data separation and acquisition unit 330, a current distribution coefficient calculation unit 340, a failure distance calculation unit 350, a failure information processing unit 360, a storage unit 370, a failure information display unit 380, and an external communication unit 390.

The reference setting unit 315 stores reference information of fault determination in accordance with a ground fault and a short circuit on the power transmission line, and supplies the information to a fault determination unit 320 which will be described later. The data collecting and storing unit 310 collects and stores the digitized three-phase voltage and current data supplied from the data storing unit 280, and supplies to the fault judging unit 320. The fault judging unit 320 judges a fault on the power transmission line according to some fault judgment criteria supplied from the criterion setting unit 315 with reference to the voltage and current data input from the data collecting and storing unit 310, and transmits the result thereof to the data separating and acquiring unit 330. The data separation and acquisition unit 330, upon receiving the fault occurrence signal generated by the fault determination unit 320 or the fault occurrence information from the I/O unit 400, separates and acquires the voltage and current data before the power transmission line fault for 30 cycles and the voltage and current data after the fault for 60 cycles, and transmits the acquired information to the current distribution coefficient calculation unit 340. Here, 1 cycle of 1.66 msec corresponds to 60 hz.

The current distribution coefficient calculation unit 340 receives the post-fault/pre-fault voltage and current data transmitted by the data separation and acquisition unit 330, calculates a current distribution coefficient from the input voltage and current data, and supplies to the fault distance calculation unit 350. Here, the current distribution coefficient is calculated by determining a voltage equation from given data and obtaining an expression about the non-faulty line and the other-end side line from the equation, which will be described with reference to fig. 4.

The fault information processing unit 350 calculates the distance to the actual fault point by obtaining an expression of the fault distance according to the current distribution coefficient provided by the current distribution coefficient calculating unit 340, and transmits the calculated actual fault distance data to the fault information processing unit 360.

The failure information processing unit 360 receives failure distance data from the failure information processing unit 350 and failure information such as post-failure/pre-failure data from the data separation and acquisition unit 330, and transmits the received data to the storage unit 370. Further, the failure information processing unit 350 displays failure distance data and various information including post/pre failure information from the failure information processing unit 350 and the data separation and acquisition unit 330 through the correction and display unit 500. The storage unit 370 stores the calculated distance information and the failure information, and the failure information display unit 380 provides the calculated distance information to the user through the correction and display unit 500. The fault information processing unit 360 communicates with the external communication unit 390 unit to transmit the calculated distance information and fault information to an external computer or a host computer.

Here, the method of fault location will be described in detail according to the above-described structure with reference to fig. 4.

First, when the fault locating device completes its initialization, first, at step S100, the three-phase voltages and currents on the power transmission line are reduced through the external main voltage transformer and main current transformer, respectively, and the reduced three-phase voltages and currents are converted into small signals of voltages and currents through the auxiliary voltage transformer 100 and the auxiliary current transformer 120.

The small signal converted into the voltage and the current at step S100 is adjusted by the signal adjusting unit 220 and supplied to the low pass filter 240. Then, the low pass filter 240 removes high frequency components from the input voltage and current signals at step S120, and performs low pass filtering by DFT (discrete fourier transform) with 1 cycle at step S140.

In other words, the digitized signal in the a/D conversion unit 260 is transmitted to the data storage unit 280 in accordance with the three-phase voltage and current quantized in the real-time transmission system. Here, the quantized real-time three-phase voltages and currents are sampled at 14 or 16 from 600 Hz voltage and current signals.

The voltage and current signals detected by DFT filtering at step S140 are calculated as (root mean square value) RMS, and the voltage and current signals calculated as RMS are compared according to pre-indicated UVR (low voltage relay device), OCGR (over current ground relay device) and OCR (over current relay device) to judge a power line fault at step S160 and at step S180.

Here, the relay device receives a voltage or a current of the system, and calculates and outputs a signal of "0" or "1" by operating according to a pre-designated input value.

Therefore, when UVR is operating, it is determined whether the magnitude of the input voltage to the system is at most a predetermined reference value (correction value). The OCGR is started by detecting a ground fault current or a zero phase sequence current flowing along the earth when the system fails, and determining whether the input ground fault current is at least a pre-adjustment reference value or a correction value. The OCR determines whether the incoming system phase current is at least a pre-conditioning reference value or correction value for its operation.

Therefore, as voltage and current information calculated by RMS is generated at step S180, if the input generated current is at least a reference value of OCR and the input generated voltage is at least a reference value of UVR or the zero-phase-sequence current is at least a reference value of OCGR, trip is performed so that the fault judging unit 320 judges a fault phase and a fault type at steps S200 and S220.

Here, it is determined whether the current state is a fault due to a power transmission line ground fault and a short circuit, and the fault type is identified as a single line ground fault, a two line short circuit, a two line ground fault, a three phase ground fault, and a three phase short circuit in the fault phase determination.

After the determination of the fault type is completed in step S220, the data after/before the fault is separated and acquired by using the input transmission line voltage and current data. In other words, in step S240, the data separation and acquisition unit 330 separates and acquires the voltage and current data before the power line fault for 30 cycles and the voltage and current data after the fault for 60 cycles.

Meanwhile, after acquiring data before/after the power line fault at step S240, it is determined whether the start mode is the external start mode at step S260. Here, if the result provided at step S260 is the external start mode, it is confirmed whether it is a DI contact, and if the start mode is the internal start mode, the fault distance is calculated according to the fault localization algorithm using the current distribution coefficient calculating unit 340 and the fault distance calculating unit 350 at step S300.

Here, the start mode sets which fault locating algorithm is executed, and when the fault locating algorithm is executed according to fault information inputted from the outside of the protection relay a, it is determined whether or not trip information of the protection relay a is inputted to the device. When the DI contact is confirmed, whether or not the fault information is input to the input port of the DI in the fault locating device is confirmed. The internal start mode refers to performing a fault locating algorithm according to fault information detected by the fault locating device itself.

Here, the fault locating algorithm will be described with reference to fig. 6 to 10.

In steps S340 and S360, the fault information and the fault distance measured by the aforementioned fault locating algorithm are output by the fault information processing unit 360 and stored in the storage unit 370, and then the operation returns to step S100 to receive instantaneous values of voltage and current.

Before each fault localization algorithm according to the fault line is disclosed below, the terminology used in the application and the symbols used in the circuit are introduced.

When a fault occurs in the parallel dual power lines, the current distribution of the fault circuit is varied in accordance with the impedance distribution in the system, as shown in fig. 6B. The circuit in fig. 6A shows a state before a failure, and the circuit in fig. 6B shows a state after a failure. Therefore, post/pre-fault information is needed to analyze these circuits for corrective fault localization.

The data stored in the storage unit 370 is used for impedance distribution of a circuit composed of desired information before a fault and voltage and current data after a fault, in order to predict a fault current and a zero phase-sequence current of a non-fault line. Here, the fault current is a current in a fault resistance including an arc resistance and a contact point resistance generated at a fault point when a ground fault and a short circuit are generated on a line of the power transmission system.

A non-faulty line refers to a line that stably supplies power to the system in the parallel dual power lines, i.e., a line adjacent to a faulty line in which a ground fault or short circuit occurs, that is, that does not have a fault.

The current distribution coefficient applied to the present invention refers to an impedance ratio corresponding to the degree of current correlation at the self end and the other end side of the faulty wire, an impedance ratio corresponding to the degree of current correlation of the faulty wire and the non-faulty wire, and the like, and is classified into zero, positive and negative phase sequences according to the corresponding phases.

When zero, positive and negative phase-sequence voltages (currents), for example va (ia), vb (ib) and vc (ic), are represented in asymmetric unbalanced three-phase circuits according to symmetric coordinates, each of them can be represented as follows according to the symmetric components of V1, V2 and V0:

Va＝V₀+V₁+V₂，Vb＝V₀+a²V₁+aV₂，Vc＝V₀+aV₁+a²V₂(ii) a And

Ia＝I₀+I₁+I₂，Ib＝I₀+a²I₁+aI₂，I_c＝I₀+aI₁+a²I₂，

wherein,

and

1+a+a²＝0

here, V₀(I₀) Referred to as zero phase-sequence voltage (current) as a common single-phase component contained in the A, B and C-phase voltages and currents.

For V₁(I₁) Phase A having V₁(I₁) (ii) a Phase B having a²V₁(a²I₁) Is a representative ratio V₁(I₁) Lag by 120 ° (or lead by 240 °); and phase C has aV₁(aI₁) Is a representative ratio V₁(I₁) Leading by 120 (or lagging by 240). In other words, at V₁(I₁) Term, the voltage (current) is called positive phase-sequence voltage(current) because it has the same rotational direction as the symmetrical three-phase voltage (current) about A, B and the C-phase.

In addition, for V₂(I₂) Phase A having V₂(I₂) (ii) a Phase B having aV₂(aI₂) Ratio of V to₂(I₂) 120 ° lead (or 240 ° lag); and phase C has a²V₂(a²I₂) Ratio of V to₂(I₂) Lagging by 120 (or leading by 240). In other words, at V₂(I₂) In terms, this voltage (current) is referred to as a negative phase-sequence voltage (current) because it has a rotational direction opposite to the symmetrical three-phase voltage (current) about A, B and the C-phase.

Here, symbols used in each appliance are defined as follows table 1:

TABLE 1

(symbol)	Definition of	Unit of
			ZS0	Zero phase sequence impedance of power supply SS	[ Europe ]]
ZS1	Positive phase-sequence impedance of power supply SS	[ Europe ]]
			ZS2	Negative phase sequence impedance of power supply SS	[ Europe ]]
ZR0	Zero phase sequence impedance of power supply SR	[ Europe ]]
			ZR1	Positive phase sequence impedance of power supply SR	[ Europe ]]
ZR2	Negative phase sequence impedance of power supply SR	[ Europe ]]
			ZL0	Zero phase sequence impedance of faulty line	[ Europe ]]
ZL1	Positive phase sequence impedance of faulty line	[ Europe ]]
			ZL2	Negative phase sequence impedance of fault line	[ Europe ]]
ZT0	Zero phase sequence impedance of non-faulted line	[ Europe ]]
			ZT1	Positive phase sequence impedance of non-faulted line	[ Europe ]]
ZT2	Negative phase sequence impedance of non-faulted line	[ Europe ]]
			Rf	Resistance of fault point	[ Europe ]]
IS0	Self-terminal zero phase sequence current	[ an ]]
			IS1	Positive phase-sequence current of self terminal	[ an ]]
IS2	Negative phase sequence current of self terminal	[ an ]]

IR0	Zero phase sequence current of the other end	[ an ]]
			IR1	Positive phase-sequence current of the other end	[ an ]]
IR2	Negative phase sequence current of the other end	[ an ]]
			IT0	Zero phase sequence current of non-fault line	[ an ]]
IT1	Positive phase-sequence current of non-faulty line	[ an ]]
			IT2	Negative phase sequence current of non-fault line	[ an ]]
If0	Zero phase sequence current towards fault point	[ an ]]
			If1	Positive phase-sequence current towards fault point	[ an ]]
If2	Negative phase sequence current towards fault point	[ an ]]
			P	Distance from relay mounting point to fault point	[ normalized value]

Next, when a fault occurs in the power transmission line, the symmetrical component circuit of the fault circuit for obtaining the current distribution coefficient is configured as follows:

fig. 7A shows a zero phase-sequence circuit for obtaining the current distribution coefficient. In the zero phase-sequence circuit shown in fig. 7A, two voltage equations along paths a and B are derived using equation 1:

(Z_S0+pZ_L0)I_S0-[Z_R0+(1-p)Z_L0]I_R0+(Z_S0+Z_R0+Z_m)I_T0＝0

(Z_S0+pZ_m)I_S0-[Z_R0+(1-p)Z_m]I_R0+(Z_S0+Z_R0+Z_T0)I_T0＝0

.... equation 1

In equation 1, the zero phase-sequence current I if the non-faulty line is cancelled_T0The zero phase-sequence current I in the self terminal is obtained by using equation 2_S0And a zero phase-sequence current I in the other end_R0Ratio of current distribution of (a):

$\frac{I_{R0}}{I_{S0}}=\frac{(Z_{T0}-Z_m)Z_{S0}+p{Z}_{L0}(Z_{S0+}{Z}_{R0}+Z_{T0})-p{Z}_m(Z_{S0}+Z_{R0}+Z_m)}{(Z_{T0}-Z_m)Z_{R0}+(1-p)Z_{L0}(Z_{S0}+Z_{R0}+Z_{T0})-(1-p)Z_m(Z_{S0}+Z_{R0}+Z_m)}$

..

Here, since the current flowing through the fault point is I_f0＝I_S0+I_R0And obtaining a zero phase sequence current distribution coefficient by using equation 3:

$D_{\mathrm{Sa}0}=\frac{I_{S0}}{I_{f0}}=\frac{I_{S0}}{I_{S0}+I_{R0}}=\frac{1}{1+(I_{R0}/I_{S0})}=\frac{p{B}_{\mathrm{Sa}0}+C_{\mathrm{sa}0}}{A_{\mathrm{Sa}0}}$

..

Wherein,

A_Sa0＝(Z_L0-Z_m)(Z_S0+Z_R0+Z_m)+(Z_T0-Z_m)(Z_S0+Z_R0+Z_L0)

B_Sa0＝(Z_m-Z_L0)(Z_S0+Z_R0+Z_m)-(Z_T0-Z_m)Z_L0and are and

C_Sa0＝(Z_L0-Z_m)(Z_S0+Z_R0+Z_m)+(Z_T0-Z_m)(Z_R0+Z_L0)

therefore, if the zero-phase-sequence current I in the other side end is eliminated from equation 1_R0To obtain the zero phase sequence current distribution coefficient of the non-fault line, the equation 4 is used to obtain the zero phase sequence current I of the self terminal_S0With zero phase-sequence current I at the other side_T0Ratio of current distribution:

$D_{\mathrm{TS}}=\frac{I_{S0}}{I_{T0}}=\frac{p{A}_{\mathrm{ST}}+B_{\mathrm{ST}}}{p{C}_{\mathrm{ST}}+D_{\mathrm{St}}}$

..

Wherein,

A_ST＝(Z_m-Z_L0)(Z_S0+Z_R0+Z_m)-(Z_T0-Z_m)Z_L0

B_ST＝(Z_L0-Z_m)(Z_S0+Z_R0+Z_m)+(Z_T0-Z_m)(Z_R0+Z_L0)

C_ST＝(Z_L0-Z_m)(Z_S0+Z_R0) And are and

D_ST＝(Z_m-Z_L0)Z_S0<1P>

therefore, the zero-phase-sequence current distribution coefficient of the non-faulty line is obtained from the above equations 3 and 5 using equation 5 in step S302 and step S304:

$D_{T0}=\frac{I_{T0}}{I_{f0}}=\frac{p{B}_{T0}+C_{T0}}{A_{T0}}$

..

Wherein,

A_T0＝(Z_L0-Z_m)(Z_S0+Z_R0+Z_m)+(Z_T0-Z_m)(Z_S0+Z_R0+Z_m)

B_T0＝(Z_L0-Z_m)(Z_S0+Z_R0)

C_T0＝(Z_m-Z_L0)Z_S0<1P>

then, with reference to the positive phase-sequence circuit shown in fig. 7B, the positive phase-sequence current distribution coefficient was obtained as follows:

the voltage equation shown in equation 6 is established according to the positive phase-sequence current distribution coefficient in the same manner as described above:

(Z_S1+pZ_L1)I_S1-[Z_R1+(1-p)Z_L1]I_R1+(Z_S1+Z_R1)I_T1＝0

Z_S1I_S1-Z_R1I_R1+(Z_S1+Z_R1+Z_T1)I_T1＝0

.... equation 6

Here, the current I is obtained using equation 7_S1And current I_R1Ratio of current distribution:

$\frac{I_{R1}}{I_{S1}}=\frac{Z_{S1}{\mathrm{<figure-callout\; id="1"\; label="Z\; T"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Z</figure-callout>}}_T+p{Z}_{L1}({\mathrm{<figure-callout\; id="1"\; label="Z\; S"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Z</figure-callout>}}_S+{\mathrm{<figure-callout\; id="1"\; label="Z\; R"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Z</figure-callout>}}_R+Z_{T1})}{Z_{R1}{\mathrm{<figure-callout\; id="1"\; label="Z\; T"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Z</figure-callout>}}_T+(1-p)Z_{L1}({\mathrm{<figure-callout\; id="1"\; label="Z\; S"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Z</figure-callout>}}_S+{\mathrm{<figure-callout\; id="1"\; label="Z\; R"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Z</figure-callout>}}_R+Z_{T1})}$

..

Here, since the current flowing through the fault point is I_f1＝I_S1+I_R1Therefore, the positive phase-sequence current distribution coefficient is obtained using equation 8:

${\mathrm{<figure-callout\; id="1"\; label="D\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">D</figure-callout>}}_{\mathrm{Sa}}=\frac{I_{S1}}{{\mathrm{<figure-callout\; id="1"\; label="I\; f"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">I</figure-callout>}}_f}=\frac{I_{S1}}{{\mathrm{<figure-callout\; id="1"\; label="I\; S"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">I</figure-callout>}}_S+I_{R1}}=\frac{1}{1+(I_{R1}/I_{S1})}\frac{\mathrm{<figure-callout\; id="1"\; label="p\; B\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">p</figure-callout>}{B}_{\mathrm{Sa}}{1}_{}+C_{\mathrm{sa}1}}{A_{\mathrm{<figure-callout\; id="1"\; label="Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Sa</figure-callout>}1}}$

.... equation 8

Wherein,

A_Sa1＝Z_L1(Z_S1+Z_R1)+Z_T1(Z_S1+Z_R1+Z_L1)

B_Sa1＝Z_L1(Z_S1+Z_R1+Z_T1) And are and

C_Sa1＝Z_L1(Z_S1+Z_R1+Z_T1)+Z_T1Z_R1

then, with reference to the negative phase-sequence circuit shown in fig. 7C, the negative phase-sequence current distribution coefficient is obtained as follows:

the negative phase-sequence current distribution coefficient in the negative phase-sequence circuit is obtained using equation 9 in the same manner as the above-described positive phase-sequence current:

$D_{\mathrm{Sa}2}=\frac{I_{S2}}{I_{f2}}=\frac{p{B}_{\mathrm{Sa}2}+C_{\mathrm{sa}2}}{A_{\mathrm{Sa}2}}$

..

Wherein,

A_Sa2＝Z_L2(Z_S2+Z_R2)+Z_T2(Z_S2+Z_R2+Z_L2)

B_Sa2＝Z_L2(Z_S2+Z_R2+Z_T2) And

C_Sa2＝Z_L2(Z_S2+Z_R2+Z_T2)+Z_T2Z_R2

here, if the positive phase-sequence impedance and the negative phase-sequence impedance are the same, the positive phase-sequence current distribution coefficient and the negative phase-sequence current distribution coefficient are obtained using equation 10:

D_Sa1＝D_Sa2

A_Sa1＝A_Sa2，B_Sa1＝B_Sa2，C_Sa1＝C_Sa2

.... equation 10

Meanwhile, a parallel dual-output line fault location method according to various fault types is described with reference to fig. 8 to 10, which uses zero, positive and negative phase-sequence current distribution coefficients as follows according to the above-described respective equations:

fig. 5A is a detailed flowchart of the occurrence of a ground fault on one power line in the fault location algorithm shown in fig. 4. The fault location method can be expressed in mainly 3 ways, wherein a fault location method using the above-described zero phase sequence equation in the case of a ground fault occurring on one power line in this application will be described.

In which the zero phase-sequence equation in the fault localization method 2 is used in the case of a ground fault occurring on one power line will be described with reference to fig. 8.

In FIG. 8, the post-fault voltage is obtained using equation 11:

V_Sa＝p[Z_L1I_Sa+(Z_L0-Z_L1)I_S0]+pZ_mI_T0+R_fI_f

.... equation 11

Here, in step S301, a voltage equation at the relay mounting point is obtained using equation 16, and the current of the non-faulty line and the current of the other side end are cancelled in steps S302 to S304, and the zero-phase-sequence current distribution coefficient is calculated.

According to the above equation, the zero-phase-sequence current and the zero-phase-sequence current distribution coefficient at the relay mounting point are used to obtain a voltage equation at the relay mounting point using equation 12 at step S305:

$V_{\mathrm{Sa}}=p[Z_{L1}{I}_{\mathrm{Sa}}+(Z_{L0}-Z_{L1})I_{S0}]+p{Z}_m\frac{I_{S0}}{D_{\mathrm{TS}}}+R_f\frac{3I_{S0}}{D_{\mathrm{Sa}0}}$

… … equation 12

In step S306, the value corresponding to each current distribution coefficient is substituted into the voltage equation established according to equation 12. Then, the voltage equation at the relay mounting point is expressed using equation 13:

$V_{\mathrm{Sa}}=p[Z_{L1}{I}_{\mathrm{Sa}}+(Z_{L0}-Z_{L1})I_{S0}]+p{Z}_m{I}_{S0}\frac{p{C}_{\mathrm{ST}}+D_{\mathrm{ST}}}{p{A}_{\mathrm{ST}}+B_{\mathrm{ST}}}+3R_f{I}_{S0}\frac{A_{\mathrm{Sa}0}}{p{B}_{\mathrm{Sa}0}+C_{\mathrm{Sa}0}}$

… … equation 13

Wherein, since pA is in equations 4 and 5_ST+B_ST＝pB_Sa0+C_Sa0They are treated as a common denominator. Therefore, the voltage at the relay mounting point is expressed using equation 14 as:

$V_{\mathrm{Sa}}=p[Z_{L1}{I}_{\mathrm{Sa}}+(Z_{L0}-Z_{L1})I_{S0}]+\frac{[p{Z}_m{I}_{S0}(p{C}_{\mathrm{ST}}+D_{\mathrm{ST}})+3R_f{I}_{S0}{A}_{\mathrm{Sa}0}]}{p{B}_{\mathrm{Sa}0}+C_{\mathrm{Sa}0}}$

… … equation 14

In step S307, each coefficient of the formula is replaced and collated with respect to the failure distance p to obtain 15 equations:

(a₁+jb₁)p²+(a₂+jb₂)p+(a₃+jb₃)+(a₄+jb₄)R_f＝0

… … equation 15

Wherein

a₁+jb₁＝[Z_L1I_Sa+(Z_L0-Z_L1)I_S0]B_Sa0+Z_mI_S0C_ST

a₂+jb₂＝[Z_L1I_Sa+(Z_L0-Z_L1)I_S0]C_Sa0+Z_mI_S0D_ST-V_SaB_Sa0

a₃+jb₃＝-V_SaC_Sa0

a₄+jb₄＝3I_S0A_Sa0

Wherein, in step S308, equation 15, which is composed of a real part and an imaginary part, is decomposed to obtain equation 16:

a₁p²+a₂p+a₃+a₄R_f＝0

b₁p²+b₂p+b₃+b₄R_f＝0

… … equation 16

In step S309, the fault resistor R is eliminated_fThe fault distance p is later found by using the quadratic expression in equation 17 (quadratic equation):

$(a_1-b_1\frac{a_4}{b_4})p^2+(a_2-b_2\frac{a_4}{b_4})p(a_3-b_3\frac{a_4}{b_4})=0$

.... equation 17

In steps S310 and S311, two roots are obtained from equation 17, where the fault distance p is a value of 0 to 1 because the total line length is set to 1.

Meanwhile, a fault locating method in the case of one line ground fault is described with reference to a circuit of one line ground fault shown in fig. 8.

Since the zero, positive and negative phase-sequence currents flowing to the fault point are the same, the current can be expressed using the current at the relay mounting point and the current distribution coefficient according to equation 18.

In the illustrated system of fig. 8, the current flowing to the fault point in the event of a line to ground fault is represented as a zero, positive and negative phase sequence using equation 18:

I_f0＝I_f1＝I_f2

..

With the aid of the currents at the relay mounting points and the current distribution coefficients, equation 18 can be expressed in equation 19:

$\frac{I_{\mathrm{Sa}0}}{D_{\mathrm{Sa}0}}=\frac{I_{\mathrm{Sa}1}}{{\mathrm{<figure-callout\; id="1"\; label="D\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">D</figure-callout>}}_{\mathrm{Sa}}}=\frac{I_{\mathrm{Sa}2}}{D_{\mathrm{Sa}2}}$

..

In equation 19, if relational expressions of zero-phase-sequence-to-positive-phase-sequence, zero-phase-sequence-to-negative-phase-sequence, and positive-phase-sequence-to-negative-phase-sequence are evolved, each relational expression is expressed as a function of a distance p from a relay mounting point to a failure point (which will be referred to as a failure distance p hereinafter).

Here, if the relational expressions of the zero-phase-sequence and zero-phase-sequence current distribution coefficients with respect to p are collated, the fault distance p is obtained according to equation 14.

I_Sa0D_Sa1＝I_Sa1D_Sa0

.... equation 20, and

$p=\frac{A_{\mathrm{Sa}1}{I}_{\mathrm{Sa}1}{C}_{\mathrm{Sa}0}-A_{\mathrm{Sa}0}{I}_{\mathrm{Sa}0}{C}_{\mathrm{Sa}1}}{A_{\mathrm{Sa}0}{I}_{\mathrm{Sa}0}{B}_{\mathrm{Sa}1}-A_{\mathrm{Sa}1}{I}_{\mathrm{Sa}1}{B}_{\mathrm{Sa}0}}$

..

Next, if the positive phase-sequence impedance and the negative phase-sequence impedance are the same, the fault distance p in the relational expression of the zero-phase-sequence and zero-phase-sequence current distribution coefficients is obtained using equation 21.

Finally, the relational expressions for the positive phase sequence and the negative phase sequence with respect to the fault distance p are collated to obtain equation 22:

$p=\frac{A_{\mathrm{Sa}1}{I}_{\mathrm{Sa}1}{C}_{\mathrm{Sa}2}-A_{\mathrm{Sa}2}{I}_{\mathrm{Sa}2}{C}_{\mathrm{Sa}1}}{A_{\mathrm{Sa}2}{I}_{\mathrm{Sa}2}{B}_{\mathrm{Sa}1}-A_{\mathrm{Sa}1}{I}_{\mathrm{Sa}1}{B}_{\mathrm{Sa}2}}=\frac{\left(A_{\mathrm{Sa}1}{C}_{\mathrm{Sa}1}\right)(I_{\mathrm{Sa}1}-I_{\mathrm{Sa}2})}{\left(A_{\mathrm{Sa}1}{B}_{\mathrm{Sa}1}\right)(I_{\mathrm{Sa}2}-I_{\mathrm{Sa}1})}$

… … equation 22

Here, if the positive phase-sequence impedance and the negative phase-sequence impedance are the same, and the positive phase-sequence current distribution coefficient and the negative phase-sequence current distribution coefficient are the same in equation 10, the currents are the same, so that the fault distance p cannot be defined as equation 22. In other words, a relational expression of positive-phase-sequence and negative-phase-sequence current distribution coefficients cannot be used.

Next, using the positive phase sequence in the fault location method 2 in the case of a ground fault on one line, the equation becomes as follows:

when the positive-phase-sequence current and the positive-phase-sequence current distribution coefficient are used, a voltage equation at the relay mounting point as equation 23 is established:

V_Sa＝p[Z_L1I_Sa+(Z_L0-Z_L1)I_S0]+pZ_mI_T0+R_fI_f

… … equation 23

Wherein the current I due to a non-faulted line flowing to the fault point_fAnd zero phase-sequence current I_T0It is not known and therefore zero phase-sequence current and zero phase-sequence current distribution coefficients at relay mounting points are utilized. Furthermore, due to I_fCan be expressed by zero, positive and negative phase sequence currents, using I_fSo that 3 equations are obtained according to equation 23.

Further, according to the above equation 23, the positive-phase-sequence current and the positive-phase-sequence current distribution coefficient are expressed using equation 24:

$V_{\mathrm{Sa}}=p[Z_{L1}{I}_{\mathrm{Sa}}+(Z_{L0}-Z_{L1})I_{S0}]</P><P>+p{Z}_m\frac{I_{S0}}{D_{\mathrm{TS}}}+R_f\frac{3I_{S1}}{{\mathrm{<figure-callout\; id="1"\; label="D\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">D</figure-callout>}}_{\mathrm{Sa}}}$

… … equation 24

Referring to the circuits shown in fig. 5A to 5C, due to the fault current I_fGenerated from a circuit after a fault, I_S1Is a pure phase fault current, eliminating the load current in the pre-fault circuit in equation 24.

Therefore, each coefficient is substituted and the respective relational expressions regarding the failure distance p are arranged so as to obtain equation 25 as a cubic equation:

(a₃+jb₃)p³+(a₂+jb₂)p²+[a₁+jb₁+(c₁+jd₁)R_f]p

+[a₀+jb₀+(c₀+jd₀)R_f]＝0

… … equation 25

Wherein

a₃+jb₃＝IZ_L1B_Sa1A_ST+I_S0Z_mB_Sa1C_ST

a₂+jb₂＝IZ_L1B_Sa1B_ST+IZ_L1C_Sa1A_ST

-V_SaB_Sa1A_ST+I_S0Z_mB_Sa1D_ST+I_S0Z_mC_Sa1C_ST

a₁+jb₁＝IZ_L1C_Sa1B_ST

-V_SaB_Sa1B_ST-V_SaC_Sa1A_ST+I_S0Z_mC_Sa1D_ST

a₀+jb₀＝-V_SaC_Sa1B_ST

c₁+jd₁＝3I_S1A_Sa1A_ST

c₀+jd₀＝3I_S1A_Sa1C_ST

$I=I_{\mathrm{Sa}}+\frac{(Z_{L0}-Z_{L1})}{Z_{L1}}{I}_{S0}$

Equation 25 is divided into a real part and an imaginary part to obtain equation 26 as two cubic equations:

a₃p³+a₂p²+(a₁+c₁R_f)p+(a₀+c₀R_f)＝0

b₃p³+b₂p²+(b₁+d₁R_f)p+(b₀+d₀R_f)＝0

… … equation 26

Here, the fault resistance R is eliminated_fSo as to obtain equation 27 as a biquadratic equation with respect to the fault distance p:

p⁴+k₁P³+k₂P²+k₃P³+k₄＝0

… … equation 27

Wherein

k₁＝(a₂d₁-b₂c₁+a₃d₀-b₃+b₀c₀)/(a₃d₁-b₃c₁)，

k₂＝(a₁b₁-b₁c₁+a₂d₂-b₂c₀)/(a₃d₁-b₃c₁)，

k₃＝(a₀d₁-b₀c₁+a₁d₀-b₁c₀)/(a₃d₁-b₃c₁)，

k₄＝(a₀d₀-b₀c₀)/(a₃d₁-b₃c₁).

Here, the fault distance p is obtained by using the quadratic expression of the biquadratic equation in equation 27 by using newton-raphson iterative calculation in equation 26.

In other words, the biquadratic equation in equation 27 is sorted into a quadratic equation with respect to the failure distance by using the quadratic equation so as to calculate the failure distance.

The method 3 for fault localization of a ground fault is described below with reference to fig. 8.

Referring to fig. 5A to 5C, the current at the relay mounting point is the pure fault current I_SafAnd the load current I_SaLThe sum of (1). They are expressed using equation 28:

I_Sa＝I_Saf+I_SaL

… … equation 28

Equation 28 is substituted into equation 11 for the voltage at the relay mounting point to obtain equation 29:

V_Sa＝p[Z_L1(I_Saf+I_SaL)+(Z_L0-Z_L1)I_S0]+pZ_mI_T0+R_fI_f

… … equation 29

Here, both sides of equation 29 are divided by I_SafTo obtain equation 30:

$\frac{V_{\mathrm{Sa}}}{I_{\mathrm{Saf}}}=p[Z_{L1}(1+\frac{I_{\mathrm{SaL}}}{I_{\mathrm{Saf}}})+(Z_{L0}-Z_{L1})\frac{I_{S0}}{I_{\mathrm{Saf}}}]+p{Z}_m\frac{I_{T0}}{I_{\mathrm{Saf}}}+R_f\frac{I_f}{I_{\mathrm{Saf}}}$

… … equation 30

Here, pure failure at relay mounting pointCurrent I_SafIs the sum of zero, positive and negative phase-sequence currents and is represented by the current flowing to the fault point and the positive and negative phase-sequence current distribution coefficients to arrive at equations 31 and 32:

I_Saf＝I_S0+I_S1+I_S2

… … equation 31, and

I_Saf＝(D_Sa0I_f0+D_Sa1I_f1+D_Sa2I_f2)＝(D_Sa0+2D_Sa1)I_f1

… … equation 32

The new current distribution coefficient is obtained by equation 31 and equation 32 as equation 33:

$D_{\mathrm{Sa}}=\frac{I_{\mathrm{<figure-callout\; id="1"\; label="Saf\; I\; f"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">Saf</figure-callout>}}}{I_f}=(D_{\mathrm{Sa}0}+2D_{\mathrm{Sa}1})=\frac{p{B}_{\mathrm{Sa}}+C_{\mathrm{Sa}}}{A_{\mathrm{Sa}}}$

… … equation 33

Wherein

A_Sa＝A_Sa0A_Sa1，

B_Sa＝B_Sa0A_Sa1+2A_Sa0B_Sa1，and

C_Sa＝C_Sa0A_Sa1+2A_Sa0C_Sa1.

Meanwhile, equations 3, 5 and 33 are used to derive equations 34, 35 and 36:

$\frac{I_{S0}}{I_{\mathrm{Saf}}}=\frac{A_{\mathrm{Sa}}}{A_{\mathrm{Sa}0}}\frac{p{B}_{\mathrm{Sa}0}+C_{\mathrm{Sa}0}}{p{B}_{\mathrm{Sa}}+C_{\mathrm{Sa}}}$

… … equation 34

$\frac{I_{T0}}{I_{\mathrm{Saf}}}=\frac{A_{\mathrm{Sa}}}{A_{\mathrm{Sc}0}}\frac{p{B}_{\mathrm{Sc}0}+C_{\mathrm{Sc}0}}{p{B}_{\mathrm{Sa}}+C_{\mathrm{Sa}}}$

… … equation 35

$\frac{I_f}{I_{\mathrm{Saf}}}=\frac{3A_{\mathrm{Sa}}}{p{B}_{\mathrm{Sa}}+C_{\mathrm{Sa}}}$

… … equation 36

Equations 34, 35 and 36 are substituted into equation 30 and sorted with respect to the fault distance p to obtain equation 37 as a quadratic equation with respect to the fault distance p:

(x₁+jy₁)p²+(x₂+jy₂)p+(x₃+jy₃)+(x₄+jy₄)R_f＝0

… … equation 37

Wherein

$x_1+\mathrm{<figure-callout\; id="1"\; label="j\; y"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">j</figure-callout>}{y}_{}{}_1=Z_{L1}(1+\frac{I_{\mathrm{Sal}}}{I_{\mathrm{Saf}}})B_{\mathrm{Sa}}+(Z_{L0}-Z_{L1})\frac{A_{\mathrm{Sa}}}{A_{\mathrm{Sa}0}}{B}_{\mathrm{Sa}0}+Z_m\frac{A_{\mathrm{Sa}}}{A_{\mathrm{Sc}0}}{B}_{\mathrm{Sc}0}$

$x_2+j{y}_2=Z_{L1}(1+\frac{I_{\mathrm{SaL}}}{I_{\mathrm{Saf}}})C_{\mathrm{Sa}}+(Z_{L0}-Z_{L1})\frac{A_{\mathrm{Sa}}}{A_{\mathrm{Sa}0}}{C}_{\mathrm{Sa}0}+Z_m\frac{A_{\mathrm{Sa}}}{A_{\mathrm{Sc}0}}{C}_{\mathrm{Sc}0}$

$-\frac{V_{\mathrm{Sa}}}{I_{\mathrm{Saf}}}{B}_{\mathrm{Sa}}$

$x_3+y_3=-\frac{V_{\mathrm{Sa}}}{I_{\mathrm{Saf}}}{C}_{\mathrm{Sa}}$

x₄+y₄＝3A_Sa

After dividing equation 37 into real and imaginary parts, the fault resistance R is eliminated_fTo obtain equation 38:

x₁p²+x₂p+x₃+x₄R_f＝0

y₁p²+y₂p+y₃+y₄R_f0 > … … equation 38

Wherein the fault distance p is obtained by using the quadratic expression of the quadratic equation (equation 39):

$(x_1-y_1\frac{x_4}{y_4})p^2+(x_2-y_2\frac{x_4}{y_4})p+(x_3-y_3\frac{x_4}{y_4})=0$

… … equation 39

Fig. 9 is a schematic circuit diagram for illustrating a system in which a short circuit occurs on a dual power line or a triple power line according to the present invention.

Here, in order to correctly localize a fault when one line ground fault or a line-to-line short circuit and two line ground faults occur on parallel dual electric lines, the equation is evolved in consideration of the fault resistance at the fault point, and the fault resistance is eliminated from the relational expression in the same manner as the ground fault so as to eliminate the influence of the fault resistance.

Therefore, the post-fault voltage equation, equation 40, is obtained at step S322 based on the fault location algorithm disclosed in fig. 5B and the line-to-line short fault circuit disclosed in fig. 8:

V_Sab＝V_Sa-V_Sb

＝V_Saf-V_Sbf+V_SaL-V_SbL+V_fa-V_fb

＝(V_S0+V_S1+V_S2)-(V_S0+a²V_S1+aV_S2)+V_SaL-V_SbL

+(V_f0+V_f1+V_f2)-(V_f0+a²V_f1+aV_f2)

＝(1-a²)V_S1+(1-a)V_S2+V_SaL-V_SbL+(1-a²)V_f1+(1-a)V_f2

… … equation 40

Wherein,

V_Saf，V_Safis a slave relayThe failed a-phase and b-phase voltages of the electric appliance installation point to the failure point,

V_SaL，V_SaLare a-phase and b-phase voltages before failure from a relay mounting point to a failure point, an

V_fa，V_fbAre the a-phase and b-phase voltages after the fault at the fault point.

Then, in step S323, the symmetrical voltages from the relay mounting point and the failure point are obtained from the deduced voltage equation (equation 41):

V_S0＝pZ_L0I_S0，V_S1＝pZ_L1I_S1，V_S2＝pZ_L2I_S2

V_f0＝pR_fI_f0，V_f1＝R_fI_f1，V_f2＝R_fI_f2

… … equation 41

In step S324, if the symmetrical voltage is substituted into the voltage equation, or refer to equation 3, or the zero-phase-sequence current distribution coefficient equation, equation 8, or the positive-phase-sequence current distribution coefficient equation, and equation 9, or the negative-phase-sequence current distribution coefficient equation, the following correlation is obtained:

I_f0＝I_S0/D_Sa0，I_f1＝I_S1/D_Sa1，I_f2＝I_S2/D_Sa2

if these current distribution coefficients are substituted into equation 40 and sorted out, the voltage V is obtained using equation 42_Sab：

$V_{\mathrm{Sab}}=p{Z}_{L1}(I_{\mathrm{Sa}}-I_{\mathrm{Sb}})+R_f-\frac{(I_{\mathrm{Saf}}-I_{\mathrm{Sbf}})}{{\mathrm{<figure-callout\; id="1"\; label="D\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">D</figure-callout>}}_{\mathrm{Sa}}}$

… … equation 42

In step S325 and step S326, if the positive phase-sequence current distribution coefficient D is set_Sa1Substituting into equation 42 and sorting, and obtaining voltage V using equation 43_Sab：

$V_{\mathrm{Sab}}=p{Z}_{L1}(I_{\mathrm{Sa}}-I_{\mathrm{Sb}})+\frac{R_f{A}_{\mathrm{Sa}1}(I_{\mathrm{Saf}}-I_{\mathrm{Sbf}})}{\mathrm{<figure-callout\; id="1"\; label="p\; B\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">p</figure-callout>}{B}_{\mathrm{Sa}}{1}_{}+{\mathrm{<figure-callout\; id="1"\; label="C\; Sa"\; filenames="C0112573800322.png,C0112573800333.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{Sa}}}$

… … equation 43

In step S327, the above values are collated with respect to the fault distance p to obtain equation 44:

(m₁+jn₁)p²+(m₂+jn₂)p+(m₃+jn₃)+(m₄+jn₄)R_f＝0

… … equation 44

Wherein,

m₁+jn₁＝Z_L1(I_Sa-I_Sb)B_Sa1，

m₂+jn₂＝Z_L1(I_Sa-I_Sb)C_Sa1-V_SabB_Sa1，

m₃+jn₃＝-V_SabC_Sa1，and

m₄+jn₄＝(I_Saf-I_Sbf)A_Sa1.

in step S328, if equation 44 is divided into real and imaginary parts, and the fault resistance R is eliminated in steps S329 and S330_fAs can be seen in equations 45 and 46 at step S331, the fault distance p can be obtained from the quadratic of the quadratic equation:

m₁p²+m₂p+m₃+m₄R_f＝0

n₁p²+n₂p+n₃+n₄R_f＝0

… … equation 45, and

$(m_1-n_1\frac{m_4}{n_4})p^2+(m_2-n_2\frac{m_4}{n_4})p+(m_3-n_3\frac{m_4}{n_4})=0$

… … equation 46

Fig. 10 is a circuit diagram for explaining a fault locating method when two power line ground short circuits and three-phase short circuits occur during the operation of parallel dual power lines according to the present invention.

Equation 47 is derived as a voltage equation from the two transmission line ground fault circuits shown in fig. 9:

V_Sa-V_Sb＝V_Saf-V_Sbf+V_SaL-V_SbL+V_fa-V_fb+V_ma-V_mb

… … equation 47

Wherein,

V_ma，V_mbis the zero phase-sequence voltage of the non-faulted line,

V_fais the a-phase voltage from the fault point to ground, an

V_fbIs the b-phase voltage from the fault point to ground.

Zero phase sequence voltage V due to non-faulty line_ma＝V_mbEquation 47 can be expressed using equation 48:

V_Sa-V_Sb＝V_Saf-V_Sbf+V_SaL-V_SbL+V_fa-V_fb

… … equation 48

Here, as can be seen from equations 48 and 40, the voltage equation at the relay mounting point at the time of the two-wire ground fault has the same form as the wire-to-wire short circuit, and the fault distance p can be obtained through the same evolution as the fault location of the wire-to-wire short circuit.

According to the present invention as discussed above, in the event of a fault on the transmission line, it is possible to calculate a fault current and a current distribution coefficient usable for predicting the zero phase-sequence current of the non-faulty line which is required for correctly locating the fault and by which it is therefore possible to correctly locate the correct distance from the relay installation point to the fault point. The fault location method of the invention is not affected by the change of the power supply impedance of the background system. In addition, the fault resistance is eliminated through the evolution relational expression according to the fault location algorithm, so that the influence of the resistance of the fault point can be completely eliminated, and therefore the correct fault distance can be calculated.

While the invention has been described with reference to certain preferred embodiments thereof, those skilled in the art will appreciate that various modifications and changes may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (9)

1. A parallel double-output electric wire fault positioning method comprises the following steps:

converting three-phase voltage and current signal values on the power transmission line into small signals;

collecting and storing the converted voltage and current values as data;

comparing the stored voltage and current data with preset reference data to judge faults and fault types on the power transmission line;

if there is a fault on the power line in response to the comparing step, separating and obtaining voltage and current data after and before the fault;

executing a fault positioning algorithm according to the acquired data according to a preset starting mode to obtain a current distribution coefficient, and calculating fault distance and fault information of a fault point by using the current distribution coefficient; and

stores the calculated fault distance and information and transmits the stored fault distance and information to the outside,

wherein the separating and acquiring step uses separating and acquiring 30 cycles of pre-fault voltage and current data of the transmission line and 60 cycles of post-fault voltage and current data.

2. The parallel dual-input electric line fault location method of claim 1, wherein the current distribution coefficients are decomposed into zero, positive and negative phase-sequence current distribution coefficients using symmetric coordinates for processing in each balanced circuit and using the voltages and currents in a fault location algorithm to locate fault points according to parallel dual-input electric line fault types.

3. The parallel dual-input electric wire fault location method according to claim 1, further performing a fault location algorithm when fault occurrence information is input from a protective relay.

4. The parallel dual-input line fault location method of claim 1, wherein the fault location algorithm is performed by discriminating by type of transmission line fault, and in case of a line to ground fault, the following steps are performed:

establishing a voltage equation and eliminating the current in a non-fault line and the other end through data after the fault so as to calculate a zero phase sequence current distribution coefficient;

establishing a voltage equation at the relay mounting point by using the calculated zero-phase-sequence current and the zero-phase-sequence current distribution coefficient;

substituting the current distribution coefficient into the established voltage equation and arranging a relational expression about the fault distance to be divided into a real part and an imaginary part; and

the steady-state resistance is eliminated from the relational expression of the fault distance divided into a real part and an imaginary part, and the relational expression is sorted into quadratic equations with respect to the fault distance to calculate the fault distance.

5. The parallel dual-input electric line fault location method according to claim 1, wherein a fault location algorithm is executed by discriminating according to fault type, and in case of a one-line ground fault, the following steps are executed:

establishing a voltage equation and eliminating the current in the non-fault line and the other end through the data after the fault so as to calculate a positive phase sequence current distribution coefficient;

establishing a voltage equation at the relay mounting point by using the calculated positive phase-sequence current and the positive phase-sequence current distribution coefficient;

substituting the current distribution coefficient into the established voltage equation and arranging a relational expression about the fault distance to be divided into a real part and an imaginary part; and

the fault resistance is eliminated and sorted into quadratic equations with respect to the fault distance to calculate the fault distance.

6. The parallel dual-output electric wire fault location method of claim 5, wherein the fault distance is calculated by using a quadratic form in a quadratic equation.

7. The parallel dual-input electric line fault localization method of claim 1, wherein the fault distance is calculated by using newton-raphson iterative calculations.

8. The parallel dual-input electric line fault localization method of claim 1, wherein the fault localization algorithm is executed by discriminating according to the fault type, and in case of a ground fault and a short circuit of the two lines, the following steps are executed:

establishing a voltage equation through data after the fault and calculating symmetrical voltages at the installation point and the fault point of the relay;

substituting the symmetrical voltage into the established voltage equation so as to calculate a positive phase sequence current distribution coefficient;

substituting the calculated positive phase sequence current distribution coefficient, and sorting a relational expression about the fault distance into a real number part and an imaginary number part; and

the fault resistance is eliminated from the separate relational expression, and the relational expression is collated into a quadratic equation with respect to the fault distance to calculate the fault distance.

9. A parallel dual-input wire fault locating device, comprising:

means for converting three-phase voltage and current signal values on the power line to small signals;

means for collecting and storing the converted voltage and current values as data;

means for comparing the stored voltage and current data with preset reference data to determine faults and fault types on the transmission line;

means for separating and acquiring voltage and current data after and before a fault if there is a fault on the power line in response to the comparison;

means for performing a fault location algorithm according to the acquired data in accordance with a preset start mode to obtain a current distribution coefficient, and for calculating fault information of a fault distance and a fault point by using the current distribution coefficient; and

means for storing the calculated faulty distance and information and transmitting the stored faulty distance and information to the outside,

wherein the collection and storage unit comprises:

the signal adjusting unit is used for adjusting three-phase voltage and current signals on the parallel double-power wires;

a low pass filter for removing high frequency components from the regulated voltage and current signals;

an A/D conversion unit for converting the voltage and current signals from which the high frequency components are removed into digital signals, an

And a storage unit for storing the digital voltage and current data.

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