JPH04299272A - Locating method for ground fault point of ac circuit - Google Patents

Abstract

PURPOSE:To provide an AC circuit capable of reducing the error due to a transient phenomenon to accurately locate a trouble point. CONSTITUTION:The current data from a current detector 2 and the voltage data from a voltage detector 3 are written in the storage region with predetermined capacity of a storage device at a definite time interval to hold a definite number of the newest current data and voltage data in the storage region. When a ground fault is generated, the writing of the current data and the voltage data in the storage region is stopped by the detection output from a ground fault detector 5. Since the current data and voltage data at the time of ground fault are fixed to the storage region by this constitution, the data of one cycle and the data of one cycle different by a half cycle in phase with respect to the data of one cycle are used to operate respective numerical values of reactance or the like corresponding to a ground fault point and the ground fault point is located based on the average value of those numerical values.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for locating a ground fault point in an AC circuit.

0002

[Background Art] Conventionally, for example, when locating a ground fault point in an AC railway feeding circuit, the current and voltage at the time of a ground fault fault and the phase difference between the two are measured, and the reactance value of the circuit is calculated from these values. to calculate the distance to the ground fault point. Note that the reason why the fault point is located based on the reactance value is to avoid the influence of fault point resistance and the like.

0003

[Problem to be solved by the invention] In the conventional method, due to the DC component of the current generated due to the transient phenomenon at the time of a ground fault,
There was a problem in that an error occurred in the calculation of the reactance value, making accurate orientation impossible. In other words, as is well known, if a ground fault occurs in a given phase, the current will immediately enter a steady state and no DC component will be generated, but if a ground fault occurs in any other phase, a transient state will occur. This phenomenon causes a DC component as a transient term in the current, making it impossible to accurately calculate the reactance value of the circuit. Once a predetermined period of time has elapsed from the time of a ground fault, the DC component as a transient component becomes negligible.However, in recent years, the performance of circuit breakers has improved, so in the event of a ground fault, the circuit breaker will operate and Since the fault current lasts only about a cycle, it is impossible to measure the current when the DC component becomes negligible.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a fault point locating method for an AC circuit that can reduce errors caused by transient phenomena and accurately locate the fault point.

[0005]

[Means for Solving the Problems] The present invention provides current data corresponding to the detection output from a current detector that detects the current of an AC circuit, and detection output from a voltage detector that detects the voltage of the AC circuit. Corresponding voltage data is written to a storage area of a predetermined capacity of the storage device at regular time intervals, and a certain number of the latest current data and voltage data are held in the storage area using a first-in, first-out method, thereby preventing ground faults in the AC circuit. The writing of the current data and voltage data to the storage area is stopped by the detection output from the fault detector that detects the occurrence of the ground fault, and the writing of the current data and voltage data to the storage area is stopped, and the 1 cycle of data and 1 whose phase differs by half a cycle from this 1 cycle of data.
The present invention is characterized in that numerical values corresponding to the ground fault points are calculated using the periodic data, and the ground fault points are located using the average value of these numerical values.

[0006]

[Operation] Current data corresponding to the detection output from the current detector that detects the current of the AC circuit and voltage data corresponding to the detection output from the voltage detector that detects the voltage of the AC circuit are collected at regular time intervals. The current data and voltage data are written in a storage area of a predetermined capacity of the storage device in a first-in, first-out manner to hold the latest constant number of current data and voltage data in the storage area. If a ground fault occurs, writing of current data and voltage data to the storage area is stopped based on a detection output from a fault detector that detects the occurrence of a ground fault in the AC circuit. As a result, the current data and voltage data at the time of the ground fault fault are fixed in the storage area, so the data for one cycle of the current data and voltage data at the time of the ground fault stored in the storage area and this one cycle data are fixed in the storage area. Using the data for one cycle whose phase differs by half a cycle from the data for 20 minutes, calculate values such as reactance corresponding to the ground fault point, and locate the ground fault point using the average value of these values. .

[0007]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a fault point locating system used to implement a fault point locating method for an AC circuit in an embodiment of the present invention. In this embodiment, an AC electric railway feeding circuit is employed as the AC circuit. The feeding circuit is equipped with a power source 1, a current detector 2 made of, for example, a CT, a voltage detector 3 made of, for example, a PT, a circuit breaker 4, and a failure detector 5. The output terminals of the voltage detector 2, the voltage detector 3, and the fault detector 5 are connected to the input terminal of the fault point locating device 6. A power source 1 supplies, for example, 50 Hz AC power to the feeding circuit. The current detector 2 detects the current of the feeding circuit and outputs a detection signal corresponding to the current. The voltage detector 3 detects the voltage of the feeding circuit and outputs a detection signal corresponding to the voltage. The circuit breaker 4 opens the feeding circuit when a ground fault occurs. The fault detector 5 detects a fault current when a ground fault occurs and outputs a detection signal. The failure point locating device 6 locates the failure point based on the current and voltage of the feeding circuit at the time of a ground fault.

FIG. 2 is a block diagram of the failure point locating device 6.
The fault location device 6 includes low-pass filters 8 and 9, sample-and-hold circuits 10 and 11, a multiplexer circuit 12, an input/output interface circuit 13, and a CPU.
14, and a storage device 15 consisting of, for example, a RAM. Low-pass filter 8 removes harmonics of the detection signal from current detector 2. Low pass filter 9 removes harmonics of the detection signal from voltage detector 3. The sample-and-hold circuit 10 samples and holds the output of the low-pass filter 8, for example, every 5/3 ms in response to a control signal from the CPU 14. Sample/hold circuit 1
1 samples and holds the output of the low-pass filter 9 at the same timing as the sample-and-hold circuit 10 based on a control signal from the CPU 14. The multiplexer circuit 12 alternately inputs the outputs of the sample and hold circuits 10 and 11 and supplies them to the A/D converter 13. The A/D converter 13 converts the output of the multiplexer circuit 12 into a digital signal and supplies it to the CPU 14. The CPU 14 receives current data according to the detection signal of the current detector 2 and the voltage detector 3.
The voltage data corresponding to the detection signal of is written into the storage device 15. In addition, the CPU 14 connects the power supply 1 and the ground fault point P shown in FIG.
The distance D between the two points is calculated and output to the output terminal 16. The storage device 15 has, for example, Mi1 to Mi1 as current data storage areas.
Address Mi50 is used, and addresses Me1 to Me50, for example, are used as storage areas for voltage data.

Next, the operation will be explained. The current in the feeding circuit is detected by a current detector 2, and an analog signal corresponding to the current is supplied to a failure point locating device 6. This signal has harmonics removed by a low-pass filter 8, sampled by a sample-and-hold circuit 10 every π/6 of the current of the feeding circuit, that is, every 5/3 ms, and then sampled by a multiplexer circuit 12 at a predetermined timing. A/D converter 13
The current data is supplied to the CPU 11, converted into a digital signal, and written to address Mi50 of the storage device 15 as current data. That is, new current data is stored at address Mi50 of the storage device 15 every 5/3 ms, and current data previously stored in the storage device 15 is moved to the previous address. As a result, the current data stored in the most recent Mi1 address is erased. As a result, the storage device 15 always holds the latest 250/3 ms worth of current data. Further, the voltage of the feeding circuit is detected by the voltage detector 3, and an analog signal corresponding to the voltage is supplied to the failure point locating device 6. This signal has harmonics removed by a low-pass filter 9, and is sampled by a sample-and-hold circuit 11 every π/6 of the feeding circuit current, that is, at the same timing as the detection current is sampled by the sample-and-hold circuit 10. - The signal is supplied to the A/D converter 13 at a predetermined timing by the plexer circuit 12, converted into a digital signal, and written by the CPU 11 to address Me50 of the storage device 15 as voltage data. That is, 5/
New voltage data is stored in the memory device 15 Me50 every 3ms.
The voltage data stored at the address and previously stored in the storage device 15 are each moved to the previous address. As a result, the voltage data stored at the Me1 address at the forefront disappears. As a result, the storage device 15 always holds the latest 250/3 ms worth of voltage data. When a ground fault occurs in the feeding circuit, a fault current flows, and the circuit breaker 4 is activated to open the feeding circuit, and the failure detector 5 is activated and a detection signal is supplied to the failure point locating device 6. As a result, the CPU 14 stops writing new data to addresses Mi50 and Me50 of the storage device 15, and causes the storage device 15 to retain the already written data at the time of the ground fault failure.

[0010] Here, the impedance Z of the feeding circuit at the time of a ground fault is expressed by the following equation 1 in a steady state.

[0011]

[Math 1]

[0012] However, R: Resistance of the feeding circuit The real part eI of e: The imaginary part of the voltage e, that is, the reactance X of the feeding circuit is as shown in Equation 2 below.

[0013]

[Math 2]

By the way, if current i and voltage e are decomposed into a real part and an imaginary part using a Fourier series, any 1
Equation 3 below holds true for the period, and Equation 4 below holds true for one period delayed by a half period from this one period.

[0015]

[Math 3]

[0016]

[Math 4]

Substituting the above number 3 into the above number 2, the following number 5 is obtained.
is obtained, and by substituting the above equation 4 into the above equation 2, the following equation 6 is obtained.

[0018]

[Math 5]

[0019]

[Math 6]

[0020] If we take the average of the above equations 5 and 6, we get the following equation 7.
is obtained.

[0021]

[Math 7]

On the other hand, the current detected by the current detector 2 is superimposed with a DC component due to a transient phenomenon at the time of a ground fault, and the resulting error ΔiR in the real part becomes as shown in the following equation 8, and the imaginary part The error ΔiI is as shown in Equation 9 below.

[0023]

[Math. 8]

[0024]

[Math. 9]

That is, when the reactance X is calculated using the above equation 2 using the current value detected by the current detector 2, an error occurs as shown in the following equation 10.

[0026]

[Math. 10]

When the above equation 10 is transformed, it becomes the following equation 11.

[0028]

[Math. 11]

The error ΔX1 in the numerator of the above equation 11 is expressed by the following equation 12, and the error ΔX2 in the denominator of the above equation 11 is expressed by the following equation 13.

[0030]

[Math. 12]

[0031]

[Math. 13]

However, θ1: Phase of voltage e θ2: Phase of current i According to the above equation 12, ΔX1 becomes as shown in FIG. 3, and according to the above equation 13, ΔX2 becomes as shown in FIG. 4, so the error ΔX of reactance X is It changes as shown in FIG. 5 depending on the calculation start phase θ. Note that the calculation start phase θ is m in Equations 3 and 4 above.
= phase at 0. From FIG. 5, reactances X1 and X2 are calculated by shifting the calculation start phase θ by a half cycle, that is, π, as shown in Equations 5 and 6 above, and reactance X is obtained by averaging X1 and X2 as shown in Equations 7 above. It can be seen that the error ΔX is effectively reduced by this. Note that since ΔiR and ΔiI actually decrease with an exponential function, the error ΔX changes as shown in FIG. 6 according to the calculation start time.

The failure point locating device 6 uses the above theory to calculate the reactance X based on the equation 7, and its operation will be explained below with reference to the flowchart shown in FIG. First, in step S1, the CPU 14 reads current data from the current detector 2 and voltage data from the voltage detector 3, and stores them in addresses Mi50 and Me50 of the storage device 15, respectively. At this time, before storing, the contents of addresses Mi2 to Mi50 and addresses Me2 to Me50 are shifted one address forward. As a result, the contents of the original addresses Mi1 and Me1 are erased. This reading is performed every 5/3 ms. Next, the process proceeds to step S2, where it is determined whether or not a detection signal from the failure detector 5 has been input, and if it has not been input, the process returns to step S1. If it has been input, the process advances to step S3, where reading of the current data from the current detector 2 and the voltage data from the voltage detector 3 is stopped, and the contents of the storage device 15 are held as they are. Next, proceeding to step S4, the reactance
Calculate. Next, proceeding to step S5, for example, Mi
Current data from address 16 to Mi27 and Me
Using the voltage data from address 16 to address Me27, reactance X2 is calculated by equations 4 and 6 above. Next, proceeding to step S6, the reactance X is calculated using the above equation 7 using X1 and X2. Next, proceeding to step S7, the distance D between the power source 1 and the ground fault point P is calculated using the following equation 14 using X.

[0034]

[Math. 14]

However, ω: frequency of power supply 1 L: inductance per unit length of the feeding circuit Next, the process advances to step S8, and after outputting the calculated value of distance D to the output terminal 16, the process returns to step S1. Note that the frequency ω and the inductance L
can be known in advance, so the distance D can be determined by equation 14 above.
can be calculated.

In this way, for example, Mi1 of the storage device 15
Reactance X1 is calculated using one cycle of current data from address 0 to Mi21 and one cycle of voltage data from address Me10 to address Me21.
One cycle of current data from address Me16 to M
The reactance X2 is calculated using one cycle of voltage data up to address e27, the average reactance X of these X1 and X2 is calculated, and the distance D is calculated from this X, so the current i due to the transient phenomenon Errors caused by DC components can be effectively reduced, and failure points can be accurately located.

Note that in the above embodiment, the reactances X1,
Although the distance D was calculated by calculating X2 and X, the distance D may also be calculated by calculating a value proportional to the reactances X1, X2 and X. In addition, in the above embodiment, the current and voltage are π/
Although the data was sampled every 6, the sampling interval is arbitrary. Further, in the above embodiment, an AC feeding circuit is used as the AC circuit, but the present invention can of course be applied to other AC circuits.

[0038]

[Effects of the Invention] As explained above, according to the present invention, current data corresponding to the detection output from the current detector that detects the current of the AC circuit and detection from the voltage detector that detects the voltage of the AC circuit are obtained. Voltage data corresponding to the output is written to a storage area of a predetermined capacity of the storage device at regular time intervals, and a certain number of the latest current data and voltage data are retained in the storage area using a first-in, first-out method, thereby preventing ground faults in AC circuits. The writing of current data and voltage data to the storage area is stopped by the detection output from the fault detector that detects the occurrence of a fault, and one cycle of the current data and voltage data at the time of the ground fault fault stored in the storage area is Using the minute data and one period's worth of data whose phase differs by half a period from this one period's worth of data, calculate each numerical value corresponding to the ground fault point,
Since the ground fault point is located using the average value of these numerical values, it is possible to satisfactorily reduce errors caused by the direct current component of the current due to transient phenomena, and the excellent effect of being able to accurately locate the fault point is achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a fault point locating system used to implement a fault point locating method for an AC circuit in an embodiment of the present invention.

FIG. 2 is a block diagram of a failure point locating device.

FIG. 3 is an explanatory diagram of changes in error in the denominator of reactance.

FIG. 4 is an explanatory diagram of changes in reactance numerator error.

FIG. 5 is an explanatory diagram of changes in reactance error.

FIG. 6 is an explanatory diagram of changes in actual reactance error.

FIG. 7 is a flowchart illustrating the operation of the failure point locating device.

[Explanation of symbols]

2 Current detector 3 Voltage detector 5 Fault detector 15 Storage device

Claims (1)

[Claims] Claim 1: Current data corresponding to the detection output from a current detector that detects the current of the AC circuit and voltage data corresponding to the detection output from the voltage detector that detects the voltage of the AC circuit are kept constant. A fault detector that detects the occurrence of a ground fault in the AC circuit by writing data into a storage area of a predetermined capacity of a storage device at time intervals and retaining the latest constant number of current data and voltage data in the storage area using a first-in, first-out method. The writing of the current data and voltage data to the storage area is stopped by the detection output from Using one period's worth of data whose phase differs by half a period from that of one period's data, calculate numerical values corresponding to each ground fault point, and locate the ground fault point using the average value of these numerical values. Characteristic method for locating ground fault points in AC circuits.