EP2082248A1

EP2082248A1 - Apparatus for measuring impedance of trolley line and method of locating fault using the same

Info

Publication number: EP2082248A1
Application number: EP07745871A
Authority: EP
Inventors: Myung-Soo Jeon; Dong-Ho Lee
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-09-21
Filing date: 2007-04-09
Publication date: 2009-07-29
Also published as: KR100821702B1; EP2082248A4; KR20080026712A; WO2008035841A1

Abstract

The present invention provides an apparatus for measuring the impedance of a trolley catenary. The apparatus is mounted on a crossing which includes a pantagraph connected to a trolley line and a ground part connected through a rail and which is movable on the rail. The apparatus includes a power analysis unit (P) disposed between the pantagraph and the ground part and adapted to measure a voltage, a current and a power factor; and a current limiter (110) connected in series between a rear end of the power analysis unit and the ground part. As described above, the present invention is advantageous in that it can measure the impedance of a trolley catenary by adjusting an actual fault current, which is currently being activated.

Description

APPARATUS FOR MEASURING IMPEDANCE OF TROLLEY LINE AND METHOD OF LOCATING FAULT USING THE

SAME

Technical Field

[1] The present invention relates, in general, to fields of the measurement of the impedance of a trolley catenary and, more particularly, to an apparatus for measuring the impedance of a trolley catenary and a method of localizing a fault using the apparatus, which can measure the line constants of the trolley catenary and analyze the status of a fault through an actual system without applying shocks to a power system, in order to detect a fault location when a ground fault occurs in a distribution system for supplying power, and to determine and analyze the status of variation in power flow when a protective relay is out of order.

[2]

Background Art

[3] Generally, a power system is always supplied with voltage and exposed to external environments, so that there exists a probability that a fault occurs due to contact with foreign materials or external shocks, as well as variation in temperature, humidity and wind. In particular, as a power system for an electric railroad consistently undergoes sudden load variation, power equipment is continuously stressed, and is then operated in abnormally harsh conditions compared to typical power equipment.

[4] Therefore, it is impossible to fundamentally prevent the occurrence of faults, and so there is a need to promptly detect and recover a fault location while minimizing the range of a fault when a fault occurs, thus promptly eliminating the fault.

[5] Therefore, a precise fault location must be calculated by a distance relay or a fault localization device installed in a substation. For this operation, the impedance R+jX from a reference point to a fault location is calculated by a distance relay or fault localization device installed in a substation or a Sectioning Post (SP), and is divided by an impedance value per unit distance, so that the distance to the fault location is calculated. Therefore, it is essential to obtain a precise impedance value to detect a precise fault location or to perform the precise operation of a protective relay.

[6] However, as shown in FIGS. 1 and 2, the impedance of a trolley catenary does not linearly increase in proportion to distance, but increases (T-R short circuit impedance) while forming a mountain-shaped curve between the locations at which a Connector of a Protective Wire (CPW) (measurement point ©) and an Autotransformer (AT) (measurement point ©) are located, because the CPW or the AT is installed at a plurality of spaced locations of a feeder line (F), unlike the impedance of a typical feeder line (F) that linearly increases in proportion to distance (T-F short circuit impedance). Further, since the value of impedance varies according to a method of installing a feeder line (F), a trolley line (T), a rail (R) or a Protective Wire (PW) and the installation location thereof, it is impossible to perform precise calculation. Therefore, in order to obtain precise line constant data corresponding to distance, the line constant data must necessarily be obtained by actual measurement.

[7] Line constants may include a serial impedance Z (resistance, inductance), parallel admittance Y (capacitance and leakage conductance), etc. Of the line constants, the line impedance Z acts on a power system in series, and is thus related to fault current, voltage drop, fault localization and the correction of a protective relay.

[8] In the prior art, a method of actually short-circuiting a system by applying low voltage and low current with the same frequency to measure line constants has been used. However, such a method is disadvantageous in that it must interrupt the traveling of an electric car and decrease a voltage to perform a test. Further, since this method simulates a ground fault in an actual system, a serious shock is applied to power equipment, such as a transformer or a current transformer (CT), due to a high fault current. Accordingly, such a method shortens the lifespan of the power equipment and becomes the cause of damage to the power equipment.

[9]

Disclosure of Invention

Technical Problem

[10] Accordingly, the present invention has been made keeping in mind the above problems, and an object of the present invention is to provide a scheme, which safely measures and detects the impedance of all sections of a trolley catenary by effectively adjusting a ground fault current, and which easily and precisely measures the impedance of a line without applying shocks to power equipment even if a high voltage is not interrupted, or the traveling of an electric car on a railroad.

[H]

Technical Solution

[12] In order to accomplish the above object, the present invention provides an apparatus for measuring an impedance of a trolley catenary, the apparatus being installed on a crossing, which includes a pantagraph connected to a trolley line and a ground part connected through a rail and which is movable on a rail, comprising a power analysis unit disposed between the pantagraph and the ground part and adapted to measure a voltage, a current and a power factor; and a current limiter connected in series between a rear end of the power analysis unit and the ground part. [13] Preferably, the apparatus may further comprise an input terminal switch controlled by an overcurrent relay, the power analysis unit being connected to a line between the input terminal switch and the ground part via the overcurrent relay.

[14] Preferably, the current limiter may be implemented using an inductor having an equivalent resistor. [15] Preferably, the inductor may comprise a plurality of taps to provide a variable inductance. [16] Preferably, the current limiter may be an inductor having an equivalent resistor coupled to a transformer through a coil connected to a motor load circuit. [17] In addition, the present invention provides a method of localizing a fault using the apparatus for measuring the impedance of the trolley catenary, comprising the steps of (a) locating the trolley catenary impedance measurement apparatus at a test point; (b) measuring a voltage(V ), a current (I ), and a power factor (cosΦ ) through a power supply stage of the trolley catenary; (c) measuring a voltage(V ), a current (I ), and a power factor (cosΦ ) through a power analysis unit (P ) of the apparatus in syn- m m chronization with the step (b); and (d) determining a trolley catenary impedance (Z ) at the test point using the following equation

where

R ^ cosΦ, and

[18]

Vi - 1 V, - 1

XΛ = sin(cos COs O₁)- sin(cos cosΦ_m)

[19] Preferably, the method may further comprise the steps of selecting a plurality of test points from a test target line section, and repeating the steps (a) to (d); and expressing line impedances corresponding to distances in the target line section as functions.

[20] Preferably, the method may further comprise the step of measuring a line impedance through the power supply stage, and reading a distance corresponding to the line impedance from the functions, thus determining a fault location.

[21] Hereinafter, preferred embodiments are provided to facilitate the understanding of the present invention. The following embodiments are provided to help the easy understanding of the present invention and are not intended to limit the present invention.

[22] Brief Description of the Drawings

[23] FIG. 1 illustrates the entire electric distribution system for a railroad car;

[24] FIG. 2 illustrates the shape of impedance relative to the distance of a trolley catenary;

[25] FIG. 3 illustrates an embodiment of an apparatus for measuring the impedance of a trolley catenary;

[26] FIG. 4 illustrates an equivalent circuit of an apparatus for measuring the impedance of a trolley catenary; and

[27] FIG. 5 illustrates another embodiment of an apparatus for measuring the impedance of a trolley catenary.

[28]

Best Mode for Carrying Out the Invention

[29] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[30] FIG. 1 illustrates the entire electric distribution system for a railroad car. A left portion of the drawing indicates a substation which is a power supply stage, and a right portion thereof indicates a trolley catenary. A trolley line T, a rail R, a feeder line F, and a protective wire PW are sequentially shown from the upper portion. Typically, fifty thousand volts is applied as a feeding voltage, and twenty five thousand volts is used as a voltage to be applied to the trolley catenary. As shown in FIG. 1, auto- transformers (ATs) are installed at regular intervals on the trolley catenary for railroad cars, and the rail R has a Connector of a Protective Wire (CPW) connected to the Protective Wire (PW).

[31] When the line constant (impedance) of the trolley line T is measured using the start point of the trolley catenary as a reference location, the line constant typically increases according to distance. However, as shown in FIG. 2, the impedance of the trolley catenary increases while forming a curve that indicates the shape of impedance relative to the distance of the trolley catenary for railroad cars, due to the influence of the ATs or the CPW installed at a plurality of spaced locations of the feeder line F. Therefore, since the impedance of the trolley catenary is different from that of a typical feeder line F that linearly increases in proportion to distance, it is difficult to calculate the impedance of the trolley catenary using operation. Accordingly, if line impedances relative to distances are measured in advance through direct measurement and are expressed as functions, a fault location can be precisely detected using the functions when a fault occurs.

[32] However, when a voltage of twenty five thousand volts is directly grounded, a high fault current of several thousand amperes flows and applies great shocks to power equipment, thus resulting in a serious risk, such as the shortening of the lifespan of the equipment or explosion of the equipment when the power equipment is tested several times.

[33] Therefore, as shown in FIG. 3, an apparatus 100 for measuring the impedance of a trolley catenary is installed on a crossing provided with a pantagraph for connecting to the trolley line T and a ground part connected through the rail R, and is constructed so that a current limiter 110, capable of adjusting the amount of current flowing between the pantagraph and the ground part, is provided to be able to measure impedance using appropriate current. Since the measurement of the impedance of the trolley catenary can be performed during the traveling of the crossing, a frequency to be used is preferably a commercial frequency.

[34] The current limiter 110 includes an equivalent resistor R and an inductor m connected in series between the rear end of a power analysis unit P and the ground m part. The inductor generates inductance and provides a reactance X , which will be described later. The current limiter 110 is connected in series between the pantagraph and the ground part, and includes taps formed to provide a variable inductance, thus limiting the amount of current. Accordingly, the amount of current flowing from the pantagraph to the ground part can be limited.

[35] The trolley catenary impedance measurement apparatus 100 is constructed such that a voltage transformer PT for transforming a high AC voltage into a low standard voltage and an input terminal switch CB controlled by an overcurrent relay OCR are provided under the pantagraph connected to the trolley line T, thus enabling the measurement apparatus 100 to be protected from overcurrent, and such that the power analysis unit P connected to the line between the input terminal switch CB and the m ground part through the overcurrent relay OCR is provided, thus individually measuring a voltage V , a current I , and a power factor cosΦ . m m m

[36] When such a trolley catenary impedance measurement apparatus 100 is used, a voltage V , a current I , and a power factor cosΦ are measured by the power analysis unit P of a power supply stage, and the voltage V , the current I and the power factor

1 m m cosΦ are measured by the power analysis unit P of the impedance measurement m m apparatus 100, and thus a trolley catenary impedance Z =R +jX can be determined using the following measurement.

[37] FIG. 4 illustrates a simplified impedance equivalent circuit in a state in which the trolley catenary impedance measurement apparatus, including the power analysis unit P of FIG. 4, is connected. If it is assumed that voltages, currents and power factors re- m spectively measured by the power analysis units P and P , are V , I , and cosΦ , and V , I , and cosΦ , the following Equations: m m m

[38] Equation 1 [39]

[40] Equation 2 [41]

V_m = (R_m+jX_m)I_m

[42] are satisfied, and I = I are satisfied, so that, when the following relations are used,

1 m [43]

[44]

[45] the following Equations, [46] Equation 3 [47]

V₁

^ ₁ = COsO₁ - cosφ m

/ m„ m

[48] Equation 4 [49]

V₁ - 1 V m, - 1

Xy = sin(cos COsO ₁)- sin(cos cosφ_m)

I m I m.

[50] are obtained. On the basis of the above Equations, the trolley catenary impedance Z

1 =R1 +jX1 is determined using the measured values V 1 , I1 , and cosΦ l and Vm , Im , and cosΦ .

[51] A method of localizing a fault using the above trolley catenary impedance measurement apparatus 100 is described below. [52] First, the taps of the trolley catenary impedance measurement apparatus are adjusted, so that the amount of current flowing through the measurement apparatus is limited to a certain amount, and thus the measurement apparatus is connected both to the pantagraph and to the ground part. Thereafter, (a) when the trolley catenary impedance measurement apparatus is located at a test point, (b) voltage V , current I and power factor cosΦ are measured by the power analysis unit P of the power supply stage of the trolley catenary. In this case, (c) the trolley catenary impedance measurement apparatus measures voltage V , current I , and power factor cosΦ using m m m the power analysis unit P .

[53] Thereafter, (d) the line impedance Z =R +jX at a moving position is determined using Equations 3 and 4 indicating correlation equations based on the voltages, currents and power factors measured by the power analysis units P and P .

[54] In this case, a plurality of test points are selected from a test target line section, and the above steps (a) to (d) are repeatedly performed, so that test results can be expressed as functions of line impedances relative to distance in the target line section. In this case, when a fault occurs, the power supply stage measures line impedance and reads a distance corresponding to the line impedance from the functions, thus determining a fault location.

[55] The power analysis unit P of the power supply stage and the power analysis unit P

1 m of the impedance measurement apparatus are operated to be synchronized with each other. Further, the function of allowing the values measured by the power analysis unit P to be received in real time by the power analysis unit P of the impedance measurement apparatus through communication, and calculating the impedance at the location through which the trolley catenary impedance measurement apparatus passes, is provided. Contrary to the above method, it is possible for the power analysis unit P of the substation to calculate the data measured by the power analysis unit P of the m measurement apparatus, and it is also possible to synchronize the power analysis unit P of the substation and the power analysis unit P of the measurement apparatus with

1 m each other, to respectively receive required data and to subsequently calculate the data.

[56] Further, impedance values relative to distances calculated at corresponding locations can be expressed as a distance-impedance graph and can be used as the impedance trace of an actual system. The impedance values can be calculated for respective orders of harmonics.

[57] Both a method of installing the trolley catenary impedance measurement apparatus of the present invention on a separate crossing to perform measurement, as described above, and a method of installing the measurement apparatus of the present invention in an electric car in travel and measuring the trolley catenary impedance, are possible.

[58] FIG. 5 illustrates an example of the installation of the measurement apparatus of the present invention in an electric car in travel, which shows that a current limiter 110, implemented using an inductor that has an equivalent resistor coupled to a transformer through a coil, is connected to the motor load circuit of the electric car. A transformer PT and a current transformer CT installed in the control device of the electric car can be used for the purpose of this invention, so that the load current and load factor of the electric car measured by the power analysis unit P are compared to data measured by the power analysis unit P installed in a substation, on the basis of the voltage of a load stage. Accordingly, the complex impedance of the trolley catenary is calculated by summing the impedance at the location, through which the electric car passes, and the impedance at the location (substation), at which P is installed, using the same method as the trolley catenary impedance measurement method. Impedance values relative to distances at respective locations are calculated in association with the distances between the passing locations of the electric car and the starting point thereof, and thus an impedance trace based on the impedance values is created and utilized.

[59] Meanwhile, those skilled in the art will appreciate that the present invention is not limited to the above preferred embodiments, and various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. It should be notified that, when the implementations of the modifications, additions and substitutions belong to the scope of the accompanying claims, the technical spirit thereof also belongs to the scope of the present invention.

[60] As described above, the present invention is advantageous in that it adjusts an actual fault current, which is currently being activated, thus measuring the impedance of the trolley catenary.

[61]

Industrial Applicability

[62] As described above, the present invention is advantageous in that it adjusts an actual fault current, which is currently being activated, thus measuring the impedance of a trolley catenary. In particular, the calculation of a line impedance is difficult in a power feed system, such as for an electric railroad, so that the line resistance and reactance, which will appear when a fault occurs, are detected using the apparatus and method of the present invention, and impedances corresponding to respective locations are arranged into a database, thus precisely detecting a fault location and perfectly protecting the protection sections of a distance relay when a fault occurs. It is apparent to those skilled in the art that the present invention can also be usefully applied to a typical high voltage distribution system as well as a distribution system for electric cars.

Claims

[1] An apparatus for measuring an impedance of a trolley catenary, the apparatus being installed on a crossing, which includes a pantagraph connected to a trolley line and a ground part connected through a rail and which is movable on a rail, comprising: a power analysis unit disposed between the pantagraph and the ground part and adapted to measure a voltage, a current and a power factor; and a current limiter connected in series between a rear end of the power analysis unit and the ground part.

[2] The apparatus according to claim 1 , further comprising an input terminal switch controlled by an overcurrent relay, the power analysis unit being connected to a line between the input terminal switch and the ground part via the overcurrent relay.

[3] The apparatus according to claim 1, wherein the current limiter is implemented using an inductor having an equivalent resistor.

[4] The apparatus according to claim 3, wherein the inductor comprises a plurality of taps to provide a variable inductance.

[5] The apparatus according to claim 3, wherein the current limiter is an inductor having an equivalent resistor coupled to a transformer through a coil connected to a motor load circuit.

[6] A method of localizing a fault using the apparatus for measuring the impedance of the trolley catenary disclosed in any of claims 1 to 5, comprising the steps of:

(a) locating the trolley catenary impedance measurement apparatus at a test point;

(b) measuring a voltage (V ), a current (I ), and a power factor(cosΦ ) from a power supply stage of the trolley catenary;

(c) measuring a voltage (V ), a current (I ), and a power f actor (cosΦ ) through a power analysis unit (P ) of the apparatus in synchronization with the step (b); m and

(d) determining a trolley catenary impedance (Z ) at the test point using the following equation:

Z₁ =R^jX₁ where

V₁ V m,

* l = COSO₁ - cosφ

I m I m m and

V₁ V_n

Xy = sin (cos COsO₁ )- sin (cos cosφ_m)

[7] The method according to claim 6, further comprising the steps of: selecting a plurality of test points from a test target line section, and repeating the steps (a) to (d); and expressing line impedances corresponding to distances in the target line section as functions.

[8] The method according to claim 6, further comprising the step of measuring a line impedance through the power supply stage, and reading a distance corresponding to the line impedance from the functions, thus determining a fault location.