EP3123184A1

EP3123184A1 - Arc fault location

Info

Publication number: EP3123184A1
Application number: EP15714621.8A
Authority: EP
Inventors: David Thomas; Mark Sumner; Yang Cao; Jing Li
Original assignee: University of Nottingham
Current assignee: University of Nottingham
Priority date: 2014-03-28
Filing date: 2015-03-27
Publication date: 2017-02-01
Also published as: WO2015145170A1; GB201405585D0

Abstract

The invention relates to arc fault location in electrical power circuits, and in particular to methods of locating series arc faults through analysing transient data. Embodiments disclosed include a method of locating a series arc fault (101) in an electrical circuit (300), the method comprising the steps of: sampling current and voltage data from a supply end (303) and a load end (304) of a transmission line of the electrical circuit (300) over a time period covering a fault event; transforming the sampled data into the frequency domain; for a plurality of estimated locations of the fault, calculating an estimated supply end current and an estimated load end current from the transformed sample data; and determining a location of the series arc fault (101) based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations.

Description

ARC FAULT LOCATION

Field of the Invention

The invention relates to arc fault location in electrical power circuits, and in particular to methods of locating series arc faults through analysing transient data.

Background

Series arc faults typically result from loose and degrading contacts, vibration and conductor breaks. Such faults can be present in otherwise healthy systems and hence can cause significant damage to cables or nearby equipment around if left undetected [see references 1 & 2] . Many different detection schemes have been investigated, which monitor the supply current and use signal processing techniques such as the Fourier Transform, Wavelet Transform, Wavelet packet decomposition and current variation analyses [see references 3-5] to indicate the presence of an arc fault. However, it is important to develop the accuracy and speed of series arc fault location schemes to limit damage and for stable and reliable system protection, especially for protecting systems such as aircrafts, ships and trains, in which it is difficult to remove or isolate the faulted line sections without accurately knowing the fault position.

Various methods have been developed for fault location based on impedance measurement theory. By recording the current and voltage data at both ends of the transmission line (or only at the supply end), the impedance can be calculated [see references 6-9] . A method of active impedance estimation uses an injection unit to apply a very short current transient into the system and analyse the voltage response [see references 9- 1 1] . In such schemes, the majority of fault conditions would have significantly lower impedance than the nominal load, for example a bolted short circuit fault. Hence it is possible to estimate the distance from the signal measurement point to the fault. However, when a series arc fault occurs in the system, the impedance no longer has a linear relationship with the fault position according to the current path in the circuit. In this case, an impedance measurement method would fail to accurately locate the fault.

It is an object of the invention to address one or more of the above mentioned problems. Summary of the Invention

In accordance with a first aspect of the invention there is provided a method of locating a series arc fault in an electrical circuit, the method comprising the steps of: sampling current and voltage data from a supply end and a load end of a transmission line of the electrical circuit over a time period covering a fault event; transforming the sampled data into the frequency domain;

for a plurality of estimated locations of the fault, calculating an estimated supply end current and an estimated load end current from the transformed sample data; and

determining a location of the series arc fault based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations.

The invention provides a new double-ended scheme which is particularly suitable for locating series arc faults. When an arc fault occurs, a short time period of the fault transient data during a fault event can be captured and used for the fault calculation, allowing the method to be used for accurately and quickly locating a series arc fault in an electrical circuit within a specific location or range of locations. The time period may be less than 100 ms, 50 ms, 10 ms or 5 ms, and is optionally greater than 1 ms. Sampling the data over a short period allows for a faster determination of the location of the series arc fault.

The transformed calculated current data may be compared to the estimated current data over a frequency range, for example a range between 5 kHz and 30 kHz. Using a frequency range rather than a single frequency allows for variability in the signals, which may be noisy, to be averaged out, resulting in a more reliable determination of the fault location. The difference between the estimated supply end and load end current data for each of the plurality of estimated locations may therefore be determined from an average value over a range of frequencies.

The frequency range may be generally within the range 5kHz to 70kHz. Optionally, the frequency range may be within the range 5kHz to 30kHz, 5kHz to 50kHz, 30kHz to 50kHz, 30kHz to 70kHz, or 50kHz to 70kHz. The plurality of estimated locations may correspond to an incremental series of locations along a transmission line portion of the electrical circuit between the supply end and the load end. The incremental series of locations may for example be uniformly distributed along the transmission line portion of the electrical circuit.

The method may further comprise repeating the step of calculating the estimated supply end and load end currents for a plurality of estimated locations in the region of the determined location, and determining a location within the region based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations within the region. Iterating the method can narrow down the location from a coarsely defined region to a more narrowly defined region, thereby resulting in a more accurate determination of location without having to greatly increase the overall number of estimated locations. The method may comprise the preceding step of detecting a series arc fault in the transmission line of the electrical circuit, wherein the steps of transforming, calculating and determining are triggered by the detection of a series arc fault in the transmission line. The step of sampling may also be triggered, or alternatively sampling may be operating continuously so that location of the arc fault can proceed immediately upon detection rather than needing to wait until a subsequent arc event.

In accordance with a second aspect of the invention there is provided a system for locating a series arc fault in an electrical circuit, the system comprising:

current and voltage sampling units configured to sample current and voltage data from a supply end and a load end of the electrical; and

a processing unit configured to:

receive sampled current and voltage data circuit from the current and voltage sampling units over a time period covering a fault event;

transform the sampled data into the frequency domain;

for a plurality of estimated locations of the fault, calculate an estimated supply end current and an estimated load end current from the transformed sample data; and determine a location of the series arc fault based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations. The system according to the second aspect of the invention may comprise features corresponding to those described above in relation to the first aspect of the invention.

In accordance with a third aspect of the invention there is provided a computer program for instructing a processing unit to perform the method according to the method of the first aspect. The computer program may be provided in the form of a non-transitory computer-readable medium, such as a computer-readable disc or memory unit. Detailed Description

The invention is described in further detail below by way of example and with reference to the accompanying drawings, in which:

figure 1 is a schematic circuit diagram of an electrical circuit with a series arc fault;

figure 2 is an illustration of a two-conductor transmission line model;

figure 3 is an equivalent circuit of an electrical transmission line with a series arc fault;

figure 4 is a flow diagram of an exemplary method of locating an arc fault; figure 5 is a photograph of an experimental arc fault generation apparatus; figure 6 is a schematic circuit diagram illustrating different possible fault positions in an experimental system;

figures 7a and 7b are current and voltage plots as a function of time for an experimental circuit with an arc fault;

figure 7c is a current plot as a function of a time during arc initiation;

figures 8a-d are plots of current and voltage over time for a supply end and a load end of an experimental circuit with an arc fault;

figure 9 is a plot of the magnitude of current error as a function of frequency for various modelled fault positions with a fault at a first position;

figure 10 is a plot of the magnitude of current error as a function of frequency for various modelled fault positions with a fault at a second position;

figure 1 1 is a photograph of an experimental arc fault generation apparatus; figure 12 is a schematic representation of different possible fault locations in an experimental system on a shaking table;

figures 13a-d are plots of current and voltage over time for a supply end and a load end of an experimental circuit with an arc fault; figure 14 is a plot of the magnitude of current error as a function of frequency for various modelled fault positions and

figure 15 is a schematic diagram of a system according to an embodiment of the invention connected to an electrical circuit.

In accordance with embodiments of the invention, a method of arc fault location is based on impedance estimation. The basis of this method is considered within a simple electrical system 100 as shown in Fig. 1 . Z_s is the supply impedance and Zi_oad is the equivalent load impedance. Assuming Z, is the total transmission line impedance between the supply 102 and the load, Z_x is the line impedance between the supply and the arc fault position, and Z,__x is the remaining part of the line impedance.

The arc fault 101 can be considered as a voltage source, which can impose voltage and current transients over a wide frequency range onto the circuit 100. A first conductor line 103 acts as the supply path while a second conductor line 104 is the return path. The line impedance Z_x can be considered to be made up of a series resistance, a series inductance and a shunt capacitance per unit length. The electrical representation of a line section is shown in Fig. 2. A Thevenin equivalent circuit 300 with the supply short-circuited is shown in Fig. 3. The arc fault 101 provides a voltage transient V_f to the circuit 300 with a fault resistance of R_f.

Two measurement points 301 , 302 are located at the supply end 303 and the load end 304. During the arc fault, as shown in Fig. 3 , the voltage and current at the supply end measurement point 301 can be derived by using Kirchhoff' s voltage law: V[ = V_i - 21_i - ^Zx/₂ ( 1 )

I = I_± - V; - ja>C_x (2) where Ii and Vi are the current and voltage measured at the supply end in the frequency domain by using a Fourier Transform, ^x/₂ is the resistance and inductance of half the length of the line in front of the fault, C_x is the line capacitance of the line, which has admittance of j(oC_x in the frequency domain, and ω is the angle frequency. I is the calculated current passing through the arc fault 101 from the supply end 303.

From the load end 304, similar equations can be derived as follows, v₂' = v₂ + 2i₂ - ^Z(t-*y₂ (3) where I₂ and V₂ are the measured current and voltage at the load end, 1 is the resistance and inductance of half of the remaining line, C t-_¾) ^1S the capacitance of this line, and 1₂' is the calculated current flowing through the arc to the load end.

From Fig. 3 it follows that I should be equal to I₂ , which is the key point of this method as I being equal to I₂ only occurs when the estimated fault position is exactly the same as the actual fault position. If an incorrect position is estimated and calculated, I and I₂ will not match with each other.

Therefore the difference between and I₂ can be used as a reference value to locate the fault. This difference may be defined as the current error.

Current Error = I — I₂ (5) The magnitude of this current error can therefore be used to determine the location of the series arc fault 101.

When the parameters of the transmission line are known, the current error value can be calculated with a defined step increment along the whole length of the line, from the supply end to the load end. From these calculated values, the minimum value indicates that its length corresponds to the real fault position. A more accurate determination of the location of the fault can be determined by increasing the number of increments, up to a resolution limit dependent on various factors (discussed further below) .

Fig. 4 is a flowchart illustrating an exemplary method of series arc fault location based on the double-ended algorithm described above. The current and voltage transient from the supply and load ends are recorded and transformed into the frequency domain using a Fourier transform method. To minimize the edge effects that result in spectrum leakage from FFT, a window function such as a Kaiser Window may be applied onto the data. For each possible fault position, the current error values in the frequency domain can be calculated according to equations ( 1 - 5) above. According to the simulation and experimental results, the current transient tends to have larger low frequency components than high frequency components . It has, however, been found that current error values in the high frequency range from 5 kHz to 30 kHz can provide more accurate and stable results . This range includes a set of points, which can effectively reduce the influence from any single point due to the arc noise.

Referring further to Fig. 4, after the method is started (step 401 ), an initialization step (step 402) sets the line impedance Z and a number N of possible fault positions F_i5 where i ranges from 1 to N. The current and voltage transient data are sampled over a time period (step 403 ), resulting in sampled current and voltage data at the supply end I_s, V_s, and at the load end Ii_oad, i_oad- A frequency transform is applied (step 404), typically by FFT with a window function, to the sampled current and voltage data to obtain current and voltage data in the frequency domain for the supply end I_s(f), V_s(f) and the load end Ii_oad(f), Vi_oad(f) . The method then compares each of the estimated fault positions Fi by calculating the estimated current V from the supply end current and the estimated current V ₂ D from the load end current and deriving a magnitude of the current error from their difference (step 405), i.e. from \ V - V ₂ D \ - The method may for example calculate a current error for each estimated fault location in sequence by starting at i= l and incrementing i each time a current error is calculated (step 406) . Once i reaches N (step 407), the method moves on to the final step of finding a calculated fault position F_k from the estimated fault position Fi having the minimum current error (step 408). The method then ends (step 409) . The method, or at least steps 405 to 408, may be repeated for a narrower range of locations once a coarse range has been defined.

An experimental test has been designed and carried out to verify the method described above. The test circuit consists of an arc generation unit, a LRC cable unit, a resistance load and a DC power supply. Fig. 5 is a photograph showing the arc generation unit 500. A drawn, contact arc is generated by moving two electrodes 501 , 502 apart. A first electrode 501 with a flat surface is held stationary, while a second electrode 502 having a polished point is moved away from the first electrode 501 during the test. These two electrodes 501 , 502 are in contact at the beginning of the test, thereby closing the circuit. A stepper motor is used to control movement of the second electrode 502 away from the first electrode 501 at a constant velocity. This system also provides a feedback signal to track the electrode separation distance.

An LRC cable unit is provided as part of the experimental arrangement, having inductors, resistors and capacitors for simulating a two-conductor transmission line . The parameters of the LRC unit were based on the impedance of a 5 -core, 6mm² armoured cable, having a voltage rating of 300V phase to neutral, 500V phase to phase and a current rating of 40A. The impedance of the core was calibrated by using impedance measurement equipment (an LCR Digibridge) . The parameters of the cable are shown in Table 1 below

Table 1 - Experimental cable parameters

The whole test LRC unit 600 included four identical sections 601 -604 of LRC components . An arc fault could thereby be imposed at five different positions F l to F5 in the unit, as illustrated in Fig. 6. Each LRC section 601 -604, using the model as described in Fig. 2, represented a transmission line of around 300m in length. A resistance load 605 of 58 Ω was located at the end of the LRC cable unit 600. A digital bench power supply was used as the power source 606 having a variable DC voltage output of up to 720 V.

The current and voltage data was measured at both the supply end and the load end. A 4-channel transducer board was built using a current transducer LA55 -P and a voltage transducer LV25 -P (both available from LEM : www. lem.com) . For data capture synchronization, a National Instruments NI 9222 module [see reference 12] was used to capture four channels of data simultaneously.

Before the arc fault location tests, some tests of arc fault generation were carried out. The arc current and voltage during an arc fault are shown in Fig. 7(a) and (b), with the arc current in more detail during initiation of the arc in Fig 7(c) . There is a rapid fall in current at the onset 701 of the arc fault, a gradual fall in current over a long time period 702 during which the second electrode is moving away from the first electrode, and a fall to zero current when arcing stops at an end point 703. Fig. 7(c) shows the arc current as a function of time during the short period of time of onset 701 of the arc fault, covering around 150 ms in total. The data shown in Fig. 7 was obtained using a DC supply voltage of 60 V, a resistance load of 9 Ω, a gap of 2 mm and using a tungsten electrode.

According to the experimental test, arc initiation involves a transient period with some short spikes 704, as shown in Fig. 7(c). These spikes 704 occur when the two charged electrodes begin to separate and the intervening air begins to breakdown, generating an arc. Some spikes last no more than 1ms, while others can last several milliseconds . When such a transient is detected, for example using the current variation method [see reference 1 ], the arc fault location method may be implemented to detect the location of the fault.

A set of tests were carried out with a DC supply voltage of 300V and a resistance load of 58 Ω as described in the experimental setup. Faults could be imposed at five different positions F 1 -F5 of the cable unit 600, as shown in Fig. 6. The measured voltage and current transients during arc initiation from both the supply and load ends are plotted in Fig. 8, with Figs. 8a and 8b showing the supply end and load end currents, and Figs. 8c and 8d the supply end and load end voltages. As can be seen from these plots, only a short period of data covering a fault event, which may be as short as 2ms, is needed for the arc fault location algorithm to operate. In this case, the arc fault was set to occur at the position of F4, corresponding to a location 900m from the source.

After applying the measured voltage and current data to the models of equations ( 1 - 4) above, the current passing through the arc fault can be estimated from the supply end and the load end. A Fourier Transform is then used to present the data in the frequency domain. Based on known impedance parameters of the cables, the current error values in the frequency domain are then calculated for each estimated location, the results of which are shown in Fig. 9. It is initially assumed that the fault may occur at any point from F l to F5, so five curves 901 -905 of the current error values are depicted, corresponding to each respective location F 1 -F5. In the frequency range from 5 kHz to 30 kHz the estimated position of F4, corresponding to curve 904, gives the minimum overall current error value, which indicates the correct fault position is F4. The curve 901 corresponding to a fault position at F l gives the maximum overall current error. This fault point is also the point furthest away from the actual fault position.

The results of a further test with the arc fault at F2 (corresponding to 300m from the source) are presented in Fig. 10. As before, curves 1001 - 1005 correspond to current errors for estimated locations F 1 -F5 respectively. As expected, the minimum overall current error occurs for curve 1002, corresponding to the actual fault location at F2.

A further experimental test has been carried out to verify the method described above in conditions designed to simulate the vibrations caused by aircraft, vehicles or ships. Figure 1 1 shows a picture of an arc generator 1 100. Arc generator 1 100 consists of a fixed ring terminal 1 101 fixed on, and in physical contact with, a threaded part of a copper bolt. A loose ring terminal 1 102 has a loose contact with an unthreaded part of the copper bolt. Movement of the loose ring terminal 1 102 is limited by two fixed nuts on the copper bolt. Arc generator 1 100 sits on the shaker head 1 103 of a shaking table. The shaking table can cause vibrations varying between 8 Hz and 20 Hz.

Before the arc initiation, arc generator 1 100 is steady, and the loose ring terminal 1 102 has physical contact with the copper bolt and fixed ring terminal 1 101 so that a load current can flow through the two ring terminals and the copper bolt. During the experiment, the shaking table is operated to cause vibrations in the arc generator 1 100, creating a gap between loose ring terminal 1 102 and the copper bolt. A series arc is generated between the loose ring terminal 1 102 and the copper bolt. Figure 12 shows a schematic representation of the experimental setup 1200. In the power systems of aircraft or ships, the length of transmission cables is normally less than 100m. For the experiment, therefore, a 3-core 2.5mm² steel wire armored cable of length 100m was used as the transmission line. As shown in figure 12, the 100m cable is cut into six sections, 1201 , 1202, 1203, 1204, 1205, and 1206. Sections 1201 , 1202, 1203, 1204, 1205, 1206 have lengths 2m, 8m, 30m, 50m, 8m, and 2m respectively. Five connectors, C I , C2, C3, C4, and C5 are located between the cable sections. Any of connectors C I , C2, C3, C4, and C5 can be connected to the arc fault generator 1 100. A DC voltage source 1207 providing a voltage of 50V is connected to cable section 1201 , and a load resistance 1208 of 10.3Ω is connected to cable section 1206.

Figure 13 shows the transient of the supply and load side current and voltage used to locate the arc fault location for the case when the fault was located at C5 - i.e. 98m away from voltage source 1207. The above method was applied to these data to produce the frequency dependent current error values shown in figure 14. For the model it was assumed that the fault could be located at any of 1 1 points corresponding to 0m, 10m, 20m, 30m, 40m, 50m, 60m, 70m, 80m, 90m, or 100m along the cable from voltage source 1207. The calculated current error for each of these points is shown in figure 4. The lowest current error, line 1401 , corresponds to the 100m point. This is in very good agreement with the real arc fault location at 98m.

Full test results from the seven possible connection points for arc generator 1 100 (C l - C5, and the connections between voltage source 1207 and cable section 1201 , and load resistance 1208 and cable section 1206) are presented in table 2 below. From these results, a very good accuracy of 10% can be observed.

Table 2 - Shaking table series arc location test results

Error =

Real arc fault Estimated fault

estimated-real „ _ _

location location X 100

total cable length

[m] [m] [%]

0 0 0

2 0 2

10 0 10

40 30 10

90 100 10

98 100 2

100 100 0 Other tests with different fault positions have also been carried out and shown to demonstrate accurate and repeatable results using the same method.

From the results as shown in Fig. 9 and Fig. 10, it can be seen that the waveform of current error tends to vary with frequency. The low frequency range (i.e. 10 kHz and below) tends to have a larger current error value, compared with the higher frequency range ( 10 to 30 kHz). This is due to the current signal having fewer high frequency components than low frequency components, and in addition the window function used can reduce the high frequency components. The method can be further improved by using the average current error across the 50kHz to 70kHz range.

Under ideal conditions, it would be expected that the current error value for a correct fault location should be zero. In experimental tests, however, a small current error value will always be found due to many reasons. Firstly, the arc fault will have noise characteristics, especially during its initiation. The transient data must therefore contain some noise that will inevitably be included in the calculation. Secondly, the parameters of the electrical components for calculation may have a small difference from the real parameters in the system, so the estimated current will be affected and hence the current error values may increase. Thirdly, the limitation of the data acquisition hardware can also induce some error. On the transducer board used in the experimental apparatus, the overall accuracy of the voltage transducer is ±0.9 % and the current transducer is ±0.65 % [see references 13 and 14), which makes the data resolution around 6 bits or even lower, i.e. an accuracy of around 1 in 64 or around 1.5 %. Considering the effects of data acquisition resolution, simulation work has been carried out for further investigation. If the data resolution can be improved to 10 bits, the arc fault location method should be able to locate a series arc fault in a 100 m length transmission line with an accuracy of 5 %, i.e. be able to locate a fault to within a 5 m length. Figure 15 illustrates in schematic form an exemplary system 1500 connected to an electrical circuit 100 of the type shown in figure 1 , the system 1500 being configured to carry out a method of series arc fault location as described above. The system 1500 comprises a processing unit 1501 connected to current sensors 1502, 1503 and voltage sensors 1504, 1505 at a supply end and a load end of the circuit 100. The processing unit 1501 comprises the various components required to sample and analyse data obtained from the current and voltage sensors 1502- 1505 in order to determine a location of a series arc fault 101 in the electrical circuit 100. The processing unit 1501 may also be configured to determine the presence of a series arc fault 101 , for example as disclosed in references 1 -5, which may be used to trigger the processing unit 1501 to begin the process of locating the detected arc fault. The processing unit 1501 may be a general purpose computer or an application specific processor, and is loaded with a computer program that instructs the processing unit to perform the series arc fault location method. The processing unit 1501 may be provided as a single unit, or may be distributed among different components depending on the particular application. The processing unit 1501 may also be configured to receive and process signals from more than one set of sensors. In the case of an electrical system having multiple transmission lines, a single set of sensors may be switchable between the transmission lines or sets of sensors may be provided for each transmission line. The processing unit 1501 may be connected by wired or wireless connections to one or more sets of voltage and current sensors located at the load and supply ends of one or more transmission lines.

In summary, the invention provides a series arc fault location algorithm and system using double-ended data during arc initiation. Experimental tests have been carried out with an arc generation unit, showing that the method can be applied to short transient data from arc initiation to locate the fault, and experimental results indicate that the method can provide a fast and accurate location for a fault. Other embodiments are intentionally within the scope of the invention as defined by the appended claims.

References

[ 1] Y. Xiu, et al., "DC arc fault: Characteristic study and fault recognition," in Electric Power Equipment - Switching Technology (ICEPE-ST), 201 1 1 st International Conference on, 201 1 , pp. 387-390.

[2] A. Wright and C.Christopoulos, Electrical Power System Protection: Chapman & Hall, 1993.

[3] J. Andrea, et al., "Repeatable and calibrated arc fault generator," in Industrial Electronics (ISIE), 2010 IEEE International Symposium on, 2010, pp. 1022- 1026.

[4] M. Naidu, et al., "Arc fault detection scheme for 42-V automotive DC networks using current shunt," Power Electronics, IEEE Transactions on, vol. 21 , pp. 633-639, 2006.

[5] Y. Guo, et al., "Wavelet packet analysis applied in detection of low-voltage DC arc fault," in Industrial Electronics and Applications, 2009. ICIEA 2009. 4th IEEE Conference on, 2009, pp. 4013-4016.

[6] T. Takagi, et al., "Development of a New Type Fault Locator Using the One- Terminal Voltage and Current Data," Power Apparatus and Systems, IEEE Transactions on, vol. PAS- 101 , pp. 2892-2898, 1982.

[7] I. Zamora, et al., "Fault location on two-terminal transmission lines based on voltages, " Generation, Transmission and Distribution, IEE Proceedings-, vol. 143, pp. 1 -6, 1996.

[8] L. Eriksson, et al., "An Accurate Fault Locator with Compensation for Apparent Reactance in the Fault Resistance Resulting from Remote-End Infeed, " Power Engineering Review, IEEE, vol. PER-5, pp. 44-44, 1985.

[9] B. Palethorpe, et al., "System impedance measurement for use with active filter control, " in Power Electronics and Variable Speed Drives, 2000. Eighth International Conference on (IEE Conf. Publ. No. 475), 2000, pp. 24-28.

[ 10] E. Christopher, et al., "Fault location in a zonal DC marine power system using Active Impedance Estimation," in Energy Conversion Congress and Exposition (ECCE), 2010 IEEE, 2010, pp. 3050-3054.

[ 1 1] J. Wang, et al., "Fast dault setection and location for a marine power ststem using system power converters, and active impedance estimation," in Power Electronics, Machines and Drives, 2008. PEMD 2008. 4th IET Conference on, 2008, pp. 597-601.

[ 12] "NI 9222/9223, Operating Instructings and Specifications," National Instruments.

[ 13] "Voltage Transducer LV25-P Data Sheet, LEM. "

[ 14] "Current Transducer LA55-P Data Sheet, LEM. "

[ 15] WO 2013/079933 Al : Fault location in power distribution systems

Claims

1. A method of locating a series arc fault in an electrical circuit, the method comprising the steps of:

sampling current and voltage data from a supply end and a load end of a transmission line of the electrical circuit over a time period covering a fault event; transforming the sampled data into the frequency domain;

2. The method of claim 1 wherein the time period is less than 100 ms, 50 ms, 10 ms or 5 ms, and optionally greater than 1 ms.

3. The method of claim 1 or claim 2 wherein the transformed calculated current data is compared to the estimated current data over a frequency range.

4. The method of claim 3 wherein the frequency range is within the range 5kHz to 30kHz, 5kHz to 70 kHz, 30kHz to 50kHz, 30kHz to 70kHz, or 50kHz to 70kHz.

5. The method of claim 3 or claim 4 wherein the difference between the estimated supply end and load end current data for each of the plurality of estimated locations is determined from an average value over the frequency range.

6. The method of any preceding claim wherein the plurality of estimated locations correspond to an incremental series of locations along a transmission line portion of the electrical circuit between the supply end and the load end.

7. The method of claim 6 wherein the incremental series of locations are uniformly distributed along the transmission line portion of the electrical circuit.

8. The method of any preceding claim comprising repeating the step of calculating the estimated supply end and load end currents for a plurality of estimated locations in the region of the determined location, and determining a location within the region based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations within the region.

9. A system for locating a series arc fault in an electrical circuit, the system comprising:

a processing unit configured to:

transform the sampled data into the frequency domain;

for a plurality of estimated locations of the fault, calculate an estimated supply end current and an estimated load end current from the transformed sampled data; and determine a location of the series arc fault based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations.

10. The system of claim 9 wherein the time period is less than 100 ms, 50 ms, 10 ms or 5 ms, and optionally greater than 1 ms.

1 1. The system according to claim 9 or claim 10 wherein the processing unit is configured to compare the transformed calculated current data to the estimated current data over a frequency range.

12. The system of claim 1 1 wherein the frequency range is within the range 5 kHz to 70 kHz, 5kHz to 30 kHz, 30kHz to 50kHz, 30kHz to 70kHz, or 50kHz to 70kHz.

13. The system of claim 1 1 or claim 12 wherein the processing unit is configured to determine the difference between the estimated supply end and load end current data for each of the plurality of estimated locations from an average value over the frequency range.

14. The system of any one of claims 9 to 13 wherein the plurality of estimated locations correspond to an incremental series of locations along a transmission line portion of the electrical circuit between the supply end and the load end.

15. The system of claim 14 wherein the incremental series of locations are uniformly distributed along the transmission line portion of the electrical circuit.

16. The system of any one of claims 9 to 15 wherein the processing unit is configured to repeat calculating the estimated supply end and load end currents for a plurality of estimated locations in the region of the determined location, and to determine a location within the region based on a minimum difference between the estimated supply end and load end current data for one of the plurality of estimated locations within the region.

17. A computer program for instructing a processing unit to perform the method according to any one of claims 1 to 8.