GB2498563A

GB2498563A - Determination of the location of an electrical fault or disturbance

Info

Publication number: GB2498563A
Application number: GB1200986.6A
Authority: GB
Inventors: Andrew Ceri Davis
Original assignee: GE Aviation Systems Ltd
Current assignee: GE Aviation Systems Ltd
Priority date: 2012-01-20
Filing date: 2012-01-20
Publication date: 2013-07-24
Also published as: FR2986074B1; GB201200986D0; CA2801478A1; US20130187662A1; CN103217594A; FR2986074A1; JP2013156247A; BR102013001428A2

Abstract

The location of an electrical disturbance, e.g. a short or open circuit or lightning strike, in an electrical system comprising one power supply 20 and several distribution legs 1, 2, ¦.., N, is determined from the relative phase of current and voltage waveforms across an inductance L1, L2, ¦., LN of a portion of a circuit. If the current leads the voltage, then the fault is on that leg of the system. If the current lags the voltage, then the fault is on another leg. The relative phase of the current and voltage waveforms across the inductance may be determined by calculating the sign (positive or negative) of the inductance, using a controller 30 that measures both current and voltage. If a fault is detected, the controller may open an isolating switch 40 to shut down that leg whilst leaving other legs operational. The electrical system may be on an aircraft.

Description

DETERMINATION OF THE LOCATION OF AN ELECTRICAL

DISTURBANCE

This invention relates to determining the location of an electrical disturbance in one or more circuits which may be caused, for example, by a fault such as a short circuit or an open circuit or by a lightning strike.

In many applications, a single power source is connected to a plurality of electrical loads. For example, in an aircraft a single power source may supply various loads such as cockpit instruments, air supply, environmental controls etc. A short circuit or open circuit wiring fault may cause an electrical arc to occur resulting in further damage. Large parts or all of the circuit may be closed down to prevent damage being caused to the various parts of the circuit as it is not generally known from which part of the circuit the electrical disturbance originates. However, it would be desirable not to have to close down all or large parts of the circuit in the event of an electrical disturbance.

This is especially true if an external electrical event such as lightning is mistaken for an arc fault, resulting in erroneous disconnection of fully operational circuits.

According to a first aspect of the present invention there is provided an apparatus for determining the location of an electrical disturbance in a circuit.

The apparatus has one or more sensors for determining the relative phase of current and voltage waveforms across the inductance of a portion of the circuit produced by a voltage or current perturbation and a controller arranged to identify the location of the electrical disturbance within the circuit from the relative phase of the current and voltage waveforms.

Being able to determine the location of an electrical disturbance, for example within a particular distribution leg from a plurality of distribution legs connected to a single power source, enables just the leg affected by the electrical disturbance to be isolated. The remaining portions of the circuit, such as various other loads for other components and the power source may continue in operation. This provides belier availability of the overall electrical network such that it is more reliable.

Determining the relative phase of current and voltage waveforms across the circuit inductance produced by a voltage or current perturbation provides a reliable indicator of the location of the electrical disturbance, even in electrically noisy environments.

If, in a particular distribution leg, a current waveform produced by an electrical disturbance is before a voltage waveform, then the location of the electrical disturbance can be identified as being in that particular distribution leg. That particular distribution leg may then be isolated, for example using a switch. If the current waveform produced by an electrical disturbance is not before the voltage waveform, then the location of the electrical disturbance can be identified as being elsewhere, for example on the power source side of the circuit or in another distribution leg.

The relative phase of the current and voltage waveforms across the circuit inductance may be determined by calculating the sign (positive or negative) of the inductance at a particular point in the circuit.

According to a second aspect of the present invention there is provided a method for determining the location of an electrical disturbance in a circuit.

The method comprises determining the relative phase of current and voltage waveforms across the circuit inductance of a portion of the circuit produced by a voltage or current perturbation in the circuit and identifying the location of the electrical disturbance within the circuit from the determined relative phase of current and voltage waveforms in that portion of the circuit.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a schematic example of a circuit with a plurality of distribution legs and apparatus in accordance with an embodiment of the present invention for determining the location of an electrical disturbance within the circuit; Figure 2 shows a more detailed example of a circuit with an apparatus in accordance with an embodiment of the present invention; Figure 3 shows examples of waveforms produced in the circuit of Figure 1 or Figure 2 when the disturbance is on the load side of the circuit; Figure 4 shows examples of waveforms produced in the circuit of Figure 1 or Figure 2 when the disturbance is on the source side of the circuit; and Figure 5 shows a technique to reduce noise effects when determining the location of the electrical disturbance within the circuit.

Figure 1 shows an example of a circuit 10 having a plurality of distribution legs 1,2... N each connected to a single power source 20. Each distribution leg 1,2,..N has an inherent inductance Li, L2...LN. Each distribution leg 1,2...N has an electrical load to supply electrical power to, a particular electrical component. In an aircraft, for example, these may include cockpit instruments, air supply, environmental controls and/or any other electrical equipment. At least one of the distribution legs includes a controller 30 for determining the relative phase of current and voltage waveforms across the circuit inductance Li,L2. . . LN of that particular distribution leg 1,2.. .N produced by a voltage or current perturbation, such as a fault, short circuit, open circuit or lightning strike somewhere in the overall circuit 10. From the relative phase of the current and voltage waveforms, the controller 20 is able to identify the location of the electrical disturbance within the circuit 10. For example, if the controller in distribution leg 1 detects that a current waveform in that distribution leg produced by the electrical disturbance is before a corresponding voltage waveform, then the location of the of the electrical disturbance can be identified as being in that particular distribution leg 1. That particular distribution leg 1 may then be isolated from the remainder from the circuit 10, for example using switch 40. If, the current waveform in distribution leg 1 produced by an electrical disturbance is not before the corresponding voltage waveform, then the location of the electrical disturbance can be identified as being elsewhere, for example in the power source 20 side of the circuit 10 or in another distribution leg 2... N. Figure 2 shows a more detailed example of the circuit 10, but with only one distribution leg 1 illustrated. Power from the source 20 is fed to the isolation switch 40 via a cable 21 with inherent inductance LS. The power is fed out from switch 40 to the load via a second cable 22 with inherent inductance Li.

The controller 30 measures the perameters Vs (voltage to return) and the current I (load current) in the second cable 22. The controller 30 is arranged to measure the voltage V5 by any suitable means such as, for example, a suitable volt meter and to measure the current I by any suitable means such as, for example, a suitable ammeter. In this example a signal indicative of the voltage Vs is communicated to the controller 30 via line 31 and a signal indicative of the current I is communicated to the controller 30 via a line 32.

If a fault is introduced into the distribution leg 1 of the circuit, the power source may experience periodic voltage perturbations. The fault may, for example, be a result of a short circuit, open circuit or lightning event and may produce an arc which may be in series with the load or may arc to ground across the load resulting in a parallel arc. The load may have a complex, unknown impedence that may be represented as a parallel resistance R and capacitance C as illustrated in figure 2.

A convenient method of determining the relative phase of the voltage and current waveforms across the inductance Li of the distribution leg 1 during an electrical disturbance is by calculating the sign (positive or negative) of the inductance Li of the distribution leg 1. If V5 I and Vc (the voltage across the capacitive component C of the load) are known, for example by measurement, then the inductance Li of the distribution leg 1 can be calculated from the formula: VL= Li. di/dt where VL = V5 -Vc Vc is not measured. As the average voltage across the inductance Li of the distribution leg 1 is zero, V0 can be approximated by a low pass filtered version of V5 shown as Vc'.

When the inductance LI of the distribution leg 1 is calculated from V5, Vc' and I, it is has been found that perturbations occurring outside the distribution leg 1 result in a positive value for Li while perturbations occurring within distribution leg 1 result in a negative value for Li. Determining the sign (positive or negative) of the value of Li while the voltage and/or current are perturbed, enables the location of the electrical disturbance being either within the distribution leg 1 or externally of the distribution leg 1 to be determined.

The controller 30, which may be housed within the switch 40 or separately from the switch or from the entire circuit 10, for example in an external control system, microprocessor or computer for example, could measure Vs and I, and calculate vj and Li and thus determine the presence of a fault or arc within the distribution leg 1.

In order to reduce the likelihood or errors, for example from electrical noise within the circuit, additional filtering and/or event counting can be included to gain confidence in the detection of the presence of a fault in a particular distribution leg 1. That distribution leg may then be isolated for example by the controller 30 arranging for the opening of switch 40 via control line 33.

The inductance Li of the distribution leg 1 and the approximated value of the voltage across the capacitive component of the load Vcl can be determined using the equations provided below. The equations are presented in discrete time and the annotation n, n-i denote the latest and previous values of a perimeter through successive calculation cycles.

A= (i-k) (V5(n)-Vc'(n-i)) where k is a filter constant with a typical value of approximately 0.1 Li= t. AI(l(n)-l(n-l)) where t is the sample time interval Vc(n)= Vs(n)-A when used in a circuit 10 with a plurality of distribution legs 1,2...N as shown in figure 1 for example, a controller 30, for determining the presence of a fault may be provided in each distribution leg 1,2... N if desired.

Figure 3 shows examples of voltage (V5) and current (I) waveforms produced across the inductance Li in a distribution leg 1 when a fault occurs in that distribution leg 1. As can be seen, the voltage waveform occurs after the current waveform. In particular the voltage peak occurs after the current peak.

As also shown in figure 3 a detected inductance Li in the distribution leg 1 will have a negative value at the time of the electrical disturbance.

Figure 4 shows an example of the voltage and current waveforms produced in a distribution leg resulting from an electrical disturbance external to that distribution leg, for example on the source side of the circuit or in a different distribution leg 2... N. As can be seen in the waveforms of figure 4, in this example the voltage Vs waveform occurs before the current I waveform. In particular the peak voltage Vs occurs before the peak current I. As also shown in figure 4, the inductance Li in the distribution leg i has a positive value during the electrical disturbance. Since the voltage (Jo) waveform occurs before the current (I) waveform and the inductance Li in the distribution leg 1 has a positive value, it may be determined that the disturbance occurred externally to the distribution leg 1, for example on the source 20 side of the circuit 10 or in another distribution leg 2.. .N.

An indication of the location of an electrical disturbance within a circuit, for example whether on the load side or source side of a circuit and/or within which one of a number of distribution legs may result in isolation of that part of the circuit such that the remainder of the circuit may continue in operation. An indication of the part of the circuit which suffered the electrical disturbance may also be provided to a user, such as on a display panel or graphical user interface such that a user is able to examine that part of the circuit which experienced the electrical disturbance.

Figure 5 shows a technique to reduce noise effects when determining the location of an electrical disturbance within the circuit 10. In this example samples of the voltage V and current I are taken at each of a number of time windows 100,200,300 simultaneously in each waveform V3, I. The results from each waveform V5, I may be averaged over a plurality of the time windows 100,200,300 to obtain an average, reducing noise effects and providing more precise results. Clearly any appropriate number of time windows may be used and the windows may be of any appropriate length.

Many variations may be made to the examples described above whilst still falling within the scope of the present invention. For example, the relative phase of current and voltage waveforms across the circuit inductance produced by a voltage or current perturbation may be determined by any appropriate technique, such as by comparison of times at which the voltage and current peaks occur as an alternative to determining the sign (positive or negative) of the inductance within the distribution leg. Furthermore, the controller 30 may be provided by any appropriate technique such as a component provided within the circuit or within the switch mechanism 40 and/or may at least partly be provided by one or more components external to the circuit 10 which may or may not include a microprocessor or computer.

Claims

<claim-text>CLAIMS: 1. An apparatus for determining the location of an electrical disturbance in a circuit, the apparatus comprising: one or more sensors for determining the relative phase of current and voltage waveforms across the circuit inductance of a portion of the circuit produced by a voltage or current perturbation; and a controller arranged to identify the location of the electrical disturbance within the circuit from the relative phase of the current and voltage waveforms.</claim-text> <claim-text>2. The apparatus according to claim 1, wherein the controller is arranged to isolate a portion of a circuit including the location at which the electrical disturbance was identified as occurring.</claim-text> <claim-text>3. The apparatus according to claim 2, wherein the controller is arranged to isolate the portion of the circuit in which the electrical disturbance was identified as occurring by opening a switch.</claim-text> <claim-text>4. The apparatus according to any one of the preceding claims, wherein the controller is arranged to determine the relative phase of current and voltage waveforms across the circuit inductance produced by a voltage or current perturbation by determining the inductance of a portion of the circuit.</claim-text> <claim-text>5. An apparatus according to claim 4, wherein the inductance in a portion of the circuit is determined based on the rate of change of current through that portion of the circuit, the voltage across that portion of the circuit and the voltage across the capacitive component of a load within that portion of the circuit.</claim-text> <claim-text>6. An apparatus according to claim 5, wherein the voltage across the capacitive component of a load within that portion of the circuit is measured by low-pass filtering the voltage across that portion of the circuit.</claim-text> <claim-text>7. A circuit including a power source portion and one or more distribution legs each including a load and an apparatus according to any one of the preceding claims, wherein the apparatus is arranged to identify the location of an electrical disturbance within the power source portion or the one or more distribution legs.</claim-text> <claim-text>8. A circuit according to claim 7, including a plurality of distribution legs and an apparatus according to any one of claims 1 to 6 provided in each of the distribution legs to identify whether an electrical disturbance occurs in a particular one of the plurality of distribution legs.</claim-text> <claim-text>9. A method for determining the location of an electrical disturbance in a circuit, the method comprising determining the relative phase of current and voltage waveforms across the circuit inductance of a portion of the circuit produced by a voltage or current perturbation in the circuit and identifying the location of the electrical disturbance within the circuit from the determined relative phase of the current and voltage waveforms in that portion of the circuit.</claim-text> <claim-text>10. A method according to claim 9, wherein the relative phase of the current and voltage waveforms across the circuit inductance produced by a voltage or current perturbation is determined by calculating the sign (positive or negative) of the inductance of the circuit during the voltage or current perturbation.</claim-text> <claim-text>11. A method according to claim 9 or claim 10, wherein the relative phase of the current and voltage waveforms produced by a voltage or current perturbation are determined for each of a plurality of distribution legs each supplying a different load in the circuit, such that the distribution leg in which the voltage or current perturbation occurred may be identified.</claim-text> <claim-text>12. A method according to any one of claims 9 to 11, wherein the portion of the circuit identified as including the location of an electrical disturbance is isolated from the remainder of the circuit.</claim-text> <claim-text>13. An apparatus for determining the location of an electrical disturbance in a circuit substantially as herein before described with reference to the accompanying drawings.</claim-text> <claim-text>14. A method for determining the location of an electrical disturbance in a circuit substantially as herein before described with reference to the accompanying drawings.</claim-text>