AU2010202580B2

AU2010202580B2 - Device and method for signalling electric faults, unit and electric panel comprising such a device

Info

Publication number: AU2010202580B2
Application number: AU2010202580A
Authority: AU
Inventors: Jerome Meunier-Carus; Simon Tian; Clement Zeller
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2009-06-23
Filing date: 2010-06-21
Publication date: 2014-08-14
Anticipated expiration: 2030-06-21
Also published as: EP2267465A1; AU2010202580A1; EP2267465B1; ATE557282T1; CN101931209A; CN101931209B; ES2383742T3; BRPI1002181A2; BRPI1002181B1; FR2947054A1

Abstract

5 DEVICE AND METHOD FOR SIGNALLING ELECTRIC FAULTS, UNIT AND ELECTRIC PANEL COMPRISING SUCH A DEVICE 10 The electric fault signalling device comprises a differential current sensor, processing means (16) comprising fault current detection means (21) and electric fault signalling means (17, 18). Said processing means comprise means (29) for detecting a voltage on a control input (30). Signalling processing means (22) provide said signalling means (23, 24, 25) with a first signalling signal (IS1) when 15 said first detection signal (Fd1) is representative of a threshold overshoot and when said voltage detection means (29) have detected a voltage outage on said control input. The method comprises signalling (58) of a location electric fault when an overshoot (55) of said first threshold is detected and a voltage outage is detected. (Figure 3) IS1 STOREDi ;Z NO: YES 5 Id I d > SI (Fd1) NO T > D IlS1 STORED Fd2 ? IS2 STORED |S1 ,ANUAL NO' RESET? 53 'Fd17 FIG. 6

Description

Pool Secion 29 Regulabon 3.2(2) AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Device and method for signalling electric faults, unit and electric panel comprising such a device The following statement is a full description of this invention, including the best method of performing it known to us: P111ABAU/1207 I DEVICE AND METHOD FOR SIGNALLING ELECTRIC FAULTS, UNIT AND ELECTRIC PANEL COMPRISING SUCH A DEVICE 5 BACKGROUND OF THE INVENTION The invention relates to a device for signalling electric faults comprising: - current measuring means to measure a leakage, differential or residual current, 10 - processing means comprising fault current detection means connected to said current measuring means and providing a first fault detection signal when the measured current exceeds a predefined first threshold, and - means for signalling an electric fault connected to said processing means. 15 The invention also relates to a differential protection unit comprising an electric switchgear apparatus with main contacts able to tripped to open when an electric fault occurs. An electric distribution panel comprising an electric power supply line incomer and 20 several electric distribution feeders. The invention also relates to a method for signalling electric faults. State of the art 25 Figure 1 shows an example of a diagram of a differential protection unit. This unit can be a differential switch or a differential circuit breaker comprising main contacts 1 to interrupt a current in electric conductors. A sensor 3 measuring differential current Id measures a differential or residual current flowing in the 30 conductors 2. The sensor 3 generally comprises a measuring toroid arranged as a magnetic circuit 4 surrounding the conductors 2 and a secondary winding 5 providing a secondary current Is to control a trip relay 6 when a tripping threshold 2 is exceeded. The relay 6 commands opening of the contacts 1 via an operating mechanism 7. These differential protection units can be used in association with electric fault signalling devices. 5 A diagram of an electric fault signalling device is represented in figure 2. It can be fitted line-side or load-side of a differential protection device, or even be used on its own in isolated manner. The device comprises a sensor 10 measuring differential or residual current Id arranged around electric current conductors 2. The sensor 10 is generally formed by a toroid14 and a secondary winding 15 to 10 provide a measured secondary current Im representative of the differential current Id to a processing circuit 16. The processing circuit commands local or remote signalling means when a fault current threshold is exceeded. Among these signalling means, there can be an indicator 17 or a relay 18. A power supply circuit 19 is connected to the processing circuit 16 to supply power and store 15 signalling data. In known manner, electric fault signalling devices are used for preventing tripping of a differential protection unit. In this case, the signalling device has a lower detection threshold than a tripping threshold. When a fault is detected, the 20 signalling device commands a local or remote alarm or display device. This detection is generally slow and filtered to prevent spurious alarms. In other known systems, electric fault signalling devices are used to locate an electric fault after tripping. These devices have to have an auxiliary power supply 25 even in the case of tripping or opening of the line to be monitored. Furthermore, in this case, detection of an electric fault current has to be performed very rapidly as high-speed tripping and opening of the electric circuit take place. Known electric fault signalling devices do not enable electric fault prevention 30 functions before tripping and fault location functions after tripping to be associated in a single device. These functions do in fact have very different characteristics and are incompatible in the processing channel.

3 Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material formed part of the prior art base or the common general knowledge in the relevant art in Australia on or before the 5 priority date of the claims herein. Comprises/comprising and grammatical variations thereof when used in this specification are to be taken to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or 10 addition of one or more other features, integers, steps, components or groups thereof. SUMMARY OF THE INVENTION 15 It would be desirable to provide a device and a method for signalling electric faults enabling prevention functions and location functions, as well as a differential protection unit and an electric panel comprising such a device. In accordance with a first aspect of the invention, there is provided a device for 20 signalling electric faults including: - current measuring means for measuring a leakage, differential or residual current, - processing means including fault current detection means connected to said current measuring means and providing a first fault detection signal when the 25 measured current exceeds a predefined first threshold, and - means for signalling an electric fault connected to said processing means, wherein said processing means further includes: - voltage presence detection means connected to a voltage presence control input, and - signalling processing means connected to said voltage detection means and to 30 said fault current detection means to provide said signalling means with a first signalling signal when said first fault detection signal is representative of a threshold overshoot and when said voltage detection means have detected a voltage outage on said voltage presence control input.

4 Advantageously, said means for detecting fault current provide a second fault detection signal when the measured current exceeds the predefined first threshold for a predefined period, and said signalling processing means provide said signalling means with a second signalling signal when said second detection 5 signal is representative of a threshold overshoot during said predefined period. In a preferred embodiment, said signalling means command: - a first type of display representative of fault location when said processing and signalling means provide said first signalling signal, and 10 - a second type of display representative of fault prevention when said processing and signalling means provide said second signalling signal. Preferably, the first signalling signal and the second signalling signal are applied to the same signalling means and/or to the same relay. 15 Advantageously, said signalling means comprise at least one bistable indicator. Preferably, said signalling means comprise at least one bistable liquid crystal display. 20 In a particular embodiment, the device comprises a first part comprising said processing means arranged in a module able to be installed on a support in the form of a rail and a second part comprising at least said current measuring means and connected to said first part. 25 In accordance with a second aspect of the invention, there is provided a differential protection unit including an electric switchgear apparatus with main contacts able to be tripped to open when an electric fault occurs, wherein it includes an electric fault signalling device in accordance with the first aspect of the invention above, and a first part arranged next to said electric switchgear 30 apparatus and a second part supporting said current measuring means arranged facing output terminals of said electric switchgear apparatus.

4a In this unit, said voltage presence control input is preferably connected load-side from said electric switchgear apparatus. In an electric distribution panel according to the invention comprising an electric 5 power supply line incomer and several electric distribution feeders, at least one feeder comprises an electric fault signalling device as defined above. Preferably an electric distribution panel comprises at least one differential protection device line-side from at least one electric fault signalling device. 10 In accordance with a further aspect of the invention, there is provided a method for performing electric fault signalling which includes: - measurement of differential or residual fault current, - comparison of said fault current with a first detection threshold to detect a 15 threshold overshoot, - detection of an overshoot of said first threshold during a predefined period, 5 - detection of an electric voltage outage on a voltage presence control input, - signalling of a location electric fault when an overshoot of said first threshold is detected and the voltage presence detection detects a voltage outage. 5 Advantageously, the signalling method also comprises signalling of a prevention electric fault when an overshoot of said first threshold during a predefined time period takes place. Preferably, the signalling method also comprises storing of signalling of a location 10 electric fault and acknowledgement of signalling of a location electric fault. BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will become more clearly apparent from the 15 following description of particular embodiments of the invention, given for non restrictive example purposes only and represented in the accompanying drawings in which: - figure 1 represents a known differential protection device; 20 - figure 2 represents a known electric fault signalling device; - figure 3 represents a block diagram of an electric fault signalling device according to an embodiment of the invention; - figures 4 and 5 represent diagrams of modules of an electric fault signalling device according to an embodiment of the invention; 25 - figure 6 represents a flowchart of a method for signalling electric faults according to an embodiment of the invention; - figures 7, 8 and 9 represent timing diagrams of operation of devices or of methods for signalling electric faults according to embodiments of the invention; - figure 10 represents a unit comprising a differential protection device and a 30 device for signalling electric faults according to an embodiment of the invention; 6 - figure 11 represents a diagram of an electric panel comprising devices for signalling electric faults according to an embodiment of the invention arranged on protected feeders; - figure 12 represents a diagram of an electric panel comprising a differential 5 protection switchgear device and devices for signalling electric faults according to an embodiment of the invention arranged on branch-connected feeders; - figure 13 represents a device for signalling electric faults according to a first embodiment of the invention with passage of electric cables arranged next to an electric apparatus; 10 - figure 14 represents a device for signalling electric faults according to a second embodiment of the invention with electric connection load-side from an electric apparatus; - figure 15 represents a unit comprising a differential protection device and a device for signalling electric faults arranged in the same case; 15 - figure 16 represents a device for signalling electric faults according to a third embodiment of the invention comprising a line-side/load-side connection of the current conductors; - figure 17 represents a device for signalling electric faults according to a fourth embodiment of the invention comprising a remote fault current measuring 20 transformer; and - figures 18 and 19 represent a diagram and a timing diagram of control of a bistable indicator used in a device according to an embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 25 A device for signalling electric faults according to a preferred embodiment is represented in figure 3 by a block diagram. This device comprises a current measuring sensor 10 to measure a differential or residual leakage current. The sensor 10 is generally formed by a transformer in the form of a toroid arranged 30 around electric current conductors 2 and of a secondary winding 15 to provide a signal Id1 representative of a differential current Id to a processing circuit 20.

7 The processing circuit 20 comprises a signal processing module 21 to condition the secondary current signal Id1 into a signal Id2 able to be processed by analog or digital electronic circuits. The module 22 can comprise rating or threshold adjustment functions. The processing circuit 20 also comprises a global 5 processing circuit 22 to receive the signal Id2 representative of a differential current and to provide a first fault detection signal Fd1 when the measured current exceeds a predefined first threshold Sid. The threshold Sid is generally lower than tripping thresholds of differential protection devices. 10 The device for signalling electric faults also comprises signalling means for signalling an electric fault connected to circuit 22. The signalling means can in particular be an indicator 23, a relay 24 or a connection via a communication bus 25. In the embodiment of figure 3, control means are connected to the processing circuit 20. Among these control means, a switch 26 commands testing of the 15 signalling device, a switch 27 commands acknowledgement or reset in case of fault storage, and a position-change switch 28 is used for adjusting the signalling thresholds. A power supply circuit 31 supplies power to the processing device circuits. 20 In a preferred embodiment of the invention, the processing circuit 20 comprises a line voltage detection circuit 29 connected to a voltage presence control input 30 to provide a voltage presence signal VL1. In figure 3, the processing circuit 22 is connected to the voltage presence detection circuit 29 and processes the fault current Id2 to provide the signalling means with a first signalling signal IS1 when 25 said first detection signal is representative of a threshold overshoot and when the circuit 29 has detected a voltage outage on said voltage presence control input 30. Threshold overshoot may take place at the same time as or before voltage outage. 30 Voltage inputs 30 can preferably be connected line-side or load-side from current measurement of the fault signalling device. These inputs 30 can also be connected to more distant points of the electric distribution system.

8 Figure 4 represents a diagram of modules of an electric fault signalling device according to an embodiment of the invention. A comparator 40 compares the signal representative of a differential current with a threshold SId. If the threshold 5 is exceeded, a first differential fault signal Fdl is supplied to a first signalling processing module 41. The line voltage detection circuit 29 also supplies the module 41a with a signal VL1 representative of the presence of line voltage. The module 41 thus processes the signals Fd1 and VL1 and supplies the first signalling signal IS1 when the signal VL1 announces a line voltage outage during 10 the presence of a fault detection signal Fd1. The signal Fd1 can be stored in memory for a few moments to guarantee detection of a fault immediately preceding the voltage outage. Figure 4 also shows a time-out module 42 receiving the first differential fault signal Fd1 and supplying a second differential fault signal Fd2 when the first signal is present during a predefined time T. Thus, a second 15 fault current detection signal is supplied when the measured current exceeds the predefined first threshold for a predefined time T. The second signalling signal is then representative of a threshold overshoot during a predefined time. A second signalling processing module 43 receives the second signal Fd2 and supplies a second signalling signal IS2 to indicate threshold overshoot during a time T. The 20 module 43 can perform storing of the signalling in memory and then be acknowledged by a special command. Figure 5 shows a display channel of the first signalling signal. A storage module 44 receives the signal IS1 when a voltage outage occurs during or just after a 25 differential fault and supplies a stored signalling signal ISM1 to a display or to remote signalling means. A module or means 46 can be commanded to perform a reset or acknowledge of the storage module 44. Preferably, a first type of display is representative of fault location when the 30 module 41 supplies said first signalling signal IS1 and a second type of display is representative of fault prevention when the module 43 supplies said second signalling signal IS2. In another embodiment, the first signalling signal IS1 and the 9 second signalling signal IS2 can be applied to the same indicator and/or to the same relay. In this case, the prevention signal IS1 is active during normal operation and the location signal IS2 remains active after tripping and opening of an electric circuit on a fault by a switch or a circuit breaker. 5 Figure 6 represents a flowchart of a method for signalling electric faults according to an embodiment of the invention. After initialization of the method in a step 50, a step 51 checks whether a fault location signalling signal IS1 is stored. If the signal is stored, a step 52 commands display or confirms display of the signal IS1. This 10 signal can be deleted in a step 53 by a manual acknowledge for example. In normal operation, a step 54 performs measurement of differential or residual fault current. In a step 55, comparison of said fault current is made with a first detection threshold to detect a threshold overshoot. A step 56 initializes a time counter for detection of an overshoot of said first threshold for a predefined time. In a step 57, 15 detection of an electric voltage outage on a voltage presence control input is performed. If a voltage outage is detected, a step 58 announces a location electric fault since an overshoot of said first threshold takes place and the voltage presence detection detects a voltage outage. Step 58 also enables signalling of the location of an electric fault. Acknowledgement of signalling of the location of 20 an electric fault is performed in step 53. If a voltage outage is not detected, a step 59 checks end of time-out. If the fault current is still present, a step 60 supplies a second fault signal Fd2 to perform signalling of prevention of an electric fault since an overshoot of the first threshold 25 has occurred for a predefined time. In certain cases, a step 62 checks the presence of a fault before re-initialization. Figures 7, 8 and 9 represent timing diagrams of operation of electric fault signalling devices or methods according to embodiments of the invention. Figure 7 30 presents the case where a long differential fault is detected without tripping. The voltage represented by the signal VL is present right from the start at time tO. At a time t1, the differential fault current Id overshoots a threshold SId. This fault is 10 immediately indicated on an output IdS of the device. As the fault is still present after a predefined time-out D, a local display signal SD commands the display means and a signal RC commands an signalling relay. In this case, the display signal is representative of fault prevention. At a time t2, an acknowledge or reset 5 command Rs is not taken into account as the fault is still present. At a time t3, the fault current drops below the threshold SId, this change being indicated immediately on output Ids. The signals SD and RC being stored, they continue to indicate fault prevention until acknowledge command time t4. 10 Figure 8 presents the case where a short differential fault is detected. The voltage represented by the signal VL is present right from the start at time tO. At a time t5, the differential fault current overshoots a threshold SId for a short time. This overshoot is immediately indicated on an output Ids of the device. As this short overshoot has a shorter duration than the predefined time D, the signalling signals 15 SD and RC are not activated. Figure 9 presents the case where a differential fault is detected and tripping takes place. The voltage represented by the signal VL is present right from the start at time tO. At a time t7, the differential fault current Id exceeds a threshold SId. This 20 threshold overshoot is immediately indicated on an output Ids of the device. At a time t8, the voltage VL is no longer present and the fault current Id is cancelled out. The time period between times t8 and t7 is shorter than the predefined time period D. This situation is representative of a fault with tripping. The fault then has to be located after tripping. A display signal SD is supplied to local displays and a 25 stored signal RC commands a relay. In this case, the display signals are representative of a fault location signal. If the voltage VL is also used for power supply of the device, the signal SD can be interrupted whereas the relay signal RC can remain active. At a time t9, the voltage VL is again present and the fault current Id is lower than the threshold. The signals SD and RC being stored, fault 30 location signalling is continued. At a time t10, an acknowledge command re initializes the device by deleting storage of the signals. Overshoot of the threshold 11 by the current Id can be stored for a few moments to guarantee detection of a fault preceding the voltage outage. Figure 10 represents a unit 70 comprising a differential protection device 71 and 5 an electric fault signalling device 72 according to an embodiment of the invention. The differential protection device comprises main contacts 1 able to be tripped to open when an electric fault occurs. The electric fault signalling device is as defined in the embodiments described above. In this figure, a voltage presence monitoring input is connected load-side from said differential protection device. 10 Figure 11 represents a diagram of an electric panel 73 comprising electric fault signalling devices 70 according to an embodiment of the invention arranged on feeders protected by circuit breakers 75. An electric power supply incomer line 76 supplies several protected electric distribution feeders 74. One or more of the 15 feeders comprise an electric fault signalling device 70 arranged load-side of the circuit breakers 75. Figure 12 represents a diagram of an electric panel comprising a differential protection switchgear device 92 fitted line-side from several electric fault signalling 20 devices 93 arranged on branch-connected feeders 94. Figure 13 represents an electric fault signalling device according to a first embodiment of the invention with passage of electric cables arranged next to an electric apparatus 77. The signalling device comprises a first part 78 arranged 25 next to the electric apparatus 77 and a second part 79 supporting the differential current sensor arranged facing output terminals of said electric apparatus. Input terminals 30 are arranged on the first part 78. The electric apparatus is preferably a switch or a circuit breaker with or without differential protection. 30 Figure 14 represents an electric fault signalling device according to a second embodiment of the invention with electric connections 81 to be connected load side of an electric apparatus. The current sensor being inside the apparatus, 12 output terminals 82 are arranged in the case of the device. This case comprises differentiated signalling indicators 83 and 84, adjustment means 85, and auxiliary connectors 86. The connectors 86 can receive communication busses, relay outputs and/or the voltage presence input. In this embodiment, the voltage 5 presence input can also advantageously be recovered on the connections 81 load-side from the electric apparatus. Fault location is thereby indicated with the electric apparatus associated with the faulty feeder. Figure 15 represents a unit comprising a differential protection device and an 10 electric fault signalling device arranged in the same case 87. In addition to the elements of the electric fault signalling device, the case comprises a mechanical connection 88 between the differential protection device and an electric switchgear apparatus, and a test button 89 to test the differential protection function. An indicator 90 is used to display several differential fault current 15 functions. Figure 16 represents an electric fault signalling device 95 according to another embodiment of the invention comprising a line-side/load-side connection of the current conductors 2. The line-side/load-side connection can be achieved via 20 direct cable bushings 96 or via line-side connection terminals 97 and load-side connection terminals 98. Figure 17 represents an electric fault signalling device according to another embodiment of the invention comprising a remote-located fault current measuring 25 transformer. The device thus comprises a first part 78 comprising the processing circuit 20 arranged in a module able to be installed on a support 99 in the form of a rail and a second part 79 comprising at least one current measuring sensor 10 connected to the first part by an electric connection 100. 30 The signalling means can be differentiated between signalling for prevention 83 and fault location signalling 84 after a voltage outage or a trip. The indicators used can preferably be of bistable type keeping their state after being commanded 13 without being supplied with electric power. Advantageously, the bistable indicators are bistable indicator lamps or liquid crystal displays changing colour according to the polarity of the control or supply voltage. These bistable indicators can for example be of cholesteric liquid crystal type. 5 Figures 18 and 19 represent a diagram and a timing diagram of command of a bistable indicator used in a device according to an embodiment of the invention. A display processing circuit 101 commands a voltage reverser 102 to supply a bistable display 103 either with a first voltage polarity or with a reverse second 10 polarity. A diode 104 and capacitor 105 enable enough electric power to be stored to supply command of the display with a voltage VS after an electric supply voltage VDD has undergone an outage. In the timing diagram, at the time t20 voltage VS is about the same as voltage VDD. A display command supplies power to the bistable indicator lamp either with a first polarity +VB or with reverse polarity 15 -VB. Then, at the time t21, the indicator remains in its display colour corresponding to the command. The types of displays for fault prevention or for fault location can take several forms, for example with two distinct indicators. In another embodiment, a single 20 indicator can be commanded to flash to display fault prevention or to be lit steady and stored to display fault location. A change of colour of a single indicator lamp can also be representative of fault prevention or location. The differential current described above also corresponds to a residual current, a 25 leakage current, an earth fault current or a zero sequence current. The devices according to the invention apply equally well to two-pole, three-pole or four-pole electric distribution systems. In other embodiment, a device can have several processing circuits connected to 30 several current sensors. In this case, a common voltage input can be used to locate faults of several feeders.

Claims

1. Device for signalling electric faults including: - current measuring means for measuring a leakage, differential or residual current, - processing means including fault current detection means connected to said current measuring means and providing a first fault detection signal when the measured current exceeds a predefined first threshold, and - means for signalling an electric fault connected to said processing means, wherein said processing means further includes: - voltage presence detection means connected to a voltage presence control input, and - signalling processing means connected to said voltage detection means and to said fault current detection means to provide said signalling means with a first signalling signal when said first fault detection signal is representative of a threshold overshoot and when said voltage detection means have detected a voltage outage on said voltage presence control input.

2. Device according to claim 1 wherein said fault current detection means provide a second fault detection signal when the measured current exceeds said predefined first threshold for a predefined period, and said signalling detection means provide said signalling means with a second signalling signal when said second detection signal is representative of a threshold overshoot for a predefined time.

3. Device according to claim 2 wherein said signalling means command a first type of display representative of fault location when said signalling processing means provide said first signalling signal, and a second type of display representative of fault prevention when said signalling processing means provide said second signalling signal. 15

4. Device according to any one of claims 1 to 3 wherein the first signalling signal and the second signalling signal are applied to the same indicator and/or to the same relay.

5. Device according to any one of claims 1 to 4 wherein said signalling means include at least one bistable indicator.

6. Device according to any one of claims 1 to 4 wherein said signalling means include at least one bistable liquid crystal indicator.

7. Device according to any one of claims 1 to 6 wherein it includes a first part including said processing means arranged in a module able to be installed on a support in the form of a rail and a second part including at least said current measuring and connected to said first part.

8. Differential protection unit including an electric switchgear apparatus with main contacts able to be tripped to open when an electric fault occurs, wherein it includes an electric fault signalling device according to any one of claims 1 to 7, and including a first part arranged next to said electric switchgear apparatus and a second part supporting said current measuring means arranged facing output terminals of said electric switchgear apparatus.

9. Differential protection unit according to claim 8 wherein said voltage presence control input is connected load-side from said electric switchgear apparatus.

10. Electric distribution panel including an electric power supply line incomer and several electric distribution feeders wherein at least one feeder includes an electric fault signalling device according to any one of claims 1 to 7.

11. Electric distribution panel according to claim 10 wherein it includes at least one differential protection device line-side from at least one electric fault signalling device. 16

12. Electric fault signalling method wherein it includes: - measurement of differential or residual fault current, - comparison of said fault current with a first detection threshold to detect a threshold overshoot, - detection of an overshoot of said first threshold during a predefined period, - detection of an electric voltage outage on a voltage presence control input, - signalling of a location electric fault when an overshoot of said first threshold is detected and the voltage presence detection detects a voltage outage.

13. Signalling method according to claim 12 wherein it includes signalling of a prevention electric fault when an overshoot of said first threshold during a predefined time period takes place.

14. Signalling method according to any one of claims 12 or 13 wherein it includes storing of signalling of a location electric fault and acknowledgement of signalling of a location electric fault.

15. Device for signalling electric faults, substantially as hereinbefore described with reference to Figures 3 to 19 of the accompanying drawings.

16. An electric fault signalling method, substantially as hereinbefore described with reference to Figures 3 to 19 of the accompanying drawings. SCHNEIDER ELECTRIC INDUSTRIES SAS WATERMARK PATENT AND TRADE MARKS ATTORNEYS P33304AU00