Device for detecting electrical currents on or in the vicinity of electrical conductors

Abstract

The invention relates to a device for detecting electrical currents on or in the vicinity of electrical conductors with at least one Reed switch as a magnetically responsive switch, which is arranged in the vicinity of the electrical conductor such that, when there is a significant current flow through the conductor, the magnetic field created triggers the switch and initiates an evaluation electronics connected to the switch. For the detection of surge current variables and the differentiation between long-term pulsed currents and short-term pulsed currents, a plurality of Reed switches are arranged at a predetermined distance from the electrical conductor, wherein the evaluation electronics determines the response and the switching times of the respective Reed switches, determines die surge current variable from the allocation of the determined values to the respective Reed switch and the pulse form from the switching time, wherein, for the purpose of adjusting the response behavior, at least one of the Reed switches comprises a shielding for influencing the magnetic field acting on the respective Reed switch.

Claims

1. A device for detecting electrical currents on or in the vicinity of an electrical conductor with at least one reed contact as a magnetically responsive switch, which is arranged in the vicinity of the electrical conductor such that, when there is a significant current flow of more than 50 A up to 200 kA through the conductor, the developing magnetic field triggers the switch and initiates an evaluation electronics connected to the switch, characterized in that for detecting surge current variables and differentiating long-term pulse currents, on the one hand, and short-time pulse currents, on the other, a plurality of reed contacts (4; 5; 6) is arranged in a predefined distance from the electrical conductor (8), wherein the evaluation electronics (2) determines the response and the switching times of the respective reed contacts (4; 5; 6), from the allocation of the determined values to the respective reed contact, the surge current variable is detected, and from the switching time, the pulse shape is detected, wherein, for setting the response behavior, at least one of the reed contacts (9) has a shield for influencing the magnetic field (B) acting upon the respective reed contact (9).

2. The device according to claim 1, characterized in that the electrical conductor is an integral part of a lightning current arresting system or an arrester rod.

3. The device according to claim 1, characterized in that the electrical conductor is an integral part of a surge current-carrying overvoltage arrester.

4. The device according to claim 1, characterized in that the evaluation electronics (2) has a microcontroller (100) and at least one low-pass filter (90).

5. The device according to claim 4, characterized in that the data is transferred in a wireless or wired manner to a superordinate unit for long-term analysis of pulse-shaped surge currents.

6. The device according to claim 4, characterized in that a radio module (111; 140) is provided for data transmission, wherein the data transmission is only triggered after expiration of a predetermined period of time after the last surge current pulse has decayed.

7. The device according to claim 1, characterized in that it has an autonomous long-term current supply (3; 50).

8. The device according to claim 1, characterized in that at least the reed contacts (4; 5; 6) are fixed on a planar wiring carrier.

9. The device according to claim 8, characterized in that the angular position of the groups of reed contacts (4; 5; 6) with respect to the electrical conductor (8) is fixedly predefined.

10. The device according to claim 1, characterized in that a housing accommodating the components of the device is formed, which housing has a front or side surface provided with means for identifying the position of and/or attaching the electrical conductor (8).

11. The device according to claim 1, characterized in that it is in each case arranged on or in the vicinity of lightning arrester cables of rotor blades in wind turbines.

12. The device according to claim 1, characterized in that after expiration of a predetermined or settable period of time between the pulse event and data transferal, a time stamp can be generated.

13. The device according to claim 1, characterized in that the electrical conductor (8) is an integral part of constructional parts or facilities, that do not carry lightning current, in particular of hoisting cables or carrier cables of cableways or cranes.

14. Use of a device according to claim 1 for detecting and classifying lightning current and overcurrent events having a surge current character in the range from ≥50 A to 200 kA and pulse shapes as a long-term pulse with T ≥10 ms as well as pulse shapes of 10/350 μs and 8/20 μs.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS(S)

(1) FIG. 1 shows a principle arrangement of the device according to the present disclosure with three reed contacts;

(2) FIG. 2 shows a simplified block diagram of evaluation electronics of the device of FIG. 1;

(3) FIG. 3 shows a simplified block diagram of evaluation electronics of the device of FIG. 1 together with a processing and control unit being in communication with the evaluation electronics;

(4) FIG. 4 schematically shows a level of a magnetic flux density as a function of a distance from a middle axis of a conductor cable; and

(5) FIG. 5 shows a diagram highlighting the influence of a distance of a reed contact from a conductor cable on the level of a lightning current which is necessary to close said reed contact.

(6) In this regard, FIG. 1 shows a principle arrangement of the device according to the invention with three reed contacts, for example at a defined distance from the electrical conductor.

(7) FIG. 2 shows a simplified block diagram of the evaluation electronics with a low-pass filter 90 arranged downstream of the respective reed sensor 4; 5; 6, the respective output of said filter leading to a microcontroller 100 which is in communication with a radio interface 110 on its output side.

(8) In the block diagram according to FIG. 3, reed sensors 4; 5; 6 are again taken as a basis, which are in communication with an R-C low-pass filter 90.

(9) For determining the switching time of the respective reed sensor 4; 5; 6, the low-pass filters each are in communication with an input of a comparator 120, the output of which leads to the microcontroller 100 with a memory unit.

(10) In this regard, a time module 130 is present leading to the comparation input of the comparator 120. For the voltage supply, the battery 5 already explained with respect to FIG. 1 is used. By means of the time module 130 and the microcontroller 100, the detected pulse shape can be determined from the switching time of the respective reed sensor or reed contact 4; 5; 6 in a signal processing manner.

(11) The assemblies 110 and 140 form an air interface and ensure wireless data transmission of the detected surge current variables.

(12) A further signal processing and control unit 150 is in communication with a communication module 160 in order to guarantee a cloud connection over GSM. Alternatively, a classical Internet connection for data evaluation as well as long-term analysis may be realized by means of the module 170.

(13) The device according to the exemplary embodiment according to FIG. 1 takes a printed circuit board 1 as a basis, which has an evaluation unit with a radio module 2 as well as current supply of long-term stability in the form of a battery 3.

(14) At or on a planar side section of the printed circuit board 1 or the wiring carrier, three spaced apart reed contacts 4, 5 and 6 are arranged located substantially in parallel to one another. For setting the response behavior, at least one of the reed contacts may have a shield.

(15) An electrical conductor 8 is led to a quasi stop edge 7 of the printed circuit board 1. This may be, for example, an arrester cable of a rotor of a wind turbine.

(16) If a surge current flows through the arrester cable 8, a magnetic field forms around the arrester cable, which penetrates the spaced apart reed contacts 4, 5, 6 at different intensities.

(17) For example, it is assumed that the reed contact 4 has a distance of 5 mm from the conductor, the reed contact 5 has a distance of 15 mm from the conductor, and the reed contact 6 has a distance of 105 mm from the conductor.

(18) The reed contact 4 is capable of detecting long-term pulses with an Imin≥50 A and a pulse duration of T≥10 ms. Likewise, the reed contact 4 in the closest distance from the arrester cable 8 can detect surge current pulses of the pulse shape 10/350 μs with Imin≥60 A and surge current pulses of the pulse shape 8/20 μs with Imin≥70 A.

(19) The reed contact 5 is capable of detecting pulse currents of the pulse shape 10/350 μs with Imin≥200 A and pulse current of 8/20 μs with Imin≥750 A.

(20) The reed contact relay 6 located in a distance of about 105 mm from the arrester cable 8 is capable of detecting pulses of the pulse shape 10/350 μs with Imin≥4.5 kA and pulses of the pulse shape 8/20 μs with Imin 67 kA.

(21) With the help of the evaluation electronics integrated into the device, the different switching times of the reed contacts can be detected and evaluated depending on the pulse shape, so that it can be recognized, which pulse shapes having which pulse duration are concerned.

(22) By the selective response of the reed contacts in case of corresponding surge currents, a differentiation in the range from about 60 A up to 250 kA can also be performed.

(23) In case of a lightning or surge current event, this is first detected by at least one reed contact responding. After this, a differentiation of the measured current intensities is made by the response behavior of the individual reed contacts. The detected data is stored while observing the course of time or the time delta regarding subsequent events, and are then available for further evaluation.

(24) With a device according to the invention and tested in a test field, the detectable minimum current intensity is at about 45 A. With the use of three reed contacts, for example, three pulse thresholds can be defined and evaluated. In case of a corresponding expansion of the microcontroller used for evaluation, a further diversification can be performed without leaving the basic principle of the invention.

(25) Components for the long-term storage and analysis of the detected values, which possibly become necessary, may be attached spatially distant from the device according to the invention in EMI-protected premises. This is possible since preferably a wireless transmission of the measured values provided by the device to the downstream evaluation unit is performed, and this transmission is only triggerable after the last fault event has decayed.

(26) By means of a fixedly set delay time between an occurring lightning event and the sending of the event protocol, a time allocation accurate to the millisecond or a time stamp accurate to the millisecond can be achieved.

(27) The following exemplary threshold values of the reed contacts are the result of executed tests:

(28) TABLE-US-00001 TABLE 1 Triggering thresholds of the reed contacts Pulse shape reed 1 reed 2 reed 3 8/20 μs 350 A 1250 A 67 kA 10/350 μs 140 A 260 A 4.5 kA DC test field 140 A — —

(29) The triggering thresholds of the reed contacts may be greatly varied by the distance and the kind of the contacts. With these triggering thresholds, a differentiation can be made between an I.sub.cc only and a short-term pulse. If the 3.sup.rd reed contact is intended to trigger at higher current intensity, the distance may even be increased. A deviation of the triggering threshold of 10 A could be observed in the different arresting cables (95 mm.sup.2, Ø=11 mm, insulating wall thickness=2.5 mm, 50 mm.sup.2, Ø=8 mm, insulating wall thickness=2.5 mm). As compared to 8/20 pulses, the triggering threshold is significantly lower at 10/350 pulses.

(30) The following dependence of the response can be inter alia recognized between the triggering thresholds of the unshielded reed contacts of the pulses 8/20 and 10/350 has as of a certain distance from the arresting cable.

(31) $\frac{\int {\left(I_{8/20}\left(t\right)\right)}^2\mathrm{dt}}{\int {\left(I_{10/350}\left(t\right)\right)}^2\mathrm{dt}}\approx 15$

(32) According to FIG. 4, a cable through which current flows or a conductor 8 through which current flows is illustrated schematically with the surrounding magnetic field lines B. The corresponding reed contact 9 is radially oriented toward the magnetic field of the conductor 8 such that its connections and contacts are exposed to the magnetic flux density B. When the response flux density or the magnetic sensitivity of the reed contact 9 is reached, the contacts will close.

(33) Reaching the response flux density of the reed contact 9 depends in this case on the current intensity within the cable 8, the distance of the reed contact 9, the sensitivity of the reed contact 9, and the orientation of the reed contact 9 toward the conductor cable 8.

(34) Moreover, the response behavior may be changed by influencing the magnetic flux B, for example, by introducing materials of higher permeability.

(35) In FIG. 4, the level of the magnetic flux density is shown in principle as a function of the distance R from the middle axis of the conductor cable 8. The illustrated axes are to be understood in a logarithmic way. The minimum distance of the reed contact 9 is in this case limited by the geometry of the conductor 8 and the necessary, possibly insulated attachment. In FIG. 4, line 10 represents the magnetic flux density for a high current intensity, and line 11 represents the magnetic flux density for a low current intensity. Line 13 characterizes the triggering threshold of a reed contact 9 of low sensitivity, and line 12 characterizes a sensitive reed contact 9.

(36) In case of a small current flow and a correspondingly low magnetic flux density 11 through the conductor cable 8, the triggering threshold of a reed contact 9 of low sensitivity 13 will not be reached even in case of the smallest distance to be technically realized of the reed contact 9 from the conductor cable 8. A detection of the current will not be performed under these circumstances. Nevertheless, in order to cause a detection with such a reed contact 9, it is possible to increase the concentration of the magnetic field lines surrounding the conductor cable 8 coaxially in certain areas and being in contact with the connections of the reed contact, for example, by ferromagnetic materials.

(37) Such an arrangement, however may be costly and possibly be avoided by using a more sensitive reed contact (line 12). Such a contact can detect the corresponding current or its magnetic flux density even at a distance of a few millimeters or centimeters. Only at larger distances or clearances, the magnetic flow density of the current (line 11) falls below the sensitivity of a corresponding reed contact (line 12), whereby a detection possibly is no longer possible.

(38) On the contrary, in case of a high current, the magnetic flux density (line 10) up to a great distance is far above the high sensitivity of the reed contact (line 12). Due to the limited device size, such distances often are not practicable for a technical application.

(39) The bandwidth of the sensitivity of available reed contacts is limited. It is moreover disadvantageous that the response time of the reed contacts generally rises with an increasing insensitivity, so that the desired detection of short-term pulse currents becomes not possible or only at significant temporal delays.

(40) The magnetic flux density of long-term currents of a few 10 A and pulse currents of several 100 kA, however is greatly different, so that even in case of insensitive sensors at desired high detection threshold values in case of lightning currents, the necessary distances are considerable and can amount up to several meters resulting in restrictions of use.

(41) In order to be able to realize high current thresholds for pulse currents and in particular lightning currents of the pulse shape of 10/350 μs in compact devices, the sensors can be provided with a complete or partial shield. For oriented sensitivity, the shields may also have windows. Thus, the shield has a weakening or a recess through which the magnetic field can partially penetrate.

(42) According to FIG. 5, the operating mode of the mentioned shield is explained by way of example.

(43) In the representation, the distance r.sub.sw of the sensor 9 from the conductor cable 8 is delineated in millimeters, up to which distance an unshielded reed contact 9 having a sensitivity of about 15 AT will still close depending on the level of the lightning currents.

(44) An experimentally determined progress with delineated measurement points (shade of grey) makes it obvious that, in case of desired threshold values of 200 kA or higher, the reed contact should be mounted at a distance of several meters from the conductor cable.

(45) It becomes clear that already at relatively low lightning currents of only 20 kA, a considerable distance of about 75 cm should be observed, when the exceeding of such a current level in the conductor cable 8 should be detected.

(46) At very high current threshold values, a compact measurement arrangement or a measurement arrangement constructed in a housing can hardly be realized. Reed contacts of higher insensitivity shift these distances only marginally and include the disadvantage of temporally allocating the closing to the actual current event. The orientation of the reed contact into an insensitive position toward the conductor cable, is highly sensitive in terms of positioning and attachment and involves very high constructional demands regarding the structure of corresponding devices and their installation.

(47) According to FIG. 5, a structurally identical reed contact is used, for example with a steel tube of a wall thickness in the range of one up to a few millimeters. This is illustrated by reference numeral 14 in a simplified manner. The arrow 15 shows the action of this simple arrangement or of the distance in case of which the current source (current >50 kA 10/350 μs) can be detected. From about 2 m distance of the unshielded reed contact or sensor, the distance shifts to a few millimeters or centimeters.

(48) In case of even higher pulse currents, a double shield 16 or triple shield 17 may also be used instead of a simple shield.

(49) In this case, the shields, for example, and the steel tubes are separated by intermediate layers or air.

(50) In these examples and in case of the same reed contact, the distance for detecting the threshold values of current >100 kA or >150 kA is reduced from a range of several meters to a few centimeters.

(51) It becomes obvious that very compact devices can be realized for detecting very different current thresholds using the idea of the shield. The reed contacts or such employed sensors may be configured, when the same reed contacts and the same distance from the conductor cable are used, due to the use of different shields, for a plurality of different threshold values of the pulse currents.

(52) Complementarily, there is the possibility of partially reducing the shield or introducing an opening into the shield. A grid-like or mesh-like shield could also be used in this respect. This measure does not only allow orientation characteristics to be realized. Rather, the sensitivity can be influenced even with the same geometry of the shield.

(53) The shield 18, basically corresponding to the geometry of the simple shield 14, had been provided with a partial opening, whereby a current threshold of 20 kA at a distance of a few millimeters can be detected in FIG. 5. If the simple shield without the weakening 14 was used, this current threshold possibly could not be realized technically due to the too strong shielding.

(54) The action of the shield by a ferromagnetic material is based in this case on the higher permeability of the shielding material. The magnetic field lines are deflected until the saturation of the material is reached, whereby the magnetic field in the area of the reed contacts is weakened substantially and thus closing of the reed contact is prevented until the saturation of the shield is reached.

(55) Apart from the selection of the ferromagnetic material or the combination of such materials as well as of their magnetic properties, the action of the shield can be influenced by the geometry and positioning of the reed contact within the shield.

(56) This thus results in a multitude of options to adapt the shield for using reed contacts to the task of detecting and evaluating long-term currents or pulse currents in compact devices or arrangements.