DEVICE FOR TAPPING VOLTAGE

Abstract: In a device for tapping electric voltage from an electric three-phase cable at a central distribution station (15) with a main fuse and a holder (17) therefor for each phase, each main fuse holder (17) has two contact members adapted to be electrically connected to each other by a fuse inserted in the holder for electric interconnection of the parts of the phase conductor in question located on each side of the fuse and connected to a respective contact member. The device comprises two contact elements (1) adapted to be inserted into a main fuse holder (17) each, beforehand released from the main fuse, into a position in which they are in electric contact with only the first one of the contact members (18), namely the one being connected to the part of the phase conductor in question which is still under voltage when the fuse is removed, and means (2, 19) for holding the contact elements (1) in this position for tapping the voltage existing between the two phase conductors in question.

Description: Device for tapping voltage FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a device for tapping electric voltage from an electric three-phase cable at a central dis¬ tribution station with a main fuse and a holder therefore for each phase. Each main fuse holder having two contact members adapted to be electrically connected to each other by a fuse inserted in the holder for electric interconnection of the parts of the phase conductor in question located on each side of the fuse and connected to the respective contact member. A device of this type is hitherto not known, but is would in many situations be desirable to have such a device available in order to tap voltage from a three-phase circuit, preferably so as to connect any type of load, such as tools, light fittings and the like, to a voltage. The central distribution stations in question are the ones located in ordinary living houses for distribution of the electric voltages emanating from the incoming power supply mains among various cables leading through a fuse each to different part socket-outlets or taps for connection of loads, such as glow lamps, kitchen stoves and the like. Such a central distribution station has a main fuse for each phase for interrupting the feeding of voltage in the up-stream direction from the place for distribution of the voltages of the three- phase cable. All kinds of such central distribution stations are comprised within the application field of the device mentioned above, for instance also central distribution sta¬ tions in industrial buildings. A device of the type mentioned in the introduction is particu¬ larly useful in those cases in which the voltage, for example as a result of different works on the electricity supply network, for security reasons has to be interrupted at the level of the central distribution station by switching a line breaker off and/or unscrewing the main fuses. However, a device of this type would also be useful in the case that it is desirable to provide a voltage tap close to a central distribution station, where such a tap does not exist, but it is of no importance whether the three-phase cable is interrupted up-streams of said distribution place or not. In way of a not limitative example, the special field of use "works in installation of electricity meters" may be mentioned. Such an electricity meter, which is adapted to measure the energy amount consumed by the consumers connected to the central distribution station, is arranged down-streams of the line breaker and the main fuses with respect to the direction of the three-phase cable arriving to the station. As a result of this the voltage to the conductors leading to the meter is interrupted before said works are started by switching off the line breaker and/or unscrewing the main fuses. Since the central distribution station is frequently located in a room without windows or in any case with insufficient lighting, such as cellars, some kind of further lightening is required for making it possible to carry out the works with the electricity meter. For this reason either an electric torch or a battery apparatus for connection of a glow lamp has been used. The works are frequently made easier if an electrically driven drilling machine may be utilized, and in such cases such a battery apparatus with several taps is desired. The disadvan¬ tage of the torch case consists in that it is difficult to direct the torch in a suitable direction at the same time as electric energy for a tool, such as a drilling machine, is missing. The torch is generally held between the teeth of the worker, and it is evident that this is not very comfortable. A battery apparatus is comparatively soon discharged, and when a worker has to carry out many installations works during one and the same day he has to carry a plurality of battery apparatus, which are expensive, with himself, to avoid interruptions of his work for recharging of the battery apparatus. Thus, it would be desirable to be able to in a simple way tap voltage from a three-phase cable, without letting the voltage reach the electricity meter, so as to use the voltage tapped to facili¬ tating the work with the electricity meter by connecting suitable loads thereto. SUMMARY OF THE INVENTION The object of the present invention is to provide a device of the type mentioned in the introduction, which is simple, functions well and in a simple and secure way may carry out its function. According to the invention this object is obtained by providing a device of this type with the characteristics defined in the characterizing part of the appended claim 1. Thus, the invention is based on the understanding that it is possible to remove at least two main fuses and introduce a contact element into two of these empty fuse holders into electric contact with the contact member which is connected to that part of the phase conductor in question which is still under voltage, so as to hold the contact elements in this position and tap the voltage existing between the two phase conductors, in most countries 380 volts. This voltage may then be used in the way required in a certain situation, it may for example be led to one or several socket-outlets for plugs for connection of one or several loads of the kind mentioned above. These loads may be adapted to the voltage existing between the two phase conductors or a transformer is connected between the contact elements and the socket-outlets so as to transform the voltage between the phase conductors into the voltage to which the loads are adapted. Accordingly, by means of the device according to the invention, the problems discussed above are solved. Further advantages and advantageous characteristics of the invention will appear from the following description and the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a speci¬ fic description of a preferred embodiment of the invention cited as an example. In the drawings: Fig 1 is a perspective view of a preferred embodiment of a device according to the invention, a portion of an electric cable being cut away for the sake of clearness, Fig 2 is a perspective view of a part of the device according to Fig l ready for introduction of the contact elements in two main fuse holders of the central distribution station, Fig 3 is a partially sectioned side view of a part of the device according to Fig 1 and 2, showing a contact element in electric contact with the first contact member of a main fuse holder, and Fig 4 is a perspective view of an electricity worker who installs an electricity meter at a central distribution station while utilizing the device according to the invention according to Fig 1. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The device shown i Fig 1 comprises two contact elements 1 of electric conducting material. The contact elements are consti¬ tuted by pins received in centric and axially extending re¬ cesses in cylindrical bodies 2 of electric insulating material. The pins 1 are spring loaded, so that starting from the rest position shown in Fig 1, they may be further introduced into the recesses of the bodies 2, while storing potential energy in the spring means. Each body 2 is provided with a deep slot surrounding the pin 1 and being concentric thereto, in which a sleeve 3 of electric insulating material is received displace- able in substantially that direction in which the pin 1 points. The sleeve 3 is connected to spring means for storing potential energy on pressing the sleeve into the deep slot starting from the unloaded rest position shown in Fig 1. The sleeve 3 is adapted to, in the position shown in Fig 1, project beyond the outer end of the pin, so as to prevent unintentional contact between the pin and any part of the body of a person holding the device. The cylindric bodies 2 are guidedly translationally displace- ably arranged on a rigid member 4 having the form of an elon¬ gated case with an open side 5, in which it has parallel rigid edges 6, which engages into slots arranged in the periphery of the cylindric bodies. The outside diameter of the cylindric bodies is greater than the inside dimension of the rigid member 4 in the direction perpendicular to the displacement direction and the center axis of the bodies, the part of each body 2 located below the edges 6 being chamfered so as to be adapted to the elongated lateral walls 7 of the rigid member in order o prevent the bodies 2 from turning in the rigid member. A flex 9 containing two electric conductors is led through one end wall 8 of the rigid member and said flex may have an arbitrary suitable length and an intermediate portion thereof is cut away in the figure. The electric conductors 10 are electrically connected to a pin 1 each through bores in the parts of the cylindric bodies located in the rigid member. The flex 9 is led to a case 11 with a handle 12 for carrying it. The electric conductors 10 are connected to opposite ends of the primary winding of a transformer disposed in the case 11. The two ends of the secondary winding of the transformer are connected to a terminal each of each of two socket-outlets for plugs 13. Thus, on connection of a voltage between the pins 1 this voltage will be transformed to a suitable voltage, which is provided at the socket-outlet 13 and which enables tapping of electric energy by inserting a plug connected to a load therein and thereby constituting a closed electric socket. It is generally desired to transform the voltage applied between the pins 1 down by a factor 3 , so that the voltage of the pins with respect to earth is obtained in the socket-outlet 13. When there is a voltage of 380 V between the pins 1 and a desired voltage of 220 V at the socket-outlets 13, the primary coil may have about 1700 turns and the secondary coil about 985 turns. If in this case a copper wire with a diameter of 0.4 mm is used as coil material a power of about 180 W is obtained at the socket-outlets. When necessary, windings making tapping of a higher power possible may of course be arranged. The alternative voltage of the three-phase network has in general a frequency of 50 Hz, but the device with the transformer functions just as well for other frequencies, for example 60 Hz. Over the secondary winding of the transformer may, for example in the above case over 8 turns of the winding, a light emitting diode 14 be arranged for indicating that voltage is provided at the taps 13. Preferably, a fuse 15 interrupting the voltage feed to the socket-outlets 13 on temporary overloads may be arranged. Thanks to this a person handling means connected to the device and the electric network are protected. In Fig 2 it is shown how the device shown in Fig l is intended to be applied on a central distribution station 15 with a line breaker 16 and a main fuse holder 17 for each phase. The cylindric bodies 2 are displaced along the rigid member 4, so that they have a mutual distance corresponding to the distance between two of the main fuse holders. It is of no importance which two of the main fuse holders are selected. When this distance has been adjusted the bodies are simultaneously introduced in a fuse holder each. Reference is now made also to Fig 3. Each fuse holder comprises a first contact member 18 located at the bottom thereof and connected to that part of the phase conductor in question which is still under voltage when the fuse is removed, as well as a second contact member located in the lateral wall of the holder and connected to that part of the phase conductor in question which is disconnected from voltage when the fuse is removed. When introducing the body 2 into the fuse holder 17 the sleeve 3 projecting furthest away will first hit surfaces surrounding the first contact member 18 and upon continued insertion of the body 2 be pressed into the same while storing potential energy in the spring means connected thereto. This will cause the pin 1 to arrive into abutment against the first contact member 18, and when the body 2 is sufficiently inserted this will be under spring load. The body 2 has a circumferential slot in which a O-ring 19 is received. The O-ring 19 is so dimensioned and located on the body 2 that it after obtaining electric contact between the pin 1 and the first contact member 18 comes into engagement with the internal threads arranged in the wall of the fuse holder and thereby retains the body and thus the pin in this position against the action of the spring means of the pin and the sleeve. The advantage of the arrangement of the two bodies 2 on a rigid member consists in that they will be simultaneously introduced into a fuse holder each, so that the risk for touching one pin 1 when the other 1 is in electric contact with a contact member 18 and according under voltage will be avoided. However, if for any reason only one pin 1 would be inserted in a fuse holder and the body 2 having the other pin would be located beside the central distribution station 15, the sleeves 3 prevent uninten¬ tional and dangerous touching of the pin 1. The pins may for example have a diameter of 5 mm and the sleeves 3 an inside diameter of 7 mm and an outside diameter of 9 mm, and the latter will in the axial direction project 2 mm beyond the pins in the rest position according to Fig 1. Central distribution stations arranged in dwelling-houses and industrial premises have in general different types of main fuse holders with different mutual distances. One and the same device may easily be adapted to the central distribution station in question, since on one hand the mutual distance of the bodies 2 may be adjusted by displacing them with respect to the rigid member and on the other hand the O-rings may be changed for o-rings having another outside diameter. For example, O-rings with an outside diameter of 22 mm and 28 mm are suitable for conventional fuse holders for dwelling-houses and industries, respectively, in Sweden. The main thing is that the inside diameter of the O-ring in question is smaller than the outside diameter of the cylindric body so as to surely retain the ring in a fixed position-on the cylindrical body. Fig 4 shows how the device according to the invention is uti¬ lized in connection with an installation of an electric meter at a central distribution station 15. A lamp 20 and a drilling machine 21 are connected to the socket-outlets 13 of the device. When mounting the meter it may be necessary to drill a great number of times, for instance bores for three screws for fixing the meter and 14 screws for attaching different plinths may be required. Thanks to the device according to the inven¬ tion the electricity worker may carry out an efficient work under good working conditions, especially lighting saving the eyes. The invention is of course not in any way restricted to the embodiment described above, but several possibilities to modify it will be apparent to a man with ordinary skill in the art without departing from the basic idea of the invention. The O-rings may for example be exchanged for an annular rib integ¬ ral with the bodies. The bodies could have a form other than cylindrical and other retaining means than the o-rings could be arranged, for instance any type of device which fastens the device according to the invention on the central distribution station. It would also be possible that the bodies had an outer thread for screwing them into the respective fuse holder, and than they have to be rotatably arranged on the rigid member. How¬ ever, it is not necessary that the device has a rigid member, but the bodies coul be freely moveable with respect to each other, but from the security point of view this will not be recommended. Furthermore, only one or none of the bodies may be displaceable along the rigid member. The displaceability will be of no need in the cases where the works are constantly carried out on the same type of central distribution stations. It is not necessary that any body is introduced into the main fuse holders, it would also be possible that only a contact element is inserted in these from an insulating disc or case, which is arranged and fastened onto the fuse holders. The conductors leading from the contact elements could be directly connected to a socket outlet for plugs, so as to connect a load which is adapted for the voltage existing between the two phase conductors of the three-phase cable. The sleeves protecting against contact could be removed and the pins could be completely pushed into the bodies into a statio¬ nary position, from which they could be influenced to project to a suitable extent from the bodies through tripping a snap-in coupling. Furthermore, the contact elements could have an arbitrary design, for instance a disc form.

Claims: Claims 1. A device for tapping electric voltage from an electric three-phase cable at a central distribution station (15) with a main fuse and a holder (17) therefor for each phase, each main fuse holder (17) having two contact members adapted to be electrically connected to each other by a fuse inserted in the holder for electric interconnection of the parts of the phase conductor in question located on each side of the fuse and connected to the respective contact member, c h a r a c t e ¬ r i z e d in that the device comprises two contact elements (1) adapted to be inserted into a main fuse holder (17) each, beforehand released from the main fuse, into a position in which they are in electric contact with only a first one of the contact members (18), namely the one being connected to that part of the phase conductor in question which is still under voltage when the fuse is removed, and means (2, 19) for holding the contact elements (1) in this position for tapping the voltage existing between the two phase conductors in question. 2. A device according to claim 1, c h a r a c t e r i z e d in that, the holding means comprises two bodies (2) of electric insulating material, that the two contact elements (1) are provided on a first end of a body each, that the bodies are designed to be introduced, with the first end first, into a main fuse holder (17) each into a position in which the contact elements (1) bear against the first contact members (18), and that the bodies are provided with members (19) arranged to upon reaching this position fix them in the main fuse holders. 3. A device according to claim 2, c h a r a c t e r i z e d in that the bodies (2) have a substantially cylindrical shape with a diameter slightly smaller than the inside diameter of the main fuse holders, and that an annular rib (19) of deformable material surrounds each body and is adapted to, upon intro¬ ducing the body to the position establishing electric contact into an internally threaded main fuse holder (17), be pressed into a thread while deformed and counteract removal of the body from this position. 4. A device according to claim 3, c h a r a c t e r i z e d in that said annular rib (19) is an O-ring of elastic material with a smaller inside diameter than the outside diameter of the bodies, and that the substantially cylindrical bodies (2) have a circumferential groove adapted to receive said O-ring (19) and counteract displacement thereof along the body. 5. A device according to any of the claims 2-4, c h a r a c ¬ t e r i z e d in that the bodies (2) are disposed with their first ends substantially parallel to each other on one and the same rigid member (4) and so that they only simultaneously may be introduced in one main fuse holder (17) each. 6. A device according to claim 5, c h a r a c t e r i z e d in that the bodies (2) and the rigid member (4) have means (6) in mutual engagement, said means being adapted to permit a guided translational displacement of each body (2) along the rigid member (4) so as to adapt the distance between the bodies to central distribution stations (15) with different distances between the main fuse holder (17) . 7. A device according to any of the claims (2-6), c h a r a c ¬ t e r i z e d in that the contact elements consist of pins (1) of conducting material received in recesses in said first end of the bodies (2) displaceable in their longitudinal direction and projecting out of these recesses, and that first spring means storing potential energy are associated with the pin for storing potential energy upon pressing this from an unloaded rest position into the recess. 8. A device according to claim 7, c h a r a c t e r i z e d in that said first end of each body (2) is provided with a deep slot surrounding said pin (1), that a sleeve (3) of electric insulating material is received in the slot displaceable substantially in that direction in which the pin (1) points, that second spring means storing potential energy are associ¬ ated with the sleeve (3) for storing potential energy upon pressing this from an unloaded rest position into the deep slot, and that the sleeve (3) is adapted to, in this rest position and when the pin (1) is in its rest position, project beyond the outer end of the pin so as to prevent unintentional contact between the pin and any part of the body of a person holding the device and on introducing the body into a main fuse holder hit the first contact member or surfaces surrounding this and while compressing the second spring means be intro¬ duced deeper into the slot into a position in which the pin (1) is allowed to bear against the first contact member (18). 9. A device according to any of the preceding claims, c h a r a c t e r i z e d in that it comprises two electric conductors (10) connected to one of said contact elements (1) each and at least a socket-outlet (13) for plugs, the two terminals of said socket-outlet being connected to one of said electric conductors each. 10. A device according to claim 9, c h a r a c t e r i z e d in that it comprises a voltage transformer, that the electric conductors (10) running from the contact elements (1) are connected to opposite ends of the primary winding of the transformer, that the terminals of said socket-outlet (13) for plugs are connected to opposite ends of the secondary winding of the transformer, and that the ratio between the number of turns of the primary and secondary windings is adapted to the voltage between the two phase conductors of the three-phase cable and the voltage required by a distinct load (20, 21) desired to be connected to the socket-outlet (13) for plugs.

Inventors: NILSSON JAN, SVENSSON KARL-ARNE, NILSSON, JAN, SVENSSON, KARL-ARNE
Applicants: SVENSSON KARL ARNE, SVENSSON, KARL-ARNE
Application year: 1990
Main classification: H01R19
IPC codes: H01H85, H01R13