Patent Publication Number: US-5835000-A

Title: Current transformer assemblies

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to current transformer assemblies. 
     Current transformers are often used to monitor current flow in a circuit, such as for the purpose of detecting excessive power consumption and providing a warning signal or disconnection of power supply. Current transformers take the form of a toroid having a number of turns of a wire. The central aperture of the transformer is threaded onto the current-carrying conductor and the output current is taken from flying leads attached to the toroid winding. This can create a problem because it is necessary to break the current-carrying conductor when the transformer needs to be replaced. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved current transformer assembly. 
     According to one aspect of the present invention there is provided a current transformer assembly including a mounting plate having at least one pair of electrical contacts on a first surface of the plate, the contacts being connected through the plate to a conductor extending between said contacts on the opposite surface of the plate, and the assembly including a current transformer encompassing the or each conductor, and mounting means by which the transformer assembly can be retained with a cooperating assembly and make connection of said contacts. 
     The assembly preferably includes a connector accessible on the first surface of the plate, the output of the or each current transformer being connected with the connector. The assembly preferably includes a housing, the housing enclosing the opposite surface of the plate. The contacts may be of cylindrical shape and project above the first surface and below the opposite surface of the plate. The assembly may include three pairs of contacts and three current transformers embracing respective conductors extending between respective contacts of each pair. The or each current coil is preferably a toroidal transformer threaded onto the or each respective conductor. The mounting means may comprise a plurality of bolts projecting from the first surface of the plate. The assembly may include a relay connected in series with the or each conductor, the relay preferably being controlled in response to the output of the or each respective current transformer. 
     A current transformer assembly according to the present invention will now be described, by way of example, with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the assembly; 
     FIG. 2 is a perspective view of a part of the assembly, disassembled; 
     FIG. 3 is a plan view showing the transformer assembly mounted on an equipment panel; and 
     FIG. 4 is a perspective, exploded view of an alternative assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference first to FIGS. 1 to 2, the assembly 1 comprises an outer housing 2 of square shape with a closed bottom. The top of the housing 2 is closed by a removable top mounting plate 3 of an electrically non-conductive material. The top plate 3 supports on its upper surface three pairs of electrical contacts 4 and 4&#39;, 5 and 5&#39;, and 6 and 6&#39;. The contacts 4 to 6 are of cylindrical shape and project through the plate, extending a short distance above and below the plate. The two contacts 4 and 4&#39;, 5 and 5&#39;, and 6 and 6&#39; in each pair are connected together below the plate 3 by current-carrying conductors 8 in the form of thick wires or bars. The central part of the wires 8 is spaced below the lower surface of the plate 3 to allow a toroidal, current transformer 9 to be threaded onto each wire. The transformers 9 can be of any conventional kind and are retained in position on the wires 8 by an adhesive. Output wires 10 from each transformer 9 are connected to the rear of a rectangular, multi-pin connector 11 mounted in an aperture in the plate 3, the top of the connector being accessible on the upper surface of the plate. 
     The plate 3 also has four fixing bolts 20 to 23 projecting upwardly at each corner of the plate, which are used to secure the transformer assembly 1 to a cooperating assembly in the form of an equipment panel 30, as shown in FIG. 3. The equipment panel 30 has three, recessed inlet contacts 31 and three outlet contacts 32, arranged to align with and receive respective ones of the inlet and outlet contacts 4 to 6 on the transformer assembly 1. The inlet contacts 31 on the equipment panel 30 are connected to respective ones of three-phase current-carrying busbars 33; the outlet contacts 32 are connected to respective outlet busbars 34. The panel 30 has four apertures 38 located to receive the four fixing bolts 20 to 23 on the transformer assembly 1, so that it is retained on the panel by the bolts. The panel 30 also has a multi-pin connector 36 located to mate with the connector 11 on the transformer assembly 1. Wires 37 extend from the connector 36 to an electrical monitoring unit 38. 
     In use, the current-carrying busbars 33 are interconnected with the outlet busbars 34 via the wires 8 in the transformer assembly 1. Accordingly, each current transformer 9 will produce an output current proportional to the current flowing along the wire 8 embraced by the transformer. This output current is supplied via the wires 10 to the connector 11 and via the connector 36 and wires 37 to the monitoring unit 38. If any of the current transformers 9 should fail or malfunction, the transformer assembly 1 can be simply removed and replaced. This can be done easily and quickly. The housing 2 ensures that the components of the transformer assembly are protected from contaminants; it also prevents inadvertent access to high voltages. 
     The transformer assembly may include additional components, as shown in FIG. 4. In this arrangement, the housing contains a three-phase relay or contactor unit 50. The contactor unit 50 contains conventional solid state or electromechanical relays and is connected to the wires 8&#39; from the contacts 4 to 6 so that, by opening the relays, current is prevented from being supplied to the output contacts. The contactor 50 may be controlled directly by the outputs from the current transformers 9 or by the monitoring unit 38, via the connector.