GB1603686A - Current transformer system - Google Patents

Abstract

To protect the secondary circuit of a main current transformer to be connected upstream against unwanted disconnection, the current transformer arrangement, having at least one ring core transformer (RW), contains a conducting body (LK) acting as primary winding which passes through the ring core (RK), and a terminal connection at the primary side which is constructed as a plug-in device (ST) and engages end sections (KE1, KE2) on both sides of the conducting body (LK). This produces a rugged and reliable-contact connection to the secondary circuit of the main current transformer to be connected upstream. <IMAGE>

Description

(54) CURRENT TRANSFORMER SYSTEM (71) We, BBC BROWN, BOVERI & COMPANY LIMITED, Baden, Switzerland, a Swiss Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a current transformer system for connection to the secondary of a preceding main current transformer.

Transformer systems of this kind are widely used in electric network proection as connecting elements between main current transformers on the power side and various types of protective relays. The current transformer of the system will then function as an input current transformer for the relay circuit.

In certain known transformer systems the primary winding consists of only a single turn of a conductor extending through a toroid core which in turn is connected into the secondary winding of the preceding current transformer. This calls for special requirements with regard to the terminal connections, because the secondary winding of the preceding main transformer must not be disconnected during operation and reliable contact connection is therefore absolutely necessary. Thus a detachable terminal connection, which can be simply manipulated, between the toroid core transformer or input transformer and the preceding main transformer, is desirable.

It is therefore the object of the invention to provide a current transformer system with a primary terminal connection which can be simply engaged and released, providing reliable contact and being of a simple construction.

According to the invention there is provided a current transformer system for connection to the secondary winding of a main current transformer, and comprising a core transformer, a conductor member extending through the core to function as a primary transformer winding, the conductor having end portions at least one of which is provided with an annular groove, and plug-in means having a pair of resilient arms for respective removable engagement with said end portions, at least one of said arms being slotted to provide two spaced prongs which are received in a said annular groove.

An embodiment of the invention will now be described by way of examole with refev- ence to the accompanying drawings wherein: Figure 1 is a perspective view of a multiple current transformer system with terminal devices; Figure 2 is an axial section through a toroid core transformer with the associated terminal plug device; Figure 2a is a modified structural element of the terminal plug device relating to the embodiment illustrated in Figure 2; and Figure 3 is a special embodiment of a toroid core transformer shown as a perspective view.

In Figure 1, a plurality of toroid core transformers RW, each having a coaxial conductor member LK as a primary winding, are disposed on a circuit board which functions as a support T.

An associated terminal connection for each transformer RW comprises a terminal plug device ST having a pair of contact arms KAi, KA2. The end portions KAIL, KAE2 of the contact arms KA1, KA, are constructed in resilient bifurcated form and are provided with U-shaped slots which form a pair of spaced engaging prongs as shown.

The conductor member YK has end portions KE, and KE2 which form contact elements for connection to the plug device and are part of the primary winding of each transformer.

Each of the end portions KE, and KE2 has an annular groove for respective engagement by the spaced prongs of the U-shaned slots in the end portions KATE1, KAE2. This provides an excellent and reliable electrical and mechanical connection, a feature which is particularly important in view of the forces which occur in the event of excess current flow.

The double-sided arrangement as described whereby the end portions KE1 and KE. of the conductor member LK are each provided with an annular groove for engagement by slots in the end portions KATE, and KATE, of the contact arms of the plug device, may of course be regarded as generally convenient.

Thus in a modified embodiment shown in Figure 2a one of the contact arm end portions KAE has an inwardly curved end face which bears resiliently on a contact end portion KE of the conductor member LK functioning as the primary winding, in the coupled position of the plug-in device ST indicated in broken lines in Figure 2a. This results in comparatively large spring travel for the cooperating contact elements, a feature which is advantageous in some cases.

A contact switch KS which is closed in the disengaged inoperative position of the plug-in device ST but which is open on the engaged connected position is provided between the contact arms KA1 and KA2 of the plug device ST. Thus when the terminal connection is detached the switch KS will automatically short-circuit the secondary of a preceding main current transformer.

The contact switch KS is formed by circuit portions KVAS1, KAS2 of the contact arms KA1 and KA2 which resiliently bear against each other. The contact switch KS is opened by a separating element TR when the terminal connection is coupled to the conductor member LK. The separating element TR in the example shown is an edge portion of the circuit board T which supports the transformers. The insulating material of the circuit board ensures reliable separation of the shortcircuiting contacts when the plug connection is engaged. In the modification according to Figure 2a the spread position of the contact arms is obtained by the contact arm end portion KAE bearing on the end portion of the conductor member LK.

As shown in Figure 2 the secondary winding SW of the transformer is arranged in toroid configuration on the toroid core RK. To ob- tain a particularly simple and space-saving electrical connection between the secondary winding and the connected circuit, usually a printed circuit, on the support T, a sector like connecting device AV with solderable contact pins S is disposed in the manner shown in Figure 3 on the toroid core RK.

The secondary winding SW extends over a corresponding residual sector of the toroid core. An embodiment of this kind also offers the advantage that the interior of the toroid core remains freely accessible for the insertion of the conductor member LK.

WHAT WE CLAIM IS: 1. A current transformer system for connection to the secondary winding of a main current transformer, and comprising a core transformer, a conductor member extending through the core to a function as a primary transformer winding, the conductor having end portions at least one of which is provided with an annular groove, and plug-in means having a pair of resilient arms for respective removable engagement with said end portions, at least one of said arms being slotted to provide two spaced prongs which are received in a said annular groove.

2. A current transformer system as claimed in Claim 1, wherein one of said arms is slotted to form said two spaced prongs, a said annular groove being provided in one of said end portions for receiving the two spaced prongs of said one arm, the other arm of said plug-in means bearing resiliently against the other end portion of said conductor.

3. A current transformer system as claimed in Claim 2 wherein a normally closed switch is disposed between said resilient arms, said arms being moved apart upon engagement with said end portions of the conductor member, whereby to open the switch.

4. A current transformer system as claimed in Claim 3, wherein said switch is formed by portions of said arms resiliently urged to touch each other in said normally closed position of switch.

5. A current transformer system as claimed in any one of Claims 2 to 4, wherein the or each transformer is mounted on a circuit board, an edge portion of the circuit board forming separating means for separating said arms upon engagement with the end portions of said conductor member.

6. A current transformer system as claimed in Claim 6, wherein a sector-shaped connector is mounted to said core transformer, said connector having spaced terminal pins for the secondary winding.

7. A current transformer system as claimed in any preceding claim wherein said core transformer is toroidal.

8. A current transformer system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. The double-sided arrangement as described whereby the end portions KE1 and KE. of the conductor member LK are each provided with an annular groove for engagement by slots in the end portions KATE, and KATE, of the contact arms of the plug device, may of course be regarded as generally convenient. Thus in a modified embodiment shown in Figure 2a one of the contact arm end portions KAE has an inwardly curved end face which bears resiliently on a contact end portion KE of the conductor member LK functioning as the primary winding, in the coupled position of the plug-in device ST indicated in broken lines in Figure 2a. This results in comparatively large spring travel for the cooperating contact elements, a feature which is advantageous in some cases. A contact switch KS which is closed in the disengaged inoperative position of the plug-in device ST but which is open on the engaged connected position is provided between the contact arms KA1 and KA2 of the plug device ST. Thus when the terminal connection is detached the switch KS will automatically short-circuit the secondary of a preceding main current transformer. The contact switch KS is formed by circuit portions KVAS1, KAS2 of the contact arms KA1 and KA2 which resiliently bear against each other. The contact switch KS is opened by a separating element TR when the terminal connection is coupled to the conductor member LK. The separating element TR in the example shown is an edge portion of the circuit board T which supports the transformers. The insulating material of the circuit board ensures reliable separation of the shortcircuiting contacts when the plug connection is engaged. In the modification according to Figure 2a the spread position of the contact arms is obtained by the contact arm end portion KAE bearing on the end portion of the conductor member LK. As shown in Figure 2 the secondary winding SW of the transformer is arranged in toroid configuration on the toroid core RK. To ob- tain a particularly simple and space-saving electrical connection between the secondary winding and the connected circuit, usually a printed circuit, on the support T, a sector like connecting device AV with solderable contact pins S is disposed in the manner shown in Figure 3 on the toroid core RK. The secondary winding SW extends over a corresponding residual sector of the toroid core. An embodiment of this kind also offers the advantage that the interior of the toroid core remains freely accessible for the insertion of the conductor member LK. WHAT WE CLAIM IS:

1. A current transformer system for connection to the secondary winding of a main current transformer, and comprising a core transformer, a conductor member extending through the core to a function as a primary transformer winding, the conductor having end portions at least one of which is provided with an annular groove, and plug-in means having a pair of resilient arms for respective removable engagement with said end portions, at least one of said arms being slotted to provide two spaced prongs which are received in a said annular groove.

2. A current transformer system as claimed in Claim 1, wherein one of said arms is slotted to form said two spaced prongs, a said annular groove being provided in one of said end portions for receiving the two spaced prongs of said one arm, the other arm of said plug-in means bearing resiliently against the other end portion of said conductor.

3. A current transformer system as claimed in Claim 2 wherein a normally closed switch is disposed between said resilient arms, said arms being moved apart upon engagement with said end portions of the conductor member, whereby to open the switch.

4. A current transformer system as claimed in Claim 3, wherein said switch is formed by portions of said arms resiliently urged to touch each other in said normally closed position of switch.

5. A current transformer system as claimed in any one of Claims 2 to 4, wherein the or each transformer is mounted on a circuit board, an edge portion of the circuit board forming separating means for separating said arms upon engagement with the end portions of said conductor member.

6. A current transformer system as claimed in Claim 6, wherein a sector-shaped connector is mounted to said core transformer, said connector having spaced terminal pins for the secondary winding.

7. A current transformer system as claimed in any preceding claim wherein said core transformer is toroidal.

8. A current transformer system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.