Patent Description:
Embodiments of the inventive subject matter generally relate to techniques for transforming current. More particularly, the embodiments of the inventive subject matter relate to a current transformer having multiple primary winding branches.

Embodiments described herein include a current transformer. The current transformer may comprise a primary winding configured to carry a primary current wherein the primary winding has one or more primary winding branches coupled in parallel and secondary windings having a plurality of turns configured to induce a secondary current from at least one of the one or more of the primary winding branches and an end user coupled to the secondary winding.

Embodiments described herein may include the current transformer wherein there are two primary winding branches.

Embodiments described herein may include the current transformer wherein there is one secondary winding inducing the secondary current from one of the primary winding branches.

Embodiments described herein may include the current transformer wherein there is one secondary winding on each of the two primary winding branches inducing the secondary current from each of the primary winding branches.

Embodiments described herein may include the current transformer wherein each of the primary winding branches has different impedance, and the primary current is divided among the primary branches based on their impedance.

Embodiments described herein may include the current transformer wherein the primary current is divided evenly between the primary current branches.

Embodiments described herein may include the current transformer wherein there are three primary winding branches.

Embodiments described herein may include the current transformer wherein the primary current is divided evenly between the three primary current branches.

Embodiments described herein may include the current transformer wherein there is one secondary winding on each of the three primary winding branches inducing the secondary current from each of the three primary winding branches.

Embodiments described herein may include the current transformer wherein the primary current is an alternating current.

Embodiments described herein may include the current transformer wherein there are a plurality of primary winding branches and the primary current in each of the primary winding branches has a different value.

Embodiments described herein may include the current transformer wherein the end user is configured to measure the primary current.

Embodiments described herein may include the current transformer wherein the end user is configured to supply auxiliary power to a circuit.

Embodiments described herein may include a method of reducing a current to an end user comprising flowing a primary current through a primary winding in a current transformer, dividing the primary current between a plurality of primary winding branches which are in parallel in the primary winding, inducing a secondary current in at least one secondary winding of a plurality of secondary windings from one or more of the primary winding branches, and sending the secondary current to the end user.

Embodiments described herein may further comprise measuring the secondary current with the end user.

Embodiments described herein may further comprise dividing the primary current by changing the impedance of at least one of the primary branches and thereby flowing more, or less, current through that branch.

Embodiments described herein may further comprise dividing the primary current evenly between the primary winding branches.

Embodiments described herein may further comprise inducing the secondary current through multiple secondary windings coupled to each of the primary winding branches.

The present embodiments may be better understood, and numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

The description that follows includes exemplary apparatus, methods, techniques, and instruction sequences that embody techniques of the present inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.

<FIG> depicts a schematic drawing of a circuit <NUM> having a current transformer <NUM> in an embodiment. The current transformer <NUM> may consist of a primary winding <NUM> having a plurality of primary winding branches 104A-N. The primary winding <NUM> is configured to carry a primary current <NUM> in a parallel circuit through the current transformer <NUM> via the primary winding branches 104A-N. The primary current <NUM> will be divided in the primary winding branches 104A-N based on the branch parameters, as will be discussed below. One or more of the primary winding branches 104A-N may have one or more turns <NUM>. At least one of the primary winding branches 104A-N is connected to or coupled with a secondary winding <NUM>. The secondary winding <NUM> may have a plurality of turns <NUM>. The secondary winding <NUM> may be coupled to an end user <NUM>. The current transformer <NUM>, as shown, produces a secondary current <NUM> in the one or more secondary windings <NUM>, which is proportional to the primary current <NUM> being carried through the corresponding primary winding branch 104A-N. As shown, there is a core <NUM> located proximate the primary winding branch <NUM> and secondary winding <NUM>. Because the primary current <NUM> is divided in the corresponding primary winding branches 104AN, the resulting reduction in current in the corresponding primary winding branches 104AN allows for fewer turns <NUM> in the secondary winding <NUM>. The fewer turns <NUM> allow the current transformer <NUM> to be much smaller and lighter than conventional current transformers.

The primary winding <NUM> may be connected in series with the load and may carry the current <NUM> flowing to the load. The primary winding <NUM> may have any number of the primary winding branches 104A-N. The primary winding branches 104A-N are configured to split the primary current <NUM> between the branches based on the impedance and/or resistance of each of the primary winding branches 104A-N. For example, if the impedance were the same in each of primary winding branches 104A-N, each of the branches would carry a substantially equal portion of the current <NUM>. In another example, each of the primary winding branches 104A-N could have a different impedance and/or resistance. Therefore, one of the primary winding branches 104A-N may carry a larger proportion of the current <NUM> while the other branches carry a smaller portion of the current <NUM>. The smaller portion of current <NUM> flowing through one or more of the primary winding branches 104A-N may allow the secondary windings <NUM> to have significantly less turns <NUM> than a conventional current transformer as will be discussed in more detail below.

The primary winding branches 104A-N that are coupled to the secondary windings <NUM> may have any number of turns <NUM> including one turn, or a flat turn. The number of turns <NUM> in the primary winding branches 104A-N will depend on the specifications of the current transformer and what the desired turn ratio is for each particular primary winding branch 104A-N. Each of the primary winding branches 104AN can have any configuration including, but not limited to, a single flat turn, a coil of heavy duty wire wrapped around the core, a conductor, a bus bar, and the like.

When the current transformer <NUM> is integrated with electronic circuits, the input, or the end user application, may be AC or DC.

The secondary winding <NUM> is located in close proximity to the one or more turns <NUM> of one or more of the primary winding branches 104A-N. The smaller portion of the current <NUM> flowing through the one or more primary winding branches 104A-N produces an alternating magnetic flux in the secondary winding <NUM>. The magnetic flux then induces alternating current, the secondary current <NUM>, in the secondary winding <NUM>. The secondary current <NUM> in the secondary winding <NUM> is proportional to the current flowing through the primary winding branch <NUM>. The secondary winding <NUM> may have any number of turns <NUM> between one and several thousand, in order to take a relatively large load current <NUM> in the one or more primary winding branches 104A-N and convert it to the smaller amplitude current <NUM>. The ratio between the number of turns <NUM> in the one or more primary winding branches 104A-N and the number of turns <NUM> in the associated secondary winding <NUM> is the turn ratio or branch turn ratio. The branch turn ratio will be specifically designed for the secondary current <NUM> needs of the end user <NUM> in the secondary winding <NUM>. Because each of the branch currents 106A-N has a reduced current, the number of windings <NUM> in each of the secondary windings <NUM> is greatly reduced from traditional current transformers. The number of turns <NUM> and therefore branch turn ratio will be specified based on any suitable uses for the current transformer <NUM> including, but not limited to, the ratio, the burden, or class.

The end user <NUM> may be any suitable device for use with the secondary branch current <NUM>. The end user <NUM> application may be for measurement of the primary current <NUM>, for example with an ammeter in one embodiment. It should be appreciated that the end user <NUM> may be any suitable device using AC or DC including, but not limited to, measurement devices for revenue metering, power factor meters, watt-hour meters, protective systems including but not limited to protective relay devices, power generation, plant monitoring systems, fault recorders, overall electric grid monitoring, building (energy) management systems, controls, sensors, instrumentation, auxiliary supplies, self-power supplies, and the like.

<FIG> depicts an example of the current transformer <NUM> having three primary winding branches 104A-C. In this embodiment, each of the primary winding branches 104A-C are coupled to secondary windings <NUM>, although it should be appreciated that there may be any suitable number of secondary windings <NUM>. The primary current 106A-C in the primary winding branches 104A-C will be divided based on the impendence/resistance in each of the primary winding branches 104A-C. In one example, the primary current 106A-C in the primary winding branches 104A-C is substantially equal at <NUM>% in each branch due to equal impedance/resistance in each branch. In another example, the primary current 106A may be <NUM>% of the total primary current <NUM> and the primary current 106B and 106C are each <NUM>% of the total primary current <NUM>. Although several examples of primary current 106A-N have been described it should be appreciated that any feasible current division between the primary winding branches 104A-C is envisioned.

The secondary windings 110A-C associated with each of the primary winding branches 104A-C may have any suitable number of turns <NUM>. The number of turns <NUM> in each secondary winding 110A-C may be specifically designed based on the specific end user 114A-C. Therefore, the number of turns <NUM> in each of the secondary windings 110A-C may be different or the same. The reduced primary current 106A-C in each of the primary winding branches 104A-C allows the number of turns <NUM> in each of the secondary windings 110A-C to be greatly reduced relative to a conventional current transformer. Although there are secondary windings 110A-C associated with each of the primary winding branches 104A-C, it should be appreciated that there may be any suitable number or configuration of secondary windings <NUM>. Further, it should be appreciated that although three primary winding branches 104A-C are shown, there may be more primary winding branches 104A-N to suit the needs of the current transformer <NUM> and the end users <NUM>.

<FIG> depicts the current transformer <NUM> having multiple primary winding branches 104A-B coupled to the secondary winding <NUM> on one of the branches. In this example, the end user <NUM> is an ammeter for CT testing. In one embodiment, the primary current <NUM> is divided evenly between the two primary winding branches 104A and 104B. In this example, the primary current <NUM> is 10A and the primary current 106A and 106B in each of the primary winding branches 104A and 104B is 5A. Because the primary current <NUM> is divided, the observed output current by the end user <NUM> would also be divided proportional to the percentage of primary current 106B in the primary winding branch 104B. In this example, the observed output current is <NUM> mA. In another example, the primary current 106B being measured may be reduced more than half, by adding more primary winding branches 104A-N and/or increasing the impedance in the primary winding branch 106B. Thus, the 10A primary current 106B may be reduced to any suitable percentage of the total primary current in a range lower than <NUM>%.

The number of turns <NUM> in the secondary winding <NUM> will be reduced proportional to the reduction in current in the primary winding branch <NUM>. Therefore, the size and weight of the secondary winding <NUM> will be greatly reduced in the current transformer <NUM> described herein. This size reduction will make the current transformer <NUM> much more compact than the conventional current transformers. This size reduction will greatly decrease the size of switch racks, switch gears, and panels where the current transformer <NUM> is used. Further, the space needed for storing the current transformer <NUM> will be greatly reduced. The weight and size reduction will make shipping and packing the current transformers <NUM> more affordable.

The current transformer <NUM> as described herein allows the primary current <NUM> rating to be greatly increased over conventional transformers because the primary current is divided between the primary winding branches 104A-N. For example, the current transformer <NUM> disclosed herein is able to handle current ratings of the primary current larger than 6000A and up to approximately <NUM>,<NUM> A. Further, the current transformer <NUM> described herein has short time thermal current ratings that are greatly reduced for the 104N branch when compared to conventional transformers.

In another example, the primary current <NUM> is 4000A in an <NUM> kV system voltage circuit. The ratio between the primary current <NUM> and secondary current <NUM> may be 4000A/5A. With this ratio, the secondary windings of a conventional current transformer would require approximately a <NUM>-kilogram (<NUM> Lb. ) transformer and a cabinet at least 350x165x300 mm (<NUM>. Using the current transformer <NUM> having multiple primary branches 104A-N would reduce the size and weight of the current transformer significantly. For example, when using the system with the primary current <NUM> divided by <NUM>% in two primary winding branches 104A and 104B, as depicted in <FIG>, the current transformer <NUM> may have a weight reduction of at least <NUM>-<NUM> Kgs (<NUM>-<NUM> pounds) and the overall size halved. This weight and size reduction could be more using a lower percentage of the split primary current 106A-N in the primary winding branches 104A-N using one of the methods described herein.

<FIG> depicts a flow diagram illustrating a method of operating a system including the current transformer <NUM>. The flow diagram begins at block <NUM> wherein a primary current <NUM> is flowed through a primary winding 104A-N of a current transformer <NUM>. The flow diagram continues at block <NUM> wherein the primary current <NUM> is divided between the plurality of primary winding branches 104A-N. As described, herein the primary current <NUM> may be divided among any number of primary winding branches 104A-N with varying current in each of the primary winding branches 104A-N. The flow diagram continues at block <NUM> wherein a secondary current <NUM> is induced in one or more secondary windings <NUM>. The configuration of the primary winding branches 104A-N and the secondary windings can be any configuration described herein. The flow diagram continues at block <NUM> wherein the secondary current is sent to the end user <NUM>. The end user <NUM> may be any of the end users described herein. The flow diagram continues at block <NUM> where a task is performed by the end user <NUM>. The task may be any suitable task with the secondary current including, but not limited to, measuring, supplying power, protection of circuits, any use described herein and the like.

While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is limited only by the claims. Many variations, modifications, additions and improvements are possible.

Claim 1:
A current transformer (<NUM>), comprising:
a magnetic core (<NUM>);
a primary winding (<NUM>) configured to carry a primary current (<NUM>) wherein the primary winding
comprises a plurality of primary winding branches (104A-104N) in parallel;
a plurality of secondary windings (<NUM>, 110A, 110B, 110C) magnetically coupled to at least one of the primary winding branches, each secondary winding having a plurality of turns (<NUM>) configured to induce a secondary current (<NUM>) from at least one of the plurality of primary winding branches; and
wherein each of the plurality of secondary windings is configured to be coupled to an end user (<NUM>).