Transformers are used extensively used in all electrical and electronic applications. Transformers are useful to step voltages up or down, to couple signal energy from one stage to another, or for impedance matching. Other applications include magnetic circuits with solenoids and motor stators. There are single and multiphase potential transformers. There are current transformers for sensing current and powering electronic trip units for circuit interrupters such as circuit breakers and other electrical distribution devices.
One example of a circuit breaker current transformer assembly is described in U.S. Pat. Nos. 4,591,942 and 4,884,048 which patents are hereby incorporated by reference. The transformer assembly described therein senses a current overload condition and signals a static strip unit which provides thermal and magnetic response characteristics for the circuit breaker. The transformer is made of a laminated magnetic core with two bobbins containing a secondary winding of insulated wire and a primary winding or strap.
Ideally, the transformer assembly utilized by a circuit breaker with an electronic trip unit produces current, voltage and power from one or more phase currents connected to the circuit breaker to supply the circuit breaker electronic trip unit. The signal supplied to the trip unit for processing needs go be proportional to a wide range of phase currents. The electronic trip unit must also be isolated from potentially destructive voltage surges in any of the phases.
As the devices which carry the transformer become increasingly smaller themselves, there is a need to achieve these ideal characteristics in a more compact design. Furthermore, the space available is rarely designed with the transformer of primary concern. Thus, there is a need to have the flexibility of varying the design of the transformer to work around the other components in the device.
Having a limited size or uniformity of the available space causes many problems. For example, the coil bobbin of the transformer can be made longer only if the sides are made thinner. This requires additional laminations of magnetic material on the core sides to maintain a constant flux density along the magnetic path, More laminations, however, quickly offers diminishing returns as the increase in air gaps between the laminations acts to decrease the gain in flux density.
In view of the increasing size restriction for transformers, there is a need for a more compact transformer which increases the size of the coil bobbin without reducing the effectiveness of the magnetic core and allows the core size to also increase. There is another need for an inexpensively manufactured transformer which can modify its shape to use the maximum space available in a uniform or non-uniform enclosure.