A. Field of the Invention
The present invention relates to transformers. More particularly, the present invention relates to a transformer encapsulated in a protective mold of fiberglass embedded resin.
B. Description of the Prior Art
A transformer comprises two or more coupled windings of a wire and a laminated bobbin or core for holding the windings to concentrate magnetic flux. An alternating voltage (AC) applied to one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. Varying the relative number of turns between primary and secondary windings determines the ratio of the input and output voltages, thus transforming the voltage by stepping it up or down between circuits.
The transformer transforms electrical current received from a primary coil side of circuit into a magnetic flux, which is transferred in a different current through the core to a secondary coil side of circuit ideally without any movement between the transformer parts. Its purpose is to change the electricity into a desired value wherein between the change of voltage and the corresponding change of the current ampere the voltage change is mainly used.
When the transformer is used to power in a power circuit, the power transformer is primarily desired to function better for the simple and sophisticated operation of higher end device circuitries. For example, audio devices need signal flowing through a pure and simple path as well as a stable clean DC as in illuminating devices. To this end, transformers use the laminated metal core. Metal cores easily create magnetic flux and increases effectiveness of the transformer. Most metal cores are made from silicon steel sheets for their superior electrical properties in creating the magnetic flux with ease. Also as a measure to reduce Foucault current or Eddie current layers of 0.3 mm thin metal plates form the core. The superimposed surfaces of the metal layers are insulated from each other and carefully bonded together avoiding any gaps to deteriorate efficiency.
Generally, when an electric current flows through a conducting line, certain magnetic field is formed around the conductor. And moving the current on conductor with respect to the magnetic field will induce an electric voltage. Alternating current with the frequency of 60 Hz applied to the transformer primary winding will result in a magnetic field expanding and contracting around the coil winding. Such magnetic field movement induces a voltage across the ends of the secondary coil winding. Induced secondary coil voltage is determined by the winding ratio between the primary and secondary coils. By having various winding ratios desired output voltages might be obtained simultaneously.
Transformers are adapted to have multiple secondary coils for providing various voltages needed by various circuit components. However, transformers themselves inherently have the problem of producing 60 Hz hum to be introduced into circuits around the transformers.
Besides its low cost to manufacture, because transformers in the open type of system have quality issues including emission of noise and unprotected impacts from external forces encapsulation of transformer has been performed using materials and structures with unlimited varieties.
With special consideration on reliable voltage insulation among others, mold-in type transformers currently available generally comprise a dielectric sheet, a first dielectric tape for fastening a core, a second dielectric tape for insulating windings around a bobbin or core and a volatile dipping solution. However, this method of making transformers needs the initial step of aligning the dielectric sheet to make a good fit with the winding bobbin and subsequent steps of securing the core with wraps of the dielectric tape and then another tape for insulating the windings which renders the whole process relatively complex. The final step has been dipping the transformer assembly into a bath of dielectric liquid followed by a curing step wherein the dielectric liquid is a volatile material like a liquid varnish that leaves little ingredients on the transformer product resulting in poor insulation voltage and insulation resistance and thus leaving the coils unprotected from contacting objects that may break the windings.
Different from the tape and varnish approach, potting consists of placing components in a potting cup then pouring a potting compound into the vessel. This compound may be either air- or oven-cured depending upon the type of material used. This manufacturing process traditionally has offered superior levels of thermal conductivity and corona resistance. Still, potting tends to be very labor and time intensive.
However, manufacturing transformers can be more simplified taking advantage of newly introduced thermoplastics. The three dimensional moldability of thermoplastics offers ways to add additional functionality into the part without adding extra components or manufacturing steps. No harmful volatile organic compounds (VOCs) are released as they are with many potting compounds. In addition, the process has a faster cycle time because thermoplastics eliminate several steps. A potting cup is no longer needed as with the insertion of the delicate components into the cup, and the labor-intensive potting operation or the oven-curing step. While potting cure times can last from one hour to days, thermoplastic encapsulation cycle times are generally from ten to sixty seconds that is a dramatic reduction. Thermoplastics generally perform better in thermal cycle, have a smaller size and lighter weight, and are more durable.
Encapsulation with standard thermoplastics on transformers typically leads to hot spot temperature reductions relative to open structures, due to the inherent thermal transfer advantages of conduction relative to convection. Use of a thermally conductive plastic can provide even greater thermal benefits. Key to this behavior is the intimate contact with the windings enabled by encapsulation. For reference, air has a low thermal conductivity of approximately 0.01 W/mK, and standard thermoplastics are 0.1 to 0.35 W/mK. Thermally conductive polymers can be as high as from 0.5 W/mK to 50 W/mK.
Subsequent benefits of providing a good thermal conductivity include reduced component sizes, faster electrical response times and longer component life. Thermoplastic encapsulation of transformers enables the design of a system with improved acoustic and vibratory characteristics. Thermoplastic encapsulation tends to dampen transformer vibration. Thermoplastic components are more rugged and pass higher voltage withstand tests so they are safer in operation. With encapsulation, a newly unified structure is produced where its resonant frequencies can be controlled and shifted using a proprietary process control technology and by the tailoring of the encapsulant stiffness and loss factor properties. Depending on the specific system requirements, encapsulant properties are modified to develop polymers ranging from ultra stiff composites to flexible thermoplastic elastomers. An encapsulating composition comprises a glass reinforced resin or a liquid crystal polymer. Injection molding to encapsulate transformers provides significant advantages in attenuation of noise and vibration and an ability to shift the frequencies of peak amplitude.
Also, in an electric device like ballast, the transformer is normally enclosed in a metal housing with a too tight space to dissipate heat, which is not only a waste of the electric energy but also a cause to shorten the life of the transformer resulting in early failure of the surrounding circuits in the same housing. Such conventional configurations do not allow ready dissipation of heat due to lack of space in the compact housing and confinement of the transformer by the surrounding components.
To solve this problem, the present invention provides a universal transformer geometry that may be applied to wide varieties of available materials in order to maximize a transformer performance against harmful heat and noise.