US1806408A - Transformer - Google Patents

Description

May 19, 1931. w. A. MUDGE ET AL 1,806,408

TRANSFORMER Filed Oct. 2, 1928 n e l Patented May 19, 1931 UNITED STATES PATENT 1 OFFICE WILLIAM ALVIN MUDGE AND CLARENCE GmRGE BIEBER, OF HUNTINGTON, WEST VIRGINIA l TRANSFORMER Application led October 2, 1928. SerialV No. 309,843..

This invention relates to an improvement in alternatin current transformers, and reterial.

lates particu arly to low `power transformers,'i. e., transformers-whose power output is not substantially in excess of five hundred watts, andpreferably lower.

Low power transformers are required in a great many different kinds of electrical appliances. They are used for instance in supplying the cathode voltage to alternating current radio tubes, radio sets employing rectified and filtered alternating current, electric clocks run by small motors, and other apparatus. As generally constructed, a fluctuation in the primary voltage, such as the fluctuation that occurs in the usual commercial one hundred .ten volt line causes a corresponding fluctuation in the secondary or output circuit of the transformer. This nonuniform output of the transformer is undesirable in most types of work for which such transformers are intended. Most devices employing a low power transformer require a constant source of energy for their operation.

Heretofore a ballast lamp in series with the primary circuit or other re ulator has been employed for eliminating uctuations in the output of the transformer.

According to the present invention we provide a low power transformer for producing and maintaining a constant energy output independent of the normal uctuation in the supply or primary voltage.

It 1s well understood by those skilled in the art that a transformer is an electrical device having two electriccircuits, a primary and a secondary linked by a common magnetic circuit formed by the core of the transformer. The amount of energy which can be transferred from the primary to the secondary through the core is limited by the magnetic saturation value of the core ma- When a transformer is loaded so that the core of the transformer is working at or near its saturation point, an increase in the voltage impressed across the core of the transformer produces nc further appreciable increase in the energywhich the core carries across to the secondary of the transformer. If the core of the transformer is not working at or near its saturation point, increases in the voltage across the primary result in corresponding increases in the energy carried by the core to the secondary of the transformer with a consequent variation in that the primary winding will not dangeri ously overheat and to avoid a high energy waste.

According to our invention the transformer is designed to operate at or near the saturation point of the core material. The saturation point for certain Well known core materials is shown vin the accompanying drawing showing typical B-H curves for various well known materials, together with a chart of the saturation values of certain metals with their corresponding flux densities.

With reference to the drawing, it inay be stated that the BH curve for any magnetic material shows the relationship between the magnetic induction and the magnetizing force producing that induction, the B value being rated in gausses and the H value being gilberts percentimeter. Permeability is the relationship of B to H, and the point of saturation is the highest point of the curve.

In order to operate at or near the` saturation point of the core material in a small transformer, it is possible to use either a very small amount (1 to 3 ounces) of silicon steel, or one of the usual core materials having' a very high saturation value', or a moderate amount (l to 10 pounds) of a material having a much lower saturation value. rlhe use of a very small amount of material having a high saturation value for constant energy output is okijectionable becauseof the fact that it is necessary to use a large number of primar turns in order to secure a sufficiently high pr1- mar im edance.

T ere ore, according to the present invention, we use a core material not generally considered desirable for transformer urposes. We use a core material having oth high permeability and a low saturation point. By choosing a core material having both high permeability and low saturation, 1t is easy to obtain a high primary impedance without the use of an excessively great number of turns in the primary winding. At the same time, the low saturation value of the material makes it possible to operate near the saturation point of the core even though the transformer is deliveringonly a few watts.

In the accompanying drawing it will be seen that annealed sheet Monel metal has a low saturation value, its saturation value not exceeding approximately twenty-two hundred gausses. Nickel has a saturation value of approximately six thousand gausses. Both Monel metal and nickel are therefore not metals which would ordinarily be considered desirable for transformer core purposes. According to the present invention we prefer to use a metal containing nickel in a large l propo-rtion wherein the saturation Value is relatively low.

The saturation value of nickel and nickel alloys, such as Monel metal, is very low as compared with some well known transformer core materials. Pure iron, for instance, has a s aturation value of approximately twenty-two thousand gausses. Some alloys of iron and cobalt have even higher saturation values. The saturation Value for silicon steel is approximately twenty-one thousand; nineteen thousand for silicon contents of one 1-4.5%-. Permalloy, on the other hand, has a relatively low saturation value approximately ten thousand gausses.

According to our invention, typical core materials having desirable characteristics may be grouped as follows:

l. Copper-nickel alloyscontaining 60- nickel, l0-40% copper, trace-5% manganese, trace-10% iron, trace-2% silicon and none-.25% carbon. Moneli metal, which contains approximately 68% nickel, 29% copper, 1% manganese and 2% iron, together with small amounts of carbon and silicon, is a commercial alloy of this type. f

2. Iron-mckel alloys-containing more than 30% nickel and less than 70% iron with l small amounts of carbon, silicon and manganese. nickel, and 20% iron is a commercial alloy of this type. v

Nickel, containing not less than nickel with 5% of cobalt, iron, manganese, copper, silicon and carbon. Commercially pure nickel containing 99% of nickel is a commercial material of this type.

By using a core material in a transformer containing one of the above alloys, or other metal having similar saturation values in relation to the ermeability, the transformer has both a su cient-ly high primary imped- Permalloy, which contains 80% ance to avoid dangerous overheating, together with a core capable of carrying only a predetermined amount of energy to the secondary. Hence the secondary delivers a constant amount of energy independent of the fiuctuto the operation of various devices requiring a low power constant source of energy for their operation, and is both cheaper and more durable than the transformer heretofore provided for such purposes wherein the transformer is used with a ballast lamp or other more complicated voltage regulator.

We claim: A transformer having a core composed at least in part of Monel metal.

In testimony whereof we have hereunto set our hands.

WILLIAM ALVIN MUDGE. CLARENCE GEORGE BIEBER.

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