US1642198A - High-frequency furnace circuit - Google Patents

Description

- l 1,642,198 Sept. 13s 1927- F GERTH ET AL HIGH FREQUENCY FURNACC CIRCUIT Filed Feb. 15, 1926 r Patented Sept. 13,-19727..

, UNITED STATES 4 1,642,198 lPATENT OFFICE.

FELIX GERTH AND WILHELM FISCHER, OF? BERLIN-TEMPELHOF, GERMANY, AS- SIGNORS TO C. LORENZ AKTIENGESELLSCHAFT, OF BERLIN-TEMPELHOF, GER- MANY.

HIGH-FREQUENCY FURNACE CIRCUIT.

Application filled February 13, 1926, Serial-No. 88,015, andiin Germany February 18, 1927.

This invention relates to high-frequency furnaces, but it may be understood that the invention is not limited to this special type `of high-frequency loads, but may be applied I to' other types of load systems with which a high-frequency machine is to be connected.

It is well known to generate heat in electric conducting materials, in exposing them to the influence of the magnetic field of a.

surrounding coil carrying a high-frequency current. The'material known as the resistor may thereby be regarded as the secondary of a transformer. The power transformed into heat is proportional to the square of the induced and consequently also of the inducing current. Moreover, the current in the secondary increases according to the number of turns surrounding the furnace crucible supposingthe current in the primary to be at constant value.

Therefore a great number of .primary turns is necessarily to be looked for. The

high-frequency current may be obtained by arc or spark discharges, ormay directly be supplied by a high-frequency alternator, for which latter mode of supply the connections given by the invention have a special practical importance. l

However there are great disadvantages in supplying. the 'furnace coil directly by the generator. As the coil of the furnace, because of its self-inductance, presentsa considerable resistance to the high-frequency currents, it is unfavorable to connect the furnace coil directly with' the terminals of the high-frequency generator. By connecting a variable condenser in the known manner in parallel relationship to .the furnace coil and tuning the circuit thus obtained to the .alternator frequency, the alternator may bei freed from wattless currents and its efiiciency improved, this connection being known under the 'term of parallel resonance. Further it is well known that the efficiency of an electric system has its greatest value, if 'theinner resistance of the generator is equal to the resistanceof the outerload circuit. This condition is obviously in the most cases not to be realized in connecting a given alternator with a given load according to the aforesaid manner.

Another method of connecting a high-frequency alternator with the heatingcoil of a high-frequency furnace hitherto known consists in inserting a condenser eventually in connection with a further tuning coil in series with the coil of 'the furnace, or in other words in employing a series resonance connection instead of the above mentioned parallel resonance connection. The advantage of Athis arrangement lies in that'the generator may be designed for nornial voltages and yet that the number of the furnace turns and consequently the efficiency of the latter may bev increased. If the nat-` ural frequency of this circuit is tuned to the frequency of the current of the high-frequency generator, the working of the generator may be considerably improved. As has already been set forth 'the furnace coil requires a great number of ampere-turns i. e. very strong currents if the resistor is to be heated to a. very high temperature; when tuning to resonance, however, the value of the cos p obtained by'this connection is a very low one due to the high wattless currents which also pass through the generator producing considerable losses. The generator therefore, has to be designed with respect to the Whole power output ,(apparent power) and'its size will be a multiple of the size corresponding to its pure wattless power output.

It is the object of the present invention to overcome .these `disadvantages inherent to both a pure parallel resonance connection and a series resonance connection. The invention consists in :that the generator isV coupled to a part of a timing means of a circuit containing the load impedance of the furnace coil and additional tuning means and being tuned to the generator frequency,` so that in other words on the one hand the Iwattless currents of the furnace coil are compensated and on the other hand the inner resistance of the alternator may be adapted forV the resistance of the load resistance by means of transformation.v Most favorablya direct coupling is employed which may be made variable by means of tappings, this presenting the possibility to the alternator to supply only the pure/.watt power for the resonant circuit containing the load impedance of the heating coil. But an inductive or capacity coupling will do as well. In all ofv the cases a very great amplitude of the currents in the furnace coil is attained, if the circuit containing this coil is at least approximately resonant to the generator frel quency and the alternator is counter-connected only to a part of the voltage drop in this resonant circuit and at the same time has to supply only the Watt power dissipated in the resonant circuit, and may be designed for normal values.

In order that the invention may be best understood reference should be taken to the accompanying drawings of Which Fig. 1 represents the Well known series resonance con-` nection, and Figures 2, 3 and 4 connections according to the invention, Fig. 2 employing a direct coupling of the generator to a part of the circuit resonant to the generator frequency and consisting of the load impedance and additional timing means, Whereas Figures 3 and f4 show a corresponding inductive and capacity coupling. The re erences in the single figures corresponding to each other refer to like elements.- H is a high-frequency alternator, which may be of the usual variable inductancev type, .F represents the heating coil of a high-frequency furnace, but which may be replaced by some other high-frequency load impedance, S represents an additional tuning self-induction coil and C a capacity placed in series with the furnace coil. Referring to Figure 1, the circuit H C S F is tuned to the alternator frequency and presents the disadvantages above referred to. According to Figure 2, the alternator is coupled directly with the part S, of a selfinductance forming part of the resonant circuit S, SCF, Which part may be made variable by 'means of tappings for the reason to be described as follows. In Figure 3 the coupling is an inductive one by means of the transformer T andin Figure 4 there is employed a capacity coupling by means of capacity C1. In Fig. 2 the circuit S, SCF, in Figure 3 the circuit FCS and secondary of T, and in Figure'4 the circuit FCS@1 are tuned to the frequency 'of the `high-frequency alternator H.

Further by suitably dimensioning the transformation ratio of the alternator to the resonant circuit e. the tapping at coil S1 in Fig. 2, or the'ratio of primary and secondaryturns of the transformer 'l in Fig. 3 and the Value of the capacity C, in Fig. 4, it may be obtained that the alternator Works at its highest -efliciency and is only loaded With Wattless currents. This is apparently the case, When the terminal voltage of the alternator having a fixed Value by its excitation and its number of revolutions is equal to thevoltage drop at the terminals of the part of the resonant circuit to Which it is counterconnecte-d and may also be explained in that the circuitcontainingrthe load coil carries -very high resonance currents, very high at least With respect to the current flowing through the alternator and the alternator is Working upon this circuit like upon a supply line fed by other considerably stronger alternators, and that this terminal voltage having a constant fixed value it is forced to supply a leading or a lagging or a pure Wattless current 'according lo the voltage of the resonant circuit it is oiiiitercon nected to, the potentials at thel alternator terminals and the coupling element of the resonant circuit being necessarily at equal value.

A high-frequency furnace inclu-ded into a A ing action Will therefore decrease continually.

According to a further feature of the invention this disadvantage is' overcome by employing in the resonant circuit timing means to be continuously varied during operationv such as variometers, variable condensers eventually 'in connection with condensers and inductances provided With tappings, by means of which the variation of the impedance of the furnace coil may continuously be balance-d in order to maintain the original tuning conditions. But it may be seenthat the coupling of the alternator in this case must be regulated .too accordingly and according to this novel feature of the invention the circuit parallel to the alternator must contain equally. continuously variably tuning means, or the transformation ratio of the alternator to the resonant circuit is made' variable. Referring to Fig- Fure 2-'4 this latter condition may be ob- .tained by substituting the self-inductance of Fig. 2 by a variable inductancc Varionieter, or by making the tapping continuously variable), or by making the coupling by transformer T Fig. 3 equally variable by use of a vario-coupler or by employing a variable condenser C1 in the arrangement according to Fig. 4.

What we claim is n 1. ln current supplying means for high frequency melting furnaces, a high frequency alternator machine, a load4 impedance, a circuit including said impedance, said circuit having a natural frequency substantially resonant With the machine frequency, tuning means in said'circuit in series with the load impedance, and timing means in said circuit in parallel with the load impedance and vari ably connected with the terminals of the alternator machine.

2. In current supplying means for high frequency melting furnaces, a high frequency alternator machine, a heating coil, a circuit including said coil, said c'ircuit having a natural frequency substantially resonant with the machine frequency, `tuning means in said c1rcu1t 1n series with the heatlng coll,-

and tuning means in said circuit in parallel with the coil and variably connected with thev terminals of the alternator machine.

8. In current supplying means for high frequency melting furnaces, a high frequency alternator machine, a load impedance, a circuit including said impedance, said circuit having a natural frequency substantially resonant with the machine frequency, tuning means in said circuit in series with the load lmpedance, and a varlable inductance 1n saldv I,circuit in parallel with the load impedance and connected with thel terminals of the alternator machine. y

4.' In a high-frequency current supply 'circuit for high-frequency melting furnaces, a high-frequency dynamo machine, a heating coil 'to beY supplied by said machine, a circuit Substantially resonant to the'generator frequency and containing said heating-coil,

and a variablel inductance forming part of said resonant circuit and connected to the terminals of the dynamo machine.

5. In a high-frequency feed circuit forhigh-frequency melting furnaces, a high-frequency dynamo machine, a heating coil to be supplied by .said machine, a circuit substantiall'yresonan't to the machine frequency and v containing said' heating coil, tuning means in said circuit, and an inductance forming part ofsaid resonant circuit and connected with theterminals of the dynamol machine. 6. In `a high-frequency feed circuit for high-frequency melting furnaces a highfrequency' dynamo machine, a heating coil to be sippliedby' said machine, a circuitl substantially resonantgto the machine frequency and containing said heating coil, tuning means in said circuit, and coupling means between said c1rcu1t and the dynamo machine, said means being in parallel with said circuit and connected to the terminals of the dynamo machine.- y

7. .In a high-,frequency feed circuit for high-frequency melting furnaces, a highfrequency dynamo machine, a load impedance to be supplied by said machine, a circuit substantially resonant to the frequency of the' machine and containing said load impedance, variable tuning means in said cirsuit, and variable coupling means between sald dynamomachine and said clrcuit.

8. In a high-frequency feed circuit forhigh-frequency melting furnaces, a highfrequency dynamo machine, a heatin coil to be supplied by said machine, a circuit substantially resonant to the machine frequency and containing said heating coil,

.tuning means in series in said circuit, aninductance shunted across said circuit, and Y means for .Variably connecting said inductance to the terminalsof the dynamo machine.' l

to be supplied by said machine, a circuitsubstantially resonant to the machine frequency and containing said heating. coil, a variableinductance 'in said circuit, and a yvariable coupling between said circuit and the dynamo machine.

. 11. In a high-frequency vfeed circuit for high-frequency melting furnaces, a highfrequency 'dynamo machine, a heating coil to be supplied by said machine, a circuit substantially resonant -to the machine frequency and containing said heating coil, variable tuning means in saidv circuit and in series' with said coils, and a variable parallel coupling between said circuit and said dynamo machine. f

In testimony whereof we have aixed our signatures. V

' v DR. FELIX GERTH.

Dn. vVVILVHELM FISCHER.

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