Field of the Invention

The present invention relates to the device for stabilizing the current. Background of the Invention

For numerous reasons, such as deficiency of resources and energy and environmental destruction, it is the global tendancy to save as much as possible in all areas of economy and social life. Electro-mechanical engineering, too, developes in association with the saving. Reduction of power dissipation and increase in lifetime of electric equipments may be one of the methods for realizing saving strategy in electro-mechanical engineering.

Such undesirable and unintended accidents as overload, short circuit or single phase have detrimental effects upon effective use of the power and lifetime of the electric equipments.

In order to prevent overload, short circuit or single phase, the electric equipments should be provided with stabilized power source.

The power source may be referred to the voltage source from the viewpoint of the voltage or may be referred to the current source from the viewpoint of the current.

Up to now numerous transformers embodying various principles have been known in the art that provide voltages limited to a certain extent. The power source with such voltages is called as the voltage source, which is electric potential energy source. The voltage source ensures the application of the Ohm's Law: l=U/R, according to which the current changes in inverse ratio to the resistance as the load resistance changes. However, in practice most electric equipments request the current source that provides the current which remains unchaged during operation even though the load resistance changes widely, rapidly and continuously since the work done by the electric power is the current not the voltage. This means that the electric equipments preferably require the current stabilizers rather than the voltage stabilizers.

The available components that limit the current are the resistors (R), the inductors (L) and the capacitors (C). However, these components have drawbacks of consuming much energy for limiting the current and costing a great deal for manufacturing.

Anyhow, the most effective component for limiting the current among the three components is the capacitor which lets the alternative current flow through. However, as mentioned above, the manufacturing cost is expensive.

The applicant of the present invention with an idea that the capacitor can be replaced by the transformer which allows the passing of the alternative current came to a conclusion that the reconstruction of the transformer can overcome the weak point of the transformer which has no ability to limit the current as required by the load.

It is an object of the present invention to provide device for stabilizing the current that can provide a desirable current by simple and cost-effective reconstruction of the existing transformers which offer opportunities to largely save energy and materials.

It is another object of the present invention to provide device for stabilizing the current that can provide a suitable current to electric equipments of any capacity, from hundred watts up to tens of thousands of kilowatts.

It is further object of the present invention to provide device for stabilizing the current that enables the elimination of expensive additional devices/means for for preventing or reducing unwanted electric effects such as overload, short circuit or single phase. These and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description and accompanying figures.

Summary of the Invention Present invention concerns the device providing the stabilized current by simply reconstructing the conventional transformer with its structure of the core to strictly limit the load current.

Present invention discloses the device for stabilizing the current having the core whose first and second legs are different in size, i.e., the sectional area of the second leg is smaller than that of the first leg, thereby preventing the current from exceeding its strictly restricted limit in case the short circuit occurs, and providing and maintaining highly stabilized working current even if the load resistance widely changes.

The core of the device for stabilizing the current comprises a first leg and a second leg, a primary winding disposed around the first leg, a secondary winding disposed around the second leg, a compensating winding disposed around the first leg and connected with the secondary winding.

In embodiments according to the present invention the ratio (Ks) of the sectional area of the second leg (S ₂ ) to the sectional area of the first leg (Si) is selected within the range of 0.6-0.95. (K _S =S ₂ /S ₁ =0.6~0.95)

In order to prevent the production of saturation in the second leg having aforementioned ratio of sectional areas, the voltage per turn of the primary winding should be determined on the basis of the voltage per turn of the secondary winding. Fig. 1 illustrates an embodiment of the invention embodying its basic principle. As shown in the figure, the sectional area of the first leg ST is larger than the sectional area of the second leg S ₂ , being wound around the said legs are respective primary and secondary windings Wi, W ₂ . Such structure enables to prevent the output short circuit, however, as could be recognized through Fig. 1 b, the desired stability of the current is not achievable.

Fig. 2 illustrates an embodiment of the invention embodying its main principle. As shown in the figure, the compensating winding W _c is disposed around the first leg and connected with the secondary winding W ₂ in such a way that its voltage U _c joins with the voltage of the secondary winding U ₂ . As could be understood from Fig. 2 b, such structure not only enables to prevent the output short circuit but to ensure desired stability of the current as well.

Fig.3 illustrates an embodiment of the invention for producing two stabilized output current in one device for stabilizing the current, wherein the second leg is composed of two sublegs, each of which wound with the respective secondary windings W ₂ i, W ₂ 2 and the ratio of the sectional area of each of the said sublegs to the sectional area of the first leg is selected within the range of 0.3-0.475.

Figs.4 and 5 illustrate alternative embodiments according to the invention, where the device for stabilizing the current needs no grounding at its output terminal, the primary winding W-i acts as a compensating winding if whole or part of it is connected with the secondary winding W ₂ .

Successful application of the present invention in a three-phase device for stabilizing the current can be achieved by V-connection of two or Y-connection of three single-phase devices for stabilizing the current.

Detailed Description of the Invention

Present invention has unlimited coverage, i.e., the invention can be utilized in all electric equipments, regardless of their capacity and use. Following description discloses a few examples thereof.

Fig.6 illustrates various arrangements utilizing the present invention in the welding systems. In order to apply present invention in the welding systems, the ratio (K _s ) of the sectional area of the second leg (S ₂ ) to the sectional area of the first leg (Si) is selected within the range of 0.6~0.85(K _S =S ₂ /Si=0.6~0.85) and the no-load output voltage is selected to be less than 10V in case of the spot welders and 45~55V in case of the rest welders.

Utilization of the present invention in welding systems provides possibility of miniaturizing the body of the welders for convenient transport and operation by drastically reducing the necessary amount of core and coil.

Fig. 7 illustrates circuit diagrams utilizing the present invention in the power supply system of the three-phase plasma generators, wherein the ratio (K _s ) of the sectional area of the second leg (S ₂ ) to the sectional area of the first leg (Si) is selected within the range of 0.75-0.8 (K _s =S ₂ /S ₁ =0.75-0.8).

Fig.7 a illustrates a circuit diagram employing the device for stabilizing the current in a grounded power supply system of a three-phase plasma generator of 380V, wherein the transformer should be reconstructed according to present invention in such a way that its capacity be 20-24KVA.

Fig.7 b illustrates a circuit diagram employing the device for stabilizing the current in the existing three-phase insulating transformer of 100KVA for the power supply system of the three-phase plasma generator, wherein upto five plasma generators can be engaged with the power supply system.

Fig.8 illustrates an arrangement employing the device for stabilizing the current in a power supply system for the electric arc melting furnace.

The large-sized transformers for the electric furnaces are conventionally connected with the three-phase reactors, which results in large space requirements, power dissipation and decrease in efficiency. Therefore, it is preferred that the three-phase reactors be replaced with the three-phase divices for stabilizing the current, volumes and weights of which are below 1/10 -1/100 of the three-phase reactors. The benefits of the employing the devices for stabilizing the current in the DC electric furnaces are saving of electrodes to more than 50% and cutdown of costs caused by expensive high-power rectifiers to half. Such benefits can increase the productivity to over 30% while decreasing production cost by 30%. Fig.9 illustrates an arrangement employing the device for stabilizing the current in a flexible starting system of the DC motors.

At the starting of the motors, they have the starting current whose intensity is 4-7 times larger than that of the rated currency, which needs to be limited. Utilization of the present invention ideally enables the flexible starting of the motors by limiting the starting currents to be about 1.5~2 times larger than the rated currency.

Present invention offers the opportunity for rectifiers to use cheaper diodes whose overload-resisting ability is only one third or even a quarter of diodes used before, and furthermore, prevents the rectifiers (or any other equipments) from destruction due to overload without the help of any protection means such as the fuses, thereby decreasing the purchasing and operating costs by half.

Fig.10 illustrates circuit diagrams employing the device for stabilizing the current in a flexible starting system of an AC induction motor (of squirrel-caged or wound - rotor type). An AC induction motor requires currents 2 to 4 times larger than the rated current at its starting and this can be achieved by employing the device for stabilizing the current.

Utilization of the present invention in the flexible starting system of the motors defends the motors against destruction caused by the overload or the short circuit to convert equipments into semipermanent equipments.

Present invention is applicable in the flexible starting system of motors of all capacities and voltages including single-phase micro or small motors, or three- phase small, medium, large or extra-large motors and low, medium or high voltage (3300V) motors. With the utilization of the present invention in the high-power wound -rotor induction motors, there is no need to arrange a slip ring for dragging out a rotor winding to connect it with a starting device as is being done at the existing motors, thereby eliminating complicated operating means and saving considerable quantity of materials.

Fig.11 illustrates arrangements employing the device for stabilizing the current in the rectifying systems for electrochemical industries such as the electroplating and the electrolyzing, wherein the ratio (K _s ) of the sectional area of the second leg (S ₂ ) to the sectional area of the first leg (S-i) is selected within the range of 0.75~0.8 (K _S =S ₂ /S =0.75~0.8).

The large rectifying systems for electrochemical industries usually require very low working voltage ranging from a few to tens of volts while the working current ranges from tens of thousands to hundreds of thousands of amperes. Therefore the currents should be stabilized, otherwise the temperature and the concentration of the electrolyte may be affected, which results in poor working quality, low productivity and waste of the power.

A small sized three-phase device for stabilizing the current can be engaged with the existing large transformer for the rectifying systems either in its front or behind it as shown in Figs. 1 1a and 1 1 b. However, it is recommended that the small sized three-phase transformers for the electroplating devices be reconstructed according the present invention.

Fig. 12 illustrates circuit diagram employing the device for stabilizing the current in the feeding transformer engaged with the electric power system.

Since the feeding transformers in general are too large to reconstruct their cores in accordance with present invention, it is preferred that the three-phase device for stabilizing the current for the flexible starting be arranged at the low voltage side of the feeding transformer.

Generally existing feeding transformers have been strongly recommended that they be accompanied with the quick-operating circuit-breakers that could block the feeding circuits within a few milliseconds to protect against terrible destruction due to short circuit at its receiving end. However, such circuit-breakers encounter financial problems owing to extraordinary costs.

The circuit-breakers can be replaced with the three-phase devices for stabilizing the current whose body is just 1/100 of the feeding transformer (as shown in Fig.12) to provide the power with suitable output voltage and little waveform distortion under the rated load, and to reduce the output voltage to zero if the current 1.2-1.5 times larger than the rated current passes through.

Hence, without the help of the circuit-breakers, present invention disallows the passing of unrated power, thereby strictly controlling the power distribution.

As decribed above, present invention makes it possible to save at least 30% or usually 50~70%, or more preferably 80~90% of the consuming power when comparing with the existing technics for limiting the current and prevents the electric equipments from destruction due to the Overload, short circuit or single phase without using expensive additional devices. With the help of the present invention, the electric or electronic equipments of whether small or high power, or for household or industrial use, can be converted into semipermanent equipments.

Although the invention has been shown and described with exemplary embodiments, it should be understood that numerous applications can be made without departing from the spirit and scope of the present invention. Accordingly, the present invention has been shown and described by way of illustration rather than limitation.

References

A, B, C: the input phase

A' , B\ C : the output phase

X, Y, Z: the input phase

X', Y\ Z' the output phase

IR: the current on the resistance side

N: the grounding

PR: the power on the resistance side

R: the resistance

Si : the sectional area of the first leg

S ₂ : the sectional area of the second leg

S _Y : the sectional area of the yoke

t: : the time

U ₀ : the voltage on the resistance side

Ui : the voltage of the primary winding

U ₂ : the voltage of the secondary winding

U21 : the voltage of the secondary winding

U ₂₂ : the voltage of the secondary winding

U _c : the voltage of the compensating winding

U _DC : the voltage of the DC outlet

U _R : the voltage on the resistance side

U _R0 : the output voltage on the resistance side the turns of the primary winding

W ₂ : the turns of the secondary winding

W _c : the compensating winding Description of Drawings

Fig. 1a schematically illustrates the basic principle of the present invention and Fig. 1b is an equivalent load characteristic curve.

Fig. 2a schematically illustrates main principle of the present invention and Fig. 2b is an equivalent load characteristic curve.

Fig.3 illustrates an embodiment of the invention for producing two stabilized output current in one device for stabilizing the current.

Fig.4 schematically illustrates an embodiment where the whole of the primary winding is connected with the secondary winding to act as a compensating winding.

Fig.5a schematically illustrates an embodiment where a part of the primary winding is connected with the secondary winding to act as a compensating winding and fig.5b is an equivalent load characteristic curve showing the curve changes depending on the number of turns of the compensating winding. Fig.6 illustrates various arrangements and circuit diagrams utilizing the present invention in the welding systems.

a) a multiple winding device for stabilizing the current for single welder b) a single winding device for stabilizing the current r for single welder

c) a multiple winding device for stabilizing the current for two welders d) a device for stabilizing the current for multiple (upto 5-8) welders

e) a device for stabilizing the current for a DC welder

f) a device for stabilizing the current for a spot welder

g) a device for stabilizing the current for a DC high-frequency welder.

Fig.7a illustrates a circuit diagram employing the device for stabilizing the current in a grounded power supply system of a three-phase plasma generator of 380V. Fig.7 b illustrates a circuit diagram employing the device for stabilizing the current in the power supply system of the three-phase plasma generator, which can be engaged with upto five plasma generators.

Fig. 8a illustrates circuit diagrams utilizing the present invention in the power supply system for an AC arc melting furnace.

Fig. 8b illustrates circuit diagrams utilizing the present invention in the power supply system for a DC arc melting furnace.

Fig.9 illustrates an arrangement employing the device for stabilizing the current in a flexible starting system of DC motors and an equivalent characteristic curve of the flexible starting.

Fig.10a and 10b illustrates arrangements and circuit diagrams employing the device for stabilizing the current in a flexible starting system of an AC induction motor (of squirrel-caged or wound -rotor type).

Fig.10c illustrates a circuit diagram employing the device for stabilizing the current in a flexible starting system of a three-phase AC induction motor.

Fig.10d is a current characteristics curve of the flexible starting of the AC induction motor employing the device for stabilizing the current.

Fig.1 1a illustrates an arrangement employing the device for stabilizing the current in front of the existing large transformer for the rectifying system of the electrochemical industry.

Fig. 1 b illustrates an arrangement employing the device for stabilizing the current at the back of the existing large transformer for the rectifying system of the electrochemical industry.

Fig. 12a illustrates an arrangement employing the device for stabilizing the current in a feeding transformer for boosting the voltage.

Fig. 12b illustrates an arrangement employing the device for stabilizing the current in a feeding transformer for lowering the voltage.