WO1997003451A1

WO1997003451A1 - Power saving apparatus using mutual inductive reactor

Info

Publication number: WO1997003451A1
Application number: PCT/KR1995/000086
Authority: WO
Inventors: Yeong Choon Chung; Hang Heui Cho
Original assignee: Yeong Choon Chung; Hang Heui Cho
Priority date: 1995-07-07
Filing date: 1995-07-07
Publication date: 1997-01-30
Also published as: AU2937295A

Abstract

A mutual inductive reactor including a primary coil wound around a core of a closed magnetic circuit and connected to an input power source, and a secondary coil wound around the core of the closed magnetic circuit and connected to a load in series, the secondary coil being connected at a winding start point thereof to a winding start point of the primary coil. The mutual inductive reactor utilizes the principle that the power transformation ratio between the primary and secondary coils in transformer is usually 1 : 1. The mutual inductive reactor achieves power saving through an improvement in the power factor and an appropriate voltage drop obtained by a combination of the mutual induction effect obtained by the primary voltage coil and the reactance integrating effect obtained by the secondary current coil. The mutual inductive reactor also achieves a stable supply of required power to a load by determining variations in the input voltage and load.

Description

POWER SAVING APPARATUS USING MUTUAL INDUCTIVE REACTOR

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a power saving apparatus, and more particularly to a mutual inductive reactor for achieving an improvement in the power factor and an improvement in power saving by utilizing a mutual magnetic induction action and a current feedback action, and a power saving apparatus using such a mutual inductive reactor.

Description of the Prior Art

Basically, power saving is to reduce loads other than required works or to reduce the amount of electric power to a power range having no influence on the works. Based on such a concept, a power saving effect has been conventionally obtained by controlling the voltage and current to appropriately supply them, or by improving the power factor for reactance component load using a phase- leading capacitor or an electronic controller. In a conventional power saving apparatus wherein an improvement in the power factor is obtained, a phase-leading capacitor serves to mutually compensate a phenomenon that for the reactance, the phase of current lags behind the phase of voltage with a phenomenon that for the capacitance, the current phase leads on the voltage phase, thereby improving the power factor. In this apparatus, however, appropriate capacitors should be opened and closed depending on the amount of load. Furthermore, this apparatus involves a degradation in insulation characteristic, a reduction in capacitance and an increase in cost.

In rotary power machines such as AC induction motors, a transformer or slidable phase controller for dropping the supply power to an appropriate voltage level has been used to achieve power saving. This method is based on the fact that the actual operating load is typically 60 to 70 % of the rated output power.

As a method for obtaining the power saving effect, capacitors, transformers or electronic inverters have been knowingly used to improve the power factor or to drop the voltage, as mentioned above. However, the power saving apparatus employing the transformer or slidable phase controller has no utility because it is of a large capacity and is expensive. On the other hand, the phase control or switching control system employing the electronic inverter has problems in cost and reliability and problems of electromagnetic influence and noise.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a linear power saving apparatus for saving the power supplied from a power source to a load, capable of appropriately improving the power factor and appropriately dropping the voltage so as to attenuate an increase in the loss of inactive power occurring when the load has a reactance component or when the power factor is degraded due to the AC impedance of a power receiving-side load circuit.

Another object of the invention is to provide a power saving method capable of supplying a high quality power to a load without any damage to the AC waveform of input voltage.

Another object of the invention is to provide an apparatus for and a method of improving the power factor by an active feedback current based on the consumed power of a reactor at the side of a load, without using any phase-leading capacitor.

Another object of the invention is to provide an apparatus for and a method of saving power, on the basis of the principle that the power transformation ratio between the primary and secondary coils in a transformer which is a general power transforming device becomes 1 : 1 ultimately, by decreasing the power supplied to the secondary current coil by a certain quantity and feeding back the surplus power to the primary voltage coil, thereby obtaining a power saving effect corresponding to the feedback power, so that the power consumption and the power transformation capacity can be reduced.

Another object of the present invention is to provide a mutual inductive reactor capable of not only achieving a compactness in construction by use of a core and windings constructed to provide only the quantity of power required for an appropriate voltage drop, but also obtaining a power saving effect resulted from the appropriate voltage drop and improvement in power, a waveform shaping effect for electrical noise included in an input by virtue of a co-action of the inductance and self-induction of the reactor, and an effect to smooth an abrupt variation in rush current.

Another object of the invention is to provide a control circuit for a power saving apparatus, capable of always achieving a stable supply of required power to a load by using a mutual inductive reactor and determining the amount of current flowing through the load and the condition of input voltage.

In accordance with one aspect, the present invention provides a mutual inductive reactor comprising: a primary coil wound around a core of a closed magnetic circuit and connected to an input power source; and a secondary coil wound around the core of the closed magnetic circuit and connected to a load in series, the secondary coil being connected at a winding start point thereof to a winding start point of the primary coil.

In accordance with another aspect, the present invention provides a power saving apparatus comprising: three-phase power sources; and three mutual inductive reactors each having a primary coil and a secondary coil both connected to each corresponding one of the three- phase power sources, the primary coils of the mutual inductive reactors being connected at winding end points thereof in parallel together, and the secondary coils of the mutual inductive reactors being connected at winding end points thereof to inputs of a load, respectively, whereby the mutual inductive reactors constitute a three- phase load circuit.

In accordance with another aspect, the present invention provides a power saving apparatus comprising: three-phase power sources; and three mutual inductive reactors each having a primary coil and a secondary coil both connected to each corresponding one of the three- phase power sources, the primary coils of the mutual inductive reactors being connected at winding end points thereof to a ground line, and the secondary coils of the mutual inductive reactors being connected at winding end points thereof to inputs of a load having an output connected to the ground line, respectively, whereby the mutual inductive reactors constitute a single-phase load circuit. In accordance with another aspect, the present invention provides a power saving apparatus comprising: a mutual inductive reactor having a primary voltage coil connected to an input power source and a secondary current coil connected to a load; primary voltage detection and control means for detecting a voltage across the primary voltage coil of the mutual inductive reactor, comparing the detected voltage with a first reference voltage and outputting a control signal based on the result of the comparison; secondary voltage detection and control means for detecting a voltage across the secondary current coil of the mutual inductive reactor, comparing the detected voltage with a second reference voltage and outputting a control signal based on the result of the comparison; an OR gate for ORing the control signals from the primary and secondary voltage detection and control means; and switching means adapted to be switched between a first contact position for directly connecting the load to the input power source and a second contact position for connecting the load in series to the secondary current coil, in accordance with an output signal from the OR gate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which: FIGS. IA to IC are circuit diagrams respectively illustrating various conventional power supplying circuits having different constructions, wherein

FIG. IA shows a power supplying circuit employing a double winding transformer, FIG. IB shows a power supplying circuit employing a single winding transformer, and

FIG. IC shows a power supplying circuit employing a reactor;

FIG. 2 is a circuit diagram illustrating a power supplying circuit employing a mutual inductive reactor in accordance with the present invention;

FIG. 3 is a circuit diagram for explaining the function and effect of the mutual inductive reactor shown in FIG. 2; FIG. 4A is an equivalent circuit diagram of the mutual inductive reactor shown in FIG. 2;

FIG. 4B is an equivalent circuit diagram of a conventional reactor;

FIG. 4C is an equivalent circuit diagram illustrating the impedance distribution for a load circuit;

FIG. 5 is a diagram for explaining the voltage drop and boosting in accordance with the present invention;

FIGS. 6A and 6B are diagrams for explaining an improvement in the power factor in accordance with the present invention;

FIG. 7 is a vector diagram illustrating the improvement in the power factor in accordance with the present invention;

FIGS. 8A and 8B are diagrams for explaining current smoothing and waveform shaping functions of the mutual inductive reactor in accordance with the present invention, wherein

FIG. 8A explains the current smoothing function, and

FIG. 8B explains the waveform shaping functions; FIG. 9 is a circuit diagram illustrating a three- phase three-wire load circuit including mutual inductive reactors in accordance with an embodiment of the present invention;

FIG. 10 is a circuit diagram illustrating a three- phase four-wire load circuit including mutual inductive reactors in accordance with another embodiment of the present invention;

FIG. 11 is a circuit diagram illustrating a control circuit for a power saving apparatus equipped with the mutual inductive reactor according to another embodiment of the present invention;

FIGS. 12A and 12B are diagrams for explaining the control principle of the control circuit in accordance with the present invention, wherein FIG. 12A explains the primary voltage detection and control of the control circuit, and

FIG. 12B explains the secondary voltage detection and control of the control circuit;

FIG. 13 is a circuit diagram illustrating a detailed construction of the control circuit shown in FIG. 11; and

FIGS. 14A and 14B are diagrams for explaining functions of the control circuit shown in FIG. 11, wherein

FIG. 14A explains the function of a primary voltage detection and control unit constituting a part of the control circuit, and

FIG. 14B explains the function of a secondary voltage detection and control unit constituting a part of the control circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention utilizes the voltage drop principle of a mutual inductive reactor. This voltage drop principle of the mutual inductive reactor in accordance with the present invention will be described by comparing it with the conventional transformer system used to drop the voltage in the load side. First, the size of the reactor in accordance with the present invention is compared to that of the conventional self induction type power transforming device such as transformer or reactor, on the basis of the amount of transformed electric power to be required.

FIGS. IA to IC illustrate various conventional power supplying circuits having different constructions. respectively, all of which are adapted to, for example, obtain a voltage drop of 20 V from an input voltage V_j of 220V, that is, to obtain an output voltage V₂ of 200 V. Referring to FIG. IA, there is illustrated a power supplying circuit employing a double winding transformer. In this case, the double winding transformer 1 has the number of primary winding turns determined by the following equation:

V_} x 10

4.44 x f x Bm x S

where, n_j : Number of Primary Winding Turns;

V-. : Primary Voltage; f : Power Frequency (Hz); Bm : Magnetic Flux Density of Core; and

S : Cross-sectional Area of Core.

On the other hand, input and output voltages of the double winding transformer 1 have the following relationship:

where, n₂ : Number of Secondary Winding Turns; and

V₂ : Secondary Voltage. Therefore, the ratio between the input and output voltages is the same as the ratio between the numbers of primary and secondary winding turns.

Accordingly, the number of secondary winding turns n₂ should be proportional to 200 V. As a result, it requires a sufficient copper wire size to meet the load- side current. For example, where the load-side current is 1 A, a transformer having the capacity of 200 VA (200 VA = 200 V x 1 A) is required. FIG. IB illustrates a power supplying circuit employing a single winding transformer. Similar to the double winding transformer, this single winding transformer requires a capacity of 200 VA so that current of 1 A can be supplied for the load-side voltage of 200 V. In other words, the capacity of the transformer should be equal to or more than the maximum load-side capacity in order to obtain the voltage and current amount required at the side of the load.

Meanwhile, FIG. IC illustrates a power supplying circuit wherein a reactor or resistor is connected in series to a load-side circuit. In this case, the output voltage V is dropped by the voltage generated across the reactor 3, thereby achieving a power saving effect.

Where the power supplying circuit of FIG. IC is adapted to obtain an output voltage of 200 V from an input voltage from 220 V, however, the reactor 3 must be of the 20 VA grade because the voltage across the reactor 3 should be 20 V for IA, the current of the load circuit (20 VA = 20 V x 1 A). Moreover, this power supplying circuit involves a degradation in the efficiency at the side of the load circuit because a power consumption based on P = I²R(Z). Consequently, this power supplying circuit employing the reactor or resistor connected in series to the load circuit has little utility for the purpose of voltage drop in AC circuits.

Referring to FIG. 2, there is illustrated a power supplying circuit employing a mutual inductive reactor constituted by a double winding transformer to obtain a voltage drop in accordance with the present invention. As shown in FIG. 2, the mutual inductive reactor includes a primary coil n_j and a secondary coil n wound around the core of the same closed-magnetic circuit. The primary coil UJ. is coupled to an input power source whereas the secondary coil n₂ is connected in series to a load 10. The winding start point Pl of the primary coil n_j is connected to the winding start point P2 of the secondary coil n so that the transformer constitutes a mutual inductive reactor. The present invention is characterized by a power saving apparatus using such a mutual inductive reactor. In accordance with the present invention, the number of winding turns of the secondary coil n and the current coil voltage V_χ across the mutual inductive reactor are determined by the difference between the input and output voltages V_j and V₂ (V_j - V₂). -13-

In other words, the number of winding turns of the secondary coil n₂ in accordance with the present invention is determined by "V_χ (Current Coil Voltage) x I_L (Load- side Current)", that is, the difference between the input and output voltages V-. and V , even though the number of winding turns of the secondary coil n in the conventional double winding transformer is proportional to the output voltage V .

For example, the conventional transformer should have a capacity of 200 VA in the case of requiring an output voltage V₂ of 200 V dropped from the input voltage by 20 V when current is 1 A. Under the same condition, the mutual inductive reactor in accordance with the present invention requires only a small capacity of 20 VA (20 VA = 20 V x 1 A) corresponding to about 1/10 of the capacity required in the conventional transformer.

The voltage drop principle of the mutual inductive reactor in accordance with the present invention will now be described in more detail. In the transformer 9 of the present invention, the winding start point Pl of the primary coil τi-. is connected to the winding start point P2 of the secondary coil n . The secondary coil n is connected at its winding end point to one input of the load 10 so that it can be connected in series to the primary coil n₁ via the load 10. The other input of the load 10 is connected to the winding end point of the primary coil n^. With such an arrangement, the load 10 is subjected to the voltage V₂ attenuated from the input voltage V_j by the voltage V_χ induced on the secondary coil n₂ (V₂ = V_j - V_χ). Where the winding start and end points of the second coil n₂ are connected in opposite phases to the load 10, the output voltage V₂ corresponds to the sum of the input voltage V_j and the voltage V_χ (V₂ -= V_j + v_χ). in this case, the primary voltage can be boosted. Such voltage drop and boosting in accordance with the present invention are illustrated in FIG. 5.

In order to explain the function and effect of the present invention in more detail, a circuit shown in FIG. 3 is exemplarily illustrated, which includes a mutual inductive reactor circuit according to the present invention. The following description will be made in conjunction with two states occurring in the circuit of FIG. 3. The first state is that an input voltage V_j is connected to a terminal S at the side of the mutual inductive reactor circuit according to the present invention whereas the second state is that the input voltage V_j is connected to a terminal D at the side of a load.

In the mutual inductive reactor of the present invention, its primary coil n_j is a voltage coil Vcoil connected in parallel to the input voltage V_j. The primary coil n^ is wound around a core made of ferromagnetic core material so that it can perform a mutual electromagnetic induction. In other words, the reactor of the present invention is an electric power transforming device having a combination of the mutual induction transformer function and the reactor function. Referring to FIG. 4A, there is illustrated a functional equivalent circuit of the mutual inductive reactor in accordance with the present invention. As shown in FIG. 4A, an antiphase voltage Vref to the primary voltage coil n^ connected to a source voltage Vs is induced on the secondary coil n₂ by an electromagnetic induction generated by the primary voltage coil n_j. By this antiphase voltage Vref, a voltage drop occurs at the side of the load 10. The secondary coil n2, which is connected in series to the load 10, is a current coil Icoil serving to generate an electromagnetic induction in the primary voltage coil n^ in proportion to a load current. The secondary current coil n also serves to provide a power feedback effect.

The power feedback effect is exhibited in the form of an improvement in the power factor, namely, a current phase compensation effect. The power factor improving effect of the mutual inductive reactor according to the present invention will now be described. When a switch 70 is coupled to the terminal D at the side of the load 10 in the input circuit of FIG. 3, the current I resulting from the input voltage V_j lags in phase behind the voltage E by 90" if the circuit inductance for the load 10 is assumed as forward inductance, as shown in FIG. 6A.

Since the average power P+ is the same as the inactive power P- in the above case, the power factor becomes zero. As a result, there is no active power. Where the switch 30 is coupled to the terminal S at the side of the reactor circuit in the circuit of FIG. 3, the input voltage V_j is applied to the voltage coil n^ which, in turn, induces an antiphase voltage to be applied to the current coil n₂. As the antiphase voltage is applied to the current coil n₂, a current attenuated by the antiphase voltage flows through the current coil n₂ and the load 10. This current then serves to generate a voltage E' having the same phase as the current I by its electromagnetic induction effect. The voltage E' has a voltage level determined by the turn ratio (n_j : n ) between the primary and secondary coils n^ and n₂. This voltage E* is applied to the voltage coil n^. Since the phase difference between the voltages E and E' is 90°, these voltages E and E' are combined together, thereby exerting an electromagnetic induction effect on the current coil n . If the actual current phase reaches 45° in this case, the power factor of 70 % is obtained.

Heretofore, the function and effect of the phase of current flowing through the current coil n₂ of the mutual inductive reactor according to the present invention and the load 10 have been described under the assumption that the load 10 is the forward inductance. Although an actual influence on the current phase is varied depending on the circuit impedance and the load impedance, the principle of the power factor improving mechanism is the same as mentioned above. The power factor improving mechanism according to the present invention will be described in more detail in conjunction with theories associated therewith.

Generally, the power factor PF can be expressed by the following equation:

Active Power

PF =

Input Voltage x Input Current

Referring to the above equation, it can be understood that the power factor is increased as the input current decreases.

In either case of using the conventional series reactor of FIG. IC or using the mutual inductive reactor of FIG. 2 according to the present invention, accordingly, the impedance distribution for the load circuit is exhibited as shown in FIG. 4C. Where the series reactor of FIG. 1, the mutual inductive reactor of FIG. 2 and the load 10 have the same inductance, they may exhibit the same power factor improving effect.

However, the actual functional equivalent circuit according to the present invention has an impedance Z_j of Vref + C + R, as shown in FIG. 4A. On the other hand, the conventional reactor has an impedance of L + C + R, as shown in FIG. 4B. In other words, the secondary current coil n₂ of the present invention has an electrically dynamic impedance whereas the conventional reactor serves only as an AC resistor because it has an electrically simple impedance. The input current I flowing through the mutual inductive reactor of the present invention is expressed as follows:

Vs - Vref I =

Z. + z₂

On the other hand, the input current I flowing through the conventional simple reactor is expressed as follows:

Vs I =

The loss of power P occurring at the reactor shown in FIG. 4 is expressed as follows:

P -= Iτ2' x Z-(L + C + R) The loss of power P occurring at the secondary current coil n₂ of the mutual inductive reactor according to the present invention can calculated using the equation "P = I² x Z_j(L + C + R)". Since the values of C and R in the mutual inductive reactor of the present invention are those of an dynamic impedance for generating the voltage Vref, they are considerably less than those of the impedance (L + R + C) for obtaining a voltage drop V_L only by use of a simple AC resistor. Accordingly, the loss of power occurring at the secondary current coil n₂ of the present invention is very less than that occurring at the conventional reactor shown in FIG. IC.

The secondary current coil n of the present invention narrows the current phase with respect to the power factor obtained by the phase difference between the voltage and current for the load with the above-mentioned inductance components. The narrowed current phase can be expressed as "P = EIcosθ (W) . By virtue of the narrowed current phase, the average power P+ is increased whereas the inactive power P- is decreased, as shown in FIG. 6B.

The above effects are depicted in the vector diagram of FIG. 7. The current phase angle θs in the case that the input power switch 70 of FIG. 3 is connected to the terminal S at the side of the reactor circuit according to the present invention is smaller by "Λθ" than the current phase angle θp in the case that the input power switch 70 is connected to the terminal D at the side of the load. The vector diagram of FIG. 7 shows the power reduction effect obtained by the reduction in current phase angle.

Now, current limiting and filtering operations of the mutual inductive reactor according to the present invention will be described.

Even when the mutual inductive reactor of FIG. 2 according to the present invention receives at its primary input a voltage having a waveform distorted due to a switching output voltage from an inverter or other electrical impact as shown by the waveform 13 in FIG. 8A, it outputs at its secondary output a shaped voltage as shown by the waveform 14 in FIG. 8A. Although the mutual inductive reactor receives an instantaneously transient voltage, the current resulting from its secondary output voltage V₂ has a smooth waveform as shown by the waveform 16 in FIG. 8B.

These functions of the mutual inductive reactor according to the present invention are based on a co- operation of the integral effect obtained by the reactance components of the secondary current coil n with the induction effect for compensating the induced voltages of opposite phases respectively across the primary and secondary coils n_j and n with each other and compensating a serge voltage, a transient voltage and a noise voltage with one another by the mutual actions of the voltage and current coils n-. and n₂ shown in FIG. 4A, namely, the voltage drop and boosting action thereof shown in FIG. 5.

The effect obtained depending on the turn ratio between the primary and secondary windings of the mutual inductive reactor 9 according to the present invention will be described. The windings of the mutual inductive reactor according to the present invention may be the combination of a transformer and a reactor.

In this case, the number of turns of each winding can be calculated using the following general equation:

1

T/V = (1-1)

4.44 f x B x A x 10^"8

where, T/V: Number of winding turns per Voltage of 1 V; f : Frequency (Hz);

B : Magnetic Flux Density of Core (Gauss); and A : Cross-sectional Area of Core (cm²).

Let's consider a mutual inductive reactor having the following conditions:

f: 60 (Hz);

B: 15,000 (Gauss); and

A: 14.95 (cm²). In this case, T/V of the mutual inductive reactor is 1.7 turn by the following calculation using the equation (1-1):

T/V =

4.44 x 60 x 15,000 x 14.95 x 10^"

= 1.7 (Turn)

If the input voltage V_j in this case is 218 V and the no-load voltage induced across the current coil n₂ is 14 V, the number of turns of the current coil, namely, secondary coil n₂ is 24. In this case, the number of turns of the voltage coil, namely, primary coil n_j is 371.

Meanwhile, the relationship between the current I-. flowing through the primary coil n_j and the current I₂ flowing through the secondary coil n₂ can be expressed as follows:

n_j x l_j = n* x I- (1-2)

From the equation (1-2), the following equation can be derived: n-. x I-

If the load power capacity in the above case is 5 KVA, I₂ is about 23 A by the following calculation:

Load Power Capacity (KVA) =

Input Voltage (V<)

5 (KVA) = ^ 23 A

218 (V)

Accordingly, the current l_j flowing through the primary coil n_j can be calculated using the equation (1-3) as follows:

23 (A) x 24 (Turn)

*1 =

371 (Turn)

= 1.48 1.5) A

Based on the intensity of each current calculated as mentioned above, the copper wire diameter of each corresponding coil can be determined. That is, the primary coil n₁ has a diameter bearing 1.5 A whereas the secondary coil n₂ has a diameter bearing 23 A.

Now, an influence on the input voltage by a variation in actual load current occurring when the mutual inductive reactor designed as mentioned above in accordance with the present invention will be described. This influence is a variation in the voltage across the primary coil ni caused by a variation in the load current I flowing through the secondary coil n₂.

For the mutual inductive reactor, let's assume that the following conditions are given:

Load Output Voltage (V₂) : 205 V Current Coil Voltage (V_χ) : 15 V Input Voltage (V.) : 220 V Load Current (l_j) : 17 A

In this case, the load current l_j flowing through the voltage coil can be calculated using the equation (1-3) as follows:

17 (A) x 24 (Turn)

371 (Turn)

= 1.099 1.1) A Meanwhile, the voltage V^ across the voltage coil can be expressed as follows:

Current Coil Voltage (V_χ) x Load Current (I₂)

^v»l =

Voltage Coil Current (l_j)

(1-4)

In the above case, the voltage V-*_j can be calculated using the equation (1-4) as follows:

15 (V) x 17 (A)

^VN1 =

1.1 (A)

= 231.8 (V)

The primary voltage coil is subjected to a voltage feedback effect obtained by the voltage fed back by the mutual induction action of the secondary coil n₂, that is, the difference between the voltage across the primary voltage coil V^ and the input voltage V- (11.8 (V) = 231.8 (V) - 220 (V)). By virtue of such a voltage feedback effect, the power factor is influenced. Heretofore, the basic arrangement of the single-phase power source in the mutual inductive reactor according to the present invention and the effect obtained thereby have been described.

Referring to FIG. 9, there is illustrated a three- phase three-wire (3φ 3W) load circuit including mutual inductive reactors in accordance with an embodiment of the present invention. As shown in FIG. 9, the three-phase three-wire (3φ 3W) load circuit has three input power source lines connected at their terminals R, S and T to respective winding start turns of the primary coils n of the mutual inductive reactors 17, 18 and 19 according to the present invention. The load circuit also has a common terminal 9 to which the winding end turns of the primary coils n_j of the mutual inductive reactors 17, 18 and 19. With such an arrangement, the mutual inductive reactors 17, 18 and 19 are connected in parallel to the input power source lines R, S and T, respectively. The secondary coils n of the mutual inductive reactors 17, 18 and 19 are connected in series between respective input power source lines R, S and T and respective corresponding input lines 8, 80 and 81 of loads L.

On the other hand, FIG. 10 illustrates a three-phase four-wire (3φ 4W) load circuit including mutual inductive reactors in accordance with another embodiment of the present invention. As shown in FIG. 10, the primary coils n_j of the mutual inductive reactors 17, 18 and 19 are connected at their winding start turns respectively to the three input power source lines R, S and T of the three- phase four-wire (3φ 4W) load circuit. The winding end turns of the primary coils n₁ are connected in common to a ground line N of the lad circuit via a common line 51. With such an arrangement, the ground line N and the input power sources are connected in parallel to the input power source lines R, S and T. The secondary coils n₂ of the mutual inductive reactors 17, 18 and 19 are connected in series between respective input power source lines R, S and T and respective corresponding input lines 8, 80 and 81 of loads L.

Heretofore, the function and effect of the mutual inductive reactor according to the present invention and the application of the reactor to power circuits have been described. Now, an embodiment of the present invention relating to a power saving apparatus using the mutual inductive reactor according to the present invention will be described. In implementation of a practical power saving apparatus, there is a problem that the apparatus has a difficulty to satisfy a wide load condition and various power source situations because the relationship between input and output voltages in the apparatus is difficult to appropriate cope with a given load condition and a given input voltage condition only by the mutual inductive reactor of the present invention.

For example, in a motor operation involving a severe load variation, a certain voltage drop aiming for an improvement in the power factor provides a considerable power saving effect obtained during the motor operation is maintained at a normal state because the load factor is 60 to 70 % of the rated load factor in the normal motor operation. Upon starting the motor or when the load factor is abruptly increased, however, it is required to boost the voltage or supply 100 % of the source voltage so that a sufficient power can be supplied. When the input voltage is dropped below a certain level, the load- side voltage from the mutual inductive reactor is dropped to a level interfering with the normal motor operation. In this case, it is also required to boost the voltage or supply 100 % of the source voltage.

In this regard, still another object of the present invention is to realize the implementation of a useful power saving apparatus utilizing the characteristics of mutual inductive reactors.

As mentioned above, in the mutual inductive reactor of the present invention shown in FIG. 2, the primary and secondary coils n^ and n₂ are electromagnetically coupled in parallel to the input power source V_s.

The number of winding turns of the primary coil n^ is determined by the voltage V_j from the input power source V_s whereas the number of winding turns of the secondary coil n₂ is determined by an arbitrary appropriate voltage drop V_χ. In this case, the output voltage V₂ is determined to be "V_j - V_χ". The power is also reduced by

Where the normal operating voltage range of the load 10 is 220 V ± 15 % and the input voltage V- iε 220 V, a voltage range from 187 V to 253 V is allowed by the mutual inductive reactor. Where the voltage V_χ across the secondary current coil n₂ is 15 V and the input voltage V is 190 V, however, the voltage supplied to the load 10 is only 175 V. In this case, the load is difficult to normally perform its work. As a result, it is necessary to provide means for directly connecting the input voltage V_j to the load, rather than the power saving effect of the mutual inductive reactor.

Meanwhile, the current flowing through the secondary current coil n₂ is greatly increased when the work to be performed by the load 10 increases over a predetermined reference level or when a high intensity of current is required due to an overload. Since the voltage V_χ across the secondary current coil n₂ is also greatly increased in this case, based on the relation "V_χ = I₂*R", the load- side output voltage V is decreased by the voltage V_χ. As a result, the resulting output voltage is difficult to sufficiently provide the power to be required in the load 10.

In either case, the mutual inductive reactor involves a problem in utility because it also provides a counter function to its power saving function.

Referring to FIG. 11, there is illustrated a control circuit for a power saving apparatus equipped with the mutual inductive reactor according to the present invention. As shown in FIG. 11, the control circuit includes a primary voltage detection and control unit 20 for detecting the input voltage of the input power source connected in parallel to the primary voltage coil n_j of the mutual inductive reactor, comparing the detected voltage with a reference voltage and outputting a control signal on the basis of the comparison result. By the primary voltage detection and control unit 20, a variation in the input voltage is monitored. The control circuit also includes a secondary voltage detection and control unit 21 for detecting a voltage V_χ across the secondary current coil n₂ of the mutual inductive reactor, comparing the detected voltage with a reference voltage and outputting a control signal on the basis of the comparison result. By the secondary voltage detection and control unit 21, the amount of current I₂ flowing through the secondary current coil n₂ is monitored. The control circuit also includes a switching unit for directly connecting the load 10 to the input power source or connecting the load 10 in series to the secondary current coil n₂ in accordance with each of the control signals respectively output from the units 20 and 21. The switching unit has two fixed contacts 24 and 25 respectively connected to the input power source and the secondary current coil n₂. With such a construction, the control circuit controls the mutual inductive reactor to appropriately cope with variable conditions of the input power source and load.

In FIG. 11, the reference numeral 23 denotes an OR gate for ORing the control signals output from the units 20 and 21 and sending the resultant signal to the switching unit as a control signal.

As shown in FIG. 13, the primary voltage detection and control unit 20 includes a bridge-type full-wave rectifier 33 for detecting a voltage between a center tap of the primary voltage coil n^ and the winding start point of the primary voltage coil n^ and rectifying the detected voltage. A hysterisis circuit 35 is coupled to the rectifier 33 to receive the rectified output from the rectifier 33. The primary voltage detection and control unit 20 also includes a comparing amplifier 36 for receiving the output from the hysterisis circuit 35 at its negative input and comparing the received voltage with a reference voltage V , received at its positive input. The hysterisis circuit 35 has a hysterisis operating point for the reference voltage V_jr. The comparing amplifier 36 sends its output signal to one input of the OR gate 23.

On the other hand, the secondary voltage detection and control unit 21 includes a bridge-type full-wave rectifier 34 for detecting the voltage V_χ across the secondary current coil n and rectifying the detected voltage, a comparing amplifier 37 for receiving the output from the rectifier 34 at its negative input and comparing the received voltage with a reference voltage V_ZL received at its positive input, and a timer 38 connected to the output of the comparing amplifier 37. The timer 38 is adapted to output a high level signal for a predetermined time when an input received therein is triggered. The timer 38 comprises a monostable multivibrator constructed to enable a re-triggering. The output of the timer 38 is connected to the other input of the OR gate 23. To the OR gate 23, power relays 43 and 44 are coupled, which serve to activate the switching operation of the switching unit. The power relay 43 is coupled to the OR gate 23 via a NOT gate 40 whereas the power relay 44 is directly coupled to the OR gate 23. Operation of the control circuit will now be described. This operation involves two control operations. The first control operation is to automatically achieve a direct connection of the load circuit to the input power source when the voltage V-. from the input power source is dropped below the reference voltage V-_L that is depicted by the waveform 28 in FIG. 12A and is lower than the rated voltage 27 depicted by the waveform 27 in FIG. 12A. The second control operation is to automatically achieve the direct connection of the load circuit to the input power source when the current coil voltage V_χ across the secondary current coil n is higher than the reference voltage V^. The first control operation will be first described in conjunction with FIG. 13.

Once the rectifier 13 of the primary voltage detection and control unit 20 detects the voltage between the center tap of the primary voltage coil n_j and the winding start point of the primary voltage coil n^, it rectifies and smooths the detected voltage and then sends the resulting voltage to the hysterisis circuit 35 which has its hysterisis operating point for the reference voltage V_T1. The hysterisis circuit 35 applies the voltage received therein to the negative input of the comparing amplifier 36 which also receives the reference voltage V_It, 41 at its positive input. The comparing amplifier 36 compares the voltage received from the hysterisis circuit 35 with the reference voltage V-^ and outputs a control voltage based on the result of the comparison. FIG. 14A shows the control voltage output from the comparing amplifier 36. When the voltage from the input voltage source V_j applied to the negative input of the comparing amplifier 36 after being rectified is lower than the reference voltage V_TL applied to the positive input of the comparing amplifier 36, the output from the comparing amplifier 36 has the high level H.

When the OR gate 23 receives this high level output at its one input, it outputs a high level signal. The high level output from the OR gate 23 is applied to the power relay 44 which is, in turn, relayed ON. The output from the OR gate 23 is also applied to the NOT gate 40 which, in turn, outputs a low level signal. The power relay 43 receives the low level output from the NOT gate 40, so that it is relayed OFF. By these relay operations of the power relays 43 and 44, the load input line 26 is connected to the contact 24 associated with the power relay 44 so that it is directly connected to the input power source.

On the contrary, when the voltage from the input voltage source V_j is a normal voltage not less than the reference voltage V_IL is applied, the comparing amplifier 36 outputs a low level signal. By the low level output from the comparing amplifier 36, the power relay 43 is relayed ON, thereby causing the load input line 26 to be connected to the contact 25 associated with the power relay 43. As a result, a normally saved power can be supplied.

Now, the second control operation will be described. Since the secondary current coil n of the mutual inductive reactor is connected to the load 10 in series, the current I₂ flowing through the secondary current coil n is increased as the load current flowing through the load 10 increases. At this time, the current coil voltage V_χ is also increased in proportion to the increase in current in accordance with the Ohm's Law (E(V_χ) = I«R). Such relation between the current I₂ and the current coil voltage V_χ is shown in FIG. 12B. In accordance with the present invention, the control circuit can detect directly the current coil voltage V_χ from the secondary current coil n₂ without using any additional current detecting device and achieve a direct connection of the load to the input power source when the detected current coil voltage V_χ is higher than the reference voltage V-^.

Once the rectifier 34 of the current coil voltage detection and control unit 21 detects the voltage V_χ across the secondary current coil n₂, it full-wave rectifies the detected voltage and then sends the resulting voltage to the negative input of the comparing amplifier 37 which also receives the reference voltage V_ZL, 40 at its positive input. The secondary current coil voltage V_χ output from the rectifier 34 after being full-wave rectified has the waveform shown by "V_χ" in FIG. 14B. When the load current is increased as upon starting, for example, a motor, the current coil voltage V_χ, which is applied to the comparing amplifier 37, is higher than the reference voltage V-^, as shown in FIG. 14B. In this case, the output 371 of the comparing amplifier 37 has a high level.

When the current coil voltage V_χ is lower than the reference voltage V-^ in a normal operation of the motor, as shown by the waveform V_χl in FIG. 14B, the output 371 of the comparing amplifier 37 has a low level.

The output from the comparing amplifier 37 is applied to the timer 38 which, in turn, triggers the received signal and outputs a high level signal 381 for a predetermined time. As shown in FIG. 14B, the timer 38 outputs continuously the high level signal 380 upon receiving the continuous signal 370.

When the output from the timer 38 has the high level, namely, when a large amount of current flows as upon starting the motor, the power relay 44 is relayed ON, thereby causing the load input line 26 to be connected to the contact 24 associated with the power relay 44. As a result, the load input line 26 is directly connected to the input power source. In this case, a sufficient power is supplied to the load.

When the load current is decreased below an appropriate amount of current, the power relay 43 is relayed ON, thereby causing the load input line 26 to be connected to the contact 25 associated with the relay 43. As a result, a normally saved power can be supplied.

The power relays 43 and 44 may comprise silicon controlled rectifiers, triacs or solid state relays.

The above-mentioned control circuit according to the present invention makes it possible to practically use the power saving characteristic of the mutual inductive reactor. Accordingly, it is possible to provide a power saving apparatus capable of achieving a smooth power supplying while coping with variations in the input voltage and load and thereby without any interference with a normal operation of the load.

As apparent from the above description, the present invention provides a power-saving mutual inductive reactor capable of providing a power transformation effect with a minimum capacity required for a voltage drop, a power factor improvement effect, a noise removal effect and a rush current smoothing effect by combining the principle of transformer with the characteristic of reactor involving an integral effect. By virtue of such a reactor, the present invention also provides a power saving apparatus of the linear type capable of achieving a stable power supplying while coping with variations in the input voltage and load without causing a trouble such as degradation in the source voltage due to the damage thereof or generation of noise involved in the conventional phase control or switching pulsewidth modulation types.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A mutual inductive reactor comprising: a primary coil wound around a core of a closed magnetic circuit and connected to an input power source; and a secondary coil wound around the core of the closed magnetic circuit and connected to a load in series, the secondary coil being connected at a winding start point thereof to a winding start point of the primary coil.

2. A power saving apparatus comprising: three-phase power sources; and three mutual inductive reactors each having a primary coil and a secondary coil both connected to each corresponding one of the three-phase power sources, the primary coils of the mutual inductive reactors being connected at winding end points thereof in parallel together, and the secondary coils of the mutual inductive reactors being connected at winding end points thereof to inputs of a load, respectively, whereby the mutual inductive reactors constitute a three-phase load circuit.

3. A power saving apparatus comprising: three-phase power sources; and three mutual inductive reactors each having a primary coil and a secondary coil both connected to each corresponding one of the three-phase power sources, the primary coils of the mutual inductive reactors being connected at winding end points thereof to a ground line, and the secondary coils of the mutual inductive reactors being connected at winding end points thereof to inputs of a load having an output connected to the ground line, respectively, whereby the mutual inductive reactors constitute a single-phase load circuit.

4. A power saving apparatus comprising: a mutual inductive reactor having a primary voltage coil connected to an input power source and a secondary current coil connected to a load; primary voltage detection and control means for detecting a voltage across the primary voltage coil of the mutual inductive reactor, comparing the detected voltage with a first reference voltage and outputting a control signal based on the result of the comparison; secondary voltage detection and control means for detecting a voltage across the secondary current coil of the mutual inductive reactor, comparing the detected voltage with a second reference voltage and outputting a control signal based on the result of the comparison; an OR gate for ORing the control signals from the primary and secondary voltage detection and control means; and switching means adapted to be switched between a first contact position for directly connecting the load to the input power source and a second contact position for connecting the load in series to the secondary current coil, in accordance with an output signal from the OR gate.

5. A power saving apparatus in accordance with claim 4, wherein the primary voltage detection and control means comprises: a bridge-type full-wave rectifier for detecting a voltage between a center tap led out of an optional position on the primary voltage coil and a winding start point of the primary voltage coil and rectifying the detected voltage; a hysterisis circuit coupled to the rectifier to receive an output from the rectifier; and a comparing amplifier for receiving an output from the hysterisis circuit at a negative input thereof and comparing the received voltage with the first reference voltage received at a positive input thereof, the comparing amplifier being connected at an output terminal thereof to one input terminal of the OR gate.

6. A power saving apparatus in accordance with claim 4 or claim 5, wherein the secondary voltage detection and control means comprises: a bridge-type full-wave rectifier for detecting the voltage across the secondary current coil and rectifying the detected voltage; a comparing amplifier for receiving an output from the rectifier at a negative input thereof and comparing the received voltage with the second reference voltage received at a positive input thereof; and a timer connected to an output terminal of the comparing amplifier, the timer being connected at an output terminal thereof to the other input terminal of the OR gate.