AU654869B2

AU654869B2 - Rectifier

Info

Publication number: AU654869B2
Application number: AU22086/92A
Authority: AU
Inventors: Toyohiko Kiyohara
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1991-09-06
Filing date: 1992-09-02
Publication date: 1994-11-24
Anticipated expiration: 2012-09-02
Also published as: DE4229303B4; JP2562853B2; DE4229303A1; JPH0568377A; CH684376A5; AU2208692A

Description

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.U a c~ P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATIC STANDARD PATENT 654869 o 9 sr r e r r r

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Invention Title: RECTIFIER trir Irrr t t t t ft t c C t I r The following statement is a full description of this invention, including the best method of performing it known to us: i -N'T GH&CO REF: P10718-JT:CLC:RK S0884 I

RECTIFIER

BACKGROUND OF THE INVENTION FIELD'OF THE INVENTION The present invention relates to a structure effective to reduce a surge generated in a control winding circuit of self-saturation magnetic amplifiers in a rectifier.

*ff' DESCRIPTION OF THE RELATED ART IO As shown in a description of a current control panel for electrochemical applications on the pages 822 to 828 of Mitsubishi Electric Technical Reports, Vol.41, No.6, (1967), rectifiers containing self-saturation magnetic amplifiers have been widely used as a high current DC power source.

Si15 Figure 3 is a circuit diagram of a conventional three-phase t full-wave rectifier having self-saturation magnetic amplifiers. In this figure, 1 is, for example, a three-phase transformer having star-connected primary windings and delta-connected secondary windings, and the secondary outputs of this transformer 1 are connected to a three-phase bridge rectifier circuit (rectifier) having a control circuit. 2u to 2z are rectification diodes connected to the secondary outputs of phase U to Z, respectively, of this i three-phase transformer 1 (more specifically, diodes 2u and 2x are connected to phase Ua, diodes 2v and 2y to phase Va, pj 2 and diodes 2w and 2z to phase Wa). 3u to 3z are selfsaturation magnetic amplifiers for phase U to Z which are connected in series to each of the rectification diodes. 31u to 31z are main circuit conductors acting as primary windings of the self-saturation amplifiers 3u to 3z. 32u to 32z are control windings, secondary windings, of the self-saturation magnetic amplifiers 3u to 3z. 33u to 33z are iron cores of the self-saturation magnetic amplifiers 3u to 3z. 4 is a DC reactor, and 5 is a control DC power source which is connected to the control windings in the order of 32u...32z via DC reactor 4, thus a control circuit is formed wherein the control DC power source 5 supplies a current to magnetize the iron cores 33u to 33z in the opposite direction to that by the main circuit current. Figure 4 is a perspective view of one of self-saturation magnetic amplifiers 3u to 3z. In this figure, 31 is a main circuit conductor, 32 is a control winding, and 33 is an iron core.

Generally, the main circuit ccaductor 31 has a one-turn winding around the iron core 33 and the control winding 32 has 5 to 7 turns also around the iron core 33. Figure 5 is a graph showing the relation between magnetic flux cD and magnetic field H in the self-saturation magnetic amplifiers 3u to 3z. In this figure, the horizontal axis represents magnetic field H wherein the right direction represents the direction of the magnetization by the main circuit current h,

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.1 3 and the left direction represents the direction of the magnetization by the control winding current. The vertical axis represents the magnetic flux D wherein Dr represents the change in the magnetic flux which occurs when the main circuit current rises from 0 to the rated value keeping the control winding current to 0, and Dc represents the change in the magnetic flux which occurs when the main circuit S current rises from 0 to the rated value while a control .6 winding current flows. Point A in this figure represents the S magnetic flux corresponding to the condition where a control winding current flows but there is no main circuit current.

Point B represents the magnetic flux in the condition where S there is neither a control winding current nor a main circuit current, and point C represents the magnetic flux in the condition where the rated value of the main circuit current flows.

The operation of this rectifier is as follows. Let us assume that the diode 2u in phase U of Figure 3 is now just turned on and the current begins to flow through it.

20 Turning-on of this main circuit current will cause the change in the magnetic flux in the iron core 33u by the amount of 4c because the self-saturation magnetic amplifier 3u was magnetized to the value designated by point A in Figure 5 representing the relation between magnetic flux D 85 and magnetic field H by the control current in the control 2 2 I I I I C-

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-4winding 32u which had been supplied in advance of the turning-on of the diode 2u by the control DC power source via the DC reactor 4. Then the voltage corresponding to the change in the magnetic flux by the amount of Dc is absorbed across the main circuit conductor 31u. Similar changes also occur in phase V to Z. Here, the amount of the change in the magnetic flux, Dc, can be adjusted in the range of Ir to Pc by controlling the amount of the control current supplied in c advance by the control DC power source 5. Thus, the output IQ voltage of the rectifier is adjustable by controlling the output of the control DC power source 5. In this operation, DC reactor 4 absorbs the voltages generated in the control windings 32u to 32z of the self-saturation magnetic amplifiers 3u to 3z. That is, while the DC reactor 4 absorbs the voltages, the self-saturation magnetic amplifiers 3u to 3z act as transformers between the main circuit conductors S 31u to 31z and the control windings 32u to 32z. Hence, the S CC control windings generate the voltages 5 to 7 (turns ratio between the control windings and the main circuit conductors) times as large as the voltages generated across the main circuit conductors 31u to 31z. Because these voltages are absorbed by the DC reactor 4, the control DC power source, 5 is protected from surges of excessive voltages.

In the following, it is considered what happens if a i i i surge, such as a lightning surge, enters the primary windings of the three-phase transformer 1. An off-state diode could turn on for an instant depending on the timing of the surge, the windings of the three-phase transformer 1, stray capacitances in the transformer, etc. That is, in the case that a lightning surge enters a certain phase of the primary of the three-phase transformer 1 when diodes 2u and 2y in phase U and Y are in on-state, there is some possibility that all of three diodes 2v, 2w and 2x in phase f0 V, W and X might be turned on simultaneously at that instant of the surge arrival. In this case, the lightning surge voltage is transmitted to the main circuit of the rectifier via the three-phase transformer 1, and furthermore the surge voltage is transmitted to the control windings 32v, 32w and 115 32x via the self-saturation magnetic amplifiers 3v, 3w and 0 3x. Even in this case the self-saturation magnetic amplifiers 3v, 3w and 3x act as a transformer, thus the surge voltages 5 to 7 times as large as those in the main circuit are generated in the control windings. Because all these control windings are connected in series, these individual surge voltages are added to each other and a very high surge voltage is brought about. Then, this very high surge voltage causes the dielectric breakdown between the control windings and the main circuit or the ground.

Therefore an arc occurs which might 2esults in a fire in the I -6rectifier, or a dielectric breakdown at the DC reactor which further causes an attack of a surge to the control DC power source 5, thus the rectifier might fall into uncontrollable confusion. Penetration of these surges cannot be avoided even in the case that a high performance surge arrester is equipped at the primary of the three-phase transformer 1, because similar surge transmission and breakdown can occur for a certain surge voltage wave form coming to the primary of the three-phase transformer 1, for example, in such a case that the voltage of the primary at the positive peak value turns over into a negative value for an instant due to connection of the three-phase transformer o 1 1 stray capacitances distributed there.

Because conventional rectifiers having self-saturation 15 magnetic amplifiers are composed as described above, they have problems that when a surge such as a lightning surge .l comes, a very high surge voltage is generated in a control winding of self-saturation magnetic amplifiers which might damage a control circuit which might further cause an tq 20 uncontrollable condition, or which might result in an arc in a rectifier to lead to a fire.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems described above. It is a more specific object of 7 at t

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'a 4>, this invention to provide a rectifier that does not fall into uncontrollable condition or does not have a fire even when a surge such as a lightning surge comes.

In a rectifier according to the present invention, self-saturated magnetic amplifiers contained in it are divided into three groups, phase U and X, phase V and Y, and phase W and Z, and control windings in each group are connected in series and at least one DC reactor is put between each group.

r In a rectifier of this invention, connection between each control winding of a self-saturation magnetic amplifier of each phase is optimized and plural DC reactors are equipped so that each DC reactor absorbs each portion of the surge broken up. Thus, surge voltages in a control circuit can be suppressed to a small value.

1 0 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a circuit diagram showing an embodiment of this invention; Figure 2 is a circuit diagram showing an another embodiment of this invention; Figure 3 is a circuit diagram showing a conventional rectifier; Figure 4 is a perspective view of q self-saturation magnetic amplifier; and ii -8- Figure 5 is a graph showing a relation between magnetic flux D and magnetic field H in a self-saturation magnetic amplifier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to figures, the first preferred embodiment of this invention is described next. Figure 1 is a circuit diagram showing the first embodiment of this invention, *o where the same members as those in the conventional .0 rectifier are designated by the same signs. 401 is a DC reactor having a third of inductance of that of the conventional DC reactor 4, which is provided between a .o.o control DC power source 5 and a control winding 32u in phase U. 402 is a DC reactor having an inductance similar to that .15 of DC reactor 401, provided between a control winding 32x in phase X and a control winding 32v in phase V. 403 is a DC reactor having an inductance similar to that of DC reactor 4 *4 401, provided between a control winding 3 2 y in phase Y and a control winding 32w in phase W. A control circuit is composed of a control DC power source 5. a DC reactor 401, control windings 32u and 32x, a DC reactor 402, control windings 32v and 32y, a DC reactor 403, and control windings 32w and 32z all of which are connected in the -rder described above with a final connection coming back to the control DC power source 5. As in the conventionLi rectifier, :I 9 each control winding is connected so that the current in each control winding makes magnetization in each iron core in the opposite direction to that made by a main circuit current.

This rectifier of the present invention operates as follows. During ordinary operation of a three-phase fullwave rectifier (three-phase bridge rectifier), at least 2 C diodes are in on-state. For example, when a diode 2u in ,phase U is on, either a diode 2y in phase Y or a diode 2z in ClO phase Z is also on at the same time. The rated main circuit current ilows through these two diodes in on-state, therefore a self-saturation magnetic amplifier has a representing the relation between magnetic flux l and magnetic field H, thus the self-saturation magnetic amplifier is absolutely saturated in magnetic flux. On the C I other hand, self-saturation magnetic amplifiers in the (that is, 3x in phase X against phase U, 3v in phase V against phase Y, 3w in phase W against phase Z) have a magnetic flux corresponding to point A in Figure 5. Here, let us assume that the secondary voltages of the three-phase transformer are now just turned over for an instant due to a surge voltage. Then, the self-saturation magnetic amplifiers in the phase where the diodes are on and the

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10 rated current flows remains at point C with almost no change in a magnetic flux (D because a current cannot drop to 0 instantly due to reactances of conductors in that phase, but, on the other hand, the self-saturation magnetic amplifiers in the phase where diodes are off shows the eapid change in a magnetic 'lux D from point A to point C immediately after the turning-over of the voltages. These resultant large changes in a magnetic flux bring about a large surge voltage to the control windings. In the case I that both diodes, for example both of diode 2w in phase W and diode 2z in phase Z, are in on-state and both selfsaturation magnetic amplifiers have a magnetic flux corresponding to point A, either diode 2w or 2z turns on depending on the polarity of the surge voltage wave form.

For example, in the case that the voltage turned over to the rcCC positive, only diode 2w turns on and a large surge voltage S( appears at only the control winding 32w. In contrast, in the case that the voltage turned over to the negative, only diode 2z turns on and a large surge voltage appears at only the control winding 3;z. That is, if a control winding 32u is connected to a control winding 32x, and 32v to 32y, 32w to 32z, then a surge voltage occurs only in either of control windings in each group. Furthermore, if DC reactors 401, 402 and 403 are provided between these groups of control windings as shown in Figure 1, then each DC reactor S 11i has the responsibility for absorption of a voltage corresponding to only a surge generated at one control winding. Besides, as for the voltage with respect to the main circuit or with respect to the ground, only a voltage appears which corresponds to a surge voltage generated at one control winding in the maximum case. Thus, the amount of the surge voltage can be reduced to about a third of that in the conventional rectifier. As a result, easier electrical .9oo insulation is adaptable. Moreover, it is possible to obtain 0 9 The second embodiment is described below. ofta g. In the first embodiment described above, three DC reactors 401, 402, and 403 are enutilized, but this invention can be modified so that a control cirwinding in the maximum case. Thus, the amountd of fothe surge voltage chaving an inbe reduced to about a fourthird of that inof a DC reactor 4 used in a conventional rectifier. As a result, easier electrical 'F insulation is adaptable. Moreover, a control circuit is possibr example to obtainhe potential of the control DC power source or ais fixedre due to an ar.

g e nerated in each control winding can ribe distributed equallbelow.

25 In both of the first and second embodiments described 4/4 '1 0 .I ;:connected in series to form a closed circuit;

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2 1 above, contro wi- 12above, control windings are connected in the order of 32u and 32x, 32v and 3 2 y, and then finally 32w and 32y, however the order is not restricted to that and another orders, for example such an order 32u and 32x, 32w and 32z, and finally 32v and 32y, are also possible to get the same effect.

Furthermore, in the first embodiment, a way of connecting three DC reactors 401, 402, and 403 is not t rrt restricted to that described above, however another ways of cr" connection, for example such a way that a control winding S 32u is connected to a control DC power source 5 directly without a DC reactor, and, instead, a DC reactor 401 is put between a control winding 32z and the DC power source 5, are nct' possible to get the same effect.

As described above, in this invention, self-saturation amplifiers are divided into three groups of phase U and X, phase V and Y, and phase W and Z, and control windings in each group are connected in series and furthermore DC r i reactors are distributed so that at least one DC reactor is provided between each group. Thus, surge voltages in a control circuit can be reduced to a third to a fourth of that in conventional system. Therefore, easier electrical Sinsulation can be adaptable for protecting a control DC power source from a surge. Besides, it is possible to obtain a rectifier that is protected froii a fire due to an arc.

i A 1 7 13 In both of the above embodiments described above, the rectifiers have a three-phase bridge circuit construction respectively, however the present application can adapt to the rectifiers having other circuit constructions, e.g. a double star connection.

*e 0 9000 00 0 0W 00 00 0 06 00 00 0 0000 0* 6 00*0 Ob 0* 9 9900 6000 0~ 0 0* .9 0000 o 0

Claims

9., 9.. CLAIMS DEFINING THE IiVENTION ARE AS ~LLOWS: WHAT IST LT AIMED 1. A rectifier having self-saturation magnetic amplifiers comprising: a rectifier circuit wherein phase U, V and W are connected to a positive DC output and phase X, Y and Z are connected to a negative DC output; self-saturation magnetic amplifiers in said each phase having: primary windings each of which is composed of a main o circuit conductor of said each phase U, V, W, X, Y, and Z; and secondary windings acting as control windings each of which is coupled' electromagnetically with said each main circuit conductor; and a control circuit for adjusting an output voltage of said rectifier, which comprises said each control winding, .15 a DC reactor, and a control DC power source all of which are 0 connected in series to form a closed circuit; and characterized in that said control circuit comprises: a group of said control windings of said phase U and said phase I which are connected in series; a group of said control windings of said phase V and said phase Y which are connected in series; a group 'of said control windings of said phase W and said phase Z which are connected in series; one or more DC reactors which are connected between said each group of control windings respectively; .r i- i s 15 said control DC power source which supplies an adjustable current to said each control winding so that said current in each control winding produces magnetic fields in the opposite direction to magnetic fields produced by a main circuit current; wherein said each group of control windings, said DC reactors, said control DC power source are connected in series to form said closed circuit. otO oa 04 0 66 90 c., C 'e *9 c 1O *a 9* 04 0090 *9a OC 0 0# C,' 4~ 20 2. A rectifier having self-saturation magnetic amplifiers as defined in claim 1, wherein one DC reactor is provided for every connection between said each group of said control windings connected in series. 3. A rectifier having self-saturation magnetic amplifiers as defined in claim 2, wherein said each DC reactor has the same value of inductance. 4. A rectifier having self-saturation magnetic amplifiers as defined in claim 1, wherein said DC reactors are provided: between said each group of said control windings connected in series; and between said control DC power source and said group of said control windings. ABSTRACT OF THE DISCLOSURE: A rectifier having self-saturation magnetic amplifiers, wherein a surge voltage, which is generated in a control circuit when a lightning surge enters the rectifier, is suppressed to a small value. In this invention, self- saturation magnetic amplifiers are divided into three groups of phase U and X, phase V and Y, and phase W and Z, wherein control windings in each group are connected in series. S Furthermore, DC reactors 401, 402, and 403 are distributed S so that at least one DC reactor is provided between each Soi group of the control windings. CS St S CC C 16 A rectifier having self-saturation magnetic amplifiers as defined in claim 4, wherein said each DC reactor has the same value of inductance. 6. A rectifier having self-saturation magnetic amplifiers and substantially as hereinbefore described with reference to figures 1 or 2 in conjunction with figures 4 and 5 of the accompanying drawings. O* 9 f e* Dated this 1st day of September 1992 4 MITSUBISHI DENKI KABUSHIKI KAISHA By their Patent Attorney GRIFFITH HACK CO. i i