JP2004194369A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter which secures the insulation to earth of a low-voltage instrument even if the neutral point of a transformer is not grounded, and wherein a grounding point can be set to a single point. <P>SOLUTION: This power converter is composed of a transformer 2 which has a primary winding 2a connected to a three-phase high-voltage power source 1, an electric circuit 3 which is connected to the secondary winding 2b of this transformer 2, a grounded first casing 6a which houses the transformer 2 and the electric circuit 3, and a second casing 6b which houses the electric circuit 3 and is arranged inside the first casing 6a. The second casing 6b and the charge part of the electric circuit 3 are connected with each other via impedance. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power converter, and more particularly to a power converter in which a high voltage is input to a primary winding of a transformer and an electric circuit such as a semiconductor power conversion circuit is connected to a secondary winding that outputs a low voltage. About.
[0002]
[Prior art]
A system in which a high voltage is input to a primary winding of a transformer, a low voltage is output from a secondary winding, and an electric circuit such as a power conversion circuit is connected to the low voltage side is, for example, an industrial motor drive device. Used in such as. In such a system, the neutral point on the low voltage side of the transformer is usually grounded (for example, see Non-Patent Document 1). This is because even if there is a situation where the high-voltage primary winding and the low-voltage secondary winding come into contact due to insulation breakdown or the like (this is called a contact accident), the low-voltage side has a ground potential. The main purpose is to avoid high voltage.
[0003]
However, if the neutral point of the secondary winding on the low voltage side of the transformer is grounded, an excessive ground fault current may flow when a ground fault occurs inside the electric circuit or the motor.
[0004]
Also, in order not to be affected by the fluctuation of the neutral point potential due to the ground fault current,
The housing for housing the transformer and the housing for housing the electric circuit are connected to a ground electrode different from the above-described neutral ground electrode. In addition, transient phenomena such as when the power was turned on sometimes caused noise due to fluctuations in the potential of the housing to adversely affect monitoring equipment.To reduce this, the grounding electrode of the housing that houses the transformer and the electrical circuit In some cases, the grounding electrode of the housing that houses the power supply is separated. A technique for separating a ground point in order to prevent a malfunction of a circuit due to a change in a ground potential due to a transient change or the like as described above is described in, for example, Patent Document 1.
[0005]
[Non-patent document 1]
Ohmsha, Ed., "Electrical Equipment Technical Standards and Interpretation for Autumn 2001", Ohmsha, July 15, 2001, p. 4, p. 51-52
[0006]
[Patent Document 1]
Japanese Patent Publication No. 2-21206 (page 2, FIG. 2)
[0007]
[Problems to be solved by the invention]
As described above, in the prior art, the electric circuit on the secondary side of the transformer is grounded by grounding the three-phase neutral point potential of the secondary winding. A high voltage is not generated between the electric circuit and the ground or the housing. However, the grounding of the three-phase neutral point to suppress the voltage rise of the housing due to the ground fault current needs to be provided independently of the grounding of the housing, and the transient potential fluctuation affects the low voltage side. It has been desired to separate the grounding electrode of the housing that houses the transformer from the grounding electrode of the housing that houses the electric circuit so as not to affect the power supply. Providing three grounding poles in this way complicates grounding work and requires a great deal of labor and cost for installation and wiring work of the device.
[0008]
In addition, as described above, the ground of the housing of the transformer and the housing of the electric circuit are separated, and a detection circuit for monitoring the operation state of the transformer and the electric circuit is provided to share the monitoring circuit. The monitoring circuit may malfunction due to the difference in ground potential between the two detection circuits, and the monitoring circuit for the transformer and the monitoring circuit for the electric circuit cannot be shared.
[0009]
Further, when the three-phase neutral point potential of the secondary winding is grounded, when a ground fault occurs in the secondary winding output or the electric circuit, two points between the ground fault point and the three-phase neutral point are generated. Connected to the ground, a large ground fault current flows through this loop when the phase voltage of the secondary winding is applied. However, even if a ground fault occurs in any of the three phases, this ground fault current is detected and cut off It is necessary to. Therefore, for safety, it is necessary to add a function of interrupting a ground fault current such as a fuse to all three phases.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to secure the ground insulation of low-voltage equipment without grounding a neutral point of a transformer, and to be able to use a common ground point. It is to provide a simple power conversion device.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a first invention of the present invention is to provide a transformer having a primary winding and a low-voltage secondary winding connected to a high-voltage three-phase AC power supply, An electric circuit connected to a next winding, a first housing that houses the transformer and the electric circuit, and a grounded first housing that houses the electric circuit, and is disposed inside the first housing. A second housing, wherein the second housing and the charging section of the electric circuit are connected via an impedance.
[0012]
According to a second aspect of the present invention, there is provided a transformer having a primary winding and a plurality of low-voltage secondary windings connected to a high-voltage three-phase AC power supply, and a plurality of two-phase transformers of the transformer. A plurality of electric circuits respectively connected to a next winding, a first housing that houses the transformer and the plurality of electric circuits, and a first housing that houses the plurality of electric circuits, And a plurality of second housings disposed inside the first housing, wherein each of the plurality of second housings and each of the charging units of the plurality of electric circuits are connected to each other by impedance. The connection is made via
[0013]
According to a third aspect of the present invention, there is provided a transformer having a primary winding and a low-voltage secondary winding connected to a high-voltage three-phase AC power supply, and a secondary winding connected to the transformer. Grounded first housing for housing the transformer, a second housing for housing the electric circuit, and a grounded third housing for housing the second housing. Composed of the body and
The second case and the charging section of the electric circuit are connected via an impedance.
[0014]
Further, a fourth invention of the present invention relates to a transformer having a primary winding and a plurality of low-voltage secondary windings connected to a high-voltage three-phase AC power supply, and a plurality of transformers having two or more low-voltage secondary windings. A plurality of electric circuits respectively connected to the next winding, a grounded first housing for housing the transformer, and a plurality of second housings for housing the plurality of electric circuits, respectively; And a grounded third housing that collectively houses the plurality of second housings, each of the plurality of second housings and a charging unit for the plurality of electric circuits. Are connected via an impedance.
[0015]
According to the present invention, when the primary winding and the secondary winding contact each other without grounding the neutral point of the secondary winding and without providing a high-voltage or low-voltage grounding pole respectively. In addition, it is possible to provide a power conversion device that can ensure ground insulation of low-voltage equipment.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
(First Embodiment)
FIG. 1 is a circuit diagram showing a first embodiment of the power converter according to the present invention.
[0018]
A three-phase AC power is supplied to an electric circuit 3 from a high-voltage three-phase power supply 1 via a transformer 2.
[0019]
The transformer 2 has a primary winding 2a and a secondary winding 2b, and an electric circuit 3 is connected to the secondary winding 2b via a fuse 4 connected to two of the three phases. The electric circuit 3 includes a converter circuit in which the power device 3a is bridge-connected, a series circuit including resistors 9a and 9b connected in parallel to the DC output, and a load 3b.
[0020]
The transformer 2 and the electric circuit 3 are housed in a common housing 6a, and the housing 6a is connected to a ground electrode 7a and grounded. A second housing 6b housing the electric circuit 3 is disposed inside the housing 6a, and the housing 6b is connected to the midpoint of the series circuit including the resistors 9a and 9b. Have been.
[0021]
The input current of the transformer 2 is detected by the AC current transformer CT1, and the load current of the electric circuit 3 is detected by the DC current transformer CT2, both of which are input to the monitoring circuit 5a. The reference potential of the monitoring circuit 5a is connected to the housing 6a via the ground resistor 8a.
[0022]
By adopting the circuit configuration as described above and fixing the potential of the housing 6b to the potential of the charged part of the electric circuit 3, even if a contact accident occurs between the primary winding and the secondary winding of the transformer, Thus, no high voltage is applied between the housing 6b and the electric circuit 3. Accordingly, the withstand voltage between the electric circuit 3 and the housing 6b is determined only by the voltage of the electric circuit 3, so that the electric circuit 3 can adopt the insulation design standard for low-voltage equipment. In this case, the dielectric strength between the housing 6a and the housing 6b is increased. Furthermore, if the housing 6b is connected to the neutral point of the DC output voltage of the converter circuit in which the power device 3a is bridge-connected, the above-mentioned withstand voltage can be suppressed low.
[0023]
Although FIG. 1 shows a configuration in which the load 3b is included in the electric circuit 3 and housed in the housing 6b, for example, when the load 3b is an electric motor, the load 3b is connected to the housing 6a and the housing 6b. It is good also as a structure arrange | positioned outside.
[0024]
As described above, according to the present embodiment, a configuration having only one ground electrode 7a is possible, and the neutral point of the secondary winding of the transformer, the housing of the transformer, and the housing of the electric circuit are provided in three places. Compared with the conventional device which requires a ground electrode, installation wiring work of the device such as ground wiring and installation of the ground electrode becomes extremely easy.
[0025]
Also, when power is applied to the primary winding 2a of the transformer 2, the stray capacitance between the primary side of the transformer 2 and the housing 6a and the floating of the primary and secondary circuits of the transformer 2 Due to the capacitance, the housing 6a and the secondary side circuit transiently generate a voltage change with respect to the ground, but all the circuits including the monitoring circuit 5a are connected to the housing 6a via the stray capacitance or the ground impedance. Therefore, generation of a potential difference between circuits is reduced. Therefore, even if the monitoring circuit 5a is shared, the monitoring circuit 5a operates normally.
[0026]
In the above configuration, the detector for monitoring the operation state of the transformer 2 and the electric circuit 3 is an example using a current detector. However, this may be a detector for detecting a voltage or a temperature. In addition, monitoring may be performed by combining these.
[0027]
Furthermore, when a ground fault occurs in the electric circuit 3, only the ground fault point is connected to the ground, but since the neutral point of the secondary winding 2b of the transformer 2 is not grounded as in the related art. Since a loop through which a ground fault current flows is not formed, there is no need to cut off the ground fault current. Therefore, the function of detecting or interrupting the fault current only has to interrupt the short-circuit current at the time of the line-to-line short-circuit fault. As shown in FIG. 1, it is sufficient to provide the fuse 4 in any two of the three phases. Further, it is also possible to adopt a configuration in which the fuse 4 is omitted, a current of any two phases out of three phases is detected, and a circuit breaker (not shown) of the input of the transformer 2 is operated based on the abnormal value.
[0028]
(Second embodiment)
FIG. 2 is a circuit configuration diagram of a power converter according to a second embodiment of the present invention. Regarding each part of the second embodiment, the same parts as those of the power conversion device according to the first embodiment of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. This second embodiment is different from the first embodiment in that a housing 6c that houses the transformer 2 and is connected to a ground electrode 7b is provided instead of the housing 6a in FIG. The electric circuit 3 and the housing 6b for housing the electric circuit 3 are collectively housed in the housing 6d, and the housing 6d is connected to the ground electrode 7d. And a monitoring circuit 5b connected to the housing 6d via the grounding resistor 8c.
[0029]
The second embodiment is effective when the installation location of the transformer 2 and the electric circuit 3 is far away, and it is difficult to arrange the housings for housing them in a row. In FIG. 2, the ground electrodes 7b and 7c are different, but they may be shared by one. In this case, the housings 6c and 6d are connected to one ground electrode, for example, 7b by a ground wire.
[0030]
Even if such a configuration is adopted, the insulation between the electric circuit 3 and the housing 6d may be based on the insulation design standard of the low-voltage equipment, as in the first embodiment, and only one or two ground electrodes may be used. And installation and wiring work of the device such as ground wiring and installation of the ground electrode becomes easier as compared with the conventional device which requires three ground electrodes.
[0031]
Further, when a ground fault occurs in the electric circuit 3, only the ground fault point is connected to the ground, but since the neutral point of the secondary winding 2b of the transformer 2 is not grounded as in the related art. No loop through which a ground fault current flows is formed. Therefore, there is no need to cut off the ground fault current, and the fault current detection or cutoff function may be considered in consideration of the cutoff of the short-circuit current at the time of line-to-line short-circuit fault. The current detection or cutoff function is provided in any two phases. Is enough.
[0032]
In the above description of the first and second embodiments, it is assumed that the secondary winding 2b of the transformer 2, the electric circuit 3 connected thereto, and the housing 6b that houses the electric circuit 3 are each one. However, a configuration in which all of them are plural may be used. In this case, the electric circuit 3 is connected to each of the plurality of secondary windings 2b, and the housing 6b is configured to house each electric circuit 3 separately.
[0033]
【The invention's effect】
As described above, according to the power converter of the present invention, a power converter capable of securing the ground insulation of a low-voltage device without grounding the neutral point of the transformer and having a common ground point is provided. Can be provided.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a power conversion device according to a first embodiment of the present invention.
FIG. 2 is a circuit configuration diagram of a power conversion device according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Three-phase high voltage power supply 2 Transformer 2a Primary winding 2b Secondary winding 3 Electric circuit 3a Power device 3b Load 4 Fuse 5a, 5b Monitoring circuit 6a, 6b, 6c, 6d Housing 7a, 7b, 7c Ground pole 8a , 8b, 8c Ground resistors 9a, 9b Resistors

Claims (7)

A transformer having a primary winding and a low voltage secondary winding connected to a high voltage three phase AC power source;
An electrical circuit connected to the secondary winding of the transformer,
A grounded first housing that houses the transformer and the electric circuit;
A second housing that houses the electric circuit and is disposed inside the first housing;
The power converter, wherein the second housing and the charging section of the electric circuit are connected via an impedance. A transformer having a primary winding connected to a high-voltage three-phase AC power supply and a plurality of low-voltage secondary windings;
A plurality of electric circuits respectively connected to a plurality of secondary windings of the transformer;
A grounded first housing that houses the transformer and the plurality of electric circuits;
A plurality of second housings respectively housing the plurality of electric circuits and arranged inside the first housing,
A power conversion device, wherein each of the plurality of second housings and each of the charging units of the plurality of electric circuits are connected via an impedance. A transformer having a primary winding and a low voltage secondary winding connected to a high voltage three phase AC power source;
An electrical circuit connected to the secondary winding of the transformer,
A grounded first housing that houses the transformer;
A second housing for housing the electric circuit;
And a grounded third housing for housing the second housing.
The power converter, wherein the second housing and the charging section of the electric circuit are connected via an impedance. A transformer having a primary winding connected to a high-voltage three-phase AC power supply and a plurality of low-voltage secondary windings;
A plurality of electric circuits respectively connected to a plurality of secondary windings of the transformer;
A grounded first housing that houses the transformer;
A plurality of second housings each accommodating the plurality of electric circuits,
A grounded third housing that collectively houses the plurality of second housings,
A power conversion device, wherein each of the plurality of second housings and each of the charging units of the plurality of electric circuits are connected via an impedance. 5. The electric circuit according to claim 1, further comprising a converter circuit that converts power from AC to DC, and wherein the charging unit is an intermediate potential portion of a DC output of the converter circuit. 6. Item 2. The power converter according to item 1. A reference potential section of a monitoring circuit that monitors at least one of a current, a voltage, and a temperature of a primary winding of the transformer and at least one of an output current and an output voltage of the electric circuit; The power converter according to claim 1, wherein the power converter is connected to a body via an impedance. At least one of means for detecting an arbitrary two-phase current among three-phase connections connecting the secondary winding of the transformer and the electric circuit, and means for interrupting an arbitrary two-phase current is provided. The power converter according to any one of claims 1 to 4, characterized in that:

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