JP2003270273A - Current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current sensor which is applicable to multiple ratings, does not need replacement of a CT and an I/V converter although the rating is changed, easily changes the rating, is produced in large quantities, reduces a cost and enhances a tolerance against an overload. <P>SOLUTION: The I/V converter 5 is provided with a load resistor circuit 7 comprising a plurality of resistor groups 7a-7c and converting a secondary current of the CT 1 into a voltage, a protection circuit 6 for limiting the voltage, and a selective connection circuit 8 for selectively connecting a secondary side of the CT 1 and each resistor group 7a-7c of the load resistor circuit 7 so as to adapt to a primary rating of the CT 1 is connected to an output of a secondary winding 1b of the CT 1 with a large number of windings. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor which is housed in a power receiving and distribution board or the like and takes out an output proportional to the current of a high voltage circuit.

[0002]

2. Description of the Related Art As a current sensor of this type, there is a CT (current transformer) type, and in FIG.
a having a and a secondary winding 1b, the secondary winding 1b
Is connected to the digital relay 2, and the output of the secondary winding 1b is input into the digital relay 2, and the output of the auxiliary CT3 and the auxiliary CT3 for reducing the level of the output current is A / D converted. The D conversion unit 4 is provided.
In the CT method, the number of turns is changed for each primary rating, and the secondary rated current is generally "5A" or "1A". Protection relays and measuring instruments use this current for detection and measurement. ing. In general, a through type with a simple structure and low cost is used, but when the rating is low, the number of secondary windings decreases and it becomes difficult to adjust the error. A winding type (WCT) is used in which the number of primary windings also increases. Overload measures (short-time withstand current) at low ratings differ depending on the body size and rated current, but in many cases they do not meet the specifications of the cubicle to be applied, and considering the application, it is currently ignored. is there.

As a current sensor, there is a Rogowski coil type, which is based on an air-core toroidal coil and has a structure having a through wire for canceling the influence of magnetic noise orthogonal to the coil. There is no saturation due to the core, and one model can be applied to a wide range of ratings.
However, a circuit for switching the rating is necessary. Since the secondary output of the Rogowski coil has a differentiated voltage waveform, an integrating circuit is connected to the output side to obtain a signal proportional to the primary current. In addition, since the secondary output of the Rogowski coil is very small, it can be protected by a resistor, a diode, etc. as a measure against overload, and it is easy to match the specifications of the cubicle even with a low rating.

[0004]

However, in the above-mentioned conventional CT type current sensor, the number of turns varies depending on the rating, so that inventory or mass production cannot be performed, the cost becomes high, and the delivery time becomes long. Also, when the CT rating was changed, the CT body had to be changed, and the work of reassembling on site was also necessary. Also, as described above, the through type is generally used because it has a simple structure and is inexpensive, but at a low rating, the number of secondary windings decreases and error adjustment becomes difficult, so the winding type is used. It Therefore, the increase in the number of primary windings accompanying the increase in the number of secondary windings makes the structure complicated and makes it difficult to reduce the size. In addition, the weight is increased and the cost is increased. Furthermore, although it depends on the rated current and size, in the case of manufacturing with the same type, it is necessary to make the wire diameter smaller as the number of primary windings increases as the rating becomes lower, and overload measures may not meet the specifications of the applicable cubicle. In many cases, it is currently ignored although the use is considered. On the other hand, if importance is attached to measures against overload at a low rating, the size and weight increase, which is a factor that prevents the cubicles from being reduced in size.

Further, in the Rogowski coil type current sensor, since the number of magnetic flux is small due to the air core and the energy of the secondary output is small, the influence of load resistance and the influence of noise on the lead wire are large. . In addition to the need for a shield structure for the central conductor and the main body, and because the secondary output is a differential voltage, an integrator circuit is required to obtain a signal proportional to the primary current, which complicates the structure and reduces the cost. It became high. Furthermore, since the output is a low voltage source output, it is difficult to configure the rating switching circuit with only passive components, resulting in a high cost and a reliability problem.

The present invention has been made to solve the above problems, and has a wide applicable current range.
Applicable to multiple ratings and even if the ratings change, C
The purpose is to obtain a current sensor that does not require replacement of the T or I / V converter, makes it easy to change the rating locally, enables mass production, reduces costs, and has a high overload withstanding capability, especially at low ratings. And

[0007]

According to a first aspect of the present invention, there is provided a CT in which a measured current is applied to a primary winding and a large number of secondary windings are formed, and a plurality of resistance portions. And a load resistance circuit for inputting a secondary current of CT and converting it into a voltage, and a secondary side of CT and each resistance portion of the load resistance circuit are selectively arranged so as to correspond to the primary rating of CT. An I / V converter having a selective connection circuit to be connected is provided, and current detection is performed according to the output voltage of the I / V converter.

In the current sensor according to the second aspect of the present invention, each resistance portion of the I / V converter is constituted by a resistance value and the number of groups that can correspond to the primary rated value of CT.

In the current sensor according to the third aspect of the invention, a protection circuit for limiting the input voltage is provided on the input side of the I / V converter.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration diagram of a current sensor according to Embodiment 1 of the present invention. In CT1, a large number of secondary windings 1b are formed in order to reduce a secondary current. Reference numeral 5 denotes an I / V converter to which the output of the secondary winding 1b of CT1 is input.
The V converter 5 includes a protection circuit 6 to which the output of the secondary winding 1b is input, a load resistance circuit 7 that receives the output of the protection circuit 6 and converts the output to a voltage, the protection circuit 6 and the load resistance circuit 7 And a selective connection circuit 8 for selectively connecting and.

The protection circuit 6 is a voltage clip circuit composed of a diode, a varistor or the like, and when an overcurrent flows in the primary side of the CT1 (in a short-time withstand current state).
Moreover, it is possible to prevent the secondary winding 1b from being short-circuited and the load resistance circuit 7 and the digital relay 9 from being thermally destroyed due to the increase in the secondary voltage of CT1. The load resistance circuit 7 includes a resistance group 7a
To 7c, the number and combination of resistance groups and resistance values are determined so as to correspond to all primary rated values of CT1, and the combination of the resistance groups 7a to 7c is a selective connection circuit including crossovers and the like. Selected by 8.

The I / V converter 5 is grounded (FG is an abbreviation for frame ground) and is also connected to a digital relay 9 via a connection cable 10. The digital relay 9 has an I / V conversion function. The output of the device 5 is input, an auxiliary VT 11 that adjusts the level of the output voltage to the level of the digital relay 9, that is, a level that lowers the level, and an A / D converter 12 that A / D converts the output of the auxiliary VT 11 are provided. ing.

In the above structure, the primary winding 1a of CT1
When a current to be measured flows into the secondary winding 1b, the number of windings in the secondary winding 1b of CT1 is increased, so that a small secondary current flows, and this small secondary current is input to the I / V converter 5 and I This secondary current is converted into a voltage by the load resistance circuit 7 of the / V converter 5, and at the time of this conversion, tap switching of the selective connection circuit 8 is performed along with the change of the primary rating of CT1.
Further, the protection circuit 6 clips the voltage due to the secondary current.
The output voltage of the I / V converter 5 is input to the digital relay 9 or a measuring device via the connection cable 10 to perform current detection and current measurement.

In the first embodiment, since the secondary current of CT1 is reduced, the applicable current range of CT1 is widened and it is applicable to multi-rated CT. The selection of the resistance value of the load resistance circuit 7 corresponding to each rating is performed by tap switching in the selective connection circuit 8. Therefore, even if the primary rating of CT1 is changed, CT1 and I
It is not necessary to replace the / V converter 5, and the selective connection circuit 8
It is possible to sufficiently cope with the tap switching in. Therefore, it is easy to change the rating locally, mass production is possible, and cost can be reduced. Further, since the protection circuit 6 which is a voltage clipping circuit is provided, even if an excessive current flows in the primary side of CT1, a large voltage is not generated in the I / V converter 5, and the secondary coil 1b of CT1 and the load are not generated. It is possible to prevent and protect the resistance circuit 7 and the digital relay 9 from damage. For this reason, the overload resistance becomes high, and the effect at the time of low rating becomes large.

Second Embodiment In the first embodiment, the I / V converter 5 is provided separately from the digital relay 9, but the IV converter 5 may be provided in a secondary connection device such as the digital relay 9. Has the same effect.

[0016]

As described above, according to claims 1 and 2 of the present invention, since the number of secondary windings of CT is increased to reduce the secondary current of CT, the applicable current range of CT is wide. Becomes
Applicable to multi-rated CT. In addition, since the resistance value of the load resistance circuit corresponding to each rating is selected by the selective connection circuit, even if the primary rating of CT is changed, it is not necessary to replace the CT or I / V converter. It is possible to sufficiently cope with this by switching the connection circuit. Therefore, it is easy to change the rating locally, mass production is possible, and cost can be reduced.

Further, according to claim 3, since the protection circuit for limiting the input voltage is provided on the input side of the I / V converter, the CT is provided.
Even if an excessive current flows to the primary side of the CT, a large voltage is not generated in the I / V converter, and the secondary coil of CT, the load resistance circuit,
Prevent secondary connection devices such as digital relays from being destroyed. For this reason, the overload resistance is increased, and the effect is particularly large at the time of low rating.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a current sensor according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional current sensor.

[Explanation of symbols]

1 ... CT 1a ... Primary winding 1b ... secondary winding 5 ... I / V converter 6 ... Protection circuit 7. Load resistance circuit 7a to 7c ... Resistance group 8 ... Selective connection circuit 9 ... Digital relay

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadayoshi Machimura             2-17 Osaki, Shinagawa-ku, Tokyo Stock market             Shameidensha (72) Inventor Tadashi Yokoyama             2-17 Osaki, Shinagawa-ku, Tokyo Stock market             Shameidensha (72) Inventor Toshio Narita             2-17 Osaki, Shinagawa-ku, Tokyo Stock market             Shameidensha F-term (reference) 2G025 AA17 AB14 AC04                 2G035 AA16 AA17 AB08 AC01 AC16                       AD10 AD19 AD54

Claims (3)

[Claims] 1. A current to be measured is applied to a primary winding, and a CT having a large number of secondary windings and a plurality of resistance portions are provided. And a I / V converter having a selective connection circuit that selectively connects the secondary side of the CT and each resistance portion of the load resistance circuit so as to correspond to the primary rating of the CT, A current sensor characterized in that a current is detected according to an output voltage of an I / V converter. 2. The current sensor according to claim 1, wherein each resistance portion of the I / V converter is constituted by a resistance value and a number of groups so as to correspond to a primary rated value of CT. 3. A protection circuit for limiting the input voltage is provided on the input side of the I / V converter.
The described current sensor.