JP2022132916A - Input converter, and protective relay device - Google Patents

Abstract

To provide an input converter capable of measuring current values over a wide range without complicating a structure, and a protective relay device.SOLUTION: An input converter comprises a first transformer and a second transformer. The input converter is connected to a power system. The first transformer is a core type transformer including a winding core, a primary-side coil and a secondary-side coil which are wound around the winding core. The second transformer is the core type transformer and has a high sensitivity range different from the first transformer. The primary-side coil of the first transformer and the primary-side coil of the second transformer are connected in series, and the secondary-side coil of the first transformer and the secondary-side coil of the second transformer are connected in series.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to input transducers and protection relay devices.

In order to protect the power system, there is a protection relay device that measures the current flowing through the transmission line and detects whether an accident due to a ground fault or short circuit has occurred in the transmission line. A protection relay device measures a current value using an input converter equipped with a current transformer (CT, Current Transformer) using an iron core.

In the input converter, the primary and secondary windings wound around the iron core are insulated, and the primary and secondary windings are connected to the power system and the protective relay device, respectively. there is The input converter used in the protection relay is connected to a current transformer (main current transformer) that is directly connected to the power system, and is isolated from the power system and relatively It converts a large current into a level of current suitable for computation by an electronic circuit. For this reason, it is also called an auxiliary current transformer or an auxiliary CT in contrast to the main current transformer.

Such an auxiliary CT is required to measure a wide range of current values, from large currents that can flow during system faults to small currents that normally flow, while maintaining a certain degree of resolution. For this reason, there is a method for measuring a wide range of current values by a method of forming a hybrid iron core made of different materials suitable for a large current region and a small current region respectively. Combining such iron cores made of different materials tends to complicate the structure, which poses a problem in terms of manufacturing.

JP 2011-155158 A

A problem to be solved by the present invention is to provide an input converter and a protection relay device capable of measuring current values in a wide range without complicating the structure.

An input converter of an embodiment has a first current transformer and a second current transformer. The input converter is connected to the power system. The first current transformer is a core-type current transformer having a wound core, a primary winding wound around the wound core, and a secondary winding. The second current transformer is the core-type current transformer and has a sensitive range different from that of the first current transformer. The primary winding of the first current transformer and the primary winding of the second current transformer are connected in series, and the secondary winding of the first current transformer and the second current transformer are connected in series. is connected in series with the secondary winding of the device.

2 is a block diagram showing an example of the configuration of the input converter 10 of the embodiment; FIG. The figure which shows the equivalent circuit which considered only the secondary side of the input converter 10 of embodiment. The figure which shows the characteristic of the 1st current transformer 11 of the input converter 10 of embodiment, and the 2nd current transformer 12. FIG. 1 is a block diagram showing an example of the configuration of a protection relay system 1 of an embodiment; FIG.

Hereinafter, input converters and protection relay devices according to embodiments will be described with reference to the drawings. In the following description, a case in which the input converter is applied to a protection relay device will be described as an example, but the present invention is not limited to this. The input converter may be applied to various power equipment provided in the current system.

FIG. 1 is a block diagram showing an example of the configuration of the input converter 10 of the embodiment. The input converter 10 comprises, for example, a first current transformer 11 and a second current transformer 12 . The first current transformer 11 and the second current transformer 12 are conventional so-called core-type current transformers. The first current transformer 11 includes a core 110 (wound core), a primary winding 112A wound around the core 110, and a secondary winding 112B. The second current transformer 12 includes an iron core 120, a primary winding 122A wound around the iron core 120, and a secondary winding 122B.

In the input converter 10, the primary sides, that is, the primary side winding 112A and the primary side winding 122A are connected in series, and the secondary sides, that is, the secondary side winding 112B and the secondary side winding are connected in series. 122B are connected in series. A load resistor R is connected to the secondary side.

For example, as shown in FIG. 4, the input converter 10 is provided in a protection relay device 30, the primary side is connected to the electric power system (the transmission line 2 in the example of FIG. 4), and the secondary side is the protection relay It is connected to the relay arithmetic unit 20 of the device 30 . In the input converter 10, the primary-side current CA flowing through the primary-side windings (primary-side winding 112A and primary-side winding 122A) generates magnetic flux around it, and the generated magnetic flux is transferred to the iron core (iron core 110 and iron core 110). 120) collects magnetism. A change in magnetic flux collected in the iron core induces an excitation voltage in the secondary windings (secondary winding 112B and secondary winding 122B), and the secondary windings are induced in accordance with the excitation voltage. A secondary current CB flows through. That is, when the primary side current CA flows, the secondary side current CB also flows, and this works in the direction of canceling out the magnetic flux generated in the iron core.

FIG. 2 is a diagram showing an equivalent circuit considering only the secondary side of the input converter 10 of the embodiment. The same excitation current CC flows through both transformers (virtual inductors L1 and L2 on the equivalent circuit) with respect to the primary side current CA. The sum of the excitation voltages generated across both ends of both transformers is applied to the load resistor R, and a secondary current CB flows through the secondary side. As a result, an output corresponding to the primary side current CA is transmitted to the secondary side.

The density of the magnetic flux generated in the iron core (magnetic flux density) B is proportional to the excitation current I flowing through the winding and the number of turns N of the winding, and inversely proportional to the cross-sectional area S of the iron core, as shown in the following equation (1). do.

B∝(I×N)/S (1)

By adjusting the number of turns N on the primary side and the secondary side, the protection relay device 30 can handle a current value flowing on the secondary side with respect to a relatively large current flowing on the primary side. Convert to current level suitable for calculation.

In this embodiment, one of the first current transformer 11 and the second current transformer 12 is used as a protection current transformer, and the other is used as a measurement current transformer. The protection current transformer and the instrumentation current transformer have different sensitivity ranges. The high sensitivity range is the range in which the current transformer can accurately measure the current value.

Equation (1) applies to a limited range of excitation currents I, not to arbitrary magnitudes of excitation currents I. For example, the formula (1) indicates that the exciting current I and the magnetic flux density B are proportional. A phenomenon called magnetic flux saturation occurs when B does not increase. In a region where the magnetic flux density B is saturated, that is, in a region where the exciting current I is large, the magnetic flux density B does not follow changes in the exciting current I, so the current value cannot be measured with high accuracy. It is also known that when the excitation current I is very small, the ratio (magnetic permeability) of the magnetic flux density B to the strength of the generated magnetic field becomes small. That is, in a region where the excitation current I is small, the change in the magnetic flux density B changes with respect to the change in the excitation current I, so the current value cannot be measured with high accuracy. The value at which the magnetic flux density B reaches the saturation region and the value at which the magnetic permeability changes differ depending on the material of the iron core, the configuration of the rectifier, and the like. That is, the high sensitivity range differs depending on the rectifier.

A protective current transformer is a current transformer that is insensitive in the region of small currents but sensitive in the region of large currents. The current transformer for protection measures a large current that is assumed to flow in the power system when a system fault occurs in the power system.

Instrumentation current transformers are current transformers that are sensitive in the region of small currents. A current transformer for measurement is intended to measure a small current flowing through a power system during normal times when a system fault does not occur in the power system. Note that the small current region is a current below a predetermined rated current value, and the high current region is a current greater than the predetermined rated current value. The rated current may be arbitrarily determined according to the scale and conditions of the power system. The rated current shall indicate the rated current of the primary side unless otherwise specified.

In general, current transformers for protection and current transformers for measurement are configured separately Matters (including auxiliary CT)” [searched June 7, 2019], Internet <URL: https://www.jeea.or.jp/course/contents/02109/index_small.html>). Input transducers also follow this, and generally have separate configurations for measurement and protection.

In contrast, in this embodiment, the input converter 10 includes a first current transformer 11 and a second current transformer 12 . Therefore, one input converter 10 can cover the range measured by the current transformer for protection and the range measured by the current transformer for measurement.

In the following description, the case where the first current transformer 11 is a protection current transformer and the second current transformer 12 is a measurement current transformer will be described as an example. However, it is not limited to this, and the relationship between the two may be reversed.

Since the protective current transformer, which is the first current transformer 11, measures a large current, the value of the exciting current I in the equation (1) increases. The magnetic flux density B increases in proportion to the value of the exciting current I, and when the magnetic flux density B reaches the saturation region, the magnetic flux saturation makes it difficult to accurately measure the current value. Therefore, in the first current transformer 11, for example, the cross-sectional area S of the iron core 110 is increased, or the number of turns N of the winding on the primary side with respect to the secondary side is reduced, so that a large excitation current I flows. is designed so that the magnetic flux density B does not reach the saturation region. Also, the first current transformer 11 may be designed using a material with a high saturated magnetic flux density for the iron core 110 .

The measuring current transformer, which is the second current transformer 12, needs to accurately measure a small current. The second current transformer 12 is designed, for example, to increase the number of turns N on the secondary side with respect to the primary side to suppress the secondary side current CB so that a minute secondary side current CB can be detected. Alternatively, a material having a high magnetic permeability may be used for the core 120 so that a minute secondary current CB can be detected.

FIG. 3 is a diagram schematically showing respective characteristics of the first current transformer 11 and the second current transformer 12 of the input converter 10 of the embodiment. The horizontal axis of FIG. 3 indicates the primary side current CA, and the vertical axis indicates the secondary side current CB. As shown in FIG. 3, the first current transformer 11 exhibits linearity in the range of primary side currents CA2 to CA3 larger than the rated current. That is, the high sensitivity range 1 in which the first current transformer 11 can accurately measure is the range of the primary side currents CA2 to CA3. The second current transformer 12 exhibits linearity in the range of primary side currents CA1 to CA2 smaller than the rated current. That is, the high sensitivity range 2 in which the second current transformer 12 can accurately measure is the range of the primary side currents CA1 to CA2.

In an actual input converter 10, a first current transformer 11 and a second current transformer 12 are connected in series. Therefore, it is considered that the characteristics of the input converter 10 are the sum of the secondary currents CB of the first current transformer 11 and the second current transformer 12 . That is, in the input converter 10, the second current transformer 12 is dominant in the range of the primary side currents CA1-CA2, and the first current transformer 11 is dominant in the range of the primary side currents CA2-CA3. This allows the input converter 10 to accurately measure current values in a wide range of the primary side currents CA1 to CA3.

FIG. 4 is a block diagram showing an example of the configuration of the protection relay system 1 of the embodiment. The protection relay system 1 includes, for example, a transmission line 2, a main current transformer 3, a main current transformer 4, a circuit breaker 5, and a protection relay device 30. The main current transformers 3 and 4 are connected to the transmission line 2 on the primary side and to the protection relay device 30 on the secondary side. The main current transformer 3 and the main current transformer 4 transmit a current value corresponding to the magnitude of the current flowing through the transmission line 2 to the protection relay device 30 . A circuit breaker 5 is provided in the transmission line 2 . The main current transformer 3 brings the power transmission line 2 into an energized state or an interrupted state according to the control signal from the protective relay device 30 . Here, the transmission line 2 between the main current transformer 3 and the main current transformer 4 is an example of "protection section to be protected" by the protection relay device 30 .

The protection relay device 30 includes input converters 10-1 and 10-2 and a relay operation unit 20, for example. The input converter 10-1 has a primary side connected to the secondary side of the main current transformer 3, and a secondary side connected to the relay operation unit 20. FIG. The input converter 10-1 transmits a current value corresponding to the magnitude of the current flowing through the secondary side of the main current transformer 3 to the relay operation unit 20. The input converter 10-2 has a primary side connected to the secondary side of the main current transformer 4, and a secondary side connected to the relay operation unit 20. FIG. The input converter 10-2 transmits a current value corresponding to the magnitude of the current flowing through the secondary side of the main current transformer 4 to the relay operation unit 20.

The relay computation unit 20 includes, for example, a measurement section 22, a determination section 24, and a storage section 26. The measurement unit 22 and the determination unit 24 are realized by executing a program (software) by a hardware processor such as a CPU (Central Processing Unit). Some or all of these components are hardware (circuit part; circuitry) or by cooperation of software and hardware. The program may be stored in advance in a storage device (a storage device with a non-transitory storage medium) such as a HDD (Hard Disk Drive) or flash memory, or may be stored in a removable storage such as a DVD or CD-ROM. It may be stored in a medium (non-transitory storage medium) and installed by loading the storage medium into a drive device.

The measurement unit 22 measures the current value of the current flowing through the power transmission line 2 based on the secondary side outputs of the input converters 10-1 and 10-2. The measurement unit 22 causes the storage unit 26 to store the measured current value together with attribute information indicating the measurement time and the measurement point. The determination unit 24 determines whether or not a system accident such as a short circuit or ground fault has occurred in the transmission line 2 based on the secondary side outputs of the input converters 10-1 and 10-2. The determination unit 24 outputs a control signal to the circuit breaker 5 according to the determination result. For example, when determining that a grid fault has occurred in the transmission line 2 , the determination unit 24 outputs a control signal to set the circuit breaker 5 in the cut-off state.

The storage unit 26 is, for example, an HDD (Hard Disk Drive), a flash memory, a RAM (Random Access Memory), or the like. The storage unit 26 stores information in which the value of the current flowing through the transmission line 2 measured by the measurement unit 22 is associated with the attribute information.

As explained above, the input converter 10 of the embodiment includes the first current transformer 11 and the second current transformer 12 . A primary winding 112A of the first current transformer 11 and a primary winding 122A of the second current transformer 12 are connected in series. A secondary winding 112B of the first current transformer 11 and a secondary winding 122B of the second current transformer 12 are connected in series. Thereby, the input converter 10 of the embodiment has a high sensitivity range of the first current transformer 11 in which the first current transformer 11 is dominant and a second current transformer in which the second current transformer 12 is dominant. Both of the sensitive ranges of the instrument 12 can be measured. Moreover, since the first current transformer 11 and the second current transformer 12 are so-called core-type current transformers, their structures are not complicated. Therefore, it is possible to measure a wide range of current values without complicating the structure.

Further, in the input converter 10 of the embodiment, one of the current transformers (for example, the first current transformer 11) has a high sensitivity range of a small current smaller than the rated current, and a system fault occurs in the power system. It is used for measurement to measure the current value flowing through the power equipment provided in the power system during normal times when the power system is not in use. The other current transformer (for example, the second current transformer 12) has a high-sensitivity range of a large current larger than the rated current, and is used for protection to protect the power equipment in the event of a system fault in the power system. used for Therefore, the input converter 10 of the embodiment can serve both as a current transformer for measurement and for protection.

In addition, the protection relay device 30 of the embodiment is equipped with the input converter 10, so that it can measure current values in a wide range while also serving as a current transformer for measurement and protection without complicating the structure. is possible.

According to at least one embodiment described above, the input converter 10 includes the first current transformer 11 and the second current transformer 12, so that a wide range of current values can be measured without complicating the structure. It is possible to

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

REFERENCE SIGNS LIST 1 protection relay system 10 input converter 11 first current transformer 12 second current transformer 20 relay operation unit 22 measurement unit 24 determination unit 26 storage unit 30 …protective relay device

Claims (4)

An input converter connected to a power system,
a first current transformer, which is a core-type current transformer having a wound core, a primary winding wound around the wound core, and a secondary winding;
a second current transformer, which is the core-type current transformer, and has a high sensitivity range different from that of the first current transformer;
has
The primary winding of the first current transformer and the primary winding of the second current transformer are connected in series, and the secondary winding of the first current transformer and the second current transformer are connected in series. is connected in series with the secondary winding of the
input converter. Of the first current transformer and the second current transformer,
On the other hand, current transformers measure the current value flowing through power equipment installed in the power system in normal times when there is no system fault in the power system, with the area of small current smaller than the rated current as the high sensitivity range. used for
The other current transformer has a high-sensitivity range that is larger than the rated current, and is used for protection of the power equipment in the event of a system fault in the power system.
2. Input converter according to claim 1. A protection relay device comprising an input converter,
The input converter is
a first current transformer, which is a core-type current transformer having a wound core, a primary winding wound around the wound core, and a secondary winding;
a second current transformer, which is the core-type current transformer, and has a high sensitivity range different from that of the first current transformer;
has
The primary winding of the first current transformer and the primary winding of the second current transformer are connected in series, and the secondary winding of the first current transformer and the second current transformer are connected in series. is connected in series with the secondary winding of the
Protective relay device. Using the input converter having the first current transformer and the second current transformer, regardless of whether the current value of the current flowing through the protection section to be protected by the self-protection relay device is greater than the rated current First, a measurement unit that measures the value of the current flowing through the protection section;
Based on the current value measured by the input converter, whether a system fault has occurred when a large current larger than the rated current value or a small current smaller than the rated current flows in the protection section. a determination unit that detects whether the
further comprising
The protection relay device according to claim 3.

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