JP2001319818A - Input transformer for protective relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an input transformer for a digital protective relay which is not saturated magnetically even against the current which occurs when a power system is short-circuited and reduced in size and weight. SOLUTION: The input transformer for a digital protective relay is provided with an air-core transformer which is constituted by winding a secondary winding around an annular core formed of an insulating material and having a prescribed cross-sectional area and a primary winding on the secondary winding around the core.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input converter of a current input section of a digital protection relay used for a protection device of an electric power system.

[0002]

2. Description of the Related Art A conventional general digital type protection relay used for a protection device of a power system or the like is configured as shown in FIG. In the figure, reference numeral 11 denotes an input converter, which is connected to the secondary side of a current transformer for detecting a current of a power system or a voltage transformer for detecting a voltage, and capable of processing the detected current or voltage by an electronic circuit. They are converted into current signals or voltage signals. The configuration of the input converter 11 is a configuration in which a primary winding and a secondary winding are wound around an iron core, and the cross-sectional area of the iron core is set so that magnetic saturation does not occur at the maximum value of the input current. ing. 12 is an analog input unit,
Analog filter 12 for removing bands other than the used frequency
a, sample and hold 12 for sampling an input signal
b, a multiplexer 1 for selecting an input signal to be AD-converted
2c and an AD converter 12d. Reference numeral 13 denotes an arithmetic processing unit that processes input signal data that has been subjected to AD conversion, and includes a CPU, a RAM, and a ROM. Input converter 11, analog input unit 12, and arithmetic processing unit 13
Constitutes a digital relay unit and is mounted on the control panel.

[0003]

The input converter 11 of the conventional digital protection relay configured as described above has the following features.
When magnetic saturation occurs with respect to the input current, the current value of the power system is not correctly sent to the arithmetic processing unit 13 and proper system protection cannot be performed. Therefore, the iron core needs to have a cross-sectional area that does not saturate with respect to the current value detected at the time of short-circuiting, which is the maximum current value of the power system used, and the input converter 11 having the required cross-sectional area has a large size. However, the weight is heavy, and it is difficult to reduce the size and weight of the digital protection relay.

The present invention has been made to solve the above problems, and does not saturate the current at the time of short circuit.
An object of the present invention is to provide an input converter of a protection relay which is reduced in size.

[0005]

According to an input converter of a protection relay according to a first aspect of the present invention, a secondary winding is wound around an annular core having a predetermined cross-sectional area made of an insulating material. And an air-core transformer in which the primary winding is wound on the upper layer of the secondary winding.

According to a second aspect of the present invention, there is provided an input converter for a protection relay, comprising an electrostatic shield formed of a conductive material on the entire surface between the primary winding and the secondary winding of the air-core transformer of the first aspect. It is arranged.

According to a third aspect of the present invention, there is provided an input converter for a protection relay, wherein the primary winding and the secondary winding of the air-core transformer according to the first or second aspect of the invention have a pair of lead wires. It is a twist lead made by twisting wires.

According to a fourth aspect of the present invention, there is provided an input converter for a protection relay, wherein the air-core transformer and the integrator according to the first to third aspects are housed in a protective case made of a conductive material. It is.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 shows the configuration of the input converter of the protection relay according to the first embodiment. In the figure, reference numeral 21 denotes an air-core transformer, and a secondary winding 21 is attached to an annular core 21a having a predetermined sectional area made of an insulating material.
c is wound uniformly, and the primary winding 2 is
1b is wound uniformly, the primary connection lead 22 is drawn out from the primary winding 21b, and the secondary connection lead 23 is drawn out from the secondary winding 21c. 25 is the air core transformer 2
1 is an integrator that is connected to the secondary winding 21c and integrates the output voltage of the secondary winding 21c. The voltage dividing resistor 25a divides the output voltage of the secondary winding 21c into an appropriate voltage, and the operational amplifier 25b. , And a capacitor 25c. Reference numeral 26 denotes a low frequency region compensation circuit for preventing the integrator 25 from integrating the low frequency region. 27 is an output side connection lead. Air core transformer 21, primary connection lead 22, secondary connection lead 23, integrator 25, low frequency region compensation circuit 25
The input converter 20 is constituted by the output-side connection leads 27.

The air-core transformer 21 of the input converter 20 of the protection relay configured as described above has frequency characteristics as shown in FIGS. 2 (a) and 2 (b). FIG. 2A shows the secondary-side connection lead 2 when the primary winding 21b of the air-core transformer 21 is energized while changing the frequency of an alternating current with a constant current value.
3 shows a frequency characteristic of a current gain between both ends of the secondary connection lead 3. The frequency and a current gain between both ends of the secondary connection lead 23 are in a proportional relationship. FIG. 2B shows the voltage gain between the terminals of the output-side connection lead 27 when the frequency of the AC voltage with a constant voltage is changed and applied between both ends of the secondary-side connection lead 23 of the air-core transformer 21. The frequency characteristics of the applied AC voltage and the voltage gain between both ends of the output-side connection lead 27 are in inverse proportion. The input converter 20 of FIG. 1 adds a low frequency region compensation circuit 26 to the integrator 25 so as not to integrate in the low frequency region, and the gain of the output side connection lead 27 of the integrator 25 is as shown in FIG. , Except for the low frequency region.

In the input converter 20 of the protection relay shown in FIG. 1, when a current detected from the power system is input to the primary winding 21b, the secondary connection lead 23 of the secondary winding 21c of the air-core transformer 21 is connected. Appears across the primary winding 21
2B, the phase is delayed by π / 2 with respect to the current input to b, and the frequency characteristic of the current gain has the relationship shown in FIG.
When the integrator 25 is connected to the connection lead 23 of the secondary winding 21b, the voltage appearing between the terminals of the output-side connection lead 27 is equal to the voltage between the terminals of the secondary connection lead 23 of the secondary winding 21c. On the other hand, the phase advances by π / 2, and the frequency characteristics of the voltage gain have the relationship shown in FIG. By adding a low frequency region compensation circuit 26 that does not integrate the low frequency region to the integrator 25, the capacitor 25c is charged by the input offset voltage of the operational amplifier 25b of the integrator 25 and the integrator 25 is charged.
5 prevents the output voltage from rising to the power supply voltage and preventing a correct output from being obtained.

By combining the air-core transformer 21 and the integrator 25 to which the low-frequency region compensation circuit 26 is added, the characteristic shown in FIG. 3 in which the frequency characteristic is constant in the same phase as the input current is obtained. By setting the gain attenuation region in the low frequency region to a low frequency that is not normally used, the frequency characteristics of a constant modified gain over the entire frequency band in actual use for the same input AC current are obtained. Further, by changing the value of the voltage dividing resistor 25a, a configuration in which the transformation ratio of the input converter 20 can be arbitrarily set is obtained.

As described above, by using the air-core transformer 21 as the input converter 20 of the protection relay, a configuration capable of accurately converting the range of the detected current is formed in a small size, and the protection relay device can be downsized. it can. Further, the air-core transformer 21 that does not use an iron core has no eddy current loss in the iron core, the loss in the primary winding 21b and the secondary winding 21c is small, the calorific value is also small, and there is no need for forced cooling. In addition, the protection relay device can be mounted in a high-density panel that is not limited to the mounting position, and the installation space can be reduced.

Embodiment 2 FIG. The second embodiment has a configuration in which an electrostatic shield is arranged between the layers of the primary winding and the secondary winding of the air-core transformer of the first embodiment. FIG. 4 shows a cross-sectional view of the air-core transformer. In the figure, 31a is a winding core, 31b is a primary winding, and 31c is a secondary winding, which are the same as those of the first embodiment shown in FIG. Reference numeral 35 denotes an electrostatic shield disposed on the entire surface between the wound layers of the primary winding 31b and the secondary winding 31c, and a plate-like, foil-like, or net-like conductive material is inserted between the entire surfaces of the layers. It is arranged so that a closed circuit cannot be formed in the direction around the heart, and is grounded when used. Core 31a,
Primary winding 31b, secondary winding 31c and electrostatic shield 3
5 constitutes an air core transformer 31.

Air core transformer 31 with electrostatic shield 35
Is used for the input converter of the protection relay, the primary winding 31
b and the secondary winding 31c are electromagnetically shielded, so that noise entering from the primary side to the secondary side is shielded, mutual interference between the primary side and the secondary side is avoided, and a highly reliable protection relay that does not malfunction is provided. Can be configured.

Embodiment 3 Embodiment 3 is a configuration in which the influence of the surrounding magnetic field on the connection lead wires of the primary winding and the secondary winding of the air-core transformer is avoided. FIG. 5 shows the configuration of the third embodiment. In the figure, the air-core transformer 21 is the same as in the first embodiment. Reference numeral 42 denotes a primary connection lead of the primary winding 21b, and reference numeral 43 denotes a secondary connection lead of the secondary winding 21c, which is a twist lead formed by twisting two connection wires. Although not shown, the output-side connection lead is similarly a twist lead.

When each connection lead is formed by twisting a pair of lead wires and is subjected to electromagnetic induction from the surrounding magnetic field, the induced voltage becomes opposite in polarity for each twist and is canceled out. An input converter that avoids the influence of the surrounding magnetic field that enters from 22, 22 or the like can be configured. In the case of the second embodiment as well, a similar effect can be obtained by making the connection lead a twist lead.

Embodiment 4 Embodiment 4 has a configuration in which an air-core transformer and an integrator to which a low-frequency region compensation circuit is added are housed in a protective case made of a conductive material. 6 (a), 6
(B) shows a configuration in a state of being housed in a protective case. FIG.
6A is a plan view, and FIG. 6B is a side sectional view. In the figure, the air-core transformer 21, the integrator 25, and the low-frequency region compensation circuit 26 are the same as those of the first embodiment shown in FIG. Reference numeral 51 denotes a protective case formed of a conductive material.

As described above, the air-core transformer 21, the integrator 25,
When the low-frequency area compensation circuit 26 is housed in the protective case 51, it is shielded from the surrounding magnetic field, and an input converter in which the influence of the surrounding magnetic field is avoided can be configured.

[0020]

According to a first aspect of the present invention, there is provided an input converter for a protection relay, comprising an air core transformer in which a secondary winding and a primary winding are wound around a core formed of an insulating material in an annular shape. Therefore, the input converter that can convert accurately even if the detected current value is large is small, the amount of heat generation is small, and it can be mounted in a high-density panel that is not restricted to the mounting position as a protective relay device, and the installation space is small. The size can be reduced.

According to a second aspect of the present invention, there is provided an input converter for a protection relay, wherein an electrostatic shield formed of a conductive material is disposed between the primary winding and the secondary winding of the air-core transformer of the first aspect. With this configuration, the primary winding and the secondary winding are electromagnetically shielded to avoid mutual interference from the primary side to the secondary side, so that a highly reliable protection relay that does not malfunction can be configured.

According to a third aspect of the present invention, there is provided an input converter for a protection relay, wherein each connection lead wire of the secondary winding and the primary winding of the air-core transformer according to the first or second aspect is a pair. Since the leads are twisted and twisted, an input converter can be constructed which avoids the influence of the surrounding magnetic field that enters from the connection leads.

According to a fourth aspect of the present invention, there is provided an input converter for a protection relay, wherein the air-core transformer, the low-frequency region compensation circuit and the integrator according to the first to third aspects are provided in a protective case formed of a conductive material. , The input converters of the air-core transformer, the integrator, and the low-frequency region compensation circuit are shielded, and an input converter that avoids the influence of the surrounding magnetic field can be configured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an input converter according to a first embodiment.

FIG. 2 is a frequency characteristic diagram of a current gain and a voltage gain of the air-core transformer.

FIG. 3 is a frequency characteristic diagram of a transformation gain of the air-core transformer.

FIG. 4 is a sectional view of an air core transformer according to a second embodiment.

FIG. 5 is an explanatory diagram illustrating a state of a connection lead according to a third embodiment;

FIG. 6 is a plan view and a cross-sectional view of a state where the input converter according to the fourth embodiment is accommodated in a protective case.

FIG. 7 is a block diagram of a conventional input converter.

[Explanation of symbols]

1 input converter, 21 air-core transformer, 21a core, 2
1b Primary winding, 21c Secondary winding, 22 Primary connection lead, 23 Secondary connection lead, 25 Integrator, 26
Low frequency region compensation circuit, 27 output side connection lead, 31
Air core transformer, 31a core, 31b primary winding, 31
c Secondary winding, 35 electrostatic shield, 42 primary connection lead, 43 secondary connection lead, 51 protective case.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E081 AA02 BB08 DD11 DD22 5G042 BB02 BB11 5H410 CC03 DD03 EA12 EA16 EB14 EB38 FF05 FF22 FF29

Claims (4)

[Claims] An air-core transformer in which a secondary winding is wound around an annular core having a predetermined sectional area made of an insulating material, and a primary winding is wound on an upper layer of the secondary winding. An input converter for a protection relay, comprising: 2. The electrostatic shield according to claim 1, wherein an electrostatic shield formed of a conductive material in a plate shape is disposed on the entire surface between the layers of the primary winding and the secondary winding of the air-core transformer. Input converter for protection relay. 3. The connection lead wire of the primary winding and the secondary winding of the air-core transformer is a twisted lead wire in which a pair of lead wires are twisted, respectively. Input transformer for protection relay. 4. The input conversion of a protection relay according to claim 1, wherein the air-core transformer and the integrator are housed in a protection case formed of a conductive material. vessel.