JPH0684671A - Transformer incorporating current transformer - Google Patents

Abstract

PURPOSE:To lower voltage to be transferred to transformer side upon intrusion of surge through a transformer terminal. CONSTITUTION:Current transformers 28, 29 are provided for the wires 25, 26 connecting a bushing 22 with coils of transformer elements 23, 24 housed in a tank 21. Cores of the current transformers 28, 29 are not grounded and grounded shield members 40, 41 are disposed between the connecting wires 25, 26 and the current transformers 28, 29 or around the current transformers 28, 29. Consequently, capacitance between the connecting wires 25, 26 and the current transformers 28, 29 goes substantially zero and the voltage to be transferred to the current transformers 28, 29 is suppressed. When the grounded shield members 40, 41 are disposed around the current transformers 28, 29, earth capacities of the current transformers 28, 29 increase significantly and the voltage V to be transferred to the current transformers 28, 29 is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer with a built-in current transformer, and more particularly to a transformer with a built-in current transformer designed to reduce the transition voltage to the current transformer when a surge enters.

[0002]

2. Description of the Related Art A transformer is a current transformer for measuring the current of a transformer or a load supplied through the transformer, or for a ratio differential relay for detecting an abnormality of the transformer. Is generally provided.

In the case of an ordinary transformer, a bushing type current transformer is used as the current transformer. This bushing type current transformer is provided in a bushing that constitutes a high-voltage side terminal of a transformer, and is configured to detect a current flowing through an inner conductor of the bushing (the same as a current flowing through a primary coil of the transformer).

However, recently, there are transformers having a structure in which a plurality of transformer contents are housed in a tank, and transformers using a cable-integrated connector without using bushings as transformer terminals. In the former case having a plurality of transformer contents, if the bushing type current transformer is used, the current of the entire transformer is detected, and the current flowing through each transformer contents cannot be detected individually. In the latter case of using the cable-integrated connector, a bushing type current transformer cannot be used because a bushing is not used.

Therefore, a transformer that cannot use such a bushing type current transformer is constructed as a built-in current transformer in which the current transformer is arranged in the tank. FIG. 4 shows the conventional configuration of this transformer with a built-in current transformer. In the tank 1, for example, two transformer contents 2 and 3 are stored. The transformer contents 2 and 3 are connected to the conductor 5 of the bushing 4 provided on the upper portion of the tank 1 as the high-voltage side terminal of the transformer via the connecting lines 6 and 7. On the other hand, two current transformers 8 and 9 are arranged in the tank 1, and the connecting wires 6 and 7 penetrate the inside of the current transformers 8 and 9.

Each of the current transformers 8 and 9 is a penetrating current transformer in which a secondary coil is wound around the outer circumference of an annular iron core, and lead wires 8a and 9a extending from both ends of the coil are provided in the tank 1. The external lead wire 11 is connected to the external lead wire 11 via the relay terminal 10 in order to maintain airtightness inside and outside.
Is connected to the measuring device 13 via the terminal box 12.
Then, in the measuring device 13, the external lead wire connected to one of both ends of the coils of the current transformers 8 and 9 is grounded.

[0007]

By the way, when a lightning impulse surge, a switching surge of a circuit breaker, or the like invades the transformer, the surge propagates through the connecting lines 6 and 7 and is deposited in the transformer contents 2 and 3. However, it passes through the current transformers 8 and 9 on the way. At that time, the surge is transferred to the current transformers 8 and 9. The value of this transition voltage V2s is expressed by V2s = V1 [C12 / (C12 + C2e)] (1). Here, V1 is the connection line 6 at the time of surge intrusion.
7 is the ground potential, C12 is the capacitance between the connecting lines 6 and 7 and the current transformers 8 and 9, and C2e is the ground capacitance of the current transformers 8 and 9.

When the surge enters the transformer, in the bushing type current transformer, the current transformer is surrounded by the bushing mounting seat at the ground potential, and therefore the electrostatic capacitance C2e to the ground.
Is large, so that the transition voltage V2s to the current transformer is kept low.

However, in the transformer with a built-in current transformer, since the current transformers 8 and 9 are separated from the tank 1 at the ground potential, the value of the ground capacitance C2e does not become so large. Therefore, the value of the transition voltage V2s becomes considerably large, and the insulation of the current transformers 8 and 9 and the lead wires 8a and 9a may be destroyed.

The present invention has been made in view of the above circumstances, and an object thereof is to reduce the transition voltage to the current transformer side even if a surge enters from a transformer terminal, and to insulate the current transformer and its lead wires. The purpose is to provide a transformer with a built-in current transformer that does not have the risk of being destroyed.

[0011]

DISCLOSURE OF THE INVENTION A transformer with a built-in current transformer according to the present invention stores the contents of a transformer in a tank, and a coil between the transformer and a transformer terminal provided in the tank. When installing a current transformer that is connected by a connecting wire and detects the current flowing in this connecting wire, make the iron core of this current transformer non-grounded, and between the current transformer and the connecting wire, or the outer circumference of the current transformer. Further, a grounded shield member is provided.

[0012]

[Operation] The iron core of the current transformer is not grounded, and the grounded shield member is arranged between the current transformer and the connection line.
The electrostatic capacitance C12 between the connection line and the current transformer becomes almost zero, and the transition voltage V2s to the current transformer can be suppressed small.

Further, by disposing a grounded shield member around the current transformer, the electrostatic capacitance C2s of the current transformer becomes a very large value, and the transition voltage V2s to the current transformer is kept small. You can

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a transformer with a built-in current transformer according to the present description will be described below with reference to FIGS.

FIG. 1 is a sectional view showing an embodiment of a transformer with a built-in current transformer according to the present invention, FIG. 2 is a partially cutaway perspective view of the current transformer, and FIG. 3 shows another embodiment of the present invention. It is a perspective view of a current transformer. First, in FIG. 1 showing the overall configuration of the transformer, 21
Is a tank of a transformer, and a bushing 22 is provided above the tank as a high-voltage side terminal of the transformer. Further, in the tank 21, for example, two transformer contents 23 and 24 are arranged. Then, the primary coils of the transformer contents 23 and 24 are connected to the conductors of the bushing 22 via the connection wires 25 and 26. Here, as is well known, the transformer contents 2
Clamps 23a and 24a for fastening the laminated steel plates forming the iron cores are provided on the upper and lower portions of the iron cores 3 and 24, respectively.

On the other hand, two current transformers 2 are provided in the tank 21.
8, 29 are provided. The current transformers 28 and 29 are attached to columns 30 and 30 made of an insulating material such as wood and fixed to the upper clamps 23a and 24a of the transformer contents 23 and 24. As shown in FIG. 2, the current transformers 28 and 29 include a coil 3 with an annular core 31 with an insulating layer 32a interposed therebetween.
3 is wound, and an insulating layer 32b is further provided on the outer side of the coil 33.
Is provided. The connecting wires 25 and 26 penetrate the inside of the annular core 31 of the current transformers 28 and 29.

Lead wires 34 and 35 are connected to both ends of the coil 33 of the current transformers 28 and 29 as shown in FIG. Both lead wires 34, 35 are connected to an external lead wire 37 via a relay terminal 36, and the external lead wire 37 is connected to a measuring device 39 via a terminal box 38. Then, in the measuring device 39, the external lead wire 3 connected to one of both ends of the coil 33 of each of the current transformers 28 and 29.
7 is grounded. In the current transformers 28 and 29, the annular iron core 31 of the current transformers 28 and 29 is not grounded, and the cylindrical shield members 40 and 41 are arranged between the current transformers 28 and 29 and the connecting wires 25 and 26. The shield members 40 and 41 are connected to the clamps 23a and 24a of the transformer contents located in the vicinity thereof via lead wires (not shown) and grounded.

Therefore, since the connecting lines 25 and 26 face the shield members 40 and 41 which are grounded and do not face the current transformers 28 and 29, the static electricity between the connecting lines 25 and 26 and the current transformers 28 and 29 is fixed. The capacitance C12 becomes almost zero. As a result, since the numerator in equation (1) becomes almost zero, the transition voltage V2s to the current transformer also becomes almost zero, and even if a surge enters the transformer terminals, the current transformers 28 and 29 and the lead wires 34, The insulation of 35 is not threatened.

In the case of the embodiment shown in FIG. 2, a sufficient insulation distance must be provided between the connecting wires 25 and 26 and the shield members 40 and 41. Therefore, the current transformers 28 and 29 become large, which may affect the size of the entire transformer. In such a case, it is advisable to adopt the configuration shown in FIG. 3 as another embodiment of the present invention.

In FIG. 3, the shield members 40 and 41 are arranged around the outer circumferences of the current transformers 28 and 29, respectively.
It is intended to cover the whole of the. Shield member 4
0 and 41 are grounded and are at ground potential, current transformer 28,
Since the insulation level of 29 against the ground is low, the shield members 40 and 41 can be arranged near the outer peripheral surfaces of the current transformers 28 and 29. Therefore, the outer dimensions of the current transformers 28 and 29 can be reduced, and the ground capacitance C of the current transformers 28 and 29 can be reduced.
Since 2e can be set to a very large value, the denominator in the above equation (1) has a large value, so that the transition voltage V2s to the current transformer can be set to a small value and a surge is generated at the transformer terminal. Even if it enters, it does not threaten the insulation of the current transformers 28, 29 and the lead wires 34, 35.

[0021]

As is clear from the above description, in the transformer with built-in current transformer of the present invention, since the transition voltage from the connection line to the current transformer can be set to a small value, the transformer terminal is Even if a surge invades, there is an excellent effect that the risk of breaking the insulation of the current transformer and the lead wire can be eliminated.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a transformer with a built-in current transformer according to the present invention.

FIG. 2 is a partially cutaway perspective view of a current transformer.

FIG. 3 is a perspective view of a current transformer according to another embodiment of the present invention.

FIG. 4 is a sectional view showing a conventional transformer with a built-in current transformer.

[Explanation of symbols]

In the drawing, 21 is a tank, 22 is a bushing, and 23, 24.
Is the contents of the transformer, 23a and 24a are clamps, 25 and 26
Is a connecting wire, 28 and 29 are current transformers, 34 and 35 are lead wires, 39 is a measuring device, and 40 and 41 are shield members.

Claims (2)

[Claims] 1. A tank, a transformer content housed in the tank, a connection line for connecting a coil of the transformer and a transformer terminal provided in the tank, and a connection line to the connection line. A current transformer for detecting a flowing current, wherein an iron core of the current transformer is not grounded, and a grounded shield member is arranged between the current transformer and a connection line. Built-in current transformer. 2. A tank, a transformer content housed in the tank, a connection line for connecting a coil of the transformer and a transformer terminal provided in the tank, and a connection line to the connection line. A current transformer for detecting a flowing current, wherein an iron core of the current transformer is not grounded, and a shield member grounded around the outer periphery of the current transformer is provided. Shape transformer.