JP3121248B2 - Current transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current transformer connected to an input section of various relays, and more particularly, to a current transformer having improved residual magnetic characteristics and residual current characteristics.

[0002]

2. Description of the Related Art In order to minimize residual magnetism that may cause a malfunction when a breaker is turned on again, a transformer having an iron core with a gap is provided at an input portion of a ratio differential relay for protecting a generator or a motor. Current transformers (so-called current transformers with remanent magnetic properties) are often used. Since this current transformer has a large primary current (for example, 800 A or more) and a large number of secondary windings, even if the characteristics (magnetizing force and iron loss) of the air-gapped core are relatively poor, the current transformer error is not significantly affected. .

On the other hand, when a zero-phase current (fault current) of a three-phase circuit of a transmission and distribution line is detected by a ground fault relay, a zero-phase current transformer is used or a residual circuit through which the zero-phase current flows is opened. In addition, a separately provided zero-phase tertiary winding is connected in series to form a tertiary triangular open connection, to which a ground fault overcurrent relay or the like is connected.

In this case, the current flowing in the zero-phase current circuit is a vector sum of the current corresponding to the zero-phase current and the residual current flowing only by the positive-phase / negative-phase current. All that is required of the relay is a current corresponding to the zero-phase current, and not only a residual current is unnecessary, but also a useless current that limits the detection sensitivity of the current corresponding to the zero-phase current. Therefore, in order to reduce the residual current, it is necessary to reduce variations in core characteristics and loss of the core.

For this reason, for example, when a current transformer having an iron core with a gap is used at the input part of the ratio differential relay and the ground fault overcurrent relay, the residual magnetic characteristics are sufficient in terms of the residual magnetic characteristics, but the residual current is reduced due to the loss of the iron core. The characteristics deteriorate. Also,
When a zero-phase tertiary winding is wound around a core with a gap, the tertiary winding usually has a very small number of turns (usually 20 turns).
The current transformer ratio error increases according to the variation in the core characteristics,
The variation of the current ratio error also increases with each current transformer.

Conventionally, therefore, a zero-phase current transformer is used exclusively for a ground fault overcurrent relay without using a tertiary triangular open-circuit current transformer, and a ratio-differential relay is provided exclusively with a remanent magnetic characteristic. Current transformers were installed separately.

[0007]

However, the use of current transformers dedicated to individual relays causes an increase in cost, and furthermore, the characteristics of current transformers vary, the complexity of insulation treatment, and the use of equipment. Problems such as an increase in the size of the whole will occur. Therefore, the present invention is intended to solve the above-mentioned problems by satisfying both the residual magnetic characteristics and the residual current characteristics with a single current transformer.

[0008]

In order to achieve the above object, the present invention provides a first iron core having an air gap, a secondary winding wound around the iron core, and a coaxial core with respect to the first iron core. A second iron core as a closed iron core disposed thereon, a zero-phase tertiary winding wound around the iron core, and connected in series for three phases to form an open triangular connection; and a second iron core. And the start and end of the winding are short-circuited to form a closed loop,
Magnetic flux that causes open-circuit voltage induced in the phase tertiary winding
Open-circuit voltage suppression short-circuit winding for extinguishing
1, second core, secondary winding, zero-phase tertiary winding, open-circuit voltage suppression
The short-circuit winding is integrally molded with resin.
You.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view showing the internal structure of this embodiment. In the figure, 11 is a pair of gaps 1
2, and an insulator (not shown) such as a polyester film is inserted into the gap 12. A secondary winding 13 of a current transformer is wound around the iron core 11, and both ends of the secondary winding 13 are connected to terminals 14a and 14b. The iron core 11, the air gap 12, and the secondary winding 13 constitute a current transformer in consideration of residual magnetic characteristics.

Reference numeral 15 denotes a second iron core, which is a closed iron core. The iron core 15 is wound with a zero-phase tertiary winding 16 for detecting a ground fault. Both ends of the zero-phase tertiary winding 16 are terminals 14
c, 14d, and these terminals 14
The zero-phase tertiary windings 16 for three phases are connected in series via c and 14d, and a ground fault overcurrent relay or the like (not shown) is connected to the series circuit. Here, since the zero-phase tertiary winding 16 is wound around the closed iron core, the loss of the iron core is small, the residual current characteristics can be improved, and the current ratio error of each current transformer can be reduced. it can.

Further, an open-circuit voltage suppressing short-circuit winding 17 is wound around the second iron core 15, and both ends of the winding 17 are connected and short-circuited at a connecting portion 17a to form a closed loop. Here, both ends of the open-circuit voltage suppression short-circuit winding 17 may be connected to terminals (not shown), and these terminals may be short-circuited.
The burden may be connected.

Zero-phase tertiary winding 1 wound on second iron core 15
6 corresponds to the secondary winding of the current transformer having a small number of turns,
If the iron core 15 is easily saturated and no treatment is performed, the secondary winding of the current transformer is opened and the terminals 14c,
An abnormal open voltage may occur between 14d. Therefore, a sufficient cross-sectional area for the overcurrent and a saturation for the iron core 15 are provided so that the magnetic flux for canceling the magnetic flux for generating the open-circuit voltage is generated by the short-circuit current flowing through the open-circuit voltage suppressing short-circuit winding 17. Thus, the open-circuit voltage suppressing short-circuit winding 17 having a sufficient margin is wound around the iron core 15.

As a result, even when the zero-phase tertiary winding 16 is connected in an open triangular connection, an open voltage is not generated at both ends of the winding 16 and safety can be improved. At the same time, iron core 1
5 can be constituted by an annular core, so that a current transformer having good residual current characteristics can be provided.

As described above, the first and second iron cores 11, 15 on which the windings 13, 16, 17 are wound are arranged coaxially.
The current transformer for one phase according to the present invention is constituted by integrally molding the whole formed like a double core current transformer with a resin 18 or the like.

[0015]

As described above, according to the present invention, a single current transformer is provided with a first iron core having a gap and a second iron core which is a closed iron core. While winding the winding,
Because the zero-phase tertiary winding and the open-circuit voltage suppression short-circuit winding are wound around the second core, they are excellent in residual magnetic characteristics and residual current characteristics, for example, as current transformers for ratio differential relays and ground-fault relays. Current transformer can be realized. For this reason,
Compared with the case where a dedicated current transformer is installed according to the type of the relay, the cost can be reduced, the insulation process can be facilitated, and the installation space can be reduced by downsizing.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an internal structure of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 1st iron core 12 Air gap 13 Secondary winding 14a, 14b, 14c, 14d Terminal 15 2nd iron core 16 Zero-phase tertiary winding 17 Open-circuit voltage suppression short-circuit winding 17a Connection part 18 Resin

Claims (1)

(57) [Claims] 1. A first iron core having an air gap, a secondary winding wound around the iron core, a second iron core as a closed iron core arranged coaxially with the first iron core, and A zero-phase tertiary winding wound around an iron core and connected in series with three phases to form an open triangular connection; a second core wound around a zero-phase tertiary winding; and
The beginning and end of the winding are short-circuited to form a closed loop,
The magnetic flux that causes the open voltage induced in the tertiary winding
An open-circuit voltage suppressing short-circuit winding for extinguishing, the first and second iron cores, a secondary winding, a zero-phase tertiary winding, and an open circuit.
A current transformer, wherein the voltage suppression short-circuit winding is integrally molded with resin .