JPH05326301A - Grounding type instrument transformer - Google Patents

Abstract

PURPOSE:To enhance the safety of grounding structure of a neutral point terminal by installing a capacitor having a specified pressure resistance and capacity outside a vessel of a grounding circuit at the neutral point terminal of high voltage winding and allowing the grounding circuit to be opened when the neutral point terminal is connected to the capacitor. CONSTITUTION:A neutral point terminal 4 of a high voltage winding 2 is adapted to lead out to the outside of a vessel 5 and grounded in a low voltage terminal box 6 by way of a changeover switch 8. On the other hand, the low voltage terminal box provides a capacitor 9 which has insulation resistance of some kv and a large enough static capacity which divides the voltage applied to a high voltage terminal 3 to and below the insulation resistance of the neutral point terminal 4 and whose end is grounded where the neutral point terminal 4, after it is installed, will not be opened, but it is constantly connected to either a grounding terminal 10 or the capacitor 9 or both of them. This construction makes it possible to allow the neutral terminal point 4 of the high voltage winding to keep constantly a grounded state and an insulated state as well against the DC voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grounding-type instrument transformer, and more particularly to a grounding-type instrument transformer having a neutral point-end grounding structure which is highly reliable in terms of insulation.

[0002]

2. Description of the Related Art A transformer for an instrument is generally used to transform a voltage of a high voltage circuit into a low voltage proportional to the voltage for use in a measuring instrument or a relay. A voltage transformer that is used by connecting both ends of a high-voltage winding to a high-voltage circuit and ground, respectively, is called a grounding-type voltage transformer, and is always grounded during operation. The neutral terminal side is designed for low insulation performance.

Since the grounding type instrument transformer is grounded at the neutral point terminal of the high voltage winding, it is necessary to make a contact when measuring the insulation resistance of the high voltage circuit to which the grounding type instrument transformer is connected. It was necessary to open the neutral point terminal of the transformer for the terrain instrument to insulate it from the ground circuit.

[0004]

Since the neutral point terminal side of the high voltage winding of the grounding type instrument transformer is designed to have a low insulation performance, the high voltage winding when the neutral point end is opened. It was necessary to apply a voltage to the neutral voltage terminal dielectric strength or less. In addition, after measuring the insulation resistance, the neutral point must be surely grounded before starting operation.If the neutral point is not grounded, the neutral point is connected to the high voltage end of the high voltage winding. When a voltage higher than the insulation performance is applied, the high voltage winding portion is damaged.

The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a grounding type instrument transformer having a grounding structure of a neutral point end which is safe and highly reliable.

[0006]

In order to achieve the above-mentioned object, the present invention has an iron core constituting a magnetic circuit and a high voltage end wound around the legs of the iron core to connect the high voltage end to the high voltage circuit. A high voltage winding used by grounding the sex point,
In a transformer configuration for a grounding type instrument in which an insulating gas is housed in a container, a capacitor having a predetermined withstand voltage and capacity is provided outside the container of the ground circuit at the neutral point end of the high voltage winding, and the neutral It is characterized in that the ground circuit is opened on condition that the point end is connected to the capacitor.

[0007]

According to the present invention, when a voltage is generated due to induction or the like in a high voltage circuit to which a grounding type instrument transformer whose neutral point end is opened is connected, even if it is stopped, it is erroneous. Even if a high voltage is applied due to this, the voltage to which the neutral point end is exposed can be made equal to or lower than the dielectric strength of the neutral point terminal side.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of the present invention. In FIG. 1, reference numeral 1 is a grounding type instrument transformer, which is always grounded to a high voltage end 3 of a high voltage winding 2 connected to a system. Has a neutral point end 4 The neutral point end 4 of the high voltage winding 2 is
It is led out of the container 5 via an insulating terminal 7 in a low-voltage terminal box 6 provided on the side wall of the container 5, and is grounded in the low-voltage terminal box 6 via a switching switch 8. On the other hand, the low voltage terminal box 6 has a dielectric strength of several kilovolts, and the high voltage end 3
There is provided a capacitor 9 having a capacitance large enough to divide the voltage applied to the capacitor to a dielectric strength of the neutral point end 4 or less and one end of which is grounded.

The switching switch 8 connects the neutral point end 4 to the ground terminal 1
0 is connected to the capacitor 9 so that connection can be made. When the connection is made, the neutral point end 4 is once connected to both circuits of the ground terminal 10 and the capacitor 9, and then one of the circuits is connected. It is configured to be detached. That is, the neutral point end 4 is not opened after being installed, and is always connected to one or both of the ground terminal 10 and the capacitor 9. Further, an alarm device which operates at a voltage generated when a voltage of 50% or more of the rated voltage is applied to the high voltage end 3 of the high voltage winding 2 of the grounded instrument transformer 1 is connected to both ends of the capacitor 9. I'll do it.

Next, the operation of this embodiment will be described.
The neutral point end 4 of the high-voltage winding 2 of the grounded instrument transformer 1 is always connected to one or both of the ground terminal 10 and the capacitor 9 and is not opened. Even if there is a voltage in the high-voltage circuit to which the device 1 is connected, the neutral point end 4 is only exposed to the ground potential or a voltage divided by capacitance below its own dielectric strength, and the capacitor 9 is also exposed. By changing the connection, it is possible to insulate the high-voltage wire winding 2 of the grounded instrument transformer 1 in terms of DC voltage.

Further, when the voltage of 50% or more of the rated voltage is applied to the high voltage circuit with the neutral point end 4 being connected to the capacitor 9, the alarm voltage exceeds the operating voltage of the alarm device. Thus, it is possible to inform that the neutral point end 4 is not connected to the ground terminal 10.

As described above, according to the present embodiment, the neutral point end 4 of the high voltage winding 2 of the grounded instrument transformer 1 is connected to the ground terminal 10 in a normal state and has a ground potential. However, in order to measure the insulation resistance of the high-voltage circuit to which the grounding-type voltage transformer 1 is connected, when it is disconnected from the grounding terminal 10, it is insulated in terms of DC voltage without opening. The connection is changed to the capacitor 9.

Therefore, even if there is an induced voltage in the high-voltage circuit to which the grounding type instrument transformer 1 is connected, the neutral point end 4 should be a low voltage whose capacity is divided below its dielectric strength. It is possible to provide a highly reliable grounding instrument transformer. Also, after measuring the insulation resistance, a voltage is applied to the high voltage circuit with the neutral point 4 not connected to the grounding terminal 10. Even if the voltage is applied, the voltage at the neutral point 4 can be suppressed below the dielectric strength of the neutral point terminal 4 of the grounding type instrument transformer, and the grounding type instrument transformer can be protected from dielectric breakdown and a fault condition can be indicated by an alarm. There are a number of advantages such as being able to detect and return to normal.

In the configuration of the present embodiment described above, the switching switch 8 having the function that the switching between the ground terminal 10 and the capacitor 9 is always connected to one or both sides and the neutral point end 4 is not opened has been described. However, the same function may be artificially performed by using two switching switches, and in this embodiment, an alarm device that operates at a voltage of 50% or more of the rated voltage is provided. The same effect can be obtained by changing the operating voltage of the alarm device according to the purpose.

FIG. 2 is a constitutional view of another embodiment of the present invention, which is different from the above embodiment in that the neutral point end 4 is connected to the capacitor 9 to be connected to the ground terminal 10 and via the switch 8. The only difference is that the configuration is such that it is connected to the ground terminal 10. Therefore, the same parts are designated by the same reference numerals and the description thereof is omitted.

In this embodiment, when the grounding circuit is opened, it is grounded via the capacitor 9 in terms of AC voltage, but can be insulated in terms of DC voltage.
This does not hinder the insulation measurement of the high-voltage circuit to which the grounded voltage transformer 1 is connected.

Further, when the neutral point end 4 is opened from the ground circuit and a voltage of 50% or more of the rated voltage is applied to the high voltage circuit without being grounded, the voltage exceeds the operating voltage of the alarm device. Therefore, an alarm can inform that the neutral point end 4 is not connected to the ground terminal 10. In addition to these effects, it goes without saying that the same effects as those described in the above embodiment can be obtained.

[0018]

As described above, according to the present invention,
The neutral point end of the high voltage winding of the transformer for grounding type instrument is always in the grounding state or a low voltage state close to the grounding potential for AC voltage, and is almost insulated for DC voltage. Not hindering the insulation resistance measurement performed with DC voltage, and even if the neutral point terminal is forgotten to be grounded after the insulation resistance measurement, a voltage higher than the dielectric strength of the neutral point is applied. It is possible to provide a highly reliable grounding-type instrument transformer because it is possible to protect the grounding-type instrumentation transformer from dielectric breakdown by eliminating the problem.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a grounding type instrument transformer according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a grounding type instrument transformer according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transformer for grounding type instrument, 2 ... High voltage winding, 3 ... High voltage end, 4 ... Neutral point end, 5 ... Container, 6 ... Low voltage terminal box, 7 ... Insulation terminal, 8 ... Switching switch, 9 ... capacitor, 10 ... ground terminal.

Claims (1)

[Claims] 1. An iron core forming a magnetic circuit, and a high voltage winding wound around the legs of the iron core so as to connect the high voltage end to the high voltage circuit and ground the neutral end. In a transformer configuration for a grounding type instrument in which an insulating gas is housed in a container, a capacitor having a predetermined withstand voltage and capacity is provided outside the container of the ground circuit at the neutral point end of the high voltage winding, A grounding type instrument transformer, characterized in that the grounding circuit is opened on condition that the sex point is connected to the capacitor.