JPH09168231A - Opened secondary protection device of transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reliable opened secondary side protection device for a transformer by preventing a diode for protecting the opened secondary side of a transformer from resulting in open mode failure. SOLUTION: Two diodes 17, 17 are connected in parallel in opposite directions for conductor parts 12, 12 where the secondary sides of a transformer are connected and at the same time a conductive plate 18 is provided to short- circuit the conductor parts 12, 12 when temperature reaches a specific value by receiving the heat build-up of the diodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary side open protection device for a current transformer, which prevents the secondary side output of the current transformer from being opened.

[0002]

2. Description of the Related Art Conventionally, in a device for inputting a secondary output of a current transformer (hereinafter referred to as "CT") to measure an AC current, in order to easily attach and detach the measuring device,
The secondary output signal line of the current transformer is connected to the socket in advance, and the measuring device is attached to and detached from the socket as needed. However, when the measuring instrument is pulled out from the socket, the secondary output of CT is opened, high voltage is generated, and the iron core overheats, leading to an accident. Therefore, a protective device that prevents the secondary side of the CT from being opened even when the measuring instrument is removed from the socket is connected between the terminals of the socket to which the secondary output signal line of the CT is connected.

FIG. 7 is a circuit diagram showing an example of a measuring circuit using such a protection device. In FIG. 7, CT is a current transformer provided in the measuring object, and Aux.CT is an auxiliary CT provided in the input part of the measuring instrument. The protection device is configured by connecting the secondary output of the CT to the primary side of the auxiliary CT, and connecting two diodes in opposite directions to each other in parallel at both ends thereof.

[0004]

When the conventional protection device shown in FIG. 7 is used, since the diode of the protection device is applied with a voltage less than its forward voltage drop when the measuring instrument is connected, No current flows through the diode,
Also, the measuring device can perform the measurement without being affected by the diode of the protection device. If the measuring device is removed in the state shown in FIG. 7, the secondary output voltage of CT rises, and a current flows through the diode of the protection device alternately every half cycle.
As a result, the secondary side output voltage of the CT is suppressed to the forward voltage drop of the diode, and the CT is protected from its secondary side opening.

However, when a large current flows for a long time in the object to be measured with the measuring device removed, the diode in the protective device becomes overheated, the life of the diode is shortened, and in terms of reliability. There was a risk of problems. Also,
Should one or both diodes in the protection device fail in open mode, the secondary side of the current transformer will be opened, leading to a major accident.

An object of the present invention is to provide a highly reliable secondary side open protection device for a current transformer which solves the above-mentioned problems.

[0007]

SUMMARY OF THE INVENTION The present invention is a device for protecting a current transformer from its secondary side opening by means of a diode. In order to prevent the secondary side from being opened, as described in claim 1, the diode is heated and deformed,
A conductive plate is provided that short-circuits between the conductor portions to which the secondary side output of the current transformer is connected when the temperature reaches a predetermined temperature.

Further, according to the present invention, a heat-sensitive agent that discolors at the predetermined temperature is provided on the conductive plate so that the protection state of the conductive plate can be confirmed from the outside.

In the secondary side open-circuit protection device for a current transformer according to claim 1, if the measuring device is removed and only the protection device is connected to the secondary side of the current transformer, the diode is released. Prevent the secondary side of the current transformer from opening. If a large current flows for a long time in the current path to be measured and the diode becomes overheated, the conductive plate receives the heat and is deformed, and between the conductor parts to which the secondary side output of the current transformer is connected. Are short-circuited by the conductive plate. This stops the energization of the diode, prevents failure of the diode, and protects the current transformer from its secondary side opening. If the conductive plate is made of a material having reversibility to thermal deformation, a current flows through the conductive plate in a state where the conductive plate is short-circuited between the conductor portions, so that the conductive plate itself generates heat and maintains its deformed state. Even if the conductive plate itself does not generate heat enough to maintain its deformed state, if the conductive plate returns to its original shape, the diode heats up again and the conductive plate is deformed as a result. By repeating the plate deformation operation, the diode is prevented from abnormal overheating. If a material having an irreversible thermal deformation is used as the conductive plate, the conductive plate is deformed by the heat generated by the diode, and then the conductor portions are kept short-circuited.

In the secondary side open protection device for a current transformer according to a second aspect, the conductive plate is deformed due to overheating of the diode, so that the conductor portions between the secondary side outputs of the current transformer are electrically connected. When the plate is short-circuited, the heat-sensitive agent provided on the conductive plate is discolored, and the state is shown to the outside. If the heat-sensitive agent is a heat-sensitive agent having reversibility to thermochromism, it can be confirmed from the outside by the color of the heat-sensitive agent whether or not the conductive plate is short-circuited between the conductor portions. If a heat-sensitive agent having an irreversible property of thermal discoloration is used, a record that the conductive plate short-circuits between the conductor portions can be confirmed from the display color.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The configuration of a secondary side open protection device for a current transformer and a measuring circuit using the same according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a right side view showing a state in which a measuring device is attached to a socket. FIG. 2 is a front view of the socket. In FIG. 1, 2 is a socket, 3 is a socket 2
It is a measuring instrument that is configured to be detachable with respect to. As shown in FIG. 2, the socket 2 is provided with a connector 21 into which a plurality of pins protruding from the measuring device 3 are inserted. 22a ~
Reference numeral 22h is a connection terminal for pulling out each terminal of the connector 21 to the outside. The conductor portion of the protective device 1 is connected to 22e and 22f of these connection terminals. The protective device 1 is provided with a connection terminal screw 11 for connecting the secondary side of the CT.

FIG. 3A is a top view of the protective device, and FIG.
Is a right side view thereof. In FIG. 3, 13 is a conductor portion 12.
It is a mounting hole provided in the socket 2 and is used when screwed and fixed to the connection terminal of the socket 2 as shown in FIG. Further, the case 15 of the protective device is provided with a window 14 for showing the color of the heat sensitive agent of the conductive plate provided inside, which will be described later, to the outside. The connection terminal screw 11 is electrically connected to the conductor portion 12, and the connection terminal screw 11 connects the secondary side output of the CT.

FIG. 4 is a diagram showing the internal structure of the protective device. In FIG. 4, reference numeral 17 is a diode connected in parallel in opposite directions between the conductor portions 12-12. Also, 18
Is a conductive plate adhered to the diodes 17 and 17, and a sheet 19 having a heat sensitive agent is attached to the surface thereof. 16
Is a screw hole for attaching the connection terminal screw 11 shown in FIG. Instead of attaching the sheet 19 to the conductive plate 18, the thermosensitive discoloration paint may be directly applied.

FIG. 5 is a sectional view through the diode section shown in FIG. Usually, as shown in (A), the conductive plate 18 is separated from the conductor portions 12, 12. If the measuring device 3 shown in FIG. 1 is removed from the socket 2 and a state in which a large current flows to the measuring object provided with CT continues,
The diode 17 overheats and the conductive plate 18
When the conductor plate 12 is deformed due to the heat generated by the above and reaches a predetermined temperature, the conductor plate 18 comes into contact with the conductor portion 12 and short-circuits between the conductor portions 12-12.

FIG. 6 is a circuit diagram of the entire measuring circuit.
In this way, the diodes 17 and 17 in opposite directions are connected in parallel to the secondary output of the CT, and the switch including the conductor portion and the conductive plate 18 is provided.

If a material having an irreversible thermal deformation such as a shape memory alloy exhibiting a thermal martensitic transformation is used as the conductive plate 18 and a material having an irreversible thermal discoloration is used as the heat-sensitive agent, the space between the conductor portions is It can be confirmed from the color of the heat sensitive agent that it is in a short circuit state. Therefore, the protection device which has once performed such a protection operation is not reused and is thereafter discarded. In addition, if a material having reversibility to thermal deformation such as bimetal is used as the conductive plate 18 and a material having reversibility to thermal discoloration such as a heat sensitive agent using liquid crystal is used as the heat sensitive agent, the shape of the conductive plate 18 is reduced. Since the color of the sheet 19 and the color of the sheet 19 always correspond to each other, even if the protective device has once performed the protective operation, the temperature of the conductive plate 18 decreases due to the measuring device being mounted in the socket after that. If 18 is separated from the conductor portion 12, normal measurement can be performed as it is. Even if the conductive plate is reversible to thermal deformation, if the heat-sensitive agent is irreversible to thermal discoloration, the fact that the diode has once been overheated will be recorded as the display color of the heat-sensitive agent. Based on this, it is possible to confirm that the diode has been stressed, and it is possible to operate without using such a protective device continuously.

[0018]

According to the first aspect of the present invention, the measuring device is removed and the protective device is simply connected to the secondary side of the current transformer, and the current path to be measured is kept large for a long time. Even if the diode becomes overheated due to the flow of current, the conductive plate receives the heat and is deformed, and the conductive plate is short-circuited between the conductors connected to the secondary side output of the current transformer. Therefore, failure of the diode is prevented and the current transformer is protected from its secondary side opening. As a result, accidents due to opening of the secondary side of the current transformer are reliably prevented.

According to the second aspect of the present invention, since the protection operation state due to the deformation of the conductive plate is displayed as the display color to the outside, the operation state of the protection device can be easily confirmed.

[Brief description of the drawings]

FIG. 1 is a right side view showing the configuration of a measuring device using a secondary side open protection device for a current transformer according to an embodiment of the present invention.

FIG. 2 is a front view of a socket portion in the configuration shown in FIG.

FIG. 3 is a front view and a right side view of a secondary side open protection device for a current transformer.

FIG. 4 is a diagram showing an internal structure of a secondary side open protection device for a current transformer.

5 is a cross-sectional view through a diode and a conductive plate portion in FIG.

FIG. 6 is a circuit diagram of a measuring device according to an example.

FIG. 7 is a circuit diagram of a measuring device using a conventional secondary side open protection device for a current transformer.

[Explanation of symbols]

 1-Protection device 2-Socket 3-Measuring device 11-Connecting terminal screw 12-Conductor part 13-Mounting hole 14-Window 15-Case 16-Connecting terminal screw mounting hole 17-Diode 18-Conductive plate 19-Heat sensitive agent forming sheet 21-Connector 22a-22h-Connecting terminal CT-Current transformer Aux.CT-Auxiliary current transformer

Claims (2)

[Claims] 1. A conductor part to which a secondary side output of a current transformer is connected, and two diodes are connected in parallel to the conductor part in opposite directions to open the current transformer. A secondary side open protection device for a current transformer, which is provided with a conductive plate which is protected from heat and is deformed by heat generated by the diode and short-circuits between the conductor parts when a predetermined temperature is reached. 2. The secondary side open protection device for a current transformer according to claim 1, wherein a heat sensitive agent that changes color at the predetermined temperature is provided on the conductive plate.