JP4051157B2 - Neon transformer ground fault detection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit for detecting a secondary ground fault in a neon transformer for lighting a neon tube or an argon tube.
[0002]
[Prior art]
FIG. 6 shows a ground fault detection circuit of this type of conventional neon transformer. One end of the primary winding 12 of the leakage transformer (neon transformer) 11 is connected to the input terminal 14 through the switch 13, and the other end of the primary winding 12 is connected to the input terminal 15. The winding start ends C of the two secondary windings 16 and 17 are connected to each other and connected to the ground terminal 18 of the transformer case 36, that is, connected to the case 36. Then, the ground terminal is grounded to the ground, both winding end ends of the secondary windings 16 and 17 are connected to the output terminals 21 and 22, and a sign lamp 23 such as a neon tube or an argon tube is connected between the output terminals 21 and 22. Is done. AC power, for example, commercial power, is input between the input terminals 14 and 15, which is boosted by the transformer 11 and the sign lamp 23 is lit.
[0003]
When the sign lamp 23 or its wiring comes into contact with the case 36 or the like, that is, when a ground fault occurs, a protection circuit 10 is provided to detect this and cut off the input AC power. In the vicinity of the secondary windings 16 and 17, tertiary windings 25 and 26 that are magnetically coupled thereto are provided as part of the protection circuit 10. Normally, under the lowermost layer of the secondary windings 16 and 17, the tertiary windings 25 and 26 are wound around the magnetic core, and between the secondary windings 16 and 17 and the tertiary windings 25 and 26. Is provided with a high withstand voltage insulating material layer having a withstand voltage of about 6000 to 7000 V to increase electrical insulation and sufficiently large magnetic coupling.
[0004]
One ends of the tertiary windings 25 and 26 are connected in opposite phases so that the induced voltages cancel each other, and the other ends of the tertiary windings 25 and 26 are connected to the input side of the rectifying and smoothing circuit 27. The output side of the rectifying and smoothing circuit 27 is connected to both ends of a parallel circuit of a resistor 31 and a capacitor 32 through a Zener diode 28, and both ends are connected to the gate and cathode of the triac 33. The triac 33 is connected between the input terminals 14 and 15 through a relay 34, and the switch 13 is configured by a relay contact of the relay 34.
[0005]
In a normal state, the voltages induced in the tertiary windings 25 and 26 are substantially equal and have opposite phases, so the input voltage of the rectifying and smoothing circuit 27 is substantially zero. However, when the sine lamp 23 or its wiring is grounded, both ends of the grounded secondary winding are short-circuited, and the induced voltage of the tertiary winding coupled to the secondary winding is significantly reduced. Therefore, the entire induced voltage of the other tertiary winding is applied to the rectifying / smoothing circuit 27. This voltage is rectified and smoothed, the output voltage rises, and the Zener diode 28 is turned on. As a result, the triac 33 is turned on, the relay 34 is operated, the switch 13 is opened, and the supply of input AC power to the transformer 11 is interrupted. The relay contact of the switch 13 is connected to the normally open side NO, and an operation holding current flows through the relay 34 through this.
[0006]
[Problems to be solved by the invention]
As described above, in order to detect a secondary side ground fault, two tertiary windings are conventionally used. The tertiary winding is provided under the lowermost layer (inside) of the two secondary windings via a high-voltage insulator. For this reason, it takes time to provide the tertiary winding, and the production efficiency of the neon transformer is lowered accordingly.
[0007]
An object of the present invention is to provide a ground fault detection circuit for a neon transformer that can detect a ground fault without using a tertiary winding.
[0008]
[Means for Solving the Problems]
According to the present invention, voltage detecting means for detecting when a voltage exceeding a predetermined value is generated between the secondary winding and the ground terminal is provided, and the power supply to the primary winding is detected by the detection output of the voltage detecting means. The power supply is cut off.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a basic configuration of the present invention, and the same reference numerals are given to portions corresponding to FIG. In the present invention, the voltage detection means 41 is inserted between the connection point (the neutral point of the secondary winding) C between the secondary windings 16 and 17 and the ground terminal 18 of the transformer. This is a case where a series circuit of a Zener diode 42 as a threshold element and a light emitting element 43L of a photocoupler 43 is used as the voltage detecting means 41. In this example, a resistance element 44 is connected in parallel with the voltage detection means 41, and a rectifying diode 45 is connected in series with the voltage detection means 41. A series circuit of the light receiving element 43P of the photocoupler 43 and the relay 34 is connected between the input terminals 14 and 15. The contact 13 of the relay 34 is inserted between the input terminal 14 and the primary winding 12, and the normally open contact NO is connected to the input terminal 15 through the relay 34.
[0010]
In this configuration, if the secondary side of the transformer 11 is in a normal state with no ground fault, the potential of the neutral point C of the secondary windings 16 and 17 is almost zero, and the neutral point C and ground The voltage between the terminals 18 is also almost zero. Therefore, the voltage detection means 41 does not detect the voltage. In addition, current does not flow through the light emitting element 43 </ b> L, and power is supplied from the input terminals 14 and 15 to the primary winding 12.
[0011]
If the secondary side of the transformer 11, that is, the sine lamp 23 or its wiring is grounded, for example, if the output terminal 21 side is grounded, the grounding point becomes the reference potential, and a secondary voltage appears at the neutral point C. The zener diode 42 is turned on by the voltage, the light emitting element 43L emits light, a current flows through the light receiving element 43P, the relay 34 operates, the contact 13 is switched to the normally open side NO, and the power supply power to the primary winding 12 And the self-holding current flows through the relay 34. That is, when a ground fault occurs, this is detected by the voltage detection means 41, the supply of power to the primary winding 12 is cut off, and it is avoided that a current continues to flow through the ground fault point and a fire occurs. .
[0012]
From the viewpoint of fire prevention, the secondary side wiring may be passed through a flexible tube called a metal conduit. In this case, a high impedance based on the electrostatic capacitance between the metal conduit and the wiring is generated, and the secondary side voltage is divided by the electrostatic capacitance impedance and the impedance of the voltage detecting means 41, and the voltage is detected even in the normal state. A voltage for detecting the voltage by the means 41 is applied to the voltage detecting means 41, and there is a risk of malfunction. The resistance value of the resistance element 44 is selected so that this malfunction does not occur, and the voltage applied to the voltage detection means 41 is not more than a predetermined value, that is, the Zener diode 42 is not conducted in a normal state. When a ground fault occurs in this state, the capacitance impedance becomes almost zero at that point, and a voltage sufficient to detect the ground fault is applied to the voltage detecting means 41.
[0013]
In the voltage detection means 41 shown in FIG. 1, there is a case where the current for reliably operating the light emitting element 43L is insufficient. To solve such a problem, for example, a configuration as shown in FIG.
That is, the voltage across the resistor element 44 is rectified by the rectifier circuit 46 including the diode 45, and the rectified output is applied to the series circuit of the Zener diode 42 as the threshold element and the resistor elements 47-48. 49, the light emitting element 43L is applied to the series circuit, and the connection point of the resistance elements 47 and 48 is connected to the base of the transistor 49. A Zener diode 51 for protecting the transistor 49 is connected between the collector and the emitter of the transistor 49 as necessary.
[0014]
When the voltage across the resistance element 44 exceeds a predetermined value, the Zener diode 42 is turned on by the output of the rectifier circuit 46, the base current is supplied to the transistor 49, the transistor 49 is turned on, and the light emitting element 43L emits light. The voltage at which the transistor 49 is conducted is set by the Zener diode 42 and the resistance elements 47 and 48.
As the voltage detecting means 41, as shown in FIG. 3, a smoothing circuit including a capacitor 52 and a resistance element 53 may be provided in the rectifying circuit 46, and the rectified output may be smoothed and applied to the Zener diode 42. Further, a thyristor 54 may be used as a switching element instead of the transistor 49. Furthermore, it is better to connect the light emitting element 43L to the anode side rather than the cathode side of the thyristor 54. That is, when the light emitting element 43L is inserted into the cathode side (emitter side in the case of the transistor 49) of the thyristor 54, the voltage at which the thyristor 54 (transistor 49) is turned on changes due to the impedance variation of the light emitting element 43L. The Zener diode 55 inserted on the cathode side of the thyristor 54 is to prevent the thyristor 54 from conducting due to noise and may be omitted.
[0015]
If the secondary side is grounded and the neutral point C is at a high potential, this voltage is applied to the non-connection side terminal 15 of the commercial power supply via the photocoupler 43, and the photocoupler 43 may be destroyed. In some cases, as shown in FIG. 1, the protection element 56 connected between the neutral point C and the input terminal 15 is turned on, and the photocoupler 43 is protected.
[0016]
In the configuration shown in FIG. 1, if the midpoint of the load (sign lamp 23) is grounded, it becomes difficult to detect a ground fault on the secondary side. At this point, it is determined that the midpoint of the load is not grounded. However, if the midpoint of the load is grounded due to a construction error, the supply of power to the primary winding 12 is stopped using the voltage detection means 41 so that the neon tower does not operate. .
[0017]
For this reason, the two magnetic circuits respectively composed of the two secondary windings 16 and 17 of the neon transformer are unbalanced from each other. For example, as shown in FIG. 4, the primary winding 12 is wound on the rectangular magnetic core 61, and the secondary windings 16 and 17 are wound on the magnetic core 61 on both sides of the primary winding 12. Leakage cores 62 and 63 are provided between the primary winding 12 and the secondary windings 16 and 17 to shunt the magnetic path of the rectangular magnetic core 61. In this embodiment, the widths t1 and t2 of the leakage cores 62 and 63 are made different from each other, the magnetic flux leakage characteristics are made different, and the magnetic circuits 64 and 65 respectively constituted by the secondary windings 16 and 17 are unbalanced. Let For example, t1 is about 10 to 30% smaller than the width t of the rectangular magnetic core 61, and t2 is about 10 to 30% larger than t.
[0018]
As in the case shown in FIG. 1, such a neon transformer 11, as shown in FIG. 5, any of the voltage detection means 41 shown in FIGS. 1 to 3 is interposed between the neutral point C and the ground terminal 18. Or connect. In this configuration, if the midpoint of the load side is not grounded and is in a normal state, the voltage at the neutral point C is almost zero and the voltage detection means 41 does not detect the voltage. However, when the middle point of the load is grounded as shown in FIG. 5, currents 66 and 67 passing through the grounding point, the ground terminal 18, and the secondary windings 16 and 17 flow, respectively. Due to the difference in magnetic characteristics of the magnetic circuits 64 and 65, the values of the currents 66 and 67 are different, and a current of these differences, for example, about several mA flows between the neutral point C and the ground terminal 18, which is voltage detection. Detected by the means 41, the relay 34 operates to cut off the supply of power to the primary winding 12.
[0019]
In order to make the leakage flux characteristics of the leakage cores 62 and 63 different, in addition to changing the width of the leakage cores 62 and 63, the lengths G1 and G2 of the magnetic gaps may be made different from each other. Alternatively, both the widths t1 and t2 and the lengths G1 and G2 may be different from each other. In short, the magnetic characteristics of the magnetic circuits 64 and 65 may be made different from each other. However, if the unbalance of the magnetic circuits 64 and 65 is increased too much, the lighting characteristics of the sign lamp will be affected. Therefore, in terms of width, as described above, each of about ± 10 to 30% is preferable with respect to the reference.
[0020]
According to the configuration shown in FIG. 5, when the midpoint of the load side is grounded as described above, the supply of the power supply is stopped, and as is clear from the description of FIGS. When an entanglement accident occurs, this is detected and supply of power supply is stopped. The power supply may be cut off without using a relay, and a semiconductor switching element such as a triac may be used.
[0021]
【The invention's effect】
As described above, according to the present invention, it is possible to detect a ground fault on the secondary side without providing a third winding in the neon transformer and to cut off the supply of power. Therefore, the production of the neon transformer becomes easier than before, and the productivity is improved.
In addition, as shown in FIG. 4, the supply of the power supply is stopped when the neutral point of the load is grounded by making the magnetic circuit formed by the two secondary windings unbalanced as shown in FIG. .
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a modification of the voltage detecting means 41 in FIG.
FIG. 3 is a circuit diagram showing still another modified example of the voltage detecting means 41 in FIG. 1;
FIG. 4 is a diagram showing an example of a neon transformer in which the magnetic circuit of two secondary windings is unbalanced.
FIG. 5 is a circuit diagram showing another embodiment of the present invention.
FIG. 6 is a circuit diagram showing a ground fault detection circuit of a conventional neon transformer.

Claims (6)

In a neon transformer in which one point or neutral point of the secondary winding is connected to the earth terminal of the transformer, it is provided between the neutral point of the secondary winding and the earth terminal, and a predetermined value or more between these points. Voltage detecting means for detecting this voltage, and power shut-off means for shutting off the power supply to the primary winding by the detection output of the voltage detecting means . A ground fault detection circuit for a neon transformer in which two magnetic circuits each composed of a secondary winding are unbalanced with each other . Flux leakage characteristics of the leakage core respectively provided to the two magnetic circuits is different from each other, ground fault detection circuit of neon transformer according to claim 1, characterized in that it is with the unbalanced. When the voltage between the above voltage detection means and said neutral point and said ground terminal is equal to or higher than a predetermined value, any one of claims 1 to 2, characterized in that the threshold means for flowing a current between these Neon transformer ground fault detection circuit described in 1. The voltage detecting means is connected between the rectifying circuit for rectifying the voltage between the neutral point and the ground terminal and applying the voltage to the threshold means, and the neutral point and the ground terminal. 4. The ground fault detection circuit for a neon transformer according to claim 3 , further comprising a switching element that is turned on by an output based on a voltage that is equal to or higher than a predetermined value of the threshold means. The power shut-off means includes a light emitting element of a photocoupler inserted on the neutral point side of the switching element, and a series circuit of a light receiving element of the photocoupler and a relay is connected between a pair of input terminals of a primary winding. The relay contact is inserted in series between the input terminal and the primary winding, and when the relay contact is cut off, a self-holding current by power supply flows through the relay. neon transformer ground fault detection circuit according to claim 3 or 4, wherein to. In parallel with said voltage detecting means, ground faults neon transformer according to any one of claims 1 to 5 resistive element is characterized in that it is connected between the neutral point and the ground terminal Detection circuit.

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