JPH07170663A - Current transformer with safety circuit - Google Patents

Abstract

PURPOSE:To provide a current transformer with a safety circuit for suppressing the increase in magnetic flux of a current transformer automatically and preventing a transformer from overheat by detecting the open state of a current transformer due to the disconnection, etc., of a load. CONSTITUTION:A secondary coil winding 2 and a short-circuiting coil winding for connecting a load 6 are wound around a current transformer 1 and at the same time a thermostat 4 which is activated by detecting the temperature of the current transformer 1 is provided and then both terminals of the short- circuited coil winding are connected to the thermostat 4. Also, the operation point and recovery point of the thermostat 4 have hysteresis and a resistor is connected serially to the connection point of the thermostat 4, thus causing the heat build-up to enable the thermostat 4 to be self-retained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency constant current power supply system using a current transformer, and a safety circuit for preventing abnormal voltage generation on the secondary side due to load disconnection or the like and overheating of the current transformer. It is related to the attached current transformer.

[0002]

2. Description of the Related Art The applicant has developed a high-frequency constant-current power supply system in which a high-frequency constant-current power supply is used to supply power to a discharge tube using a current transformer, and has already been registered as a utility model. Refer to Japanese Unexamined Patent Publication No. Sho 64-5360, "Wireless Discharge Tube Lighting Equipment". An outline thereof will be described with reference to FIG. 3. A single power supply line 12 connected to a high frequency constant current power supply 11 is allowed to freely pass a current transformer 13, and its secondary winding 14 is directly connected to both terminals of a discharge tube 15. It was done,
Before the discharge tube 15 starts discharging, no current flows in the secondary winding 14, so that the iron core of the current transformer 13 is saturated and a voltage higher than the discharge starting voltage of the discharge tube 15 appears in the secondary winding 14. After the discharge tube 15 starts to discharge due to this voltage, a constant current flows through the secondary winding 14 according to the turn ratio.

However, the discharge tube 15 may be broken or the discharge tube 1
When 5 is removed, a voltage higher than the discharge voltage of the discharge tube 15 appears in the secondary winding 14 of the current transformer 13, so if the terminal of the secondary winding 14 is accidentally touched when replacing the discharge tube. There is a drawback that there is a risk of electric shock, and that the magnetic flux increases and the iron loss remarkably increases, so that it is dangerous if the transformer is overheated and left as it is.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to detect when a load of a current transformer is opened due to a disconnection or the like and automatically suppress an increase in magnetic flux of the current transformer to generate a high voltage. It is an object of the present invention to provide a current transformer with a safety circuit for preventing a danger due to overheating of a transformer or a transformer.

[0005]

In order to solve the above-mentioned problems, a current transformer with a safety circuit according to the present invention has a secondary winding and a short-circuit winding for connecting a load to the current transformer, and A thermostat that operates by detecting the temperature of the current transformer is provided, and both terminals of the short-circuit winding are connected to the thermostat. Further, the operating point and the returning point of the thermostat have hysteresis, and a resistor is connected in series to the contact part of the thermostat so that the thermostat self-holds by its heat generation.

[0006]

[Operation] When the secondary winding is opened due to the disconnection of the load connected to the secondary winding, a large amount of magnetic flux equivalent to the primary current multiplied by the primary winding is generated, resulting in a high level between the terminals of the secondary winding. As the voltage is generated, iron loss rapidly increases and the core temperature rises. When the temperature rises to a predetermined temperature, the thermostat detects this and short-circuits the short-circuit winding, which reduces the magnetic flux, lowers the terminal voltage of the secondary winding, and lowers the core temperature. If the operating point and return point of the thermostat have hysteresis, when the core temperature drops to the return point of the thermostat, the short-circuit winding is released, the magnetic flux increases, and the core temperature starts to rise again. Repeat the operation of. If a resistor is connected in series to the contact point of the thermostat, the operating state of the thermostat is maintained by itself due to the heat generated by the resistor even if the core temperature drops.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. The secondary winding 2 and the short-circuit winding 3 are wound (for example) 30 turns and 5 turns on the annular current transformer 1, respectively. Further, a thermostat 4 including a heat sensitive element and a contact portion is closely arranged on the core portion thereof, and both terminals of the short-circuit winding 3 are connected to the switch of the thermostat 4. The thermostat 4 has hysteresis in its operating point and reset point (for example, 90 ° C).
It is set to turn on at 60 ° C and turn off at 60 ° C.

The current transformer 1 has (for example) 40 kH
It is assumed that the power supply line 5 through which a high-frequency constant current of z, 20 A flows is loosened (that is, wound as one turn of the primary winding), and the secondary winding 2 is used with the load 6 connected thereto. Now, assuming that the secondary winding 2 is opened due to the disconnection of the load 6, etc.,
Since all of the primary current 20A acts as an exciting current, a large amount of magnetic flux corresponding to the primary current × the primary winding is generated in the core, a high voltage appears between the terminals of the secondary winding 2, and the iron loss rapidly increases. Therefore, the temperature of the core rises rapidly.

When the core temperature reaches 90 ° C., the thermostat 4 detects this and short-circuits the short-circuit winding 3, causing a short-circuit current of 20 A / 5 = 4 A to flow in the short-circuit winding 3 to cause magnetic flux in the core. Decreases, the terminal voltage of the secondary winding 2 decreases, and the core temperature starts to decrease. When the core temperature drops to 60 ° C., the thermostat 4 is turned off, the short-circuit winding 3 is opened, and the core temperature starts to rise again. When the core temperature reaches 90 ° C., the thermostat 4 is turned on again, and thereafter the same on / off operation is repeated.

FIG. 2 shows a thermostat according to the second embodiment of the present invention. The other structure is exactly the same as that of the first embodiment. The thermostat 4 has a structure in which one of the contact points 4a is provided at the tip of a bimetal 4b having self-resistance, and when the bimetal 4b once energizes, the self-resistance heats up so that the thermostat maintains its operating state. It has become. Therefore, the secondary winding 2
Is released and the magnetic flux increases and the core temperature rises, the contact portion 4a turns on (for example) at 70 ° C. to short-circuit the short-circuit winding 3, and even if the magnetic flux decreases and the core temperature falls below this, the bimetal 4b The on-state of the contact portion 4a is self-maintained by the heat generated by the resistance, and the terminal voltage of the secondary winding 2 is maintained in a low state.

If a resistor is connected in series to the thermostat and this resistor is arranged in the vicinity of the heat sensitive element without using a bimetal having self-resistance, the self-holding operation can be performed in exactly the same manner. Also, instead of the annular core, a well-known E-shaped core, U-shaped core, or these I
It is also possible to use a combination with a mold core. Furthermore, the number of turns of the secondary winding and the short-circuited winding of the current transformer, the operating point and the returning point of the thermostat, etc. are not limited to those in the above embodiment, but can be changed as appropriate according to the usage conditions.

[0012]

As described above, the current transformer with the safety circuit of the present invention detects the rise of the core temperature when the load of the current transformer is in the open state and automatically short-circuits the short-circuit winding. It is safe because it can prevent abnormal voltage generation on the secondary side and overheat of the current transformer, and it has an excellent effect that the mechanism is simple, the number of components is small, the operation is reliable, and there is no risk of failure. It plays.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a side view of the thermostat according to the second embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a conventional technique.

[Explanation of symbols]

1 current transformer 2 secondary winding 3 short-circuit winding 4 thermostat 4a contact part 4b
Bimetal 5 Power supply line 6 Load 11 Constant current power supply 12 Power supply line 13
Current transformer 14 Secondary winding 15 Discharge tube

Claims (3)

[Claims] 1. A thermostat for winding a secondary winding and a short-circuit winding for connecting a load to a current transformer and detecting the temperature of the current transformer to operate the both terminals of the short-circuit winding as a thermostat. A current transformer with a safety circuit characterized by being connected. 2. The current transformer with a safety circuit according to claim 1, wherein the operating point and the returning point of the thermostat have hysteresis. 3. The current transformer with a safety circuit according to claim 1, wherein a resistor is connected in series to the contact portion of the thermostat, and the thermostat self-holds by the heat generated by the resistor.