JP5744602B2 - Current transformer protection device - Google Patents

Description

The present invention relates to a current transformer protection device for protecting a current transformer from an abnormal voltage.

The current transformer is a device including a primary coil connected to an AC power source, a secondary coil having a larger number of windings than the primary coil, and an iron core, and both the primary coil and the secondary coil are provided on the iron core. It has a wound structure. A circuit including an AC power supply and a primary coil (hereinafter referred to as “primary side circuit unit”) is provided with a load resistance having a predetermined value, and when the AC power supply is activated, a current flows through the primary coil. Further, when a current flows through the primary coil, a magnetic field is generated in the iron core, the magnetic field acts on the secondary coil, and a current also flows through the secondary coil. In this case, the current flowing through the secondary coil is a value of N1 / N2 of the primary coil current, where N1 is the number of turns of the primary coil and N2 is the number of turns of the secondary coil. In this case, since N1 has a smaller number of windings than N2, N1 / N2 is smaller than 1. Therefore, a current smaller than that of the primary coil can be passed through the secondary coil.

As described above, the current transformer can flow the current converted into an appropriate amount to the secondary coil. For this reason, if a current supply object such as a measuring instrument or an electronic device is connected to the secondary coil, a current that is not damaged can be passed through the current supply object.

As this current supply object, for example, an ammeter that measures the value of the current flowing through the inside of a device or apparatus can be cited. A large current may flow during measurement (for example, 300 A or more) depending on the device or apparatus to be measured, but such a large current cannot be directly passed to the ammeter. For this reason, an ammeter is connected to the secondary coil of the current transformer, and the current transformer is interposed between the power source and the ammeter. As a result, the current converted to an appropriate value can be passed through the ammeter.

At this time, it is formed by connecting the secondary coil and the ammeter because the internal conductor of the ammeter was disconnected or the ammeter was removed without stopping the power supply of the primary circuit section. When power is supplied from the power supply in a state where the circuit to be opened is open, an extremely high abnormal voltage is generated at the open point, which may damage the current transformer. The invention described in the following patent document is disclosed as a technique for protecting the current transformer from this abnormal voltage.

JP 2007-035808 A JP 2007-214462 A

The invention described in Patent Document 1 is configured to include a lightning arrester and a current detector connected to a secondary circuit of the current transformer, and a contact connected in parallel to the lightning arrester and the current detector. . When a current flows through the secondary circuit of the current transformer with the contact open, the lightning arrester is energized and the energized current flows through the current detector. When the current flowing through the current detector exceeds a predetermined threshold, it is determined that an abnormal voltage has occurred, and the contact is closed. Thereby, even if it is a case where an electric current flows into a secondary side circuit in the state in which the contact was open | released, a current transformer can be protected from generation | occurrence | production of an abnormal voltage.

The invention described in Patent Document 2 includes a circuit protection unit that cuts off an abnormal voltage generated at a secondary terminal of a current transformer, a rectification unit that rectifies a voltage signal that has passed through the circuit protection unit, a rectified voltage signal, and a reference voltage And a short circuit circuit (such as a relay coil) that short-circuits the secondary terminal of the current transformer in the open state. When the comparison unit determines that the voltage signal that has been rectified and input exceeds the reference voltage, a signal for closing the secondary terminal is output to the short circuit unit, and the secondary circuit is closed. Thereby, even if it is a case where an electric current flows into a secondary terminal in the state where a secondary side circuit is open, a current transformer can be protected from generation | occurrence | production of an abnormal voltage.

However, in the invention described in Patent Document 1, there is no specific description how to short-circuit the circuit after the abnormal voltage occurs in the secondary circuit of the current transformer and the surge arrester operates. Also, since there is only one lightning arrester arranged in the circuit, if the lightning arrester is damaged without being able to withstand the abnormal voltage, the protection function from the abnormal voltage will not be performed thereafter. Furthermore, the present invention has a configuration in which a current flows through the lightning arrester and the current detector regardless of whether or not the voltage is abnormal. Therefore, when an ammeter, a lightning arrester, and a current detector are connected in parallel to measure the current value, the current flowing through the secondary circuit is normal and the lightning arrester, even during normal operation.・ Divert to current detector side. As a result, an error occurs between the value converted as the current value flowing through the device to be measured and the current value actually flowing through the ammeter, making it impossible to perform highly reliable measurement.

The invention described in Patent Document 2 has only one circuit protection unit that cuts off the overvoltage (abnormal voltage) generated at the secondary terminal of the current transformer. If the circuit protection unit is damaged due to time overvoltage, etc., the secondary terminal protection function cannot be performed thereafter. Further, although a varistor is used as the protection circuit unit, even if the voltage of the varistor is lower than the overvoltage applied to the secondary terminal, a small amount of current flows. Therefore, during current measurement, the current generated at the secondary terminal is shunted between the ammeter side and the circuit protection unit side. As a result, it is not possible to accurately measure the current value flowing through the device to be measured.

The present invention can protect a current transformer even when an abnormal voltage is generated in the current transformer for a long time. On the other hand, when the abnormal voltage is not generated, It is an object of the present invention to provide a current transformer protection device that does not divert current to a time circuit portion.

The current transformer protection device according to the present invention for solving the above-mentioned problems is
Connected to a current transformer,
The current transformer is used to flow an appropriate current to an ammeter that measures a current value supplied from an external power source,
A circuit part for an abnormality when both ends are connected to the secondary coil of the current transformer,
A plurality of nonlinear resistance units that are connected to the abnormal circuit portion and exhibit nonlinear resistance change characteristics, and output an abnormal current when an abnormal voltage is input;
An abnormal current detection unit that detects the abnormal current output from at least one of the plurality of nonlinear resistance units;
A circuit short-circuit unit that is connected to the abnormal-time current detection unit and determines that the abnormal voltage has occurred when the abnormal-time current detection unit detects the abnormal-current and short-circuits the abnormal-time circuit unit When,
When it is determined that an abnormal voltage has occurred in the short circuit portion,
AC power supply drive stopping means for stopping the drive of the AC power supply connected to the current transformer,
External notification means for transmitting abnormal voltage occurrence information to an alarm device installed outside;
Including
When the circuit short-circuit portion short-circuits the abnormal-time circuit portion, an abnormal-time current flows through the abnormal-time circuit portion, and the abnormal voltage decreases accordingly.

Further, according to the present invention, when a plurality of non-linear resistance units input a voltage higher than a predetermined threshold voltage, an abnormal current is output, and the threshold voltage is different for each of the plurality of non-linear resistance units. preferable. In the present invention, it is preferable that the nonlinear resistance portion is a gas-filled discharge tube.

According to the present invention, even when an abnormal voltage is generated in the current transformer for a long time, the current transformer can be protected. On the other hand, when the abnormal voltage is not generated, the current is not shunted to the protection device side. A current transformer protection device can be provided.

Schematic diagram showing a first embodiment according to the present invention Circuit diagram of current transformer protection device 10 Schematic diagram showing a second embodiment of the present invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be implemented in many different modes and should not be construed as being limited to the description of the embodiments described below. In this embodiment, the current supply object that is connected to the secondary coil of the current transformer and receives the supply of current generated in the secondary coil is an ammeter, but it is another current supply object. Is applicable.

FIG. 1 is a schematic diagram showing a first embodiment according to the present invention. The current transformer protection device 10 according to the present embodiment includes a non-linear resistance unit 110, an abnormal current detection unit 120, a circuit short-circuit unit 130, and an abnormal circuit unit 140. The abnormal circuit unit 140 passes through the non-linear resistance unit 110 and includes a contact point 141 at a different location. When the contact point 141 is closed, the abnormal circuit 140 becomes a closed loop. In addition, both ends of the circuit unit for abnormality 140 are connected to the secondary coil 231 of the current transformer 20. In this case, the abnormality circuit unit 140 is connected in parallel to the ammeter 40 that is also connected to the secondary coil 231. In the present embodiment, the secondary coil 231 and the abnormal circuit unit 140 are connected by the conductive wires 50a and 50b.

When the AC power supply 30 is driven and an AC voltage is applied to the primary side circuit unit 220 (a circuit formed by connecting the AC power supply 30, the primary coil 221 and the load resistor 222 of the current transformer 20), the primary coil 221 is applied. And the current flows through the secondary coil 231 of the current transformer 20 through the iron core 240. The number of windings of the secondary coil 231 is larger than that of the primary coil. Therefore, a smaller amount of current flows through the ammeter 40 than the primary coil 221.

At this time, if the circuit formed by connecting the secondary coil 231 and the ammeter 40 (hereinafter, “circuit through the ammeter 40”) is closed (the circuit through the ammeter 40 forms a closed loop). The current transformer 20 operates normally. That is, the current transformer protection device 10 does not operate. However, if an open point occurs in the circuit through the ammeter 40 due to, for example, the lead wire in the ammeter 40 being disconnected, the non-linear resistance unit 110 in the current transformer protection device 10 is in an abnormal state. The current detection unit 120, the circuit short-circuit unit 130, and the like are activated to short-circuit the circuit unit for abnormality 140 in the current transformer protection device 10. As a result, the circuit part for abnormal time 140 becomes a closed loop and a current flows, and the abnormal voltage decreases accordingly.

Here, the abnormal voltage refers to a high voltage generated in the circuit and the circuit unit for abnormal time 140 when an open point occurs in the circuit passing through the ammeter 40. Specifically, when the number of windings of the primary coil of the current transformer 20 is N1 and the number of windings of the secondary coil is N2, the voltage of the value obtained by multiplying the input voltage of the AC power supply 30 by N2 / N1 ( If the input voltage of the AC voltage 30 is 100 V, the number of turns of the primary coil is N1 = 10, and the number of turns of the secondary coil is N2 = 100, a voltage of 100 V × 100/10 = 1000 V is generated. However, since this voltage value (a value obtained by multiplying the input voltage of the AC power supply 30 by N2 / N1) is a theoretically calculated value, it accurately includes a range in the vicinity of the theoretical value.

FIG. 2 is a diagram showing a circuit configuration in the current transformer protection device 10 according to the present invention. As shown in FIG. 2, the non-linear resistance unit 110 is connected to an abnormal circuit unit 140. The non-linear resistance unit 110 has a property that the internal resistance value changes in accordance with the value of the input voltage (that is, exhibits a non-linear resistance change characteristic), for example, a surge protection device that exhibits non-linear current-voltage characteristics. And lightning arresters. In particular, from the viewpoint of preventing current shunting to the abnormal circuit unit 140 when the current transformer 20 operates normally, the nonlinear resistance unit 110 has an input voltage of a predetermined value (hereinafter referred to as “threshold voltage”). If it does not exceed it, it exhibits a remarkably high internal resistance value (that is, it exhibits properties as an insulator and does not pass current), while if it exceeds the threshold voltage, it has a property that the internal resistance value decreases (that is, non-linear resistance) The portion 110 is energized). A gas discharge tube is particularly preferable as the material having this property. The threshold voltage is preferably higher than a voltage generated in a circuit or the like passing through the ammeter 40 at a normal time and lower than an abnormal voltage.

The abnormal current detection unit 120 (see FIG. 1) detects an abnormal current that flows when an abnormal voltage is generated, and transmits the detected abnormal current to the circuit short-circuit unit 130. As shown in FIG. 2, in this embodiment, the abnormal current detection unit 120 includes an abnormal current detection transformer 121 including a coil 121a through which a conducting wire located on the current output side of the nonlinear resistance unit 110 is inserted. An operational amplifier 122 that converts and amplifies the current flowing in the coil 121a of the abnormal current detection transformer 121 into a voltage, and a smoothing circuit 123 (consisting of a diode 123a and a capacitor 123b) that converts the voltage amplified by the operational amplifier 122 into a DC voltage. When a DC voltage converted by the smoothing circuit 123 is applied, a latch circuit 124 that holds the voltage application state for a predetermined time is provided, and these are sequentially connected.

However, the abnormal current detection unit 120 is not limited to this as long as it can detect the abnormal current from the nonlinear resistance unit 110. For example, instead of the abnormal current detection transformer 121, the nonlinear resistance unit 110 is replaced. A resistance element is arranged on the current output side of the current, and an abnormal current is detected by measuring a change in voltage when the abnormal current output from the non-linear resistance unit 110 flows through the resistance element. May be.

When the abnormal current detection unit 120 detects the presence or absence of the abnormal current, a voltage having a predetermined value is output to the circuit short-circuit unit 130 described later. Thereby, it can be transmitted to the circuit short-circuit portion 130 that an abnormal current has occurred.

The circuit short-circuit unit 130 (see FIG. 1) is for short-circuiting the abnormal-time circuit unit 140 in the current transformer protection device 10 when an abnormal voltage is generated. As shown in FIG. 2, the circuit short-circuit unit 130 determines an abnormal voltage that causes a current to flow between the emitter and the collector when a voltage is applied to the base connected to the above-described abnormality current detection unit 120 (latch circuit 124). And a relay element 132 including a relay coil 132a in which a magnetic field is induced when a current flows. The relay element 132 is provided in the vicinity of the contact point 141 of the abnormality circuit 140. When a magnetic field is induced in the relay coil 132a, the generated magnetic field acts on the contact point 141, the contact point 141 is closed, and the circuit for abnormal time 140 is short-circuited.

In the present embodiment, the relay element 132 is used to short-circuit the abnormal circuit unit 140. However, the present invention is not limited to this as long as the abnormal circuit unit 140 can be short-circuited. Instead of the relay element 132, a configuration may be provided in which a digital circuit or the like capable of controlling on / off of the circuit unit for abnormality 140 is provided. However, in this case, those having no leakage current at the time of opening are preferable.

Here, in this embodiment, as shown in FIG. 2, a plurality of the above-described nonlinear resistance unit 110, abnormal current detection unit 120, and circuit short-circuit unit 130 are provided (two in FIG. 2 each). Have been described). This is because even when one of the non-linear resistance units 110 is damaged due to an abnormal voltage being applied for a long time, the abnormal-time current detection unit 120 and the circuit short-circuit unit 130 connected thereto are not functioning. This is because the other non-linear resistance unit 110 or the like is activated to short-circuit the circuit unit for abnormal time 140 (even if the non-linear resistance unit 110, the current detecting unit for abnormal time 120, and the circuit short-circuit unit 130 are provided one by one. Of course, the protection function of the current transformer 20 can be fulfilled).

In this case, the nonlinear resistance units 110 are preferably connected in parallel. Further, if the above-described threshold voltage is made different for each non-linear resistance unit 110, it is possible to cope even when an abnormal voltage takes a long time. In addition, as a method for changing the threshold voltage for each nonlinear resistance unit 110, surge protection devices of different types / standards are used, or surge protection devices of the same type / standard are connected in series, Depending on the number, it is conceivable to change the threshold voltage for each nonlinear resistance unit.

In FIG. 1 and FIG. 2, one abnormal current detection unit 120 and one circuit short-circuit unit 130 are connected to one nonlinear resistance unit 110, but the number of connections (combinations) is limited to this. It is not something that can be done. For example, a set of abnormal current detection units 120 and a circuit short-circuit unit 130 may be connected to the plurality of nonlinear resistance units 110 (in this case, the current output side of the plurality of nonlinear resistance units 110 connected in parallel) In addition, an arrangement method such as connecting the abnormality current detection unit 120 and the circuit short-circuit unit 130 in series is conceivable. Conversely, a plurality of sets of abnormal current detection units 120 and circuit short-circuit units 130 may be connected to one nonlinear resistance unit 110.

Next, the operation of the current transformer protection device 10 according to the present embodiment will be described. When an abnormal voltage is applied to the non-linear resistance unit 110 arranged in the circuit unit for abnormal time 140 in the current transformer protection device 10 due to an open point in the circuit through the ammeter 40, the resistance of the non-linear resistance unit 110 is reduced. The electric current (current at the time of abnormality) flows and is output.

The outputted abnormal current is inputted to the abnormal current detecting unit 120 arranged on the current output side of the nonlinear resistance unit 110. In the present embodiment, as shown in FIG. 2, when an abnormal current is output from the non-linear resistance unit 110, a current flows through a conducting wire inserted into the coil 121 a of the abnormal current detection transformer 121. As a result, a secondary current corresponding to the turn ratio between the conducting wire and the coil 121a flows through the coil 121a, and this secondary current is input to the operational amplifier 122 connected to the coil 121a and amplified to a predetermined voltage. Subsequently, the amplified voltage is input to the smoothing circuit 123 and converted into a DC voltage. Further, this DC voltage is input to the latch circuit 124, and the state where the voltage is applied is maintained. This state is continued until a release switch (not shown) provided separately in the protection device 10 is input.

The voltage output from the latch circuit 124 is input to the base of the transistor 131 in the circuit short-circuit unit 130, and a current flows between the emitter and collector of the transistor 131. The obtained current is input to the relay coil 132a of the relay element 132 connected to the collector of the transistor 131. Thereby, a magnetic field is induced in the relay coil 132a, and the contact point 141 is closed. As a result, the circuit part for abnormal time 140 becomes a closed loop, current flows, and the abnormal voltage decreases.

Even if an abnormal voltage is generated in the current transformer 20 by the above-described series of operations, the current transformer protection device 10 according to the present invention instantaneously shorts the abnormal-time circuit unit 140 to generate the abnormal voltage. suppress. Thereby, damage to current transformer 20 can be prevented. As shown in FIG. 2, even when a plurality of nonlinear resistance units 110, abnormal current detection units 120, and circuit short-circuit units 130 are provided in the current transformer protection device 10, The process up to short circuit is similar.

Next, a second embodiment according to the present invention will be described with reference to FIG. In addition, about the part which comprises 2nd embodiment, the same code | symbol is attached | subjected about the part same as 1st embodiment shown in FIG.1 and FIG.2, and description is abbreviate | omitted.

The current transformer protection device 50 according to the second embodiment includes an AC power source drive stop unit 510 that causes the current transformer protection device 10 according to the first embodiment described above to stop driving the AC power source 30, and a current transformer. 20 is provided with external notification means 520 for notifying an outside worker or the like that an abnormal voltage has occurred.

The AC power supply driving stop means 510 stops the driving of the AC power supply 30 that supplies power to the primary circuit section 220 of the current transformer 20 when an abnormal voltage occurs. In this embodiment, it is the structure containing the contact point 511 which receives the effect | action of the induction magnetic field produced when an electric current flows into the relay element 132 contained in the circuit short circuit part 130, and operate | moves. When the contact point 511 is closed, the AC power supply stop circuit 530 formed by connecting the AC power supply drive stopping means 510 and the AC power supply 30 is short-circuited.

When the AC power supply stopping circuit 530 is short-circuited, a switch portion (not shown) of the AC power supply 30 is activated, and the drive of the AC power supply 30 is stopped. Thereby, when an abnormal voltage arises, the supply of electric power to the current transformer 20 of the AC power supply 30 can be automatically stopped. The AC power supply drive stopping means 510 is not limited to this as long as the drive of the AC power supply 30 is stopped.

When an abnormal voltage is generated in the current transformer 20, the external notification unit 520 transmits abnormal voltage generation information to the alarm device 60 installed outside in order to notify the operator or the like to that effect. The external notification unit 520 and the alarm device 60 are connected via a wired or wireless communication path. In the present embodiment, a contact point 522 that receives an action from the relay element 132 included in the circuit short-circuit unit 130 is provided in the transmission circuit 521 to the alarm device 60 provided in the external notification unit 520, and the relay of the relay element 132 is provided. When a current flows through the coil 132a, the contact point 522 is configured to operate so as to short-circuit the transmission circuit. Thereby, generation | occurrence | production of abnormal voltage can be transmitted to the alarm device 60, and the fact can be notified to an operator etc.

As described above, according to the present invention, the current generated in the secondary coil 231 of the current transformer 20 is not shunted to a part other than the circuit through the ammeter 40 at the normal time when no abnormal voltage is generated. That is, an error does not occur between the current value actually flowing through the ammeter 40 and the current value indicated on the meter of the ammeter 40 (or so small that it can be ignored). Therefore, an operation test of a test apparatus (an other current supply object (for example, a watt hour meter for measuring power consumption)) that performs an operation test of the ammeter 40 before shipping (a test whether accurate measurement is possible). The same applies to the test apparatus that performs the above), and when the present invention is incorporated, it is possible to test with high accuracy whether or not the ammeter 40 or the like operates properly. However, it goes without saying that the present invention can be implemented in other applications.

10 Current Transformer Protection Device 20 According to First Embodiment Current Transformer 30 AC Power Supply 40 Ammeter (Current Supply Object)
50 Current Transformer Protection Device 60 according to Second Embodiment External Alarm Device 110 Nonlinear Resistance Unit 120 Abnormal Current Detection Unit 130 Circuit Short-Circuit Unit 131 Transistor 132 Relay Element 140 Abnormal Circuit Unit 221 Current Transformer Primary Coil 231 Secondary coil 510 of current transformer AC power supply drive stop means 520 External notification means 530 AC power supply stop circuit

Claims (6)

A current transformer protection device connected to the current transformer,
The current transformer is used to flow an appropriate current to an ammeter that measures a current value supplied from an external power source,
A circuit part for an abnormality when both ends are connected to the secondary coil of the current transformer,
A plurality of nonlinear resistance units that are connected to the abnormal circuit portion and exhibit nonlinear resistance change characteristics, and output an abnormal current when an abnormal voltage is input;
An abnormal current detection unit that detects the abnormal current output from at least one of the plurality of nonlinear resistance units;
A circuit short-circuit unit that is connected to the abnormal-time current detection unit and determines that the abnormal voltage has occurred when the abnormal-time current detection unit detects the abnormal-current and short-circuits the abnormal-time circuit unit When,
When it is determined that an abnormal voltage has occurred in the short circuit portion,
AC power supply drive stopping means for stopping the drive of the AC power supply connected to the current transformer,
External notification means for transmitting abnormal voltage occurrence information to an alarm device installed outside;
Including
When the circuit short-circuit unit short-circuits the abnormal-time circuit unit, an abnormal-time current flows through the abnormal-time circuit unit, and the abnormal voltage decreases accordingly. The plurality of nonlinear resistance units output the abnormal current when a voltage equal to or higher than a predetermined threshold voltage is input,
The current transformer protection device according to claim 1, wherein the threshold voltage is different for each of the plurality of nonlinear resistance units. More than the same number of the non-linear resistance unit as the abnormal current detection unit is provided,
At least one abnormal current detection unit is connected to each of the non-linear resistance units,
The current transformer protection device according to claim 1 or 2, wherein an abnormal current from each nonlinear resistance unit is output to a specific abnormal current detection unit. More than the same number of the circuit short-circuit portions as the abnormal-time current detection portions are provided,
The current transformer protection device according to any one of claims 1 to 3, wherein at least one circuit short-circuit portion is connected to each of the abnormal-time current detection units. The circuit short-circuit part includes a relay element,
5. The change according to claim 1, wherein a current flows through a relay coil of the relay element, whereby a contact point of the abnormal circuit portion is closed and the abnormal circuit portion is short-circuited. 6. Current protector. The current transformer protection device according to any one of claims 1 to 5, wherein the nonlinear resistance portion is a gas-filled discharge tube.

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