Secondary open circuit protector of current transformer

Abstract

The invention discloses a current transformer secondary open circuit protector, which relates to the technical field of power protection and comprises a first current transformer, a second current transformer, a central processing unit, a nonlinear resistor and a switch. The switch is connected to a tested circuit through a primary winding in the first current transformer; the central processing unit is used for sensing whether the primary side circuit of the second current transformer is open or not, the central processing unit is further used for outputting an action signal according to a signal sensed by the second current transformer, and the action signal is used for controlling the switch to be switched on; the non-linear resistor is connected in parallel between the primary winding of the first current transformer and the ground wire, and the non-linear resistor is used for limiting overvoltage generated when the primary side of the current transformer is open-circuited. And the overvoltage generated during the secondary open circuit of the protected circuit is limited.

Description

Technical Field

[0001] The invention relates to the technical field of power protection, and in particular to a current transformer secondary open circuit protector. Background Art

[0002] The current transformer secondary open circuit protector in the prior art Once the secondary winding and its circuit of the current transformer are open during operation, an overvoltage of several thousand volts or even tens of thousands of volts will be generated. This will not only damage the insulation of the secondary system, but also cause the transformer to be overexcited and burnt, and even endanger the life safety of the operator. Based on this, the present application proposes a current transformer secondary open circuit protector. Summary of the invention

[0003] The invention provides a current transformer secondary open circuit protector, which limits the overvoltage generated when the secondary circuit of a protected line is open.

[0004] According to one aspect of the present disclosure, a current transformer secondary open circuit protector is provided, the protector comprising: A first current transformer, a second current transformer, a central processing unit, a nonlinear resistor, and a switch; the switch is connected to the measured line through the primary winding in the first current transformer; The central processor is used to sense whether the primary side line of the second current transformer is open circuited, and the central processor is also used to output an action signal according to the signal sensed from the second current transformer, and the action signal is used to control the switch to close; The nonlinear resistor is connected in parallel between the primary winding of the first current transformer and the ground wire, and is used to limit the overvoltage generated when the primary side of the current transformer is open-circuited.

[0005] In a possible implementation, when the protected line is normal, the current of the first current transformer is less than or equal to the current of the second current transformer, and the switch changes from a closed state to an open state. When the voltage signal of the central processor sensing whether an open circuit occurs on the primary side of the second current transformer is less than the voltage threshold, no action signal is sent from the output pin of the central processor, both ends of the protector are in an open circuit state, and the leakage current is zero.

[0006] In one possible implementation, when an abnormal overcurrent occurs in the primary coil of the second current transformer or an open circuit occurs in the primary side line of the second current transformer, the central processor senses an increase in the voltage of the secondary winding of the second current transformer, and the central processor outputs an action signal based on the sensed signal of the increase in the voltage of the secondary winding of the current transformer. The action signal is used to control the closing of the switch, and the nonlinear resistor is used to limit the overvoltage generated when the protected line is open.

[0007] In a possible implementation, the central processor is further configured to collect a current value sensed by the first current transformer, determine whether the switch is closed based on the current value, and determine that the switch is closed when the current value sensed by the first current transformer increases.

[0008] In a possible implementation, the protector further includes a display light, and the display light is used to indicate a closed switch.

[0009] In a possible implementation manner, the primary winding of the first current transformer and the primary winding of the second current transformer are connected in series in the protected line.

[0010] In a possible implementation, the protector further includes a display, which is used to display the fault circuit and has a passive contact signal output.

[0011] In a possible implementation, the protector includes a plurality of nonlinear resistors, a plurality of switches, a plurality of first groups of current transformers, and a plurality of second current transformers, and the protector protects a plurality of lines simultaneously.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The disclosed embodiment of the current transformer secondary open circuit protector has a central processing unit for sensing whether the primary side circuit of the second current transformer is open circuited. The central processing unit is also used to output an action signal according to the signal sensed from the second current transformer. The action signal is used to control the closing of the switch. When an abnormal overcurrent occurs in the primary coil of the second current transformer or the primary side circuit of the second current transformer is open circuited, the central processing unit senses that the voltage of the secondary winding of the second current transformer increases. The central processing unit outputs an action signal according to the sensed signal of the voltage increase of the secondary winding of the current transformer. The action signal is used to control the closing of the switch. The nonlinear resistor is used to limit the overvoltage generated when the protected circuit is open circuited. In this way, the protector limits the overvoltage generated when the tested circuit is open circuited through the nonlinear resistor, and has the functions of action contact output, automatic light display, automatic locking differential protection, manual or automatic reset function after action, and a protector with various different functions in multiple combinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of a current transformer secondary open circuit protector according to an embodiment of the present disclosure is shown.

[0014] Figure 2 A schematic diagram of a current transformer secondary open circuit protector in the prior art is shown.

[0015] Figure 3 A schematic diagram of a current transformer secondary open circuit protector according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0016] Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0017] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0018] In addition, in order to better illustrate the present disclosure, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present disclosure can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present disclosure.

[0019] Figure 2 The protector in the prior art does not include CT1, CT2 and FR. When the protected line is open in the system, KA switches from opening to closing, short-circuiting the circuit so that the protected line is no longer open, protecting the entire circuit. The defects are: the closing action time is relatively long, generally the entire cycle time from signal collection to signal sending and relay action time is about 3 seconds. If the system has high-frequency overvoltage or impact overvoltage, the equipment will burn out before it acts. The casing is not flame-retardant material, and the burning point expands to burn the entire cabinet.

[0020] During the operation of the protector in the prior art, there are generally 9 circuits. The on-site equipment of the standby circuit is not short-circuited, and the entire circuit is in an open circuit state. The starting voltage of the protector is 170V, and the circuit is not closed until the starting value KA is reached. The entire circuit is in an open circuit state, the equipment is burned, and protection cannot be performed.

[0021] According to one aspect of the present disclosure, a current transformer secondary open circuit protector is provided, the protector comprising: A first current transformer CT1, a second current transformer CT2, a central processor, a nonlinear resistor FR, and a switch KA; the switch KA is connected to the measured line through the primary winding in the first current transformer; the secondary side of the second current transformer CT2 is connected to a meter for monitoring current changes.

[0022] The primary side of the first current transformer CT1 and the primary side of the second current transformer CT2 are connected to the three phases of the measured line through the contacts A431, A432, and A433. The primary side of the first current transformer CT1 and the primary side of the second current transformer CT2 are grounded through the contact N431. Contacts A431 A432 and A433 are grounded through coils LHa, LHb, and LHc, respectively.

[0023] The central processor is used to sense whether the primary side line of the second current transformer CT2 is open (CT signal is introduced). The central processor is also used to output an action signal according to the signal sensed from the second current transformer, and the action signal is used to control the switch KA to close; the switches of the 18-20 nodes in the switch KA are opened or closed at the same time.

[0024] The nonlinear resistor is connected in parallel between the primary winding of the first current transformer and the ground wire (grounded through the contact 21), and the nonlinear resistor is used to limit the overvoltage generated when the primary side of the current transformer is open.

[0025] In a possible implementation, when the protected line is normal, the current of the first current transformer is less than or equal to the current of the second current transformer, and the switch changes from a closed state to an open state. When the voltage signal of the central processor sensing whether an open circuit occurs on the primary side of the second current transformer is less than the voltage threshold, no action signal is sent from the output pin of the central processor, both ends of the protector are in an open circuit state, and the leakage current is zero.

[0026] In one possible implementation, when an abnormal overcurrent occurs in the primary coil of the second current transformer or an open circuit occurs in the primary side line of the second current transformer, the central processor senses an increase in the voltage of the secondary winding of the second current transformer, and the central processor outputs an action signal (sends an action signal) based on the sensed signal of the increase in the voltage of the secondary winding of the current transformer. The action signal is used to control the closing of the switch, and the nonlinear resistor is used to limit the overvoltage generated when the protected line is open.

[0027] The current transformer secondary open circuit protector includes a FR nonlinear resistor with close to ideal protection characteristics. The protector is connected across the two ends of the CT1 secondary winding. During normal operation, the leakage current is extremely small and presents a high resistance state of more than 100MΩ; the voltage generated when the measured line is open is much higher than the normal operating voltage. At this time, the protector acts quickly and presents a low resistance state close to a short circuit, effectively limiting overvoltage.

[0028] For example, when the measured line is open-circuited or an abnormal overcurrent occurs in the primary winding of the current transformer, the voltage generated in the secondary winding is much higher than the normal operating voltage (the value depends on the parameters of the CT itself and the operating conditions). At this time, the microcontroller (central processing unit) in the overvoltage protector connected in parallel to the secondary side of the current transformer receives a voltage value greater than the programmed specified voltage, and its output pin sends a signal to cause the protector to act instantly. The protector closes and shorts the KA of the secondary winding of CT1 and displays a light. At the same time, when high-frequency overvoltage and high voltage values ​​are generated, FR is used to divide the voltage. At this time, the device issues an alarm and can be reset manually or automatically after the fault is eliminated (60 seconds).

[0029] In a possible implementation, the central processing unit is also used to collect the current value sensed by the first current transformer (CT signal introduction), and judge whether the switch is closed based on the current value. When the current value sensed by the first current transformer increases, it is judged that the switch is closed.

[0030] In a possible implementation, the protector further includes a display light, and the display light is used to indicate a closed switch.

[0031] In a possible implementation manner, the primary winding of the first current transformer and the primary winding of the second current transformer are connected in series in the protected line.

[0032] In a possible implementation, the protector further includes a display, which is used to display the fault circuit and has a passive contact signal output.

[0033] In a possible implementation, the protector includes a plurality of nonlinear resistors, a plurality of switches, a plurality of first groups of current transformers, and a plurality of second current transformers, and the protector protects a plurality of lines simultaneously.

[0034] like Figure 3 The protector can provide protection for multiple circuits at most. Figure 3 The protector includes three groups of CT1, three groups of CT2 and three groups of switches. The protector can protect multiple lines at the same time.

[0035] After the protector is activated, the fault circuit is displayed on the panel, and a passive contact signal is output. After the fault is eliminated, press the manual reset button, and the circuit will return to its original state and resume normal operation. The protector can be used again after reset, and its service life can reach tens of thousands of times, and it operates stably and reliably.

[0036] The protector of this application has the following advantages: 1. Under normal circumstances, KA is closed, which solves the problem of the backup circuit of the entire circuit being disconnected.

[0037] 2. Other problems such as loose wiring or poor contact in the normal circuit 3. The FR strengthening circuit is connected in parallel in the circuit to solve the problems of excessive current and high-frequency overvoltage or impact overvoltage. At the same time, the KA point is shunted to protect the equipment and make it safer and more reliable.

[0038] Table 1 shows the technical parameters of the protector: ; The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A current transformer secondary open circuit protector, characterized in that: The protector comprises: A first current transformer, a second current transformer, a central processing unit, a nonlinear resistor, and a switch; the switch is connected to the measured line through the primary winding in the first current transformer; The central processor is used to sense whether the primary side line of the second current transformer is open circuited, and the central processor is also used to output an action signal according to the signal sensed from the second current transformer, and the action signal is used to control the switch to close; The nonlinear resistor is connected in parallel between the primary winding of the first current transformer and the ground wire, and is used to limit the overvoltage generated when the primary side of the current transformer is open-circuited.

2. A current transformer secondary open circuit protector according to claim 1, characterized in that: When the protected line is normal, the current of the first current transformer is less than or equal to the current of the second current transformer, and the switch changes from the closed state to the open state. When the voltage signal of the central processor sensing whether an open circuit occurs on the primary side of the second current transformer is less than the voltage threshold, no action signal is sent from the output pin of the central processor, both ends of the protector are in an open circuit state, and the leakage current is zero.

3. A current transformer secondary open circuit protector according to claim 1, characterized in that: When an abnormal overcurrent occurs in the primary coil of the second current transformer or an open circuit occurs in the primary side line of the second current transformer, the central processor senses an increase in the voltage of the secondary winding of the second current transformer, and the central processor outputs an action signal based on the sensed signal of the increase in the voltage of the secondary winding of the current transformer. The action signal is used to control the closing of the switch, and the nonlinear resistor is used to limit the overvoltage generated when the protected line is open.

4. A current transformer secondary open circuit protector according to claim 3, characterized in that: The central processing unit is also used to collect the current value sensed by the first current transformer, and judge whether the switch is closed according to the current value. When the current value sensed by the first current transformer increases, it is judged that the switch is closed.

5. A current transformer secondary open circuit protector according to claim 1, characterized in that: The protector also includes a display light, which is used to indicate a closed switch.

6. A current transformer secondary open circuit protector according to claim 1, characterized in that: The primary winding of the first current transformer and the primary winding of the second current transformer are connected in series in the protected line.

7. A current transformer secondary open circuit protector according to claim 1, characterized in that: The protector also includes a display, which is used to display the fault circuit and has a passive contact signal output.

8. A current transformer secondary open circuit protector according to claim 1, characterized in that: The protector comprises a plurality of nonlinear resistors, a plurality of switches, a plurality of first groups of current transformers, and a plurality of second current transformers. The protector protects a plurality of lines at the same time.

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