Multi-purpose low-power passive current transformer measurement protection interface circuit

Abstract

The invention discloses a multipurpose low-power passive current transformer measurement protection interface circuit which comprises a low-power passive current transformer, a secondary wiring terminal strip, an I / V conversion circuit, a program control amplification circuit, a summing circuit, an amplification circuit, a verification circuit and a measurement protection device. According to the invention, the difficulty and cost of the multipurpose low-power passive current transformer and a rear-connected measurement protection device thereof are reduced, and intelligent gear shifting can be carried out according to the current range of a measured power grid, so that the universality of the multipurpose low-power passive current transformer is improved.

Description

Technical Field

[0001] This invention relates to a measurement and protection interface circuit, and more particularly to a multi-purpose low-power passive current transformer measurement and protection interface circuit, belonging to the field of smart grid technology. Background Technology

[0002] The multi-purpose low-power passive current transformer is characterized by its versatility and low power compared to existing passive current transformers. Both are mainly used for sampling current at key nodes in power grids. Existing passive current transformers have two secondary coils. One secondary coil output is used for measurement and metering current sampling, and the other secondary coil output is used for protection and alarm current sampling. At the primary rated current, the secondary rated current is 5A (or 1A). Because the protection setting is set to 20 times the rated current and a certain accuracy is required, the power of this current transformer is very high, resulting in high weight, size, and cost.

[0003] Multipurpose low-power passive current transformers use the same secondary coil for measurement, protection, and sampling (meaning multipurpose) and have relatively low rated output power and current (meaning low power), thus greatly reducing weight, size, and cost. They are gradually gaining widespread recognition and application.

[0004] Since the measurement and protection current of the multi-purpose low-power passive current transformer is sampled from the same secondary coil output, and the protection current setting is required to be 20 times the rated current, the A / D range of the subsequent measurement and protection device must be very wide to ensure sufficient accuracy when measuring small currents and protecting large currents. This will increase the difficulty and cost of the subsequent measurement and protection device. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multi-purpose low-power passive current transformer measurement and protection interface circuit, thereby reducing the difficulty and cost of multi-purpose low-power passive current transformers and their subsequent measurement and protection devices.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A multi-purpose low-power passive current transformer measurement and protection interface circuit includes a low-power passive current transformer, a secondary terminal block, an I / V conversion circuit, a programmable amplifier circuit, an adder circuit, an amplifier circuit, a verification circuit, and a measurement and protection device. The two output terminals of the low-power passive current transformer are respectively connected to the first set of two input terminals of the secondary terminal block. The second set of two input terminals of the secondary terminal block is connected to the current output of a three-phase programmable standard power source or a microprocessor-based relay protection tester. The first set of two output terminals of the secondary terminal block is respectively connected to the two input terminals of the I / V conversion circuit. The second set of two output terminals are connected to the two input terminals of the verification circuit, the output terminal of the I / V conversion circuit is connected to the first input terminal of the programmable amplifier circuit, the output terminal of the programmable amplifier circuit is connected to the first input terminal of the adder circuit, the output terminal of the verification circuit is connected to the second input terminal of the adder circuit, the output terminal of the adder circuit is connected to the AD1 port of the measurement protection device and the input terminal of the amplifier circuit, the output terminal of the amplifier circuit is connected to the AD2 port of the measurement protection device, and the second, third, and fourth input terminals of the programmable amplifier circuit are connected to the IO1, IO2, and IO3 ports of the measurement protection device, respectively.

[0007] Furthermore, the I / V conversion circuit includes a resistor R1. One end of the resistor R1 serves as the first input and output terminal of the I / V conversion circuit, and the other end of the resistor R1 is connected to the power supply VSS and serves as the second input terminal of the I / V conversion circuit.

[0008] Furthermore, the programmable amplifier circuit includes resistors R3 to R11, operational amplifier U1A, and an 8-channel multiplexer U2. One end of resistor R3 serves as the first input terminal of the programmable amplifier circuit, and the other end of resistor R3 is connected to the inverting input terminal of operational amplifier U1A. One end of resistor R4 is connected to the power supply VSS, and the other end of resistor R4 is connected to the non-inverting input terminal of operational amplifier U1A, the X0 port of the 8-channel multiplexer U2, one end of resistors R5, R6, R7, R8, R9, R10, and R11. The other ends of resistors R5, R6, R7, R8, R9, R10, and R11 are sequentially connected to the X1, X2, X3, X4, X5, X6, and X7 ports of the 8-channel multiplexer U2. The INH and GND ports of the 8-channel multiplexer U2 are connected to the power supply VSS. The VCC port of the 8-channel multiplexer U2 is connected to the +5V power supply. The VEE port of the 8-channel multiplexer U2 is connected to the -5V power supply. The A, B, and C ports of the 8-channel multiplexer U2 are used as the second, third, and fourth input terminals of the 8-channel multiplexer U2, respectively, and the signals AA, BB, and CC are input sequentially. The X port of the 8-channel multiplexer U2 is connected to the output terminal of the operational amplifier U1A and serves as the output terminal of the 8-channel multiplexer U2.

[0009] Furthermore, the 8-channel multiplexer U2 uses the HCF4051 chip.

[0010] Furthermore, the adder circuit includes resistors R12, R13, and R14, and an operational amplifier U1D. One end of resistor R12 serves as the first input terminal of the adder circuit, and one end of resistor R13 serves as the second input terminal of the adder circuit. The other end of resistor R12 is connected to one end of resistor R14, the other end of resistor R13, and the inverting input terminal of operational amplifier U1D. The non-inverting input terminal of operational amplifier U1D is connected to the power supply VSS. The output terminal of operational amplifier U1D is connected to the other end of resistor R14 and serves as the output terminal of the adder circuit, generating the signal IABH.

[0011] Furthermore, the amplifier circuit includes resistors R15, R16, and R17, and an operational amplifier U1C. One end of resistor R15 serves as the input terminal of the amplifier circuit, and the other end of resistor R15 is connected to the inverting input terminal of operational amplifier U1C. One end of resistor R16 is connected to the power supply VSS, and the other end of resistor R16 is connected to the non-inverting input terminal of operational amplifier U1C and one end of resistor R17. The output terminal of operational amplifier U1C is connected to the other end of resistor R17 and serves as the output terminal of the amplifier circuit, generating the signal IACL.

[0012] Furthermore, the verification circuit includes a test current transformer CTA2, a resistor R2, and an operational amplifier U1B. The two input terminals of the test current transformer CTA2 serve as the two input terminals of the verification circuit. One output of the test current transformer CTA2 is connected to one end of the resistor R2 and the non-inverting input terminal of the operational amplifier U1B to generate the signal IABH12. The other output of the test current transformer CTA2 is connected to the other end of the resistor R2 and connected to the power supply VSS. The output terminal of the operational amplifier U1B is connected to the inverting input terminal of the operational amplifier U1B and serves as the output terminal of the verification circuit.

[0013] Furthermore, the measurement protection device includes an MCU microcontroller U3, which uses an STM32F407 chip.

[0014] Compared with the prior art, the present invention has the following advantages and effects: The present invention provides a multi-purpose low-power passive current transformer measurement and protection interface circuit, thereby reducing the difficulty and cost of multi-purpose low-power passive current transformers and their subsequent measurement and protection devices, and can intelligently adjust the range according to the magnitude range of the measured grid current, thereby increasing the versatility of multi-purpose low-power passive current transformers. Attached Figure Description

[0015] Figure 1 This is a circuit diagram of a multi-purpose low-power passive current transformer measurement and protection interface circuit according to the present invention. Detailed Implementation

[0016] To illustrate in detail the technical solutions adopted by the present invention to achieve the intended technical objectives, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Furthermore, the technical means or technical features in the embodiments of the present invention can be replaced without creative effort. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0017] like Figure 1As shown, the present invention discloses a multi-purpose low-power passive current transformer measurement and protection interface circuit, comprising a low-power passive current transformer 01, a secondary terminal block 02, an I / V conversion circuit 03, a programmable amplifier circuit 04, an adder circuit 05, an amplifier circuit 06, a verification circuit 07, and a measurement and protection device 08. The two output terminals of the low-power passive current transformer 01 are respectively connected to the first set of two input terminals of the secondary terminal block 02. The second set of two input terminals of the secondary terminal block 02 is connected to the current output of a three-phase programmable standard power source or a microcomputer relay protection tester. The first set of two output terminals of the secondary terminal block 02 is respectively connected to the two input terminals of the I / V conversion circuit 03. The secondary terminal block... The second set of two output terminals of row 02 are connected to the two input terminals of the verification circuit 07 respectively. The output terminal of the I / V conversion circuit 03 is connected to the first input terminal of the programmable amplifier circuit 04. The first output terminal of the programmable amplifier circuit 04 is connected to the first input terminal of the adder circuit 05. The output terminal of the verification circuit 07 is connected to the second input terminal of the adder circuit 05. The output terminal of the adder circuit 05 is connected to the AD1 port of the measurement protection device 08 and the input terminal of the amplifier circuit 06. The output terminal of the amplifier circuit 06 is connected to the AD2 port of the measurement protection device 08. The second, third, and fourth input terminals of the programmable amplifier circuit 04 are connected to the IO1, IO2, and IO3 ports of the measurement protection device 08 respectively.

[0018] Low-power passive current transformer 01 is actually low-power passive current transformer CTA1. Pins 2 and 4 of low-power passive current transformer CTA1 serve as its two outputs. Traditional current transformers have different CT ratios depending on the load size, such as 600 / X, 500 / X, 400 / X, 300 / X, 200 / X, etc. The X value of traditional current transformers is fixed at 5A or 1A, while the X value of low-power current transformers is 0.1A or 0.01A. A 600 / X current transformer has a primary rated current of 600A and a secondary output current of X.

[0019] The first set of two input terminals of the secondary terminal block 02 is connected to the output terminal of the low-power passive current transformer 01. The second set of two input terminals of the secondary terminal block 02 is connected to the current output of the three-phase programmable standard power source or microcomputer relay protection tester. The first set of outputs of the secondary terminal block 02 is sent to the I / V conversion circuit 03, and the second set of outputs of the secondary terminal block 02 is sent to the verification circuit 07.

[0020] The I / V conversion circuit 03 includes a resistor R1. One end of the resistor R1 serves as both the first input and output terminal of the I / V conversion circuit, while the other end of the resistor R1 is connected to the power supply VSS and serves as the second input terminal of the I / V conversion circuit. The I / V conversion circuit 03 converts the current X into a voltage Y, where Y = X * R1.

[0021] The programmable amplifier circuit 04 includes resistors R3 to R11, operational amplifier U1A, and an 8-channel multiplexer U2. One end of resistor R3 serves as the first input terminal of the programmable amplifier circuit, and the other end of resistor R3 is connected to the inverting input terminal of operational amplifier U1A. One end of resistor R4 is connected to the power supply VSS, and the other end of resistor R4 is connected to the non-inverting input terminal of operational amplifier U1A, the X0 port of the 8-channel multiplexer U2, one end of resistors R5, R6, R7, R8, R9, R10, and R11. The other ends of resistors R5, R6, R7, R8, R9, R10, and R11 are sequentially connected to the X1, X2, X3, X4, X5, X6, and X7 ports of the 8-channel multiplexer U2. The INH and GND ports of the 8-channel multiplexer U2 are connected to the power supply VSS. The VCC port of the 8-channel multiplexer U2 is connected to the +5V power supply. The VEE port of the 8-channel multiplexer U2 is connected to the -5V power supply. The A, B, and C ports of the 8-channel multiplexer U2 are used as the second, third, and fourth input terminals of the 8-channel multiplexer U2, respectively, and the signals AA, BB, and CC are input sequentially. The X port of the 8-channel multiplexer U2 is connected to the output terminal of the operational amplifier U1A and serves as the output terminal of the 8-channel multiplexer U2.

[0022] The programmable amplifier circuit 04 selects one of the X0 to X7 ports of the 8-channel multiplexer U2 based on the chip select signals AA, BB, and CC provided by the measurement and protection device 08. The X0 to X7 ports correspond to eight amplification factors: 1x, 1.2x, 1.5x, 2x, 3x, 4x, 6x, and 12x, respectively. When the 600 / X current transformer is used in applications with a rated current of only 50A, the secondary output current is (50 / 600)X. This current, after passing through the I / V conversion circuit 03, also outputs a voltage of only (50 / 600)Y. Directly supplying this voltage to the measurement and protection device 08 results in a low measurement accuracy due to its small voltage. Now, based on the input CT ratio of 50, the measurement and protection device 08 selects a channel with a 12x amplification factor for the programmable amplifier circuit 04. The output voltage of the programmable amplifier circuit 04 then returns to Y, and this voltage improves the measurement accuracy of the measurement and protection device 08.

[0023] Among them, the 8-channel multiplexer U2 uses the HCF4051 chip.

[0024] Adder circuit 05 includes resistors R12, R13, and R14, and operational amplifier U1D. One end of resistor R12 serves as the first input terminal of the adder circuit, and one end of resistor R13 serves as the second input terminal. The other end of resistor R12 is connected to one end of resistor R14, the other end of resistor R13, and the inverting input terminal of operational amplifier U1D. The non-inverting input terminal of operational amplifier U1D is connected to power supply VSS. The output terminal of operational amplifier U1D is connected to the other end of resistor R14 and serves as the output terminal of the adder circuit, generating the signal IABH. One input of adder circuit 05 is the output of the programmable amplifier circuit after the multi-purpose low-power passive current transformer passes through the I / V conversion circuit, and the other input is the output of the verification circuit. These two inputs correspond to the working scenario and the verification scenario, respectively, and these two scenarios will not operate simultaneously; the adder circuit enables switching between the two scenarios. One output of adder circuit 05 is directly connected to the AD1 channel of the 08 measurement and protection device for wide-range protection. The output of adder circuit 05 is routed to amplifier circuit 06.

[0025] Amplifier circuit 06 includes resistors R15, R16, and R17, and operational amplifier U1C. One end of resistor R15 serves as the input terminal of the amplifier circuit, and the other end of resistor R15 is connected to the inverting input terminal of operational amplifier U1C. One end of resistor R16 is connected to the power supply VSS, and the other end of resistor R16 is connected to the non-inverting input terminal of operational amplifier U1C and one end of resistor R17. The output terminal of operational amplifier U1C is connected to the other end of resistor R17 and serves as the output terminal of the amplifier circuit, generating signal IACL to the AD2 channel of the 08 measurement protection device for high-precision measurement of small currents.

[0026] The verification circuit 07 includes a test current transformer CTA2, a resistor R2, and an operational amplifier U1B. The two input terminals of the test current transformer CTA2 serve as the two input terminals of the verification circuit. These are connected to the current output of a three-phase programmable standard power source or a microprocessor-based relay protection tester via the second input of the secondary terminal block 02. One output of the test current transformer CTA2 is connected to one end of resistor R2 and the non-inverting input terminal of operational amplifier U1B, generating the signal IABH12. The other output of the test current transformer CTA2 is connected to the other end of resistor R2 and then to the power supply VSS. The output terminal of operational amplifier U1B is connected to its inverting input terminal and serves as the output terminal of the verification circuit. The input current of verification circuit 07 is the output current of the three-phase programmable standard power source or microprocessor-based relay protection tester, making it compatible with all commercially available three-phase programmable standard power sources or microprocessor-based relay protection testers, facilitating on-site verification of the device.

[0027] The measurement protection device 08 includes an MCU microcontroller U3, which uses an STM32F407 chip. When signals CC, BB, AA = 000, the X0 port of the 8-channel multiplexer U2 is connected to the X port of the 8-channel multiplexer U2 (1 channel); when signals CC, BB, AA = 001, the X1 port of the 8-channel multiplexer U2 is connected to the X port of the 8-channel multiplexer U2 (1.2 channels); when signals CC, BB, AA = 010, the X2 port of the 8-channel multiplexer U2 is connected to the X port of the 8-channel multiplexer U2 (1.5 channels); and so on. When the CT ratio of the measurement protection device 08 is 600, the outputs of IO3, IO2, and IO1 are 000, and the programmable amplifier circuit 04 selects 1 channel; when the CT ratio of the measurement protection device 08 is 500, the outputs of IO3, IO2, and IO1 are 001, and the programmable amplifier circuit 04 selects 1.2 channels.

[0028] Traditional current transformer replacement scenarios include: 1. Requiring the purchase of a new current transformer with a new CT ratio, increasing costs; 2. Requiring a power outage to remove the old current transformer and then install the new one; 3. Conducting joint commissioning and testing of the new current transformer and protection devices, wasting normal production time and increasing the workload of installation and commissioning.

[0029] The multi-purpose low-power passive current transformer replacement scenarios of this invention are as follows: 1. The new CT ratio is issued to the measurement and protection device through the background system, and the measurement and protection device completes the process instantly; 2. Or the new CT ratio is set through local operation of the measurement and protection device; 3. By comparison, the replacement of the multi-purpose low-power passive current transformer is cost-effective, time-saving and labor-saving.

[0030] This invention provides a measurement and protection interface circuit for a multi-purpose low-power passive current transformer, thereby reducing the difficulty and cost of multi-purpose low-power passive current transformers and their subsequent measurement and protection devices, and enabling intelligent range adjustment according to the range of the measured grid current, thus increasing the versatility of the multi-purpose low-power passive current transformer.

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A multi-purpose low-power passive current transformer measurement and protection interface circuit, characterized in that: This system includes a low-power passive current transformer, a secondary terminal block, an I / V conversion circuit, a programmable amplifier circuit, an adder circuit, an amplifier circuit, a verification circuit, and a measurement and protection device. The two outputs of the low-power passive current transformer are connected to the first set of two inputs of the secondary terminal block. The second set of two inputs of the secondary terminal block is connected to the current output of a three-phase programmable standard power source or a microprocessor-based relay protection tester. The first set of two outputs of the secondary terminal block is connected to the two inputs of the I / V conversion circuit. The second set of two outputs of the secondary terminal block... The two input terminals of the verification circuit are connected. The output terminal of the I / V conversion circuit is connected to the first input terminal of the programmable amplifier circuit. The output terminal of the programmable amplifier circuit is connected to the first input terminal of the adder circuit. The output terminal of the verification circuit is connected to the second input terminal of the adder circuit. The output terminal of the adder circuit is connected to the AD1 port of the measurement protection device and the input terminal of the amplifier circuit. The output terminal of the amplifier circuit is connected to the AD2 port of the measurement protection device. The second, third, and fourth input terminals of the programmable amplifier circuit are connected to the IO1, IO2, and IO3 ports of the measurement protection device, respectively.

2. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 1, characterized in that: The I / V conversion circuit includes a resistor R1. One end of the resistor R1 serves as the first input and output terminal of the I / V conversion circuit, and the other end of the resistor R1 is connected to the power supply VSS and serves as the second input terminal of the I / V conversion circuit.

3. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 1, characterized in that: The programmable amplifier circuit includes resistors R3 to R11, operational amplifier U1A, and an 8-channel multiplexer U2. One end of resistor R3 serves as the first input terminal of the programmable amplifier circuit, and the other end of resistor R3 is connected to the inverting input terminal of operational amplifier U1A. One end of resistor R4 is connected to the power supply VSS, and the other end of resistor R4 is connected to the non-inverting input terminal of operational amplifier U1A, the X0 port of the 8-channel multiplexer U2, one end of resistors R5, R6, R7, R8, R9, R10, and R11. The other ends of resistors R5, R6, R7, R8, R9, R10, and R11 are sequentially connected to the X1, X2, X3, X4, X5, X6, and X7 ports of the 8-channel multiplexer U2. The INH and GND ports of the 8-channel multiplexer U2 are connected to the power supply VSS. The VCC port of the 8-channel multiplexer U2 is connected to the +5V power supply. The VEE port of the 8-channel multiplexer U2 is connected to the -5V power supply. The A, B, and C ports of the 8-channel multiplexer U2 are used as the second, third, and fourth input terminals of the 8-channel multiplexer U2, respectively, and the signals AA, BB, and CC are input sequentially. The X port of the 8-channel multiplexer U2 is connected to the output terminal of the operational amplifier U1A and serves as the output terminal of the 8-channel multiplexer U2.

4. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 3, characterized in that: The 8-channel multiplexer U2 uses the HCF4051 chip.

5. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 1, characterized in that: The adder circuit includes resistors R12, R13, and R14, and operational amplifier U1D. One end of resistor R12 serves as the first input terminal of the adder circuit, and one end of resistor R13 serves as the second input terminal of the adder circuit. The other end of resistor R12 is connected to one end of resistor R14, the other end of resistor R13, and the inverting input terminal of operational amplifier U1D. The non-inverting input terminal of operational amplifier U1D is connected to power supply VSS. The output terminal of operational amplifier U1D is connected to the other end of resistor R14 and serves as the output terminal of the adder circuit, generating the signal IABH.

6. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 1, characterized in that: The amplifier circuit includes resistors R15, R16, and R17, and an operational amplifier U1C. One end of resistor R15 serves as the input terminal of the amplifier circuit, and the other end of resistor R15 is connected to the inverting input terminal of operational amplifier U1C. One end of resistor R16 is connected to the power supply VSS, and the other end of resistor R16 is connected to the non-inverting input terminal of operational amplifier U1C and one end of resistor R17. The output terminal of operational amplifier U1C is connected to the other end of resistor R17 and serves as the output terminal of the amplifier circuit, generating the signal IACL.

7. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 1, characterized in that: The verification circuit includes a test current transformer CTA2, a resistor R2, and an operational amplifier U1B. The two input terminals of the test current transformer CTA2 serve as the two input terminals of the verification circuit. One output of the test current transformer CTA2 is connected to one end of the resistor R2 and the non-inverting input terminal of the operational amplifier U1B to generate the signal IABH12. The other output of the test current transformer CTA2 is connected to the other end of the resistor R2 and connected to the power supply VSS. The output terminal of the operational amplifier U1B is connected to the inverting input terminal of the operational amplifier U1B and serves as the output terminal of the verification circuit.

8. The multi-purpose low-power passive current transformer measurement and protection interface circuit according to claim 1, characterized in that: The measurement and protection device includes an MCU microcontroller U3, which uses an STM32F407 chip.

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