High-precision AC isolation sampling circuit replacing traditional PT

Abstract

The invention provides a high-precision alternating current isolation sampling circuit replacing a traditional PT, and belongs to the field of voltage sampling, the high-precision alternating current isolation sampling circuit comprises a resistor R1, a resistor R2, a voltage follower U1A and an isolation amplifier U2AA, one end of the resistor R1 is connected with a piezoresistor RV1 and one end of a secondary side of a voltage transformer, the other end of the resistor R1 is connected with the resistor R2, a resistor R3 and a diode TVS1, and the isolation amplifier U2AA is connected with the voltage follower U1A. The other end of the resistor R2 is connected with the non-inverting input end of the voltage follower U1A, the inverting input end of the voltage follower U1A is connected with the resistor R4, and the other end of the piezoresistor RV1 is connected with the resistor R5 and the other end of the secondary side of the voltage transformer. And meanwhile, the harm caused by the short circuit of the secondary side of the voltage transformer is also solved.

Description

Technical Field

[0001] The invention relates to the technical field of voltage sampling, and in particular to a high-precision AC isolation sampling circuit that replaces a traditional PT. Background Art

[0002] In the power system, voltage transformers play a vital role. Voltage transformers can convert high voltage signals into corresponding low voltage signals, so that power meters and protection devices can accurately collect voltage. This is crucial for the normal operation and dispatch of power systems. Voltage transformers can help measure voltage fluctuations and other anomalies, thereby predicting potential problems and avoiding damage to the normal operation of power systems. Widely used protection modules use the precise data provided by voltage transformers to determine whether there is a fault, thereby preventing power equipment and power systems from being completely destroyed.

[0003] Disadvantages of existing technology:

[0004] 1: The sampling error is large. The linearity of traditional voltage transformers is generally 0.2%;

[0005] 2: The sampling range is narrow. The sampling range of traditional voltage transformers is generally 20% to 120% Un;

[0006] 3. Large temperature drift. The traditional voltage transformer is composed of windings. High and low temperatures have a great impact on its quality factors.

[0007] 4: There are great safety hazards. If the secondary side of the traditional voltage transformer is short-circuited, the primary and secondary currents will increase sharply, causing the winding to heat up or even burn the insulation, resulting in the high voltage on the primary side being connected to the low voltage circuit on the secondary side, endangering the safety of people and equipment. Summary of the invention

[0008] In order to make up for the deficiencies of the prior art, the embodiments of the present application propose a high-precision AC isolation sampling circuit that replaces the traditional PT to solve the problems existing in the prior art.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A high-precision AC isolation sampling circuit that replaces a traditional PT includes a resistor R1, a resistor R2, a voltage follower U1A and an isolation amplifier U2AA, wherein one end of the resistor R1 is connected to a varistor RV1 and one end of a secondary side of a voltage transformer, the other end of the resistor R1 is connected to a resistor R2, a resistor R3 and a diode TVS1, the other end of the resistor R2 is connected to a positive input end of the voltage follower U1A, the negative input end of the voltage follower U1A is connected to a resistor R4, the other end of the varistor RV1 is connected to a resistor R5 and the other end of the secondary side of the voltage transformer, the other end of the resistor R5 is connected to the other end of the resistor R3 and the other end of the diode TVS1, and the other end of the resistor R4 is connected to the positive input end of the voltage follower U1A. One end, capacitor C2, pin 3 of isolation amplifier U2AA and pin 4 of isolation amplifier U2AA, the other end of resistor R4 is connected to the output end of voltage follower U1A and pin 2 of isolation amplifier U2AA, the other end of capacitor C2 is connected to pin 1 of isolation amplifier U2AA, pin 5 of isolation amplifier U2AA is connected to capacitor C1 and ground, pin 6 of isolation amplifier U2AA is connected to resistor R6, the other end of resistor R6 is connected to capacitor C3 and output end CH0_P, pin 7 of isolation amplifier U2AA is connected to resistor R7, the other end of resistor R7 is connected to the other end of capacitor C3 and output end CH0_N.

[0011] As a further technical solution of the present invention: the model of the voltage follower U1A is LM358.

[0012] As a further technical solution of the present invention: the model of the isolation amplifier U2AA is CA-I S1300B25G.

[0013] As a further technical solution of the present invention: the diode TVS1 is a transient voltage suppression diode.

[0014] As a further technical solution of the present invention: the output terminal CH0_P and the output terminal CH0_P are connected to the output of the isolation amplifier / the differential analog input channel of the AD chip.

[0015] As a further technical solution of the present invention: the resistors R1, R3 and R5 are low temperature drift 25ppm resistors.

[0016] As a further technical solution of the present invention: the resistors R1 and R5 are high-power resistors above 2W.

[0017] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0018] 1: Solve the hazards caused by short circuit on the secondary side of the voltage transformer;

[0019] 2: The sampling accuracy is high, and the error is generally within 0.01%;

[0020] 3: Wide sampling range, 0.5%~150%Un (Un is the rated value);

[0021] 4: Small temperature influence, temperature drift is ±1ppm / ℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Design a block diagram for the present invention. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Reference Figure 1 A high-precision AC isolation sampling circuit that replaces the traditional PT includes a resistor R1, a resistor R2, a voltage follower U1A and an isolation amplifier U2AA, one end of the resistor R1 is connected to a varistor RV1 and one end of a secondary side of a voltage transformer, the other end of the resistor R1 is connected to a resistor R2, a resistor R3 and a diode TVS1, the other end of the resistor R2 is connected to a positive input end of the voltage follower U1A, the inverting input end of the voltage follower U1A is connected to a resistor R4, the other end of the varistor RV1 is connected to a resistor R5 and the other end of the secondary side of the voltage transformer, the other end of the resistor R5 is connected to the other end of the resistor R3 and the diode TVS1 The other end, capacitor C2, pin 3 of isolation amplifier U2AA and pin 4 of isolation amplifier U2AA, the other end of resistor R4 is connected to the output end of voltage follower U1A and pin 2 of isolation amplifier U2AA, the other end of capacitor C2 is connected to pin 1 of isolation amplifier U2AA, pin 5 of isolation amplifier U2AA is connected to capacitor C1 and ground, pin 6 of isolation amplifier U2AA is connected to resistor R6, the other end of resistor R6 is connected to capacitor C3 and output end CH0_P, pin 7 of isolation amplifier U2AA is connected to resistor R7, the other end of resistor R7 is connected to the other end of capacitor C3 and output end CH0_N.

[0025] Among them, the model of voltage follower U1A is LM358. The model of isolation amplifier U2AA is CA-IS1300B25G. Diode TVS1 is a transient voltage suppression diode. Output terminal CH0_P and output terminal CH0_P are connected to the output of the isolation amplifier / differential analog input channel of the AD chip. Resistors R1, R3, and R5 are low temperature drift 25ppm resistors. Resistors R1 and R5 are high power resistors above 2W.

[0026] Here’s how it works:

[0027] When the power grid is operating normally, a high voltage of several KV or even tens of KV is connected to the primary high voltage PT, and an AC voltage signal U1 of 0V to several hundred V will be generated on its secondary side. The voltage signal U1 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to one end of the resistor R3, and the other end of the resistor R3 is connected to one end of the resistor R5, and the other end of the resistor R5 is connected to UN. Resistors R1, R3, and R5 use low temperature drift 25ppm resistors, and resistors R1 and R5 use high power resistors of more than 2W. Resistors R1, R3, and R5 form a resistor voltage divider circuit. After voltage division, U2 = R3 / (R1+R3+R5)*U1 is obtained. When selecting the resistor value, it should be noted that when the voltage signal U1 is the largest, the voltage value of U2 must be guaranteed to be within 250mV.

[0028] Resistors R2, R4 and operational amplifier U1 form a voltage follower circuit. Voltage signal U2 outputs voltage signal U3 through the voltage follower circuit, and U3 = U2.

[0029] The voltage signal U3 is connected to the positive input terminal of the isolation amplifier U2A, and the negative input terminal is directly grounded. After the voltage signal U3 passes through the isolation amplifier CA-IS1300, a voltage signal U4 is obtained, U4=8.2*U3 (8.2 is the gain of the isolation amplifier CA-IS1300).

[0030] In this circuit, the varistor RV1 plays the role of differential mode lightning surge protection, while preventing the harm caused by the 10KV high voltage breakdown of the primary voltage transformer.

[0031] In this circuit, resistors R1 and R5 play a role in common-mode lightning surge protection, preventing common-mode surges from damaging the subsequent circuit and breaking down the device.

[0032] In this circuit, the voltage follower U1 plays the role of buffering, isolation and improving the load capacity.

[0033] In this circuit, the isolation amplifier U2A plays the role of signal amplification and isolation, and has the advantages of low temperature drift, high precision, wide input range, and high isolation.

[0034] In this circuit, resistor R6, resistor R7 and capacitor C3 form a second-order RC low-pass filter circuit, which mainly suppresses high-frequency interference.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0036] In addition, it should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment have also been appropriately combined to form other implementation modes that are easy for those skilled in the art to understand.

Claims

1. A high-precision AC isolation sampling circuit that replaces the traditional PT, including a resistor R1, a resistor R2, a voltage follower U1A and an isolation amplifier U2AA, characterized in that: One end of the resistor R1 is connected to the varistor RV1 and one end of the secondary side of the voltage transformer, the other end of the resistor R1 is connected to the resistor R2, the resistor R3 and the diode TVS1, the other end of the resistor R2 is connected to the positive phase input end of the voltage follower U1A, the negative phase input end of the voltage follower U1A is connected to the resistor R4, the other end of the varistor RV1 is connected to the resistor R5 and the other end of the secondary side of the voltage transformer, the other end of the resistor R5 is connected to the other end of the resistor R3, the other end of the diode TVS1, the capacitor C2, the pin 3 of the isolation amplifier U2AA and the isolation amplifier The other end of the resistor R4 is connected to the output end of the voltage follower U1A and the pin 2 of the isolation amplifier U2AA, the other end of the capacitor C2 is connected to the pin 1 of the isolation amplifier U2AA, the pin 5 of the isolation amplifier U2AA is connected to the capacitor C1 and the ground terminal, the pin 6 of the isolation amplifier U2AA is connected to the resistor R6, the other end of the resistor R6 is connected to the capacitor C3 and the output terminal CH0_P, the pin 7 of the isolation amplifier U2AA is connected to the resistor R7, the other end of the resistor R7 is connected to the other end of the capacitor C3 and the output terminal CH0_N.

2. According to claim 1, a high-precision AC isolation sampling circuit that replaces the traditional PT is characterized in that: The model of the voltage follower U1A is LM358.

3. A high-precision AC isolation sampling circuit that replaces the traditional PT according to claim 2, characterized in that: The model of the isolation amplifier U2AA is CA-IS1300B25G.

4. The high-precision AC isolation sampling circuit replacing the traditional PT according to claim 1 is characterized in that: The diode TVS1 is a transient voltage suppression diode.

5. The high-precision AC isolation sampling circuit that replaces the traditional PT according to claim 1 is characterized in that: The output terminal CH0_P and the output terminal CH0_P are connected to the output of the isolation amplifier / the differential analog input channel of the AD chip.

6. The high-precision AC isolation sampling circuit replacing the traditional PT according to claim 1 is characterized in that: The resistors R1, R3 and R5 are low temperature drift 25ppm resistors.

7. The high-precision AC isolation sampling circuit replacing the traditional PT according to claim 1 is characterized in that: The resistor R1 and the resistor R5 are high power resistors above 2W.

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