A high-reliability lightning surge protection circuit for power distribution automation terminals

Abstract

This utility model discloses a high-reliability lightning surge protection circuit for a power distribution automation terminal, including an input discharge circuit, an AC rectifier circuit, and a filter circuit. The input discharge circuit includes Y capacitors C1, C2, and C3, as well as a relay K1, a varistor RV1, RV2, and RV3. The coil of relay K1 is connected between the positive terminal Vout and the negative terminal GND of the switching power supply output. This utility model not only meets the requirements for insulation strength testing and lightning surge testing, but also has the advantages of small size, low cost, and high reliability.

Description

Technical Field

[0001] This utility model relates to a protection circuit, specifically a lightning surge protection circuit for a power distribution automation terminal. Background Technology

[0002] Distribution automation terminals must not only ensure they will not break down under a certain insulation voltage, but also possess a certain surge immunity capability to withstand impacts from lightning strikes, switching transients, and other disturbances. Therefore, before leaving the factory, distribution automation terminals need to undergo insulation strength tests and surge (impulse) immunity tests.

[0003] The traditional solution involves connecting a varistor and a gas discharge tube in parallel between the input power supply and ground to improve insulation strength and surge immunity. However, insulation strength tests for distribution automation terminal equipment typically require a voltage of 2500VAC, with a peak voltage of 2500V * 1.414 = 3535V. This means that both the varistor and the gas discharge tube must have an operating voltage greater than 3535V. Surge (impulse) immunity tests, on the other hand, require the operating voltage of both the varistor and the gas discharge tube to be less than 4000VDC. Since the varistor has a 10% tolerance and the gas discharge tube has a 20% tolerance, this solution is difficult to implement in practice while simultaneously meeting both insulation strength and surge immunity requirements.

[0004] To address the aforementioned issues, existing technologies have proposed solutions using safety capacitors and common-mode inductors. For example, Chinese invention patent application CN117638832A proposes a common-mode lightning surge protection circuit that balances equipment insulation withstand voltage performance. It places only a safety capacitor (Y capacitor) between the power input and the protective earth (PE) casing for discharge, while a large-capacity common-mode inductor is used for filtering in subsequent circuits. However, this design requires a large-capacity common-mode inductor to meet surge (impulse) immunity test requirements, resulting in large size and high cost. Utility Model Content

[0005] This utility model proposes a high-reliability lightning surge protection circuit for power distribution automation terminals. Its purpose is to solve the problem that existing solutions require the use of large-capacity common-mode inductors to suppress common-mode interference, resulting in excessive size.

[0006] The technical solution of this utility model is as follows:

[0007] A high-reliability lightning surge protection circuit for a power distribution automation terminal includes an AC rectifier circuit and a filter circuit. The three-phase input terminals of the power distribution automation terminal are connected to the input terminals of the switching power supply of the power distribution automation terminal in sequence through the AC rectifier circuit and the filter circuit. The filter circuit is equipped with a common-mode inductor. The high-reliability lightning surge protection circuit for the power distribution automation terminal also includes an input discharge circuit.

[0008] The input discharge circuit includes Y capacitors C1, C2, and C3. The three-phase input terminals UA, UB, and UC are connected to the metal casing connection terminal PE of the power distribution automation terminal through Y capacitors C1, C2, and C3, respectively.

[0009] The input discharge circuit also includes a relay K1, a varistor RV1, a varistor RV2, and a varistor RV3. The three-phase input terminals UA, UB, and UC are respectively connected to one end of the normally open contact of the relay K1 through the varistor RV1, varistor RV2, and varistor RV3. The other end of the normally open contact of the relay K1 is connected to the metal casing connection terminal PE.

[0010] The coil of relay K1 is connected between the positive terminal Vout and the negative terminal GND of the switching power supply output.

[0011] As a further improvement to the high-reliability lightning surge protection circuit of the power distribution automation terminal: the AC rectifier circuit includes rectifier bridge V1 and rectifier bridge V2, UA and UB are respectively connected to the two AC input terminals of rectifier bridge V1, and UC is simultaneously connected to the two AC input terminals of rectifier bridge V2.

[0012] The AC rectifier circuit also includes a varistor RV4; the positive output of rectifier bridge V1 is connected to the positive output of rectifier bridge V2, and is also connected to one end of varistor RV4; the negative output of rectifier bridge V1 is connected to the negative output of rectifier bridge V2, and is also connected to the other end of varistor RV4; one end and the other end of varistor RV4 serve as the positive and negative outputs of the AC rectifier circuit, respectively.

[0013] As a further improvement to the high-reliability lightning surge protection circuit of the power distribution automation terminal, the filtering circuit includes an LC differential mode filter circuit, a two-stage common mode filter circuit, and a capacitor energy storage filter circuit connected in sequence between the AC rectifier circuit and the switching power supply.

[0014] As a further improvement to the high-reliability lightning surge protection circuit of the power distribution automation terminal: the LC differential mode filter circuit includes inductor L1, inductor L2 and X capacitor C4;

[0015] The positive output terminal of the AC rectifier circuit is connected to one end of the X capacitor C4 through inductor L1, and the negative output terminal of the AC rectifier circuit is connected to the other end of the X capacitor C4 through inductor L2.

[0016] One end of capacitor C4 serves as the positive and negative output terminals of the LC differential filter circuit, respectively.

[0017] As a further improvement to the high-reliability lightning surge protection circuit of the power distribution automation terminal: the secondary common-mode filter circuit includes a common-mode inductor L3, a common-mode inductor L4, an X capacitor C5, a Y capacitor C6, and a Y capacitor C7;

[0018] The positive and negative output terminals of the LC differential mode filter circuit are connected to the two input terminals of the common mode inductor L3, respectively. The two output terminals of the common mode inductor L3 are connected to the two ends of the X capacitor C5, respectively. One end of the X capacitor C5 is connected to the metal casing connection terminal PE through the Y capacitor C6, and the other end of the X capacitor C5 is connected to the metal casing connection terminal PE through the Y capacitor C7. The two ends of the X capacitor C5 are also connected to the two input terminals of the common mode inductor L4, respectively. The two output terminals of the common mode inductor L4 are the positive and negative output terminals of the two-stage common mode filter circuit, respectively.

[0019] As a further improvement to the high-reliability lightning surge protection circuit of the power distribution automation terminal: the capacitor energy storage filter circuit includes a resistor R1, an X capacitor C8, an electrolytic capacitor C9, a film capacitor C10, and a capacitor C11.

[0020] The positive and negative output terminals of the two-stage common-mode filter circuit are connected to the two ends of capacitor X C8, respectively. Resistor R1, electrolytic capacitor C9, film capacitor C10 and capacitor C11 are connected in parallel with capacitor X C8, respectively. The two ends of capacitor X C8 are connected to the positive and negative input terminals of the switching power supply, respectively.

[0021] Compared to existing technologies, this invention offers the following advantages: By incorporating a relay into the input discharge circuit, the relay remains open during insulation strength testing because the equipment is not connected to operating voltage. The relay's withstand voltage characteristic is sufficient to meet the insulation strength requirements. During surge (impulse) immunity testing, the relay automatically closes under the influence of the switching power supply output. Since three varistors are connected in the input discharge circuit, the filter circuit does not require a large-capacity common-mode inductor. This invention not only meets the requirements for insulation strength testing and lightning surge testing but also boasts advantages such as small size, low cost, and high reliability. Attached Figure Description

[0022] Figure 1 This is the circuit diagram of this utility model. Detailed Implementation

[0023] The technical solution of this utility model will be described in detail below with reference to the accompanying drawings:

[0024] like Figure 1 A high-reliability lightning surge protection circuit for power distribution automation terminals includes an input discharge circuit, an AC rectifier circuit, and a filter circuit.

[0025] The three-phase input terminals of the power distribution automation terminal are connected to the input terminals of the power distribution automation terminal's switching power supply in sequence through an AC rectifier circuit and a filter circuit.

[0026] The input discharge circuit includes Y capacitors C1, C2, and C3. The three-phase input terminals UA, UB, and UC are connected to the metal casing connection terminal PE of the power distribution automation terminal through Y capacitors C1, C2, and C3, respectively.

[0027] The input discharge circuit also includes a relay K1, a varistor RV1, a varistor RV2, and a varistor RV3. The three-phase input terminals UA, UB, and UC are respectively connected to one end of the normally open contact of the relay K1 through the varistor RV1, varistor RV2, and varistor RV3. The other end of the normally open contact of the relay K1 is connected to the metal casing connection terminal PE.

[0028] The coil of relay K1 is connected between the positive terminal Vout and the negative terminal GND of the switching power supply output.

[0029] The withstand voltage between the normally open contacts of the relay must be greater than 2500V. If a relay with a lower withstand voltage is selected, a gas discharge tube needs to be connected in series in the circuit. However, an excessively high operating value of the gas discharge tube may reduce its ability to filter common-mode signals. Relays such as Hongfa HF140FF or HF161F-W are suitable, both with a withstand voltage between normally open contacts of AC2500V. Hongfa HF36F-W relays are also an option, with a withstand voltage between normally open contacts of AC3000V. Varistors RV1-RV3 can be selected from models such as 20D821K, 20D911K, and 20D112K. The breakdown voltage of 20D821K is 820V, 20D911K is 910V, and 20D112K is 1000V. For higher surge test ratings, 32D varistor models can be selected.

[0030] Furthermore, the AC rectifier circuit includes rectifier bridges V1 and V2. UA and UB are connected to the two AC input terminals of rectifier bridge V1, respectively, and UC is simultaneously connected to the two AC input terminals of rectifier bridge V2. The AC rectifier circuit also includes a varistor RV4. The positive output terminal of rectifier bridge V1 is connected to the positive output terminal of rectifier bridge V2 and to one end of varistor RV4. The negative output terminal of rectifier bridge V1 is connected to the negative output terminal of rectifier bridge V2 and to the other end of varistor RV4. One end and the other end of varistor RV4 serve as the positive and negative output terminals of the AC rectifier circuit, respectively.

[0031] The RV4 varistor can be selected as 14D471K, which has a breakdown voltage of 470V. For higher surge test ratings, 20D or 32D varistor models can be selected.

[0032] Furthermore, the filtering circuit includes an LC differential mode filter circuit, a two-stage common mode filter circuit, and a capacitor energy storage filter circuit connected in sequence between the AC rectifier circuit and the switching power supply.

[0033] The LC differential-mode filter circuit includes inductors L1 and L2, and capacitor C4. The positive output terminal of the AC rectifier circuit is connected to one end of capacitor C4 through inductor L1, and the negative output terminal of the AC rectifier circuit is connected to the other end of capacitor C4 through inductor L2. One end and the other end of capacitor C4 serve as the positive and negative output terminals of the LC differential-mode filter circuit, respectively.

[0034] The two-stage common-mode filter circuit includes a common-mode inductor L3, a common-mode inductor L4, an X capacitor C5, a Y capacitor C6, and a Y capacitor C7. The positive and negative output terminals of the LC differential-mode filter circuit are connected to the two input terminals of the common-mode inductor L3, respectively. The two output terminals of the common-mode inductor L3 are connected to the two ends of the X capacitor C5, respectively. One end of the X capacitor C5 is connected to the PE terminal of the metal casing through the Y capacitor C6, and the other end of the X capacitor C5 is connected to the PE terminal of the metal casing through the Y capacitor C7. The two ends of the X capacitor C5 are also connected to the two input terminals of the common-mode inductor L4, respectively. The two output terminals of the common-mode inductor L4 are the positive and negative output terminals of the two-stage common-mode filter circuit, respectively.

[0035] The capacitor energy storage and filtering circuit includes a resistor R1, an X capacitor C8, an electrolytic capacitor C9, a film capacitor C10, and a capacitor C11. The positive and negative output terminals of the two-stage common-mode filter circuit are connected to the two ends of the X capacitor C8, respectively. The resistor R1, electrolytic capacitor C9, film capacitor C10, and capacitor C11 are connected in parallel with the X capacitor C8. The two ends of the X capacitor C8 are connected to the positive and negative input terminals of the switching power supply, respectively.

[0036] The discharge resistor R1 is generally selected as a resistor in the MΩ range or a resistor in the hundreds of KΩ range. Its main function is to discharge the safety capacitor X capacitor and the energy storage capacitor, while the power must meet the design requirements.

[0037] The high voltage DC+ obtained through the capacitor energy storage and filtering circuit is converted into an isolated low voltage Vout through the switching power supply, and Vout supplies power to the entire power distribution automation terminal.

[0038] The circuit operates as follows during testing:

[0039] 1. When performing insulation strength testing, the equipment is not powered on. Short-circuit UA, UB, and UC to conduct a 2500V test on the PE casing. At this time, relay K1 is not energized, and there is a withstand voltage between the normally open contacts. The overall withstand voltage of the equipment is the lowest value of the varistor RV1, RV2, and RV3 plus the withstand voltage between the contacts of relay K1. Since the withstand voltage between the normally open contacts of the selected relay is greater than 2500V, the insulation strength test can be easily met.

[0040] 2. Surge (impulse) immunity tests include ±4000V common-mode surge tests and ±2000V differential-mode surge tests:

[0041] 2.1. Surge common mode test of ±4000V.

[0042] When the device is powered on, a voltage exists between Vout and GND, energizing the relay K1 coil and closing its normally open contacts. During surge common-mode testing, safety capacitors C1, C2, and C3 absorb some energy, while varistors RV1, RV2, and RV3 clamp the high voltage, protecting downstream circuits from overvoltage damage. However, the varistors have a relatively high residual voltage, which, after passing through the rectifier bridge and common-mode inductor L3, significantly attenuates the interference signal. Simultaneously, L3, together with safety capacitors C6 and C7, forms an LC absorption capacitor, filtering out high-frequency interference components. Finally, the common-mode interference signal is isolated from the switching power supply by common-mode inductor L4.

[0043] 2.2 Surge differential mode test of ±2000V.

[0044] Surge differential mode tests of ±2000V are performed between UA and UB, UB and UC, and UA and UC respectively. Taking UA and UB as an example: When the equipment is powered on, there will be a voltage between Vout and GND, energizing the coil of relay K1 and closing its normally open contact. During the surge differential mode test, the varistor RV1 and RV2 between UA and UB clamp the surge signal, protecting the downstream circuit from overvoltage damage. After the rectifier bridge, the varistor RV4 clamps the signal again. L1 and C4 form an LC filter circuit, and L2 and C4 also form an LC filter circuit. C4, L3, and C5 form a π-type filter, and C5, L4, and C8 similarly form a π-type filter. The film capacitor C10 has a strong ability to filter high-frequency signals, ultimately isolating the differential mode interference signal outside the switching power supply.

[0045] After testing, this circuit can meet the insulation strength test requirements of 3000VAC and above, as well as the lightning surge test requirements of 0.5KVAC~12KVAC. It also has the advantages of small size, low cost and high reliability.

Claims

1. A high-reliability lightning surge protection circuit for a power distribution automation terminal, comprising an AC rectifier circuit and a filter circuit, wherein the three-phase input terminals of the power distribution automation terminal are sequentially connected to the input terminals of the switching power supply of the power distribution automation terminal through the AC rectifier circuit and the filter circuit, and the filter circuit includes a common-mode inductor; characterized in that: The high-reliability lightning surge protection circuit for power distribution automation terminals also includes an input discharge circuit; The input discharge circuit includes Y capacitors C1, C2, and C3. The three-phase input terminals UA, UB, and UC are connected to the metal casing connection terminal PE of the power distribution automation terminal through Y capacitors C1, C2, and C3, respectively. The input discharge circuit also includes a relay K1, a varistor RV1, a varistor RV2, and a varistor RV3. The three-phase input terminals UA, UB, and UC are respectively connected to one end of the normally open contact of the relay K1 through the varistor RV1, varistor RV2, and varistor RV3. The other end of the normally open contact of the relay K1 is connected to the metal casing connection terminal PE. The coil of relay K1 is connected between the positive terminal Vout and the negative terminal GND of the switching power supply output. The AC rectifier circuit includes rectifier bridge V1 and rectifier bridge V2. The three-phase input terminals UA and UB are respectively connected to the two AC input terminals of rectifier bridge V1, and the three-phase input terminal UC is simultaneously connected to the two AC input terminals of rectifier bridge V2. The AC rectifier circuit also includes a varistor RV4; the positive output of rectifier bridge V1 is connected to the positive output of rectifier bridge V2, and is also connected to one end of varistor RV4; the negative output of rectifier bridge V1 is connected to the negative output of rectifier bridge V2, and is also connected to the other end of varistor RV4; one end and the other end of varistor RV4 serve as the positive and negative output terminals of the AC rectifier circuit, respectively. The filtering circuit includes an LC differential mode filter circuit, a two-stage common mode filter circuit, and a capacitor energy storage filter circuit connected sequentially between the AC rectifier circuit and the switching power supply. The LC differential mode filter circuit includes inductor L1, inductor L2, and X capacitor C4; The positive output terminal of the AC rectifier circuit is connected to one end of the X capacitor C4 through inductor L1, and the negative output terminal of the AC rectifier circuit is connected to the other end of the X capacitor C4 through inductor L2. One end of capacitor C4 serves as the positive and negative output terminals of the LC differential-mode filter circuit, respectively. The secondary common-mode filter circuit includes a common-mode inductor L3, a common-mode inductor L4, an X capacitor C5, a Y capacitor C6, and a Y capacitor C7; The positive and negative output terminals of the LC differential-mode filter circuit are connected to the two input terminals of the common-mode inductor L3, respectively. The two output terminals of the common-mode inductor L3 are connected to the two ends of the X capacitor C5. One end of the X capacitor C5 is connected to the metal casing connection terminal PE through the Y capacitor C6, and the other end of the X capacitor C5 is connected to the metal casing connection terminal PE through the Y capacitor C7. The two ends of the X capacitor C5 are also connected to the two input terminals of the common-mode inductor L4, respectively. The two output terminals of the common-mode inductor L4 are the positive and negative output terminals of the two-stage common-mode filter circuit, respectively. The capacitor energy storage and filtering circuit includes resistor R1, capacitor C8 (X), electrolytic capacitor C9, film capacitor C10, and capacitor C11. The positive and negative output terminals of the two-stage common-mode filter circuit are connected to the two ends of capacitor X C8, respectively. Resistor R1, electrolytic capacitor C9, film capacitor C10 and capacitor C11 are connected in parallel with capacitor X C8, respectively. The two ends of capacitor X C8 are connected to the positive and negative input terminals of the switching power supply, respectively.

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