A current phase compensation circuit for transformer differential protection

Abstract

The application discloses a current phase compensation circuit for transformer differential protection, and mainly solves the problem of excessive error of current differential quantity and braking quantity in traditional differential protection scheme, which reduces the sensitivity and reliability of protection. The circuit comprises a load, a transformer set, a filter set and a main inverter set connected in sequence, further comprises a driving circuit connected with the main inverter set, a PWM control circuit connected with the driving circuit, a phase-shifting unit circuit connected with the PWM control circuit and a phase detection circuit connected with the phase-shifting unit circuit. The application detects the phase of three-phase power supply connected with the transformer through the phase detection circuit, realizes the current phase compensation of the input three-phase power supply through the control of the phase-shifting unit circuit by the control signal fed back by the phase detection circuit, and feeds back to the inverter set through the PWM control circuit and the driving circuit, so as to reduce the error of current differential quantity and braking quantity, and improve the sensitivity and reliability of differential protection.

Description

Technical Field

[0001] This invention belongs to the field of transformer protection technology, specifically, it relates to a current phase compensation circuit for transformer differential protection. Background Technology

[0002] In nuclear waste disposal, a continuous power supply is typically required to ensure safety during the nuclear reprocessing process. Therefore, nuclear reprocessing units usually need to have their own backup power supplies. Power transformers, as a large number of main electrical devices used in power systems, are essential for the reliable operation of the power system. In existing technology, three-phase transformers generally employ a dual configuration of longitudinal differential protection and gas protection as the main protection. In traditional longitudinal differential protection, the current transformer is installed on the lead-out line between the transformer and the circuit breaker, capable of detecting phase-to-phase short-circuit faults in the transformer windings and leads, as well as ground faults and inter-turn short-circuit faults in the grid-side windings and leads of a directly grounded neutral system. The current flowing through the differential relay is the unbalanced current during normal transformer operation or external faults, and the total fault current during internal faults. To meet selectivity requirements, the operating current of the differential relay must be greater than the maximum unbalanced current.

[0003] According to the technical specification for relay protection and automatic safety devices GB / T14285-2006, high-power transformers require differential protection as their main protection. Compared with ordinary transformers, multi-winding phase-shifting transformers have a special electrical structure, with a large number of secondary windings and phase shifts between windings that are not integer clock points. Differential protection schemes suitable for ordinary transformers cannot meet the differential protection requirements of multi-winding phase-shifting transformers. Continuing to use traditional differential protection schemes will result in excessive errors in the calculated differential current and braking quantity, reducing the sensitivity and reliability of the protection, and easily causing false tripping or failure to trip. Summary of the Invention

[0004] The purpose of this invention is to provide a current phase compensation circuit for transformer differential protection, which mainly solves the problem that the error between the current differential amount and the braking amount in traditional differential protection schemes is too large, which reduces the sensitivity and reliability of the protection.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A current phase compensation circuit for transformer differential protection includes a load, a transformer group, a filter group, and a main inverter group connected in sequence. It also includes a drive circuit connected to the main inverter group, a PWM control circuit connected to the drive circuit, a phase shifting unit circuit connected to the PWM control circuit, and a phase detection circuit connected to the phase shifting unit circuit.

[0007] The phase-shifting unit circuit includes a transistor Q1 whose base is connected to the phase detection circuit; a resistor R4 whose one end is connected to the collector of transistor Q1 and whose other end is connected to a +5V voltage; a resistor R5 whose one end is connected to the +5V voltage port of resistor R1; a transistor Q2 whose collector is connected to the other end of resistor R5 and whose base is grounded; a resistor R6 whose one end is connected to the emitters of both transistors Q1 and Q2 and whose other end is connected to a -5V voltage; a capacitor C4 whose one end is connected to the emitter of transistor Q1 and whose other end is connected to the input signal; a capacitor C5 whose one end is connected to the collector of transistor Q2; a resistor R7 whose one end is connected to the collector of transistor Q1 and whose other end is connected to the other end of capacitor C5; a capacitor C6 whose one end is connected to the common terminal of resistor R7 and capacitor C5; and a resistor R8 whose one end is connected to the other end of capacitor C6 and whose other end is grounded. The common terminal of resistor R7, capacitor C5, and capacitor C6 serves as the output terminal of the phase-shifting unit circuit.

[0008] Furthermore, in this invention, the phase detection circuit includes an isolating switch K. The first phase voltage and the second phase voltage of the three-phase AC power supply are respectively applied to the first input control terminal and the second input control terminal of the isolating switch K. The phase detection circuit outputs a control signal to one end of the capacitor C4 of the phase shifting unit circuit according to the signal of the controlled output terminal of the isolating switch K. The first phase voltage is connected to the first input control terminal through a series resistor R9 and a diode D1, and the second phase voltage is connected to the second input control terminal through a resistor R10. A diode D2 is also connected between the first input control terminal and the second input control terminal.

[0009] Furthermore, in this invention, the drive circuit includes a coupling device chip IC1 of model HCPL-3180, a capacitor C7 connected in parallel with one end connected to the ANODE pin of chip IC1 and the other end grounded, a resistor R11, a resistor R12 connected to the ANODE pin of chip IC1, a plug P1 connected to the other end of resistor R12, a capacitor C8 connected to the VCC pin of chip IC1 and the other end grounded, and a plug P2 connected to the VO pin of chip IC1; wherein, the N / C, CATHODE, and VEE pins of chip IC1 are grounded, and the VCC pin of chip IC1 is connected to a 10V voltage; wherein, plug P1 is connected to the PWM control circuit, and plug P2 is connected to the main inverter group.

[0010] Further, in this invention, the PWM control circuit includes a PWM logic controller, an electrolytic capacitor C9 whose positive terminal is connected to the PB7 pin of the PWM logic controller and whose negative terminal is grounded, a resistor R21 connected to the PB7 pin of the PWM logic controller, a capacitor C10 whose one end is connected to the other end of the resistor R21 and the PB6 pin of the PWM logic controller and whose other end is grounded, a capacitor C11 whose one end is connected to the PC3 pin of the PWM logic controller and whose other end is grounded, resistors R14 and R15 connected to the PB5 pin of the PWM logic controller, a capacitor C12 connected between the other ends of resistors R14 and R15, a resistor R16 and a capacitor C13 connected in parallel with one end connected to the PB4 pin of the PWM logic controller and whose other end is grounded, and a resistor connected between the PB4 pin and the PC1 pin of the PWM logic controller. R17, resistor R18 connected between pins PA5 and PA4 of the PWM logic controller, inductor L4 connected to pin PA5 of the PWM logic controller, diode D3 whose negative terminal is connected to pin PB6 of the PWM logic controller and whose positive terminal is connected to the other end of inductor L4 via resistor R19, diode D4 whose positive terminal is connected to the other end of inductor L4 and whose negative terminal is connected to the common terminal of resistor R15 and capacitor C12, diode D5 whose negative terminal is connected to pin PA4 of the PWM logic controller and whose positive terminal is connected to connector P1 in the drive circuit, electrolytic capacitor C14 whose positive terminal is connected to the positive terminal of diode D4 and whose negative terminal is connected to the positive terminal of diode D5, resistor R20 connected in parallel across electrolytic capacitor C14, and diode D6 whose positive terminal is connected to the output terminal of the phase shift unit circuit and whose negative terminal is connected to pin PB7 of the PWM logic controller.

[0011] Furthermore, in this invention, the filter of the filter bank is an LC filter composed of capacitors and inductors.

[0012] Furthermore, in this invention, a DC-side voltage source is connected to one side of the main inverter group.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] This invention uses a phase detection circuit to detect the phase of the three-phase power supply connected to the transformer. The control signal fed back from the phase detection circuit controls the phase shifting unit circuit to achieve current phase compensation of the input three-phase power supply. The feedback is then sent to the inverter group through a PWM control circuit and a drive circuit, thereby reducing the error between the current differential and the braking amount and improving the sensitivity and reliability of the differential protection. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0016] Figure 2This is a schematic diagram of the phase-shifting unit circuit in this invention.

[0017] Figure 3 This is a schematic diagram of the phase detection circuit in this invention.

[0018] Figure 4 This is a schematic diagram of the driving circuit in this invention.

[0019] Figure 5 This is a schematic diagram of the PWM control circuit in this invention.

[0020] Figure 6 This is a schematic diagram of the conduction of a phase-shifting unit circuit in an embodiment of the present invention.

[0021] Figure 7 This is another conduction schematic diagram of the phase-shifting unit circuit in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0023] Example

[0024] like Figure 1 As shown, this invention discloses a current phase compensation circuit for transformer differential protection, comprising a load, a transformer bank, a filter bank, and a main inverter bank connected in sequence. It also includes a drive circuit connected to the main inverter bank, a PWM control circuit connected to the drive circuit, a phase-shifting unit circuit connected to the PWM control circuit, and a phase detection circuit connected to the phase-shifting unit circuit. The filter bank uses an LC filter composed of a capacitor and an inductor. A DC voltage source is connected to one side of the main inverter bank. This compensation circuit detects the phase of the three-phase power supply connected to the transformer through the phase detection circuit. The control signal fed back from the phase detection circuit controls the phase-shifting unit circuit to achieve current phase compensation of the input three-phase power supply. This compensation is then fed back to the inverter bank through the PWM control circuit and the drive circuit, thereby reducing the error between the current differential and braking amounts and improving the sensitivity and reliability of the differential protection.

[0025] like Figure 2As shown, in this embodiment, the phase-shifting unit circuit includes a transistor Q1 whose base is connected to the phase detection circuit; a resistor R4 whose one end is connected to the collector of transistor Q1 and whose other end is connected to a +5V voltage; a resistor R5 whose one end is connected to the port of resistor R1 connected to a +5V voltage; a transistor Q2 whose collector is connected to the other end of resistor R5 and whose base is grounded; a resistor R6 whose one end is connected to the emitters of both transistors Q1 and Q2 and whose other end is connected to a -5V voltage; and a resistor R6 whose one end is connected to the emitter of transistor Q1. A capacitor C4 is connected to the emitter of transistor Q1 and the other end is connected to the input signal; a capacitor C5 is connected to the collector of transistor Q2; a resistor R7 is connected to the collector of transistor Q1 and the other end is connected to the other end of capacitor C5; a capacitor C6 is connected to the common terminal of resistor R7 and capacitor C5; and a resistor R8 is connected to the other end of capacitor C6 and grounded. The common terminal of resistor R7, capacitor C5, and capacitor C6 serves as the output terminal of the phase-shifting unit circuit. In this embodiment, the input signal is a three-phase power supply. When transistor Q1 is on and Q2 is off, as shown... Figure 6 As shown, the circuit before the signal passes through the collector is composed of pure resistors, denoted as region A; the circuit after the signal passes through the collector is denoted as region B. Since region A is composed of pure resistors, the signal phase is unaffected. Region B contains an RC circuit, which can generate a phase shift. In region B, resistor R8 is connected in parallel with capacitor C5 and resistor R7, forming a complex impedance:

[0026]

[0027] Let s = jω = j2πf, then the above equation can be simplified to:

[0028]

[0029] Resistor R7 is connected in series with Z8, acting as a voltage divider across Z8. Therefore, the output voltage v0 is:

[0030]

[0031] In the formula, v′ i Assuming the input voltage, substituting equation (2) into equation (3) yields:

[0032]

[0033] Where, v′ i If the phase of the signal is the same as that of v0, then the phase shift of the input signal by this phase shift path is:

[0034]

[0035] Similarly, when transistor Q1 is cut off and Q2 is turned on, as Figure 7 As shown, the circuit is labeled as region A and region B. From the parallel connection of capacitor C4, resistor R8, and resistor R7, we can obtain:

[0036]

[0037] Capacitor C4 is connected in series with R′8, acting as a voltage divider across R′8. Therefore, the output voltage v0 is:

[0038]

[0039] Substituting equation (6) into equation (7), we get:

[0040]

[0041] For differential protection, the total phase shift of the output signal depends on the difference between the phase shifts of the two branches:

[0042] Δθ = Δθ1 - Δθ2;

[0043] Δθ is the phase shift amount compensated by the phase shift unit circuit.

[0044] In this embodiment, the phase detection circuit includes an isolating switch K. The first phase voltage and the second phase voltage of the three-phase AC power supply are respectively applied to the first input control terminal and the second input control terminal of the isolating switch K. The phase detection circuit outputs a control signal to one end of the capacitor C4 of the phase shifting unit circuit according to the signal of the controlled output terminal of the isolating switch K. The first phase voltage is connected to the first input control terminal through a series resistor R9 and a diode D1, and the second phase voltage is connected to the second input control terminal through a resistor R10. A diode D2 is also connected between the first input control terminal and the second input control terminal. In this embodiment, the first phase is denoted as U phase and the second phase as V phase. The isolating switch K is for U and V phases. If either U phase or V phase is missing, the control terminal of the isolating switch K is closed, causing the isolating switch K to output a corresponding control signal to the phase shifting unit circuit.

[0045] In this embodiment, the drive circuit includes a coupling device chip IC1 of model HCPL-3180, a capacitor C7 connected in parallel with one end connected to the ANODE pin of chip IC1 and the other end grounded, a resistor R11 connected to the ANODE pin of chip IC1, a connector P1 connected to the other end of resistor R12, a capacitor C8 connected to the VCC pin of chip IC1 and the other end grounded, and a connector P2 connected to the VO pin of chip IC1. The N / C, CATHODE, and VEE pins of chip IC1 are grounded, and the VCC pin of chip IC1 is connected to a 10V voltage. Connector P1 is connected to the PWM control circuit, and connector P2 is connected to the main inverter group.

[0046] In this embodiment, the PWM control circuit includes a PWM logic controller, an electrolytic capacitor C9 whose positive terminal is connected to the PB7 pin of the PWM logic controller and whose negative terminal is grounded, a resistor R21 connected to the PB7 pin of the PWM logic controller, a capacitor C10 whose one end is connected to the other end of the resistor R21 and the PB6 pin of the PWM logic controller and whose other end is grounded, a capacitor C11 whose one end is connected to the PC3 pin of the PWM logic controller and whose other end is grounded, resistors R14 and R15 connected to the PB5 pin of the PWM logic controller, a capacitor C12 connected between the other ends of resistors R14 and R15, a resistor R16 and a capacitor C13 connected in parallel with one end connected to the PB4 pin of the PWM logic controller and whose other end is grounded, and a resistor R1 connected between the PB4 pin and the PC1 pin of the PWM logic controller. 7. Resistor R18 connected between pins PA5 and PA4 of the PWM logic controller; inductor L4 connected to pin PA5 of the PWM logic controller; diode D3 whose negative terminal is connected to pin PB6 of the PWM logic controller and whose positive terminal is connected to the other end of inductor L4 via resistor R19; diode D4 whose positive terminal is connected to the other end of inductor L4 and whose negative terminal is connected to the common terminal of resistor R15 and capacitor C12; diode D5 whose negative terminal is connected to pin PA4 of the PWM logic controller and whose positive terminal is connected to connector P1 in the drive circuit; electrolytic capacitor C14 whose positive terminal is connected to the positive terminal of diode D4 and whose negative terminal is connected to the positive terminal of diode D5; resistor R20 connected in parallel across electrolytic capacitor C14; and diode D6 whose positive terminal is connected to the output terminal of the phase-shifting unit circuit and whose negative terminal is connected to pin PB7 of the PWM logic controller. The PWM control circuit is mainly used for feedback control of the drive circuit, thereby reducing the error between current differential and braking amount.

[0047] Through the above design, the control signal fed back by the phase detection circuit of the present invention controls the phase shifting unit circuit to achieve current phase compensation of the input three-phase power supply, and feeds it back to the inverter group through the PWM control circuit and drive circuit, thereby reducing the error between the current differential amount and the braking amount, and improving the sensitivity and reliability of differential protection.

[0048] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A current phase compensation circuit for transformer differential protection, comprising a load, a transformer bank, a filter bank, and a main inverter bank connected in sequence, characterized in that, It also includes a drive circuit connected to the main inverter group, a PWM control circuit connected to the drive circuit, a phase shifting unit circuit connected to the PWM control circuit, and a phase detection circuit connected to the phase shifting unit circuit. The phase-shifting unit circuit includes a transistor Q1 whose base is connected to the phase detection circuit; a resistor R4 whose one end is connected to the collector of transistor Q1 and whose other end is connected to a +5V voltage; a resistor R5 whose one end is connected to the port of resistor R1 connected to a +5V voltage; a transistor Q2 whose collector is connected to the other end of resistor R5 and whose base is grounded; a resistor R6 whose one end is connected to the emitters of both transistors Q1 and Q2 and whose other end is connected to a -5V voltage; a capacitor C4 whose one end is connected to the emitter of transistor Q1 and whose other end is connected to the input signal; a capacitor C5 whose one end is connected to the collector of transistor Q2; a resistor R7 whose one end is connected to the collector of transistor Q1 and whose other end is connected to the other end of capacitor C5; a capacitor C6 whose one end is connected to the common terminal of resistor R7 and capacitor C5; and a resistor R8 whose one end is connected to the other end of capacitor C6 and whose other end is grounded. The common terminal of resistor R7, capacitor C5, and capacitor C6 serves as the output terminal of the phase-shifting unit circuit. The phase detection circuit includes an isolating switch K. The first phase voltage and the second phase voltage of the three-phase AC power supply are respectively applied to the first input control terminal and the second input control terminal of the isolating switch K. The phase detection circuit outputs a control signal to one end of the capacitor C4 of the phase shifting unit circuit according to the signal of the controlled output terminal of the isolating switch K. The first phase voltage is connected to the first input control terminal through a series resistor R9 and a diode D1, and the second phase voltage is connected to the second input control terminal through a resistor R10. A diode D2 is also connected between the first input control terminal and the second input control terminal. The PWM control circuit includes a PWM logic controller, an electrolytic capacitor C9 with its positive terminal connected to pin PB7 of the PWM logic controller and its negative terminal grounded, a resistor R21 connected to pin PB7 of the PWM logic controller, a capacitor C10 with one end connected to pin PB6 of the PWM logic controller and the other end grounded, a capacitor C11 with one end connected to pin PC3 of the PWM logic controller and the other end grounded, resistors R14 and R15 connected to pin PB5 of the PWM logic controller, a capacitor C12 connected between the other ends of resistors R14 and R15, a resistor R16 and a capacitor C13 connected in parallel with one end connected to pin PB4 of the PWM logic controller and the other end grounded, and a resistor R17 connected between pin PB4 and pin PC1 of the PWM logic controller. The following components are connected: a resistor R18 between pins PA5 and PA4 of the PWM logic controller; an inductor L4 connected to pin PA5 of the PWM logic controller; a diode D3 whose negative terminal is connected to pin PB6 of the PWM logic controller and whose positive terminal is connected to the other end of inductor L4 via resistor R19; a diode D4 whose positive terminal is connected to the other end of inductor L4 and whose negative terminal is connected to the common terminal of resistor R15 and capacitor C12; a diode D5 whose negative terminal is connected to pin PA4 of the PWM logic controller and whose positive terminal is connected to connector P1 in the drive circuit; an electrolytic capacitor C14 whose positive terminal is connected to the positive terminal of diode D4 and whose negative terminal is connected to the positive terminal of diode D5; a resistor R20 connected in parallel across electrolytic capacitor C14; and a diode D6 whose positive terminal is connected to the output terminal of the phase-shifting unit circuit and whose negative terminal is connected to pin PB7 of the PWM logic controller.

2. The current phase compensation circuit for transformer differential protection according to claim 1, characterized in that, The drive circuit includes a coupling device chip IC1 of model HCPL-3180, a capacitor C7 connected in parallel with one end connected to the ANODE pin of chip IC1 and the other end grounded, a resistor R11 connected to the ANODE pin of chip IC1, a connector P1 connected to the other end of resistor R12, a capacitor C8 connected to the VCC pin of chip IC1 and the other end grounded, and a connector P2 connected to the VO pin of chip IC1. The N / C, CATHODE, and VEE pins of chip IC1 are grounded, and the VCC pin of chip IC1 is connected to a 10V voltage. Connector P1 is connected to the PWM control circuit, and connector P2 is connected to the main inverter group.

3. The current phase compensation circuit for transformer differential protection according to claim 2, characterized in that, The filters in the filter bank are LC filters composed of capacitors and inductors.

4. The current phase compensation circuit for transformer differential protection according to claim 3, characterized in that, The main inverter unit is connected to a DC voltage source on one side.

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