Device for measuring converter transformer valve side alternating current voltage

Abstract

The invention discloses a device for measuring a converter transformer valve side AC voltage, and the device comprises a main body unit which is composed of a resistance-capacitance voltage divider and is used for carrying out the voltage division of an AC-DC superposed voltage; and the secondary voltage dividing unit is connected in parallel with a capacitive voltage divider on an output terminal of the resistance-capacitance voltage divider and is used for isolating direct current voltage from the direct current component output by the main body unit. The problem of converter transformer valve side AC voltage measurement is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage electrical equipment, and particularly to a device for measuring the AC voltage on the valve side of a converter transformer. Background Art

[0002] Compared with AC power transmission, DC power transmission has the following advantages: (1) For DC overhead transmission lines, only positive and negative conductors are required, the tower structure is simple, the line cost is low, and the loss is small. (2) DC cable lines have a large transmission capacity, low cost, small loss, are not easily aged, have a long service life, and the transmission distance is not restricted. (3) DC power transmission does not have the stability problems of AC power transmission, which is beneficial for long-distance and large-capacity power transmission. (4) Using DC power transmission to achieve asynchronous networking between power systems can not increase the short-circuit capacity of the interconnected power grids, and there is no need to replace circuit breakers and take current-limiting measures due to the increase in short-circuit capacity. (5) The active power transmitted by DC power transmission and the reactive power consumed by the converters can be controlled by the control system, and this fast controllability can be used to improve the operating performance of the AC system. (6) Under the action of direct current, only resistance works, and inductance and capacitance do not work. DC power transmission uses the earth as a return circuit, and the DC current flows deep into the earth with very low resistivity. (7) DC power transmission can be conveniently constructed in phases and expanded, which is beneficial for giving full play to the investment benefits. (8) The active power transmitted by DC power transmission and the reactive power consumed by the two-terminal converter stations can be quickly controlled manually and automatically, which is beneficial for the economic operation and modern management of the power grid.

[0003] As early as 1882, a 2 kV DC power transmission project was built in Germany. After more than a hundred years of development, today, the highest voltage level of DC projects has reached ±1100 kV.

[0004] DC measuring devices are important equipment in DC projects, mainly used to provide voltage signals for voltage metering, voltage monitoring, and relay protection devices in DC projects. In today's DC systems, the positions of DC measuring devices in the DC system are as Figure 5 shown, including on the converter side and on the pole line, mainly used to measure DC voltage.

[0005] However, due to the actual needs of some projects, a voltage measuring device needs to be installed on the valve side of the converter transformer to measure the AC component of the voltage on the valve side of the converter transformer and provide a voltage signal for the neutral point offset protection of the control and protection system. The installation position and voltage of the voltage measuring device at this time are as Figure 6 shown.

[0006] Since this voltage measuring device needs to measure the AC voltage with a high DC component, neither traditional DC voltage measuring devices nor AC voltage measuring devices are applicable. Summary of the Invention

[0007] To address the above technical problems, in combination with the characteristics of the AC voltage measurement device and the DC voltage measurement device, and fully considering the insulation performance and measurement performance of the equipment under this working condition, the present invention proposes a device for measuring the AC voltage on the valve side of a converter transformer, which can achieve accurate measurement of the AC voltage in this application scenario and provide a voltage signal for the neutral point offset protection of the control and protection system. The device includes:

[0008] Including:

[0009] A main body unit, composed of a resistor-capacitor voltage divider, for dividing the AC-DC superimposed voltage;

[0010] A secondary voltage dividing unit, with a capacitor voltage divider connected in parallel to the output terminal of the resistor-capacitor voltage divider, for isolating the DC voltage of the DC component output by the main body unit.

[0011] Furthermore, the resistor-capacitor voltage divider includes:

[0012] Capacitors C1 and C2, resistors R1 and R2; where capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider;

[0013] Connect the high-voltage part and the low-voltage part in series to form the resistor-capacitor voltage divider;

[0014] The output terminal of the resistor-capacitor voltage divider outputs the divided AC-DC superimposed voltage.

[0015] Furthermore, the value of resistor R1 is between 100 MΩ and 500 MΩ, and is composed of multiple chip high-voltage glass glaze resistors connected in series and parallel;

[0016] Capacitor C1 has an oil-impregnated film-paper composite insulation structure, is composed of multiple capacitors connected in series, and the capacitance value is between 2 nF and 200 nF;

[0017] The numerical relationship between R1, C1 and R2, C2 is:

[0018]

[0019] Furthermore, the capacitor voltage divider of the secondary voltage dividing part includes: capacitors C3 and C4;

[0020] The AC voltage division ratio output by the secondary voltage dividing part is:

[0021]

[0022] The present invention also provides a device for measuring the AC voltage on the valve side of a converter transformer, including:

[0023] A main body unit, composed of a resistor-capacitor voltage divider, for dividing the AC-DC superimposed voltage;

[0024] The passive filter unit, which is composed of a passive high-pass filter, is used to connect a passive high-pass filter to the output terminals of the resistor-capacitor voltage divider to filter out the DC voltage component output by the main unit.

[0025] Furthermore, the resistor-capacitor voltage divider includes:

[0026] Capacitors C1 and C2, and resistors R1 and R2; wherein capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider;

[0027] The high-voltage part and the low-voltage part are connected in series to form the resistor-capacitor voltage divider;

[0028] The output terminals of the resistor-capacitor voltage divider output the superimposed AC-DC voltage after voltage division.

[0029] Furthermore, the value of resistor R1 is taken between 100 MΩ and 500 MΩ, and is composed of multiple chip high-voltage glass glaze resistors connected in series and parallel;

[0030] Capacitor C1 has an oil-impregnated film-paper composite insulation structure and is composed of multiple capacitors connected in series, and the capacitance value is taken between 2 nF and 200 nF;

[0031] The numerical relationship between R1, C1 and R2, C2 is:

[0032]

[0033] Furthermore, the passive high-pass filter includes: capacitor C3 and resistor R3;

[0034] The cut-off frequency of the passive high-pass filter is 10 Hz, and the relationship formula between C3 and R3 is as follows;

[0035]

[0036] Among them, R3 ≤ 1.43 kΩ, and C2 ≥ 100C3.

[0037] The present invention also provides a device for measuring the AC voltage on the valve side of a converter transformer, including:

[0038] The main unit, which is composed of a resistor-capacitor voltage divider, is used to divide the superimposed AC-DC voltage;

[0039] The active filter unit, which is composed of an active high-pass filter, is used to connect an active high-pass filter to the output terminals of the resistor-capacitor voltage divider to filter out the DC voltage component output by the main unit.

[0040] Furthermore, the resistor-capacitor voltage divider includes:

[0041] Capacitors C1 and C2, resistors R1 and R2; among them, capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider;

[0042] Connect the high-voltage part and the low-voltage part in series to form the resistor-capacitor voltage divider;

[0043] The output terminal of the resistor-capacitor voltage divider outputs the superimposed AC and DC voltage after voltage division.

[0044] Furthermore, the value of resistor R1 is taken between 100 MΩ and 500 MΩ, and is composed of multiple chip high-voltage glass glaze resistors connected in series and parallel;

[0045] Capacitor C1 has an oil-impregnated film-paper composite insulation structure, is composed of multiple capacitors connected in series, and the capacitance value is taken between 2 nF and 200 nF;

[0046] The numerical relationship between R1, C1 and R2, C2 is as follows:

[0047]

[0048] Furthermore, an active high-pass filter, including: capacitor C3, resistor R4, resistor R f and an operational amplifier;

[0049] If the cut-off frequency of the active high-pass filter is 10 Hz, the relationship between C3 and R3 is as follows;

[0050]

[0051] The input-output voltage ratio of the active high-pass filter is:

[0052]

[0053] Among them, V2 is the output voltage, V1 is the input voltage, R f is the feedback resistor, j is the imaginary unit, and ω is the angular frequency;

[0054] Set the amplification factor of the active high-pass filter to 1, then

[0055]

[0056] Then at 50 Hz, R3, C3 and R f need to satisfy the following relationship:

[0057] ωC3(R f +R3) = 1.

[0059] A device for measuring the AC voltage on the valve side of a converter transformer is proposed in the present invention. By using a resistor-capacitor voltage divider and secondary voltage division or high-pass filtering, on the one hand, the insulation problems of the equipment under AC and DC voltages are fully considered, and on the other hand, the input requirements of the control and protection device are fully considered, that is, only the AC voltage signal under AC and DC voltages is measured, solving the problem of measuring the AC voltage on the valve side of the converter transformer and providing effective support for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 FIG. is a structural diagram of a device for measuring the AC voltage on the valve side of a converter transformer provided by an embodiment of the present invention;

[0061] Figure 2 FIG. is a structural diagram of another device for measuring the AC voltage on the valve side of a converter transformer provided by an embodiment of the present invention;

[0062] Figure 3 FIG. is a structural diagram of another device for measuring the AC voltage on the valve side of a converter transformer provided by an embodiment of the present invention;

[0063] Figure 4 FIG. is the position of the DC measurement device in the DC system provided by an embodiment of the present invention;

[0064] Figure 5 FIG. is the position (VT1) of the voltage measurement device on the valve side of the converter transformer provided by an embodiment of the present invention;

[0065] Figure 6 FIG. is the voltage waveform on the valve side of the converter transformer provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0066] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0067] The present invention proposes a device for measuring the AC voltage on the valve side of a converter transformer. By utilizing the advantage of the uniform electric field of the resistor-capacitor voltage divider under the AC-DC superposed electric field, and at the same time, fully considering the characteristic that the measured signal has a high DC voltage component, through impedance matching, the parameter matching principle of the resistor-capacitor voltage divider is determined, effectively solving the measurement of the AC voltage on the valve side of the converter transformer.

[0068] To achieve the above object, the technical solution of the present invention is as follows:

[0069] The present invention proposes a device for measuring the AC voltage on the valve side of a converter transformer. There are mainly three implementation solutions. The first technical solution is a device using a capacitor voltage divider for secondary voltage division, such as Figure 1As shown in the figure, it includes two parts, a main unit and a secondary voltage dividing unit. The main unit is composed of a resistor-capacitor voltage divider and is used to divide the AC-DC superimposed voltage; the secondary voltage dividing unit is a capacitor voltage divider connected in parallel to the output terminal of the resistor-capacitor voltage divider and is used to isolate the DC voltage from the DC component output by the main unit.

[0070] The resistor-capacitor voltage divider includes:

[0071] Capacitors C1 and C2, resistors R1 and R2; among them, capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider;

[0072] The high-voltage part and the low-voltage part are connected in series to form the resistor-capacitor voltage divider;

[0073] The output terminal of the resistor-capacitor voltage divider outputs the divided AC-DC superimposed voltage.

[0074] The value of resistor R1 is between 100 MΩ and 500 MΩ and is composed of multiple chip-type high-voltage glass glaze resistors connected in series and parallel;

[0075] Capacitor C1 has an oil-impregnated film-paper composite insulation structure and is composed of multiple capacitors connected in series, and the capacitance value is between 2 nF and 200 nF;

[0076] The main unit is an oil-immersed device and is filled with capacitor oil inside.

[0077] The numerical relationship between R1, C1 and R2, C2 is:

[0078]

[0079] Since the signal after the AC-DC superimposed voltage is divided by the resistor-capacitor voltage divider still has a high DC component, and the high DC component will affect the insulation of the control and protection device. Therefore,

[0080] A capacitor voltage divider is connected in parallel to the output terminal of the resistor-capacitor voltage divider to isolate the DC voltage. Therefore, the secondary voltage dividing part of this device is a resistor-capacitor voltage divider, which is composed of C3 and C4.

[0081] The AC voltage division ratio output by the secondary voltage dividing part is:

[0082]

[0083] Inside the control and protection device, there is a small PT or resistor divider for further voltage division. For the secondary voltage division method of the capacitor divider used, its load-carrying capacity needs to be fully considered. Taking the 143 kΩ resistor divider as the secondary voltage division device of the control and protection device voltage as an example, in this case, the value of C1 needs to reach about 200 nF, and the value of C3 needs to reach 200 - 300 nF.

[0084] The second technical solution is a device using a passive high-pass filter for DC filtering, and its structure diagram is as Figure 2 shown.

[0085] This device is also divided into two parts, including a main unit and a passive filtering unit. The main unit, composed of a resistor-capacitor divider, is used for voltage division of the AC-DC superimposed voltage; the passive filtering unit, composed of a passive high-pass filter, is used to connect a passive high-pass filter to the output terminal of the resistor-capacitor divider to filter out the DC voltage component output by the main unit.

[0086] The resistor-capacitor divider includes:

[0087] Capacitors C1 and C2, resistors R1 and R2; among them, capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor divider;

[0088] Connect the high-voltage part and the low-voltage part in series to form the resistor-capacitor divider;

[0089] The output terminal of the resistor-capacitor divider outputs the AC-DC superimposed voltage after voltage division.

[0090] The value of resistor R1 is between 100 MΩ and 500 MΩ, and is composed of multiple chip-type high-voltage glass glaze resistors connected in series and parallel;

[0091] Capacitor C1 has an oil-impregnated film-paper composite insulation structure, is composed of multiple capacitors connected in series, and the capacitance value is between 2 nF and 200 nF;

[0092] The main unit is an oil-immersed device, and its interior is filled with capacitor oil.

[0093] The numerical relationship between R1, C1 and R2, C2 is:

[0094]

[0095] The passive high-pass filter includes: capacitor C3 and resistor R3;

[0096] The cut-off frequency of the passive high-pass filter is 10 Hz, and the relationship formula between C3 and R3 is as follows;

[0097]

[0098] Among them, R3 ≤ 1.43 kΩ, and C2 ≥ 100C3.

[0099] The third technical solution is a device using an active high-pass filter, and its structural diagram is as Figure 3 shown.

[0100] This device is also divided into two parts, including: a main body unit and an active filtering unit; the main body unit is composed of a resistor-capacitor voltage divider and is used to divide the AC-DC superimposed voltage; an active high-pass filter is connected to the output terminal of the capacitor voltage divider and is used to filter out the DC voltage component output by the main body unit.

[0101] The resistor-capacitor voltage divider includes:

[0102] Capacitors C1 and C2, resistors R1 and R2; among them, capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider;

[0103] The high-voltage part and the low-voltage part are connected in series to form the resistor-capacitor voltage divider;

[0104] The output terminal of the resistor-capacitor voltage divider outputs the divided AC-DC superimposed voltage.

[0105] The value of resistor R1 is between 100 MΩ and 500 MΩ and is composed of multiple chip-type high-voltage glass glaze resistors connected in series and parallel;

[0106] Capacitor C1 has an oil-impregnated film-paper composite insulation structure and is composed of multiple capacitors connected in series, and the capacitance value is between 2 nF and 200 nF;

[0107] The main body unit is an oil-immersed device and is filled with capacitor oil inside.

[0108] The numerical relationship between R1, C1 and R2, C2 is:

[0109]

[0110] The active high-pass filter includes: capacitor C3, resistor R4, resistor R f and an operational amplifier;

[0111] If the cut-off frequency of the active high-pass filter is 10 Hz, the relationship formula between C3 and R3 is as follows;

[0112]

[0113] The input-output voltage ratio of the active high-pass filter is:

[0114]

[0115] Among them, V2 is the output voltage, V1 is the input voltage, Rf is the feedback resistor, j is the imaginary unit, and ω is the angular frequency;

[0116] Since only the DC voltage component needs to be filtered out, therefore, the amplification factor of the active high-pass filter is set to 1, then

[0117]

[0118] Then at 50 Hz, R3, C3 and R f need to satisfy the following relational expression:

[0119] ωC3(R f +R3) = 1.

[0121] A device for measuring the AC voltage on the valve side of a converter transformer proposed by the present invention utilizes a resistor-capacitor voltage divider and secondary voltage division or high-pass filtering. On the one hand, it fully considers the insulation problem of the equipment under AC and DC voltages, and on the other hand, it fully considers the input requirements of the control and protection device, that is, only measures the AC voltage signal under AC and DC voltages, solves the problem of measuring the AC voltage on the valve side of the converter transformer, and provides effective support for engineering applications.

[0122] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0123] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the processes and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the specified functions in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0124] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured product including an instruction device, and the instruction device realizes the functions in the processFigure 1 one process or multiple processes and / or blocks Figure 1 the functions specified in one block or multiple blocks

[0125] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the specific implementation manners of the present invention can still be modified or equivalently replaced. Any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A device for measuring the AC voltage on the valve side of a converter transformer, characterized in that Comprising: A main body unit, composed of a resistor-capacitor voltage divider, for dividing the AC-DC superimposed voltage. A secondary voltage dividing unit, with a capacitor voltage divider connected in parallel to the output terminal of the resistor-capacitor voltage divider, for isolating the DC voltage of the DC component output by the main body unit.

2. The measuring device according to claim 1, characterized in that, The resistor-capacitor voltage divider includes: Capacitors C1 and C2, resistors R1 and R2; wherein capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider. The high-voltage part and the low-voltage part are connected in series to form the resistor-capacitor voltage divider. The output terminal of the resistor-capacitor voltage divider outputs the divided AC-DC superimposed voltage.

3. The device according to claim 2, wherein The value of resistor R1 is between 100 MΩ and 500 MΩ, and is composed of multiple chip-type high-voltage glass glaze resistors connected in series and parallel. Capacitor C1 has an oil-impregnated film-paper composite insulation structure, is composed of multiple capacitors connected in series, and the capacitance value is between 2 nF and 200 nF. The numerical relationship between R1, C1 and R2, C2 is:

4. The device according to claim 1, characterized in that The capacitor voltage divider of the secondary voltage dividing part includes: capacitors C3 and C4. The AC voltage division ratio output by the secondary voltage dividing part is:

5. A device for measuring the AC voltage on the valve side of a converter transformer, characterized in that, Comprising: A main body unit, composed of a resistor-capacitor voltage divider, for dividing the AC-DC superimposed voltage. A passive filter unit, composed of a passive high-pass filter, for connecting a passive high-pass filter to the output terminal of the resistor-capacitor voltage divider, for filtering out the DC voltage component output by the main body unit.

6. The device according to claim 1, characterized in that, The resistor-capacitor voltage divider includes: Capacitors C1 and C2, resistors R1 and R2; wherein capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider. The high-voltage part and the low-voltage part are connected in series to form the resistor-capacitor voltage divider. The output terminal of the resistor-capacitor voltage divider outputs the divided AC-DC superimposed voltage.

7. The device according to claim 6, characterized in that, The value of resistor R1 is between 100 MΩ and 500 MΩ, and is composed of multiple chip-type high-voltage glass glaze resistors connected in series and parallel. Capacitor C1 has an oil-impregnated film-paper composite insulation structure, is composed of multiple capacitors connected in series, and the capacitance value is between 2 nF and 200 nF. The numerical relationship between R1, C1 and R2, C2 is:

8. The device according to claim 5, characterized in that, The passive high-pass filter includes: capacitor C3 and resistor R3. If the cut-off frequency of the passive high-pass filter is 10 Hz, the relationship formula between C3 and R3 is as follows; Wherein, R3 ≤ 1.43 kΩ, C2 ≥ 100C3.

9. A device for measuring the AC voltage on the valve side of a converter transformer, characterized in that, Comprising: A main body unit, composed of a resistor-capacitor voltage divider, for dividing the AC-DC superimposed voltage. An active filter unit, composed of an active high-pass filter, for connecting an active high-pass filter to the output terminal of the resistor-capacitor voltage divider, for filtering out the DC voltage component output by the main body unit.

10. The device according to claim 1, characterized in that, The resistor-capacitor voltage divider includes: Capacitors C1 and C2, resistors R1 and R2; wherein capacitor C1 and resistor R1 are connected in parallel to form the high-voltage part of the resistor-capacitor voltage divider; capacitor C2 and R2 are connected in parallel to form the low-voltage part of the resistor-capacitor voltage divider. The high-voltage part and the low-voltage part are connected in series to form the resistor-capacitor voltage divider. The output terminal of the resistor-capacitor voltage divider outputs the divided AC-DC superimposed voltage.

11. The device according to claim 10, characterized in that, The value of resistor R1 is between 100 MΩ and 500 MΩ, and it is composed of multiple chip high-voltage glass glaze resistors connected in series and parallel; Capacitor C1 has an oil-impregnated film-paper composite insulation structure and is composed of multiple capacitors connected in series. The capacitance value is between 2 nF and 200 nF; The numerical relationship between R1, C1 and R2, C2 is:

12. The device according to claim 9, wherein Active high-pass filter, comprising: capacitor C3, resistor R4, resistor R f and operational amplifier; If the cut-off frequency of the active high-pass filter is 10 Hz, the relationship formula between C3 and R3 is as follows; The input-output voltage ratio of the active high-pass filter is: Among them, V2 is the output voltage, V1 is the input voltage, R f is the feedback resistor, j is the imaginary unit, and ω is the angular frequency; If the amplification factor of the active high-pass filter is set to 1, then Then at 50 Hz, R3, C3 and R f shall satisfy the following relational expression: ωC3(R f +R3) = 1.

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