A method and system for calculating light used in transformer optical differential protection based on polarization-maintaining method

Abstract

An optical calculation method and system for transformer optical differential protection based on polarization-maintaining method, relating to the technical field of relay protection. The present invention is to solve the problem of mismatch between the current phase and amplitude on both sides of the protection object when the optical differential protection in line protection is applied to the field of transformer protection at the level of differential current optical calculation scheme. The present invention adopts an optical calculation scheme of polarization-maintaining method, and the outgoing light of the light source passes through three optical current transformers in sequence. Polarization-maintaining optical fiber is used to maintain the polarization state of the incident and outgoing optical signals of each transformer, so that the final output optical signal generates an optical rotation angle that is strictly proportional to the differential current; a filter circuit is used to detect the carrier signal and the modulation wave signal of the output optical signal of the third optical current transformer and calculate the modulation ratio, and the differential current is calculated using the modulation ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of relay protection. Background Art

[0002] Relay protection is an important part of the power grid security defense system. The power system requires protection devices to reliably and quickly remove faults to ensure the safe operation of the power grid and avoid major power outages. Reliable and fast protection requires accurate measurement. However, due to fundamental problems such as electromagnetic saturation and limited frequency band, the improvement of the transient performance of conventional electromagnetic transformers has encountered bottlenecks. The improvement of the reliability and speed of protection devices has therefore been hindered.

[0003] Optical differential protection is a new concept of relay protection in power systems. It can solve the above problems well and also bring many new functions and features. It is based on key technologies such as optical measurement, optical calculation, optical drive and optical transmission, and can realize full optical protection of power grid. Optical differential protection makes full use of the transient characteristics of optical current sensors to realize full waveform protection based on optics, which is a major change in relay protection technology. At present, optical differential protection is mainly used in the field of line protection.

[0004] Optical differential protection cannot be directly applied in the field of transformer protection. It is necessary to solve the problem of unequal amplitude and phase of the line current on both sides of the protection object caused by the transformer ratio and connection group. Under normal operation and out-of-zone fault conditions, according to the assumptions of the line model, the currents on both sides of the protection object are basically the same, the differential current is close to zero, and the optical differential protection is reliable and does not operate. However, in the transformer model, the transformer ratio causes the line currents on both sides to have a multiple relationship, and the power system usually uses a star-delta connected transformer. The different wiring methods on the high and low voltage sides cause the line currents on both sides to have a phase difference. Therefore, directly introducing the star-side current and the delta-side current of the transformer into the differential protection will cause the differential current to be too large, which is easy to trigger the protection malfunction. Summary of the invention

[0005] The present invention aims to solve the problem of unequal amplitude and phase of line current on both sides of the protection object caused by transformer ratio and connection mode when optical differential protection is applied to transformer protection. A method and system for calculating light used in transformer optical differential protection based on polarization maintaining mode is provided.

[0006] A polarization-maintaining optical differential protection optical computing system for transformers comprises: a light source 1, a first optical current transformer 2, a second optical current transformer 3, a third optical current transformer 4 and a processing unit 5;

[0007] The optical signal emitted by the light source 1 passes through the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 in sequence, so that the optical signal generates an optical rotation angle The output light of the third optical current transformer 4 is incident on the processing unit 5, and optical signals are transmitted between the light source 1 and the first optical current transformer 2 and between the third optical current transformer 4 and the processing unit 5 through multimode optical fiber, and optical signals are transmitted between the first optical current transformer 2 and the second optical current transformer 3 and between the second optical current transformer 3 and the third optical current transformer 4 through polarization-maintaining optical fiber;

[0008] The Faraday magneto-optical elements of the first optical current transformer 2 and the third optical current transformer 4 are respectively located on the high-voltage side and the low-voltage side of the protected phase of the transformer, and the Faraday magneto-optical element of the second optical current transformer 3 is located on the high-voltage side of the protected adjacent phase of the transformer. Under normal operation, the phase difference between the high-voltage side of the protected phase and its adjacent phase is the same as the phase of the low-voltage side of the protected phase. The Faraday magneto-optical elements of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 can sense the magnetic field generated by the current on their respective sides, and the angles between the optical paths of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 and the current directions on their respective sides satisfy:

[0009]

[0010] Among them, θ Y1 is the angle between the optical path of the first optical current transformer 2 and the current direction on its side, θ Y2 is the angle between the optical path of the second optical current transformer 3 and the current direction on its side, θ d3 is the angle between the optical path of the third optical current transformer 4 and the current direction on its side, n T is the transformer ratio;

[0011] The processing unit 5 includes the following units:

[0012] Filter unit: used to detect the carrier signal J of the optical signal output by the third optical current transformer 4 by using a filter circuit DC and the modulated wave signal J AC ,

[0013] Modulation ratio calculation unit: used to calculate the modulation ratio m according to the following formula:

[0014]

[0015] Differential current calculation unit: used to calculate the differential current i according to the following formula d :

[0016]

[0017] Wherein, V is the Field constant of the Faraday magneto-optical element in the optical current transformer, and L is the ratio of the magnetic field integral of the Faraday magneto-optical element in the optical current transformer to the current measured by the optical current transformer.

[0018] Furthermore, the first optical current transformer 2 comprises: a first collimator, a polarizer, a first Faraday magneto-optical element and a second collimator.

[0019] The second optical current transformer 3 comprises: a third collimator, a second Faraday magneto-optical element and a fourth collimator.

[0020] The third optical current transformer 4 comprises: a fifth collimator, a third Faraday magneto-optical element, an analyzer and a sixth collimator.

[0021] The first collimator and the sixth collimator are both multimode fiber collimators, and the second collimator, the third collimator, the fourth collimator and the fifth collimator are all polarization-maintaining fiber collimators;

[0022] The output light of the light source 1 is collimated by the first collimator and then incident on the polarizer to become polarized light. The polarized light passes through the first Faraday magneto-optical element and is incident on the second collimator. The light signal after collimation by the second collimator is incident on the third collimator. The light signal after collimation by the third collimator is incident on the fourth collimator through the second Faraday magneto-optical element. The light signal after collimation by the fourth collimator is incident on the fifth collimator. The light signal after collimation by the fifth collimator is incident on the analyzer through the third Faraday magneto-optical element. The output light of the analyzer is collimated by the sixth collimator and then incident on the processing unit 5.

[0023] Furthermore, the above optical rotation angle

[0024] in, is the angle at which the polarized light is rotated by the magnetic field sensed by the first optical current transformer 2, is the angle at which the light emitted by the first optical current transformer 2 is rotated by the magnetic field sensed by the second optical current transformer 3, It is the angle at which the light emitted by the second optical current transformer 3 is rotated by the magnetic field sensed by the third optical current transformer 4 .

[0025] Furthermore, the light source 1 is an SLD light source, and the wavelength of its emitted light is 850 nm.

[0026] A method for calculating light for transformer optical differential protection based on polarization-maintaining mode, the method is implemented based on a system for calculating light for transformer optical differential protection based on polarization-maintaining mode, the system comprising: a light source 1, a first optical current transformer 2, a second optical current transformer 3 and a third optical current transformer 4;

[0027] The optical signal emitted by the light source 1 passes through the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 in sequence, so that the optical signal generates an optical rotation angle The optical signal is transmitted between the light source 1 and the first optical current transformer 2 through a multimode optical fiber, and the optical signal is transmitted between the first optical current transformer 2 and the second optical current transformer 3 and between the second optical current transformer 3 and the third optical current transformer 4 through a polarization-maintaining optical fiber;

[0028] The Faraday magneto-optical elements of the first optical current transformer 2 and the third optical current transformer 4 are respectively located on the high-voltage side and the low-voltage side of the protected phase of the transformer, and the Faraday magneto-optical element of the second optical current transformer 3 is located on the high-voltage side of the protected adjacent phase of the transformer. Under normal operation, the phase difference between the high-voltage side of the protected phase and its adjacent phase is the same as the phase of the low-voltage side of the protected phase. The Faraday magneto-optical elements of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 can sense the magnetic field generated by the current on their respective sides, and the angles between the optical paths of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 and the current directions on their respective sides satisfy:

[0029]

[0030] Among them, θ Y1 is the angle between the first optical current transformer 2 and the current direction on its side, θ Y2 is the angle between the second optical current transformer 3 and the current direction on its side, θ d3 is the angle between the third optical current transformer 4 and the current direction on its side, n T is the transformer ratio;

[0031] The light calculation method for transformer optical differential protection is:

[0032] The filter circuit is used to detect the carrier signal J of the optical signal output by the third optical current transformer. DC and the modulated wave signal J AC ,

[0033] The modulation ratio m is calculated using the following formula:

[0034]

[0035] Using the modulation ratio m, the differential current i is calculated according to the following formula: d :

[0036]

[0037] Wherein, V is the Field constant of the Faraday magneto-optical element in the optical current transformer, and L is the ratio of the magnetic field integral of the Faraday magneto-optical element in the optical current transformer to the current measured by the optical current transformer.

[0038] Furthermore, the first optical current transformer 2 comprises: a first collimator, a polarizer, a first Faraday magneto-optical element and a second collimator.

[0039] The second optical current transformer 3 comprises: a third collimator, a second Faraday magneto-optical element and a fourth collimator.

[0040] The third optical current transformer 4 comprises: a fifth collimator, a third Faraday magneto-optical element, an analyzer and a sixth collimator.

[0041] The first collimator and the sixth collimator are both multimode fiber collimators, and the second collimator, the third collimator, the fourth collimator and the fifth collimator are all polarization-maintaining fiber collimators;

[0042] The output light of the light source 1 is collimated by the first collimator and then incident on the polarizer to become polarized light. The polarized light passes through the first Faraday magneto-optical element and is incident on the second collimator. The light signal after collimation by the second collimator is incident on the third collimator. The light signal after collimation by the third collimator is incident on the fourth collimator through the second Faraday magneto-optical element. The light signal after collimation by the fourth collimator is incident on the fifth collimator. The light signal after collimation by the fifth collimator is incident on the analyzer through the third Faraday magneto-optical element. The output light of the analyzer is collimated by the sixth collimator and then incident on the processing unit 5.

[0043] Furthermore, the above optical rotation angle

[0044] in, is the angle at which the polarized light is rotated by the magnetic field sensed by the first optical current transformer 2, is the angle at which the light emitted by the first optical current transformer 2 is rotated by the magnetic field sensed by the second optical current transformer 3, It is the angle at which the light emitted by the second optical current transformer 3 is rotated by the magnetic field sensed by the third optical current transformer 4 .

[0045] Furthermore, the light source 1 is an SLD light source, and the wavelength of its emitted light is 850 nm.

[0046] The present invention sets the installation angle of each optical current transformer and the reference direction of the magnetic field it senses according to the protection criterion, and uses polarization-maintaining optical fiber to connect multiple optical current transformers corresponding to the currents to be measured, so as to simultaneously realize the optical addition and subtraction operations of the Faraday rotation angles on one optical path system, thereby realizing the addition and subtraction operations of the currents to be measured of different proportions.

[0047] The beneficial effects of the present invention are:

[0048] (1) The optical calculation implementation system for transformer optical differential protection based on polarization-maintaining method proposed in the present invention provides a differential current optical calculation solution for applying optical differential protection in the field of transformer protection. By changing the calculation method of differential current to adapt it to the requirements of transformer protection, the problem of excessive differential current caused by the mismatch of current phase and amplitude on both sides of the transformer is effectively solved. By adopting the optical calculation solution of polarization-maintaining method, the system can realize accurate differential current calculation and improve the reliability of transformer protection.

[0049] (2) The optical current transformer used in the present invention has good transient measurement capability. The sensor is completely composed of optical materials and does not have the problem of magnetic saturation. It also has natural insulation ability and strong anti-electromagnetic interference ability, and can provide accurate electrical quantity information for protection judgment.

[0050] (3) Optical measurement based on optical current transformer can accurately reflect the transformer excitation inrush current, providing a good measurement method for quickly and effectively detecting and identifying transformer excitation inrush current. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic diagram of the principle of Faraday magneto-optical rotation effect;

[0052] Figure 2 It is a schematic diagram of the installation angle of the first, second and third optical current transformers;

[0053] Figure 3 Schematic diagram of the system for transformer optical differential protection using optical calculation and polarization maintenance. DETAILED DESCRIPTION

[0054] The fault conditions of power systems are complex. In addition to the power frequency components, the fault electrical quantities also contain a large number of non-periodic components and harmonic components. Looking at the history of relay protection development, the development of rapid protection is usually accompanied by the expansion of the amount of protection information. It can be seen that using the time domain full waveform information of the fault electrical quantity to construct the protection criterion not only enriches the fault information, but is also the future development trend of rapid protection.

[0055] Optical differential protection uses the sum of the instantaneous values ​​of the currents on both sides of the line rather than the sum of the power frequency quantities to construct the operating current. The specific criterion is expressed as:

[0056] g(i M +i N )≥I set0 (1)

[0057] Where g() represents the optical differential protection function, i M 、i Nis the instantaneous value of the phase current on both sides of the line MN, I set0 is the set value.

[0058] When optical differential protection is applied to the protection of Yd11 transformer, in order to make the differential current zero during normal operation and out-of-zone faults, the problem of inconsistency in current amplitude and phase on both sides of the transformer needs to be solved. Among them, the phase inconsistency can be solved by changing the wiring method of the longitudinal differential protection, that is, the star-side current is replaced by the two-phase current difference; the amplitude inconsistency can be solved by changing the current ratio on both sides of the connected relay. Since the star-side current uses the two-phase current difference, the amplitude increases. times, and considering the transformation ratio of the transformer, the ratio of the current on the star side and the triangle side should be In summary, the transformer optical differential protection criterion taking phase A as an example can be expressed as:

[0059]

[0060] In the formula, f A () represents the A phase differential protection function, i YA 、i YB is the instantaneous value of the current of phases A and B of the star side line, i dA is the instantaneous value of phase A current of the triangle side line, I set is the set value, n T is the transformer ratio, expressed as:

[0061]

[0062] Among them, U Y is the transformer star side line voltage, U d is the line voltage on the triangle side.

[0063] Optical computing is a technology that uses photons instead of electrons to perform computational processing and data transmission. The optical measurement element of the transformer optical differential protection provides a basic medium for optical computing for protection, without the need to add other optical devices. The calculation of the transformer optical differential protection only involves optical operations such as addition, subtraction, and proportion, which is a simple calculation and can be achieved by adjusting the magnetic field direction of the current to be measured and the installation position of the optical current transformer on the simulated optical path. According to the principle of Faraday's magneto-optical effect, the measured current i and the Faraday rotation angle In direct proportion, such as Figure 1 As shown, it is expressed as:

[0064]

[0065] In the formula, V is the Field constant of the Faraday magneto-optical element material; L is the multiple relationship between the magnetic field integral of the Faraday magneto-optical element and the current i, and θ is the angle between the light propagation direction in the optical current transformer and the conductor to be measured. When the structural parameter L of the optical current transformer is a fixed constant, the addition, subtraction and proportional operation of the current to be measured in formula (3) can be realized by optical addition and subtraction of the Faraday rotation angle on the analog optical path, that is:

[0066]

[0067] In the formula, i YA 、i YB and i dA are the conductor current to be measured, θ YA ,θ YB and θ dA are the light propagation direction in the optical current transformer and the corresponding conductor i to be measured. YA 、i YB and i dA The angle of and They are the corresponding conductor i to be tested YA 、i YB and i dA The Faraday rotation angle generated by magneto-optical rotation. According to formula (5), by adjusting the magnetic field direction of the current to be measured sensed by the Faraday magneto-optical element and the installation angle θ of different optical current transformers, the addition and subtraction operations of different proportions of the current to be measured can be realized at the optical path level. The application of optical computing technology in transformer optical differential protection is an important breakthrough in relay protection and will have an unpredictable impact on the development of protection technology.

[0068] Based on the above ideas, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0069] Specific implementation method 1: refer to Figures 1 to 3 Specifically describe this embodiment, the optical calculation system for transformer optical differential protection based on polarization maintaining method described in this embodiment includes: light source 1, a first optical current transformer 2, a second optical current transformer 3, a third optical current transformer 4 and a processing unit 5.

[0070] The first optical current transformer 2 comprises: a first collimator, a polarizer, a first Faraday magneto-optical element and a second collimator;

[0071] The second optical current transformer 3 comprises: a third collimator, a second Faraday magneto-optical element and a fourth collimator;

[0072] The third optical current transformer 4 includes: a fifth collimator, a third Faraday magneto-optical element, an analyzer and a sixth collimator.

[0073] The angle between the transmission axes of the analyzer and the polarizer is -π / 4.

[0074] The first collimator and the sixth collimator are both multimode fiber collimators, and the second collimator, the third collimator, the fourth collimator and the fifth collimator are all polarization-maintaining fiber collimators.

[0075] Light source 1 is an SLD light source, and the wavelength of its emitted light is 850nm, providing a stable light source for the system. The emitted light of light source 1 is collimated by the first collimator and then incident on the polarizer to become polarized light. The polarized light passes through the first Faraday magneto-optical element and is incident on the second collimator. Based on the Faraday magneto-optical effect, the first current flowing through the high-voltage side of the protected object A phase is i YA , the polarization plane of polarized light is generated and the current i YA The first rotation is proportional to the size, and the rotation angle is Rotate now The polarized light after the angle is the first polarized light. The first polarized light collimated by the second collimator is incident on the third collimator, and the optical signal collimated by the third collimator passes through the second Faraday magneto-optical element. The first polarized light passes through the second Faraday magneto-optical element, which has the same material and structure as the first Faraday magneto-optical element. Based on the Faraday magneto-optical effect, the current i YB Under the modulation of the first polarized light, the polarization plane of the first polarized light is generated and the current i YB A second rotation proportional to the size of the rotation angle Rotate now The first polarized light after the angle is the second polarized light. The second polarized light after collimation by the fourth collimator is incident on the fifth collimator, and the optical signal after collimation by the fifth collimator is incident on the analyzer through the third Faraday magneto-optical element. The second polarized light passes through the third Faraday magneto-optical element, which has the same material and structure as the first Faraday magneto-optical element, and based on the Faraday magneto-optical effect, the current i dA Under the modulation of the second polarized light, the polarization plane of the second polarized light is generated and the current i dA sinθ dA A third rotation proportional to the size of the rotation angle Rotation Angle and The output light of the analyzer is collimated by the sixth collimator and then incident on the processing unit 5 .

[0076] Through the transmission of the above optical path, due to the light propagation direction in the first optical current transformer and the current i sensed by the first Faraday magneto-optical element YA The magnetic field B generated is parallel to the optical path YA The direction of light propagation in the second optical current transformer is the same as the direction of light propagation in the second Faraday magneto-optical element sensed by the current i YB The magnetic field generated is B YB The direction of light propagation in the third optical current transformer is opposite to the direction of light propagation in the third optical current transformer and the direction of light propagation in the third Faraday magneto-optical element sensed by the current i dA The magnetic field B generated is parallel to the optical path dA sinθ dA The direction is the same, so the emitted light of the light source 1 passes through the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 in sequence, so that the optical signal generates an optical rotation angle And there are:

[0077]

[0078] in, is the angle at which the polarized light is rotated by the magnetic field sensed by the first optical current transformer 2, is the angle at which the light emitted by the first optical current transformer 2 is rotated by the magnetic field sensed by the second optical current transformer 3, It is the angle at which the light emitted by the second optical current transformer 3 is rotated by the magnetic field sensed by the third optical current transformer 4 .

[0079] The optical signal is transmitted between the light source 1 and the first optical current transformer 2, and between the third optical current transformer 4 and the processing unit 5 through a multimode optical fiber, so as to realize high-speed transmission of the optical signal. The optical signal is transmitted between the first optical current transformer 2 and the second optical current transformer 3, and between the second optical current transformer 3 and the third optical current transformer 4 through a polarization-maintaining optical fiber. The polarization-maintaining optical fiber of the short line can meet the wiring requirements of the transformer differential protection under the existing technological level, and at the same time, it can also ensure the polarization-maintaining stability of the polarization-maintaining optical fiber, ensure that the polarization state of the optical signal remains unchanged during the transmission process, and thus ensure the reliability of the transformer optical differential protection.

[0080] In actual power systems, three-phase transformers are used, and the Yd11 connection method is usually adopted, in which the high-voltage side of the transformer is usually star-connected and the low-voltage side is triangle-connected. The Faraday magneto-optical elements of the first optical current transformer 2 and the third optical current transformer 4 are respectively located on the high-voltage side and the low-voltage side of the protected phase of the transformer. The Faraday magneto-optical element of the second optical current transformer 3 is located on the high-voltage side of the protected adjacent phase of the transformer. Under normal operating conditions, the phase difference between the high-voltage side of the protected phase and its adjacent phase is the same as the phase of the low-voltage side of the protected phase. The Faraday magneto-optical elements of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 sense the magnetic field generated by the current on their respective sides, and the angles between the optical paths of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 and the current directions on their respective sides satisfy:

[0081]

[0082] Among them, θ Y1 is the angle between the optical path of the first optical current transformer 2 and the current direction on its side, θ Y2 is the angle between the optical path of the second optical current transformer 3 and the current direction on its side, θ d3 is the angle between the optical path of the third optical current transformer 4 and the current direction on its side, n T is the transformer ratio;

[0083] The processing unit 5 includes the following units:

[0084] Filter unit: used to detect the carrier signal J of the optical signal output by the third optical current transformer using a filter circuit DC and the modulated wave signal J AC ,

[0085] Modulation ratio calculation unit: used to calculate the modulation ratio m according to the following formula:

[0086]

[0087] Differential current calculation unit: used to calculate the differential current i according to the following formula d :

[0088]

[0089] Wherein, V is the Field constant of the Faraday magneto-optical element in the optical current transformer, and L is the ratio of the magnetic field integral of the Faraday magneto-optical element in the optical current transformer to the current measured by the optical current transformer.

[0090] In this embodiment, if Figure 3As shown, the transformer protection object is phase A. When the light propagation direction is determined, if the magnetic field direction of the current sensed by the Faraday magneto-optical element is parallel to the light path direction and the rotation direction of the Faraday optical rotation angle remains unchanged, then the rotation direction of the Faraday optical rotation angle remains unchanged, otherwise the rotation direction of the Faraday optical rotation angle is opposite. According to the current addition and subtraction relationship in formula 3, the light propagation direction of the first, second, and third optical current transformers and their sensed magnetic field reference directions are set as follows:

[0091] The light propagation direction of the first optical current transformer is consistent with the current i sensed by the first Faraday magneto-optical element. YA The magnetic field B generated is parallel to the optical path YA The direction of light propagation in the second optical current transformer is the same as the direction of light propagation in the second Faraday magneto-optical element sensed by the current i YB The magnetic field generated is B YB The direction of light propagation in the third optical current transformer is opposite to the direction of light propagation in the third optical current transformer and the direction of light propagation in the third Faraday magneto-optical element sensed by the current i dA The magnetic field generated is B dA The direction of sinθ is the same, so the polarization plane rotation angle of the polarized light after three rotations carries the protection criterion required Current information, thus, the optical system can realize addition and subtraction operations of different proportions of the current to be measured by the difference in the rotation direction of the Faraday rotation angle under the special setting.

[0092] Specific implementation method 2: This implementation method describes an optical calculation method for transformer optical differential protection based on polarization maintaining method. The optical calculation polarization maintaining method is implemented based on an optical calculation system for transformer optical differential protection based on polarization maintaining method, and the system includes: a light source 1, a first optical current transformer 2, a second optical current transformer 3 and a third optical current transformer 4.

[0093] The first optical current transformer 2 comprises: a first collimator, a polarizer, a first Faraday magneto-optical element and a second collimator;

[0094] The second optical current transformer 3 comprises: a third collimator, a second Faraday magneto-optical element and a fourth collimator;

[0095] The third optical current transformer 4 includes: a fifth collimator, a third Faraday magneto-optical element, an analyzer and a sixth collimator.

[0096] The angle between the transmission axes of the analyzer and the polarizer is -π / 4.

[0097] The first collimator and the sixth collimator are both multimode fiber collimators, and the second collimator, the third collimator, the fourth collimator and the fifth collimator are all polarization-maintaining fiber collimators.

[0098] The light source 1 is an SLD light source, and the wavelength of its emitted light is 850nm. The emitted light of the light source 1 is collimated by the first collimator and then incident on the polarizer to become polarized light. The polarized light passes through the first Faraday magneto-optical element and is incident on the second collimator. The optical signal collimated by the second collimator is incident on the third collimator. The optical signal collimated by the third collimator is incident on the fourth collimator through the second Faraday magneto-optical element. The optical signal collimated by the fourth collimator is incident on the fifth collimator. The optical signal collimated by the fifth collimator is incident on the analyzer through the third Faraday magneto-optical element. The emitted light of the analyzer is collimated by the sixth collimator and then incident on the processing unit 5. Through the above optical path, the emitted light of the light source 1 passes through the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 in sequence, so that the optical signal generates an optical rotation angle And there are:

[0099]

[0100] in, is the angle at which the polarized light is rotated by the magnetic field sensed by the first optical current transformer 2, is the angle at which the light emitted by the first optical current transformer 2 is rotated by the magnetic field sensed by the second optical current transformer 3, It is the angle at which the light emitted by the second optical current transformer 3 is rotated by the magnetic field sensed by the third optical current transformer 4 .

[0101] The optical signal is transmitted between the light source 1 and the first optical current transformer 2, and between the third optical current transformer 4 and the processing unit 5 via a multimode optical fiber.

[0102] Optical signals are transmitted between the first optical current transformer 2 and the second optical current transformer 3 as well as between the second optical current transformer 3 and the third optical current transformer 4 through polarization-maintaining optical fibers.

[0103] The Faraday magneto-optical elements of the first optical current transformer 2 and the third optical current transformer 4 are respectively located on the high-voltage side and the low-voltage side of the protected phase of the transformer, and the Faraday magneto-optical element of the second optical current transformer 3 is located on the high-voltage side of the protected adjacent phase of the transformer. Under normal operation of the transformer, the phase difference between the high-voltage side of the protected phase and its adjacent phase is the same as the phase of the low-voltage side of the protected phase. The Faraday magneto-optical elements of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 sense the magnetic field generated by the current on their respective sides, and the angles between the optical paths of the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 and the current directions on their respective sides satisfy:

[0104]

[0105] Among them, θY1 is the angle between the first optical current transformer 2 and the current direction on its side, θ Y2 is the angle between the second optical current transformer 3 and the current direction on its side, θ d3 is the angle between the third optical current transformer 4 and the current direction on its side, n T is the transformer ratio.

[0106] The light calculation method for transformer optical differential protection is:

[0107] The filter circuit is used to detect the carrier signal J of the optical signal output by the third optical current transformer. DC and the modulated wave signal J AC ,

[0108]

[0109] Among them, P0 is the light intensity of the light source, P out is the intensity of the light emitted by the third optical current transformer.

[0110] The modulation ratio m is calculated using the following formula:

[0111]

[0112] Using the modulation ratio m, the differential current i is calculated according to the following formula: d :

[0113]

[0114] Wherein, V is the Field constant of the Faraday magneto-optical element in the optical current transformer, and L is the ratio of the magnetic field integral of the Faraday magneto-optical element in the optical current transformer to the current measured by the optical current transformer.

[0115] The present invention realizes the addition and subtraction operations of instantaneous values ​​of different proportions of currents to be measured in the optical transformer differential protection criterion through optical addition and subtraction operations of Faraday rotation angle at the analog optical path level. The entire optical path system sequentially traverses the optical elements, namely, the light source, the multimode optical fiber, the first optical current transformer, the polarization-maintaining optical fiber, the second optical current transformer, the polarization-maintaining optical fiber, the third optical current transformer and the processing unit. The optical signal after passing through the three optical current transformers carries all the current information required for the protection criterion. Among them, the proportional operation of different currents to be measured is realized by adjusting the installation angle of the optical current transformer and then controlling the size of the Faraday rotation angle, and the addition and subtraction operations of different currents to be measured are realized by adjusting the propagation direction of light and the direction of the magnetic field parallel to the optical path generated by the current to be measured sensed by the Faraday magneto-optical element to control the rotation direction of the Faraday rotation angle. The application of optical computing technology in transformer optical differential protection is an important breakthrough in relay protection and will have an unpredictable impact on the development of protection technology.

[0116] The transformer optical differential protection optical calculation implementation system based on the polarization-maintaining method proposed in the present invention provides a differential current optical calculation solution for applying optical differential protection in the field of transformer protection. By changing the calculation method of differential current to adapt it to the requirements of transformer protection, the problem of excessive differential current caused by the mismatch of current phase and amplitude on both sides of the transformer is effectively solved. By adopting the optical calculation scheme of the polarization-maintaining method, the system can realize accurate differential current calculation and improve the reliability of transformer protection. The optical current transformer used in the present invention has good transient measurement capability. The sensor is completely composed of optical materials and does not have the problem of magnetic saturation. At the same time, it has natural insulation ability and strong anti-electromagnetic interference ability, and can provide accurate electrical quantity information for protection judgment. Optical measurement based on optical current transformer can accurately reflect the excitation surge current of the transformer, and provides a good measurement means for quickly and effectively detecting and identifying the excitation surge current of the transformer.

[0117] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. An optical computing system for transformer optical differential protection based on polarization maintaining method, characterized in that: include: A light source (1), a first optical current transformer (2), a second optical current transformer (3), a third optical current transformer (4) and a processing unit (5); The optical signal emitted by the light source (1) passes through the first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) in sequence, so that the optical signal generates an optical rotation angle The output light of the third optical current transformer (4) is incident on the processing unit (5), the optical signal is transmitted between the light source (1) and the first optical current transformer (2) and between the third optical current transformer (4) and the processing unit (5) through a multimode optical fiber, and the optical signal is transmitted between the first optical current transformer (2) and the second optical current transformer (3) and between the second optical current transformer (3) and the third optical current transformer (4) through a polarization-maintaining optical fiber; The Faraday magneto-optical elements of the first optical current transformer (2) and the third optical current transformer (4) are respectively located on the high-voltage side and the low-voltage side of the protected phase of the transformer, and the Faraday magneto-optical element of the second optical current transformer (3) is located on the high-voltage side of the protected adjacent phase of the transformer. Under normal operation of the transformer, the phase difference between the high-voltage side of the protected phase and its adjacent phase is the same as the phase of the low-voltage side of the protected phase. The Faraday magneto-optical elements of the first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) can sense the magnetic field generated by the current on their respective sides, and the angles between the optical paths of the first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) and the current directions on their respective sides satisfy: Among them, θ Y1 is the angle between the optical path of the first optical current transformer (2) and the current direction on its side, θ Y2 is the angle between the optical path of the second optical current transformer (3) and the current direction on its side, θ d3 is the angle between the optical path of the third optical current transformer (4) and the current direction on its side, n T is the transformer ratio; The processing unit (5) comprises the following units: Filter unit: used to detect the carrier signal J of the optical signal output by the third optical current transformer (4) by using a filter circuit DC and the modulated wave signal J AC , Modulation ratio calculation unit: used to calculate the modulation ratio m according to the following formula: Differential current calculation unit: used to calculate the differential current i according to the following formula d : Wherein, V is the Field constant of the Faraday magneto-optical element in the third optical current transformer (4), and L is the ratio of the magnetic field integral of the Faraday magneto-optical element in the third optical current transformer (4) to the current measured by the third optical current transformer (4).

2. The optical computing system for transformer optical differential protection based on polarization maintaining method according to claim 1, characterized in that: The first optical current transformer (2) comprises: a first collimator, a polarizer, a first Faraday magneto-optical element and a second collimator. The second optical current transformer (3) comprises: a third collimator, a second Faraday magneto-optical element and a fourth collimator, The third optical current transformer (4) comprises: a fifth collimator, a third Faraday magneto-optical element, an analyzer and a sixth collimator, The first collimator and the sixth collimator are both multimode fiber collimators, and the second collimator, the third collimator, the fourth collimator and the fifth collimator are all polarization-maintaining fiber collimators; The output light of the light source (1) is collimated by the first collimator and then incident on the polarizer to become polarized light. The polarized light passes through the first Faraday magneto-optical element and then incident on the second collimator. The light signal collimated by the second collimator is incident on the third collimator. The light signal collimated by the third collimator passes through the second Faraday magneto-optical element and then incident on the fourth collimator. The light signal collimated by the fourth collimator is incident on the fifth collimator. The light signal collimated by the fifth collimator passes through the third Faraday magneto-optical element and then incident on the analyzer. The output light of the analyzer is collimated by the sixth collimator and then incident on the processing unit (5).

3. The optical computing system for transformer optical differential protection based on polarization maintaining method according to claim 1 or 2, characterized in that: The optical rotation angle in, is the angle at which the polarized light is rotated by the magnetic field sensed by the first optical current transformer (2), is the angle at which the light emitted by the first optical current transformer (2) is rotated by the magnetic field sensed by the second optical current transformer (3), The angle at which the light emitted by the second optical current transformer (3) is rotated by the magnetic field sensed by the third optical current transformer (4).

4. The optical computing system for transformer optical differential protection based on polarization maintaining method according to claim 3 is characterized in that: The light source (1) is an SLD light source, and the wavelength of its emitted light is 850 nm.

5. A method for calculating light used in transformer optical differential protection based on polarization-maintaining method, characterized in that: The optical calculation method for transformer optical differential protection is implemented based on an optical calculation system for transformer optical differential protection based on a polarization-maintaining method, the system comprising: a light source (1), a first optical current transformer (2), a second optical current transformer (3) and a third optical current transformer (4); The optical signal emitted by the light source (1) passes through the first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) in sequence, so that the optical signal generates an optical rotation angle An optical signal is transmitted between the light source (1) and the first optical current transformer (2) via a multimode optical fiber, and an optical signal is transmitted between the first optical current transformer (2) and the second optical current transformer (3) and between the second optical current transformer (3) and the third optical current transformer (4) via a polarization-maintaining optical fiber; The Faraday magneto-optical elements of the first optical current transformer (2) and the third optical current transformer (4) are respectively located on the high-voltage side and the low-voltage side of the protected phase of the transformer, and the Faraday magneto-optical element of the second optical current transformer (3) is located on the high-voltage side of the protected adjacent phase of the transformer. Under normal operation of the transformer, the phase difference between the high-voltage side of the protected phase and its adjacent phase is the same as the phase of the low-voltage side of the protected phase. The Faraday magneto-optical elements of the first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) can sense the magnetic field generated by the current on their respective sides, and the angles between the optical paths of the first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) and the current directions on their respective sides satisfy: Among them, θ Y1 is the angle between the first optical current transformer (2) and the current direction on its side, θ Y2 is the angle between the second optical current transformer (3) and the current direction on its side, θ d3 is the angle between the third optical current transformer (4) and the current direction on its side, n T is the transformer ratio; The light calculation method for transformer optical differential protection is: The filter circuit is used to detect the carrier signal J of the optical signal output by the third optical current transformer. DC and the modulated wave signal J AC , The modulation ratio m is calculated using the following formula: Using the modulation ratio m, the differential current i is calculated according to the following formula: d : Wherein, V is the Field constant of the Faraday magneto-optical element in the third optical current transformer (4), and L is the ratio of the magnetic field integral of the Faraday magneto-optical element in the third optical current transformer (4) to the current measured by the third optical current transformer (4).

6. The method for calculating light used in transformer optical differential protection based on polarization-maintaining method according to claim 5, characterized in that: The first optical current transformer (2) comprises: a first collimator, a polarizer, a first Faraday magneto-optical element and a second collimator. The second optical current transformer (3) comprises: a third collimator, a second Faraday magneto-optical element and a fourth collimator, The third optical current transformer (4) comprises: a fifth collimator, a third Faraday magneto-optical element, an analyzer and a sixth collimator, The first collimator and the sixth collimator are both multimode fiber collimators, and the second collimator, the third collimator, the fourth collimator and the fifth collimator are all polarization-maintaining fiber collimators; The output light of the light source (1) is collimated by the first collimator and then incident on the polarizer to become polarized light. The polarized light passes through the first Faraday magneto-optical element and then incident on the second collimator. The light signal collimated by the second collimator is incident on the third collimator. The light signal collimated by the third collimator passes through the second Faraday magneto-optical element and then incident on the fourth collimator. The light signal collimated by the fourth collimator is incident on the fifth collimator. The light signal collimated by the fifth collimator passes through the third Faraday magneto-optical element and then incident on the analyzer. The output light of the analyzer is collimated by the sixth collimator and then incident on the processing unit (5).

7. A method for calculating light used in transformer optical differential protection based on polarization-maintaining method according to claim 5 or 6, characterized in that: The optical rotation angle in, is the angle at which the polarized light is rotated by the magnetic field sensed by the first optical current transformer (2), is the angle at which the light emitted by the first optical current transformer (2) is rotated by the magnetic field sensed by the second optical current transformer (3), The angle at which the light emitted by the second optical current transformer (3) is rotated by the magnetic field sensed by the third optical current transformer (4).

8. The method for calculating light used in transformer optical differential protection based on polarization-maintaining method according to claim 7, characterized in that: The light source (1) is an SLD light source, and the wavelength of its emitted light is 850 nm.

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