Faraday magneto-optical effect based optical computing method and system for relay protection

Abstract

A Faraday magneto-optical effect based optical computing method and system for relay protection, relating to the technical field of relay protection of power systems. The present invention aims to solve the problem that the current amplitudes and phases of lines on two sides of a protected object are not equal due to a transformer ratio and a connection group when optical differential protection is introduced into the field of transformer protection. In the present invention, a cascade optical computing solution is used; three optical current transformers are connected in series on one optical path, and a final output optical signal is formed by means of cascaded multiplication of outputs of the three optical current transformers and carries an angle of optical rotation containing differential current information; and a filter circuit is used to detect a carrier signal and a modulation wave signal of the optical signal outputted by the third optical current transformer, then a modulation ratio is calculated, and finally, a differential current is calculated.

Description

Light calculation method and system for relay protection based on Faraday magneto-optical effect Technical Field

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

[0002] New power systems place higher demands on the speed of relay protection and the information used for protection. With the gradual formation of ultra-high voltage AC / DC hybrid systems and the continued growth of renewable energy grid-connected capacity, the low inertia, weak interference immunity, and multi-timescale response characteristics of power electronic devices have resulted in new power systems dominated by renewable energy having smaller time constants (milliseconds), making them more susceptible to disturbance propagation when impacted. In other words, when a system fault occurs but the fault removal mechanism fails to operate quickly, the fault propagates rapidly and permeates rapidly. To ensure the safe and stable operation of new power systems, corresponding relay protection technologies must possess higher speed. Throughout the history of protection development, every breakthrough in principle has been accompanied by an increase in the amount of protection information required. Full waveform information, which includes comprehensive fault information, is naturally excellent protection information, and fully utilizing full waveform information to construct protection criteria is an inevitable trend in the development of relay protection.

[0003] Compared with traditional power frequency differential protection, optical differential protection can meet the requirements of new power systems for relay protection in terms of speed and protection information. At present, optical differential protection is mainly used in the field of line protection. Optical differential protection uses optical current transformers as a measurement method. In principle, it uses instantaneous values ​​as characteristic quantities for protection, and no longer extracts power frequency components. It retains full waveform information that can fully reflect faults, does not require digital filter window processing, and can respond to faults quickly. The optical differential protection device uses a cascaded optical calculation scheme to directly calculate the differential current on the analog optical path, which simplifies the design and implementation of the protection device and helps reduce costs.

[0004] However, when introducing optical differential protection into the field of transformer protection, it is necessary to solve the problem of unequal amplitude and phase of the line currents on both sides of the protected 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 protected 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, in which the high-voltage side adopts a star connection method and the low-voltage side adopts a delta connection method. The different connection methods of the high and low voltage sides cause the phase difference of the line currents on both sides. Therefore, directly introducing the high-voltage side current and the low-voltage side current of the transformer into the differential protection will result in an excessively large differential current, which is easy to trigger the protection to malfunction. Summary of the Invention

[0005] The present invention aims to solve the problem of unequal amplitude and phase of line currents on both sides of the protected object caused by the transformer ratio and connection group when optical differential protection is introduced into the field of transformer protection. A method and system for calculating the optical power of relay protection based on the Faraday magneto-optical rotation effect are provided.

[0006] The optical calculation system for relay protection based on the Faraday magneto-optical effect 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 carries the optical rotation angle containing the differential current information. , 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, the first optical current transformer 2 and the second optical current transformer 3, the second optical current transformer 3 and the third optical current transformer 4, and the third optical current transformer 4 and the processing unit 5 through the multimode 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 operating conditions, the phase difference between the high-voltage side of the protected phase and the protected 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 angle between the optical path of the first optical current transformer 2, the second optical current transformer 3, and the third optical current transformer 4 and the current direction on their respective sides satisfies:

[0009] ;

[0010] in, is the angle between the optical path of the first optical current transformer 2 and the current direction on its side, is the angle between the optical path of the second optical current transformer 3 and the current direction on its side, is the angle between the optical path of the third optical current transformer 4 and the current direction on its side, is the transformer ratio;

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

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

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

[0014] ,

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

[0016] ,

[0017] in, is the Field constant of the Faraday magneto-optical element in the optical current transformer, It 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, the second optical current transformer 3 and the third optical current transformer 4 have the same internal structure and all include a collimator, a polarizer, a Faraday magneto-optical element and an analyzer.

[0019] The incident light is collimated by the collimator and then enters the polarizer to become polarized light. The polarized light passes through the Faraday magneto-optical element and rotates under the modulation of the magnetic field where the Faraday magneto-optical element is located. The rotated polarized light passes through the analyzer and then exits through the collimator.

[0020] The output end of the polarization analyzer includes Output and Output end, the transmission axis of the polarizer and the analyzer Output and The angles of the transmission axis at the output end are and ,

[0021] The optical signals output by the first optical current transformer 2 and the third optical current transformer 4 are both polarized by their polarization analyzers. The output terminal outputs the optical signal output by the second optical current transformer 3 from its polarization analyzer. Output terminal output.

[0022] Furthermore, the optical rotation angle ,

[0023] 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 from the second optical current transformer 3 is rotated by the magnetic field sensed by the third optical current transformer 4 .

[0024] Furthermore, the light intensity of the optical signal output by the third optical current transformer 4 is for:

[0025] ,

[0026] in, is the intensity of the light emitted by light source 1.

[0027] Furthermore, the light source 1 is an SLD light source with a wavelength of 850 nm.

[0028] A light calculation method for relay protection based on the Faraday magneto-optical effect is implemented based on a light calculation system for transformer optical differential protection, which includes:

[0029] Light source 1, first optical current transformer 2, second optical current transformer 3 and third optical current transformer 4;

[0030] 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 carries the optical rotation angle containing the differential current information. , optical signals are transmitted between the light source 1 and the first optical current transformer 2, 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 multimode optical fiber;

[0031] 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 operating conditions, the phase difference between the high-voltage side of the protected phase and the protected 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 angle between the optical path of the first optical current transformer 2, the second optical current transformer 3, and the third optical current transformer 4 and the current direction on their respective sides satisfies:

[0032] ,

[0033] in, is the angle between the optical path of the first optical current transformer 2 and the current direction on its side, is the angle between the optical path of the second optical current transformer 3 and the current direction on its side, is the angle between the optical path of the third optical current transformer 4 and the current direction on its side, is the transformer ratio;

[0034] The calculation method for the light used in the transformer optical differential protection is:

[0035] The filter circuit is used to detect the carrier signal of the optical signal output by the third optical current transformer 4. and modulated wave signal ,

[0036] The modulation ratio is calculated according to the following formula :

[0037] ,

[0038] The differential current is calculated according to the following formula :

[0039] ,

[0040] in, is the Field constant of the Faraday magneto-optical element in the optical current transformer, It 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.

[0041] Furthermore, the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 have the same internal structure and all include a collimator, a polarizer, a Faraday magneto-optical element and an analyzer.

[0042] The incident light is collimated by the collimator and then enters the polarizer to become polarized light. The polarized light passes through the Faraday magneto-optical element and rotates under the modulation of the magnetic field where the Faraday magneto-optical element is located. The rotated polarized light passes through the analyzer and then exits through the collimator.

[0043] The output end of the polarization analyzer includes Output and Output end, the transmission axis of the polarizer and the analyzer Output and The angles of the transmission axis at the output end are and ,

[0044] The optical signals output by the first optical current transformer 2 and the third optical current transformer 4 are both polarized by their polarization analyzers. The output terminal outputs the optical signal output by the second optical current transformer 3 from its polarization analyzer. Output terminal output.

[0045] Furthermore, the optical rotation angle ,

[0046] 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 from the second optical current transformer 3 is rotated by the magnetic field sensed by the third optical current transformer 4 .

[0047] Furthermore, the light intensity of the optical signal output by the third optical current transformer 4 is for:

[0048] ,

[0049] in, is the intensity of the light emitted by light source 1.

[0050] Furthermore, the light source 1 is an SLD light source with a wavelength of 850 nm.

[0051] The beneficial effects of the present invention are:

[0052] (1) The optical calculation method and system for relay protection based on the Faraday magneto-optical rotation effect proposed in the present invention solves the problem of mismatch between the phase and amplitude of the current on both sides of the protection object when the optical differential protection in the line is directly applied to the field of transformer protection. For transformer protection, directly introducing the high-voltage side and low-voltage side currents into the differential circuit will result in excessive differential current because the phase and amplitude of the current on both sides of the protection object do not match. In order to solve this problem, the present invention proposes a calculation method for transformer optical differential protection. In this method, the differential current is expressed as the addition and subtraction operation of the instantaneous values ​​of three different proportions of the measured current to eliminate the influence of phase and amplitude mismatch. In order to implement this calculation method, a cascade optical calculation scheme is adopted, which is specifically manifested in that three optical current transformers are connected in series on an optical path system, and the cascade multiplication of the transformer output signals is used to realize the optical addition and subtraction operation of the Faraday rotation angle, thereby realizing the differential current calculation in the transformer optical differential protection.

[0053] (2) The optical current transformer used in this invention is based on the principle of the Faraday magneto-optical effect and has excellent dynamic measurement capabilities. It can accurately measure the power frequency, non-periodic components, and various harmonic components in the system without the problem of magnetic saturation, making it an ideal product for achieving real-time measurement of full-waveform signals. Optical measurement can not only accurately reflect the transient currents on both sides of the protection object, but also reflect the transformer's excitation inrush current with high fidelity, providing an excellent measurement method for quickly and effectively detecting and identifying transformer excitation inrush current and preventing protection malfunctions. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG1 is a schematic diagram showing the principle of the Faraday magneto-optical rotation effect;

[0055] Figure 2 is a schematic diagram of the Faraday magneto-optical element sensing the direction of the magnetic field;

[0056] Figure 3 is a schematic diagram of an optical calculation system for relay protection based on the Faraday magneto-optical effect. DETAILED DESCRIPTION

[0057] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described 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 making creative work are within 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 in the absence of conflict.

[0058] 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

[0059] (1)

[0060] Where, represents the optical differential protection function, 、 is the instantaneous value of the phase current on both sides of line MN, is the set value.

[0061] When optical differential protection is applied to the Yd11 connection group transformer protection, in order to ensure that the differential current is zero during normal operation and out-of-zone faults, it is necessary to solve the problem of inconsistent current amplitude and phase on both sides of the transformer. Among them, phase inconsistency can be solved by changing the wiring method of the longitudinal differential protection, that is, the high-voltage side current is replaced by the two-phase current difference; amplitude inconsistency can be solved by changing the current ratio on both sides of the connected relay. Since the high-voltage side current uses the two-phase current difference, the amplitude increases. times, and considering the transformer ratio, the ratio of the high-voltage side and low-voltage side currents should be In summary, the transformer optical differential protection criterion taking phase A as an example can be expressed as:

[0062] (2)

[0063] Where, represents the differential protection function of phase A, 、 is the instantaneous value of the A and B phase currents of the high-voltage side line, is the instantaneous value of phase A current on the low-voltage side line, is the set value, is the transformer ratio, expressed as:

[0064] (3)

[0065] in, is the transformer high-voltage side line voltage, is the low voltage side line voltage.

[0066] The key to realizing optical differential protection of transformers based on optical calculation is to realize addition and subtraction operations of different proportions of the current to be measured through optical addition and subtraction operations of Faraday optical rotation angle. The calculation of optical differential protection of transformers only involves optical operations such as addition, subtraction, and proportion, which is a simple calculation. It can be achieved by adjusting the direction of the magnetic field of the current to be measured sensed by the Faraday magneto-optical element and the installation position of the optical current transformer on the simulated optical path. According to the principle of Faraday magneto-optical rotation effect, the current to be measured and Faraday rotation angle In direct proportion, as shown in Figure 1, it can be expressed as:

[0067] (4)

[0068] Where, is the Field constant of the Faraday magneto-optical element material; is the magnetic field integral and current of the Faraday magneto-optical element The multiple relationship of is the angle between the light propagation direction in the optical current transformer and the conductor to be measured. To determine the constant, the addition and subtraction operations of the instantaneous values ​​of the current to be measured at different ratios in formula (2) can be realized by optical addition and subtraction of the Faraday rotation angle on the analog optical path, that is:

[0069] (5)

[0070] Where, 、 and are the conductor current to be measured, 、 and are the light propagation direction in the optical current transformer and the corresponding conductor to be measured. 、 and The angle of 、 and They correspond to the conductors to be tested 、 and The Faraday rotation angle produced by the magneto-optical rotation effect.

[0071] According to Equation (5), current proportional calculations can be achieved by varying the optical current transformer installation angles, and current addition and subtraction calculations can be achieved by optical addition and subtraction of Faraday rotation angles. The application of optical computing technology to transformer optical differential protection is a significant breakthrough in relay protection and will have an unpredictable impact on the development of protection technology.

[0072] Based on the above foundation, the following specific implementation methods are given.

[0073] Specific embodiment 1: This embodiment is described in detail with reference to Figures 1 to 3. The optical calculation system for relay protection based on the Faraday magneto-optical rotation effect described in this embodiment takes the A-phase differential circuit of the transformer optical differential protection as an example. The protected phase of the transformer is phase A, and its high-voltage side current is , the low voltage side line current is ; The adjacent phase is phase B, and its high-voltage side line current is .

[0074] The optical calculation system for relay protection based on the Faraday magneto-optical effect includes: 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 first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 have the same internal structure and all include a collimator, a polarizer, a Faraday magneto-optical element and an analyzer. The analyzer is a polarization beam splitter prism, including Output and Output end, the transmission axis of the polarizer and the analyzer Output and The angles of the transmission axis at the output end are and The optical current transformer is used to sense the required current information to be measured.

[0075] Light source 1 includes an SLD light source with a wavelength of 850nm, which provides the system with the required stable light source. The light emitted by light source 1 is incident on the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 in sequence through the multimode optical fiber, so that the optical signal carries the optical rotation angle containing the differential current information. , the output light of the third optical current transformer 4 is incident on the processing unit 5. 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 operating conditions of the transformer, the phase difference between the high-voltage side of the protected phase and the protected adjacent phase is the same as the phase of the low-voltage side of the protected phase.

[0076] 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 are capable of sensing 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:

[0077] ,

[0078] in, is the angle between the optical path of the first optical current transformer 2 and the current direction on its side, is the angle between the optical path of the second optical current transformer 3 and the current direction on its side, is the angle between the optical path of the third optical current transformer 4 and the current direction on its side, is the transformer ratio.

[0079] In this embodiment, the light propagation direction of the first optical current transformer 2 and the second optical current transformer 3 is perpendicular to the conductor, that is, The light propagation direction of the third optical current transformer 4 forms an acute angle with the conductor direction.

[0080] In the first optical current transformer 2, the incident light is the light intensity emitted by the light source 1. The incident light is collimated by the collimator and then enters the polarizer to become polarized light. The polarized light is then incident on the Faraday magneto-optical element. According to the Faraday magneto-optical effect, when the direction of light propagation is determined, the direction of the magnetic field generated by the current parallel to the optical path remains unchanged, and the direction of the Faraday optical rotation angle remains unchanged. Otherwise, the direction of the Faraday optical rotation angle is opposite. Set the current Magnetic field acting on Faraday magneto-optical element The reference direction is the same as the direction of light propagation. Under the modulation of the polarization plane of polarized light, the polarization plane of polarized light is generated and the current A positive rotation proportional to the size, with an angle of rotation of The light emitted from the Faraday magneto-optical element is polarized by the analyzer. According to Malus's law, the light intensity of the light emitted by the first optical current transformer 2 is .

[0081] Similarly, in the second optical current transformer 3, the current Magnetic field acting on Faraday magneto-optical element Same as the direction of light propagation, in the magnetic field Under the modulation of the polarization plane of polarized light, the polarization plane of polarized light is generated and the current A positive rotation proportional to the size, with an angle of rotation of The light emitted from the Faraday magneto-optical element is polarized by the analyzer. According to Malus's law, the light intensity of the light emitted by the second optical current transformer 3 is .

[0082] In the third optical current transformer 4, the current Magnetic field acting on Faraday magneto-optical element Same as the direction of light propagation, in the magnetic field Under the modulation of the polarization plane of polarized light, the polarization plane of polarized light is generated and the current A positive rotation proportional to the size, with an angle of rotation of The light emitted from the Faraday magneto-optical element is polarized by the analyzer. According to Malus's law, the intensity of the light emitted by the third optical current transformer 4 is .

[0083] Generally, the Faraday rotation angle is relatively small, and the following formula is approximately true:

[0084] , substitute this formula into the light intensity formula of the output optical signal of the third optical current transformer 4, and ignore the higher-order terms, then:

[0085] .

[0086] The processing unit 5 includes the following modules:

[0087] Filter unit: A filter circuit is used to detect the carrier signal of the optical signal output by the third optical current transformer and modulated wave signal ,

[0088] Modulation ratio calculation unit: Calculate the modulation ratio according to the following formula :

[0089] ,

[0090] Differential current calculation unit: Calculates the differential current according to the following formula :

[0091] ,

[0092] ,

[0093] in, is the Field constant of the Faraday magneto-optical element in the optical current transformer, It 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.

[0094] The above-mentioned optical path system connects three optical current transformers in series on an analog optical path, so that the final output optical signal appears in the form of a cascade of the output signals of the three transformers, realizing the addition and subtraction operations of the instantaneous values ​​of the three currents to be measured with different proportions for the transformer optical differential protection at the optical path level.

[0095] This embodiment connects three optical current transformers in series on a simulated optical path. The outputs of the three series-connected optical current transformers are cascaded and multiplied to achieve optical addition and subtraction of Faraday rotation angles, thereby implementing addition and subtraction of instantaneous values ​​of different proportions of the measured current in the optical transformer differential protection criterion. The proportional calculation of different measured currents is achieved by adjusting the installation angle of the optical current transformers, while the addition and subtraction of Faraday rotation angles is achieved by adjusting the direction of the magnetic field acting on the magneto-optical element by the measured current and properly setting the polarization angle of the output light from the polarizer and analyzer. The entire optical path system starts with a light source, and the light beam enters the first, second, and third optical current transformers in sequence through a multimode optical fiber. The system output is a cascaded multiplication of the outputs of the three transformers, and the output result includes optical addition and subtraction information of the Faraday rotation angle. The entire system implements the transformer optical current differential algorithm at the analog optical path level, improving the reliability of protection.

[0096] Specific embodiment 2: The optical calculation method for relay protection based on the Faraday magneto-optical effect described in this embodiment is implemented based on an optical calculation system for transformer optical differential protection, which includes: a light source 1, a first optical current transformer 2, a second optical current transformer 3, and a third optical current transformer 4. The internal components of the first optical current transformer 2, the second optical current transformer 3, and the third optical current transformer 4 are the same, and all include a collimator, a polarizer, a Faraday magneto-optical element, and an analyzer. The analyzer polarization splitter prism includes Output and Output end, the transmission axis of the polarizer and the analyzer Output and The angles of the transmission axis at the output end are and The optical current transformer is used to sense the required current information to be measured.

[0097] Light source 1 includes an SLD light source with a wavelength of 850nm, which provides the system with the required stable light source. The light emitted by light source 1 is incident on the first optical current transformer 2, the second optical current transformer 3 and the third optical current transformer 4 in sequence through the multimode optical fiber, so that the optical signal carries the optical rotation angle containing the differential current information. , the output light of the third optical current transformer 4 is incident on the processing unit 5. 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 operating conditions of the transformer, the phase difference between the high-voltage side of the protected phase and the protected adjacent phase is the same as the phase of the low-voltage side of the protected phase.

[0098] 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 are capable of sensing 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:

[0099] ,

[0100] in, is the angle between the optical path of the first optical current transformer 2 and the current direction on its side, is the angle between the optical path of the second optical current transformer 3 and the current direction on its side, is the angle between the optical path of the third optical current transformer 4 and the current direction on its side, is the transformer ratio.

[0101] In this embodiment, the light propagation direction of the first optical current transformer 2 and the second optical current transformer 3 is perpendicular to the conductor, that is, The light propagation direction of the third optical current transformer 4 forms an acute angle with the conductor direction.

[0102] In the first optical current transformer 2, the incident light is the light intensity emitted by the light source 1. The incident light is collimated by the collimator and then enters the polarizer to become polarized light. The polarized light is then incident on the Faraday magneto-optical element. According to the Faraday magneto-optical effect, when the direction of light propagation is determined, the direction of the magnetic field generated by the current parallel to the optical path remains unchanged, and the direction of the Faraday optical rotation angle remains unchanged. Otherwise, the direction of the Faraday optical rotation angle is opposite. Set the current Magnetic field acting on Faraday magneto-optical element The reference direction is the same as the direction of light propagation. Under the modulation of the polarization plane of polarized light, the polarization plane of polarized light is generated and the current A positive rotation proportional to the size, with an angle of rotation of The light emitted from the Faraday magneto-optical element is polarized by the analyzer. According to Malus's law, the light intensity of the light emitted by the first optical current transformer 2 is .

[0103] Similarly, in the second optical current transformer 3, the current Magnetic field acting on Faraday magneto-optical element The reference direction is the same as the direction of light propagation. Under the modulation of the polarization plane of polarized light, the polarization plane of polarized light is generated and the current A positive rotation proportional to the size, with an angle of rotation of The light emitted from the Faraday magneto-optical element is polarized by the analyzer. According to Malus's law, the light intensity of the light emitted by the second optical current transformer 3 is .

[0104] In the third optical current transformer 4, the current Magnetic field acting on Faraday magneto-optical element The reference direction is the same as the direction of light propagation. Under the modulation of the polarization plane of polarized light, the polarization plane of polarized light is generated and the current A positive rotation proportional to the size, with an angle of rotation of The light emitted from the Faraday magneto-optical element is polarized by the analyzer. According to Malus's law, the intensity of the emitted light is .

[0105] Generally, the Faraday rotation angle is relatively small, and the following formula is approximately true:

[0106] , substitute this formula into the light intensity formula of the output optical signal of the third optical current transformer 4, and ignore the higher-order terms, then:

[0107] ,

[0108] The calculation method for the light used in the transformer optical differential protection is:

[0109] The carrier signal of the optical signal output by the third optical current transformer is detected by a filter circuit and modulated wave signal ,

[0110] The modulation ratio is calculated according to the following formula :

[0111] ,

[0112] The differential current is calculated according to the following formula :

[0113] ,

[0114] ,

[0115] in, is the Field constant of the Faraday magneto-optical element in the optical current transformer, It 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.

[0116] The optical calculation method and system for relay protection based on the Faraday magneto-optical rotation effect proposed in the present invention solves the problem of mismatch in the phase and amplitude of the current on both sides of the protected object when the optical differential protection in the line is directly applied to the field of transformer protection. For transformer protection, directly introducing the high-voltage side and low-voltage side currents into the differential circuit will result in excessive differential current because the phase and amplitude of the current on both sides of the protected object do not match. To solve this problem, the present invention proposes a calculation method for transformer optical differential protection. In this method, the differential current is expressed as the addition and subtraction operations of the instantaneous values ​​of three different proportions of the measured current to eliminate the influence of phase and amplitude mismatch. In order to implement this calculation method, a cascade optical calculation scheme is adopted, which is specifically manifested in that three optical current transformers are connected in series on an optical path system, and the cascade multiplication of the transformer output signals is used to realize the optical addition and subtraction operations of the Faraday rotation angle, thereby realizing the differential current calculation in the transformer optical differential protection. The optical current transformer employed in this invention, based on the Faraday magneto-optical effect, possesses excellent dynamic measurement capabilities. It accurately measures power frequency quantities, non-periodic components, and various harmonic components in the system, without the risk of magnetic saturation. This makes it an ideal product for real-time measurement of full-waveform signals. Optical measurement not only accurately reflects transient currents on both sides of the protected object but also accurately reflects transformer magnetizing inrush currents. This provides an excellent measurement method for quickly and effectively detecting and identifying transformer magnetizing inrush currents and preventing malfunctions of protective devices.

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

Claims

1. An optical computing system for relay protection based on Faraday magneto-optical effect, 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 carries the optical rotation angle containing the differential current information. , 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), between the first optical current transformer (2) and the second optical current transformer (3), between the second optical current transformer (3) and the third optical current transformer (4), and between the third optical current transformer (4) and the processing unit (5) through the multimode 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 operating conditions, the phase difference between the high-voltage side of the protected phase and the protected 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: ； in, is the angle between the optical path of the first optical current transformer (2) and the current direction on its side, is the angle between the optical path of the second optical current transformer (3) and the current direction on its side, is the angle between the optical path of the third optical current transformer (4) and the current direction on its side, is the transformer ratio; The processing unit (5) comprises the following modules: Filter unit: used to detect the carrier signal of the optical signal output by the third optical current transformer (4) by using a filter circuit and modulated wave signal ， Modulation ratio calculation unit: used to calculate the modulation ratio according to the following formula ： ， Differential current calculation unit: used to calculate the differential current according to the following formula ： ， in, is the Field constant of the Faraday magneto-optical element in the optical current transformer, It 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.

2. The optical computing system for relay protection based on Faraday magneto-optical effect according to claim 1, characterized in that: The first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) have the same internal structure and all include a collimator, a polarizer, a Faraday magneto-optical element and an analyzer. The incident light is collimated by the collimator and then enters the polarizer to become polarized light. The polarized light passes through the Faraday magneto-optical element and rotates under the modulation of the magnetic field where the Faraday magneto-optical element is located. The rotated polarized light passes through the analyzer and then is emitted through the collimator. The output end of the polarization analyzer includes Output and At the output end, the transmission axis of the polarizer and the analyzer Output and The angles of the transmission axes at the output end are and ， The optical signals output by the first optical current transformer (2) and the third optical current transformer (4) are both obtained from the polarization analyzers thereof. The output terminal outputs the optical signal output by the second optical current transformer (3) from its polarization analyzer. Output terminal output.

3. The optical computing system for relay protection based on Faraday magneto-optical effect 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 relay protection based on Faraday magneto-optical effect according to claim 3, characterized in that: The light intensity of the optical signal output by the third optical current transformer (4) for: ， in, is the intensity of the light emitted by the light source (1).

5. The optical computing system for relay protection based on Faraday magneto-optical effect according to claim 1, characterized in that: The light source (1) is an SLD light source with a wavelength of 850 nm.

6. A light calculation method for relay protection based on Faraday magneto-optical effect, 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, which includes: 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 carries the optical rotation angle containing the differential current information. , optical signals are transmitted between the light source (1) and the first optical current transformer (2), 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 multimode optical fibers; 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 operating conditions, the phase difference between the high-voltage side of the protected phase and the protected 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: ， in, is the angle between the optical path of the first optical current transformer (2) and the current direction on its side, is the angle between the optical path of the second optical current transformer (3) and the current direction on its side, is the angle between the optical path of the third optical current transformer (4) and the current direction on its side, is the transformer ratio; The light calculation method for transformer optical differential protection is: A filter circuit is used to detect the carrier signal of the optical signal output by the third optical current transformer (4). and modulated wave signal ， The modulation ratio is calculated according to the following formula ： ， The differential current is calculated according to the following formula ： ， in, is the Field constant of the Faraday magneto-optical element in the optical current transformer, It 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.

7. The method for calculating light for relay protection based on Faraday magneto-optical effect according to claim 6, characterized in that: The first optical current transformer (2), the second optical current transformer (3) and the third optical current transformer (4) have the same internal structure and all include a collimator, a polarizer, a Faraday magneto-optical element and an analyzer. The incident light is collimated by the collimator and then enters the polarizer to become polarized light. The polarized light passes through the Faraday magneto-optical element and rotates under the modulation of the magnetic field where the Faraday magneto-optical element is located. The rotated polarized light passes through the analyzer and then is emitted through the collimator. The output end of the polarization analyzer includes Output and At the output end, the transmission axis of the polarizer and the analyzer Output and The angles of the transmission axes at the output end are and ， The optical signals output by the first optical current transformer (2) and the third optical current transformer (4) are both obtained from the polarization analyzers thereof. The output terminal outputs the optical signal output by the second optical current transformer (3) from its polarization analyzer. Output terminal output.

8. The optical calculation method for relay protection based on Faraday magneto-optical effect according to claim 6 or 7, 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).

9. The method for calculating light for relay protection based on Faraday magneto-optical effect according to claim 8, characterized in that: The light intensity of the optical signal output by the third optical current transformer (4) for: ， in, is the intensity of the light emitted by the light source (1).

10. The optical calculation method for relay protection based on Faraday magneto-optical effect according to claim 6, characterized in that: The light source (1) is an SLD light source with a wavelength of 850 nm.

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