CN212845562U - Optical zero sequence current transformer - Google Patents

Abstract

The application provides an optical zero sequence current transformer, includes: an optical path system unit comprising: a light source that emits a light signal; the optical circulator is optically connected with the light source; the integrated optical component is optically connected with the optical circulator and realizes the functions of polarization, modulation and polarization detection of optical signals; a sensing fiber ring optically connected to the integrated optical assembly; the optical detector is optically connected with the optical circulator; the signal processing unit is electrically connected with the integrated optical component and the optical detector respectively; the light source, the optical circulator, the integrated optical assembly and the sensing optical fiber ring are sequentially connected. The optical zero-sequence current transformer solves the problems of inconvenient installation of the zero-sequence current transformer, zero-sequence current measurement error caused by uneven arrangement of three-phase conductors and lower zero-sequence current measurement precision.

Description

Optical zero sequence current transformer

Technical Field

The utility model belongs to the technical field of electric power system, concretely relates to optics zero sequence current transformer.

Background

A Current Transformer (CT) is an important device for monitoring the operating state of an electric power system, and measurement, monitoring and protection control in a substation depends on the CT to obtain Current information required for measurement, metering and protection. The traditional current transformer is an electromagnetic transformer, and the electromagnetic transformer can not meet the development requirements of power system automation, digital networks and the like due to the reasons of heavy volume, complex insulation structure, easiness in magnetic saturation, easiness in ferromagnetic resonance, small dynamic measurement range, narrow response frequency band and the like. The Optical Current Transformer (OCT) has the advantages of simple insulating structure, small volume, light weight, good linearity, no magnetic saturation and ferromagnetic resonance problem and the like, can replace the traditional electromagnetic transformer, and has wide application prospect. Particularly, the electromagnetic current transformer can be well replaced in the zero sequence current transformer measurement of a power plant.

At present, the electromagnetic zero sequence Current Transformer (CT) in a power plant has the following problems:

(1) the model selection is difficult. The CT applied to the large synchronous generator adopts the straight-through CT because of higher voltage and large current. For zero sequence CT, three-phase current-carrying conductors simultaneously penetrate through the center of CT, and the zero sequence CT needs to identify small zero sequence current in large load current, so that the electromagnetic CT has great challenge, and the problems of small number of turns of CT windings, large magnetic leakage flux, poor precision and the like exist. For example, in a synchronous generator with an expanded unit connection mode, the rated current is generally in the range of 2000A-7000A, but when a single-phase ground fault occurs, the zero-sequence current at the generator end is relatively very small, generally in the range of 1A-20A, and the maximum zero-sequence current does not exceed 1% of the rated current of the generator; the three-phase current passes through a window of the CT, the zero-sequence current of 20A can not be detected under the condition that the three-phase current of thousands of amperes flows, and the requirement on zero-sequence CT measurement is very high.

(2) The requirements on the size and the installation space of the CT are high. The outgoing line interval of the terminal conductors of the large-scale generator sets is usually large, and the terminal interval distance of the large-scale generator sets of a part of power plants exceeds several meters, so that the appropriate size CT is difficult to select. Meanwhile, the problem that the electromagnetic CT cannot be installed due to small reserved space exists on site, for example, the machine end is a closed common-phase bus, and the electromagnetic CT cannot be installed due to small space between a conductor and a box body.

(3) When three-phase conductors at the machine end are irregularly arranged, if three-phase copper bars are parallelly led out, the electromagnetic CT can detect false zero-sequence current caused by asymmetry of a conductor space magnetic field, and the larger the current is, the greater the influence on the measurement accuracy is. The common light CT is also possibly influenced by the arrangement of three-phase copper bars because the common light CT cannot be completely magnetically closed, and the zero sequence current measurement accuracy is reduced.

The above information disclosed in this background section is only for enhancement of understanding of the background of the application and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.

SUMMERY OF THE UTILITY MODEL

The application provides an optical zero sequence current transformer, which improves the space utilization rate and reduces the volume of the zero sequence current transformer.

According to the application, the optical zero sequence current transformer comprises: an optical path system unit comprising: a light source that emits a light signal; an optical circulator optically connected to the light source; the integrated optical component is optically connected with the optical circulator and realizes the functions of polarization, modulation and polarization detection of optical signals; a sensing fiber optic ring optically connected to the integrated optical assembly; the optical detector is optically connected with the optical circulator; the signal processing unit is respectively connected with the integrated optical component and the optical detector; wherein the light source, the optical circulator, the integrated optical assembly, and the sensing fiber ring are connected in sequence.

According to some embodiments of the present application, the optical circulator comprises: an input port optically connected to the light source for receiving an optical signal; a bi-directional port optically connected to the integrated optical component for receiving and outputting optical signals; and the output port is optically connected with the optical detector and is used for outputting optical signals.

According to some embodiments of the application, the integrated optical assembly comprises: the polarization module is provided with a light transmission shaft, converts disordered input light into polarization maintaining light transmitted by the light transmission shaft, and simultaneously realizes polarization analyzing effect on the polarization maintaining light input reversely; the double refraction modulation module is provided with a fast light transmission main shaft and a slow light transmission main shaft; wherein the principal axis of output transmission of the polarizing module is at an angle of 45 ° or 135 ° to the fast axis alignment of the birefringent modulating module.

According to some embodiments of the present application, the optical zero sequence current transformer further comprises a delay fiber disposed between the integrated optical component and the sensing fiber ring.

According to some embodiments of the present application, the sensing fiber loop comprises: one end of the transmission optical cable is optically connected with the integrated optical component through the delay optical fiber, and the other end of the transmission optical cable is connected with the lambda/4 optical fiber wave plate; the lambda/4 optical fiber wave plate is connected with the transmission optical cable in a fusion mode; one end of the sensing optical fiber is connected with the lambda/4 optical fiber wave plate in a fusion mode, and the other end of the sensing optical fiber is a free end; and the reflecting mirror is arranged at the free end of the sensing optical fiber and is aligned and abutted with the lambda/4 optical fiber wave plate.

According to some embodiments of the present application, the sensing fiber comprises: and winding the periphery of the tested three-phase current-carrying conductor into a multi-turn annular structure, and simultaneously winding the three-phase current-carrying conductor in the multi-turn annular structure to form a closed magnetic circuit.

According to some embodiments of the present application, the transmission cable is fusion spliced to the delay fiber at 0 °.

According to some embodiments of the application, the transmission cable is fusion spliced to the λ/4 fiber wave plate at 45 °.

According to some embodiments of the present application, the λ/4 fiber wave plate and the mirror are synchronously disposed outside the sensing fiber ring, and the connection fiber between the two devices and the sensing fiber ring.

According to some embodiments of the application, the λ/4 fiber wave plate is arranged synchronously with the reflector, and the distance between the λ/4 fiber wave plate and the sensing fiber is larger than a preset distance.

According to some embodiments of the application, the predetermined distance is one meter.

According to some embodiments of the application, the optical zero sequence current transformer further comprises: the lambda/4 optical fiber wave plate, the reflecting mirror and the sensing optical fiber are arranged in the bendable sheath.

According to some embodiments of the present application, the bendable sheath outer surface marks the λ/4 fiber wave plate and the mirror position.

According to some embodiments of the present application, the signal processing unit includes: the signal processing unit is electrically connected or in signal connection with the optical detector; and the signal processing unit is electrically or signal-connected with the integrated optical component.

According to some embodiments, the optical zero-sequence current transformer provided by the application has the advantages of small volume, light weight and large dynamic range, and solves the problems of difficult model selection and large installation size of zero-sequence CT; the sensing optical fiber ring is made into an optical cable form, can be wound on site, flexibly adapts to the arrangement condition of a conductor on site, and solves the problems of overlarge CT size, narrow and irregular installation space and the like; the lambda/4 optical fiber wave plate and the reflector are synchronously arranged beyond the preset distance of the sensing optical fiber ring, so that the problems that the lambda/4 optical fiber wave plate and the reflector cannot be closed perfectly and the OCT measurement precision is easily influenced by the arrangement of three-phase conductors are solved; the optical circulator and the integrated optical component are adopted to replace a 2 multiplied by 2 coupler, a polarizer and a phase modulator, the available light intensity is higher, the angle alignment precision and stability are higher, the reciprocity of the optical path of the optical current transformer is optimized, and the measurement accuracy of the zero sequence current is improved.

Drawings

Fig. 1 is a schematic structural diagram of an optical zero-sequence current transformer in an exemplary embodiment of the present application;

fig. 2 is a schematic structural diagram of an optical zero-sequence current transformer in another exemplary embodiment of the present application.

List of reference numerals

100 optical path system unit

101 light source

102 optical circulator

104 integrated optical assembly

106 sensing fiber ring

108A phase current carrying conductor

109B phase current carrying conductor

110C phase current carrying conductor

112 photo detector

114 signal processing unit

200 optical path system unit

201 delay optical fiber

202 transmission optical cable

208 lambda/4 optical fiber wave plate

210 sensing optical fiber

212 mirror

Detailed Description

The invention will be described in more detail with reference to the following figures and examples, so that the aspects of the invention and their advantages can be better understood. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The terms "first," "second," "third," and "fourth," etc. in the description and claims of this application and in the accompanying drawings are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

The optical zero sequence current transformer respectively induces primary current on three-phase current-carrying conductors passing through the inside of the transformer through Faraday effect, when a lambda/4 wave plate and a reflector are perfectly closed, the response sensitivity of the transformer to three-phase current is completely consistent, and the response of the three-phase current is synthesized, namely the response is equivalent to zero sequence current response.

Under the normal state, the three-phase current is balanced, and the zero-sequence current is close to 0A, so that the zero-sequence CT has higher measurement accuracy for dealing with the small current; however, the operating current on the three-phase conductor is generally large (the power plant may exceed 10kA for a single phase), and the zero-sequence current is generally less than 1% of the operating current, so that a large zero-sequence current error may be caused if the responses of the zero-sequence CT to the three-phase current are slightly different, and therefore it is necessary to ensure that the λ/4 wave plate 208 and the mirror 212 are perfectly closed to form a closed magnetic circuit, otherwise, the three-phase response of the CT is inconsistent and a false zero-sequence current is generated because the distances from the three-phase conductor to the λ/4 wave plate and the closing point of the mirror are inconsistent. In the optical current transformer with the conventional structure, the closing error of the lambda/4 wave plate and the reflector is difficult to control within 1 cm.

In view of the above, the present application will be described below with reference to specific examples.

Fig. 1 is a schematic structural diagram of an optical zero-sequence current transformer in an exemplary embodiment of the present application.

Referring to fig. 1, according to an exemplary embodiment of the present application, an optical zero sequence current transformer includes: an optical path system unit 100 and a signal processing unit 114. The optical path system unit 100 includes: a light source 101 that emits a light signal; an optical circulator 102 optically connected to the light source 101; an integrated optical assembly 104 optically connected to the optical circulator 102, the integrated optical assembly 104 comprising a polarization module and a modulation module; a sensing fiber ring 106 optically coupled to the integrated optical assembly 104; and a light detector 112 optically connected to the optical circulator 102; and a signal processing unit 114 connected to the integrated optical assembly 104 and the light detector 112, respectively. Wherein, the light source 101, the optical circulator 102, the integrated optical component 104 and the sensing optical fiber ring 106 are connected in sequence. For example, light source 101, which may comprise a laser, emits a laser beam.

As shown in fig. 1, according to some embodiments, the optical circulator 102 is optically connected to the light source. The optical circulator 102 includes an input port optically connected to the optical source for receiving the optical signal; a bi-directional port optically connected to the integrated optical assembly for receiving and outputting optical signals; and the output port is optically connected with the optical detector and is used for outputting optical signals. In this embodiment, the optical circulator 102 can losslessly transmit the optical signal from the input port a to the bidirectional port b, and at the same time can receive the optical signal from the bidirectional port b and transmit the optical signal to the output port c. The optical circulator 102 is used in the optical zero-sequence current transformer to replace a 2 × 2 coupler widely used in the prior art, which means that the light splitting loss of the coupler is avoided to be close to 50%, so that the light utilization rate in the optical zero-sequence current transformer provided by the application is improved to be close to 4 times, the signal-to-noise ratio of a system is effectively improved, and the zero-sequence current sensitivity of the transformer is improved.

Referring to fig. 1, the integrated optical assembly 104 is optically connected to the optical circulator 102 to transmit optical signals to each other. According to some embodiments, the integrated optical assembly 104 integrates the polarization module and the birefringence modulation module together, and simultaneously performs functions of polarization, modulation and polarization reduction on the optical signal, so as to replace a separate arrangement mode of a polarizer and a modulator in the prior art, achieve higher integration level, and improve space utilization rate. In this embodiment, the integrated optical assembly 104 combines the transmission axis of the polarization module and the birefringence modulation module with fast and slow optical transmission axes, and the output transmission axis of the polarization module and the fast axis of the birefringence modulation module are aligned at an angle of 45 ° or 135 °, and the modulation axis angle can improve the accuracy and reduce the loss of the separate modulation during the connection process. The integrated optical component 104 can optimize the reciprocity of the optical path of the optical current transformer, reduce the crosstalk of the optical path and improve the current measurement precision and the anti-interference capability of the transformer.

As shown in fig. 1, a sensing fiber loop 106 is optically connected to the integrated optical assembly 104. In some embodiments, the sensing fiber ring 106 is wound around the three-phase current-carrying conductors 108, 109, and 110 to be measured to form a closed multi-turn ring structure, and the three-phase current-carrying conductors 108, 109, and 110 are simultaneously wound in the ring, so that the sensing fiber ring can form a perfect closed optical path, and the current-carrying conductors form a closed magnetic path, thereby ensuring the corresponding consistency of the three phases. In this embodiment, the high birefringence elliptical-maintaining optical fiber is used as the sensing optical fiber loop 106, so that the influence of the bending or temperature change of the sensing optical fiber 4 on the linear birefringence of the optical fiber can be effectively suppressed, and the small current precision of the sensing loop is improved. The sensing optical fiber can be flexibly wound by a plurality of turns according to the application requirement of the CT, so that the sensing optical fiber 4 can be conveniently detected to carry a weak signal of Faraday phase shift, and the measurement precision and the stability of small current can be ensured.

As shown in fig. 1, according to some embodiments, the input of the light detector 112 is optically connected to the c-terminal of the optical circulator 102. The output of the photodetector 112 is connected to the input of a signal processing unit 114.

The signal processing unit 114 is converted into a digital signal by an analog-digital a/D converter, and the signal processing unit calculates and outputs the zero sequence current value to be measured. Meanwhile, the signal processing unit generates a digital modulation signal, which is converted into an analog signal by a digital-to-analog D/a converter and applied to a modulation module in the integrated optical module 104. In the present embodiment, the connection of the signal processing unit 114 to the light detector 112 and the integrated optical assembly 104 includes an electrical connection or a signal connection, although the connection relationship is not limited thereto.

As shown in fig. 1, a light source 101, an optical circulator 102, an integrated optical component 104, and a sensing fiber ring 106 in the optical zero sequence current transformer are connected in sequence. The optical zero-sequence current transformer is based on Ampere (Ampere) loop law and Faraday magneto-optical effect, and indirectly measures the zero-sequence current value after three-phase current combination by detecting the phase difference formed between two beams of polarized light transmitted in a sensing optical fiber ring arranged at the periphery of 108, 109 and 110 three-phase current-carrying conductors.

According to some embodiments, the optical zero sequence current transformer for detecting zero sequence current provided by the application has the advantages of small volume, light weight and large dynamic range, and is flexibly suitable for field arrangement conditions of power equipment.

Fig. 2 is a schematic structural diagram of an optical zero-sequence current transformer in another exemplary embodiment of the present application.

Referring to fig. 2, according to some embodiments, the optical zero sequence current transformer comprises an optical path system unit 200 and a signal processing unit 114. The optical path system unit is provided with a light source 101, an optical circulator 102, an integrated optical component 104, a delay optical fiber 201, a sensing optical fiber loop 106 and a light detector 112. The parts are connected in series in the optical path system unit, with the delay fiber 201 disposed between the integrated optical component 104 and the sensing fiber loop 106.

Referring to fig. 2, the functions and principles of the components of the light source 101, the optical circulator 102, the integrated optical assembly 104, the optical detector 112 and the signal processing unit 114 in fig. 1 are similar and will not be described herein again. In this embodiment, the optical zero sequence current transformer further includes a delay fiber 201 for transmitting the optical signal in the delay fiber for a certain time to adapt to the processing time required by the signal processing unit 114. It is further noted that in some embodiments, the light source 101, the optical circulator 102, and the integrated optical assembly 104 are all fused together with a polarization maintaining fiber at 0 °.

As shown in FIG. 2, according to some embodiments, the sensing fiber loop 106 is comprised of a transmission cable 202, a λ/4 fiber plate (λ/4 plate) 208, a sensing fiber 210, and a mirror 212. For example, one end of the transmission cable 202 is optically connected to the integrated optical module 104 through the delay fiber 201, and the other end of the transmission cable 202 is connected to the λ/4 fiber waveplate 208. And the lambda/4 optical fiber wave plate 208 is connected with the transmission optical cable 202 in a fusion mode. One end of the sensing optical fiber 210 is connected with the lambda/4 optical fiber wave plate 208 in a welding mode, a multi-ring annular structure is wound on the peripheries of the three-phase current-carrying conductors 108, 109 and 110 to be detected, the three-phase current-carrying conductors are simultaneously wound in the sensing optical fiber 210 to form a closed magnetic circuit, and the other end of the sensing optical fiber 210 is a free end. And a mirror 212 disposed at the free end of the sensing fiber 210 and in close proximity to the λ/4 fiber plate 208.

As shown in fig. 2, in the present embodiment, the transmission cable 202 is connected between the delay fiber 201 and the λ/4 plate 208, and the transmission cable 202 and the delay fiber 201 are fusion-spliced at 0 °. The transmission optical cable 202 is an optical cable having a core of polarization maintaining fiber, which is a panda type polarization maintaining fiber like the delay fiber 201. The transmission optical cable 202 and the lambda/4 wave plate 208 are connected in a fusion mode at an optical fiber fusion point of 45 degrees, the lambda/4 wave plate 208 and the annular sensing optical fiber 210 are in fusion connection at any angle, and the reflecting mirror 212 is a reflecting film coated on the tail section of the annular sensing optical fiber 210.

As shown in fig. 2, according to some embodiments, the ring-shaped sensing fiber 210 provides a closed optical path for transmitting two orthogonal polarized lights on one hand, and sensitively induces a closed magnetic field formed around a current in a current-carrying conductor passing therethrough to form a phase difference between the two polarized lights on the other hand. Referring to fig. 2, the sensing fiber loop may be arranged in any shape including, but not limited to, circular, elliptical, racetrack, etc. 108. 109, 110A, B, C three-phase current-carrying conductors can be arranged in the optical fiber ring in any mode, and the closed magnetic fields of the three-phase conductors in the optical fiber ring are superposed and are equivalent to the influence of zero-sequence current.

Theoretically, the sensing optical fiber 210 of the optical fiber sensing ring 106 is wound on the current-carrying conductor to be measured, and the λ/4 wave plate 208 is completely aligned with the reflector 212, so that the sensing optical fiber 4 forms a complete closed loop, and then the sensing optical fiber 210 of the complete closed loop is not influenced by the position of the current-carrying conductor in the loop according to the ampere loop law and the faraday magneto-optical effect of the optical fiber. However, in practice, when it is installed, the λ/4 wave plate 208 and the mirror 212 may not be aligned completely, and the optical zero sequence current transformer is still affected by the position of the current-carrying conductor, and the closer the current-carrying conductor is to the positions of the λ/4 wave plate 208 and the mirror 212, the more significant the effect is.

Referring to fig. 2, in view of the technical defects in the practical application, the λ/4 fiber wave plate 208 and the reflector 212 of the optical zero sequence current transformer provided by the present application need to be arranged at a linear distance greater than a preset distance outside the multi-turn ring structure of the sensing fiber 210 in synchronization. For example, the preset distance may be set to one meter. According to some embodiments, the λ/4 plate 208 and the mirror 212 are simultaneously pulled out of the sensing fiber 210 by more than one meter, are arranged at a position far away from the current carrying conductor, and are aligned and abutted, and the sensing fibers 210 on the path are arranged in parallel and abutted. By utilizing the position arrangement, the sensing optical fiber 210 is basically not influenced by a three-phase current magnetic field any more, and even if the sensing optical fiber and the three-phase current magnetic field are slightly misaligned in the spatial position, the zero-sequence current precision cannot be greatly influenced, so that the zero-sequence current measurement precision of the mutual inductor can be ensured, and the problem that the conventional optical zero-sequence current mutual inductor cannot meet the application requirement due to the fact that perfect closing cannot be realized is solved.

According to some embodiments, the λ/4 wave plate 208, the sensing fiber 210 and the reflector 212 are integrally inserted into a flexible sheath, and made into a cable form, which can support winding in an engineering field, support installation in any size and shape, and greatly improve convenience and universality of installation and maintenance.

As shown in fig. 2, the working process of the novel optical zero sequence current transformer of the present application is described in detail as follows.

Light emitted by a light source 101 is transmitted to an integrated optical component 104 through a light circulator 102, a polarization module in the integrated optical component 104 generates linearly polarized light, the polarization direction of the linearly polarized light and a birefringence modulation module are provided with a fast light transmission main shaft and a slow light transmission main shaft, the output light transmission main shaft of the polarization module and the fast axis of the birefringence modulation module are aligned at an angle of 45 degrees or 135 degrees, the linearly polarized light is divided into two beams of orthogonal linearly polarized light, the two beams of orthogonal linearly polarized light are respectively injected into the fast axis and the slow axis of a polarization maintaining optical fiber, are modulated after passing through the modulation module, and are transmitted to a sensing optical fiber ring 106 along a polarization maintaining delay. The orthogonal linearly polarized light reaches the λ/4 fiber wave plate 208, becomes left circularly polarized Light (LHCP) and right circularly polarized light (RHCP), and enters the sensing fiber.

Referring to fig. 2, when polarized light reaches the sensing fiber 210, primary currents on the three-phase current-carrying conductors respectively form magnetic fields around the conductors, and simultaneously generate a faraday magneto-optical effect on the sensing fiber 210. The two circularly polarized lights in the sensing fiber 210 have different propagation speeds due to the combined action of the three-phase current magnetic fields, and the lights with the phase difference are reflected by the reflector 212. Two beams of circularly polarized light are returned along the original optical path after exchanging mode fields, so that the Faraday phase shift in the sensing optical fiber is doubled. And is converted into two orthogonal linearly polarized light with mutually exchanged modes by the lambda/4 optical fiber wave plate 208 again, namely the linearly polarized light originally transmitted along the fast axis of the polarization maintaining optical fiber is transmitted along the slow axis at the moment. The linearly polarized light that originally transmitted along the slow axis of the polarization maintaining fiber is now transmitted along the fast axis. Two beams of light carrying phase information of the faraday effect are returned to the polarization module in the integrated optical component 104 to interfere, and the interfered optical signals reach the optical detector 112 through the optical circulator to complete photoelectric conversion.

The signal processing unit 114 receives the electrical signal converted by the photodetector 112, converts the electrical signal into a digital quantity through an analog-to-digital a/D chip, performs demodulation operation, and calculates a faraday phase shift carried in the interference optical signal, thereby obtaining a zero sequence current to be measured. Meanwhile, the signal processing unit 114 generates a digital modulation signal, which is converted into an analog quantity through a digital-analog D/a chip, and the analog quantity is applied to a modulation module in the integrated optical component as a control quantity, thereby realizing modulation of the whole optical zero-sequence current transformer.

According to some embodiments, the optical cable made of the sensing optical fiber ring can be wound on site, flexibly adapts to the site position arrangement condition, and solves the problems that a current transformer is irregular in the prior art and the like.

According to some embodiments, the optical current transformer in each of the above embodiments uses an optical circulator and an integrated optical component instead of a 2 × 2 coupler, a polarizer and a phase modulator, and has higher available light intensity, higher angle alignment accuracy and stability, and optimizes reciprocity of an optical path of the optical current transformer, and improves zero-sequence current measurement accuracy.

According to some embodiments, the λ/4 optical fiber wave plate and the reflector which are far from the sensing optical fiber in the optical zero-sequence current transformer solve the problem that the two devices in the prior art cannot be closed perfectly, so that the measurement accuracy of the transformer is not affected by the arrangement of three-phase conductors.

It should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious changes and modifications may be made without departing from the scope of the present invention.

Claims (14)

1. An optical zero sequence current transformer, characterized by comprising:

an optical path system unit comprising:

a light source that emits a light signal;

an optical circulator optically connected to the light source;

the integrated optical component is optically connected with the optical circulator and realizes the functions of polarization, modulation and polarization detection of optical signals;

a sensing fiber optic ring optically connected to the integrated optical assembly;

the optical detector is optically connected with the optical circulator;

the signal processing unit is respectively connected with the integrated optical component and the optical detector;

wherein the light source, the optical circulator, the integrated optical assembly, and the sensing fiber ring are connected in sequence.

2. The optical zero sequence current transformer of claim 1, characterized in that the optical circulator comprises:

an input port optically connected to the light source for receiving an optical signal;

a bi-directional port optically connected to the integrated optical component for receiving and outputting optical signals;

and the output port is optically connected with the optical detector and is used for outputting optical signals.

3. Optical zero sequence current transformer according to claim 1, characterized in that the integrated optical assembly comprises:

the polarization module is provided with a light-transmitting main shaft;

the double refraction modulation module is provided with a fast light transmission main shaft and a slow light transmission main shaft;

wherein the principal axis of output transmission of the polarizing module is at an angle of 45 ° or 135 ° to the fast axis alignment of the birefringent modulating module.

4. The optical zero sequence current transformer of claim 1, further comprising:

a delay fiber disposed between the integrated optical component and the sensing fiber loop.

5. The optical zero sequence current transformer of claim 4, wherein the sensing fiber ring comprises:

one end of the transmission optical cable is optically connected with the integrated optical component through the delay optical fiber, and the other end of the transmission optical cable is connected with the lambda/4 optical fiber wave plate;

the lambda/4 optical fiber wave plate is connected with the transmission optical cable in a fusion mode;

one end of the sensing optical fiber is connected with the lambda/4 optical fiber wave plate in a fusion mode, and the other end of the sensing optical fiber is a free end;

and the reflecting mirror is arranged at the free end of the sensing optical fiber and is aligned and closely arranged with the lambda/4 optical fiber wave plate.

6. The optical zero sequence current transformer of claim 4, wherein the sensing fiber comprises:

and winding the periphery of the tested three-phase current-carrying conductor into a multi-turn annular structure, and simultaneously winding the three-phase current-carrying conductor in the multi-turn annular structure to form a closed magnetic circuit.

7. The optical zero sequence current transformer of claim 5, wherein the transmission optical cable and the delay fiber are fusion-spliced at 0 °.

8. The optical zero sequence current transformer of claim 5, wherein the transmission cable is fusion-spliced with the λ/4 fiber wave plate at 45 °.

9. The optical zero sequence current transformer of claim 5, wherein the λ/4 fiber wave plate and the reflector are synchronously disposed outside the sensing fiber ring, and two devices are arranged in parallel with the connecting fiber between the sensing fiber ring.

10. The optical zero sequence current transformer of claim 9, wherein the λ/4 fiber wave plate is arranged in synchronization with the mirror, and the distance from the sensing fiber ring is greater than a preset distance.

11. The optical zero sequence current transformer according to claim 10, characterized in that the preset distance is one meter.

12. The optical zero sequence current transformer of claim 5, further comprising:

the lambda/4 optical fiber wave plate, the reflecting mirror and the sensing optical fiber are arranged in the bendable sheath.

13. The optical zero sequence current transformer of claim 12, wherein the outer surface of the bendable sheath marks the λ/4 fiber wave plate and the mirror position.

14. Optical zero sequence current transformer according to claim 1, characterized in that the signal processing unit comprises:

the signal processing unit is electrically connected or in signal connection with the optical detector;

the signal processing unit is electrically connected or in signal connection with the integrated optical component.

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