CN211905488U

CN211905488U - Closed-loop demodulation all-fiber current transformer

Info

Publication number: CN211905488U
Application number: CN201922218405.3U
Authority: CN
Inventors: 赵俊; 姜琦; 孙小菡
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2019-12-12
Filing date: 2019-12-12
Publication date: 2020-11-10
Anticipated expiration: 2029-12-12

Abstract

The utility model discloses a closed loop demodulation all-fiber current transformer. The closed-loop demodulation all-fiber current transformer is characterized in that a closed-loop demodulation device is added on the existing reflection type current transformer, compensation phase shift is introduced through step waves, and nonreciprocal phase shift caused by current is counteracted, so that the dynamic measurement range of a system is improved, meanwhile, a signal processing unit adopts a square wave modulation mode, and nonreciprocal 90-degree phase offset is introduced into an optical fiber coil, so that the problems of cosine sensitivity and directivity are solved, and finally, the measurement error of the system is reduced.

Description

Closed-loop demodulation all-fiber current transformer

Technical Field

The utility model belongs to the technical field of the optical fiber sensing, in particular to closed loop demodulation all-fiber current transformer.

Background

Electromagnetic transformers have long played an important role in monitoring the operation of electrical power systems. Measurement monitoring and protection control in substations relies on it to obtain information on the current, voltage, etc. required for measurement, metering, protection. With the improvement of the voltage of a power grid and the development of intelligent primary and secondary equipment, the traditional electromagnetic mutual inductor gradually has exposed the defects of weak electrical insulation, heavy volume, small dynamic range, iron core saturation, ferromagnetic resonance overvoltage and the like.

Along with the deep development of the automation technology of the transformer substation, novel intelligent primary equipment with the mutual permeation and fusion of primary equipment and secondary equipment appears. The optical current sensor is a new type of current sensor which introduces optical technology and components into the current sensing field and uses light as a sensing means and an information carrier. The advantages are mainly shown in that: the signal is little influenced by external electromagnetic interference in the transmission process, and meanwhile, the bandwidth is wide, the capacity is large, and the transmission distance is less limited; the sensor takes an optical device as an element and has the advantages of good insulation, small volume, light weight and high safety. Therefore, the optical current sensor has been paid great attention from the world since the advent, and has become a popular choice for replacing the conventional electromagnetic current sensor.

The optical fiber used by the all-fiber current sensor (FOCT) is a communication carrier and a sensing device, the sensing optical fiber is wound around a conductor to be measured, and a magnetic field generated around a power-on measuring lead influences signal light in the optical fiber, so that the purpose of measuring current is achieved. The all-fiber current sensor scheme integrates the advantages of an electromagnetic mutual inductor and an optical current sensor, derives the advantages of simple assembly, good flexibility, capability of increasing and decreasing the number of wound boxes according to requirements and the like, and meanwhile, along with the great reduction of the manufacturing cost of the optical fiber, the manufacturing cost is gradually low, so that the all-fiber current sensor is widely researched. However, since the optical fiber of the sensor head is made to withstand external influences such as temperature, vibration, pressure, etc., the sensitivity to temperature and vibration is higher than that of the optical glass type current sensor, which is a big obstacle to the practical use of the all-fiber type current sensor.

The all-fiber current sensor mainly comprises a single-light-path current transformer, a double-light-path current transformer, an interference optical current transformer and a reflection current transformer at present. The reflection type current transformer has the advantage of interference resistance, and is more suitable for being used as a current transformer on site. In the reflective current transformer, pipelines through which two coherent light beams pass in the transmission process are completely consistent and are transmitted in the same medium, external interference and element manufacturing deviation can affect the two light beams simultaneously, and the absolute difference of errors is offset; the light advancing directions are always the same, and phase difference is not introduced; the optical fiber is reflected by the reflector, the optical transmission path of the sensing optical fiber with the same length is doubled, and the sensitivity is improved. However, the reflective current transformer has many practical problems, and these problems may cause errors in the measurement result.

SUMMERY OF THE UTILITY MODEL

In order to solve the technical problem that the above-mentioned background art provided, the utility model provides a closed loop demodulation all-fiber current transformer.

In order to realize the technical purpose, the utility model discloses a technical scheme does:

a closed-loop demodulation all-fiber current transformer comprises an all-fiber current transformer and a closed-loop demodulation device; the all-fiber current transformer comprises a light source generator, a coupler, a polarizer, a phase modulator, a polarization maintaining fiber, an 1/4 wave plate, a sensing fiber and a reflector; the closed-loop demodulation device comprises a detector, an A/D converter, a signal processing unit and a D/A converter; the light emitted by the light source generator is input into the polarizer through the coupler to form linearly polarized light, the polarizer and the phase modulator are fused at an angle of 45 degrees, the linearly polarized light is injected into the polarization maintaining fiber at 45 degrees through the phase modulator, the light is divided into two orthogonal linearly polarized light beams which are respectively transmitted along the fast axis and the slow axis of the polarization maintaining fiber, after the two linearly polarized light beams are respectively changed into left circularly polarized light and right circularly polarized light by an 1/4 wave plate, enters the sensing optical fiber surrounding the measured current, exchanges polarization modes after being reflected by a reflecting mirror arranged at the tail end of the sensing optical fiber, passes through the sensing optical fiber again to reach 1/4 wave plates, two beams of circularly polarized light are recovered into two beams of linearly polarized light through a 1/4 wave plate, the two beams of linearly polarized light reach the polarizer through the polarization maintaining fiber and the phase modulator in sequence, interfere at the polarizer, and finally output light carrying phase information through the coupler; the detector collects light output by the coupler and converts the light into an electric signal, the electric signal is subjected to analog-to-digital conversion by the A/D converter and then transmitted to the signal processing unit, the signal processing unit demodulates the information of the current to be detected according to the received digital signal, the signal processing unit outputs a square wave modulation digital signal, the square wave modulation digital signal is subjected to digital-to-analog conversion by the D/A converter and then input to the phase modulator, so that non-reciprocal 90-degree phase offset is introduced into the polarization maintaining optical fiber, the signal processing unit outputs a step wave modulation digital signal, and the step wave modulation digital signal is subjected to digital-to-analog conversion by the D/A converter and then input to the phase modulator, so that feedback compensation phase shift is introduced into the polarization maintaining optical fiber.

Adopt the beneficial effect that above-mentioned technical scheme brought:

the utility model discloses a closed-loop demodulation all-fiber current transformer has added closed-loop demodulating equipment on current reflection formula current transformer, introduces the compensation phase shift through the ladder wave, and the nonreciprocal phase shift that the offset current arouses to improve the dynamic measurement scope of system, signal processing unit adopts square wave modulation mode simultaneously, introduces nonreciprocal 90 phase offset in fiber coil, in order to solve the problem of cosine sensitivity and directionality, finally reduces system measurement error.

Drawings

Fig. 1 is a structural diagram of the closed-loop demodulation all-fiber current transformer of the present invention;

description of reference numerals: 1: a light source generator; 2: a coupler; 3: a polarizer; 4: a phase modulator; 5: a polarization maintaining fiber coil; 6: 1/4 a wave plate; 7: a mirror; 8: a sensing optical fiber; 9: a detector; 10: an A/D converter; 11: a signal processing unit; 12: measuring the current to be measured; 13: a D/A converter; 14: a step wave modulation signal; 15: a square wave modulation signal; 16: and (6) a tested lead.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in fig. 1, a closed-loop demodulation all-fiber current transformer includes an all-fiber current transformer and a closed-loop demodulation device; the all-fiber current transformer comprises a light source generator 1, a coupler 2, a polarizer 3, a phase modulator 4, a polarization maintaining fiber 5, an 1/4 wave plate 6, a reflector 7 and a sensing fiber 8; the closed loop demodulation means comprise a detector 9, an a/D converter 10, a signal processing unit 11 and a D/a converter 13.

Light emitted by a light source generator is input into a polarizer through a coupler to form linearly polarized light, the polarizer and a phase modulator are welded in a 45-degree angle mode, the linearly polarized light is injected into a polarization maintaining optical fiber through the phase modulator at 45 degrees, then is divided into two beams of orthogonal linearly polarized light and is transmitted along the fast axis and the slow axis of the polarization maintaining optical fiber respectively, and the two beams of linearly polarized light are changed into left-handed circularly polarized light and right-handed circularly polarized light respectively through an 1/4 wave plate and then enter a sensing optical fiber surrounding the periphery of the measured current. The sensing optical fiber is used as a Faraday material and is wound outside the primary conductor to sense a magnetic field generated by the measured current, and the Faraday magneto-optical effect enables two beams of circular polarization to generate phase difference which is in direct proportion to the magnitude of the measured current. Two bundles of circularly polarized light exchange polarization modes after being reflected by a reflector arranged at the tail end of the sensing optical fiber, pass through the sensing optical fiber again, enable the generated nonreciprocal phase shift to be doubled, recover the two bundles of circularly polarized light into two bundles of linearly polarized light through an 1/4 wave plate, reach a polarizer through a polarization maintaining optical fiber and a phase modulator in sequence, interfere at the polarizer, and finally output light carrying phase information through a coupler.

The detector collects light output by the coupler and converts the light into an electric signal, the electric signal is subjected to analog-to-digital conversion by the A/D converter and then is transmitted to the signal processing unit, and the signal processing unit demodulates the information of the measured current according to the received digital signal.

Two beams of light which are interfered respectively pass through the fast axis and the slow axis of the polarization maintaining optical fiber and the same path, and the completely reciprocal structure can effectively counteract common mode disturbance generated by external stress and temperature. The interference output result is a cosine function, the response sensitivity is low near zero phase difference, the measurement range is limited, and the interference result cannot reflect the defects of directionality of input current and the like. In order to solve the problems of cosine sensitivity and directivity, the signal processing unit adopts a square wave modulation mode and introduces non-reciprocal 90-degree phase bias into the optical fiber coil. Meanwhile, in order to improve the linearity and the dynamic range, a closed-loop detection scheme is adopted, and the non-reciprocal phase shift caused by the current is offset by introducing the compensation phase shift through the step wave.

The embodiment is only for explaining the technical thought of the utility model, can not limit with this the utility model discloses a protection scope, all according to the utility model provides a technical thought, any change of doing on technical scheme basis all falls into the utility model discloses within the protection scope.

Claims

1. A closed-loop demodulation all-fiber current transformer is characterized by comprising an all-fiber current transformer and a closed-loop demodulation device; the all-fiber current transformer comprises a light source generator, a coupler, a polarizer, a phase modulator, a polarization maintaining fiber, an 1/4 wave plate, a sensing fiber and a reflector; the closed-loop demodulation device comprises a detector, an A/D converter, a signal processing unit and a D/A converter; the light emitted by the light source generator is input into the polarizer through the coupler to form linearly polarized light, the polarizer and the phase modulator are fused at an angle of 45 degrees, the linearly polarized light is injected into the polarization maintaining fiber at 45 degrees through the phase modulator, the light is divided into two orthogonal linearly polarized light beams which are respectively transmitted along the fast axis and the slow axis of the polarization maintaining fiber, after the two linearly polarized light beams are respectively changed into left circularly polarized light and right circularly polarized light by an 1/4 wave plate, enters the sensing optical fiber surrounding the measured current, exchanges polarization modes after being reflected by a reflecting mirror arranged at the tail end of the sensing optical fiber, passes through the sensing optical fiber again to reach 1/4 wave plates, two beams of circularly polarized light are recovered into two beams of linearly polarized light through a 1/4 wave plate, the two beams of linearly polarized light reach the polarizer through the polarization maintaining fiber and the phase modulator in sequence, interfere at the polarizer, and finally output light carrying phase information through the coupler; the detector collects light output by the coupler and converts the light into an electric signal, the electric signal is subjected to analog-to-digital conversion by the A/D converter and then transmitted to the signal processing unit, the signal processing unit demodulates the information of the current to be detected according to the received digital signal, the signal processing unit outputs a square wave modulation digital signal, the square wave modulation digital signal is subjected to digital-to-analog conversion by the D/A converter and then input to the phase modulator, so that non-reciprocal 90-degree phase offset is introduced into the polarization maintaining optical fiber, the signal processing unit outputs a step wave modulation digital signal, and the step wave modulation digital signal is subjected to digital-to-analog conversion by the D/A converter and then input to the phase modulator, so that feedback compensation phase shift is introduced into the polarization maintaining optical fiber.