A fiber-optic current transformer using a laser resonator

Abstract

The application discloses a fiber current transformer constituted by a laser resonant cavity, relates to a current detection technical field, and particularly relates to a fiber current transformer in a high-voltage transmission line, which utilizes fiber sensing technology to rapidly detect the current in a wire and is suitable for real-time detection of the current in a high-voltage line; the fiber current transformer comprises a 980nm pumping source, a wavelength division multiplexer, an erbium-doped optical fiber, a 1 / 4 wave plate, a 1550nm Faraday magneto-optic effect optical fiber coil, a mirror, a 1550nm fiber grating, a photoelectric detector and a spectrum analyzer; and has the advantages of high sensitivity, high resolution, fast inquiry speed, no phase deviation and no sine response.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current detection, in particular to a fiber-optic current transformer in high-voltage transmission line, which utilizes fiber-optic sensing technology to quickly detect the current in the conductor and is suitable for real-time detection of current in high-voltage line. BACKGROUND

[0002] At present, the commonly used current detection methods in the prior art include the following:

[0003] (1) Shunt based on Ohm's law: simple principle, high accuracy and fast response when detecting small current; large error when detecting large current, and high heat dissipation requirement. Since the shunt has direct electrical contact with the measured current loop, it needs to be powered off during installation, which increases the time, labor and material costs, and some power applications do not allow power off, which limits the use of shunts.

[0004] (2) Hall sensor: the measurement loop has no direct electrical contact with the measured current loop, ensuring personnel and equipment safety, but due to the presence of the core, the Hall sensor is usually large in size and weight, and is easily disturbed by external magnetic fields, which can easily saturate when detecting large currents.

[0005] (3) Electronic current transformer: including active electronic transformer and optical (passive electronic) transformer. Compared with traditional electromagnetic transformers, electronic transformers have the characteristics of simple insulation, no magnetic saturation, wide dynamic range, digital output, small size and easy integration, and electronic transformers also need to consider several other demand factors. For example, simplify the insulation structure to improve insulation safety, reduce manufacturing cost, reduce size and weight.

[0006] Most of the current fiber-optic current transformers monitor the magneto-optical phase shift by detecting the intensity of the interference signal, usually introducing an additional phase bias to make the system work at the point of maximum sensitivity, or using a phase modulator to fix the initial working point. However, the initial adjusted working point will be affected by the external environment, affecting the sensitivity. In addition, the measurement range of the magneto-optical phase shift of these sensors is limited within ±π / 2. SUMMARY

[0007] The present application aims to provide a fiber-optic current transformer using a laser resonant cavity to solve the problems raised in the background art, which provides a fiber-optic current transformer demodulation scheme with high sensitivity, high resolution, fast interrogation speed, no phase deviation and no sinusoidal response using laser resonant technology.

[0008] In order to achieve the above object, the present application provides the following technical scheme: a fiber current transformer using a laser resonant cavity, comprising a 980nm pump source, a wavelength division multiplexer, an erbium-doped optical fiber, a 1 / 4 wave plate, a 1550nm Faraday magneto-optic effect fiber coil, a mirror, a 1550nm fiber grating, a photodetector, and a spectrum analyzer; the light emitted by the laser pump source passes through the 980 / 1550 wavelength division multiplexer, and then passes through the erbium-doped optical fiber gain along the optical path, passes through the 1 / 4 wave plate and the magneto-optic sensing fiber around the energized wire, is reflected by the mirror at the end of the optical path, returns along the original optical path, and then passes through the magneto-optic sensing fiber, the 1 / 4 wave plate, the erbium-doped optical fiber, and the wavelength division multiplexer along the 1550 receiving end to reach the 1550nm fiber grating; the laser resonates in the resonant cavity composed of the 1550nm fiber grating, various devices in the optical path system, and the mirror at the end of the optical path, is transmitted into the photodetector through the 1550nm fiber grating, is down-converted from an optical signal to an electrical signal, and the beat frequency signal can be observed by the spectrum analyzer; when there is no current in the wire, a group of beat frequency signals can be observed; when there is current in the wire, two groups of beat frequency signals can be observed; and when the current in the wire changes, the second group of beat frequency signals will move.

[0009] After the polarized light of the orthogonal mode in the fiber laser resonant cavity passes through the 1 / 4 wave plate, a left-handed circularly polarized light and a right-handed circularly polarized light are formed. When there is current in the wire, due to the Faraday magneto-optic effect, the left-handed and right-handed circularly polarized light propagating in the magneto-optic effect sensing fiber will produce a phase difference, so that two groups of beat frequency signals can be observed on the spectrum analyzer; when the current changes, the phase difference produced by the left-handed and right-handed circularly polarized light propagating in the magneto-optic effect sensing fiber will change, and thus one group of beat frequency signals will move.

[0010] Since the laser resonates in the resonant cavity, the magneto-optic effect of one round trip length of the magneto-optic effect sensing fiber is received every time the laser oscillates, and the Faraday magneto-optic effect is non-reciprocal, so that the magneto-optic effect of the sensing fiber is superimposed twice every round trip, and after multiple oscillations, the sensitivity is high. When demodulating the sensing information, the optical domain detection has poor stability and high cost, while the electrical domain detection has low cost and good stability. The sensing signal is down-converted from the optical domain to the electrical domain by the photodetector, the beat frequency change is directly detected in the electrical domain to realize current sensing, which greatly reduces the demodulation cost, avoids the problems of the observation signal being affected by the system environmental noise and the need to use a lock-in amplifier to detect a weak intensity signal, and simplifies the system structure.

[0011] In order to further optimize the present application, the following technical scheme can be preferred:

[0012] A kind of optical fiber current transformer using laser resonant cavity, vertical cavity semiconductor laser, optical fiber coupler, 1 / 4 wave plate, Faraday magneto-optic effect optical fiber, mirror, photodetector, spectrum analyzer constitute optical fiber current sensing system.

[0013] Preferably, laser resonant cavity uses vertical cavity semiconductor laser as laser light source and mirror, saves using 980nm pump light source, wavelength division multiplexer, 1550nm Bragg grating, erbium-doped fiber, builds fiber laser system, further simplifies system structure.

[0014] The present application has the following beneficial effects:

[0015] 1, ordinary optical fiber current transformer measures one round-trip magneto-optic effect, the present application constitutes laser resonant cavity and measures the magneto-optic effect of multiple oscillations, with higher sensitivity.

[0016] 2, ordinary optical fiber current transformer detects the intensity of interference signal in time domain to detect current size, the present application places the optical part of optical fiber current transformer into laser resonant cavity, constitutes laser, and laser resonates in resonant cavity, maps current size to frequency domain, and detects beat frequency signal in frequency domain.Effectively avoid the influence of system noise, loss, light source power fluctuation on measurement resolution and error in the process of traditional signal detection in time domain.

[0017] 3, the present application uses laser resonant technology, without introducing additional phase bias, thereby solving the problem of unstable sensitivity.No need for optoelectronic modulation and Y-shaped waveguide detection, greatly simplifying system structure and reducing manufacturing cost.

[0018] 4, ordinary optical fiber current transformer is limited within ±π / 2 due to detecting magneto-optic phase shift by intensity, and the present application detects the size of current by observing the change of frequency by laser resonance, so that the dynamic measurement range is not limited.

[0019] 5, when demodulating sensing information, optical domain detection demodulation speed is slow and cost is high, while electric domain detection cost is low and stability is good.The present application uses photodetector to down-convert current sensing information from optical domain to electric domain, and detects in frequency domain rather than in time domain, with strong anti-interference ability and greatly reduced demodulation cost. BRIEF DESCRIPTION OF DRAWINGS

[0020] Fig. 1 It is the overall structure schematic view of optical fiber current transformer in embodiment 1;

[0021] Fig. 2 It is the overall structure schematic view of optical fiber current transformer in embodiment 2;

[0022] Wherein, 1 - spectrum analyzer, 2 - photodetector, 3 - fiber Bragg grating, 4 - 980nm pump source, 5 - wavelength division multiplexer, 6 - 1 / 4 wave plate, 7 - power supply wire, 8 - Faraday magneto-optic effect fiber, 9 - vertical cavity semiconductor laser, 10 - fiber coupler. DETAILED DESCRIPTION

[0023] 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.

[0024] As Figs. 1-2 shown,

[0025] Embodiment 1:

[0026] The fiber current sensing system comprises a 980nm pump source, a wavelength division multiplexer, a doped fiber amplifier, a 1 / 4 wave plate, a Faraday magneto-optic effect sensing fiber, a mirror, a fiber grating, a photodetector and a spectrum analyzer.

[0027] Embodiment 2:

[0028] The fiber current sensing system comprises a vertical cavity semiconductor laser, a fiber coupler, a 1 / 4 wave plate, a Faraday magneto-optic effect fiber, a mirror, a photodetector and a spectrum analyzer.

[0029] Embodiment 3:

[0030] The above two systems are added with a polarizer to form a fiber current sensing system which can observe envelope changes on a spectrum analyzer.

[0031] Method for measuring current by laser beat frequency

[0032] When a current passes through the wire, the excited orthogonal polarized light in the resonant cavity passes through the 1 / 4 wave plate to form a left circularly polarized light and a right circularly polarized light, and when passing through the Faraday magneto-optic effect sensing fiber, due to the existence of the Faraday magneto-optic effect, the two circularly polarized lights will produce an optical path difference, which means that the cavity lengths of the respective laser resonant cavities are different, so that two groups of beat frequency signals can be observed on the spectrum analyzer. When the current changes, the optical path difference produced by the left circularly polarized light and the right circularly polarized light when the laser passes through the Faraday magneto-optic effect sensing fiber will change, at which time a group of beat frequency signals can be observed to move on the spectrum analyzer.

[0033] The working principle of the device is as follows: 980nm pump light, after passing through a 980 / 1550 wavelength division multiplexer, passes through an erbium-doped optical fiber gain along the optical path, passes through a 1 / 4 wave plate, a magneto-optic induction fiber around the energized wire, is reflected by a mirror at the end of the optical path, returns along the original optical path, successively passes through the magneto-optic induction fiber, the 1 / 4 wave plate, the erbium-doped optical fiber, passes through the wavelength division multiplexer, and reaches the 1550nm fiber grating along the 1550 receiving end. The laser resonates in the resonant cavity composed of the 1550nm fiber grating, various devices in the optical path system, and the mirror at the end of the optical path. The optical signal is converted into an electrical signal by the photoelectric detector, and the beat frequency signal can be observed by the spectrum analyzer. When there is no current flowing through the wire, a group of beat frequency signals can be observed; when there is current flowing through the wire, two groups of beat frequency signals can be observed; when the current in the wire changes, the second group of beat frequency signals will move.

[0034] When current flows through the wire, the orthogonally polarized light excited in the resonant cavity will form a left-handed circularly polarized light and a right-handed circularly polarized light after passing through the 1 / 4 wave plate. When passing through the Faraday magneto-optic effect sensing fiber, due to the existence of the Faraday magneto-optic effect, the two circularly polarized lights will produce an optical path difference, which means that the cavity lengths of the respective laser resonant cavities are different. Thus, two groups of beat frequency signals can be observed on the spectrum analyzer. When the current changes, the optical path difference produced by the left-handed circularly polarized light and the right-handed circularly polarized light when the laser passes through the Faraday magneto-optic effect sensing fiber will change. At this time, a group of beat frequency signals can be observed to move on the spectrum analyzer.

[0035] According to the Faraday magneto-optic effect, the left-handed circularly polarized light and the right-handed circularly polarized light will produce a phase difference φ, where:

[0036] φ=KN F N S I

[0037] In the formula, K is a constant; N F is the number of turns of the sensing fiber; N S is the number of turns of the energized wire around the sensing fiber; I is the current flowing through the wire.

[0038] Since the orthogonally polarized light excited in the resonant cavity will form a left-handed circularly polarized light and a right-handed circularly polarized light after passing through the 1 / 4 wave plate, the two circularly polarized lights will produce a phase difference φ when passing through the magneto-optic effect sensing fiber around the energized wire. After being reflected by the mirror, they will again produce a phase difference φ when passing through the magneto-optic effect sensing fiber again. Since the magneto-optic effect is non-reciprocal, the phase difference for one round trip is: θ=2φ.

[0039] When there is no current in the wire, the frequency interval of the beat frequency signals is:

[0040]

[0041] wherein Δv is the frequency interval of the beat signal; n is the refractive index of the fiber; and L is the cavity length of the resonant cavity.

[0042] When there is current in the wire, the beat signal is:

[0043]

[0044] wherein n R is the refractive index of right-handed circularly polarized light in the Faraday magneto-optic fiber; n L is the refractive index of left-handed circularly polarized light in the Faraday magneto-optic fiber; and B is the birefringence of the Faraday magneto-optic fiber.

[0045] The birefringence of the optical fiber is:

[0046]

[0047] wherein λ is the wavelength of the laser light, and L F is the length of the Faraday magneto-optic fiber.

[0048] Thus, the corresponding relationship between the change of the beat signal and the magnitude of the current is:

[0049]

[0050] By observing the change of the beat signal of the laser resonant cavity on the spectrum analyzer, the magnitude of the current in the wire can be calculated.

[0051] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A fiber optic current transformer constructed using a laser resonant cavity, characterized in that: It includes 980nm pump source, 980nm / 1550nm wavelength division multiplexer, erbium-doped fiber, 1 / 4 wave plate, 1550nm Faraday magneto-optic effect fiber coil, mirror, 1550nm fiber grating, photodetector, spectrum analyzer; the light emitted by the laser pump source passes through the 980 / 1550 wavelength division multiplexer, then passes through the erbium-doped fiber gain along the optical path, passes through the 1 / 4 wave plate, the magneto-optic induction fiber around the electrified wire, reflects through the mirror at the end of the optical path, returns along the original optical path, successively passes through the magneto-optic induction fiber, the 1 / 4 wave plate, the erbium-doped fiber, passes through the wavelength division multiplexer, then along the 1550 receiving end, reaches the 1550nm fiber grating, the laser resonates in the resonant cavity composed of the 1550nm fiber grating, the optical path system of various devices and the mirror at the end of the optical path, is transmitted into the photodetector through the 1550nm fiber grating, converts the optical signal into the electrical signal, and the beat frequency signal is observed through the spectrum analyzer; when there is no current passing through the wire, a group of beat frequency signals are observed; when there is current in the wire, two groups of beat frequency signals are observed; when the current in the wire changes, the second group of beat frequency signals will move.

Images