Optically Driven Current Transformer with Optical Fiber Data Link

An optical fiber transmitting photoelectric coupling current transformer has been developed. In the environment of high voltage and electromagnetic fields, this device is characterized by high insulation, high reliability, small mass and high anti-interference. The structure design and operating principle of the system are introduced, measurement errors are analyzed and experimental results are given.

Design and applicability analysis of independent double acquisition circuit of all-fiber optical current transformer

The advantages of the all-fiber optical current transformer include but are not limited to being small in size,having no magnetic saturation,exhibiting high measurement accuracy,and boasting strong electromagnetic interference resistance.However,the high cost of the all-fiber optical transformer limits its promotion and application in engineering.This paper proposes a design scheme of an independent double acquisition loop for the all-fiber optical current transformer based on the single optical path.Firstly,based on the closed-loop control mode and open-loop control mode,the twochannel sampling signal demand for relay protection,and the independent dual-acquisition loop design scheme of the all-fiber optical current transformer are proposed.Secondly,the reliability and economic feasibility of the scheme are demonstrated by an analysis of system failure and cost.The results show that the scheme can actualize the acquisition function of two independent all-fiber optical current transformer products on a single all-fiber current transformer in an integrated manner,which greatly reduces the cost of the all-fiber optical current transformer in engineering applications.

Analysis of Conducted Disturbance via Current Transformer Due to Switch Operation of GIS Disconnector in UHV Substation

The characteristics of conducted disturbances via current transformer(CT)caused by switch operations in 1000 kV UHV substations are studied in this paper.Since the broadband circuit models might have limitations on the stability and accuracy for CT conducted disturbance simulation,a frequencydomain simulation method without circuit synthesis is proposed based on VFTC spectrum and CT transfer characteristics.To improve VFTC simulation accuracy,both the bushing radiation loss and frequency-dependent earth impedance are taken into consideration.Transfer characteristics of three types of windings for the 1000 kV GIS CT are ingeniously measured from a combination of fast and slow impulse tests.Through conducted disturbances simulations in UHV Wuhu substation,bushing radiation loss is found to have a suppression effect on the highfrequency response but the effect of frequency-dependent earth impedance can be ignored.As a result,the maximum amplitude of 84.5 A for the conducted disturbance is obtained,thus a fast damped oscillatory wave immunity test with no lower than Level 4 from IEC standard is suggested to test the anti-interference performance of the secondary equipment in UHV substation.

Transformer Internal and Inrush Current Fault Detection Using Machine Learning

Preventive maintenance in the transformer is performed through a dif-ferential relay protection system,and it protects the transformer from internal and external faults.However,the Current Transformer(CT)in the differential protec-tion system mal-operates during inrush currents.CT saturates due to magnetizing inrush currents and causes false tripping of the differential relays.Moreover,iden-tification of tripping in protection relay either due to inrush current or internal faults needs to be diagnosed.For the above problem,continuous monitoring of transformer breather and CT terminals with thermal camera helps detect the trip-ping in relay due to inrush or internal fault.The transformer’s internal fault leads to high breathing process in the transformer breather,never for inrush currents.During inrush currents,CT temperature is increased.Continuous monitoring of breather and CT of the transformer through thermal imaging and radiometric pix-els detect the causes of CT saturation and differentiates maloperation.Hybrid wavelet threshold image analytics(HWT-IA)based radiometric pixels analysis of the transformer breather and CT after de-noising provides an accurate result of about 95%for identification of the false tripping of differential protection system of transformer.

Transmission Line Distance Protection Under Current Transformer Saturation

Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current,operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-ahalf configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.

Novel Fiber Optic Current Transformer With New Phase Modulation Method

Based on the transverse electro-optic effect of lithium niobate crystal,combined with polarizers and Faraday rotator,this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method,and the feasibility of the scheme is verified by both the theoretical and experimental evidences.The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency,improves the sensitivity and stability of the system,and reduces the volume and cost of fiber optic current transformer.The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect,which enhances the signal to noise ratio and simplifies demodulation mode.The experimental results show that the current ratio errors measured at room temperature range from 1%to 120%of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S.The temperature stability of the current transformer is also tested,and the ratio error measured at the rated current does not exceed±0.2%in the range of-30℃to 50℃.

Toroidal Coil in Measuring Alternating Current at a Distance

This article discusses the use of a toroidal coil in measuring alternating current from a straight current-carrying wire passing perpendicularly through the coil. The sinusoidally oscillating current generates a sinusoidally oscillating magnetic field in its vicinity. This, in turn, induces a sinusoidally oscillating emf in the toroid. This (measured) emf can be used in order to calculate the magnitude of the electric current in the wire. The use of such technique might be sensitive to the location of the point at which the wire passes through the toroid. If the location is not known very precisely, this might cause errors in the value of the calculated current. We wanted to study if the result does not depend on the location of the wire at all, as is usually stated, or not. The study was done by deriving a single analytical formula for finding out the calculated current with the wire passing through any given point inside the toroid. This formula was then solved at more than 2300 points inside a toroid to see if the location of the wire affects the result or not.

Distribution characteristics of delta reservoirs reshaped by bottom currents:A case study from the second member of the Yinggehai Formation in the DF1-1 gas field,Yinggehai Basin,South China Sea

The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGHF)is the main gas-producing formation and is composed of various sedimentary types;however,a clear understanding of the sedimentary types and development patterns is lacking.Here,typical lithofacies,logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling,logging,analysis and testing data.Based on 3D seismic interpretation and attribute analysis,the origin of high-amplitude reflections is clarified,and the main types and evolution characteristics of sedimentary facies are identified.Taking gas formation upper II(IIU)as an example,the plane distribution of the delta front and bottom current channel is determined;finally,a comprehensive sedimentary model of the YGHF second member is established.This second member is a shallowly buried“bright spot”gas reservoir with weak compaction.The velocity of sandstone is slightly lower than that of mudstone,and the reflection has medium amplitude when there is no gas.The velocity of sandstone decreases considerably after gas accumulation,resulting in an increase in the wave impedance difference and high-amplitude(bright spot)reflection between sandstone and mudstone;the range of high amplitudes is consistent with that of gas-bearing traps.The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps,and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps.The study area is a delta front deposit developed on a shallow sea shelf.The lithologies of the reservoir are mainly composed of very fine sand and coarse silt,and a variety of sedimentary structural types reflect a shallow sea delta environment;upward thickening funnel type,strong toothed bell type and toothed funnel type logging facies are developed.In total,4 stages of delta front sand bodies(corresponding to progradational reflection seismic facies)derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF;these sand bodies are dated to 1.5 Ma and correspond to four gas formations.During sedimentation,many bottom current channels(corresponding to channel fill seismic facies)formed,which interacted with the superposed progradational reflections.When the provenance supply was strong in the northwest,the area was dominated by a large set of delta front deposits.In the period of relative sea level rise,surface bottom currents parallel to the coastline were dominant,and undercutting erosion was obvious,forming multistage superimposed erosion troughs.Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.

Efficient Supply Current Control Strategies for Bridgeless Interleaved AC-DC Converter

This paper presents an efficient supply current wave shaping technique for bridgeless interleaved Single Ended Primary Inductor Converter(SEPIC).The SEPIC converter converts an Alternating Current(AC)to Direct Current(DC)with the boost converter.Power Factor Correction(PFC)is progressively significant to achieve high energy efficiency.The overall system efficiency can be increased as the bridgeless topology has less conduction losses from rectifying bridges.Also,the bridgeless and interleaved techniques are incorporated in this study to achieve better performance.The performance of the system is analyzed on both current control and sensor-less techniques.Different controllers such as Proportional Integral(PI)control,peak current control,Non-Linear Carrier(NLC)control,and sensor-less current control are integrated.All the above controllers are implemented using MATrix LABoratory(MATLAB)/SIMULINK.The performance parameter,namely Power Factor(PF),Total Harmonic Distortion(THD),is computed for both open loop and closed loop condition.The sensor-less current control method is implemented using the DsPIC30F2010 controller.The circuit performance is also verified from the simulation and hardware results.The proposed controller has inbuilt Analog-to-Digital Converter(ADC),Digital-to-Analog Converter(DAC),Pulse Width Modulation(PWM)generator,and provides fast responses.

IEC61850 standard-based harmonic blocking scheme for power transformers

Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.

Modeling and Analysis for Practical CT Based on Transient Test and Parameter Identification

In the transient process of power grid faults,the transferring distortion of current transformer(CT)can seriously affect relay protection performance.Under these conditions,it is difficult to analyze the ferromagnetic characteristic of the magnetizing branch in the transient equivalent circuit of CT.The Jiles-Atherton hysteresis model(J-A model),which is widely used in digital simulations,can accurately describe the hysteresis and saturation process of the core characteristics;however,to acquire the parameters of the J-A model of current transformers in practical use is still a challenging problem.In this paper,physical tests based on a practical CT and parameter identification are presented to solve the problem.The basic hysteresis loops of P,PR,and TPY class of practical current transformers are obtained through physical tests.Thus,the J-A model parameters are identified using a hybrid genetic/simulated annealing algorithm,based on which transient simulation models of different class CTs are constructed.The effectiveness of the proposed method is verified via dynamic physical simulation tests.A typical accident is analyzed based on these models.