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Air-core inductive current sensor for fast transients measurements in distribution networks
Abstract
Observation of fast transients in power networks can provide some of the most valuable information. The transients from partial discharge can provide the information about the power line insulation state; fault-produced fast transients can also provide information about the fault or problematic section location. For measurement of fast transients, there would also need to be a very fast sensor, as the pulsed measurements could require the bandwidth range reaching in the tens of MHz range. In this paper, a sensor for fast transients measurements is presented and tested. While very simple, this sensor can offer very good performance while being inexpensive and robust. The results of performance verification measurements show very good results when testing with high-frequency pulse source, presenting the potential of such sensor.
The B-dot sensor is a type of Rogowski coil widely used in the measurement of current. However, the accuracy of the B-dot for measuring aircraft high-frequency lightning current is greatly affected by factors such as numerical integration drift, high-frequency oscillation, and calibration. In this study, a new design and optimization for improving the B-dot measuring accuracy was carried out. To correct the drift of the numerical integral of the measurement signal in differential mode, the measuring current was reconstructed based on the nonlinear least squares method. The sensor was then optimized by isolating the sampling resistance and matching the impedance with a voltage follower. A low-cost coaxial loop calibration system was also designed to calibrate the high frequency and strong magnetic fields more accurately. Finally, the optimized B-dot sensor accuracy was greatly improved with a measuring range of 30 kA/m, an error of 3.1%, and a high-frequency response of 50 MHz. Our study greatly increases the accuracy of measuring aircraft high-frequency lightning current.
This paper introduces an active method for zero current switching for resonant switched capacitor converters (SCC) with wide dynamic range. The method is demonstrated on a binary SCC that features wide range of conversion ratios. Due to the resultant high efficiency of the converter operating under soft-switching conditions, it is applicable for higher power levels up to the medium power range (100 W). The resonant operation is achieved with a single air core inductor and precise commutation at zero current. The sensing signals of the resonant currents are obtained from the flying capacitors rather than form element in which the current includes a dc component. The zero detection method developed is capable of compensating for both the processing delays (from detection to switching action) and for the large variations of the resonant characteristics (due to transition between subcircuits), and for any other component variations. A 100 W prototype with maximum input voltage of 100 V and up to 19 conversion ratios has been built and tested experimentally. The current sensing has been implemented with a simple, cost-efficient, passive sensor. For proper construction of a higher power experimental prototype with desired target efficiency, a set of design considerations for the selection of the power stage components, based on an expanded equivalent resistance concept for multiple subcircuits converter, has been delineated. In addition, a simple and efficient isolated gate driver circuitry is presented.
In this paper, sensors for the application of high voltage networks insulation diagnostics are focused on. For detection and localization of the components with insulation deterioration, observing the partial discharge transients is one of the main methods. However, as the partial discharge traces are transients of extremely short duration, monitoring of such transients is also a challenging task. This paper presents the inductive sensors that would be suitable for the on-line partial discharge monitoring and the selection of operating mode and characteristics are discussed. The issues of resonance and signal processing are analyzed for the targets of reaching highest accuracy of the measurements. Operation criteria and performance limits such as sensitivity and upper bandwidth are particularly discussed. It is presented that in order to reach highest accuracy and sensitivity the sensor should be used in damped mode. Applying the accurate air-core inductive sensors would allow the condition monitoring systems to be cheaper and thus mounted for permanent and continuous condition monitoring in various locations in the power distribution networks.
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Rogowski coil (RC) is a low-cost, air-cored, and flexible induction sensor for nonintrusive condition monitoring and thus can be used in a variety of applications. In this paper, a lumped parameter model of RC is presented and an experiment-based methodology is developed to determine its parameters. The performance of the RC is analyzed for detection and measurement of high-frequency (pulsed) signals such as partial discharge (PD) current pulses. A simple and efficient technique of numerical integration is adopted to avoid the conventional type of expensive and complex design analogue integrators. RC is modeled and simulated in the alternative transient program-electromagnetic transient program environment. The designed coil is tested to measure PDs in the laboratory. Simulated and experimental performance of RC is compared with a high-frequency current transformer. This comparison shows a good match and, hence, validates the design of RC for PD applications.
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High-frequency transients in power distribution networks can be caused by faults or this may be indication of soon to happen breakdown of isolation. In many cases monitoring and precise measurements of the high-frequency phenomena can help to determine location of fault on the line, but also lead to discovery of problematic component prior to breakdown. Equipment available in distribution substations today is not capable of monitoring such high-frequency signals. In this paper a current sensor for detecting fault and pre-fault high-frequency transients is proposed. Requirements for such a sensor are presented and a sensor design meeting the requirement is carried out.
Topics regarding sensor bandwidth and sensitivity are
discussed.
This paper gives the performance of lightning overvoltage due real lightning discharges that have occurred in distribution power lines equipped with covered conductors. Evaluation and simulations are based on real lightning data collected from the Finnish Meteorological Institute (FMI) from 1998 to 2008. The presented feeder is an overhead distribution line with a covered conductor subjected to indirect lightning strokes to ground and direct lightning strokes to a line support. Evaluation of induced overvoltage from indirect stroke to the line is analyzed with MATLAB. With the Electromagnetic Transient Program (EMTP), simulations of lightning strokes are performed with different lightning current characteristics. All cases are considered with the modelling guidelines for fast transients as specified in some lightning literature. Simulations are made to compare the resulting overvoltages and energy absorptions of surge arresters for all the analyzed cases.
The breakage of overhead covered conductors on distribution lines resulting from the short-circuit arcs caused by lightning flash becomes a challenge as the application of covered conductors increases on distribution lines. Based on various methodologies and devices developed to avoid the covered conductor breakage in the world, novel arc-guided devices, including arcing protection hardware with barbs, clamping post composite insulator, and barb electrode clamping post porcelain/composite insulator are presented in this paper. Experimental results are also presented to validate these new developed devices. Devices based on the developed technologies have been widely applied on the power grids in China successfully.
A new overhead line concept based on covered conductors is
introduced in the 24 kV distribution system. However, a neutral
evaluation is necessary to clarify the service reliability in the
Norwegian exposed climate. After one year in service in a coastal area
the corrosion attack caused by simulated insulation damages is
surprisingly high and can not be neglected. Further investigations must
be carried out to clarify the factors which influence the simulation of
lightning before recommendations for arcing and overvoltage protection
can be given
Lightning overvoltages are responsible for the majority of faults and outages that occur in Medium Voltage (MV) distribution networks. The overhead lines can be protected from the above phenomena with adequate installation of surge arresters and shield wires. Insulation enhancement can also play a significant role in minimizing outage rates of the lines, though it will not be so effective. However, high and grounded structures such as trees or buildings will naturally protect the lines from direct lightning strokes, if adequate clearance between the lines and the structures is considered. This paper presents the experimental study and electro-geometric modeling on the shielding effect of trees on direct strokes to medium voltage distribution lines. The shielding effect of a nearby tree on an MV distribution conductor is compared with that of a concrete building which has been previously investigated in the literature. It is expected that the results of the comparison will serve as good recommendations for the enhancement of lightning protection in power distribution circuits.
A dynamic model for exposure of grounded objects to direct lightning strokes has been generalized to apply to buildings and massive structures. The model also applies to the mixed situation where a slender air terminal is installed on the top of a building to provide lightning protection. The basic elements of the model comprise a general criterion for continuous upward leader inception the validity of which is independent of the building or structure topology. This is followed by initiation of an upward leader trajectory which would either lead to a successful encounter with the negative downward leader through a final jump or to an aborted positive leader. Based on recent work published by the author, the model does not require any assumption regarding the ratio between the negative and positive leader speeds as has often been done previously. The modeling procedure has been facilitated through the use of dimensionless variables relating to the proximity effect of the building on space potential distribution, leader inception space potential, critical mean ambient ground field, and, finally, the attractive radius. A slender rod of the same height as the building is used as basis for comparison.
This paper describes the behavior of water as a dielectric, in particular with reference to its use in water circuit breakers. Water is generally considered to have the properties of an electrical conductor rather than those of an insulator. There are, however, a few applications where the dielectric rather than the conductive properties of water are of importance, as, for example, in its use as the interrupting liquid in circuit breakers. Here the water between electrodes must withstand full circuit voltage during the closing operation until the electrodes are in metallic contact, and also in the opening operation following extinction of the arc, until some auxiliary switch in series can open. Since there appears to be very little published information available on the subject, further knowledge of the behavior of water as a dielectric seemed to be of considerable interest and importance. To secure this information, a study of the subject was undertaken, the results of which will be reported in this paper. Experimental data are presented which indicate that electric breakdown between electrodes immersed in water is, in general, determined by the temperature rise produced by the leakage current in the water. Breakdown appears to occur when steam generation begins. Calculation of time to cause temperature rises to 100 degrees centigrade in the water agree closely with observed time between applied voltage and breakdown.
Current transformers (CTs) are adopted in power systems to measure magnitudes of currents for metering and fault protection. Since power system fault currents contain large direct current offsets, they can saturate the iron cores of the current transformers. This saturation phenomenon in iron cores will cause the protective system to make false responses. Furthermore, bulky volume of CTs also imposes restriction on their other applications. Hall integrated circuits (ICs) have high sensitivity and quick response time, and can measure a wide range of magnetic fields. Due to these attributes, this research designs a power current microsensor based on a Hall IC without an iron core. The applying Hall IC measures the magnetic field generated by a power cable and subsequently, the electric current flowing in the electric conducting cable. A measurement framework is designed and implemented to compare a series of waveforms obtained by the Hall IC with those measured by a traditional CT. This study assesses the feasibility of replacing traditional CTs with power current microsensors based on Hall ICs.
Measuring fast current pulses requires devices with ample broad bands. The approach of this paper is to present a simple sensor based on the Faraday's Law together with an integrating and amplifying stage. Its validation is done by means of the detection of Partial Discharges (PD) in electric insulation systems following the guidelines given in the standard IEC 60270. These measurements are also taken with a high frequency current transformer with the aim of comparing the results obtained with the proposed probe.
The paper presents the results of experimental tests performed with impulse voltage with short tail (STLI: 1.2/4 mus) on composite insulators in use in the MV distribution lines and electric traction lines. The voltage-time to breakdown characteristics under 1.2/4 mus waves are presented and compared with the characteristics under standard lightning impulse (LI: 1.2/50 mus). Models based on the disruptive effect, as proposed by Kind [9], and modified by Chowdhuri [13], are also considered and applied in order to predict the Volt-time characteristics under standard and non standard lightning voltages. The viability of the application of these models to the tested insulators is considered and discussed.
Summary form only given. The LIOV (lightning-induced overvoltage)
code, a computer program developed in the framework of an international
collaboration involving the Universities of Bologna (Department of
Electrical Engineering), the Swiss Federal Institute of Technology
(Power Systems Laboratory), and the University of Rome “LA
Sapienza” (Department of Electrical Engineering), is a numerical
formulation of Maxwell's equations, using the formulation of Agrawal et
al. (1980) suitably adapted for the calculation of induced overvoltages
when lightning strikes near a horizontal overhead transmission line. In
the LIOV code, the electromagnetic field radiated by the lightning
channel is calculated using the field equations in the form given by
Uman et al. (1975) with the extension to the case of lossy ground
introduced by Cooray and Rubinstein (1994) and assuming the modified
transmission line (MTL) return-stroke current model (1988) for the
description of the spatial-temporal distribution of the lightning
current along the return-stroke channel
IN RECENT YEARS renewed interest has developed in the effect of lightning on electrical transmission lines. The most vital characteristic of lightning in most methods of calculating its effect is the current measured at the ground terminal. A large amount of data is available about the stroke current crest magnitude and a considerable amount of data is available which covers the time-to-crest of the stroke current. Despite these data there is still controversy over the time-to-crest. Measurements in the region of a microsecond are admittedly difficult. The industry is still seeking new data. In approaching this problem, it was felt that it might be conducive of results to analyze the mechanism of the return stroke and then, from the factors governing the mechanism, try to synthesize the stroke. Perhaps certain limits to the rate of rise could be ascertained. Some of the characteristics of the component factors could be obtained in the laboratory, others by computation. It was with this in mind that the present investigation was undertaken.
During the past two years, 4615 Pathfinder devices were installed on approximately 433 miles of HV and EHV transmission lines suitably divided into sample classes for significant data yield. Over approximately 70 percent of a full lightning season, 14 Pathfinder operations were recorded of which 12 were caused by lightning strokes to the top phase conductors and two resulted from a double-circuit fault caused by a stroke to the ground wire or tower. Fifty transmission lines showing an average lightning trip-out rate of only 0.175 per 100 miles per year were considered effectively shielded over the sample period of 52 000 mile-years, and were accordingly analyzed for their average ground wire heights and average shield angles. The data were plotted by insulation levels and the results compared with the predictions of an analytical model developed to serve as an extrapolating device to relate field experience to the design of new lines. Important parameters of the model were determined by calibration against the field data. It is concluded that terrain factors, as determined by the actual line profile, are of major significance and must be carefully considered in establishing effective conductor and ground wire heights. While the analytical model is theoretically capable of extension to the prediction of trip-out rates for partially effective shielding, it is concluded that more data are needed before this can be done with satisfactory confidence. Copyright © 1968 by The Institute of Electrical and Electronics Engineers, Inc.
The paper deals with a laboratory investigation into the influence of rain on the switching impulse sparkover characteristics of large-sphere and toroid plane air gaps. Tests were also carried out on coneterminated rod-plane gaps for reference purposes. The factors investigated include the high voltage electrode geometry, nature of the surface, rain intensity as well as the impulse form and polarity. Attention is also paid to the influence of rain on the statistical dispersion of the sparkover voltage and on the nature of the cumulative probability curve. A general correlation, valid for a wide variety of electrodes, has been established between the mean spark-over voltage gradient for positive switching impulses under dry conditions, and the corresponding influence of rain on the breakdown voltage.
The Rogowski-coil method of measuring electric current has
developed into a versatile measuring system with many applications
throughout industry and in research. The technique possesses many
features which offer an advantage over iron-cored current measuring
devices and these are well illustrated by considering how it can be used
for measuring transient currents. The authors describe the principle of
operation of Rogowski coils and the practical aspects of using them and
give several examples of their use in making transient measurements. The
Rogowski coil is a conceptually simple device. Its theory of operation
illustrates some basic principles of electromagnetism applied in a
practical device. The coil itself provides a demonstration of Ampere's
Law which is described by the authors
This paper addresses the lightning attractive radius concept and procedures for estimating the number of lightning flashes to power lines. Empirical data - drawn from extensive observations of lightning incidence upon various practical structures (including lines) - are related to a simple analytical model of the striking process, and a generalised expression for estimating strike incidence is presented. Comparison of the new expression with current practice, suggests that the latter may lead to underestimations of more than 50% in the height range 10 - 30 m, and additionally, that expected strike incidence to taller structures could be overestimated by 30% or more.
Since transmission towers are taller and interphase distances are longer for ultra-high voltage (UHV) transmission lines than for conventional transmission lines, it is important to know the features of direct lightning strokes to phase conductors. With this in mind, the features of direct lightning strokes to UHV transmission lines were observed and 81 datasets were obtained for seven years between 1998 and 2004. Of the 81 datasets, 79 recorded strokes from negative lightning, and the characteristic features of these direct lightning strokes were quantitatively evaluated by Electromagnetic Transients Program analysis of the current amplitude, front duration, and stroke duration. The frequency distribution of lightning strokes to each phase conductor was different from the estimated values obtained from conventional shielding models. Based on the cumulative frequency distribution of the current amplitude observed in this study, a method is proposed for calculating direct lightning stroke current as part of designing lightning protection
Insulation failure in medium voltage (10-20 kV) and electric
traction lines (3 kV DC) is mainly due to indirect and direct lightning
strokes to the lines. The overvoltages stressing the insulation have an
impulse shape with a very short tail, much shorter than the standard
1.2/50 μs wave. The paper presents the results of experimental tests
performed with a 1.2/4 μs wave, on air gaps and insulators in use in
the lines under consideration. The flashover probability distributions
and the voltage-time to breakdown characteristics under 1.2/4 μs
waves determined are presented and compared with the 1.2/50 μs
Rocket triggered lightning flashes were triggered near a
de-energized experimental distribution line while simultaneous
measurements of the induced phase to neutral voltage were performed.
Electric field, magnetic field and lightning stroke current
characteristics associated with the triggered flashes were also
measured. Analysis of 63 stroke currents and corresponding induced
voltages reveals that the peak induced voltages are roughly 63% larger
than predicted by the commonly used Rusck theory but in fairly good
agreement with modern coupling theory using measured electric and
magnetic fields as inputs. The induced voltages had peak magnitudes
between about 8 and 100 kV for stroke magnitudes ranging from a few
kiloamperes up to about 44 kA. The vertical electric field resulting
from the lightning flash was found to play a dominant role in the
induction process, but the magnetic field also contributed significantly
to the total induced voltage. These measurements suggest that induced
voltages on distribution lines are larger than expected and may lead to
more flashovers than expected
One important cause of disturbances in distribution systems is
lightning that determines permanent or transient faults in overhead
lines by direct or, more frequently, indirect strokes. The trouble
caused to customers, because of the susceptibility of some loads, may be
very severe even in the case of transient faults, i.e. those which
disappear after the opening and high-speed reclosure of protective
breakers. This paper provides an assessment of the reduction in the
number of faults caused by the lightning activity to an MV distribution
system by the addition of a shield wire. The effect of an increase in
the insulation level is also analysed
A new model for assessing the exposure of free-standing structures
and horizontal conductors above flat ground to direct lightning strokes
is introduced. A recently developed criterion for positive leader
inception modified to account for positive leaders initiated under the
influence of a negative descending lightning stroke, is discussed.
Subsequent propagation of the positive leader is analyzed to define the
point of encounter of the two leaders which determines the attractive
radius of a structure or the attractive lateral distance of a conductor.
These parameters are investigated for a wide range of heights and
return-stroke currents. A method for analyzing shielding failure and
determining the critical shielding angle is also described. The
predictions of the model are compared with field observations and
previously developed models
Partial discharge (PD) monitoring is an effective online
predictive maintenance test for medium-voltage (MV) motors, MV
generators, and MV switchgear at 4160 V and above, as well as other
electrical distribution equipment. The benefits of online testing allow
for equipment analysis and diagnostics during normal production.
Corrective actions can be planned and implemented, resulting in reduced
unscheduled downtime. An understanding of the theory related to PD, and
the relationship to early detection of insulation deterioration is
required to properly evaluate this predictive maintenance tool. This
paper presents a theory to promote the understanding of PD technology,
as well as various implementation and measurement techniques that have
evolved in the industry. Data interpretation, corrective actions, and
application to electrical distribution equipment is also reviewed
In this paper, the Rogowski coil is modeled as a distributed-element transmission line. The elements in the distributed transmission line are modeled using physically based equations. It allows self and transfer impedances of the Rogowski coil to be modeled using the physical dimensions and the material properties of the coil. The models of the impedances were verified by measurements in the frequency domain on three Rogowski coils. The coils mounted on the power cable were modeled and simulated in the time domain and afterward compared with the measurements.
A Model Experiment of Lightning Attractive Characteristics of Insulated Power Distribution Line
- Y Goto
- Y Sato
- K Kato
- I Ono
- T Takeda
Y.Goto, Y.Sato, K.Kato, I.Ono & T.Takeda, "A Model Experiment of Lightning Attractive Characteristics of Insulated Power Distribution Line", Proc. of 24"' ICLP, Birmingham, U.K., pp.611-15, 1998.
Calculated Lightning Performance of Electric Traction Lines Equipped with Shield Wires
- A Carrus
- E Cinieri
- A Fumi
A. Carrus, E. Cinieri, A. Fumi: " Calculated Lightning Performance of Electric Traction Lines Equipped with Shield Wires, " Proceedings of the Int. Conf. on 'Lightning and Power Systems, London, June 5-7, 1984. IEE Conference Publication No. 236, pp.135-139.
A Simplified Method for Estimating Lightning Perfor-mance of transmission Lines
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IEEE WG, "A Simplified Method for Estimating Lightning Perfor-mance of transmission Lines",IEEE 84, SM698-7, 1984.
Lightning Induced Voltages on overhead power lines " Task Force 33.01.01 of Study Committee 33
- C A Nucci
C. A. Nucci, " Lightning Induced Voltages on overhead power lines " Task Force 33.01.01 of Study Committee 33, ELECTRA, October 1995; 162: 121-145.
Breakdown Behaviour of Air Spark-gaps with Non Standard Lightning Voltages
- A Carrus
- E Cinieri
- C Mazzetti
- A Fumi
A. Carrus, E. Cinieri, C. Mazzetti, A. Fumi: " Breakdown Behaviour of Air Spark-gaps with Non Standard Lightning Voltages ", 7th International Conference on Gas Discharges and their Applications, London, 31 August-3 September 1982.
Design of MV nd HV Covered Conductor Overhead Lines " 17 th International Conference on Electricity Distribution (CIRED)
- L Tapio
L. Tapio, " Design of MV nd HV Covered Conductor Overhead Lines " 17 th International Conference on Electricity Distribution (CIRED) " Barcelona May 2003.