Sag Measurements Research Articles

Monitoring Dynamic Thermal Line rating of overhead conductor using real time sag measurement by GPS

Monitoring Dynamic Thermal Line rating of overhead conductor using real time sag measurement by GPS

Optimal mechanical sag estimator for leveled span overhead transmission line conductor

Mechanical sag of the overhead transmission line (OTL) is a critical parameter for power system operation. However, remote locations of the conductor limit observability of sag. To monitor sag, distributed (DMS) or point measurement systems (PMS) are used. But, due to the limitation of DMS to use ruling span method, PMS is preferred. PMS requires sensors on every tower; as a result, sensor and data transmission requirements are high. This paper attempts to reduce the sensor requirement and estimate the sag in leveled span. To reduce the number of sensors and identify their location a linear integer programming based optimal sensor placement approach is proposed while keeping the redundancy intact. Using this, a reduced order, least-square based state estimator is proposed to estimate the sag in leveled span configuration. The estimator uses the conductor temperature and tension at one end of the span as input. Though, designed assuming ideal leveled span configuration, it is found to work for actual operating conditions. The performance of the proposed estimator is validated on the sag and tension data obtained with simulations on PLS-CADD™. Moreover, to eliminate the bad data, sensitivity based bad data elimination approach is presented. It allows replacement of bad data with almost exact values. The results show the robustness of the proposed approach.

An improved sag detection approach based on modified Goertzel algorithm

ABSTRACTPower quality is one of the key features in developing electric networks. It has been noticed because of its impact on economy and reliability of electrical networks. There are several power quality phenomena which are categorised in recent standards and literatures. Among them, voltage sag is more common and destructive for electric networks and consumers. This article presents a new detection method to monitor voltage sag in different electric network conditions. Goertzel algorithm is shown to be effective and simple for sag measurement compared to available sag detection methods.In order to increase the detection speed and response time, the Goertzel algorithm is modified. This modification will add to the speed of sag detection. The feasibility of the proposed method is justified through a measurement set-up developed using the dSPACE R1104 Digital Signal Processor Platform. The experimental results prove that sag measurement speed is improved by twice using the proposed modified Goertzel algorithm in comparison with the original method and some established methods. The results also verify that the sag detection of the proposed method is not affected by harmonic distortion of the voltage waveform.

Overhead Transmission Line Sag Estimation Using a Simple Optomechanical System with Chirped Fiber Bragg Gratings. Part 1: Preliminary Measurements.

A method of measuring the power line wire sag using optical sensors that are insensitive to high electromagnetic fields was proposed. The advantage of this technique is that it is a non-invasive measurement of power line wire elongation using a unique optomechanical system. The proposed method replaces the sag of the power line wire with an extension of the control sample and then an expansion of the attached chirped fiber Bragg grating. This paper presents the results of the first measurements made on real aluminum-conducting steel-reinforced wire, frequently used for power line construction. It has been shown that the proper selection of the CFBG (chirped fiber Bragg grating) transducer and the appropriate choice of optical parameters of such a sensor will allow for high sensitivity of the line wire elongation and sag while reducing the sensitivity to the temperature. It has been shown that with a simple optomechanical system, a non-invasive measurement of the power line wire sag that is insensitive to temperature changes and the influence of high electromagnetic fields can be achieved.

Control Method Stretches Suspensions by Measuring the Sag of Strands in Cable-Stayed Bridges

In the article is described the method that allows on evaluation and validation of measurement correctness of dynamometers (strain gauges, tension meters) used in systems of suspensions. Control of monitoring devices such as dynamometers is recommended in inspections of suspension bridges. Control device (dynamometer) works with an anchor, and the degree of this cooperation could have a decisive impact on the correctness of the results. Method, which determines the stress in the strand (cable), depending on the sag of stayed cable, is described. This method can be used to control the accuracy of measuring devices directly on the bridge. By measuring the strand sag, it is possible to obtain information about the strength (force) which occurred in the suspension cable. Digital camera is used for the measurement of cable sag. Control measurement should be made independently from the controlled parameter but should verify this parameter directly (it is the best situation). In many cases in practice the controlled parameter is not designation by direct measurement, but the calculations, i.e. relation measured others parameters, as in the method described in the article. In such cases occurred the problem of overlapping error of measurement of intermediate parameters (data) and the evaluation of the reliability of the results. Method of control calculations made in relation to installed in the bridge measuring devices is doubtful without procedure of uncertainty estimation. Such an assessment of the accuracy can be performed using the interval numbers. With the interval numbers are possible the analysis of parametric relationship accuracy of the designation of individual parameters and uncertainty of results. Method of measurements, relations and analytical formulas, and numerical example can be found in the text of the article.

Using voltage sag measurements for advanced fault location and condition-based maintenance

The results of a condition-based maintenance system using a new fault location technique based on voltage dip measurements is discussed here. Hydro-Québec (HQ) named this system MILES for maintenance and investigation of LIneS. The technique used was presented in previous CIRED publications in 2007 and 2011 as the voltage drop-based fault location technique. So far, the MILES system has shown a very good potential for permanent and temporary-fault location on overhead radial distribution system and has been deployed on 40 feeders located mainly at HQ and also at two other Canadian utilities.

3D Power Line Extraction from Multiple Aerial Images.

Power lines are cables that carry electrical power from a power plant to an electrical substation. They must be connected between the tower structures in such a way that ensures minimum tension and sufficient clearance from the ground. Power lines can stretch and sag with the changing weather, eventually exceeding the planned tolerances. The excessive sags can then cause serious accidents, while hindering the durability of the power lines. We used photogrammetric techniques with a low-cost drone to achieve efficient 3D mapping of power lines that are often difficult to approach. Unlike the conventional image-to-object space approach, we used the object-to-image space approach using cubic grid points. We processed four strips of aerial images to automatically extract the power line points in the object space. Experimental results showed that the approach could successfully extract the positions of the power line points for power line generation and sag measurement with the elevation accuracy of a few centimeters.

Research and Application for Transmission Line Sag Measurement Method Based on Aerial Image Sequence

Sag is an important parameter of the transmission lines, which directly affects the safe and stable operation of the transmission lines. This paper proposes a new sag measurement method based on the aerial image. It selects the spacer rod on the transmission lines as the recognized target, and adopts the normalized correlation image matching algorithm and the wavelet pyramid layered search strategy to measure the pixel coordinates of the center of the spacer rod in the sequence image. And then this paper measures the three-dimensional space coordinates of the center of the spacer rod according to the active vision technology, and finally calculates the actual sag via the nonlinear least square regression algorithm. The experimental results prove that this method can improve the efficiency of the sag measurement and it is also suitable for application in complex geographical conditions.

On the Application of Single-Phase Voltage Sag Compensators in Three-Phase Systems

Voltage sag is one of the most frequent power quality problems found in industries and power system. Its effects can be numerous such as control equipment trips, process shutdown, and production losses. This paper reports three years of voltage sag measurements collected in a research lab. This site is located near many metal industries which lead to a correlation between the obtained results and possible voltage sags in these industries. From the resulting analysis, this paper proposes the usage of single-phase voltage sag compensators in three-phase systems aiming a cost-effective solution. This procedure would not wholly eliminate the voltage sag incidence but it would diminish voltage sag effects on electrical loads.

Impact of Data Errors on Sag Calculation Accuracy for Overhead Transmission Line

The difference between a designed and actual transmission-line conductor sag value due to conductor properties' dispersion and measurement errors is estimated. Total error of sag calculation is presented as a weighted sum of partial errors of six measured/specified parameters involved in the state equation. The resulting formula for weighting factors for partial error is obtained by differentiating the state equation and enables analysis of the contribution of each error. It is shown that the factors for error in elasticity modulus or in creep values are small, so these errors have a weak effect on final result error. In contrast, weights for errors in sag and temperature measurements during stringing operation are large, and these errors contribute significantly to final sag error. Derived formula for weighting factors provides the tool to evaluate the total error of sag calculation and enables establishment of the possible limits for transmission-line thermal rating. Absolute error of sag calculation for the ACSR conductor is about 1.5 m for a 350-m span and about 2 m for a 500-600 m span. Absolute sag error for the AAAC Al59 conductor is 25% less.

Sag in commercial thermoforming

Our previous analytical solution gives sag advancing implicitly as , or for , sag advances with the cube root of time for a thin wide rectangular Newtonian isothermal sheet. This previous analytical work applies to sheets that are pinned along just two edges, and not all the way around. Corresponding sagometer experimental results confirmed this cube root relation. This work compares the prediction with measured commercial thermoforming behavior on rectangular sheets that are, of course, pinned all the way around. Then sag parallel superposition is used to extend for a sheet pinned all the way around. We evaluate sag parallel superposition using a finite element method (FEM) employing ANSYS Polyflow. The equation assumes sagging sheet cylindricity, and from our FEM we find that this assumption is reliable when . We compare sag measured in commercial thermoforming, using high‐impact polystyrene (HIPS) sheets that are pinned all the way around, by extending with parallel superposition. It is found that the time evolution of the commercial sag follows nearly exactly the same shape as the isothermal prediction. We measure sag runaway, and although the isothermal analysis , predicts the sag runaway time accurately, our isothermal theory overpredicts the amount of sag in the nonisothermal commercial operation by as much as a factor of 14. It is also shown how to use sheet sag measurements from commercial thermoforming to deduce the Newtonian viscosity of a thermoforming resin at a temperature that is above its softening point. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1529–1535, 2014

Lens sag and diameter measurement of large-size microlenses using sub-pixel algorithm and optical interferometry

Abstract In this paper, an automatic optical inspection system is designed specifically to measure the diameter and lens sag of large-size microlenses: 1. The proposed algorithm of measuring lens diameter locates the lens center through the Euclidean distance array, and determines the lens edge along an initiated ray using linear interpolation with sub-pixel accuracy. 2. The lens sag is calculated from a single fringe pattern of large-size microlens, in combination with the measured lens diameter. 3. According to the experiment results, the proposed system has advantages of high applicability, rapid processing speed, and good accuracy with the RMS error≤1% of measuring a large-size microlens, but without the requirement of prior training. The system architecture of non-contact measurement would not cause scratches on the lens surface and is inexpensive, thus, which is particularly suitable for the in-line inspection of industry field.

Research on Sag Online Monitoring System for Power Transmission Wire Based on Tilt Measurement

Sag online monitoring system for power transmission wire based on tilt angle measurement was proposed, the mathematical model of catenary for power wire was established. Sag calculation models of power wire in the situation without swinging and swinging were derived. By measuring the power wire axial angle and swing angle with dual-axis tilt sensor, the sag could be accurately calculated with the wire swinging. By testing the sag detection system, the result showed that the sag detection system could meet the engineering requirements of sag measurement.

Application of GPS for Sag Measurement of Overhead Power Transmission Line

Overhead conductor sag may be measured by different methods. In the paper measurement of sag of 66KV power transmission line under shut down conditions at no wind load using standard handheld GPS receiver BT 359 has done. The real time direct measurement of overhead conductor sag is needed for the operation of power transmission system. The measurement of conductor tension, temperature and ambient weather conditions are not required to monitor in this method. The digital signal processing (DSP) techniques is used to get better accuracy of GPS measurements. The Least Square Parameter Estimation (LSPE) method for the error estimation of GPS measurements is also incorporated.

Optical measurement and modelling of parison sag and swell in blow moulding

Blow moulding is a process whereby a cylindrical parison is extruded first, then pinched between the two halves of a mould and, finally, blown into the product. Parison size and shape result from complex interactions between mandrel and die geometries, processing parameters and viscoelastic properties of the polymeric material. Moreover, parison size changes with time due to sag. An innovative, contactless and online measurement technique of the parison is shown to be an effective tool to measure precisely parison diameter and thickness and to capture dimensional changes with time. This technique employs laser lighting of the parison and hinges on the refractive properties of molten polymer. Images taken with a digital camera are processed to give a precise measurement of diameter and thickness, at different time step during extrusion. Thus, parison swell and sag have been recorded for a commercial HDPE. Influence of processing parameters such as the rotational screw speed or die gap width can be brought forward. From the measurements, thickness swell is found to possess a different behaviour from diameter swell. Moreover, sag has been measured and can be modelled from a Newtonian perspective using one dimensional convected coordinates. Parison sag is shown to be governed by two parameters: an extrusion velocity and a a single coefficient of sagging susceptibility which value has been deduced from experiments.

Non-linear representation of voltage sag profiles for fault location in distribution networks

Fault location for distribution networks with multiple laterals would requires additional information such as from fault indicators and protective devices. As SCADA systems to provide such information are limited in 11 kV or lower voltage distribution networks, effective fault location method that only use information from a measurement at primary substation is needed. This paper presents the application of calculated non-linear voltage sag profiles and voltage sag measurement at primary substation to locate a fault in distribution networks. The proposed method firstly identifies the faulted section. From the indentified section, fault distance is calculated. The method has been tested under different fault scenarios that include various fault resistance, loading variation and data measurement errors. The results indicate the possibility of using this method to support automatic fault management system.

Measuring and Predicting Dynamic Sag

Summary Weighting-material sag is a reoccurring problem with many oil-based drilling fluids. Attempts to correlate sag tendencies to various rheological properties commonly used to benchmark drilling fluids have had limited success in prevention and anticipation of sag problems in the field. This paper presents a new testing apparatus for dynamic and static settling-rate (sag) measurements, which has proved to provide a better understanding of the sag phenomena and a better means to characterize fluid performance. This apparatus greatly expands the precision of sag measurements over previous techniques and allows testing conditions similar to those experienced downhole. Good correlation has been found between settling-rate measurements and performance of drilling fluids in the field.

How to Connect a Voltage Sag-Measuring Device: Phase to Phase or Phase to Neutral?

In contrast to most other power-quality phenomena, it requires several years of measurements to obtain a good insight of the voltage sag problems at a given grid connection point. In some countries, sag measurements at high- or medium-voltage level of several years are available. This paper analyzes how to calculate the sag characteristics at lower voltage levels if the sags measured at higher voltage levels are only characterized as the largest value of the voltage drop in each phase. Whether these values are based on phase-to-phase or phase-to-neutral voltages turns out to be an important parameter and is therefore analyzed in detail. Based on this analysis, this paper gives guidelines on how new sag meters should preferably be connected (measuring phase-to-phase or phase-to-neutral voltages).

Computation and measurement of calandria tube sag in pressurized heavy water reactor

Calandria tubes and liquid injection shutdown system nozzles in a pressurized heavy water reactor are to sag due to irradiation creep and growth during plant operation. When the sag of calandria tube becomes bigger, the calandria tube possibly comes in contact with liquid injection shutdown system tube crossing beneath the calandria tube. The contact subsequently may cause the damage on the calandria tube resulting in unpredicted outage of the plant. It is therefore necessary to check the gap between the two tubes in order to periodically confirm no contact by using a proper measure during the plant life. An ultrasonic gap measurement probe assembly which can be inserted into two viewing ports of the calandria was developed in Korea and utilized to measure the sag between both tubes in the reactor. It was found that the centerlines of calandria tubes and liquid injection shutdown system tubes can be precisely detected by ultrasonic wave. The gaps between two tubes were easily obtained from the relative distance of the measured centerline elevations of the tubes. Based on the irradiation creep equation and the measurement data, a computer program to calculate the sags was also developed. With the computer program, the sag at the end of plant life was predicted.

Verification of aspheric contact lens back surfaces.

To suggest a tolerance level for the degree of asphericity of aspheric rigid gas-permeable contact lenses and to find a simple method for its verification. Using existing tolerances for the vertex radius, tolerance limits for eccentricity and p values and were calculated. A keratometer-based method and a method based on sag measurements were used to measure the vertex radius and eccentricity of eight concave progressively aspheric surfaces and six concave ellipsoidal surfaces. The results were compared with a gold standard measurement made using a high-precision mechanical instrument (Form Talysurf). The suggested tolerance for eccentricity and p value and is +/-0.05. The keratometer method was very accurate and precise at measuring the vertex radius (mean deviation +/- SD from Talysurf results, -0.002 +/- 0.008 mm). The keratometer was more precise than and similar in accuracy to the sag method for measurement of asphericity (mean deviation of keratometer method results from Talysurf results, 0.017 +/- 0.018; mean deviation of sag method results from Talysurf results using five semichords, -0.016 +/- 0.032). Neither method was precise enough to verify the asphericity within the suggested tolerance. The keratometer can be efficiently used to verify the back vertex radius within its International Organization for Standardization tolerance and the back surface asphericity within an eccentricity/p value tolerance of +/-0.1. The method is poor for progressive aspheres with large edge blending zones. Deriving the eccentricity from sag measurements is a potential alternative if the mathematical description of the surface is known. The limiting factor of this method is the accuracy and precision of individual sag measurements.