Energized Transmission Line Research Articles

On the system of ensuring electrical safety of maintenance works performed on 35 – 750 kV power transmission lines being under induced voltage implemented in the Republic of Belarus

The article studies the matters of physics of interaction of parallel overhead power transmission lines. Cases are presented, where the maximum induced voltage values are expected on individual sections of closely approaching de-energized and energized power transmission lines. Possible scenarios are presented of direct contact with an unearthed conductor (wire) of OPL in the normal operation mode. Substantiation is presented of review of the list of the lines, which, when de-energized or earthed at terminal sections (in the switchgear of substations and power plants) have the values of induced voltage on the earthed conductors, as reduced to the maximum permissible continuous current of the affecting OPL, exceeding 25 V . Criteria are identified to classify OPL as being affected by induced voltage. The article considers organizational and technical procedures applied to provide safe maintenance works under induced voltage on de-energized overhead power lines (OPL) located within an area affected by energized OPL. Attention is given to the detailed description of types of earthing of OPL, line equipment, working section and workplaces used by State Production Association Belenergo. The mathematical apparatus used in the analytical calculations of the induced voltage values has been analyzed. The technical implementation of acceptable schemes of performing the repair and maintenance works on the earthing of de-energized OPL is considered. Performing geophysical ground survey by the method of vertical electrical sounding at places of mounting special low-resistance earthing electrodes is proposed and implemented. The methodology is developed and tested for measuring induced voltage values, which sets the order of induced voltage measurements on de-energized OPL running close to energized OPL with the voltage 110 kV, and higher. Comparative analysis is presented of results of analytical calculations and experimental research. Conclusions are made supporting the approach adopted and confirming the expediency of the system of ensuring electrical safety of maintenance works performed on 35–750 kV power transmission lines being under induced voltage implemented in the Republic of Belarus.

Evaluation of Gas Pipeline Induced Voltage Associated with Parallel Transmission Line

The voltage will be induced in the pipeline due to an electromagnetic field effect generated by the parallel transmission tower. This will bring up the negative effect to the pipeline, transmission tower and people get contracts with the pipeline. A study has been carried out to determine the electromagnetic field (EMF) distribution of parallel transmission line and pipeline due to AC currents and lightning faults. Only a few of previous study focus on lightning faults. The lightning faults data for transmission line and pipeline still insufficient nowadays. A mitigation system has been developed to minimize the induced voltage on pipeline due to the electromagnetic field of energized transmission line. ANSYS Maxwell software is used for modeling. The range of induced voltage obtained is within the acceptable level of the IEEE 80-2000 standards.

The effect of ozone on polymer degradation in Polymer Core Composite Conductors

The matrix material of high voltage Polymer Core Composite Conductors used in the next generation power transmission is generally a moderately high temperature epoxy, which has the potential of experiencing extreme aging effects in-service, including severe ozone degradation. It is well known that polymers are susceptible to oxidation by ozone, due to chain scission and the breaking of crosslinks. It is also known that ozone is present around high voltage transmission systems and its concentration rapidly increases close to energized transmission lines. Therefore, the primary goals of this study were to investigate (1) the effects of aging in ozone at room temperature of a high temperature epoxy, which could be used in the polymer composite conductors and (2) the effect of ozone exposure on a hybrid polymer matrix composite rod, presently used in-service. It was found using nanoindentation that the ozone oxidation depth on the surface of neat resin specimens was limited to about 120 μm. It was also observed that exposure to 1% ozone for up to three months at room temperature did not negatively affect the flexural performance of either the neat resin epoxy, or the composite. Comparatively small variations in the bending strength and deformations of the specimens were associated with an initial increase in crosslinking of the epoxy followed by a small increase in chain scission and bond breaking. These effects also demonstrated themselves in the type of the viscoelastic behavior of the polymer after aging. The scission of the polymer chains in the neat resin and rod specimens was further evidenced by FTIR spectroscopy, where the aged neat resin specimens showed an increase in absorption around the 3500 cm−1 wavenumber associated with the formation of carbonyl groups and carboxylic acids.

The effect of floating-potential conductors on the electric field near overhead transmission lines

The use of helicopters as platforms equipped with infrared and UV detection, digital cameras and other inspection equipment is an effective method of increasing the efficiency and effectiveness of transmission line inspection. However, as a 'floating-potential conductor' near to a high-voltage transmission line, a helicopter causes distortion of the local electric field, with regions of high electric field near the helicopter's surface where the curvature is high. In this paper, these fields are investigated both by calculation and experimentally, using a simple metal sphere, and then a model of a helicopter, placed near to a short length of energized transmission line conductor.

Failure analyses of nonceramic insulators. Part 1: Brittle fracture characteristics

Nonceramic insulators, also referred to as composite, polymer or polymeric insulators, are used in overhead transmission lines with line voltages in the range of 69 to 735 kV. Despite the many benefits that nonceramic insulators offer in comparison with their porcelain counterparts, they can fail mechanically in service by rod fracture. One of the mechanical failure modes of the insulators is a failure process called brittle fracture, which is caused by the stress corrosion cracking (SCC) of the GRP rods. The process is catastrophic and unpredictable, leading to the drop of energized transmission lines. The most important characteristics of the brittle fracture process, which can occasionally affect high voltage nonceramic transmission line insulators, leading to their catastrophic in-service failures, have been presented in this article. In addition, several experimental techniques were suggested for the simulation of brittle fracture under laboratory conditions. Only the most important aspects of brittle fracture process have been discussed here.

Statistical Analysis of Field Data for Precipitation Icing Accretion on Overhead Power Lines

This paper addresses the analysis of field data gathered at the Mont Belair icing test site in Quebec. Load cell evaluations of actual icing loads on an existing 315-kV line are correlated to hourly measurements of ambient temperature, wind speed, precipitation rate, and number of signals of the Ice Rate Meter (IRM), in order to establish a numerical model for precipitation icing accretion on overhead line conductors. The correlation analysis is limited to precipitation ice events, or those mixed with relatively short periods of in-cloud icing. Emission of IRM signals is used as a criterion to distinguish the accumulation phase of an ice event, from persistence and shedding, characterized by no emission of IRM signals. The results from the analysis show that the icing rate corresponding to wet growth is much larger than that in dry conditions. What is more surprising, it was also found that the icing rate during periods when winds blow parallel to the line axis is significantly greater than that with perpendicular winds. The linear fit to the set of multivariate data is usually applicable. However, in some relatively rare cases of wet growth in heavy precipitations without IRM signals, the linear model may be inadequate and quadratic polynomials must be used. The results from the application of the numerical model are in excellent agreement with the field observations. This empirical model can be very useful for evaluation of icing loads on energized transmission lines, when there are not available measurements by load cells or other direct methods.

End-to-end relay tests use secondary injection

The advances in relay test sets, personal computers (PC), and the availability of satellite clocks have taken fault-simulated, end-to-end relay testing by secondary injection to new heights. This creative approach to relay testing allows relay technicians and engineers to comprehensively check line relays and evaluate their dynamic response to faults without staging actual faults on energized transmission lines. The testing technique offers flexibility, speed, and accuracy in testing line relays.

Aeolian vibrations: wind energy input evaluated from measurements on an energized transmission line

A brief review is given of the energy balance method used in the computation of the amplitudes of aeolian vibrations in conductors of overhead transmission lines. It is pointed out that the wind power input obtained from wind tunnel experiments should be verified for an actual line. Field tests carried out in a completely automated test station are described. From these measurements the wind power input in an actual transmission line is estimated. A comparison with results from wind tunnel data is carried out, corroborating the method now being used for the calculation of aeolian vibrations in transmission lines. In addition, the field tests showed that the wind power input strongly depends on the turbulence level and the component of the wind velocity parallel to the cable. >

Space charge drift from a +/- 400-kV direct current transmission line.

The Minnesota Environmental Quality Board completed a 3-year study of the space charge plume outside the right of way of a bipolar (+/- 400 kV) direct current transmission line in rural west central Minnesota. The purpose of the study was to determine the levels of DC potential gradient and small airs ions in the downwind plume to which humans and animals may be exposed. Potential gradient measurements show that a space charge plume is detectable downwind at least 1600 m from the transmission line. Plume relaxation rates indicate that under certain conditions one could detect the plume at twice that distance or more. Net charge in the plume assumes the polarity of the downwind energized transmission line conductor. The bipolar DC line thus electrically bisects the land through which it passes; on one side of the line there is a net positive space charge, on the other side a net negative space charge. Electric charge in the plume resides on aerosols and small air ions. Polar conductivity data substantiate the fact that small air ions of one polarity in the plume are elevated while those of opposite polarity are suppressed compared to background concentrations found in the rural environment. The resulting charge imbalance persists downwind at least 1600 m, though the median small air ion concentrations of plume polarity have adjusted to within the background range by that time with perpendicular wind speed components between 1 and 6 m/sec.

Electromagnetic Voltage Induction and Mitigation on Passive Conductors from Overhead Transmission Lines

Voltage induction on passive conductors, such as pipelines, has become a major problem with increased loads on power transmission lines. This has resulted in major efforts by utilities to mitigate these voltages to an acceptable level. Induced fields are calculated using the principle of mutual induction. Transmission line theory is utilized to cascade different sections of a conductor to give resultant voltages from multiple points of mitigation or dissimilar line sections. The model is general and may be used to predict voltage at any point on a line under the influence of an energized transmission line. Different types of mitigation may be studied and the model takes into account the interaction between points of mitigation. Computer programs are described to calculate induced fields and cascade sections for multiple mitigation. A case study is presented.

Experimental Studies of Arcing Faults on a 75-Kv. Transmission System

Qualitative results of an investigation, in which high-voltage impulses were applied to an energized transmission line, indicate that the probability of a lightning flashover developing into a power arc is increased when current is flowing past the flashover point, and when the normal frequency voltage is increased or the insulation decreased. An oscillographic study of power arcs ranging in magnitude from 8 to 800 amperes indicated that the resistance of an arc varies over the cycle and over the duration of the arc. The effective arc resistance is approximated by the ratio of the peak voltage to the peak current. The apparent power factor of the arc current and voltage is practically unity in most cases. The tests indicated that arcs formed in a capacitive circuit are more persistent than those in inductive or resistive circuits, and that the average peak volts per foot of arc length, for currents above 100 amperes peak, is about 300. The maximum overvoltage recorded on an isolated neutral 75-kv. transmission system, 134 miles in length, as a result of 63 arcing ground tests was 3.0 times normal on a sound phase. The overvoltage is essentially a fundamental frequency phenomenon in which the sound phase voltage takes its new value without going through an oscillation of appreciable magnitude.