Power lines, overhead

Capacitive interference of pipelines is of minor importance. It arises in the immediate vicinity of overhead power lines or railway power lines in the construction of pipelines where the pipe is laid on a foundation that is well insulated from soil (e.g., on dry wood). The pipeline picks up a voltage with respect to the soil. The value of this voltage depends on the voltage of the interfering conductor at the time as well as the capacities between the conductors and the pipeline. 

With aboveground, welded lengths of pipes that are insulated from the ground and that are within 10 m of overhead power lines, measures have to be taken against inadmissible capacitive interference if the following length limits are exceeded [2] ... 

Fig, 23-1 Limiting length of a parallel insulated stretch of pipe with capacitive interference by a 50-Hz, three-phase overhead power line with a nominal voltage >110 kV [2]. 

Fig. 23-2 Safe distances from high-voltage overhead power lines.

The potentials from larger grounding installations on the soil surface are essentially flatter but more extended than those from overhead power line pylons (e.g., power stations, transformers and switchboard plants). The maximum expected grounding voltage in case of failure and its variation at the soil surface can be obtained from the facility s management. 

Inductive interference on pipelines is usually only to be expected with extended and close or parallel routing with three-phase, high-voltage overhead power lines, as well as with conductors and supply lines of ac railways. 

The field strength, E, induced by grounding short-circuit currents in high-voltage overhead power lines or railway power lines, is basic in calculating the pipeline potentials (see Section 23.3.2). The field strength, E, follows from Refs. 2 and 13 ... 

Crossing with a high-voltage overhead power line at an angle greater than 55° ... 

Fig. 23-12 Limiting lengths for parallel run of high-voltage overhead power line and pipeline as a function of distance, a.

Installation of grounds, standing surface insulation, or equipotential grounding mats are necessary in the case of pipeline potentials higher than 65 V [2]. In the case of long sections of parallelism for an overhead power line and a pipeline, continuous grounding with respect to the distances and the resistances of the grounds... 

Is there any risk to its use in a specific area (e.g. close to overhead power lines) ... 

Aluminum s low density, wide availability, and corrosion resistance make it ideal for construction and for the aerospace industry. Aluminum is a soft metal, and so it is usually alloyed with copper and silicon for greater strength. Its lightness and good electrical conductivity have also led to its use for overhead power lines, and its negative electrode potential has led to its use in fuel cells. Perhaps one day your automobile will not only be made of aluminum but fueled by it, too. 

It is up to governments (and in a democracy that means the people) to decide how much, if any, pollution should be permitted. They in turn must rely upon scientists and engineers to tell them how various elements and compounds affect man and the environment, so reasonable laws can be enacted. Yet not enough is known about all the substances and their interrelations to anticipate many problems that may arise. Consider the following case, where copper from an overhead power line located in a polluted area was lethal to sheep. 

Clearance for overhead power lines Buildings 1. Adequate ladders, stairways and ... 

Later studies involving low-frequency exposure have not clearly demonstrated a correlation between low-level fields and effects on human health. One study observed a slight increase in nervous system tumors for people living within 500 m (=1600 ft) of overhead power lines, while most recent studies in this field have not found any clear evidence to relate exposure to low-frequency fields with childhood leukemia. 

Fig. 5.17 A 36 kV porcelain rod insulator of the variety used to position the overhead power lines for railways. Overall length 500 mm. (Courtesy of New Zealand Insulators, Temuka, NZ.)...

Common sources of low-level exposure to electromagnetic fields are electric and magnetic powered transport (static fields), overhead power lines, domestic electric appliances (ELF), antitheft electronic devices, or video display units (in very low to low... 

Meyers A, Clayden AD, Cartwright RA, Cartwright SC. Childhood cancer and overhead power lines A case-control study. BrJCancer 1990 62 1008-14. 

Because of its high electrical conductivity, Al is used in overhead power lines. Its high negative electrode potential has led to its use in fuel cells. 

We may never know the exact cause. Many believe that the massive ship (it was more than 800 feet long) struck an overhead power line. Others speculate that lightning ignited the hydrogen and some believe that sabotage may have been involved. 

Auger conveyors can be dangerous and it is important to follow good safety practices when they are used. Because of their length and portability, special care must be taken to keep conveyors away from overhead power lines. Contact with a power line can cause death. Also, be careful to keep hands, feet, hair, and clothing away from rotating shafts and the intake of the conveyor. Serious injury or death can result from entanglement. 

A good rule-of-thumb guide is to assume that between 15% and 25% extra capacity will be required. Hence the chosen rating will be 115% to 125% of the best-known estimate at the early design stage. This requirement also applies to power transformers and their main cables or overhead power lines, and to outgoing feeder cables to auxiliary switchboards and motor control centres. It does not usually apply to individual motor consumers, see Chapter 1. 

Allow adequate elearanee between strueture and power lines Avoid contaet of operating cranes with overhead power lines Construction management... 

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