Power line

The primary advantages of mechanical scales are that they are relatively inexpensive in smaller capacities they do not need electrical power, enhancing thein portabiUty and they do not need to be protected from power line transients or lightning strikes. 

Load-ceU mountings must be designed in such a way as to minimise the effects of extraneous forces Electrical power is required, along with power-line transient protection... 

These products are very sensitive and are best used in a controlled environment Electric power, along with suitable power line transient protection, is required Capacity range is limited, although this can be extended through the use of lever systems... 

Requires shielding and special procedures to avoid exposure of personnel to radiation Frequent recahbration is required to compensate for source decay over time Electrical power and power line transient protection required... 

The periodic shedding produces lateral forces of the same period on the cylinder. Should the cylinder be weakly supported and have a natural frequency close to the shedding frequency, it oscillates strongly in concert with the vortex street. Such behavior is responsible for the singing of power lines, the oscillation of tall smokestacks, and, most spectacularly, for the coUapse in 1940 of the newly built Tacoma Narrows suspension bridge, in Washington state, under the influence of a steady 65 km/h wind. 

Another problem, prevalent ia areas where severe icing conditions are met, is referred to as galloping of power lines. When ice forms on a power line, there is frequently a prevailing wiad which causes the ice to take a teardrop or airfoil shape. This foil provides an aerodynamic lift to the conductors and under certain conditions the conductors can go iato a resonant vibration such that large standing waves are created that exert enormous forces on the system. Miles of power lines and the towers along them have been destroyed by this phenomenon. 

A high temperature thermocouple uses sihcon carbide (146). It is also used in lightning arrestors to protect high tension power lines, and in high loss factor microwave attenuators (147). 

The by-product power takes only 40% as much energy to produce as on-purpose firing for power only. A comparison of Figure 5b and 5d illustrates this point. By-product power also takes much less equipment, as can be seen in Figure 6. By-product power also avoids the losses and capital associated with use of electricity such as power lines, transformers, and motors. As a result, by-product power is much cheaper than power purchased as electricity. 

In earlier years, to reach a remote area, where. separate telephone lines had not been laid it was normal practice to rttn them through the same poles as the HT power distribution lines (generally 11-33 kV). This was particularly true of internal communications of the electricity companies for ease of operation and to save costs and time. This commitnication was known as the magneto-telephone system. But the proximity of telephone lines to power lines adversely affected the performance of the telephone lines due to generation of overvoltages (Chapter 20) and eleetrical interferences (conductive and inductive interferences, discussed later) on the telephone lines by the power lines.. Some of these interferenees, particularly system harmonics, had the same frequency as the audio frequency of the telephone lines and alTected their audio quality. 

The running of telephone lines through power lines is long discontinued. They are now run on separate structures within a city and nearby areas at audio frequency (— 0.3-3.4 kHz), and maintain enough distance from HT power distribution lines. They are therefore almost unaffected from such disturbances. Nevertheless, interferences must be kept in mind when installing these lines so that they are out of the inductive interference zone of the power lines. The latest method in the field of communications to avoid disturbances is to use underground optical fibre cables, where possible, as discussed later. Optical fibre cables are totally immune to such disturbances. 

Use of filter circuits in the power lines at suitable locations, to drain the excessive harmonic quantities of the system into the filter circuits. 

Tliis is the prime cause of noise and distortion in an audio system. The capacitive coupling (conduction) between the power and the communication lines gives rise to such an effect. It is associated more with the voltage of the system and particularly when it is capacitor compensated. Even without the power capacitors, the leakage (coupling) capacitances between the HV or EHV power lines, particularly 132 kV and above, and the overhead communication lines play an important role and give rise to this phenomenon. Systems lower than 132 kV do not cause such a situation as a result of the insignificant capacitive effect. 

Guide for harmonic control and reactive compensation of static power converters Guide for power line canier application... 

Guide for the implementation of inductive coordination mitigation techniques and application Power line carrier coupling capacitors... 

Central Board of Irrigation and Power. India, Interference of power lines with telephone lines Technical Report No. 29. Research Scheme on Power, March (I9S2). 

The series capacitors tire connected in series with the power lines to provide reactive control to an individual load or to a power distribution or transmission system. They are therefore switched with the pow er lines and are thus permanently connected devices. 

Stray Currents from High-Voltage dc Power Lines... 

Figure 15-2a shows the stray current interference by a bipolar high-voltage dc power line [7]. When the system breaks down, large voltage cones occur in the soil at the grounding installation. A few kilometers away, the current density in the soil is relatively low. 

Inductive interference the production of electrical potentials in conductors due to the induction from alternating magnetic fields arising from short-circuit currents or operational currents in high-voltage power lines. 

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]. 

---