Current cables

The Journal fur Gasbeleuchtung mentions electrolytic corrosion damage caused by direct current cables in Berlin in 1892, and a few years later damage by tramway currents was reported in 14 German towns. As early as 1894 the electrolytic processes of stray current corrosion were explained in detail in this Journal by G.Rasch [65]. 

Bus bars of a transformer substation must not be directly grounded. They must be connected with rails by at least two insulated cables. Metal sheathing of feeder and return current cables must only then be connected with the rails or bus bar if an increase in anodic corrosion on other buried installations is absolutely excluded. The insulation of all return cables must therefore be monitored regularly. 

Installing power quality instruments and probes requires special care. It is preferred that voltage and current probe leads do not run in close proximity to high-current cables or bus, especially if they are subjected to large current inrush. This can inductively induce voltages in the leads of the probes and cause erroneous data to be displayed. Voltage and current lead runs parallel to high-current bus or cable... 

When high voltage motors are being considered, it is usually found that the minimum conductor size of the cable is determined by the let-through fault withstand capability rather than the full-load or starting current. Cable manufacturers provide graphical data for fault withstand capabilities of their cables, which are based on practical tests. These aspects are also associated with the protection system used for the motor, e.g. a contactor-fuse combination, a circuit breaker, the protective relay characteristics (thermal, inverse time with or without instantaneous or earth fault elements). 

Design current cable must carry the full load current. 

Rated Voltage (kV) Rated Capacitive-Switching Currents (Cable) (A)... 

The paper discusses the application of dynamic indentation method and apparatus for the evaluation of viscoelastic properties of polymeric materials. The three-element model of viscoelastic material has been used to calculate the rigidity and the viscosity. Using a measurements of the indentation as a function of a current velocity change on impact with the material under test, the contact force and the displacement diagrams as a function of time are plotted. Experimental results of the testing of polyvinyl chloride cable coating by dynamic indentation method and data of the static tensile test are presented. 

Exciting developments based on electromagnetic induction raced along from that time, giving us the sophisticated products our everyday lives depend on. During most of the period productive uses for eddy current technology were few and few people believed in it as a usefiil tool eddy currents caused power loss in electrical circuits and, due to the skin effect, currents flowed only in the outer surfaces of conductors when the user had paid for all the copper in the cable. The speedometer and the familiar household power meter are examples of everyday uses that we may tend to forget about. The brakes on some models of exercise bicycle are based on the same principle. 

Data Communication Wires. Electronic cables such as data communication wires employ three basic designs coaxial, twisted pair, and fiber optics (3,4) (Eig. 1). Coaxial cables are so named because the axis of curvature of its outer conductor is concentric to its inner central wire. The metal braiding wrapped around the insulated center wire acts as the return current conductor in addition to shielding the wire from various interferences. 

Impedance. Impedance defines the relationship of voltage and current in a coaxial cable. The electrical requirements of the hardware dictate the impedance values for the interconnecting cables. Most coaxial cables are designed to match the impedances required by electronic hardware. 

Electrical Connections. Electric current is brought from the transformers by air-cooled copper busbars and close to the electrode by water-cooled bus tubes and flexible cables, connecting to water-cooled copper contact plates at the electrode. The plates are held against the electrode by hydraulic pressure. The connectors are as short and as balanced as possible to allow cancelling of magnetic fields associated with individual conductors. 

Electrostatic spraying is used in shops to coat conductive objects. It is very useful for odd-shaped objects such as wire fence, cables, and piping. An electrostatic potential of 60,000 volts on the object attracts oppositely-charged paint particles the spray can wrap around and coat the side of the object opposite to the spray gun. This technique produces very uniform finishes and has the least paint loss of the three methods. However, it is slow, requires expensive equipment, produces only thin coats, and is sensitive to wind currents. 

Since the starting inrush current is kept moderate for all types of drives, it can economize not only on ratings of the switchgears and cables but also on the size of the generator when a captive power is required to feed the load. 

When there is no dedicated transformer and these circuits are connected on the system bus directly a large inductor will be essential at the incoming of the static circuits, sufficient to absorb the trapped charge within the transformer and the interconnecting cables up to the converter unit. The size of the inductor can be calculated depending on the size (kVA) of the distribution transformer, its fault level and the characteristics of its current limiting protective device. An inductor sufficient to absorb //, L of the transformer and the cables may be provided at the incoming of the sialic circuits. 

In some cases, where the nearest rating of the fuse itself is too high for the rated current, a larger cable is recommended. The thermal (/ - t) characteristics of all such components will vary from one manufacturer to another and may not be readily available with a design or a field engineer, while making the selection. The manufacturers of such components therefore as standard practice, perform this coordination for their products and make such data readily available for the user lo make a quick selection. It may be noted that OCR and fuses at least, of different brands, will require a new coordination. 

It is equal to the phase impedance of the overhead lines or cables. For low current systems, LT or HT, this impedanee is nearly equal to the resistanee of the circuit, as Due very low A l, the impedance... 

To the basic current requirement is applied the derating faetors for various service conditions, as noted in Section 1.5.4.2. The equipment, devices and components may then be cbosen to be as close (nearest higher) to this rating as possible from the available standard ratings. Based on these ratings, the minimum cross-sectional areas of the other current-carrying parts used in the circuit, such as interconnecting links and the cables-are calculated. 

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