Cables voltage drop

Appendix 1 Selection of Power cables 16/531 A 16.1 Introduction 16/531 A16.2 Technical details 16/544 A16.3 Service conditions 16/544 A 16.4 Recommended derating factors 16/544 A 16.5 Voltage drop 16/544... 

It is possible that at certain installations, even after selecting the size of the cables on the basis of the site conditions and the laying parameters as discussed above, a larger cable may become imperative as a consequence of a higher voltage drop. 

For clarity, voltage drop in the next size of cable, i.e. 3 x 95 mm, is also calculated as... 

Lower voltage drops in the lines and cables and thus lesser voltage fluctuations. 

Ohmic voltage drops resulting in losses cannot be ignored in the connecting cables with long anode cables and high protection currents [28]. Cable costs and losses must be optimized for economic reasons. The most economic calculated cable dimension depends primarily on the lowest cross-section from the thermal point of view. For various reasons the permitted voltage drop usually lies between 1 and 2 V, from which the cross-section of the cable to be installed can be calculated from Eq. (3-36). 

Another possibility is to decentralize the dc supply. Here the ac supply for the individual protection rectifiers comes from a potential-controlled central supply that is situated in the engine control room. The protection rectifiers can then be situated amidships with relatively short dc cables to the anodes. The dimension of the dc cable should maintain a voltage drop below 2 V. 

The resistance in the lead and the anode itself, which usually is so small that it can be neglected with extended cable connections, anodes or pipelines, the voltage drop in the metal must, of course, be taken into account. 

Cornelison, K, Voltage Drop Table, Anaconda Wire and Cable Co. (1984). 

The cable must be selected on the basis of full-load current rating, voltage drop on both running and start-up, and short-time current rating. 

The voltage drop in starting if the cable is for a motor circuit ... 

Thermal energy generated by the electrical resistance of a 5-mm-diameter and 4-m-long bare cable is dissipated to the surrounding air al 20°C. The voltage drop and the electric current across Ihe cable in steady operation ate measured to be 60 V and 1.5 A, respectively. Disregarding radiation, estimate the surface temperature of the cable. 

With this set-up the absolute value RS(co) and the phase angle y(f0) of the response function is measured as a function of frequency. The response function is the ratio of the voltage drop Um across the resistor Rm to the output voltage of the noise generator Ugen- After data transfer to a PC via an lEEE-interface the impedance of the sample is calculated from these values and the parameters of the set-up (impedance of the cables and the electronic devices of the analyser). 

The voltage drop in a cable is due to its series resistance and series inductive reactance. The shunt capacitive reactance is usually too large to be considered for cables installed in a typical plant. However, for long distance high voltage cables, such as submarine cables, the shunt capacitance may need to be included in the calculations of voltage drop. 

Electrical connections. Electrical coimections should be made of durable materials and, especially in the anode circuit, should be isolated well against corrosion that may occur due to anodic polarization. Cables are usually normal isolated low-voltage wires. They should have sufficient diameter for transporting the current with minimal voltage drop. Cables should be color coded or labeled to facilitate identification in junction boxes, wire bundles and at the central cabinet containing the power sources. Usually multiple coimections and cables are provided to anode and cathode circuits to ensure uninterrupted current flow in case one coimection is lost, e. g. by damage to the installation due to vandaHsm. 

Electrical cable schedule Voltage drop calculations Electrical area classification Electrical instrument interface drawings Underground electrical cable and cable trench arrangement Electrical equipment layout drawings Motor control center and power layout Load and short-circuit analysis VSDs configuration Plant lighting plan... 

It can be seen from these calculations that a 1.84 kW load supplied at a power factor of 0.4 would require a 20 A cable, while the same load at unity power factor could be supplied with an 8 A cable. There may also be the problem of higher voltage drops in the supply cables. As a result, the supply companies encourage installation engineers to improve their power factor to a value close to 1 and sometimes charge penalties if the power factor falls below 0.8. 

Table 14.3 Voltage Drop in Cables Factor. Adapted from the lEE On site Guide by Kind Permission of the Institution of Electrical Engineers...

In Great Britain, electricity is generally supplied from the National Grid to most factories where it is transformed to a 440 V, 3-phase a.c. supply at 50 hertz (Hz) with single-phase supply at 240 V. The voltage drops along mains cables may be considerable, particularly... 

Figure 3.2.8. Driven shields (zero voltage drop between cable inner and shield).

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