ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 42)

Work by Nicholson and Malak has allowed us to express the average imped-

ance of an electrical line by the formula:

where

L = μH/m (linear inductance of the electrical line)

C = μF/m (linear capacitance of the electrical line)

Work by Downey and Sutterlin has allowed us to model the electrical circuit

equivalent to an electrical line. This circuit, composed of resistances, inductances

and capacitances, may be schematized as shown in Figure 2.5.

The impedance of an electrical line is described by the following equation:

ZRf sL=+×()

(expressed in ohms)

where R is the resistance of the cable as a function of the frequency of the signal

being propagated in the cable, s is the cable’s diameter, and L is the line’s induc-

tance.

The impedance depends on the loads connected to the electrical line: electrical

devices (hairdryers, halogen lamps, and so forth) connected to the network, each

with a characteristic impedance.

These modeling elements allow us to calculate orders of magnitude for the char-

acteristic values of electrical networks that affect the transport of PLC signals.

Modeling Electrical Devices on the Network

In the same way that it is difficult to model electrical networks, it is also difficult to

model the electrical equipment connected to the network. This diverse equipment,

constantly being connected or disconnected in unpredictable ways, causes continual

variations in the network load.

Also, the equipment’s characteristics vary according to its age, the time of day,

the frequency of use, and so forth. As a result, such a model is rather imprecise.

Architecture of Electrical Networks 23

Figure 2.5 Schematic circuit of an electrical line as modeled by Downey and Sutterlin

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 42