IEEE Power & Energy Magazine - March/April 2020 - 40

wind-power plants. The high correlation between generation, line current, and high wind velocities may allow for this
increase while still maintaining safety criteria.
On the other hand, however, some situations require careful
attention to avoid violation of safety limits. The first is the nonuniformity of land characteristics, where variations in ambient
conditions may result in corresponding variations in conductor
temperature, even in high-wind generation scenarios. Also, the
characteristic dynamics of wind generation, as discussed, with
electrical and ambient phenomena responding to different time
constants may lead to gaps in the stabilization of conductor
temperature with risks of violating safety limits.
Finally, an increase in the application of real-time line
monitoring combined with a thorough analysis of monitored
data and an evolution of line models shows considerable
promise as a way of increasing the capacities of transmission
lines. This can be extremely valuable in situations of licensing and financial restrictions.

Research in EM and Thermal
Behaviors of Conductors
The optimization of electric energy transmission requires
advanced technical studies that maximize the current-carrying

(a)

capacity, aiming to increase efficiency in the operation of the
lines through innovative technologies. In this context, laboratory
tests on ACSRs were analyzed to clarify the interaction between
EM and thermal phenomena, mainly under high-current conditions. The characterization of those interacting phenomena
quantifies economic and security aspects of cable operation, that
is, joule losses and cable lifespan, and provides more accurate
calculation of technical cable properties, that is, ac resistance.
The experimental tests were divided in two parts. First,
we briefly describe the experimental procedure to measure
the current density of the three aluminum layers, as shown
in Figure 11(a) and (b). It basically consists of the insertion
of tubular current sensors in each of its 54 aluminum conductor wires, through the installation of six tubular-profile
spacer structures (a pair by layer), made of phenolic paper, as
can be seen in Figure 11(a). The arrangement was specially
designed to keep the maximum cable length undisturbed and
obtain direct measurement of the current in each aluminum
wire simultaneously.
A second stage of experimental tests involved measurement of the transient internal temperatures of the cable at
three radial positions [see Figure 11(d)] by using thermocouples embedded in the cable during its manufacturing process,

(b)

Internal
Thermocouples

Steel Core
(c)

(d)

figure 11. The R&D for EM and temperature behaviors of ACSRs. (a) The EM monitoring in individual wires. (b) The laboratory setup for EM measurements. (c) The laboratory setup for thermal measurements. (d) The detail of the internal layer
sensor. (Source: CEPEL; used with permission.)
40

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