IEEE Power & Energy Magazine - January/February 2015 - 70

Dynamic/Static Ampacity (%)

of 0.6 m/s, and full sun radiation
are applied to arrive at such estimaSubstation Control
SCADA System
tions. as we have noted, at ambient
conditions more favorable than the
TS
worst case the conductor can carry
.. Transformer
Control Center
Bay
. Substation
more current and at the same time
TS
preserve the clearance limit.
ambient weather conditions must
be known to determine the actual
ampacity of the conductor and of
the ohL, respectively. to be able
to use dynamic current ratings for
the operation of ohLs, a monitoring system that fulfills the following
Ambient
Online Calculation in
requirements must be implemented:
Data Transfer
Conditions
Control Center
the system determines the dynamic current rating depending on
ambient weather conditions and
figure 15. The principle of the dynamic rating system for 380-kV OHLs.
makes this information available to
the control center.
90% and 100%, the quadrants are colored orange. If the ratio
✔✔ the complete electrical circuit, including all compois 100% or greater, the quadrants are colored red and in addinents of the primary and secondary technology as well
tion show the remaining safe operating time.
as protection systems, has to be checked and if necessary adapted with regard to the expected maximum
current rating.
Case 2: Increasing OHL Utilization
to
use dynamic rating on 380-kV lines, a dynamic rating
with Dynamic Line Rating
system
for ohLs has been developed and incorporated into
the utilization of ohLs has increased due to increased
transmission of electrical energy in europe as well as grow- the existing operating system of tennet tSo in germany (see
ing power input from regenerative energy producers. the figure 14). this monitoring system for ohLs uses the ambient
transmission capacities of ohLs are limited, and in many temperature and the wind speed to determine the dynamic curcases the transmission lines are already bottlenecks that rent rating of the line. It is directly linked to the control center
and delivers a dynamic current rating to it (see figure 15). there
restrict power flows.
a method for increasing ohL transmission capac- is thus no need for any direct measurement of the conductor,
ity depending on ambient weather conditions will now be such as a conductor temperature measurement, when determindescribed. a dynamic rating system has been incorporated ing the dynamic current rating. to be able to use the dynamic
into the operating process of a tSo; its usability and its effect current rating, all elements of the circuit have been checked and,
on the ampacity of ohLs have been verified for 380-kV lines. if necessary, replaced. Clamps and joints along the line have
for ohL design, worst-case estimations for ambient been checked using infrared analysis, taking into account the
weather conditions are usually used. In many middle euro- aging effect of a higher current rating on these elements.
tennet's protection system had to be adapted to the higher
pean countries, an ambient temperature of 35 °C, a wind speed
current values, and mechanically switched capacitor damping
networks (mSCDns) also had to be implemented to deliver
175
sufficient reactive power at three main substations, since
highly stressed and loaded lines require greater amounts of
Dynamic Rating
reactive power. the results show that the dynamic line rating
150
can reach values far above the conventional static rating (see
figure 16), depending on the actual ambient conditions.
125
this operational experience using the dynamic rating
system
for the operation of 380-kV lines proves that it works
Static Rating
100
very well with the existing control center's technology. the
distinct increase in dynamic current rating compared with
75
the static rating verifies the dynamic system's technical and
One-Month Period
economic capability.
there are also restrictions associated with the use of
figure 16. The dynamic current rating compared with the
dynamic rating, however, which must be taken into account
static rating over one month for TenneT OHLs.
70

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january/february 2015

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