IEEE Electrification - September 2021 - 124

of the thermal de-icing techniques. These methods have
drawbacks ranging from large reactive power requirements,
service interruptions, and investment on expensive
de-icing devices. Overall, dc de-icing and high-frequency
excitation de-icing methods are the two most promising
and effective methods to de-ice. The basic ideas of these
two methods are to generate heat to melt the ice accretion.
The heat generated is calculated as the square of the line
current times the line resistance. The dc de-icing method
generates heat by providing a large dc current. The dc
de-icing method has the following advantages.
x Easy to control the generated heat accurately. The most
important issue in de-icing is to control the generated
heat accurately. If the generated heat is insufficient,
the ice cannot be removed. If the generated
heat is excessive, the heat could damage the line.
However, it is feasible to control the heat accurately
by using the dc de-icing method since we control the
dc current by electronic converters, which is easy to
achieve in practice.
x Cheap. The de-icing device only requires power electronic
converters to convert ac power into dc current.
Therefore, this device can use some cheap and
mature power electronic converters.
x Scalable. The device can easily adjust the current value
for power lines with different voltage levels. Therefore,
one device can be used for different voltage levels (e.g.,
30 kV-110 kV).
x Mobile. The dc de-icing device is small and can be
mounted on trucks. One truck can be routed to de-ice
different lines, which saves the investment cost for
de-icing devices.
On the other hand, the line is on outage while being
de-iced by using the dc de-icing method. The dc de-icing
method has two drawbacks:
1) Low energy efficiency. The generated heat by dc current
covers the entire line. However, the ice only sticks to
the line surface. The heat generated in the center of
the line cannot be directly used to melt the ice and is
partly wasted.
2) Outage. The line is on outage while being de-iced,
which could result in the power interruption.
The high-frequency excitation de-icing method uses a
different way to generate heat. It provides ac current with
a very high frequency (8-20 kHz) and, owing to the skin
effect, the current flows only on a thin surface of the line
rather than covering the whole line. Therefore, the heat is
not wasted and the energy efficiency is high. Overall, the
high-frequency excitation de-icing method has high energy
efficiency and the line can be in service while being deiced.
However, this method is not applied in practice
owing to the following drawbacks.
1) Hard to control the generated heat accurately. It is difficult
to control the generated heat while using the
high-frequency excitation de-icing method. The relationship
between the frequency and the generated
124 IEEE Electrification Magazine / SEPTEMBER 2021
heat is nonlinear which can be affected by several factors
(e.g., line parameters and weather conditions). It
is also difficult to control power electronic devices to
provide a steady and stable high-frequency current
using mobile devices.
2) Expensive. The high-frequency excitation de-icing
method relies on advanced and expensive power electronic
converters and complicated control structures
to provide high-frequency current. Additionally, the
provision of high-frequency current for an extended
period could adversely affect power electronic converters.
This issue is especially important when such
devices are applied to transmission lines (i.e., above
110-kV voltage) where de-icing requires large capacity
power electronic converters to function for an
extended period, which could be an expensive venture
in practice.
3) Poor scalability. Using the high-frequency excitation
de-icing method will generate large harmonics and
further affect the power quality. An extra trap/filter
should be installed on power lines to reduce the harmonics.
However, line trap/filter parameters should be
optimized for individual lines. Even for the same line,
trap/filter parameters would need to be adjusted in
de-icing operation due to different weather parameters.
This is almost impossible to be applied in practice
especially in a serious ice storm because there is not
enough time for power system operators to adjust
parameters for each line. Additional investments in
trap/filter will result in higher de-icing costs.
4) Communication issues. According to the test results, the
high-frequency current could generate radio interference
signals and affect the communications of nearby
wireless devices, which would also limit the use of the
high-frequency method.
5) Lack of mobility. The high-frequency excitation deicing
device uses expensive power electronic converters,
which pose additional requirements on power
system protection and control. Such requirements are
expensive, large, and heavy, which could not be
mounted on trucks.
Overall, there is still a long way to go for the high-frequency
excitation de-icing method to be applied in practice.
The existing high-frequency excitation devices are
used to test in laboratory environments rather than being
applied widely in the real world. The dc de-icing method is
currently the most economic and reliable method to be
applied in the real world.
As mentioned previously, dc ice-melting is ideal for distribution
lines. Thermal de-icing devices are designed as
fixed, mobile, and portable based on distribution network
voltage characteristics. Fixed devices are installed in substations
and can perform ac de-icing for a larger capacity
of power transmission lines. Mobile thermal de-icing
devices would require a mobile generator, which could
limit the melting flexibility and efficiency. However, the
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