ice melting methods for overhead lines
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Seminar topicTRANSCRIPT
Ice melting methods for overhead lines
Winter.lnk
Masoud Farzaneh, Professor , UQAC, CanadaTechnical Vice-President , IEEE DEISExecutive Committee Member , CIGRÉ Canada
Outline of presentation1) Introduction2) Anti-icing and de-icing systems (AI/DI)
for overhead lines3) Thermal techniques
- Conductor de-icing- Ground wire de-icing
4) Summary
Introduction Heavy ice or snow accretion may lead to major outages of
almost any type Two different strategies may be used to protect overhead
lines against extreme icing: - Constructing stronger towers and cables- Mitigating the effects of heavy ice accretion
The most practical approach is monitoring ice loads and mitigating them before they reach dangerous proportion
This approach resulted in the development and implementation of AI/DI systems in several countries
Definition of AI and DI systems
AI Techniques are used to prevent or reduce ice and snow accumulation on exposed structuresDI techniques are used to remove or reduce
ice accretion on exposed structures
Classification of AI/DI methods
Passive methods Active coatings Mechanical methods Thermal methods
Combination of rings and counterweights forwet snow removal from conductors (Saotome 1988)
Top: Snow rings. Bottom: Counterflow wires added to conductors to provoke snow shedding (Higuchi 1972)
These methods do not require an externalsource of energy
counterweights
Passive methods
Passive Icephobic coatings
Etched Al oxide /MOx/RF-sputtered Teflon®
Anodized and etched Al alloy + Teflon® impregnation.
ARFAl = 3.56
ARFAl = 3.4 to 6.3
Silver nanoparticles passivatedwith Zonyl 8740 on Al
ARFAl = 2.5 to 4
Icephobic Coatings
Active coatings and devices
Snow-melting magnetic wire developed in Japan
These coatings or devices require some electrical energy to be effective.
Example of evaluation result of LC Spiral-Rods
Mechanical methodsThese methods involve breaking the accreted ice to provoke its shedding. They are classified as follows:
Scraping methods Shock wave methods Vibrating devices
De-icing using DAC
Thermal methods
[Prud’homme 2005]
These techniques are based on the concept of heating line conductors with electrical current to force ice melting and shedding
Classification of thermal methods
Joule-effect methods- Conductor de-icing- Wire de-icing
Other methods-Dielectric losses, radiative waves, externalheat sources
Example of thermal de-icing
I F pI I ACMELT
I AC
L C T TrI V
r R t
RAC : Conductor AC resistance (in /km)LF : Latent heat of fusion (in J/kg)ρI : Ice density in kg/m3)rC : Radius of the conductor (in m)rI : Outer radius of the ice sleeve (in m)CpI : Specific heat of ice (in J/kg/C)TI : Variable expressing the temperature of the ice (in C)TA : Ambient temperature (in C)Δt : Required time for melting (in s)
VMELT: Volume of ice sector to be melted above the conductor (m3)
ACR
Current required for ice melting
Current required for de-icing different conductors
[Prud’Homme et al., 2005]
Conductor de-icing
Load shift method Reduced-voltage short-circuit Contactor load transfer Pulse electrothermal de-icer
Load shift method
The scope of application depends on the systemconfiguration, power load available and ambient conditions
This method requires no additional equipment Because it may be difficult to control the power load, this
method needs a well-defined strategy and decision tools
The basic idea is to force more current through aparticular circuit as the HV lines do not generallyproduce enough heat to melt ice
Reduced-voltage short-circuit
DC is more advantageous for long TL with large cross-section conductors because reactive losses are eliminated.
This method requires the circuit to be disconnected from the network.
The basic idea is to connect a line to a source with the other end shorted, which requires to disconnect the circuit to be de-iced from the network.
Contactor load transferThis method is based on the use of switching modules installed on bundled conductors to control the current flow within the bundle. In de-icing mode, the switching modules force the current
through one subconductor only.
The process is repeated for the other subconductors of thebundle until complete de-icing is achieved.
Pulse electrothermal de-icer
Average power can be reduced bya factor of 100 as compared to acor dc current.
Requirements for significantmodification of the conductor andits thermal limitation duringsummer time, limit the applicationof this method.
Dielectric layer
Conductor
External conductive c layer
This de-icer uses the current pulse to heat anexternal conductive coating surrounding theconductor
Ground wire de-icing
It requires a current source as well as the electricalinsulation of GW at towers.
Costs associated with the insulation installation are partlycompensated by the elimination of induction losses.
In remote areas, it ispossible to use an auxiliarydiesel generator to de-iceGW.
Other thermal methods
Method that uses steam as a heat source
Summary (1/2)
The AI/DI techniques include passive methods,active coatings and devices, mechanical and thermalmethods.Choosing the most appropriate method for aparticular line depends on the applicability of themethod, the basic energy requirement and theefficiency and cost of the infrastructure.
Summary (2/2)
Non-thermal methods are generally limited to local intervention
Thermal methods, for AI and specially DI, are recognized as the most efficient engineering approach to minimize the consequences of severe icestorms on overhead lines.
Recent publications
Thermal methods- Conductor de-icing
Reduced-voltage short-circuit The basic idea is to connect a line to a source with the
other end shorted, which requires to disconnect the circuitto be de-iced from the network.
As an approximate rule, for applied voltages of 12, 25 and69 kV, it is possible to get the required current intensity(1000 – 1500 A) for circuit lengths of 12, 25 and 69 km,respectively