Victor F. Petrenko

Breaking the ice [transmission line icing]

Icing of power transmission lines during winter storms is a persistent problem that causes outages and costs millions of dollars in repair expenses. High-frequency excitation at approximately 8-200 kHz has been proposed as a method to melt ice. The method works by a combination of two mechanisms. At these frequencies, ice is a lossy dielectric, causing heating directly in the ice. In addition, skin effect causes current to flow only in a thin layer on the surface of the line, causing resistive losses and consequent heating. In this article, we describe the design of systems to implement this method on lines up to 1000 km long. We also report experimental tests of deicing of a 1 m simulated line using dielectric losses in ice using a prototype system that applies 33 kV, 100 kHz power.

The effect of static electric fields on ice friction

The effect of an external electric dc bias applied between ice and sliders on both static and dynamic ice friction has been examined. The measurements were performed on pure polycrystalline ice in the temperature range from −5 to −30 °C and for sliding velocities from 0.5 to 8 m/s. The sliders were made of aluminum, stainless steel, and polyethylene. It was found that an application of an external dc bias to the ice/slider interface can double the force of dynamic and static friction between ice and metals and between ice and dielectrics. These new physical phenomena are discussed in terms of electrostatic pressure, effect of electric fields on ice plastic deformation, and field‐sensitive ice adhesion. Both the experimental results and the discussion show that frictional self‐electrification may play a significant role in forming the ice friction coefficient and that the friction can be modified intentionally.

Reduction of ice adhesion to stainless steel by ice electrolysis

We report a very strong and reproducible effect of a small dc bias (−21 to +21 V) on ice adhesion to stainless steel. The effect was found in ice doped with 0.5% NaCl and was absent in very pure ice grown from deionized water. The doping was used to enhance ice electric conductivity. Neither the application of ac voltage nor direct electric heating of the same power as the dc bias caused any noticeable change in ice adhesion. Different physical mechanisms of ice adhesion to metals and possible explanations to the effect are discussed. Generation of electrolytic gases resulting in interfacial cracking is thought to be responsible for the effect.

Generation of electric fields by ice and snow friction

Strong electric fields up to 2×106 V/m having potentials up to 1.6 kV were generated in the gap between ice (or snow) and metallic and dielectric sliders, including alpine skis. Experimental data on the ice frictional electrification over wide ranges of sliding velocity and temperature are presented both for metal and dielectric sliders. Several possible physical mechanisms are discussed. The observed high magnitude of the potential difference V generated by friction between ice and sliders and the dependencies of V upon the slider velocity, ice conductivity, and temperature can be best explained in terms of high density electric charges picked up by a slider from the ice surface. The observed surface charge density corresponds to strong polarization of water molecules in the surface layer of ice. The phenomenon can play a significant role in forming a frictional force.

Using dielectric losses to de-ice power transmission lines with 100 kHz high-voltage excitation

Icing of power transmission lines during winter storms is a persistent problem, causing outages and costing millions of dollars in repair expenses. Excitation at approximately 33 kV 100 kHz can be used melt ice off of power transmission lines through dielectric losses in the ice itself. Standing wave effects result in nonuniform heating if dielectric losses are used alone, but the combined effect of dielectric loss and skin-effect resistive loss can be tuned to provide uniform heating. A single high-voltage source may be used to de-ice sections of line up to 100 km long before attenuation impacts efficiency excessively. A prototype system capable of exciting a 1 m test line to 30 kV has been tested and show to be capable of removing a 7 mm ice layer from the line.

Crack velocities in freshwater and saline ice

This paper presents experimental results on both mode 1 and 2 crack velocities measured in a wide variety of ice types, columnar sea ice, columnar lake ice, laboratory-grown columnar saline ice, and freshwater columnar and granular ice, in the temperature range from −5° to −35°C. Measurements of ice electrical conductance, electrical capacitance, and electromagnetic emissions from cracks as a function of time were used to determine crack velocities in samples with dimensions ranging from 0.05 to 30 m. In laboratory-grown freshwater ice and in lake ice, average crack velocities varied from a few hundred to 1320 m/s. In contrast, in natural sea ice and laboratory-grown saline ice, crack velocity was very low at about 10 m/s. This remarkable difference in the velocity of cracks growing in freshwater and saline ice is probably due to the dynamic resistance of unfrozen water in brine pockets and/or the large size of a crack tip process zone in saline ice. It was also found that cracks propagate discontinuously in saline ice owing to the strong interaction with microstructural elements such as drainage channels.

Effect of electric fields on adhesion of ice to mercury

We report a strong and fully reversible effect of a small dc bias (−6 to +6 V) on ice adhesion to mercury. The effect was observed in ices doped with KOH, HF, and NaCl and was absent in very pure ice grown from deionized water. The ac voltage of up to 40 V did not cause any noticeable changes in ice adhesion. Different physical mechanisms of ice adhesion to metals and possible explanations of the effect are discussed. The phenomenon was used to estimate the contribution of electrostatic interactions to ice adhesion to metals.

Quasi-liquid layer theory based on the bulk first-order phase transition

The theory of the superionic phase transition (bulk first-order transition) proposed in [1] is used to explain the existence of a quasi-liquid layer at an ice surface below its melting point. An analytical expression is derived for the quasi-liquid layer thickness. Numerical estimates are made and compared with experiment. Distinction is made between the present model and other quasi-liquid layer theories.

SFM Studies of the Surface Morphology of ICE

The nature and properties of the surface layer of ice are important in many applications. This layer possesses peculiar optical, electric and mechanical properties. Various experimental techniques based on indirect measurements give different values of the thickness of this layer and different temperature domains for its existence. A new direct method for investigation of the surface layer of ice can be provided by scanning force microscopy (SFM). We studied the surface of ice using NanoScope III in the temperature range from -2 to -25°C. Images of the surface of ice and force calibration curves (FCC) were obtained in the open air and in hexane. The problem of surface melting at higher temperatures is analyzed. Stable images of the ice surface were obtained at lower temperatures. It was found that at temperatures corresponding to the transition of the surface layer to the quasi-liquid state the surface morphology and FCC change. When ice is brought in contact with hexane FCC indicate a formation of an unusually thick (∼ 1 μm) surface film.

Proton ordering in ice at an ice-metal interface

The structure of the proton sublattice of ice at an ice-metal interface is analyzed by solving the Ginzburg-Landau equation for an order parameter describing the proton ordering under an appropriate boundary condition [1, 2]. When the interaction between protons and the substrate is weak, the ice rules that govern proton order are weaker at the interface as compared to bulk ice, but to a lesser extent than at the free ice surface. In the case of strong proton-substrate interaction (clean interface and/or high conductivity of the substrate), the ice rules are stronger at the interface as compared to bulk ice, which corresponds to a more ordered proton sublattice. The latter case corresponds to a lower concentration of defects in the proton sublattice, which determine important properties of ice, such as adhesion, electrical conductivity, plasticity, and electric field distribution near the interface. A qualitative correlation is described between electrical properties of the substrate and mechanical properties of the interface, including adhesion and friction.