Insulation Loss

The outer insulation of pacing and implantable cardioverter-defibrillator (ICD) leads is relatively slippery in order to facilitate lead movement and implantation. This characteristic also plays a role in transvenous lead removal the presence of intact insulation makes sliding dilators over the lead easier. In the absence of insulation or when the insulation is damaged, removal may be challenging. 

Fig 10 5 New insulation may be provided for a damaged lead by using a piece of multipurpose catheter dashed arrow), advancing it over the lead white star) as far as possible then sliding the sheath over the catheter solid arrow). This could be useful for leads that have lost insulation for a lengthy tract, or over its entire length due to, for example, a previous removal attempt 

The possible solution may be to provide a new insulation. In these cases, the authors use a piece of multipurpose catheter, advancing it over the lead as far as possible, till the tip or close to the most proximal binding site (Fig. 10.5). Using this dress for the lead, the disadvantages induced by damage are minimized and, while the coil is held, sheath advancement and dilatation can be effectively and safely performed. 

Fig 10 6 Coil fracture induced by the dilating-sheath maneuver. This situation could be dangerous due to the risk of vessel tears or lacerations caused by disrupted metal wires 

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Ampacity A measure of the current carrying capacity of a power cable. Ampacity is determined by the maximum continuous-performance temperature of the insulation, by the heat generated in the cable (as a result of conductor and insulation losses), and by the heat-dissipating properties of the cable and its environment. 

Cryogenic tanks (h) are built up to a volume of 100 m. Their insulation loss amounts to about 1% of the design liquid inventory per day. These low heat losses at storage temperatures of about 4 K are possible due to superinsulation, thermal radiation shields and deep vacuum in the clearances of the double-walled container. The heat radiation shields transport the heat to the pipes in which either nitrogen or helium itself evaporates. A typical layout is shown in Fig. 4.4 [4.2]. 

Assume that the compressor that drives this heat pump is adiabatic with an efficiency of 0.75, but that - to compensate for insulation losses - only the reversible work appears in the hot fluid. 

Electromagnetic flow meters ate avadable with various liner and electrode materials. Liner and electrode selection is governed by the corrosion characteristics of the Hquid. Eor corrosive chemicals, fluoropolymer or ceramic liners and noble metal electrodes are commonly used polyurethane or mbber and stainless steel electrodes are often used for abrasive slurries. Some fluids tend to form an insulating coating on the electrodes introducing errors or loss of signal. To overcome this problem, specially shaped electrodes are avadable that extend into the flow stream and tend to self-clean. In another approach, the electrodes are periodically vibrated at ultrasonic frequencies. 

Electrical. Glasses are used in the electrical and electronic industries as insulators, lamp envelopes, cathode ray tubes, and encapsulators and protectors for microcircuit components, etc. Besides their abiUty to seal to metals and other glasses and to hold a vacuum and resist chemical attack, their electrical properties can be tailored to meet a wide range of needs. Generally, a glass has a high electrical resistivity, a high resistance to dielectric breakdown, and a low power factor and dielectric loss. 

Most small Hquid helium containers are unpressurized heat leak slowly bods away the Hquid, and the vapor is vented to the atmosphere. To prevent plugging of the vent lines with solidified air, check valves of some sort are included in the vent system. Containers used for air transportation are equipped with automatic venting valves that maintain a constant absolute pressure with the helium container in order to prevent Hquid flash losses at the lower pressures of flight altitudes and to prevent the inhalation of air as the pressure increases during the aircraft s descent. Improved super insulation has removed the need for Hquid nitrogen shielding from almost all small containers. 

Adding amines to coating compounds containing other polymers of hydantoin derivatives permits thermal curing of the coating compounds, which are useful as electrical insulators of wires under a broad range of conditions without loss of coating flexibiUty (101). 

Power factor, like the dielectric constant, is a property that represents a power loss that takes place when a wire insulation becomes the dielectric of a condenser because of a surrounding sheath or other conducting medium. 

Power factor losses under certain conditions cause a temperature rise in the insulation that may result in failure or reduced life of the insulation. In communication wiring the power factor of the insulation plays an important role. Here the actual power loss can represent an appreciable portion of the total energy in the circuit. In addition, this loss disturbs the circuit characteristics of the equipment at both ends of the line. 

The power factor of polyethylene which provides the measure of the power loss in the insulated conductor increases slightly with an increase in the temperature of the atmosphere or the electrical equipment, both of which may fluctuate widely. It also increases slightly with an increase in the humidity of the surroundings. 

Grade XXXPC is similar in electrical properties to Grade XXXP and suitable for punching at lower temperatures than Grade XXXP. This grade is recommended for apphcations requiring high insulation resistance and low dielectric losses under severe humidity conditions. 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

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