Power Feedthrough electrical ratings are determined by various factors, including insulator dielectric strength, geometry and system operating pressure. Please note that all ISI Catalog products are electrically rated for operation with one side in dry atmospheric conditions and the other side in vacuum with a maximum system pressure of 1x10-4 Torr. We advise that users make allowances for deviations from stated operating parameters and take adequate safety precautions when feedthroughs are operated at high voltages or high currents.

Strike, Puncture and Creep

Strike, Puncture and Creep are three industry terms used to describe electrical failure and rating criteria. Strike distance is the direct line of site distance from potential to ground. This rating is dependent on environmental and overall feedthrough geometry. Puncture distance is the distance between potential and ground through the bulk of the ceramic insulating material. This rating is dependent on both the dielectric strength of the ceramic and its geometry. Creep or Tracking distance is the distance from potential to ground along a ceramic insulator’s surface path. This rating is dependent on environment as well as the surface condition and overall length.

Electrical Performance

Proven design techniques are employed to optimize the electrical performance of ISI Power Feedthroughs. Where space is not a limitation, ceramic surfaces are made as long as possible to maximize Strike and Creep distances. If space is limited, ceramics are convoluted to achieve increased  surface distance with minimal impact on the overall length. Convoluted or fluted ceramic feedthroughs are recommended for environments where moisture or other surface contaminants may hinder electrical performance. Reducing the ceramic surface roughness will minimize surface contamination and thus improve the Tracking characteristics of the feedthrough. A common method used to reduce surface roughness is the application of high temperature glass coating, or ‘glazing’. Glazing is a proven and cost effective method for enhancing the electrical performance of a ceramic.

Conductors

Conductors are offered in various material choices. These materials are selected based on current-carrying capacity and other environmental concerns such as corrosion and magnetism. Although Copper offers the best current-carrying capacity, it has the worst corrosion resistance. Stainless Steel on the other hand has good corrosion resistance but poor current rating. Pure Nickel has excellent corrosion resistance and medium current carrying capacity.

Water Cooled Feedthroughs

Watercooled electrical components are typically used with grounded, closed-loop cooling systems and nonconductive coolants such as deionized water or ethylene glycol. If using plain tap water, the cooling system must be grounded and lines must employ nonconductive materials such as polypropylene tubing. Properly grounded water lines will provide a safe dissipation path for any power conducted by the water. Current or power ratings are usually not given for watercooled feedthroughs as the ratings
are dependent on coolant flow rates and their heat dissipating capacity. Tap water temperatures can vary dramatically from one region to another, so too will its heat dissipating capacity. Users are advised to establish safe and practical coolant flow rates based on the power requirements for their specific application and coolant heat dissipation capacity.

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