The clearance distance is the shortest distance between two conductive parts such as connector pins measured through air. These distances, called clearance and creepage, vary by application and are specified in the appropriate safety standard.įigure 1: Clearance and creepage. In order to minimize the risk of failure in high-voltage equipment and give an adequate safety margin, conductors carrying high voltages must maintain a certain minimum distance apart (separation). High Voltage Clearance & High Voltage Creepage Other fields, such as automotive, have their own set of standards established by organizations such as the SAE. Table 2: Some common safety standards (Source: Feryster) Household and similar electrical appliancesĪudio, video and similar electronic apparatus Power transformers, power supply units, switch mode power suppliesĮlectrical Apparatus for Explosive Gas Atmospheres These effects can have serious, possibly fatal, consequences in high-voltage equipment, including connectors, so there are numerous safety standards that have been developed, depending on the application. This failure is catastrophic because the current flow through the dielectric leaves voids filled with carbon and the dielectric will no longer be able to withstand the required voltage. In the case of a solid medium such as a dielectric, a dielectric breakdown occurs when the voltage stress is significant enough to cause an arc through the dielectric between the conductor and ground. At STP, air breaks down at approximately 3 kV/mm. To minimize corona effects in connector design, it’s important to maximize the distance between conductors that have large voltage differentials, use conductors with large radii, avoid designs that have sharp points or sharp edges, and use dielectrics without voids.Īrcing in Electrical Circuits & Dielectric BreakdownĪn electric arc, or arc discharge, is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current through normally nonconductive media such as air. While corona is a low-energy process, over long periods of time, it can substantially degrade insulators, causing a system to fail due to dielectric breakdown. Corona can also occur due to the ionization of air within a void in a dielectric or interface inside of a connector. This can occur at voltages as low as 300 V. The corona will occur when the strength (potential gradient) of the electric field around a conductor is high enough to form a conductive region, but not high enough to cause electrical breakdown or arcing to nearby objects. In general, as voltage increases, a corona forms around an HV conductor followed by dielectric breakdown, leading to arcing or catastrophic failure.Ī corona discharge is an electrical discharge brought on by the ionization of air surrounding a conductor that is electrically charged. ![]() Insulation that is perfectly adequate at 12 V, say, may rapidly degrade or fail altogether at 12 kV. High voltages impose severe stress on all connection system components. High-Voltage Circuit Design: Issues & Considerations Table 1: IEC voltage definitions (Source: Wikipedia) ![]() Table 1 shows the IEC definitions for low and high voltage and their defining risks. On the other hand, in electric power transmission engineering, high voltage is usually considered any voltage over ~35,000 V. The definitions may refer to the voltage between two conductors of a system, or between any conductor and ground.Īt the low end, voltages greater than 50 V applied across dry unbroken human skin can cause heart fibrillation if they produce electric currents in body tissues that happen to pass through the chest area. Two factors considered in classifying a voltage as “high voltage” are the possibility of causing a spark in air, and the danger of electric shock by contact or proximity. The numerical definition of high voltage depends on context. Connectors designed for such applications must accommodate particular safety requirements, and present special design challenges.
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