Testing earth fault resistance
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article may require cleanup to meet Wikipedia's quality standards.
Please discuss this issue on the talk page or replace this tag with a more specific message.
This article has been tagged since March 2006.

The human body conducts electricity, especially where moisture is present, such as in kitchens and bathrooms, and for that reason it is very important that any parts of electricity-using appliances have a high resistance/impedance to the outside case, and/or to any other parts that could get to be in contact with any person's skin. Insulation is provided, and its resistance should be no less than a given high value (see below), so that any current into, or out of, a user's skin is much lower than would cause any harm. By the way, what some countries call Earth would be called Ground in some other countries.

A three-phase induction motor has conductors which are insulated to withstand the full rated supply voltage.

This insulation may break down so that the insulation resistance falls below certain values.

The conductors must have an insulation resistance of greater than one hundred kilohms to function at all, and greater than one megohm ideally.

In a typical three phase induction motor circuit, an appropriate place to test is at the load side of the direct-on-line motor starter


Asymmetric fault
From Wikipedia, the free encyclopedia
Jump to: navigation, search
In power engineering, specifically three phase power, an asymmetric or unbalanced fault is a fault which does not affect each of the three phases equally. This is in contrast to a symmetric fault, where each of the phases is affected equally. In practice, most faults in power systems are unbalanced; however, as asymmetric faults are difficult to analyze, analysis of asymmetric faults is built up from a thorough understanding of symmetric faults.

Common types of asymmetric faults, and their causes:

line-to-line - a short circuit between lines, caused by ionization of air, or when lines come into physical contact, for example due to a broken insulator.
line-to-ground - a short circuit between one line and ground, very often caused by physical contact, for example due to lightning or other storm damage
double line-to-ground - two lines come into contact with the ground (and each other), also commonly due to storm damage

Symmetric fault
From Wikipedia, the free encyclopedia
Jump to: navigation, search
In power engineering, specifically three phase power, a symmetric or balanced fault is a fault which affects each of the three phases equally. This is in contrast to an asymmetric fault, where each of the phases is not affected equally. In practice, most faults in power systems are unbalanced. With this in mind, symmetric faults can be viewed as somewhat of an abstraction; however, as asymmetric faults are difficult to analyze, analysis of asymmetric faults is built up from a thorough understanding of symmetric faults.


si din granddictionaire

1 / 1


Domaine(s) : - électricité
électrotechnique


français


défaut à la terre n. m.
Équivalent(s) English earth fault



Définition :
Défaut dû à la mise en contact d'un conducteur avec la terre ou à la diminution de sa résistance d'isolement à la terre au-dessous d'une valeur spécifiée.
vezi si asta
http://www.instahelp.ro/page5.htm





--------------------------------------------------
Note added at 11 hrs (2007-03-11 17:14:46 GMT)
--------------------------------------------------

termenul e "impamantare"
http://ron.proz.com/kudoz/1745498