IEEE 4a-2001 pdf download Amendment to IEEE Standard Techniques for High-Voltage Testing
1. Overview
1.1 Scope
This amendment is applicable to dielectric tests with alternating voltages and impulse voltages, when testingan apparatus with air gaps up to 1 eter in length. lt specifies correction factors for air density and humidity.which may be applied when the specific apparatus standard allows. This amendment is to be applied inconjunction with IEEE Std 4-1995, IEEE Standard Techniques for High-Voltage Testing. The paragraphnumbering beginning at 1.3.5, equations, and figure numbers are as they were in IEEE Std 4-1978. Thus areference to this amendment for a specific clause, etc, will be the same as in the original standard.
1.2 Purpose
This amendment adds the air density and humidity correction factors of the 1978 version of IEEE Std 4 to beused with the standardized rod-gap data when testing apparatus with air gaps up to l meter in length.
Dielectric test voltage atmospheric correction factors
The atmospheric correction factors listed in 1.3.5 may be applied for gap spacing up to 1 meter in length tothe standardized rod-rod gap sparkover data for impulse test voltages found in 17.7, Table 1l of IEEE Std 4-
1995.
1.3.5 Atmospheric conditions
1.3.5.3 Atmospheric correction factors
The disruptive discharge voltage of external insulation depends upon the prevailing atmospheric conditionsUsually, the flashover voltage for a given path in air is raised by an increase in either air density or humidityHowever, when the relative humidity exceeds about 80 percent, the flashover voltage becomes irregular.especially when the flashover occurs across an insulating surface.
By applying correction factors, a measured flashover voltage may be converted to the value that would havebeen obtained under the reference atmospheric conditions. Conversely, a test voltage specified for the refer.ence conditions can be converted into the equivalent value under the prevailing test conditions.
There are two correction factors.They are as follows:
The disruptive discharge voltage is proportional k/k
If not otherwise specified by the appropriate apparatus standard, the voltage to be applied during a withstandtest on external insulation is determined by multiplying the specified withstand voltage by k,kn. Similarly,measured disruptive discharge voltages are corrected to those applicable for a standard reference atmosphereby dividing by ka/kr.
It is left to the appropriate apparatus standard to specify whether or not corrections have to be applied to thevoltage values in those cases where both external and internal insulations are involved. The test report shouldalways contain the actual atmospheric conditions during the test and it shall be indicated whether correctionshave been applied or not.
IEEE 4a-2001 pdf download
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