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This is an interpretation of IEEE Std C57.12.91-2001. Interpretations are issued to explain and clarify the intent of a standard and are not intended to constitute an alteration to the original standard or to supply consulting information. Permission is hereby granted to download and print one copy of this document. Individuals seeking permission to reproduce and/or distribute this document in its entirety or portions of this document must contact the IEEE Standard Department for the appropriate license. Use of the information contained in this document is at your own risk.
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Subclause 10.3 - Applied-voltage tests and subclause 10.3.3 - Ground connections
during the test states, "A normal power
frequency such as 60 Hz shall be used and the duration of the test shall be
1 min."
If the test lab only has 50 Hz available for testing, is that acceptable?
There are different opinions that weigh in on both sides of the issue. Some
say that if you use 50 Hz than you have to adjust the test duration to 72 seconds
to account for an equivalent number of peak voltages seen during the length
of the test. Other say that as long as the frequency is between 45-65 Hz than
a test duration of 60 seconds is fine ... one reason being that the at less
than 60 Hz the wave form is wider so that at these lower frequencies the cable
is subjected to a voltage the levels between 97% and
100% for a longer period of time per cycle. In any event, what is the Working
Group official response or ruling?
This question out to several members within the Dielectric Test Subcommittee,
both to manufacturing and utility representatives, and received five responses.
All but one commented that the test duration should be for one minute regardless
of whether the applied frequency was 50 or 60 Hz. Perhaps the most useful response
of these was actually an admonishment that we don't really need an interpretation
here since standards are already clear on this subject. Specifically, the initial
sentence of subclause 10.3.3 of C57.12.91 states: "A normal power frequency
such as 60 Hz shall be used and the duration of the test shall be 1 min."
The italicized words are key here. C57.12.91 also references IEEE 4 in Clause
2. Article 6.1.1, Requirements for the test voltage, within Clause 6, Tests
with alternating voltage, within IEEE 4 states: "The test voltage shall
be an alternating voltage having a frequency in the range of 45-65 Hz, normally
referred to as power frequency voltage." Hence, the standards are indeed
quite clear; the test duration shall be 1 min regardless of whether the applied
frequency is 60 or 50 Hz. Another response indicated that IEC standards specifies
that the 1 min duration applies to test frequencies not less than 80 % of the
rated frequency. Hence, IEEE is in line with other standards within the industry.
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