Page 889 - Industrial Power Engineering and Applications Handbook

26/840 Industrial Power Engineering and Applications Handbook
compared to the measurement taken at the start of the For LT units: Three impulses should be applied of
test should not vary by more than the following: positive polarity followed by three of negative between
the terminals joined together and the container.
For capacitance value For HT units: Fifteen impulses should be applied of
For LT units: 2% of its capacitance value positive polarity followed by fifteen of negative between
For HT units: The two test values should be corrected the bushings joined together and the container.
to the same reference of dielectric temperature, say,
20°C or as agreed. The difference between the two The value of the first peak of the test wave is specified
test values should be less than an amount corresponding in Table 26.4. During the test there should be no rupture
to either breakdown of an element or operation of an or flashover at any part of the unit, which should be
internal fuqe. verified by a cathode ray oscillograph. An oscillograph
For tan 6value should also be used to record the voltage and check the
For LT units: 2 X IO4 wave shape.
For HT units: 1 x lo4 or as agreed between the
manufacturer and the user. (6) Short-circuit discharge test

(2) Measurement of capacitor loss in terms of tan 6 The unit should be first charged by d.c. and then discharged
through a gap situated nearby. The test voltages should
This is the same as for the routine test be as follows.

(3) Voltage test between terminals For LT units
Star-connected units Test voltage 4 V, /a. The test
This is similar to the routine test (4) except the duration should be carried out between any two terminals, leaving
of the test, which should be as specified in Table 26.4. the third open.
Delta-connected units Test voltage 2V,. Any two
(4) Voltage test between terminals and container terminals of the unit should be shorted and the test
conducted between the third and the shorted terminal.
This is similar to the routine test (4) except the duration
of the test, which would be as specified in Table 26.4.
For HT units
(5) Lightning impulse voltage test between The test voltage should be 2.5 V,, irrespective of star- or
delta-connected units. The capacitor unit should be charged
terminals and container with the test voltage and discharged five times within 10
The test should be conducted generally with a wave of minutes. Within 5 minutes after the test the unit may be
1.2 to 5/50 ps as illustrated below: subjected to voltage test (3) between the terminals. The

Highest vulruge for Rated lightning impulse withstund Rated power-frequency short-durcition withstand volttrge for

Durution
Routine test 1 Type test
up to 0.66
0.66 to 1.0
1.2
2.4
3.6
7.2 40 10 s
12 60
11.5 75 ~. 1
24 9s
36 145

Notes
1 For a repeat test only 7S% of the test voltage must be applied.
2 The power frequency voltage test refers to indoor units. The outdoor capacitor units must be subjected to a wet test as in IEC 60060-1.
3 The choice between list I and list 2 will depend upon the extent of exposure of the units to the internal and external voltage surges and
the amount of surge protection, if provided.
4 It will also depend upon the condition of system grounding, i.e. whether effectively grounded. non-effectively grouned or isolated neutral
etc. For systems other than effectively grounded, list 2 must be preferred.
S For higher voltage systems, refer to the relevant Standards noted in the table of Standards provided at the end of the chapter.