Page 1009 - Industrial Power Engineering and Applications Handbook

321954 Industrial Power Engineering and Applications Handbook
welded joints will be subjected to dye penetration a UAT through the main bus section between the generator
examination and 10% of butt-welded joints, and the generator transformer which are under the
including joints on flexibles, enclosures and cumulative influence of two separate power sources, must
conductors, will be subjected to radiographic (X- be subjected to a higher withstand voltage as prescribed
ray) examination. by IS 8084 and indicated in column 4, Table 32.1(A).

32.2.3 Seismic disturbances 32.3.3 Impulse voltage withstand test (for system
In Section 14.6 we have provided a brief account of such voltages 2.4 kV and above)
disturbances as well as the recommended tests and The procedure for testing will be the same as that discussed
procedures to verify the suitability of critical enclosures for switchgear assemblies in Section 14.3.4. The impulse
and bus systems for locations that are earthquake- test voltage is applied as in Table 32.1(A) for series I
prone. For this the user is required to provide the and Table 32.2, for series I1 voltage systems with a full
manufacturer with the intensity of seismic effects at site wave standard lightning impulse of 1.2J50 (Section 17.6.1).
of the installation in the form of response spectra (RS). There should be no disruptive discharge or insulation
(See Section 14.6.) breakdown.

32.2.4 Field tests
32.3.4 Verification of temperature rise limits (or
These are to be conducted aftcr the installation and before rated continuous current capacity)
energizing the bus assembly at site:
(Recommended for systems having a current rating of
more than 400 A)
Checking for any human error This will be carried out under similar parameters of
Visual inspection of the bus assembly room condition and the type of test voltage wave to
Inspection of electrical wiring if there is any (such as those for a switchgear assembly (Section 14.3.5). The
for space heaters, cold or hot air blowing or enclosure- current in each phase should be within 2% of the specified
pressurizing or any other protective circuit) test value (rated current).
Verification of insulation resistance or measurement For LT bus systems: The length of the test piece will
of the leakage current, both before and after the be a minimum 6 m as in IEC 60439-2 with at least one
dielectric HV test, if the HV test is to be carried out. joint. The joints must be both in the conductor and in
Verification of dielectric properties - limited to power the enclosure in each phase. If the total length of the bus
frequency voltage withstand or HV test (usually not section is less than specified, the entire length of the
recommended) bus system in the fully assembled form will then be
Watertightness and air leakage test for isolated phase tested.
bus systems.
For HT bus systems: The entire length of the bus system
manufactured for a particular installation in the fully
32.3 Procedure for type tests assembled form will be tested. Each end of the bus
enclosure will be properly sealed to eliminate any heat
leakage.
Below we briefly outline the procedure for conducting The bus sample is located 600 mm above floor level.
type tests at the manufacturer's works. The ambient temperature should be within 10-40"C as
measured by the average value of at least four thermo-
32.3.1 Verification of insulation resistance or meters, two placed on each side of the enclosure on the
measurement of the leakage current centre line, at least 300 mm from it, and 600 mm from
the ends. The bus sample must be a three-phase unit as
The procedure and test requirements will remain the same well as the test equipment for a three-phase system to
as that discussed in Section 14.3.2, for metal-enclosed account for the proximity effect. This effect will not be
switchgear and controlgear assemblies. reflected if a three-phase system is tested on a single-
phase one. Similarly, a single-phase unit and single-phase
32.3.2 Verification of dielectric properties test equipment should be used for a single-phase system
(such as from the neutral side of the generator up to the
Power frequency voltage withstand or HV test neutral grounding transformer). The test will be conducted
at the rated current until a near-stable condition is reached
The procedure will be the same as that discussed for and three successive readings at not less than one-hour
switchgear assemblies (Section 14.3.3). The test voltage intervals for an LT system and 30 minutes for an HT
may be applied for one minute as shown in Tables 32.1 (A) system do not show a maximum variation of more than
or (B) for series I and Table 32.2 for series I1 voltage 1°C. To shorten the test, the current may be increased
systems. Any disruptive discharge or insulation breakdown during the initial period. The test may be conducted at a
during the application of high voltage will be considered reduced voltage, as the emphasis is on heating due to
to be dielectric failure. current. For a successful test, the hottest spot temperature
The tap-offs in a power-generating station connecting should not exceed the values in Table 32.3.