Electrical Connections
29
Bus Joint Insulation - Taping
Insulation boots are normally provided for repetitive or standard
bus joint conditions. Where boots are not provided, the bus
joints must be carefully taped to the required insulation level
as described below. See Figure 21D, which depicts taped
joints associated with a cable lug mounting arrangement for
multiple cables. Note: When the cables associated with
Figure 21D have been installed, the cable terminations and
the exposed bus must be insulated.
1. Inspect bolted joints to insure they are correctly assem-
bled, bolt heads in proper direction and hardware has
been torqued to proper value. All surfaces must be free of
dust, dirt or other foreign material.
2. Apply a mastic pad over nuts and a second pad over the
bolt heads. Use either small (15-171-988-001: 3.25” x 4.50”
(83mm x 114mm) or large (15-171-988-002: 4.50” x 6.50”
(114mm x 164mm)) size pad most suitable for joint
involved. Remove backing and press adhesive side down and
mold in place covering all sharp projections. Cover hardware
and sharp edges of bus bar if any will be against the tape.
3. Apply half-lapped layers of 4” (102mm) wide tape (15-171-
987-002) or 1” (25mm) wide tape (15-171-987-001) over
the joint. Each layer should overlap the bus bar insulation
by at least 1-1/2” (38mm). Stretching of tape 10% to 15%
in problem areas may help in eliminating voids and wrinkles.
For 5kV class equipment, use two half-lapped layers of tape
over mastic pads. For 8.25kV and 15kV class equipment,
use three half-lapped layers of tape over the mastic pads.
Avoid excessive pressure on the completed bus joint insu-
lation. If bus joints are on standoff insulators, apply tape
per the above procedures except the half-lapped tape
should overlap the insulator by at least 2” (51mm).
Figure 22. Taped Joint Insulation-Switchgear Bus to
Transformer Throat
Transformer Bus Joints - Insulation
The typical transformer to switchgear bus joint shown in
Figure 22 is different from other bus joints in the switchgear
main bus. In the transformer bus joints, there is a transition
from the fully insulated switchgear system to the transformer,
where the spacing between conductors is usually large
enough so that the conductors need not be insulated. The use
of flexible connectors in this area insures correct alignment of
the switchgear conductors to the transformer conductors. If
the installed clearance (phase-to-phase or phase-to-ground) is
less than 6” (152mm) for 8.25kV and 15kV switchgear (3.5”
(89mm) for 5kV switchgear), the joint must be insulated.
Refer to Figure 22, and insulate bus joint connections as out-
lined under “Bus Joint Insulation - Taping”.
Primary Cable Connections
All cable connections to metal-clad switchgear must be fully
insulated to comply with the ANSI C37.20.2 definition of
metal-clad switchgear. Recommendations of the cable supplier
should be followed for the installation. Typical termination con-
figuration is shown in Figure 23.
Because of considerable variations in installation requirements
and available cables, Siemens furnishes a double-bolt, double-
clamp, terminal lug as standard. All insulating and terminating
materials other than terminal lugs and cable supports are to be
furnished by the purchaser.
Figure 23. Primary Cable Termination and Insulation
Figure 24. Typical Cable Terminal Mounting and Insulation
B
A
A
B
INSULATED PHASE BARS
REAR VIEW
(BOTTOM CABLE)
BB
SIDE VIEW
(TOP CABLE)
MINIMUM CLEARANCE OVER INSULATION PHASE TO PHASE (A)
AND PHASE TO GROUND (B) SHALL BE NOT LESS THAN:
4.76 kV - 1.75" (45mm)
8.25kV & 15kV - 3.25" (83mm)
BUS INSULATION
MASTIC PAD
1" OR 4" TAPE (1/2 LAPPED)
4.76kV - 2 LAYERS
1.5"
(38mm) MIN.
8.25kV & 15kV - 3 LAYERS
OVERLAP
GROUND SENSING CT
GROUND LEAD TO
SHIELDING AT STRESS
CONE MUST PASS THRU
CT AS SHOWN FOR
PROPER RELAY
OPERATION.
BUILD UP
EQUAL TO
INSULATION
THICKNESS
2"
2"
18"
MASTIC PAD
1" OR 4" TAPE (1/2 LAPPED)
8.25 & 15kV - 3 LAYERS
BUS INSULATION
1.50" (38mm) MIN.
OVERLAP
OVERLAP
1.50" (38mm) MIN.
4.76 kV - 2 LAYERS
4"
4"
(457mm)
8.25 kV &15kV
7"
(178mm)
4.76 kV
4.76 kV
8.25 kV &15kV
(102mm)(51mm)
(51mm)
(102mm)
NOTE 1 NOTE 1
NOTE 1 NOTE 1
SIZE AND LOCATION OF STRESS
CONE AS RECOMMENDED BY
CABLE MANUFACTURER.
NOTE 1:
DIMENSIONS ARE FOR REFERENCE ONLY
UNINSULATED TRANSFORMER CONNECTION
INSULATED SWITCHGEAR BUS
FLEXIBLE CONNECTOR
MASTIC PAD
BUS INSULATION
D
D = 6.00" (152MM) MIN. for 8.25kV & 15kV
8.25 & 15kV - 3 LAYERS
1.50" (38MM) MIN.
OVERLAP
D
1" OR 4" TAPE (1/2 LAPPED)
4.76 kV - 2 LAYERS
D = 3.50" (89MM) MIN. for 4.76kV
Courtesy of NationalSwitchgear.com
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