2 Type A bushing
Storing
Store the bushing in a clean, dry place in the shipping crate.
Particular care should be taken to keep dust and dirt out of
the inside of the bushing. For long term storage, suitable
protection should be provided for the terminals and mounting
hardware. The gasket surface on the underside of the mounting
flange should be heavily greased to protect it from rust and
corrosion.
Installation
Type A bushings are shipped ready for installation. An
apparatus manufacturer may ship the bushing completely
installed, eliminating the requirement for installation in the
field. If a draw-lead bushing is removed from the transformer
for shipment, the top hardware and mounting hardware may
be removed from the bushing and packed separately. When
installing a bushing, tighten the mounting bolts a fraction of
a turn at a time, working progressively in a crisscross pattern
Draw-lead bushings
The draw-lead terminal stud for a low current bushing is
included as an integral part of the bushing. The flexible draw-
lead cable is provided by the transformer manufacturer. The
terminal stud is either brazed or crimped on to the draw-lead
cable. Remove the terminal cap, retaining pin, and stud
washer. Assemble the stud washer onto the terminal stud.
Pass a wire or cord down through the tubular porcelain and
attach it to the terminal stud on the draw-lead. Lower the
bushing into position while pulling the draw-lead up through
the porcelain. Pin the terminal stud into position. Coat the
terminal cap gasket with a thin film of light oil; then position the
gasket in the terminal cap. Tighten the terminal on the stud to
compress the gasket, thus sealing the bushing.
On a bushing of older design, the stud is brought into position
with a sealing nut. Remove the terminal cap and sealing nut
(the stud is already removed) from the top end of the bushing.
After positioning the terminal stud in the porcelain, assemble
the gasket and sealing nut on the stud. Screw on the nut
tightly to compress the gasket and seal the nut. The draw-
lead bushing uses a multiple-piece clamp, illustrated in Figure
3 for mounting on the transformer. The clamp does not require
cement.
unpacked, wipe clean of all dust, grease, oil or particles of
packing material with a dry cloth. Inspect the bushing for
damage such as cracked porcelain or damaged threads.
Type A features
The draw-lead bushing has a pin connected terminal stud.
Standard bushings rated up through 2,500 amperes use a
loose, multi-piece mounting clamp (see Figure 3). Standard
bushings rated 3,000 amperes and above have an epoxy
cement flange. A fixed conductor bushing up to 3,000 amperes
for cover or side-wall mounting is not sealed at the bottom end,
allowing oil from the transformer to circulate in the bushing.
The Type A bushing has satisfactory radio influence voltage
characteristics under normal operating conditions. The
electrical characteristics comply with ANSI requirements. The
construction is simple and sturdy and the Type A bushing has
an excellent service record.
Size of bolt (inch-thread)
Torque ft-lbf (N-m)
1
1/2 - 13
25 (34)
5/8 - 11
30 (41)
3/4 - 10
35 (48)
1
Torque values for mounting bolts should not be exceeded
Figure 1 - Type A bushing (600 amperes and below)
until all of the bolts are uniformly tight. This must be done
to prevent unequal clamping and possible damage to the
porcelain support or the mounting flange. Tighten the bolts
sufficiently to seal the bushing to the mounting flange. The
torque values listed below will provide adequate gasket
compression for sealing on all Type A bushings.