Replacing Insulator Bushing

and wire brush the area where the fusion weld is to be

space inside the tank with dry nitrogen or

made.

carbon dioxide gas and maintain a small

c. Loosen locknut 1(i, fig. 4-2) and remove it and

flow of gas during operation. If the bushing

contact nut (6). Remove conductor (5 I and second

is to be reused, exercise care in the removal

contact nut (6). Grind off the edge welds at both the

operation to avoid damaging the glass or the

mounting and cap flanges (2 and 41 using a rotary hand

remaining portion of the adapter ring and

grinder or similar tool. Keep the depth of grinding to a

stud spinning.

minimum and as even as possible. If the bushing is to be

b. Grind off the edge welds at both the mounting

reused, exercise care in the removal operation to avoid

and cap flanges (2, and 4, fig. 4-2) using a rotary hand

damaging the glass body (31 or the remaining portion of

grinder or similar tool. Keep the depth of grinding to a

the adapter ring (11 and the stud spinning. With these

minimum and as even as possible. With these two joints

two joints broken the bushing shell can then be with-

broken the bushing shell can then be withdrawn from the

drawn from the transformer, leaving its stud (81 in place

transformer, leaving its stud (8) in place, connected to the

connected to the internal winding lead.

internal winding lead.

d. Slip the bushing shell (31 over the stud (8) and

c. An alternate method of insulator removal when

insert it through the mounting hole until the stud spacer is

the bushing shell is being replaced by a new one is to cut

seated at the internal end of the bushing and the stud

away the mounting and cap flanges with a chisel. After

spinning is even with the cap flange.

removal of the shell, prize out the remainder of the old

e. Tack weld the assembly in four places and then

bushing flanges and smooth up the adapter ring and stud

use a screwdriver or similar tool to carefully expand the

spinning for rewelding.

stud spinning to bring it in contact with the entire

4-8. Replacing Insulator Bushing

perimeter of the cap flange.

a. The edge welds at the mounting and cap flanges

f. It is recommended that the fusion weld be

are specifically designed for Tungsten Inert- Gas ('I'IG)

completed in several segments with a cooling period

welding. To successfully reweld these joints using this

allowed between each section. Welding should be done

fusion method, it is important to keep the radial gap

at 8 to 12 amps dc using straight polarity (electrode

between mating parts as small as possible.

The

negative} and argon gas flow of about 200 cu. ft. / hr.

clearance should not be allowed to exceed 0.005 inches

Similar techniques should be used in making the

at any point. If a new bushing is being installed, its

mounting-flange-to-adapter-ring weld except for a slightly

flanges may have to be ground down slightly to match the

higher current of 32 to 40 amps.

ground-off edges of the adapter ring and stud spinning.

g. When the welding has been completed, pressure

b. Clean the joints of all oil, dirt, grease, paint, etc.

test the joints as outlined under "Leak Test" paragraph 4-

h. Refill transformer per paragraph 4-4.

Section III. TAP CHANGER

applied to the spring and the wedge is forced into position

4-9. General

with a wiping action, insuring positive contact.

The tap changer is the wedge-type with tap leads from the

transformer windings connected to a circular group of

nickel-plated copper rods which are held together

4-10. Tap Changer Drive Mechanism Removal

between two insulating heads. A wedge in the middle can

a. Changer must be on position "ONE" before

be moved by a crankshaft to wedge between any two

removal in order to facilitate reassembly.

adjacent rods. A spring between the wedge and

CAUTION

crankshaft maintains a high-pressure line contact between

Tap changer drive mechanisms are not

current carrying components. When the crankshaft is

interchangeable. When two or more are

turned to move the wedge from one operating position to

removed at the same time each one must be

another, pressure is gradually reduced on the spring and

identified with the transformer from which it

the wedge is withdrawn from between rods. As shaped

was removed for purposes of reassembly.

guide on the opposite side then pivots the wedge around

b. Unbolt the flange and lift out as an assembly.

to the next set of rods. As the crankshaft continues to

turn, pressure is again

4-4