ABB Type A Bedienungs- und Wartungshandbuch

General description

Type A bushings are designed for application on transformers.

Porcelain is used as the major insulation, and the single-piece

porcelain is bottom end connected to the apparatus to insulate

the conductor from the grounded mounting surface.

Type A bushings are available with voltage ratings from 1.2 to

34.5 kV. Bushings rated 600 amperes and lower have draw-

lead conductors which allow the bushings to be removed

without disturbing connections inside the transformer. Fixed

conductor bushings are available in current ratings through

18,000 amperes.

The fixed conductor bushings are center clamped with spring

washers or multiple spring mechanisms at the bottom end.

This construction provides a pressure tight seal and develops

maximum strength in the porcelain.

Safety information

Keep this document available to those responsible for the

installation, operating, and maintenance of the bushing.

The installation, operation, and maintenance of a bushing

present numerous unsafe conditions, including, but not limited

to, the following:

– High pressures

– Lethal voltages

– Moving machinery

– Heavy components

Specialized procedures and instructions are required and must

be adhered to when working on power transformers. Failure to

follow instructions could result in severe personal injury, death,

and/or product or property damage.

Additionally, all applicable safety procedures such as OSHA

requirements, regional and local safety requirements, safe

working practices, and good judgment must be used by

personnel when installing, operating, and/or maintaining such

equipment.

Safety, as defined in this document, involves two conditions:

– Personal injury or death

– Product or property damage (includes damage to the

bushing or other property, and reduced bushing life.)

Safety notations are intended to alert personnel of possible

personal injury, death or property damage. They have been

inserted in the instructional text prior to the step in which the

condition is cited. The safety notations are headed by one of

three hazard intensity levels which are defined as follows:

– Danger - immediate hazard which will result in severe

personal injury, death, or property damage.

– Warning - hazard or unsafe practice which could result in

severe personal injury, death, or property damage.

– Caution - hazard or unsafe practice which could result in

minor personal injury, or property damage.

This document contains general

procedures to be followed from the time

bushings are received until they are put

into operation.

Receiving and unpacking

When a bushing is received, examine any damage incurred

during shipment. Inspect the surface of the porcelain for small

breaks or cracks. If damage or rough handling is evident, file a

claim with the transportation company and immediately notify

ABB.

Exercise care in opening the shipping container to prevent

damage to the porcelain insulators. As each bushing is

Transformer components

Type A bushings

Instructions for installation, maintenance, and storage

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)

1/2 - 13 25 (34)

5/8 - 11 30 (41)

3/4 - 10 35 (48)

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.

Type A bushing 3

External line connections

Connections from a bus to the top end of a bushing should

be made securely to avoid loosening in service which would

cause damage to bushing gaskets. There should be sufficient

flexibility in the connections to prevent mechanical stresses

from expansion, contraction, and wind sway. Long spans of

unsupported conductor should be avoided.

Terminal connectors should be of ample size to keep the

bushing terminal temperature below 70 °C at rated current. The

use of even more generously sized connectors is recommended

to minimize bushing overheating during possible overloads. Do

not loosen the top terminals when installing the line terminal

connectors.

Fixed conductor bushing

A cover or side-wall bushing up to 3,000 amperes, with a fixed

conductor, is not sealed at the bottom (inboard) end. Insulating

oil from the transformer is permitted to enter the bushing when

it is installed and operating. Threaded clamping members at the

bottom end are assembled to seal the top (outboard) end of the

bushing with a gasket and to load the porcelain in compression.

Fixed conductor bushings rated 3,000 amperes or more

have epoxy bonded supports and gasket-to-porcelain seals.

Sometimes a clamping ring is attached with epoxy and then

bolted to a mounting support plate. Thin washers or shims are

used between the clamping ring and the support plate. These

are installed at the factory.

Do not alter the position of the washers; otherwise, leaks may

occur. Bushings with fixed conductors should be bolted to

the transformer prior to making bottom and top end terminal

connections.

!Caution

Before applying vacuum to a transformer, be certain there

is sufficient slack in the external line connections to the

bushing to allow for bushing movement caused by flexing

of the transformer cover and/or walls. Failure to relieve this

stress at the bushing connection may result in damage to

the bushing seals and loss of oil. Loss of oil will cause an

electrical failure.

Maintenance

Porcelain is the major insulation in Type A bushings and requires

little maintenance other than cleaning when operated under

very dirty conditions. Inspection should be made regularly

for cracked porcelains which could contribute to oil leakage,

especially on self-filling, side-wall mounted bushings or on

bushings used with transformers equipped with an oil expansion

tank above the cover level.

Nameplate data

Nameplate data is of special importance in answering questions

about bushings. All requests will be expedited if the factory is

furnished with the serial number, the functional style number,

version number, and the year of manufacture as stamped on the

bushing nameplate.

At a minimum, the factory should be provided with the serial

number of the bushing in question.

Field repair

Any repair of Type A bushings should be done in the factory

because of the danger of contamination to the insulation when

the seal is broken. In addition, the very high vacuum and

clamping pressure require the use of equipment not usually

available in the field. Any damage to a bushing, which might

make repair either desirable or necessary, should be reported to

the factory.

Figure 2 - Type A bushing with fixed conductor (2,000 amperes)

Figure 3 - Typical mounting clamp and cushion for bushings rated <2500A

For more information please contact:

ABB Inc.

1133 South Cavalier Drive

Alamo, Tennessee 38001, USA

Phone: +1 731 696 5561

Main: +1 800 955 8399

Fax: +1 731 696 5377

www.abb.com/electricalcomponents

Note:

The information contained in this document is for general information purposes

only. While ABB strives to keep the information up to date and correct, it makes

no representations or warranties of any kind, express or implied, about the

completeness, accuracy, reliability, suitability or availability with respect to the

information, products, services, or related graphics contained in the document for

any purpose. Any reliance placed on such information is therefore strictly at your

own risk. ABB reserves the right to discontinue any product or service at any

time.

1ZUA276100-220, rev. 2

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