OTF 420 – 800 kVOIP Transformer Outdoor Bushing

Condenser bushing type OTF

DesignThe insulating body of the OTF condenser bushing consists of

oil-impregnated insulating paper which is wound in broad webs

onto a central tube. A process developed by HSP enables these

insulating bodies to be produced in lengths of up to 10 m.

During the winding process, conductive layers made of alumi-

num foil are inserted for grading the electric field. Thanks to

the good conductivity of the foil, optimum voltage distribution

is also guaranteed in case of rapid voltage changes.

After preparation in this way, the insulating body is dried in a vac-

uum with application of heat and impregnated with insulating oil.

There is a gap between the insulating body and central tube which

dissipates heat loss from the current conductor through oil circula-

tion. The circulating flow is produced by the thermosiphon effect of

the heated oil. Due to this design, the bushings are thermally stable

to a high degree.

The insulating body is installed in a housing consisting of oilpart

cover, flange, outdoor housing and head. The outdoor porcelain is

provided with a flange and head which are cemented on. The oilpart

cover on the transformer side consists entirely of epoxy resin includ-

ing the c.t. accommodation space. This construction acts as an oil-

tight seal to the transformer in case the housing is destroyed on the

outside by any external effects. The outdoor insulator has a standard

shed profile with alternate sheds. This is a single part which is bond-

ed together adhesively from a few large partial elements.

2 | 3

All seals are designed as O-rings in self-contained chambers. In the

bushing head there is a nitrogen cushion to compensate for changes

in the volume of the oil filling due to temperature. The gas volume

is hermetically sealed from the outside atmosphere. The bushings

are fitted with a prismatic oil sight glas as standard equipment. The

oil sight glas is oil-submerged in all operating states. If the oil level

drops below the level of the oil sight glas (which is not allowed),

the ground vertical lines of the prism are easily visible with this

arrangement even from a long distance. The absence of mechanical

parts makes this indicator exceptionally reliable in operation. Tilt

protection allows the bushing to be transported in the horizontal

position. The oil sight glas must always point upwards.

For storage over a long period it is recommended that the bushing

be supported at the head so that the head is slightly higher than

the bushing flange. Bushing head and flange are made of a weather-

proof aluminum alloy, and the flange is made in one part. The seals

consist of oil-resistant Perbunan N.

All bushings have a test tap. When the cap is screwed in position,

the last layer of the condenser grading is earthed via the contact

spring located in the cap. The built-in, insulated bushing has a 4-mm

pin onto which a corresponding, resilient socket can be plugged

for test purposes. All bushings also have two M12 earthing holes

and threaded lifting holes around the flange pitch circle diameter

as standard. Transformer venting is provided on all bushings.

All bushings are designed to comply with IEC Standard 60137

and tested accordingly. Bushings that comply with IEEE Standard

or other national regulations are available on request.

Connection systemsThe OTF series offers a large number of different connection options.

A clamping piece is mounted on the top end of the bushing head

with which the conductor or draw lead bolt is fixed in position.

A releasable transverse pin prevents it slipping into the transformer

when working on the clamping device and it also acts as protection

against twisting. Double seals are provided for sealing the bolts.

The clamping piece and all screw connections on the entire bushing

consist of stainless steel. Venting of the central tube is located at

the side under the flange of the clamping piece and can thus be

operated independently of the conductor bolt. In addition to the

draw lead bolt mentioned, it is also possible to provide a through

conductor bolt, for example in case of higher current requirements.

Conductor bolts of this kind are insulated with respect to the inner

wall of the central tube with spacers.

Through conductor bolts can be supplied with a joint, preferably at

flange height or for the particular application. In order to be able to

pull the bolt through the central tube, a threaded hole is provided

at the front for screwing in an eyebolt or rod.

Customized modifications The types specified in this brochure represent standard versions.

Modifications are possible but may result in price changes or differ-

ent delivery times and must therefore be specifically requested.

The design of the bushings is documented in comprehensive delivery

specifications.

Electrical values/dimensions 4 | 5| 6

Bushing type OTF

Identification 1425-420-A1

1425-420-A2

1550-420-A1

1425-420-B1

1425-420-B2

1550-420-B1

1675-550-B

1800-550-B

2100-765

2400-800

Highest voltage for equipment Um kV 420 420 420 420 420 420 550 550 765 800

Max. service voltage: line-ground kV 242 242 242 242 242 242 318 318 442 462

Partial discharge level pC < 10 < 10 < 10 < 10 < 10 < 10 < 10 < 10 < 10 < 10

Power frequency withstand voltage: 50 Hz, 1 min kV 695 695 750 695 695 750 750 870 970 1075

Rated lightning impulse withstand voltage: 1.2/50 μs kV 1425 1425 1550 1425 1425 1550 1675 1800 2100 2400

Rated switching impulse withstand voltage: 250/2500 μs kV 950 1050 1175 950 1050 1175 1175 1300 1425 1550

Max. rated current: draw lead bolt Imax A 800 800 800 1200 1200 1200 1200 1200 1200 1200

Max. rated current: removable conductor bolt Imax A 1600 1600 1600 2000 2000 2000 2000 2000 2000 2000

Min. flashover distance SW mm 3562 3862 4162 3562 3862 4162 4762 5232 7100 7400

Creepage distance min. min. mm 12830 13940 15061 12830 13940 15061 17285 18953 26180 27290

Creepage factor: Cf l/s 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.7 3.7

Cantilever test load N 4000 4000 4000 5000 5000 5000 5000 5000 5000 5000

Creepage distance mm/kV 30.5 33.2 35.9 30.5 33.2 35.9 31.4 34.5 34.2 34.1

Dimensions D1 mm 255 255 255 280 280 280 345 345 390 390

D2 mm 150 150 150 150 150 150 150 150 170 170

D3 mm 400 400 400 400 400 400 500 500 550 550

D4 mm 450 450 450 450 450 450 550 550 600 600

D5 mm 360 360 360 360 360 360 484 484 450 450

D6 mm 410 410 410 430 430 430 490 490 580 580

D7 mm 325 325 325 325 325 325 410 410 – –

D8 mm 100 100 100 100 100 100 100 100 120 120

L6 mm 95 95 95 95 95 95 115 115 115 115

d1 mm 50 50 50 69 69 69 69 69 69 69

s mm 20 20 20 20 20 20 25 25 30 30

i mm 20 20 20 20 20 20 20 20 25 25

z 12 12 12 12 12 12 16 16 16 16

a ° 30 30 30 30 30 30 22.5 22.5 22.5 22.5

Draw lead bolt: d3 x L4 mm ≤ 1250 A = Ø 30 x 90; ≤ 1600 A = Ø 42 x 135; ≤ 2000 A = Ø 48 x 135

C.T. accommodation length E mm 0 0 0 0 0 0 0 0 0 0

L1 mm 790 790 790 790 790 790 990 990 1290 1290

L2 mm 4387 4687 4987 4687 4687 4987 5782 6252 8215 8515

L3 mm 585 585 585 585 585 585 755 755 755 755

Total length L mm 5177 5477 5777 5477 5477 5777 6772 7242 9505 9805

C.T. accommodation length E mm 300 300 300 300 300 300 300 300 300 300

L1 mm 1090 1090 1090 1090 1090 1090 1290 1290 1590 1590

Total length L mm 5477 5777 6077 5777 5777 6077 7072 7542 9805 10105

C.T. accommodation length E mm 600 600 600 600 600 600 600 600 600 600

L1 mm 1390 1390 1390 1390 1390 1390 1590 1590 1890 1890

Total length L mm 5777 6077 6377 6077 6077 6377 7372 7842 10105 10405

Dimensions screen electrodes D9 mm 180 180 180 180 180 180 180 180 175 175

D10 mm 250 250 250 250 250 250 250 250 300 300

L7 mm 250 250 250 250 250 250 250 250 300 300

L8 mm 160 160 160 160 160 160 160 160 175 175

Type series OTF dimensional drawing

Outlet end at transformer – without electrode

Outlet end at transformer – with electrode

Flange plate

L6

L

L1+E

E

L2

L3

s32

35L4

150SW

Test tapOil sight glas

30

ø d1

ø D8

L6

3 threaded holes M10 x 20; 3 x 120°

ø D2

4

5

90°

ø i

ø D9

L8

L7

30

ø D10

ø D3

ø i

ø D4

Test tap Lifting hole M16

Position of the oil level indicator at the head

Transformer air vent

2 lifting eyes

Earthing holes M12

ø D

1

ø d1 ø

D2ø

D7

ø D

6

ø D

5

ø d3

z x a°

L6

EL3

s32

35L4

150SW

pg gg g

ø D

1

ø d1 ø

D2ø

D7

ø D

6

ø D

5

6 | 7

Test tap principle:

When the test tap cap is screwed

on, the pin of the insulating bushing

is earthed. For test purposes, plug

on a 4-mm spring socket.

All dimensions in the sectional views are given in mm.

Test tap

Shed Profile

20°

13°

43

75

50

70

SW27

Round sealing ring 22 x 2.5

21.5

13

9

ø 28

Sealing area

M24 x 1.5

SW15

ø 4

45°

Condenser bushing type OTF

Recommended installation of screen electrodes

Insulating electrode with bayonet from HSP

Test voltage [kV] Um AC1min

D10/L7 (Ø 250/250) A [mm]

D10/L7 (Ø 300/300) A [mm]

Minimum distance A [mm]

420

630 500 450 360

695 675 530 410

750 850 650 450

550

750 850 650 450

790 1100 750 500

870 ■ ■ 550

800

870 ■ ■ 550

970 ■ ■ 600

1075 ■ ■ 650

■ Additional barriers required

Screen electrodesThe corresponding bushings have a metal plate at the transformer

end which has to be shielded with an electrode. The dimensions

given in the table refer to electrodes made of insulating material

that can be detached via a bayonet connection. They can be moved

upwards as well as downwards, and so allow possible installation

of a junction point for the current conductor.

The required distance to ground ‘A’ is contained in the table

“Recommended installation of shield electrodes.” Additional

insulating measures or larger distances may be necessary due

to the constraint when installing in the transformer. The bushing

can also be operated with electrodes and barrier systems not

manufactured by HSP. General speaking, the distance must

not be less than the “Minimum distance A” given in the table.

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A

C.T.

60°

References

800 kV bushing on a single-phase

transformer in China

420 kV bushing on a network interconnecting

transformer in Austria

420 kV bushing on a step-up transformer

for a power plant in Germany

HSP bushings throughout the worldThe proverbial quality and reliability of HSP products

has led to our condenser bushings being used in the

leading energy projects worldwide.

8 | 9

The HSP product range:We cover all requirements of modern high-voltage technology

up to the ultrahigh operating voltages with our products and

services. Our product portfolio is enhanced with tailored services

for our own products as well as those from other manufacturers.

1 Transformer bushing

2 SF6 bushing

3 Switchgear bushing

4 Generator bushing

In addition to standardized products, we also offer individual

special products for our customers that we manufacture with

state-of-the-art production processes. These are usually developed

by us in-house and tested in our fully equipped, internationally

accredited test bay.

420 kV bushing on a network interconnecting

transformer in Germany

1 42 3

Published by and copyright © 2010:

HSP Hochspannungsgeräte GmbHCamp-Spich-Str. 1853842 Troisdorf-SpichGermany

Tel.: +49 (0) 22 41/25 26-0Fax: +49 (0) 22 41/25 26-116

E-Mail: contact@hspkoeln.de

www.hspkoeln.de

Pub. OTF 420 – 800 kV03/10-500 TH 102-090472All rights reserved.

Brands and trademarks used in this document are the property of HSP Hochspannungsgeräte GmbH.

Subject to change without prior notice.The information in this document contains general descriptions of the technical options which are not necessarily available in every single case. The required features must therefore be defined in each individual case when concluding the contract.

Printed in Germany on elementary chlorine free paper.