dipl. ing. (fh) frank kübler krempel gmbh

TRANSFORM Partner

Dipl. Ing. (FH) Frank Kübler

KREMPEL GmbH

Cellulose based insulation materials for oil immersed transformers

Name : Frank Kübler

Education: Electrical Engineer

Fachhochschule Esslingen - University of Applied Sciences

Position: Head of Technical Service at KREMPEL GROUP

Member of IEC TC 15: “Solid electrical insulation materials”

since 2009.

06.06.2013 Frank Kübler, KREMPEL GmbH

Introduction

• From wood to paper – the paper manufacturing process

• Introduction of cellulose based materials:

- Insulating (Kraft) paper

- Presspaper

- Pressboard

- Laminated pressboard

• Introduction of IEC standards

• Applications

• Characteristics of cellulose based materials


Content

Paper manufacturing

Composition of wood:

≈ 45% Cellulose

≈ 15% Hemicellulose

≈ 35% Lignin, Resin

≈ 5 % Minerals

Pine wood

Only the pure cellulose fibres can

be used for manufacturing of high

grade insulation papers.

From wood to cellulose

In a special process known as

Kraft- or sulphate process the

cellulose fibres are extracted

from the wood.


Paper manufacturing

Cellulose is a polymer made of repeating

glucose molecules

Chemical structure of the cellulose fibres

In cellulose fibres many polymers are

connected by hydrogen bonding

Degree of polymerisation (DP):

• Length of the molecule chains

• DP value of new presspaper: approx. 1200

• End of life is reached at a DP value of 200

• Test standard: IEC 60450


Paper manufacturing

Pulper (cellulose loosening)

Vats (interim storage)

Continous crusher (grinding)

Machine vat

(suspension) Cleaner

Calender Reel cutter

(Edge cutting)

Mixer vat (additives)

Reel cutter (narrow reel)

Transverse cutter (format products)

Paper machine Finishing

Further processing

PM – dryer

or

Hot press

PM – wet part

(sheet forming)

Schematic paper manufacturing process


Insulating paper

Manufacturing of insulating paper

Flow box

Drying

• Production of a single paper layer

• Typical density of the papers: 0.8 – 1.1 g/cm³

• Special type: crepe paper

Principle of a “Fourdrinier” paper machine:


Insulating paper

Insulating paper – material standards

IEC Standard Title

IEC 60554-1 Specification for cellulosic papers for electrical purposes - Part 1:

Definitions and general requirements

IEC 60554-2 Cellulosic papers for electrical purposes

Part 2: Methods of test

IEC 606554-3-1 Specification for cellulosic papers for electrical purposes - Part 3:

Sheet 1: General purpose electrical paper

IEC 606554-3-2

Specification for cellulosic papers for electrical purposes - Part 3:

Sheet 2: Capacitor paper

IEC 606554-3-3


Sheet 3: Crepe paper

IEC 606554-3-4


Sheet 4: Electrolytic capacity paper

IEC 606554-3-5 Specification for cellulosic papers for electrical purpose - Part 3:

Sheet 5: Special papers


Picture: Essex Germany GmbH

Insulating paper

Typical application for insulating paper in transformers:

• Conductor insulation for the so called CTC

(Continuously Transposed Cable)

• Layer insulation

• Insulation of internal wiring made with crepe

paper tubes

• Other application:

- capacitors

- measurement transformers

- transformer bushings


Presspaper

Manufacturing of presspaper

Cylindrical sieves

Drying

Wet felt

• Production of multilayer (3 – 7) paper

• Typical density of the papers:

0.95 – 1.3 g/cm³

• Produced thicknesses: 0.04mm – 0.5mm

Principle of a presspaper machine:


Presspaper

Presspaper types produced by KREMPEL

Designation Krempel

Type IEC Type Colour

Transformer presspaper RPT 3055 P.2.1 B IEC 60641-3-2 natural

Low density transformer

presspaper

RPT 3055

SL P.4.1 A IEC 60641-3-2 natural

2-layer transformer presspaper RPT 3055-2 P.2.1 B IEC 60641-3-2 natural

Maschine presspaper RPG 3020 P.6.1 A IEC 60641-3-2 orange-

brown

High grade presspaper EPR 3040 P.6.1 B IEC 60641-3-2 grey-black

Krempel DPP DPP - natural; red

resin


Presspaper

Presspaper – material standards

IEC Standard Title

IEC 60641-1

Specification for pressboard and presspaper for

electrical purposes –

Part 1: Definitions and general requirements

IEC 60641-2

Pressboard and presspaper for electrical purposes -


IEC 60641-3-2

Pressboard and presspaper for electrical purposes –Part 3:

Sheet 2: Requirements for presspaper, types P.2.1, P.4.1, P.4.2,

P.4.3 and P.6.1


Presspaper

KREMPEL-DPP

• Manufactured from presspaper with a diamond-pattern resin

coating. The epoxy resin is still in the reactive B-stage.

• After application of heat and pressure for a certain time, the

partial resin coating of KREMPEL-DPP leads to bonding of

the electrical conductors with the layer insulation and mutual

bonding of the insulation material layers. The large axial and

radial mechanical forces arising in the case of a short circuit

are safely tolerated by this internal strengthening of the coil.

• At the same time the partial coating leaves empty spaces

between the insulation and the electrical conductors:

- Air and moisture can be removed more easily.

- Faster oil impregnation.


Presspaper

HV coil

LV coil

Layer insulation

Diamond dotted paper

Presspaper

Cooling channels

Corrugated pressboard

Ladder ducts and ladder grids

Strips

Internal wiring:

Crepe paper tubes

Application in oil filled distribution transformers


Pressboard

Manufacuring of pressboard:

Drying

Cylindrical sieves

• Production of multi layer pressboard:

• Typical density of the board:

0.95 – 1.3 g/cm³

• Produced thicknesses: 1.0 mm – 8.0 mm

Principle of a pressboard machine:


Pressboard

Pressboard types produced by KREMPEL

Designation Krempel Type IEC Type Colour

Hot pressed pressboard POWERBOARD AK B.3.1 A Natural

Calendered pressboard PSP 3050 B.2.1 B Natural

Mouldable pressboard PSP 3051 B.4.1 Natural

Machine pressboard PSP 3010 B.6.1 A Orange-

Brown

Laminated pressboard POWERBOARD AK LB.3.1 A.1

LB.3.1 A.2 Natural


Pressboard

Pressboard – Material standards

IEC Standard Title

IEC 60641-1

Specification for pressboard and presspaper for electrical

purposes –

Part 1: Definitions and general requirements

IEC 60641-2

Pressboard and presspaper for electrical

purposes -


IEC 60641-3-1

Pressboard and presspaper for electrical purposes –Part 3:

Sheet 1: Requirements for pressboard, types B.0.1, B.0.3,

B.2.1, B.2.3, B.3.1, B.3.3, B.4.1, B.4.3, B.5.1, B.5.3 and B.6.1


Pressboard

POWERBOARD AK

• Precompressed pressboard type B.3.1A according to

IEC 60641-3-1

• Produced in our factory in Zwönitz / Germany

• Natural coloured, made from

100 % unbleached cellulose

• POWERBOARD AK offers:

- high purity

- very good mechanical strength

- low shrinkage

- high oil absorption capacity

• Thicknesses: 1 - 8mm

• Master sheet size: 4.2m x 2.2m


Pressboard

Major production steps of POWERBOARD AK:


Laminated Pressboard

Laminated Board

Laminated board is produced by bonding several layers of KREMPEL

POWERBOARD AK with different type of bonding agents.

Our laminated board is produced according to the IEC 60673-3-1

3 types of Laminated Board are available:

•POWERBOARD AK-CG

Glued with an aqueous casein glue according

to type LB.3.1A.1

•POWERBOARD AK-PG

Glued with a polyester resin according to type LB.3.1A.2

•POWERBOARD AK-PHG

Glued with a phenolic resin similar to type LB.3.1A.2


Laminated Pressboard

Laminated pressboard – material standards

IEC Standard Title

IEC 60763-1 Laminated pressboard for electrical purposes –

Part 1: Definitions, classification and general requirements

IEC 60763-2

Specification for laminated pressboard –


IEC 60763-3-1

Laminated pressboard for electrical purposes –Part 3:

Sheet 1: Requirements for laminated precompressed

pressboard, Types LB 3.1A.1 and LB 3.1A.2


Pressboard

Application of pressboard


1 mm

Fibre Structure

• All fibres are oriented either in machine direction

or in cross machine direction.

• Due to the production process the amount of

fibres oriented in machine direction is higher

than the amount in cross direction.

• Different behaviour in the three major directions:

- Tensile strength, elongation

- Shrinkage

Th

ickn

ess

CMD d

Fibre structure of presspaper and pressboard:


Drying and Shrinkage

Shrinkage MD and CMD of POWERBOARD AK

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,00 1,00 2,00 3,00 4,00 5,00 6,00

Dim

en

sio

na

l c

ha

ng

e [

%]

Moisture content [%]

Machine Direction (3mm)

Cross Machine Direction (3mm)

Almost a linear relation

between moisture

content and shrinkage of

pressboard

Higher shrinkage in

cross direction due to

fibre orientation.


Drying Time

Drying of POWERBOARD AK

0

5

10

15

20

25

30

1 mm 3 mm 5 mm 8 mm

Dry

ing

tim

e [

h]

Thickness of Pressboard

Drying time depends mostly

on thickness of pressboard

Measuring parameter:

- Temperature: 105 °C

- Sample size:

300 mm x 50 mm

- Moisture content before

drying: approx. 5%


Drying and water absorption

0,0

1,0

2,0

3,0

4,0

5,0

6,0

0 5 10 15 20 25 30 35 40 45 50

Ch

an

ge

in

we

igh

t [%

]

Storage time[h]

Drying (1mm)

Storage at 23°C/50% r.h. (1mm)

Drying (3mm)

Storage at 23°C / 50% r.h. (3mm)

Drying parameter:

- Hot air drying at:

105°C

- Sample size:

300 mm x 50 mm

Storage parameter:

- Temperature:

23 °C / 50 % r.h.

- Sample size:

300 mm x 50 mm


Influence of moisture

Moisture in pressboard insulation means:

• Reduced dielectric strength

• Lower PD inception voltage

• Accelerated degradation of the cellulose

fibres

Influence of moisture to an oil / paper insulation

regarding PD and breakdown voltage*

Influence of moisture and temperature to aging of

oil / paper insulation*

Moisture content

*Reference:

Kahle, M.: Elektrische Isoliertechnik. Berlin, Heidelberg,

New York, London, Paris, Tokyo: Springer-Verlag 1989.


• The different production methods of cellulose based insulating materials

cause different properties and make them suitable for various applications.

• Due to the fibre orientation presspaper and pressboard are anisotropic materials

which have different properties in machine direction and cross direction.

• Due to the highly hygroscopic behaviour of cellulose based materials it is

recommended to protect dried parts from picking up moisture again.

• An optimized drying process for all pressboard insulation parts used in a

transformer is essential to ensure a long life in service.


Conclusion

dipl. ing. (fh) frank kübler krempel gmbh

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