Cellulose based insulation materials for oil immersed transformers
Dipl. Ing. (FH) Frank Kübler
KREMPEL GmbH
TRANSFORM Partner
Introduction
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.
Frank Kübler, KREMPEL GmbH
06.06.2013
Page 2
Content
•
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
Frank Kübler, KREMPEL GmbH
06.06.2013
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Paper manufacturing
From wood to cellulose
 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.
 In a special process known as
Kraft- or sulphate process the
cellulose fibres are extracted
from the wood.
Frank Kübler, KREMPEL GmbH
06.06.2013
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Paper manufacturing
Chemical structure of the cellulose fibres
Cellulose is a polymer made of repeating
glucose molecules
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
In cellulose fibres many polymers are
connected by hydrogen bonding
Frank Kübler, KREMPEL GmbH
06.06.2013
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Paper manufacturing
Schematic paper manufacturing process
Pulper
(cellulose loosening)
Continous crusher
(grinding)
Vats
(interim storage)
Finishing
Reel cutter
(Edge cutting)
Calender
Mixer vat
(additives)
Machine vat
(suspension)
Cleaner
Paper machine
PM – dryer
or
Hot press
PM – wet part
(sheet forming)
Further processing
Reel cutter
(narrow reel)
Transverse cutter
(format products)
Frank Kübler, KREMPEL GmbH
06.06.2013
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Insulating paper
Manufacturing of insulating paper
Principle of a “Fourdrinier” paper machine:
Drying
Flow box
•
Production of a single paper layer
•
Typical density of the papers: 0.8 – 1.1 g/cm³
•
Special type: crepe paper
Frank Kübler, KREMPEL GmbH
06.06.2013
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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
Specification for cellulosic papers for electrical purposes - Part 3:
Sheet 3: Crepe paper
IEC 606554-3-4
Specification for cellulosic papers for electrical purposes - Part 3:
Sheet 4: Electrolytic capacity paper
IEC 606554-3-5
Frank Kübler, KREMPEL GmbH
Specification for cellulosic papers for electrical purpose - Part 3:
Sheet 5: Special papers
06.06.2013
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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
Frank Kübler, KREMPEL GmbH
Picture: Essex Germany GmbH
06.06.2013
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Presspaper
Manufacturing of presspaper
Principle of a presspaper machine:
Wet felt
Drying
Cylindrical sieves
•
Production of multilayer (3 – 7) paper
•
Typical density of the papers:
0.95 – 1.3 g/cm³
•
Produced thicknesses: 0.04mm – 0.5mm
Frank Kübler, KREMPEL GmbH
06.06.2013
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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
RPT 3055-2
P.2.1 B IEC 60641-3-2
natural
Maschine presspaper
RPG 3020
P.6.1 A IEC 60641-3-2
orangebrown
High grade presspaper
EPR 3040
P.6.1 B IEC 60641-3-2
grey-black
DPP
-
natural; red
resin
2-layer transformer presspaper
Krempel DPP
Frank Kübler, KREMPEL GmbH
06.06.2013
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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 Part 2: Methods of test
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
Frank Kübler, KREMPEL GmbH
06.06.2013
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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.
Frank Kübler, KREMPEL GmbH
06.06.2013
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Presspaper
Application in oil filled distribution transformers

Layer insulation
Diamond dotted paper
Presspaper

Cooling channels
Corrugated pressboard
Ladder ducts and ladder grids
Strips

Internal wiring:
Crepe paper tubes
HV coil
Frank Kübler, KREMPEL GmbH
LV coil
06.06.2013
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Pressboard
Manufacuring of pressboard:
Principle of a pressboard machine:
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
Frank Kübler, KREMPEL GmbH
06.06.2013
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Pressboard
Pressboard types produced by KREMPEL
Designation
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
OrangeBrown
POWERBOARD AK
LB.3.1 A.1
LB.3.1 A.2
Natural
Laminated pressboard
Frank Kübler, KREMPEL GmbH
Krempel Type
06.06.2013
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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 Part 2: Methods of test
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
Frank Kübler, KREMPEL GmbH
06.06.2013
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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
Frank Kübler, KREMPEL GmbH
06.06.2013
Page 18
Pressboard
Major production steps of POWERBOARD AK:
Frank Kübler, KREMPEL GmbH
06.06.2013
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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
Frank Kübler, KREMPEL GmbH
06.06.2013
Page 20
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 –
Part 2: Methods of test
IEC 60763-3-1
Frank Kübler, KREMPEL GmbH
Laminated pressboard for electrical purposes –Part 3:
Sheet 1: Requirements for laminated precompressed
pressboard, Types LB 3.1A.1 and LB 3.1A.2
06.06.2013
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Pressboard
Application of pressboard
Frank Kübler, KREMPEL GmbH
06.06.2013
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Fibre Structure
Fibre structure of presspaper and pressboard:
• 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.
1 mm
Thickness
• Different behaviour in the three major directions:
- Tensile strength, elongation
- Shrinkage
d
CMD
Frank Kübler, KREMPEL GmbH
06.06.2013
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Drying and Shrinkage
Shrinkage MD and CMD of POWERBOARD AK


Almost a linear relation
between moisture
content and shrinkage of
pressboard
Higher shrinkage in
cross direction due to
fibre orientation.
Dimensional change [%]
0,80
0,70
0,60
Machine Direction (3mm)
Cross Machine Direction (3mm)
0,50
0,40
0,30
0,20
0,10
0,00
0,00
Frank Kübler, KREMPEL GmbH
1,00
2,00
3,00
4,00
Moisture content [%]
5,00
06.06.2013
6,00
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Drying and Shrinkage
Shrinkage MD and CMD of POWERBOARD AK


Almost a linear relation
between moisture
content and shrinkage of
pressboard
Higher shrinkage in
cross direction due to
fibre orientation.
Dimensional change [%]
0,80
0,70
0,60
Machine Direction (3mm)
Cross Machine Direction (3mm)
0,50
0,40
0,30
0,20
0,10
0,00
0,00
Frank Kübler, KREMPEL GmbH
1,00
2,00
3,00
4,00
Moisture content [%]
5,00
06.06.2013
6,00
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Drying Time
Drying of POWERBOARD AK
30
 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 time [h]

25
20
15
10
5
0
1 mm
3 mm
5 mm
8 mm
Thickness of Pressboard
Frank Kübler, KREMPEL GmbH
06.06.2013
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Drying and water absorption
Storage parameter:
- Temperature:
23 °C / 50 % r.h.
- Sample size:
300 mm x 50 mm
6,0
5,0
Change in weight [%]
Drying parameter:
- Hot air drying at:
105°C
- Sample size:
300 mm x 50 mm
4,0
3,0
Drying (1mm)
Storage at 23°C/50% r.h. (1mm)
Drying (3mm)
Storage at 23°C / 50% r.h. (3mm)
2,0
1,0
0,0
0
5
10
15
20
25
30
35
40
45
50
Storage time[h]
Frank Kübler, KREMPEL GmbH
06.06.2013
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Influence of moisture
Influence of moisture to an oil / paper insulation
regarding PD and breakdown voltage*
Moisture in pressboard insulation means:
•
Reduced dielectric strength
•
Lower PD inception voltage
•
Accelerated degradation of the cellulose
fibres
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.
Frank Kübler, KREMPEL GmbH
06.06.2013
Page 28
Conclusion
•
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.
Frank Kübler, KREMPEL GmbH
06.06.2013
Page 29