siemens.com/energy/transformers
Transforming future trends
into innovations
Low partial discharge (PD) transformers
Low PD – high reliability
The working life of electrical high
voltage power apparatus is primary
affected by the insulation system
quality. In transformers, secure
and stable insulation is crucial.
This specific purpose of the insulation can be seriously endangered
if partial discharge occurs inside
the insulation. This is why we take
great effort to lower partial discharge activity at test voltage level
and to keep it far below the limits
of international test standards.
PD sources in transformers
Partial discharges occur in the following
insulation components:
• Voids in solid insulation
(paper, polymer, etc.)
• Along the interfaces of multilayer solids
insulation systems
• In gas bubbles in liquid insulation
• Around conductors with a high field
stress
• A metal object at floating potential
• Small free metallic particles in the
insulation system
Success through innovation
Thanks to our major investment in
­research and our ongoing cooperation
with technical universities, we are always
state of the art when it comes to designing and producing low PD transformers.
In order to reach a low PD activity, we
employ experts at all levels. Every department, whether research, engineering or
manufacturing, is constantly working on
finding new ways and solutions to reduce
PD activity. Because in the end, low PD
activity leads the way to a long-lived
transformer and a safe power supply.
Our key factors to reach a low PD
activity at test voltage level
High material quality: To optimize the
quality of all used materials, we have to
fulfill a series of requirements. We perform
regular audits, write test and release
­reports, and do checks on a regular basis.
Manufacturing precision: Exactly defined
work instructions lead to optimal material
processing and cleanliness at the assembly. We also rely on valid gluing technol­
ogies. In addition, visual inspections are
a very important part of our working
scheme.
Cleanliness in production: A big focus
in reaching low PD activity is cleanliness,
because even small particles can endanger
the insulation. That’s why a desert environment and periodic control measurements for particles in the air are of utmost
importance.
Stable processing: To avoid gas bubbles
in liquid and voids in solid insulation, we
have to make sure that processing is at a
very stable level. Through modern drying
and vacuum technologies, we are able to
provide a high level of stability. A desert
climate zone and the optimal impregnation are also play a key role.
Answers for energy.
Where high-quality design and manufacturing meet dielectrical
requirements.
Why PD threatens the transformer
Partial discharges are the consequence
of local enhancements of the electric
field in the area of inhomogeneities,
­either in gaseous, liquid, or solid media.
PDs are breakdowns occurring in partial
regions of the insulating systems of
­various types.
PDs are unwanted because of the deteri­
oration of the insulation and the forming
of gas that may accumulate at a critical
stress area. Most of the insulation failures
of the transformer are primarily due to
partial discharges, which damage the
­insulation over the transformer’s lifetime
by gradual erosion.
How PD works
The insulation system
The insulation within a transformer consists primarily of organic dielectric materials, including mineral oil/alternative
­liquids and cellulose-based materials such
as paper and pressboard.
PD effects
Partial discharge degrades the organic
material of the electrical insulation.
PD in the insulation is the main cause
of electrical aging and failures in the
­insulation system.
PD mechanism
During PD phenomena inside electrical
insulation, high-energy electrons or ions
cause deterioration of the insulation
­material. This collision may result in
chemical decomposition in the insulation
material, which could finally lead to
a complete breakdown of the insulation.
Our technical challenge:
Holding the partial discharge activity
far below the limits of international test
stan-dards (ANSI, IEC), and fulfilling the
customer’s specification with a low PD
­activity at test voltage level.
Published by and copyright © 2014:
Siemens AG
Energy Sector
Freyeslebenstrasse 1
91058 Erlangen, Germany
Siemens AG
Energy Sector
Power Transmission Division
Transformers
Katzwanger Strasse 150
90461 Nuremberg, Germany
www.siemens.com/energy
Power Transmission Division
Printed in Germany
Dispo 19200
TH 101-140417 473745 DB 0714
siemens.com/energy/transformers