Innovative transformers
for urban environments
First ester transformer with waste heat utilization
successfully shipped on April 16, 2015
In densely populated centers of megacities such as
London, it is especially important for transformers to be
safe, quiet and environmentally friendly. The Siemens
transformer factory in Weiz has therefore developed transformers that meet these requirements particularly well
specifically for a new substation being built in the English
capital. The first of the total of three autotransformers,
with a rating of 240 MVA 400/132/13 kV, has successfully
passed the Factory Acceptance Test and will be shipped in
April 2015. Commissioning by the customer is scheduled
for March 2016.
The transformers have several special features. For example, they use synthetic ester as the insulating medium.
This fluid can be produced from renewable resources such
as rapeseed, soy and sunflower oil as well as by the esterification of alcohol and acids. Ester is biodegradable and
also features an extremely low risk of explosion and fire.
Ester-insulated transformers are therefore ideal for use in
areas subject to environmental protection and in cities.
Another special feature of the transformers slated for London is their practical use of the waste heat produced during operation, which is otherwise usually released into the
ambient air. Working together with the customer, Siemens
developed an environmentally friendly solution for heating an adjacent school building with the transformers’
waste heat by using a heat recovery system. This approach
allows approximately 340 kW of thermal energy per transformer, or more than one megawatt in total, to be used in
an environmentally friendly way.
siemens.com/energy/transformers
To address the growing interest in alternative insulating
fluids in large power transformers as well, and to continuously ensure that the ester fluids are kept strictly separate
from the standard process, which uses mineral oil, the
Weiz transformer factory has invested in a separate processing system and separate storage tanks for these fluids. Previously, the existing processing systems designed
for the traditional insulation medium (mineral oil) had to
be laboriously prepared, and special tanker trucks and railway tank cars had to be rented – at enormous cost in
resources, which has now been eliminated.
The two 100,000-liter, double-walled tanks of the processing system, which can be heated separately and meet the
safety regulations, were provided with insulation to minimize heat loss. A shared vacuum pump keeps the tank system under vacuum at all times, double filters with a mesh
size of 2.5 μm maintain reliable filtration, and a continuous moisture measuring system ensures compliance with
the required ester parameters. Screw pumps designed
specifically for pressure pumps approximately 3,000 to
10,000 liters of insulating fluid per hour, pulse-free, from
the tank system to the preparation system.
Main properties of insulating fluids
(average values)
Insulating fluid
property
Mineral oil
(IEC 60296)
Synthetic ester
(IEC 61099)
Kinematic
viscosity at 20 °C
(mm2/s)
22
70
Kinematic
viscosity at 100°C
(mm2/s)
2.6
5.25
Combustion point
(°C)
170
325
Flashpoint (°C)
160
275
Fully degradable
No
Yes
Water hazard class
Yes
None
Dielectric properties
Well known
Design changes
needed
Source material
Non-renewable fossil
source
Chemical
intermediate
product
Siemens AG
Energy Management Division
Transformers
Katzwanger Strasse 150
90461 Nuremberg, Germany
Contact:
Erwin Rauch (erwin.rauch@siemens.com)
Georg Pukel (georg.pukel@siemens.com)
Christian Sommer (christian.a.sommer@siemens.com)
Publisher and copyright 2015:
Siemens AG
Energy Management Division
Freyeslebenstrasse 1
91058 Erlangen, Germany
siemens.de/energy/transformatoren