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5
Transformers
5.1 Introduction 234
5.1.1 Overview 234
5.2 Reliability and Project Performance 236
5.3 Transformer Loss Evaluation 238
5.4 Power Transformers 240
5.4.1 Large Power Transformers 240
5.4.2 Medium Power Transformers 241
5.4.3 Small Power Transformers 241
5.5 Reactors 242
5.6 Special Transformers
for Industrial Applications 243
5.7 Phase-Shifting Transformers 245
5.8 HVDC Transformers 246
5.9 Distribution Transformers 247
5.9.1 Liquid-immersed Distribution Transformers
for European/US/Canadian Standard 247
5.9.2 Voltage Regulators 248
5.9.3 GEAFOL Cast-Resin Transformers 249
5.9.4 GEAFOL Special Transformers 254
5.10 Traction Transformers 256
5.11 Transformer Lifecycle Management 257
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5 Transformers
5.1 Introduction
5.1.1 Overview
Whether in infrastructure systems, industry or households,
transformers always play a key role in the reliable transmission
and distribution of power. The construction, rated power,
voltage level and scope of the application are all key factors that
determine the transformer’s design.
Siemens provides the right transformer for every need – from
compact distribution transformers to large power transformers
with ratings far above 1,000 MVA. The Siemens product range
covers all mainstream requirements like UHV DC applications,
low noise emission and environmentally friendly products with
alternative insulation liquids, also embedded in a complete
power system from generation via transmission to distribution
networks. The long-term reliability of a transformer begins with
its initial high quality. Then transformer lifecycle management
measures maintain that quality throughout the transformer’s
entire life.
Fig. 5.1-1 and table 5.1-1 are an overview of how various trans-
formers can be used in a network.
Global Footprint
Emerging countries are not just “extended workbenches” for
producing goods. First and foremost, they are important future
markets. Through its own local production and sales locations,
Siemens provides service to customers in the most important
global markets. The local presence of Siemens in many coun-
tries also ensures that customers have better access to Siemens
services and that they benefit from an efficient and effective
distribution of Siemens resources as part of a global network.
As Siemens factories around the world develop and produce
their products, Siemens also encourages them to share their
expertise.
Siemens meets the growing global demand for transformers in
a variety of ways: by further optimization of value-added steps
in the worldwide network, by use of approaches such as vertical
integration and by the pursuit of programs for boosting produc-
tivity.
For further information:
www.siemens.com/energy/transformers
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5.1 Introduction
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Fig. 5.1-1: Product range of Siemens transformers
Table 5.1-1: Product range of Siemens transformers
Generator and System
Transformers
Above 2.5 MVA up to more than 1,000 MVA, above 30 kV up to 1,500 kV (system and system
interconnecting transformers, with separate windings or auto-connected), with on-load tap
changers or off-circuit tap changers, of 3-phase or 1-phase design
Phase Shifters
To control the amount of active power by changing the effective phase displacement
Reactors
Liquid-immersed shunt and current-limiting reactors up to the highest rated powers
Reactors for HVDC transmission systems
HVDC Transformers
Transformers and smoothing reactors for bulk power transmission systems up to 800 kV DC
Transformers for DC coupling of different AC networks
Cast-Resin Distribution and
Power Transformers GEAFOL
100 kVA to more than 40 MVA, highest voltage for equipment up to 36 kV, of 3-phase or 1-phase
design, GEAFOL-SL substations
Liquid-immersed Distribution
Transformers
50 to 2,500 kVA, highest voltage for equipment up to 36 kV, with copper or aluminum windings,
hermetically sealed or with conservator of 3- or 1-phase design
pole mounted transformers and distribution transformers acc. to IEC with amorphous cores
Special Transformers for
Industry
Electric arc furnace transformers
Electric arc furnace series reactors
DC electric arc furnace transformers
Rectifier transformers
Converter transformers for large drives
Traction Transformers
Traction transformers mounted on rolling stock
Transformer Lifecycle
Management
Condition assessment & diagnostics
Online monitoring
Consulting & expertise
Maintenance & lifecycle extension
Spare parts & accessories
Repair & retrofit
Transport, installation & comissioning
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5.2 Reliability and Project
Performance
The quality strategy in the transformer business is based on the
three cornerstones of product, people and process quality
(fig. 5.2-1). The objective is to achieve the greatest customer
satisfaction with cost-efficient processes. This is only possible if
all employees are involved in the processes have a profound
understanding of the customer needs and specific requirements
in the transformer business.
The strategy is implemented in the form of mandatory elements.
These elements cover product and service quality, which is visible
to customers; personnel quality, which is achieved by training
and ongoing education; and process quality in all processes used.
Business and process-specific indicators must be used to ensure
that each single element is measurable and transparent.
Nine mandatory elements are defined:
tȋ Customer integration
tȋ Embedded quality in processes and projects
tȋ Consequent supplier management
tȋ Business-driven quality planning
tȋ Focused quality reporting
tȋ Qualification of employees on quality issues
tȋ Continuous improvement
tȋ Management commitment
tȋ Control and support role of quality manager
Elements of quality (mandatory elements)
Customer integration
Customer integration depends on the consistent use of:
tȋ Analysis tools for customer requirements and market studies
tȋ Analysis of customer satisfaction
tȋ Professional management of feedback from and to the
customer
tȋ Complaint management
Customer requirements need to be precisely defined in a specifi-
cation. And the specification must be continuously updated
throughout the definition phase of a transformer project. The
actual requirements must also be available to all responsible
employees.
Rapid feedback loops – in both directions – are essential in order
to increase customer trust and satisfaction.
Siemens resolves customer complaints to the customer’s satis-
faction in a timely manner through its complaint management
system.
Embedded quality in processes and projects
The quality of the processes used to produce a product has a
significant impact on the quality of the product that is actually
produced. Process discipline and process stability can be
Product/Service
quality
Process
quality
Greatest possible
customer
satisfaction …
... combined with
efficient processes
results in the best
cost position
Personnel
quality
Quality
strategy
... and best trained
and motivated employees …
Fig. 5.2-1: Cornerstones of quality strategy
achieved by a high degree of process standardization. All pro-
cesses should be standardized for all employees based on simple
procedures. If this condition is met, it is possible to implement
clearly defined work instructions (fig. 5.2-2).
Quality gates are placed at points in the process at which
quality-relevant decisions are necessary. The following quality
gates are mandatory for the power transformer business.
tȋ Bid approval
tȋ Entry order clarified
tȋ Release of design
tȋ Release of fully assembled transformer
tȋ Evaluation of project
For each quality gate, there is a clear definition of participants,
preconditions, results (traffic light) and the escalation process, if
necessary. If the result is not acceptable, the process must be
stopped until all requirements are fulfilled.
Supplier management
The quality of the product depends not only on the quality of the
own processes but also on that of the suppliers. Problems and
costs caused by inadequate supplier quality can only be reduced
by a systematic supplier management process that includes:
tȋ Selection
tȋ Assessment
tȋ Classification
tȋ Development
tȋ Phasing out of suppliers as well as the support process Supplier
Qualification
237
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A further condition for a high level of supplier quality is close
cooperation with the suppliers. Joint development of require-
ments for suppliers and processes leads to continuous improve-
ments in quality. In this context, supplier know-how can also be
used to create innovations. This aspect of the relationship with
suppliers is becoming more and more important, especially in
the transformer business.
Business-driven quality planning
Planning quality means analyzing possible future scenarios and
anticipated problems and taking preventive steps to solve those
problems. It is crucial that both current and future critical busi-
ness factors are considered in planning. That means that quality
is based on business-driven planning and specific objectives,
activities and quantitative indicators.
Focused quality reporting
Reporting is based on:
tȋ Focused key performance indicators such as non-conformance
costs, external failure rate, internal failure rate and on-time
delivery
tȋ Concrete quality incidents
tȋ Root cause analysis of quality problems including definition of
corrective and preventive measures
For customers, the reliability of transformers is of special impor-
tance. ANSI C57.117 has made an attempt to define failures.
Based on this definition, statistics on in-service failures and
reliability values can be derived. An example for power trans-
formers appears in table 5.2-1.
Qualification of employees on quality issues
People are the decisive factor influencing quality. Therefore, all
employees involved in the processes must have the skills and
abilities appropriate to the quality aspects of the process steps
they perform. Any qualification measures that may be necessary
must be determined on the basis of a careful analysis of existing
deficits.
TPD
2.01.02
Page 1/6 Page 1/6
Core assembly – stacking core
laminates
SIEMENS
PEQ
Drawn up by: Matthes Checked/approved: Dr. Knorr As of date: 2004-02
The passing on as well as the duplication of this document. use and communication of its contents is not permitted. nor may the contents be expressed. Offenders are liable to pay damages. All rights
reserved. in particular for the case of patent granting or GM-entry
1. Purpose/objective
Process description for the manufacture of transformer core
within the tolerances which are laid down
2. Scope/application
applies to all the core forms of the power transformers
does not apply to the cores of compensating reactors
3. Process overview/description
Stack of core laminations – dimensions checked by the supplier to
ensure that they agree with the drawing
Frame parts – dimensions checked by the supplier to ensure that they
agree with the drawing
Insulating parts – dimensions checked by the supplier (internal ore
external )to ensure that they agree with the drawing
washers, small accessories Job – related core drawings
Process report TPD 2.01.01
INPUTINPUT
Stacking
core
laminates
Tools
Assembly area with special support beams for fixing the core
laminations which have been put on into position
Integrated slewing mechanism for mounting the finished core
Process owner
Staff trained in core assembly
Completed core with clamping frame also completely mounted
Process report TPD 2.01.02
References/guidelines, recommendations
Stack height tolerances as in drawing N00 08 792
Arrangement of the cooling duct shims as in drawing N10 11 100
Locking the screwed connections in accordance with TPD 3.036.01
Measurement of insulation resistance with TUQ 1634
OUTPUT
TPD
2.01.02
Core assembly–stacking core
laminates
SIEMENS
PEQ
Drawn up by: Matthes Checked/approved: Dr. Knorr As of date: 2004-02
The passing on as well as the duplication of this document. use and communication of its contents is not permitted. nor may the contents be expressed. Offenders are liable to pay damages. All rights
reserved. in particular for the case of patent granting or GM-entry
Adjusting
the support
trestles
Adjusting
the support
trestles
> Setting the clearance of the support
trestles (on the support beams) for
the core-limb laminations
> The position of support trestles are to be
placed in the middle between the single
bandages
> The position and clearance of the
bandages are defined in the core
drawing
2501,200 to 1,500
3001,000 to 1,200
350800 to 1,000
450650 to 800
550< 650
Middle distance
support trestles
Max. sheet width
B
S
4. Process sequence
> Setting the middle distance of the support beams to one
another in accordance with the drawing guideline
> Tolerance +/–5 mm to the desired size
Subprocess 1:
Setting up the construction devices and limit stops
Adjusting the
construction
supports
The following clearances
apply to cores without
single bandages (e.g.
wound bandage cylinders)
:
Measure -
ment
Measure-
ment
Clearance support trestles
Measure -
ment
Measure-
ment
Fig. 5.2-2: Example of standardized working instruction
Table 5.2-1: In-service failure statistic
E T TR In-Service Failure Statistic 2000 – 2009 for Power Transformers
based on ANSI C 57.117
E T TR Plant
1
Plant
2
Plant
3
Plant
4
Plant
5
Plant
6
Plant
7*
Plant
8
Plant
9
Plant
10
Plant
11
Plant
12
Plant
13*
Plant
14**
Plant
15
N 11,278 572 1,704 755 793 774 534 – 735 1,076 705 649 994 – 1007 980
SY 51,429 2,358 7,479 3,858 3 4,326 1,996 – 3,341 4,561 4,17 2,889 4,899 – 3,781 4,771
n
F
91 9 7 10 11 1 11 – 3 6 2 7 8 – 3 13
FRe (%) 0.18 0.38 0.09 0.26 0.37 0.02 0.55 – 0.09 0.13 0.05 0.24 0.16 – 0.08 0.27
MTBF (yrs) 565 262 1068 386 273 4,326 181 – 1,114 760 2,085 413 612 – 1,26 367
* Plant 7 & 13: new plants; ** Plant 14: 9 years 2001 – 2009
N = No. of units in service
SY = No. of service years
n
F
= No. of units failed
FRe (%) = Failure rate = n
F
×
100/SY
MTBF (yrs) = Mean time between failures = 100/FRe
FRe ≤ 0.5 % excellent
0.5 % < FRe ≤ 1.0 % good
1.0 % < FRe ≤ 1.5 % satisfactory
1.5 % < FRe ≤ 2.0 % acceptable
FRe > 2.0 % not acceptable
Continuous improvement
Because “there is nothing that cannot be improved”, continuous
improvement must be an integral part in all processes.
The objective is to continue optimizing each process step. This is
also the purpose of improvement teams. Appropriate coaching
of these teams should make it possible to reach almost all
employees.
238
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5.2 Reliability and Project Perfomance
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Methods like, Kaizen, 5S and methods and tools from Six Sigma
e.g. DMAIC circle, FMEA, IPO are helpful in supporting this
continuous improvement process (fi g. 5.2-3).
Management commitment
Every manager in a company also bears responsibility for quality.
Thus, each manager’s actions must be characterized by a high
level of quality awareness.
The level of commitment shown by all levels of management in
the event of quality problems, the establishment of quality
demands and the creation of targeted quality controls in day-to-
day work together produce a culture in which there is a high
level of quality.
Control and support role of the quality manager
The role of the quality manager is of fundamental importance
for well-running processes. The quality manager combines a
supporting role with that of a neutral controller. Quality man-
agement must be directly involved in processes and projects.
The independence of the quality department and individual
quality managers in the processes and projects must be guaran-
teed and agreed by top management.
Conclusion
The quality of a transformer is based on the quality of all pro-
cesses that are necessary – from project acquisition to project
closing. The quality of the processes depends essentially on
people. Only well-trained and motivated employees are able to
guarantee that a process will be performed with a high degree
of quality.
NCC
140
120
100
DpMO
PONC x 1000 RMB
NCC
0
1000
2000
3000
4000
5000
6000
7000
DpMO
Check
Define
Measure
Analyze
Improve
DMAIC
circle
Our process
should be like this
How far are we
from the goal
What is preventing
us to fulfill the
requirements
What must be done
in order to achieve
the goal
Are we
improving?
Fig. 5.2-3: DMAIC circle
ANSI Standard C57.117, 1986,
Guide for Reporting Failure Data for Power Transformers
and Shunt Reactors on Electric Utility Power Systems.
5.3 Transformer Loss
Evaluation
The sharply increased cost of electrical energy has made it
almost mandatory for buyers of electrical machinery to carefully
evaluate the inherent losses of these items. For distribution and
power transformers, which operate continuously and most
frequently in loaded condition, this consideration is especially
important. As an example, the added cost of loss-optimized
transformers can in most cases be recovered via savings in
energy use in less than three years.
Low-loss transformers use more and better materials for their
construction and are thus intially more expensive than low-cost
transformers. By stipulating loss evaluation fi gures in the trans-
former inquiry, the manufacturer receives the necessary incen-
tive to provide a loss-optimized transformer rather than the
low-cost model. Detailed loss evaluation methods for trans-
formers have been developed and are described accurately in
the literature. These methods take the project-specifi c evalua-
tion factors of a given customer into account.
A simplifi ed method for a quick evaluation of different quoted
transformer losses makes the following assumptions:
tȋ The transformers are operated continuously.
tȋ The transformers operate at partial load, but this partial load is
constant.
tȋ Additional cost and infl ation factors are not considered.
tȋ Demand charges are based on 100 % load.
The total cost of owning and operating a transformer for one
year is thus defi ned as follows:
tȋ Capital cost (C
C
), taking into account the purchase price (C
p
),
the interest rate (p) and the depreciation period (n)
tȋ Cost of no-load loss (C
P0
) based on the no-load loss (P
0
) and
energy cost (C
e
)
tȋ Cost of load loss (C
Pk
) based on the load loss (P
k
), the
equivalent annual load factor (a) and energy cost (C
e
)
tȋ Cost resulting from demand charges (C
d
) based on the amount
set by the utility and the total kW of connected load (fi g. 5.3-1)
The following examples show the difference between a low-cost
transformer and a loss-optimized transformer (fi g. 5.3-2).
Note that the lowest purchase price is unlike the total cost of
ownership.
239
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5.3 Transformer Loss Evaluation
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5
A. Low-cost transformer
B. Loss-optimized transformer
Depreciation period
Interest rate
Energy charge
Demand charge
Equivalent annual load factor
n
p
C
e
C
d
_
= 20 years
= 12 % p.
a.
= 0.25 €
/ kWh
= 350 €
/ (kW
.
year)
= 0.8
P
0
= 19 kW
P
k
= 167 kW
C
p
= € 521, 000
P
0
= 16 kW
P
k
= 124 kW
C
p
= € 585, 000
no-load loss
load loss
purchase price
no-load loss
load loss
purchase price
C
c
521, 000
.
13.39
100
€ 69, 762 / year
C
P0
0.2
.
8,760
.
19
€ 33,
288 / year
=
=
=
=
C
Pk
0.2
.
8,760
.
0.64
.
167
€ 187,
254 / year
=
=
C
D
350 · (19 + 167)
€ 65,100
/ year
=
=
Total cost of owning and
operating this transformer
is thus:
€ 355,
404 / year
C
c
585, 000
.
13.39
100
€ 78, 332 / year
C
P0
0.2 · 8,760 · 16
€ 28,
032 / year
=
=
=
=
C
Pk
0.2 · 8,760 · 0.64 · 124
€ 139,
039 / year
=
=
C
D
350 · (16 + 124)
€ 49,
000 / year
=
=
Total cost of owning and
operating this transformer
is thus:
€ 294,
403 / year
The energy saving of the optimized distribution transformer of
€ 61,
001 per year pays for the increased purchase price in less
than one year.
Example: Distribution transformer
Depreciation
factor r = 13.39
Fig. 5.3-2: Example for cost saving with optimized distribution
transformer
Capital cost
taking into account the purchase price C
p
, the interest rate p,
and the depreciation period n
C
c
=C
p
· r
/
100 [amount
/
year]
C
p
= purchase price
= p
.
q
n
/
(q
n
–1)r = depreciation factor
q = p
/
100 + 1 = interest factor
= interest rate in % p.ap
n = depreciation period in years
C
P0
=C
e
· 8,760 h
/
year
.
P
0
= energy charges [amount
/
kWh]
C
Cost of no-load loss
based on the no-load loss P
0
, and energy cost C
e
C
e
P
0
= no-load loss [kW]
C
D
=C
d
(P
0
+ P
k
)
Cost resulting from demand charges
based on the no-load loss P
0
, and energy cost C
e
C
d
Pk
=C
e
· 8,760 h
/
year a
2
P
k
Cost of load loss
based on the load loss P
k
, the equivalent anual load factor a,
and energy cost C
e
a = constant opperation load
/
rated load
P
k
= copper loss [kW]
= demand charges [amount
/
(kW
.
year)]
Fig. 5.3-1: Calculation of the individual operation cost of a
transformer in one year
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5.4 Power Transformers
5.4.1 Large Power Transformers
In the power range above 250 MVA, generator and network
intertie transformers with off-load or on-load tap changers, or a
combination of both, are recommended. Depending on the on-site
requirements, they can be designed as multiwinding transformers
or autotransformers, in 3-phase or 1-phase versions. Even with
ratings of more than 1,000 MVA and voltages up to 1,200 kV
(800 kV), the feasibility limits have not yet been reached. We
manufacture these units according to IEC 60076 as well as other
international and national standards (e.g., ANSI/IEEE), (fig. 5.4-1).
Generator step-up (GSU) transformers
GSU units transform the voltage up from the generator voltage
level to the transmission voltage level, which may be as high as
1,200 kV system voltage. Such transformers are usually YNd-con-
nected.
In order to make an inquiry regarding a GSU power transformer,
the technical data for the items in this section are required.
Step-down transformers
Step-down transformers transform the voltage down from the
transmission voltage level to an appropriate distribution voltage
level. The power rating of step-down transformers may range up
to the power rating of the transmission line.
Fig. 5.4-1: Large power transformer
System interconnecting transformers
System interconnecting transformers connect transmission
systems with different voltages together so that active as well as
reactive power can be exchanged between the systems.
Main specification data
tȋ Standard
tȋ Installation – indoor/outdoor
tȋ Max. ambient air temperature
tȋ Rated frequency f
tȋ Vector group
tȋ Rated power S
tȋ Primary rated voltage U
rHV
tȋ Tapping range/taps
tȋ Voltage regulation
tȋ Secondary rated voltage U
rLV
tȋ Impedance u
k
at S
r
and U
r
tȋ Max. sound power level L
WA
tȋ Insulation level HV-Ph – U
m
/AC/LI
tȋ Insulation level HV-N – U
m
/AC/LI
tȋ Insulation level LV-Ph – U
m
/AC/LI
tȋ Type of cooling
tȋ HV connection technique
tȋ LV connection technique
tȋ Transportation medium
tȋ Losses
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5.4.2 Medium Power Transformers
Medium power transformers with a power range from 30 to
250 MVA and a voltage of over 72.5 kV are used as network and
generator step-up transformers (fig. 5.4-2).
Specific items
tȋ Transformer design according to national and international
standards (IEC/ANSI) with or without voltage regulation
tȋ 3-phase or 1-phase
tȋ Tank-attached radiators or separate radiator banks
Main specification data
tȋ Number of systems (HV, LV, TV)
tȋ Voltage and MVA rating
tȋ Regulation range and type
tȋ Vector group
tȋ Frequency
tȋ Losses or capitalization
tȋ Impedances
tȋ Type of cooling
tȋ Connection systems (bushing, cable)
tȋ Noise requirements (no-load, load and/or total noise)
tȋ Special insulation fluid
tȋ Application of high temperature/extra small size operation
5.4.3 Small Power Transformers
Small power transformers are distribution transformers from 5 to
30 MVA with a maximum service voltage of 145 kV. They are used
as network transformers in distribution networks (fig. 5.4-3).
This type of transformer is normally a 3-phase application and
designed according to national and international standards. The
low-voltage windings should be designed as foil or layer wind-
ings. The high-voltage windings should use layer or disc execu-
tion, including transposed conductors. Normally, the cooling
type is ONAN (oil-natural, air-natural) or ONAF (oil-natural,
air-forced). The tapping can be designed with off-circuit or
on-load tap changers (OCTC or OLTC).
Main specification data
tȋ Voltage and MVA rating
tȋ Frequency
tȋ Regulation range and type
tȋ Vector group
tȋ Losses or capitalization
tȋ Impedances
tȋ Noise requirements
tȋ Connection systems (bushing, cable)
tȋ Weight limits
tȋ Dimensions
tȋ Information about the place of installation
tȋ Special insulation fluid
tȋ Application of high temperature/extra small size operation
tȋ Type of cooling
Fig. 5.4-2: Medium power transformer with natural oil based
insulation fluid
Fig. 5.4-3: Small power transformer
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5.5 Reactors
In AC networks, shunt reactors and series reactors are widely
used in the system to limit the overvoltage or to limit the short-
circuit current. With more high-voltage overhead lines with long
transmission distance and increasing network capacity, both
types of reactors play an important role in the modern network
system.
Made for every requirements
Oil filled reactors are manufactured in two versions:
tȋ With an iron core divided by air gaps
tȋ Without an iron core, with a magnetic return circuit
Oil filled reactors offer individual solutions: They satisfy all the
specified requirements regarding voltage, rating, type of opera-
tion, low-noise and low loss and type of cooling, as well as trans-
portation and installation.
The windings, insulation tank monitoring devices and connec-
tion method are practically the same as those found in the
construction of transformers.
Shunt reactors
For extra-high-voltage (EHV) transmission lines, due to the long
distance, the space between the overhead line and the ground
naturally forms a capacitor parallel to the transmission line,
which causes an increase of voltage along the distance.
Depending on the distance, the profile of the line and the power
being transmitted, a shunt reactor is necessary either at the line
terminals or in the middle. An liquid-immersed shunt reactor is a
solution. The advanced design and production technology will
ensure the product has low loss and low noise level.
Shunt reactors also can be built as adjustable shunt reactors.
This offers the possibility in fine tuning the system voltage and
also the reduction of high voltage equipment by substitution of
several unregulated reactors by a regulated one.
Series reactors
When the network becomes larger, sometimes the short-circuit
current on a transmission line will exceed the short-circuit
current rating of the equipment. Upgrading of system voltage,
upgrading of equipment rating or employing high-impedance
transformers are far more expensive than installing liquid-
immersed series reactors in the line. The liquid-immersed design
can also significantly save space in the substation.
Specification
Typically, 3-phase or 1-phase reactors should be considered first.
Apart from the insulation level of the reactor, the vector group,
overall loss level, noise level and temperature rise should be
considered as main data for the shunt reactor.
Although the above data are also necessary for series reactors,
the rated current, impedance and thermal/dynamic stability
current should also be specified.
Fig. 5.5-1: Reactor
5
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5.6 Special Transformers for
Industrial Applications
A number of industry applications require specific industrial
transformers due to the usage of power (current) as a major
resource for production. Electric arc furnaces (EAF), ladle fur-
naces (LF) and high-current rectifiers need a specific design to
supply the necessary power at a low voltage level. These trans-
former types, as well as transformers with direct connection to a
rectifier are called special-purpose or industrial transformers,
whose design is tailor-made for high-current solutions for
industry applications.
Electric arc furnace transformers
EAF and LF transformers are required for many different furnace
processes and applications. They are built for steel furnaces,
ladle furnaces and ferroalloy furnaces, and are similar to short or
submerged arc furnace transformers (fig. 5.6-1).
EAF transformers operate under very severe conditions with
regard to frequent overcurrents and overvoltages generated by
short-circuit in the furnace and the operation of the HV circuit-
breaker. The loading is cyclic. For long-arc steel furnace opera-
tion, additional series reactance is normally required to stabilize
the arc and optimize the operation of the furnace application
process.
Specific items
EAF transformers are rigidly designed to withstand repeated
short-circuit conditions and high thermal stress, and to be
protected against operational overvoltages resulting from the
arc processes. The Siemens EAF reactors are built as 3-phase
type with an iron core, with or without magnetic return circuits.
Design options
tȋ Direct or indirect regulation
tȋ On-load or no-load tap changer (OLTC/NLTC)
tȋ Built-in reactor for long arc stability
tȋ Secondary bushing arrangements and designs
tȋ Air or water-cooled
tȋ Internal secondary phase closure (internal delta)
Main specification data
tȋ Rated power, frequency and rated voltage
tȋ Regulation range and maximum secondary current
tȋ Impedance and vector group
tȋ Type of cooling and temperature of the cooling medium
tȋ Series reactor and regulation range and type (OLTC/NLTC)
DC electric arc furnace transformers
Direct-current electric arc furnace (DC EAF) transformers are
required for many different furnace processes and applications.
They are built for steel furnaces with a Thyristor rectifier. DC EAF
transformers operate under very severe conditions, like rectifier
transformers in general but using rectifier transformers for
furnace operation. The loading is cyclic.
Fig. 5.6-1: Electric arc furnace transformer
5.6 Special Transformers for Industrial Applications
5
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Rectifier transformers
Rectifier transformers are combined with a diode or Thyristor
rectifier. The applications range from very large aluminum
electrolysis to various medium-size operations. The transformers
may have a built-in or a separate voltage regulation unit. Due to
a large variety of applications, they can have various designs up
to a combination of voltage regulation, rectifier transformers in
double-stack configuration, phase-shifting, interphase reactors,
transductors and filter-winding (fig. 5.6-2).
Specific items
Thyristor rectifiers require voltage regulation with a no-load tap
changer, if any. A diode rectifier will, in comparison, have a
longer range and a higher number of small voltage steps than an
on-load tap changer. Additionally, an auto-connected regulating
transformer can be built in the same tank (depending on trans-
port and site limitations).
Design options
tȋ Thyristor or diode rectifier
tȋ On-load or no-load tap changer (OLTC/NLTC)/filter winding
tȋ Numerous different vector groups and phase shifts possible
tȋ Interphase reactor, transductors
tȋ Secondary bushing arrangements and designs
tȋ Air or water-cooled
Main specification data
tȋ Rated power, frequency and rated voltage
tȋ Regulation range and number of steps
tȋ Impedance and vector group, shift angle
tȋ Type of cooling and temperature of the cooling medium
tȋ Bridge or interphase connection
tȋ Number of pulses of the transformer and system
tȋ Harmonics spectrum or control angle of the rectifier
tȋ Secondary bushing arrangement
Converter transformers
Converter transformers are used for large drive application, static
voltage compensation (SVC) and static frequency change (SFC).
Specific items
Converter transformers are mostly built as double-tier, with two
secondary windings, allowing a 12-pulse rectifier operation.
Such transformers normally have an additional winding as a
filter to take out harmonics. Different vector groups and phase
shifts are possible.
Main specification data
tȋ Rated power, frequency and rated voltage
tȋ Impedance and vector group, shift angle
tȋ Type of cooling and temperature of the cooling medium
tȋ Number of pulses of the transformer and system
tȋ Harmonics spectrum or control angle of the rectifier
Line Feeder
This kind of transformer realizes the connection between the
power network and the power supply for the train. Transformer
is operating in specific critical short circuit condition and over-
load condition in very high frequencies per year, higher reli-
ability is required to secure the train running in safety.
Main specification data
tȋ Rated power, frequency and rated voltage
tȋ Impedance and vector group
tȋ Overload conditions
tȋ Type of cooling and temperature of the cooling medium
tȋ Harmonics spectrum or control angle of the rectifier
Design options
tȋ Direct connection between transmission network and railway
overheadcontactline
tȋ Frequence change via DC transformation
(e.g. 50 Hz – 16,67 Hz)
tȋ Thyristor or diode rectifier
tȋ On-load or no-load tap changer (OLTC/NLTC)/filter winding
tȋ Secondary bushing arrangements and designs
tȋ Air or water-cooled
Fig. 5.6-2: Rectifier transformer for an aluminum plant
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5.7 Phase-Shifting
Transformers
A phase-shifting transformer is a device for controlling the
power flow through specific lines in a complex power transmis-
sion network.The basic function of a phase-shifting transformer
is to change the effective phase displacement between the input
voltage and the output voltage of a transmission line, thus
controlling the amount of active power that can flow in the line.
Guidance on necessary information
Beside the general information for transformers, the following
specific data are of interest (fig. 5.7-1):
tȋ Rated MVA
The apparent power at rated voltage for which the phase-
shifting transformer is designed.
tȋ Rated voltage
The phase-to-phase voltage to which operating and
performance characteristics are referred to – at no-load.
tȋ Rated phase angle
Phase angle achieved when the phase-shifting transformer
is operated under no-load condition, or if stated at full load, at
which power factor.
tȋ Phase shift direction
In one or both directions. Changeover from and to under load
or no-load condition.
tȋ Tap positions
Minimum and/or maximum number of tap positions.
tȋ Impedance
Rated impedance at rated voltage, rated MVA and zero phase
shift connection as well as permissible change in impedance
with voltage and phase angle regulation.
tȋ System short-circuit capability
When the system short-circuit level is critical to the design of
phase-shifting transformers, the maximum short-circuit fault
level shall be specified.
tȋ BIL
Basic impulse level (BIL) of source, load and neutral terminals.
tȋ Special design tests
Besides the standard lightning impulse tests at all terminals, it
has to be considered that the lightning impulse might occur
simultaneously at the source and the load terminal in case of
closed bypass breaker. If such a condition is likely to appear
during normal operation, a BIL test with source and load
terminals connected might be useful to ensure that the phase-
shifting transformer can withstand the stresses of lightning
strokes in this situation.
tȋ Special overload condition
The required overload condition and the kind of operation
(advance or retard phase angle) should be clearly stated.
Especially for the retard phase angle operation, the overload
requirements may greatly influence the cost of the phase-
shifting transformer.
tȋ Operation of phase-shifting transformer
Operation with other phase-shifting transformers in parallel or
series.
tȋ Single or dual-tank design
In most cases, a dual-core design requires a dual-tank design
as well.
tȋ Symmetric or non-symmetric type
Symmetric means that under a no-load condition the voltage
magnitude at the load side is equal to that of the source side.
For non-symmetric phase-shifting transformers, the
permissible variation in percent of rated voltage at maximum
phase angle must be stated.
tȋ Quadrature or non-quadrature type
A quadrature-type phase-shifting transformer is a unit where
the boost voltage, which creates the phase shift between
source and load terminals, is perpendicular to the line voltage
on one terminal.
tȋ Internal varistors
It has to be clarified whether internal metal oxide varistors are
allowed or not.
Fig. 5.7-1: Phase-shifting transformer
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5.8 HVDC Transformers
HVDC transformers are key components of HVDC stations. HVDC
converter and inverter stations terminate long-distance DC
transmission lines or DC sea cables. This type of transformer
provides the interface between AC grids and high power recti-
fiers and are used to control the load flow over the DC transmis-
sion lines. These actors adapt the AC grid voltage to an adequate
level which is suitable for feeding the valve system of DC con-
verter and inverter.
Design options
The design concept of HVDC transformers is mainly influenced
by the rated voltage, rated power and transportation require-
ments like dimensions, weight and mode of transportation.
Many large power HVDC converter station are located in rural
areas of low infrastructure. Frequently, special geometrical
profiles have to be fulfilled in order to move such transformers
by railway.
Typically, HVDC transformers are single phase units containing
2 winding limbs. This concept can include either 2 parallel valve
windings (two for delta or two for wye system, fig. 5.8-1) or two
different valve windings (one for delta and one for wye, fig. 5.8-
2). In order to reduce the total transportation height frequently
the core assembly includes 2 return limbs. Due to redundancy
requirements in HVDC stations 3 phase units are quite
uncommon.
The valve windings are exposed to AC and DC dielectric stress
and therefore a special insulation assembly is necessary. Further-
more, special lead systems connecting the turrets and windings
have to be installed in order to withstand the DC voltage of
rectifier. Additionally, the load current contains harmonic com-
ponents of considerable energy resulting in higher losses and
increased noise. Above all, special bushings are necessary for
the valve side to access upper and lower winding terminals of
each system from outside. Conclusively, two identical bushings
are installed for star or delta system.
For approving the proper design and quality of manufacturing
special applied DC and DC polarity reversal tests have to be
carried out. The test bay has to be equipped with DC test appa-
ratus accordingly and needs to provide adequate geometry to
withstand the DC test voltage.
Technical items
In addition to the standard parameters of power transformers,
special performance requirements have to be known for the
design of HVDC transformers. These parameters are jointly
defined by designers of the HVDC station and transformer design
engineers in order to reach a cost-effective design for the entire
equipment.
Special parameters are:
tȋ Test levels: DC applied, DC polarity reversal and long-time AC
defines the insulation assembly of the transformer
tȋ Harmonic spectrum of the load current and phase relation
Fig. 5.8-1: Converter transformer for UHVDC bipolar transmission
system ± 800 kVDC, 6,400 MW; 2,071 km: single phase;
550 kVAC, 816 kVDC; 321 MVA; high pulse wye system
feeding
Fig. 5.8-2: Converter transformer for HVDC bipolar transmission
system ± 500 kVDC; 2,500 MW: single phase; 420 kVAC;
515 kVDC; 397 MVA; wye system (left side of figure) and
delta system (right side of figure)
generate additional losses, which have to compensated by the
cooling circuit
tȋ Voltage impedance impacting the dimensions of windings and
the total height of the transformer
tȋ DC bias in load and current and transformer-neutral have to be
considered for no-load noise and no-load losses
tȋ Derivative of the load current (di/dt) is a key parameter for the
on-load tap changer
tȋ Overload requirements have to be considered for cooling
circuit and capacity of coolers
tȋ Regulation range and number of steps influence the voltage
per turn which is a key design parameter
tȋ Seismic requirements have to be considered for mechanical
strength of turrets, outlets and bushings
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5.9 Distribution
Transformers
5.9.1 Liquid-immersed Distribution
Transformers for
European/US/Canadian Standard
On the last transformation step from the power station to the
consumer, distribution transformers (DT) provide the necessary
power for systems and buildings. Accordingly, their operation
must be reliable, efficient and, at the same time, silent.
Distribution transformers are used to convert electrical energy
of higher voltage, usually up to 36 kV, to a lower voltage,
usually 250 up to 435 V, with an identical frequency before and
after the transformation. Application of the product is mainly
within suburban areas, public supply authorities and industrial
customers. Distribution transformers are usually the last item in
the chain of electrical energy supply to households and indus-
trial enterprises.
Distribution transformers are fail-safe, economical and have a
long life expectancy. These fluid-immersed transformers can be
1-phase or 3-phase. During operation, the windings can be
exposed to high electrical stress by external overloads and high
mechanical stress by short-circuits. They are made of copper or
aluminum. Low-voltage windings are made of strip or flat wire,
and the high-voltage windings are manufactured from round
wire or flat wire.
Three product classes – standard, special and renewable –
are available, as follows:
tȋ Standard distribution transformers:
ȋ– Pole mounted (fig. 5.9-1), wound core or stacked
core technology distribution transformer
(≤ 2,500 kVA, U
m
≤ 36 kV)
ȋ– Wound core or stacked core technology medium distribution
transformer (> 2,500 ≤ 6,300 kVA, U
m
≤ 36 kV)
ȋ– Large distribution transformer
(> 6.3 – 30.0 MVA, U
m
≤ 72.5 kV)
ȋ– Voltage regulator (fig. 5.9-2)
tȋ Special distribution transformers:
ȋ– Special application: self-protected DT, regulating DT (OLTC),
electronic regulate DT, low-emission DT or others
(autotransformer, transformer for converters, double-tier,
multiwinding transformer, earthing transformer)
ȋ– Environmental focus: amorphous core DT with significant
low no-load losses, DT with special low load-loss design,
low-emission DT in regard of noise and/or electromagnetic
field emissions, DT with natural or synthetic ester where
higher fire-resistance and/or biodegradability is required
tȋ Renewable distribution transformers:
ȋ– Used in wind power stations, solar power plants or sea flow/
generator power plants
Fig. 5.9-1: Pole mounted, Canada
Fig. 5.9-2: Liquid-immersed distribution transformer
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5.9.2 Voltage Regulators
Siemens invented the voltage regulator in 1932 and pioneered
its use in the United States. Voltage Regulators are tapped step
autotransformers used to ensure that a desired level of voltage
is maintained at all times. A voltage regulator comprises a
tapped autotransformer and a tap changer. The standard
voltage regulator provides ± 10 % adjustment in thirty-two
0.625 % steps. Voltage Regulators with ± 15 % and ± 20 %
regulation are available for some designs.
Voltage regulators are liquid-immersed and can be 1-phase or
3-phase. They may be self-cooled or forced air-cooled. Available
at 50 or 60 Hz and with 55 or 65 °C temperature rise, they can
be used in any electrical system to improve voltage quality.
Voltage regulator ratings are based on the percent of regulation
(i.e., 10 %). For example, a set of three 1-phase 333 kVA regula-
tors would be used with a 10 MVA transformer (e.g., 10 MVA
t
0.10/3 = 333 kVA). 1-phase voltage regulators are available in
ratings ranging from 2.5 kV to 19.9 kV and from 38.1 kVA to
889 kVA (fig. 5.9-3). 3-phase voltage regulators are available at
13.2 kV or 34.5 kV and from 500 kVA to 4,000 kVA.
Voltage regulators can be partially or completely untanked for
inspection and maintenance without disconnecting any internal
electrical or mechanical connections. After the unit is untanked,
it is possible to operate the voltage regulator mechanism and
test the control panel from an external voltage source without
any reconnections between the control and the regulator.
Standard external accessories
The standard accessories are as follows:
tȋ External metal-oxide varistor (MOV) bypass arrester
tȋ Cover-mounted terminal block with a removable gasketed
cover. It allows easy potential transformer reconnections
for operation at different voltages
tȋ Oil sampling valve
tȋ Two laser-etched nameplates
tȋ External oil sight gauge that indicates oil level at 25 °C
ambient air temperature and oil color
tȋ External position indicator that shows the tap changer position
tȋ Mounting bosses for the addition of lightning arresters to the
source (S), load (L) and source-load (SL) bushings. They shall
be fully welded around their circumference.
Accessories and options
Remote mounting kit
Extra-long control cable shall be provided for remote mounting
of the control cabinet at the base of the pole.
Sub-bases
To raise the voltage regulator to meet safe operating clearances
from the ground to the lowest live part.
Auxiliary PT
Operation at different voltages.
Testing
All voltage regulators shall be tested in accordance with the
latest ANSI C57.15 standards.
Standard tests include:
tȋ Resistance measurements of all windings
tȋ Ratio tests on all tap locations
tȋ Polarity test
tȋ No-load loss at rated voltage and rated frequency
tȋ Excitation current at rated voltage and rated frequency
tȋ Impedance and load loss at rated current and rated frequency
tȋ Applied potential
tȋ Induced potential
tȋ Insulation power factor test
tȋ Impulse test
tȋ Insulation resistance
Fig. 5.9-3: 1-phase voltage
regulator, JFR
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5.9.3 GEAFOL Cast-Resin Transformers
GEAFOL transformers have been in successful service since
1965. Many licenses have been granted to major manufacturers
throughout the world since then. Over 100,000 units have
proven themselves in power distribution or converter operation
all around the globe.
Advantages and applications
GEAFOL distribution and power transformers in ratings from 100
to approximately 50,000 kVA and lightning impulse (LI) values
up to 250 kV are full substitutes for liquid-immersed trans-
formers with comparable electrical and mechanical data. They
are designed for indoor installation close to their point of use at
the center of the major load consumers. The exclusive use of
flame-retardant insulating materials frees these transformers
from all restrictions that apply to oil-filled electrical equipment,
such as the need for oil collecting pits, fire walls, fire extin-
guishing equipment. For outdoor use, specially designed sheet
metal enclosures are available.
GEAFOL transformers are installed wherever oil-filled units
cannot be used or where use of liquid-immersed transformers
would require major constructive efforts such as inside build-
ings, in tunnels, on ships, cranes and offshore platforms, inside
wind turbines, in groundwater catchment areas and in food
processing plants. For outdoor use, specially designed sheet
metal enclosures are available.
Often these transformers are combined with their primary and
secondary switchgear and distribution boards into compact
substations that are installed directly at their point of use.
When used as static converter transformers for variable speed
drives, they can be installed together with the converters at the
drive location. This reduces construction requirements, cable
costs, transmission losses and installation costs.
GEAFOL transformers are fully LI-rated. Their noise levels are
comparable to oil-filled transformers. Taking into account the
indirect cost reductions just mentioned, they are also mostly
Fig. 5.9-4: GEAFOL cast-resin dry-type transfomer properties
* on-load tap changers on request
HV winding
Consisting of vacuum-potted
single foil-type aluminum coils.
See enlarged detail
in fig. 5.9-5
HV terminals
Variable arrangements,
for optimal station design.
HV tapping links for
adjustment to system
conditions, reconnectable
in de-energized state*
Resilient spacers
To insulate core and
windings from mechanical
vibrations, resulting in low
noise emissions
LV winding
Made of aluminum strip.
Turns firmly glued together
by means of insulating sheet
wrapper material
Temperature monitoring
By PTC or Pt 100 thermistor
detectors in the LV winding
Paint finish
on steel parts
Thick layer coating,
RAL 5009. On request:
Two-component varnish
(for aggressive
environments
or high humidity)
Clamping frame and truck
Rollers can be swung
around for lengthways
or sideways travel
Insulation
Mixture of epoxy resin
and quartz powder
makes the transformer
practically maintenance-
free, moisture-proof,
tropicalized, flame-resistant
and self-extinguishing
LV terminals
Normal arrangement:
Top, rear
Special version:
Bottom, available on
request at extra charge
Ambient class E2
Climatic category C2
(If the transformer is installed
outdoors, degree of protection
IP23 must be assured)
Three-leg core
Made of grain-oriented,
low-loss electrolaminations
insulated on both sides
Fire class F1
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U
U
2 3 4 5 6 7 8
1 2 3 4 5 6 7
2 4 6 8
1 3 5 7
Foil winding
The interlayer voltage is equal
to the interturn voltage
Round-wire winding
The interturn voltages can add up
to twice the interlayer voltage
Fig. 5.9-5: High-voltage encapsulated winding design of
GEAFOL cast-resin transformer and voltage stress of a
conventional round-wire winding (above) and the foil
winding (below)
cost-competitive. By virtue of their design, GEAFOL transformers
are practically maintenance-free.
Standards and regulations
GEAFOL cast-resin dry-type transformers comply with
IEC 60076-11, EN 60076-11 and EN 50541-1.
Characteristic properties (fig. 5.9-4)
HV winding
The high-voltage windings are wound from aluminum foil
interleaved with high-grade insulating foils. The assembled and
connected individual coils are placed in a heated mold and are
potted in a vacuum furnace with a mixture of pure silica (quartz
sand) and specially blended epoxy resins. The only connections
to the outside are casted brass nuts that are internally
bonded to the aluminum winding connections.
The external delta connections are made of
insulated copper or aluminum connectors to
guarantee an optimal installation design. The resulting high-
voltage windings are fire-resistant, moisture-proof and corro-
sion-proof, and they show excellent aging properties under all
operating conditions.
The foil windings combine a simple winding technique with a
high degree of electrical safety. The insulation is subjected to
less electrical stress than in other types of windings. In a conven-
tional round-wire winding, the interturn voltages can add up to
twice the interlayer voltage. In a foil winding, it never exceeds
the voltage per turn, because a layer consists of only one
winding turn. This results in high AC voltage and impulse
voltage withstand capacity.
Aluminum is used because the thermal expansion coefficients of
aluminum and cast resin are so similar that thermal stresses
resulting from load changes are kept to a minimum (fig. 5.9-5).
LV winding
The standard low-voltage winding with its considerably reduced
dielectric stresses is wound from single aluminum sheets with
interleaved cast-resin impregnated fiberglass fabric (prepreg).
The assembled coils are then oven-cured to form uniformly
bonded solid cylinders that are impervious to moisture. Through
the single-sheet winding design, excellent dynamic stability
under short-circuit conditions is achieved. Connections are
submerged arc-welded to the aluminum sheets and are
extended either as aluminum or copper bars to the secondary
terminals.
Fire safety
GEAFOL transformers use only flame-retardant and self-extin-
guishing materials in their construction. No additional sub-
stances, such as aluminum oxide trihydrate, which could nega-
tively influence the mechanical stability of the cast-resin
molding material, are used. Internal arcing from electrical faults
and externally applied flames do not cause the transformers to
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burst or burn. After the source of ignition is removed, the trans-
former is self-extinguishing. This design has been approved by
fire officials in many countries for installation in populated
buildings and other structures. The environmental safety of the
combustion residues has been proven in many tests (fig. 5.9-6).
Categorization of cast-resin transformers
Dry-type transformers have to be classified under the categories
listed below:
tȋ Environmental category
tȋ Climatic category
tȋ Fire category
These categories have to be shown on the rating plate of each
dry-type transformer.
The properties laid down in the standards for ratings within the
category relating to environment (humidity), climate and fire
behavior have to be demonstrated by means of tests.
These tests are described for the environmental category
(code numbers E0, E1 and E2) and for the climatic category
(code numbers C1 and C2) in IEC 60076-11. According to this
standard, the tests are to be carried out on complete trans-
formers. The tests of fire behavior (fire category code numbers
F0 and F1) are limited to tests on a duplicate of a complete
transformer that consists of a core leg, a low-voltage winding
and a high-voltage winding.
GEAFOL cast-resin transformers meet the requirements of the
highest defined protection classes:
tȋ Environmental category E2 (optional for GEAFOL-BASIC)
tȋ Climatic category C2
tȋ Fire category F1
Insulation class and temperature rise
The high-voltage winding and the low-voltage winding utilize
class F insulating materials with a mean temperature rise of
100 K (standard design).
Overload capability
GEAFOL transformers can be overloaded permanently up to 50 %
(with a corresponding increase in impedance voltage and load
losses) if additional radial cooling fans are installed (dimensions
can increase by approximately 100 mm in length and width.)
Short-time overloads are uncritical as long as the maximum
winding temperatures are not exceeded for extended periods of
time (depending on initial load and ambient air temperature).
Temperature monitoring
Each GEAFOL transformer is fitted with three temperature
sensors installed in the LV winding, and a solid-state tripping
device with relay output. The PTC thermistors used for sensing
are selected for the applicable maximum hot-spot winding
temperature.
Additional sets of sensors can be installed, e.g. for fan control
purposes. Alternatively, Pt100 sensors are available. For oper-
Fig. 5.9-6: Flammability test of cast-resin transformer
Fig. 5.9-7: Radial cooling fans on GEAFOL transformer for AF cooling
Table 5.9-1: Standard insulation levels of GEAFOL
U
m
(kV) LI (kV) AC (kV)
1.1 – 3
12 75 28
24 95* 50
36 145* 70
* other levels upon request
ating voltages of the LV winding of 3.6 kV and higher, special
temperature measuring equipment can be provided.
Auxiliary wiring is run in a protective conduit and terminated in
a central LV terminal box (optional). Each wire and terminal is
identified, and a wiring diagram is permanently attached to the
inside cover of this terminal box.
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Installation and enclosures
Indoor installation in electrical operating rooms or in various
sheet metal enclosures is the preferred method of installation.
The transformers need to be protected only against access to the
terminals or the winding surfaces, against direct sunlight and
against water. Unless sufficient ventilation is provided by the
installation location or the enclosure, forced-air cooling must be
specified or provided by others (fig. 5.9-7).
Instead of the standard open terminals, plug-type elbow con-
nectors can be supplied for the high-voltage side with LI ratings
up to 170 kV. Primary cables are usually fed to the transformer
from trenches below but can also be connected from above
(fig. 5.9-8).
Secondary connections can be made by multiple insulated
cables, or by connecting bars from either below or above.
Secondary terminals are made of aluminum (copper upon
request).
A variety of indoor and outdoor enclosures in different protec-
tion classes are available for the transformers alone, or for
indoor compact substations in conjunction with high-voltage
and low-voltage switchgear panels. PEHLA-tested housings are
also available (fig. 5.9-9).
Cost-effective recycling
The oldest of the GEAFOL cast-resin transformers that entered
production in the mid-1960s are approaching the end of their
service life. Much experience has been gathered over the years
with the processing of faulty or damaged coils from such trans-
formers. The metal materials and resin used in GEAFOL cast-resin
transformers, that is, approximately 95 % of their total mass, can
be recyled. The process used is non-polluting. Given the value of
secondary raw materials, the procedure is often cost-effective,
even with the small amounts currently being processed.
Fig. 5.9-9: GEAFOL transformer in protective housing to IP20/40
Fig. 5.9-8: GEAFOL transformer with plug-type cable connections
The GEAFOL Basic – a true GEAFOL and more
The GEAFOL Basic is based on more than 45 years of proven
GEAFOL technology and quality, but it offers numerous innova-
tions that has allowed Siemens to provide it with several very
special characteristics. For example, the GEAFOL Basic distribu-
tion transformer with a maximum rated power of 3.15 MVA and
a maximum medium voltage of 36 kV is almost ten percent
lighter than a comparable model from the proven GEAFOL series.
And this “slimming down” also positively affects the dimensions.
This could be achieved by a considerably improved heat dissipa-
tion because of the new, patented design.
Of course all GEAFOL Basic distribution transformers meet the
specifications of IEC 60076-11, EN 60076-11 and EN 50541-1.
They meet the highest requirements for safe installation in
residential and work environments with Climatic Class C2, Envi-
ronmental Class E2 (standard model meets E1; E2 is available as
option at additional costs) and Fire Classification F1. With fewer
horizontal surfaces, less dust is deposited, which leads to a
further reduction in the already minimal time and effort needed
for maintenance and also increases operational reliability.
Optimum compromise
The GEAFOL Basic distribution transformer represents an
optimum compromise between performance, safety and small
dimensions. In addition, the high degree of standardization
ensures the best possible cost-benefit ratio. Thanks to their
compact shape and comprehensive safety certification, GEAFOL
Basic distribution transformers can be used in almost every
environment.
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9
6
1
4
2
3
5
8
7
A new design for your success –
the r
eliable, space-saving GEAFOL Basic
1
Three-limb core
Made of grain-oriented, low-loss
electric sheet steel that is insulated
on both sides
2
Low-voltage winding
Made of aluminum strip; turns are
permanently bonded with insulating sheet
3
High-voltage winding
Made of individual aluminum coils using
foil technology and vacuum casting
4
Low-voltage connectors (facing up)
5
Lifting eyes
Integrated into the upper core frame
for simple transport
6
Delta connection tubes with
HV terminals
7
Clamping frame and truck
Convertible rollers for longitudinal
and transverse travel (rollers optional)
8
Insulation made of an epoxy resin/
quartz powder mixture
Makes the transformer extensively
maintenance-free, moisture-proof
and suitable for the tropics, fire-
resistant and self-extinguishing
9
High-voltage taps ±2 x 2.5 %
(on the high-voltage connector side)
to adapt to the respective network
conditions; reconnectable off load
Temperature monitoring
With PTC thermistor detector in limb V
of the low-voltage winding (in all three
phases upon request)
Painting of steel parts
High-build coating, RAL 5015:
two-component coating upon request
(for particularly aggressive environments)
Structure made of individual components
For example, windings can be individually
assembled and replaced on site
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5.9.4 GEAFOL Special Transformers
GEAFOL cast-resin transformers with oil-free
on-load tap changers
The voltage-regulating cast-resin transformers connected on the
load side of the medium-voltage power supply system feed the
plant-side distribution transformers. The on-load tap changer
controlled transformers used in these medium-voltage systems
need to have appropriately high ratings.
Siemens offers suitable transformers in its GEAFOL design
(fig. 5.9-10), which has proved successful over many years and
is available in ratings of up to 50 MVA. The range of rated
voltage extends to 36 kV, and the maximum impulse voltage is
200 kV (250 kV). The main applications of this type of trans-
former are in modern industrial plants, hospitals, office and
apartment blocks and shopping centers.
Linking 1-pole tap changer modules together by means of
insulating shafts produces a 3-pole on-load tap changer for
regulating the output voltage of 3-phase GEAFOL transformers.
In its nine operating positions, this type of tap changer has a
rated current of 500 A and a rated voltage of 900 V per step.
This allows voltage fluctuations of up to 7,200 V to be kept
under control. However, the maximum control range utilizes
only 20 % of the rated voltage.
Transformers for static converters
These are special liquid-immersed or cast-resin power trans-
formers that are designed for the special demands of thyristor
converter or diode rectifier operation.
The effects of such conversion equipment on transformers and
additional construction requirements are as follows:
tȋ Increased load by harmonic currents
tȋ Balancing of phase currents in multiple winding systems
(e.g., 12-pulse systems)
tȋ Overload capability
tȋ Types for 12-pulse systems, if required
Siemens supplies oil-filled converter transformers of all ratings
and configurations known today, and dry-type cast-resin con-
verter transformers up to 50 MVA and 250 kV LI (fig. 5.9-11).
To define and quote for such transformers, it is necessary to
know considerable details on the converter to be supplied and
Fig. 5.9-10: 16/22-MVA GEAFOL cast-resin transformer with oil-free on-load tap changer
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on the existing harmonics. These transformers are almost exclu-
sively inquired together with the respective drive or rectifier
system and are always custom-engineered for the given applica-
tion.
Neutral earthing transformers
When a neutral earthing reactor or earth-fault neutralizer is
required in a 3-phase system and no suitable neutral is available,
a neutral earthing must be provided by using a neutral earthing
transformer.
Neutral earthing transformers are available for continuous
operation or short-time operation. The zero impedance is
normally low. The standard vector groups are zigzag or wye/
delta. Some other vector groups are also possible.
Neutral earthing transformers can be built by Siemens in all
common power ratings in liquid-immersed design and in cast-
resin design.
Transformers for Silicon-reactor power feeding
These special transformers are an important component in
plants for producing polycrystalline silicon, which is needed
particularly by the solar industry for the manufacture of collec-
tors.
What’s special about these transformers is that they have to
provide five or more secondary voltages for the voltage supply
of the special thyristor controllers. The load is highly unbalanced
and is subject to harmonics that are generated by the con-
verters. Special geafol cast resin transformers with open sec-
ondary circuit have been developed for this purpose. The rated
power can be up to round about 10 MVA, and the current can
exceed an intensity of 5,000 amps depending on the reactor
type and operating mode. Depending on the reactor control
system two-winding or multi-winding transformers will be used
(fig. 5.9-12).
Fig. 5.9-11: 23-MVA GEAFOL cast resin transformer 10 kV/Dd0Dy11
Fig. 5.9-12: 4771 kVA GEAFOL converter transformer with
5 secondary tappings 10/0.33 – 2.4 kV
For further information:
Fax: ++49 (0) 70 21-5 08-4 95
www.siemens.com/energy/transformers
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5.10 Traction Transformers
Siemens produces transformers for railway applications called
traction transformers. These transformers are installed in electric
cars such as high-speed trains, electric multiple units (EMUs)
and electric locomotives. Their main purpose is transform the
overhead contact line voltage, which range mainly from 15 kV
up to 25 kV, to voltages suitable for traction converters
(between 0.7 kV and 1.5 kV) (fig. 5.10-1).
Siemens develops and produces traction transformers for rolling
stock applications of all relevant ratings, voltage levels and
customer-specific requirements.
All products are optimized with regard to individual customer
requirements such as:
tȋ Frequency, rating and voltage
tȋ Required dimensions and weights
tȋ Losses and impedance voltage characteristics
tȋ Operational cycles and frequency response behavior
tȋ Environmental requirements
Characterization
Technically, traction transformers are in general characterized as
follows:
tȋ 1-phase transformers
tȋ Ratings up to 10 MVA and above
tȋ Operating frequencies from 16⅔ to 60 Hz
tȋ Voltages: 1.5 kV DC, 3 kV DC, 15 kV, 25 kV, 11.5 kV
or other specific solutions
tȋ Weight: < 15 t
tȋ Auxiliary windings and/or heater windings according to
customer specification
tȋ Single or multiple system operation
tȋ Under floor, machine room or roof assembly
tȋ Traction windings to be used as line filters
tȋ Integrated absorption circuit reactors
tȋ Various cooling media for all ratings: mineral oil, silicone or
ester fluid for highest environmental compatibility
In case of customer request:
tȋ With cooling plant – integrated in one frame together with the
transformer or stand-alone solution
tȋ Nomex insulation for highest energy density
Examples
The examples shown in the table are typical applications where
traction transformers from Siemens were used (table 5.10-1).
Fig. 5.10-1: Traction transformer for high speed trains
Table 5.10-1: Siemens develops and produces traction transformers for rolling stock applications of all relevant ratings and voltage levels
High speed train AVE S102 for RENFE Spain Electric locomotive for ÖBB Austria
(1216 Series) for cross-european haulage
World’s most powerful series-production
freight locomotive for China
Operation: Madrid – Barcelona
Travel time: 2 h 30 min for 635 km
Number of cars: 8
Power system: 25 kV/50 Hz
Maximum power at wheel: 8,800 kW
Max. speed: 350 km/h
Number of seats: 404
4 system operation
AC 15 kV: 16⅔ Hz
AC 25 kV 50 Hz
DC 3 kV
DC 1.5 kV
Speed: 200 – 230 km/h
Weight 87 t
6 axle machine
9,600 kW on 6 axles
hauling of 20,000 t trains
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5.11 Transformer Lifecycle
Management
Introduction
Power transformers usually perform their work, humming
quietly for decades, without any interruption. Operators have
thus come to rely on their solid transformer capacity, often
performing only minimal maintenance using traditional tech-
niques (fig. 5.11-1).
Today, load requirements, additional environmental constraints
and recent corporate sustainability objectives to keep a close eye
on the operational value of the equipment, have led Siemens to
provide a comprehensive set of solutions to keep the equipment
at peak level under any operational circumstances. A new gener-
ation of asset managers is interested in the “operational” value,
including the replacement cost, instead of the depreciated
book-value over decades, which is often close to zero.
Power transformers are long-lasting capital investment goods.
Purchasing and replacement require long periods of planning
engineering and procurement. Each individual conception is
specially adapted to the specific requirements. The corre-
sponding high replacement value, and the important lead time
are in the focus.
What is TLM™?
Siemens Transformer Lifecycle Management™ (TLM™) includes
highly experienced transformer experts who provide the most
effective lifecycle solutions for power transformers of any age
and any brand.
Maintaining customers’ power transformers at peak operating
level is the prime objective of the Siemens TLM set of solutions.
Siemens TLM is based on the expertise available in all Siemens
transformer factories, which are well-known for high quality and
low failure rates. The TLM scope of services is explained in the
following briefly:
Conditon Assessment & Diagnostics (fig. 5.11-2)
tȋ Level 1: SITRAM® DIAG ESSENTIAL
tȋ Level 2: SITRAM® DIAG ADVANCED
tȋ Level 3: SITRAM® DIAG HIGH VOLTAGE TESTING
The SITRAM® DIAG program consists of three layers and provides
diagnostic modules for individual transformer and for the assess-
ment of complete installed fleets and transformer populations.
SITRAM® DIAG ESSENTIAL (Level 1)
All modules in the diagnosis Level 1 “ESSENTIAL” are to be
applied on energized transformers. The most powerful toolbox
for this application is the diagnosis of the insulating liquid.
Additional stand alone modules are available to be applied when
the oil tests and/or the operating personnel gave indication for
deficiencies or changes.
tȋ Standard oil test (8 –12 parameters)
Fig. 5.11-1: Siemens Transformer Lifecycle Management™
scope of services
Fig. 5.11-2: SITRAM® DIAG provides diagnostic modules for
individual transformers and for the assessment of
complete fleets
tȋ Dissolved Gas in Oil Analysis (DGA)
tȋ Furanic components
tȋ Moisture
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Additional stand alone modules
tȋ PD (UHF-, acoustic sensors, corona camera)
tȋ Noise measurement
tȋ Vibration measurement
tȋ Thermograph scans
SITRAM® DIAG ADVANCED (Level 2)
The extended modules are applied on de-energized and
disconnected transformers. Most measurements repeat the
measurements as shown in the manufacturers test report and by
comparing the results any differences will be highlighted. Level
2 provide information about the insulation (dielectric) condition
as well as the mechanical condition (displacements) of the
active part of a transformer.
tȋ Ratio and phase angle
tȋ Winding resistance
tȋ C-tan delta (windings and bushings)
tȋ Insulation resistance and
tȋ Polarization Index (PI)
tȋ Impedance
tȋ No load current and losses
tȋ At low voltage
tȋ FDS/PDC
tȋ FRA
Additional all modules of Level 1 apply
SITRAM® DIAG HIGH VOLTAGE TESTING (Level 3)
High-Voltage-Tests on-site is usually required following on-site
repairs, factory repairs, refurbishment or relocation and also
performed to assure the results from the level 1 and level 2
assessments. The SITRAM DIAG mobile test fields provides
solutions for all kind of HV testing and loss measurement. Heat
runs or long duration tests are feasible depending on size and
voltage level of the transformer under test. Level 3 assessment
can be combined with all modules out of level 1 and level 2.
tȋ Load losses
tȋ No load losses and currents
tȋ Applied overvoltage tests
tȋ Induced overvoltage tests
tȋ Partial discharge testing
tȋ DC testing
tȋ Heat runs
tȋ Long duration tests
Additional all modules of Level 1 and 2 apply
Online Monitoring (fig. 5.11-3)
tȋ SITRAM® GUARDS
tȋ SITRAM® CM
tȋ SITRAM® iCMS
The new Siemens third-generation SITRAM® MONITORING range
is providing compatible, modular and customized solutions for
individual power transformers (new and retrofit) and solutions
for entire transformer fleets.
In general, these systems allow a continuous monitoring of
power transformers, which are going far beyond the traditional
method of taking offline measurements. The experience demon-
strates clearly, that with Online monitoring, an improved effi-
ciency in the early detection of faults can be achieved. So that
curative and corrective maintenance actions can be planned and
scheduled well in advanced. It is also possible to use spare
capacities up to the limits. This is resulting in a higher reliability,
efficiency and longer service life of power transformers.
SITRAM Guard’s:
Standardized and approved sensor technologies as a single
solution for individual transformers.
tȋ GAS Guard (online gas-in-oil analysis)
tȋ PD-Guard (partial discharge monitoring)
tȋ BUSHING Guard (bushing monitoring)
tȋ TAPGUARD® (on-load tap changer monitoring)
SITRAM Condition Monitor (SITRAM CM):
The SITRAM Condition Monitor is a modular and customized
system, which integrates information from single sensors and
SITRAM Guard’s for each transformer individually and is able to
provide condition information about all key components. A local
data storage module and a communication interface enable the
user to access the information remotely.
SITRAM integrated Conditon Monitoring System (SITRAM iCMS):
This “Knowledge Module” solution is monitoring all transformers
in transmission and distribution substations, power generation
plants or in large industries to an existing or next generation
protection and control system. Furthermore is it able to integrate
the recorded data of a complete transformer fleet of a utility to a
superordinated system. It is based on the modular hardware
architecture of the SITRAM CM.
In addition to the monitoring hardware and software, Siemens
TLM transformer experts are available for remote nursing solu-
tions for questionable transformers, analyzing and interpretation
of recorded monitoring data.
Fig. 5.11-3: All levels of the SITRAM® MONITORING concept
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Consulting Expertise and Training
tȋ Engineering service
tȋ Advice & recommendations
tȋ Educational seminars
tȋ Custom-tailored workshops
The Siemens TLM set of solutions integrates a wide range of
services that are designed to considerably extend the life of the
operator‘s transformers. Siemens’s preferred approach is to
integrate all transformers – of any age and any brand – in the
plan that is prepared for customers so that they can make the
best decision about replacement/extension and any related
matters. Siemens TLM also offers a series of standardized cus-
tomer trainings. These programs are specifically designed to
broaden customer awareness of the various concept and design
options. Lifecycle management is, of course, an integral part of
the training.
Maintenance & Lifecycle Extension
tȋ Preventive & corrective maintenance
tȋ On site active part drying & de-gassing
tȋ Oil regeneration
tȋ Life extension products
tȋ End of life management
We’ll get your transformers back in top form – and without
service interruptions. Our TLM™ products for extending service
life minimizes the unavoidable, undetectable and ongoing aging
process that is taking place inside transformers. This internation-
ally-recognized technologies for life extension are rounded up by
a cooling efficiency retrofit solution.
SITRAM DRY (fig. 5.11-4)
The SITRAM® DRY is an advanced technology for preventive and
continuous online transformer drying. The system removes
moisture from the insulation oil through disturbing the moisture
equilibrium so that moisture diffuses from the wet insulation
paper to the dried insulation oil. This process will removing the
moisture in a gentle and smooth way from the solid insulation
and will increase the dialectical strength of the insulating oil.
tȋ Continuous online removal of moisture from solid insulation
and oil
tȋ Based on a molecular sieve technology
tȋ Easy to install on any transformer in operation
tȋ Temperature and moisture monitoring
tȋ Cartridge replacement and regeneration service
tȋ Cabinet Version (NEMA4)
tȋ New: SITRAM® DRY Smart, mobile solution for distribution
transformers very soon available
Experience the functions of SITRAM® DRY in sound and vision:
www.siemens.de/energy/sitram-dry-video
SITRAM REG
Siemens developed the SITRAM® REG technology to clean
contaminated oil and restore its dielectric properties. SITRAM®
REG is a modified reclamation process based on the IEC 60422
standard. Oil is circulated continuously through regeneration
columns.
tȋ An oil change is not required
tȋ Improves the quality of insulating oil to that of new oil
tȋ Prolongation of the lifetime and increased reliability of old
transformers
tȋ Preventive action against the progressive insulation ageing
process
tȋ Sustainable improvement in the condition of the insulation
tȋ Suitable for all power transformers
tȋ Economically independent of the current price of new oil
tȋ No service interruptions
tȋ Great and long-lasting cleaning effect
SITRAM COOL
SITRAM COOL is an add-on retrofit solution and consists of
hardware and software for the automatic, optimized control of
transformer cooling system:
tȋ Increase of the total efficiency of the transformer
tȋ Reduction of auxiliary losses
tȋ Reduction of noise level
tȋ Reduction of maintenance
tȋ If required and if applicable –> upgrading
Spare Parts & Accessories
The supply of spare parts is another strong point of Siemens
TLM. Upon request, Siemens may advise customers on what
Fig. 5.11-4: Cabinet version of the SITRAM DRY equipped with a
control module
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For further information, please contact your
local Siemens sales representative or contact:
Phone: +49 (180) 524 7000
Fax: +49 (180) 524 2471
E-mail: [email protected]
www.siemens.com/energy/TLM
accessories will best fit their needs. Examples include Buchholz
relays of various sizes, temperature sensors, oil flow alarms and
oil level indicators. In order to provide the best solution, Siemens
TLM will verify alternative products and strive to make technical
improvements using state-of-the-art technologies, particularly
important when original spare parts are not longer available.
Spare parts from Siemens TLM™ offers you (fig. 5.11-5):
tȋ Stringent quality assurance standards to ensure that spare
parts are manufactured in accordance with the Siemens OEM
specifications
tȋ Continuous improvement of technology and materials
tȋ Outage planning and support based on customized spare
parts programs
tȋ Spar part service for all transformers in the Siemens family
(SIEMENS, TU, VA TECH, Ferranti-Packard, PEEPLES)
Repair & Retrofit
Can we make your old transformer as good as new? We can
come very close and usually improve your old transformers with
Siemens new state-of-the-art technologies. One highlight of
TLM™ is the repair, overhaul, and modernization of your power
transformers. Repairs are performed in one of our dedicated
repair shops around the world, but are also done on-site when
our mobile workshops come to your facility. In addition, we can
retrofit or modernize transformers in various ways.
Whether your transformer has failed or you’re planning timely
corrective maintenance our TLM™ team of experts is available
for short-term repairs.
With its dedicated repair facilities at our technology center in
Nuremberg, Germany, and elsewhere around the world,
Siemens has created a professional setting to get your trans-
formers back into shape. Even the largest and heaviest trans-
formers in the world can be easily moved, inspected, and
repaired.
The repair facilities handle all problems that arise over the
lifecycle of a transformer, including installation of new on-load
tap changers and tapping switches, increasing performance, as
well as completely replacement of windings. In addition, all
components can be reconditioned and retrofitted with the latest
materials as needed. For everything from design to the latest
modern winding techniques to final inspection and testing, the
manufacturing processes at our renowned transformer plants
are continuously being improved. These improvements support
the maintenance and repair of your transformers (fig. 5.11-6).
Transport, Installation & Commissioning
Siemens technical experts and engineers whom work on proj-
ects that include installing new transformers or changing the
locations of old transformers, have decades of experience. They
are expert at disassembly and preparation for transport, storing
and handling of delicate components. Assembly is the daily
work of these Siemens experts, and Siemens offers its exhaus-
tive experience for complete solutions for customers so that
their equipment value remains at its peak for a long time.
Fig. 5.11-5: Maximimize the availibility of every transformer
with the TLM™spare part program
Fig. 5.11-6: Repair shop in Nuremberg, Germany
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