INNOVATIVE LIFE-CYCLE CONCEPTS FOR MEDIUM-VOLTAGE SWITCHGEAR ON BROWN COAL
SURFACE MINING DEVICES
Dr. S. Ruhland, Dr. U. Riedl
ALSTOM Sachsenwerk GmbH, Germany
The requirements for medium voltage switchgear
in
brown coal surface mining networks are
different from those in the networks of utilities. The
main differences are the mobile power consumers
in the mine such as mobile transformer stations,
power shovels or winding bridges with dimensions
of more then 400 meters in length and 50 meters
in height. As the power consumption of such a unit
is about 30 MW, the distribution network of such a
device has a rated voltage of 36 kV respective
7,2 kV.
The severe environmental conditions have a major
influence to the design, the installation and the
operation of the switchgear. Therefore it is evident
to think about the full life cycle of these
installations.
DESIGN AND INDUSTRIAL PHASE
The main aspects for the design of distribution
equipment for brown coal surface mining are the
electrical and mechanical requirements due to the
environmental situation. The electrical situation is a
network with high probability of faults. The faults
can come from the mining process itself (e.g. earth
faults coming from damages of cables or lightning
impact of the extended metal structures) or from
the mechanical movement of the mining devices
(permanent vibration and shocks).
The switchgear design has to withstand the
resulting stresses such as overvoltages and
mechanical vibration, therefore it is important to
choose the correct materials with minor influence
to the environment and with good possibility for the
later recycling process, but with high withstand
capabilities.
The design has to pass several acceptance tests
such as vibration tests with accelerations up to 1 g
and shock tests with amplitudes up to 5 g. During
the tests all mechanical and electrical interlocks
have to work safely. The insulation system and the
tightness in the case of gas insulated switchgear
have to be proven as well to ensure the function
during the whole lifetime.
All the results and measures taken to fulfil the
requirements have to be secured during the
assembling process in the factory and have to be
documented in the routine test reports.
INSTALLATION AND SERVICE PHASE
The on site installation is one of the most important
milestones during the lifetime of a switchgear. In
this period it has to be ensured, that the product
attribute’s are not influenced by the erection work.
Measures have to developed to guarantee e.g. the
integrity of the insulation system. That means
partial discharge measurements have to be
performed on site under a severe electromagnetic
environment with disturbance levels.
Other points that are important during the service
phase are:
• no maintenance on the active part of the
switchgear
• no maintenance/refilling on the gas system (in
the case of GIS)
• maintenance free mechanical drives
• choice of resistant lubrication systems
• easy adaptation of the switchgear to the needs
in the network (ratings)
• zero emission during the normal operation
• low emission in the improbable case of an
internal arc
END OF LIFE PHASE
In spite of the high lifetime of distribution
equipment the disposal at the end of the lifetime
has to be considered at the beginning of the
development. The usage of environmental friendly
materials will reduce the disposal costs and will
fulfil strong ecological requirements.
Further on the requirements from the client side
and from the disposal companies regarding the
data of amounts of different materials (kind and
amount of metals, plastics ..) have to be taken into
account during the development phase.
A common view on the full lifetime cycle (design,
service and disposal) of a medium voltage
switchgear has to be developed to tackle the
increasing number of ecological requirements in
future.
INNOVATIVE LIFE-CYCLE CONCEPTS FOR MEDIUM-VOLTAGE SWITCHGEAR ON BROWN COAL
SURFACE MINING DEVICES
Dr. S. Ruhland, Dr. U. Riedl
ALSTOM Sachsenwerk GmbH, Germany
INTRODUCTION
Using medium-voltage switchgear for brown coal
surface mining as an example, we will show the
principles according to which particular requirements and installation conditions are taken into
consideration for all life phases of a product.
ALSTOM concerning design, installation and
operation. To this effect, the complete life-cycle of
the switchgear was taken into consideration from
the start.
The following steps are defined as life phases:
•development,
•production,
•local assembly and operation,
and
•disposal.
Lignite mining and processing in Lusatia on an
industrial scale dates back to the end of the 19th
century. There are lignite fields totalling 13 billion
tons in Lusatia, 2.6 billion tons of which, which can
be extracted in an economically efficient fashion,
taking into account present ecological and social
compatibility aspects, are scheduled or planned for
mining. In this open cast mining, the lignite stratum
to be extracted reaches a thickness of 8 to 12
meters.
A typical feature of lignite open cast mining in
Lusatia are the big overburden conveyor gantries.
They are used to extract the majority of the 60 to
80 m high capping deposited on the stratum. The
maximum energy demand of open-cast mining is
60 to 80 MW, depending on the actual extraction
technology and utilisation of power. The largest
individual energy consumers are the conveyor
gantry units F60 with a maximum power utilisation
of 25 to 30 MW and an overburden extraction
capacity of 90 to 110 million m³ per year. Other
main consumers are overburden and lignite
conveyor belt systems of max. 15 to 20 MW per
operated mining complex.
Due to the continuous development of open cast
mining with an annual coal advance of 250 to 400
meters, all main consumers, such as conveyor
gantries, excavators and conveyor belt systems,
are in constant motion.
The unfavourable ambient conditions (dust
immission, humid climates, vibrations) were of
considerable importance for the choice of systems
by the operating company, and important for
PICTURE 1
Overburden conveyor gantry in
lignite open cast mining
TECHNICAL IMPLEMENTATION
The profiles requested in the table 1 can be
covered with the gas-insulated GMA and WSA
switchgear series.
Moreover, control of the additional mechanical
strains imposed on the panels as regards the
stability of the drive mechanism, the sealing
function parts of the gas compartment and the
stable behaviour regarding partial discharge (PD)
had to be ensured as well as the condition that
operating safety had to be guaranteed in the
presence of dust immission and high, alternating
air humidity values (condensation hazard).
Besides, an internal specification from the
manufacturer
requires
an
environmentally
compatible design (selection of materials,
recycling-oriented design, use of environmentally
compatible plastics) and the presence of a
disposal concept for switchgear at the end of its
service life which includes considerations of
ecological regeneration and re-use
insulating gas sulphur hexafluoride SF6.
TABLE 1
of
the
Technical requirements
Requirement criterion
Service
voltage 6
kV
12 kV
20 kA
Rated voltage Ur
Rated short-circuit
current Ik
Rated short-circuit
1 second
duration tk
Rated (service) current Ir
for circuit-breaker
switchgear
1250 A
for switch-disconnector
units
630 A
Rated insulation level
75 kV
Up
28 kV
Ud
Insulation level when the
insulating gas pressure
is reduced to ambient
pressure
Up
75 kV
Ud
28 kV
Insulation fluid of
100% SF6,
electrically active part
no solid
insulation
Leakage rate
<<1% p.a.
Partial discharge (PD)
behaviour of overall
insulation system:
PD intensity at 1.1 Ur < 15 pC
PD extinction voltage > 0.9 Ur
Mechanical endurance:
Circuit-breaker > 30000
mechanism
Switch disconnector
> 1000
mechanism
Disconnector/Earthing
> 1000
switch
Integrated voltage
detection system
acc. to IEC
61243-5
Proof of resistance to
vibration strain
Vibration
0.5 g
Shock
5.0 g
Resistance to external
IP65
environmental influences
(dust, humidity, etc.)
Proof of staff level safety
DIN EN
in case of internal faults
60298,
Criteria 1-6
Freely configurable
Possible
interface to BUS
for 100%
systems (Interbus,
of internal
Profibus etc.)
E/A
signals
Due to different design characteristics, it was not
possible to perform generally valid tests on the
GMA and WSA switchgear to confirm the suitability
of the types in question, but the inspections had to
be adapted to the particularities in question.
Service
voltage 30
kV
36 kV
16 kA
1 second
1250 A
630 A
170 kV
70 kV
145 kV
70 kV
100% SF6,
no solid
insulation
<<1% p.a.
PICTURE 2
Gas insulated single busbar
switchgear type WSA
SIGNIFICANCE FOR THE DESIGN PHASE AND
FOR THE PRODUCTION PHASE
< 15 pC
> 0.9 Ur
The customer's specific main task profile consisted
of the critical ambient conditions of lignite mining.
> 30000
Before the vibration tests were performed in
external, independent testing laboratories, the test
objects were subjected to the following
examinations:
− Partial discharge measurement
> 1000
acc. to IEC
61243-5
−
Leakage test (test of all single components
e.g. electrical and mechanical bushings
under
thermal
cycling
conditions
-40°C/+105°C, to subject the systems to
high mechanical strain; the measurements
were performed integrally using highresolution infrared (IR) spectroscopy). After
production, each switchgear unit was
subjected to an integral test using sensitive
IR spectroscopy (exception BB area of the
WS switchgear which had been tested over
the entire sealing area using a gas sensitive
detector after local assembly)
−
Functional inspection of the mechanical
drives (in the design phase, the lubricant
system was given special consideration as
0.5 g
5.0 g
IP65
DIN EN
60298,
Criteria 1-6
Possible
for 100%
of internal
E/A
signals
regards stability to moisture and abrasive
dusts with partially corrosive action)
−
Determination
of
the
mechanical
characteristic data of the drive mechanisms
(speeds etc.).
Sequence of external inspections following internal
inspections:
− Sweep sine test according to IEC 60068-2 in
all three axes
− Shock test according to IEC 60068-2 in all
three axes
TABLE 2
Vibration test parameters
Type of
test
Parameter
Testing value
Vibration
Frequency
5-150-5 Hz
Stroke/
acceleration
5 - 58 Hz
58 - 150 Hz
Shock
Frequency
change
1 oct/min
Testing time
10 cycles
Shock form
half-sine
Peak
acceleration
5g
Shock duration
11 ms
Number of
shocks
3 per
direction
± 0.035
mm
0.5 g
per axis
6 per
axis
PICTURE 3
WSA during the vibration test
During the tests performed at the Technical
University of Berlin and the at the laboratories of
the Navy of the armed forces all the functions were
controlled. That means manual and electrical
operation of the circuit breaker and the
disconnectors respective the three position switch,
observation of the change of the electrical position
indication and check of the gas density control
system.
After the tests all dielectrical
values, power
withstand voltage, lightning impulse withstand
voltage and partial discharge, could be
demonstrated.
The materials used for insulation, i.e. duroplastics
and thermoplastics, and elastomers (sealing
materials) satisfy the requirements to a large
extent. Specific accelerated tests under enhanced
mechanical strain also allow for conclusions on
positive long-term behaviour.
The corrosion protection system (painting,
electroplating, zinc-plating) also ensures protection
over the expected service life.
For the painting a combination of a cathodic dip
paint and a powder coating with an excellent
withstand against moisture and corrosive
immissions is used (proofed in time-lapsed tests
with
salt
fog
and
sulphur-dioxide).
The electroplating and hot dip zinc-plating surfaces
are optimised with additives (electroplating) and
with additional treatment of the protection-layer
(hot dip zinc-plating).
Graph 1
Measured accelerations during the
vibration test
All results of the electrical and mechanical
parameters determined in type tests are taken over
in the routine tests in the production lines, verified
there and documented accordingly.
SIGNIFICANCE FOR LOCAL ASSEMBLY AND
SWITCHGEAR OPERATION
Zero fault installation - even under the most difficult
installation conditions at the operating company’s is of paramount importance during local assembly.
All the relevant systems are checked after
assembly work. The on-site partial discharge
measurements were particularly sophisticated, as
there were powerful interference signals from
surrounding electro-technical systems already
installed during the testing phase.
After installation, all switchgear stations were
tested for leakage using mobile analysers, unless
this had already been done prior to delivery.
for the sealing elastomer systems to support
zero leakage condition
• Zero emission of gas system (only the
technically inevitable and extremely low gas
losses due to material permeation were
detected in the type tests)
• Low gas emission in the improbable case of an
accidental arc (arc resistance of gas
compartment, low plastics portion, high
recombination capacity of the thermally
decomposed
insulating
gas
sulphur
hexafluoride)
SIGNIFICANCE FOR THE END-OF-LIFE PHASE
The preparations for low-cost and ecologically
justifiable disposal of the switchgear must be made
as early as in the design phase. This step follows
the latest state of disposal technology, in spite of
the expected long service lives of 30 to 40 years.
The use of a maximum recyclable metal portion
provides optimum prerequisites to this effect. The
metal portion of the GMA and WSA switchgear
series amounts to approx. 90 % of the weight, i.e.
a very high portion for an electrotechnical mediumvoltage product.
The remaining portion consists of the insulating
materials duroplastics and increasingly of
recyclable thermoplastics), of elastomers (sealing
materials), and to a very low extent of special
materials and materials such as sulphur
hexafluoride (insulating gas), mineral molecular
sieves (desiccant in the gas compartment) and
ceramics (insulating elements for vacuum
interrupter chambers).
TABLE 3
PICTURE 4
Gasinsulated switchgear
type GMA
The following aspects were taken into
consideration for the operating phase as early as
in the design and engineering stage:
• Zero maintenance in the high-voltage section
of the switchgear; this is ensured due to
systematic enclosure (gas enclosure without
solid insulation)
• Zero maintenance drive mechanisms over a
period of several years, obtained by the
specific lubricant and corrosion protection
systems and by the selection of the metallic
materials
• Use of a chemically stable lubricant system for
the mechanical components, for the movable
and fixed contact areas in the gas section and
Materials for the type
(average weight values)
Steel
Stainless steel
Copper, aluminium, brass
Duroplastics
Thermoplastics
Other (ceramic, gas,
desiccant)
150 kg
70 kg
25 kg
6 kg
7 kg
5 kg
GMA
57 %
27 %
9%
2%
3%
2%
The insulating materials have been designed so
that the absolute plastics content is reduced even
more by reinforcing materials, such as glass fibre.
Moreover, all insulating components, if they are
adjusted for self-extinguishing action, do not
contain any halogen-type flame-retardants.
There are effective recycling concepts and
proposals for all materials. This is particularly
relevant for the insulating gas sulphur hexafluoride
which can be recovered effectively, and is recycled
after regeneration.
To inform customers and disposal companies alike
about the type, quantity and installation condition
of various materials and the individual channels of
disposal, Data Sheets for Materials and Disposal
have been prepared for the various switchgear
models to inform and instruct about handling after
the end of service life.
SUMMARY
The switchgear project performed together with the
operating company demonstrated the great
importance of precise determination of a task
profile, not only as regards the electro-technical
design, but also material and concept selection for
operation under extremely difficult ambient
conditions.
INITIAL OPERATING EXPERIENCE
Due to extensions of GMA switchgear and the
comments made by a customer, initial information
became available after two years about the extent
to which switchgear stations prove their functions
under the difficult ambient conditions described
above. The total period of operation is short
compared with the total service life, but further
long-term forecasts can be made thanks to certain
assessment methods.
Compared to the initial values, no increases of
partial discharge values were found. The perfect
gas tightness of the gas tanks was maintained; gas
measurements did not show any leakage and also
no change in the dew-point of the gas
compartments.
The inspection of the mechanical drives showed
partially loose screws in one panel, coming from
the permanent vibrations of the mining devices. As
a precaution the screws in all panels were
additional fitted by self securing nuts to avoid any
repetition of this.
Further the closing/opening coils were replaced in
the drive area. However, this was due to the fact
that the low-voltage magnets used for
closing/opening were actually designed as
undervoltage releases, and used at an even higher
voltage than the permitted service voltage.
No corrosion on metals was found, nor soiling in
the drive and control section which was due to a
sufficiently dimensioned degree of protection.
Further dates for regular assessment were agreed
upon with the customer, to obtain feedback as to
the extent to which the concept of the two variants
of gas-insulated medium-voltage switchgear
afforded long-term safe operation.
PICTURE 5
Transportation of brown coal to
the power station
When implementing the assembly, testing and
installation conditions defined in the development
stage, the customer disposes of a switchgear
ensuring safe and environmentally responsible
operation. In case of malfunctions (power supply
faults), operating safety and environmentally
compatible behaviour are still ensured.
Disposal of the product is due at the end of every
service phase. Using environmentally friendly
materials and taking account of the aspects of the
future regulations on electrical scrap, the operator
can rest assured that he has an optimally
economical and ecological solution.