Asynchronous Startup of a Salient Pole Synchronous Generator
A View on Operas Conductors (and other Features)
VF EUGM 2015, Dr. G. Maier
Contents
 Pumped Storage plants – topologies
 Impact of Asynchronous Startup on machine design
 FE Model Features
 FE Model Symmetry
 Circuits
 Controlling via motion.comi
 Further features to include in circuits
 Results
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Pumped Storage - Topologies
One question is: How to bring up the pump to synchronous speed
… by hydraulic means
T
MG
MG
HC
C
P
FC
PM
CL
MG
MG
MG
MG
PT
PT
PT
PT
Asyn Startup
T
… by electrical means
ST
ST
P
Only a few illustrational examples shown. No claim of completeness.
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MG
C
HC
T
P
PT
ST
FC
PM
CL
Motor – Generator
Clutch
Hydraulic converter
Turbine
Pump
Pump-Turbine
Starting turbine
Frequency converter
Pony motor
Current limiter
Pumped Storage – Topologies II
Shown arrangements differ by
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
Operational flexibility
 power change rate / switch over time (approx. 40 … 700s)
 Necessity of pump dewatering
 Necessity of standstill between turbine and pump operation
 Controllability of pump power

Complexity of the plant
 Number of hydraulic & electric machines and their necessary rating
 Power electronics involved
 Waterway
 Arrangement, size & complexity of surge tanks

Shaft length
 Building volume / excavation volume

Cost
Examples for pumped storage
with asynchronous startup:
 La Rance (Tidal, France)
 Lower Olt (Romania)
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Interesting. But what does
this have to do with Opera?
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Interesting. But what does
this have to do with Opera?
Asynchronous startup can yield
a rather simple arrangement, but possesses an
untypical loading of a salient pole machines damper.
E/M engineers will have to do FE.
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Impact of Asynchronous Startup on machine design
 Asynchronous startup – especially under mechanic load – causes a high load for the
damper winding
 Typical items of interest (for the electric engineer)

Startup time
 Damper bar currents
 Damper bar temperatures (considering skin effect)
 Grid disturbances (flicker, voltage dip)
 Further on for the mechanical engineer


Thermally induced stresses and
Deformations
Possible „screws“ to achieve the
desired performance are e.g. stator
winding, pole shoe contour, damper
slot geometry, damper materials,
damper bar distribution on the pole
shoe,…
in all parts of the damper system
 Today, FE is the typically chosen tool

Time to calculate: 10 … (60s) … 120s depending on topology and conditions
 Therefore there’s a strong need to keep it 2D.
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FE Model Features
Stator laminations
Stator bars (filamentary)
Pole shoe
Opera circuits including external
elements for:
 Stator winding (connected to grid)
 Field winding
 Damper winding
Damper winding (eddy current)
Field winding
(filamentary or eddy current)
Pole body
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FE Model Symmetry
 Long “time to solve” needs a fast and efficient model.
 To limit the necessary number of poles in the FE model, substituting a fractional
slot stator winding by a integer slot one can be considered.

It has to be noted, that effects connected to the stator winding scheme (e.g. pull up torques)
will appear differently in the model than in reality. If these are of interest, a model using the
exact representation of the stator winding has to be used.
 For integer slot stator windings one pole in
the FE model is sufficient, although the
circuit connections across the (negative)
symmetry boundary have to be set up with
special care.

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Verification especially of the damper circuits
against a model comprising 2 poles is
recommended.
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Damper Circuits
Elements representing
the bar to bar
connections of both
sides
Portion of the bars
outside the 2D model
Negative
symmetry
connection
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1
2
3
4
5
6
Circuits as entered in
Opera
Opera conductors
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Damper Circuits
Elements representing
the bar to bar
connections of both
sides
Portion of the bars
outside the 2D model
Negative
symmetry
connection
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1
2
3
4
5
6
Circuits as entered in
Opera
Opera conductors
Short circuit of one conductor
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Damper Circuits II
 But: The short circuit of bar 1 cannot be observed in the results.

All bars show reasonable current amplitudes
 Phase shift between bar currents is as expected
 Open circuit bar voltages (ring with very high resistivity) show a similar image. No bar stands
out of the crowd, phase shifts as expected.
0
0
What‘s wrong?!
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Damper Circuits III
Elements representing
the bar to bar
connections of one
side
Negative
symmetry
connection
 This schematic does not have one bar shorted.
 Calculated results can be explained
is 3different to4 the one 5
6  But:
1 The schematic
2
entered in Operas circuits!
Portion of the bars
outside the 2D model
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Opera conductors
Circuits as entered in
Opera
Elements representing
the bar to bar
connections of one
side
Be careful when translating Operas circuits into schematics
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Motion.comi
 For analyzing synchronous salient pole machines we use a home „grown“ pre- and post
processor for




Building the model
Setting up & controlling the analysis
Post processing & setting up the next simulation
Evaluating the results & report generation
 For easiest integration of some „special features“ of the built up asynchronous startup
models in the above environment, it would have been beneficial to have some basic result
evaluations available right at the end of the simulation.
COOL!
 Motion.comi is a comi getting called at every time step

Intended for calculating #accel for mechanically coupled models (e.g. motor – shaft – load)
 During my studies it turned out to be a bit like a
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?
(of course full of
)
Motion.comi II
 Motion.comi behaviour the user might not expect

Gets called several times before the solver calculates timestep 1
Section from .res file
...
Unlabelled and Default Drives will use:
DEFAULT: DC drive
Called at the very beginning of the run (when the
model / circuit data is set up)
Running command file
motion.comi called
Value of ttime: 0.0
motion.comi called
Value of ttime: 0.0
Warning: Variable #ACCEL has not been defined in the comi file. Using value from simple coupling.
Warning: Variable #ACCEL2 has not been defined in the comi file. Using zero.
Number of nodes = 11033, number of elements= 8314
Number of fixed Potential nodes = 28
Motion.comi:
$displayline 'motion.comi called‘
$displayline 'Value of ttime: %REAL(ttime)'
...
Checking Circuit data:
No errors found.
CIRCUIT DATA USED FOR THIS SOLUTION
Circuit 1:...
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Motion.comi III

Section from .res file
Might get called multiple times during one timestep
 Can get called with ttime not monotonic ascending (e.g. adaptive timestepping)
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...
Converged in 1 iterations to 5.0E-05 (Mu change=2.33882E-16)
motion.comi called
Value of ttime: 7.08339E-03
motion.comi called
Value of ttime: 6.66672E-03
motion.comi called
Value of ttime: 6.80561E-03
motion.comi called
Value of ttime: 6.80561E-03
motion.comi called
Value of ttime: 6.875055E-03
motion.comi called
Value of ttime: 7.08339E-03
motion.comi called
Value of ttime: 7.08339E-03
motion.comi called
Value of ttime: 6.66672E-03
motion.comi called
Value of ttime: 6.80561E-03
motion.comi called
Value of ttime: 6.80561E-03
motion.comi called
Value of ttime: 6.875055E-03
motion.comi called
Value of ttime: 7.08339E-03
motion.comi called
Value of ttime: 7.08339E-03
Converged in 1 iterations to 5.0E-05 (Mu change=2.33882E-16)
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Motion.comi:
$displayline 'motion.comi called‘
$displayline 'Value of ttime: %REAL(ttime)'
...
Motion.comi IV

Section from .res file
Loops might show unexpected behaviour
 Variables can get reset
Motion.comi:
$displayline 'motion.comi called‘
...
$displayline 'Value of ttime: %REAL(ttime)'
motion.comi called
...
Value of ttime: 8.3334E-03
$if ((#tmax-0)*#dt+#t0-ttime)<=1E-6
Opening file for reading: test.txt
$if #p_berechnet EQ 0
25 items read from file
$ open 8 test.txt read
Value of #p_ber: 0.0
$ read 8 -print
Value of #Rt #Rid4: 4.1667E-04 4.349108E-07
...
$cons #loop 1
Value of #Rt #Rid4: 8.3334E-03 2.582376E-05
Value of #p_ber: 0.0
$ errorhandler no
Command file error 150 at line 47.
$while #loop
$ end while
$displayline 'Value of #p_ber: %REAL(#p_berechnet)'
BreakError: control exited a loop
$ read 8 #Rt #Rid4 ... -print
File closed
$ breakerror
Value of #p_ber: 1.0
$displayline 'Value of #Rt #Rid4: %REAL(#Rt) %REAL(#Rid4)'
...
$ end while
motion.comi called
$ errorhandler yes
Value of ttime: 8.3334E-03
/
Converged in 1 iterations to 5.0E-05 (Mu change=2.24243E-16)
$ close 8
...
$displayline 'File closed'
motion.comi called
$cons #p_berechnet 1
Value of ttime: 8.3334E-03
$displayline 'Value of #p_ber: %REAL(#p_berechnet)'
Opening file for reading: test.txt
P_berechnet got reset!
$end if
25 items read from file
(permitting execution of the rest)
$end if
Value of #p_ber: 0.0
Value of #Rt #Rid4: 4.1667E-04 4.349108E-07
File closed
Value of #p_ber: 1.0
...
Loop reading the file gets executed only once!
(only first line; no breakerror)
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Motion comi – (my) conclusion
 When using motion.comi for anything „off label“ (for the „on label“ use see the
2D reference)

Use $displayline command in motion.comi for validation of correct execution + debugging
(especially loops + if-clauses)
 Study the .res file carefully
 Do not use code, that relies on monotonic ascending ttime or a defined call sequence of the
motion.comi
 Judge results critically and carefully
 In this case, simulations finally had to be done +/- completely outside of our
processing environment. New comi file for controlling simulation setup,
postprocessing, result evaluation + restarts. Motion.comi used only to a very
minor extent.
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Further features – saturable reactors in circuits
 Saturable reactors change their value typically depending on the current.
 Opera permits functional inductances and capacitances in circuits.

Different from resistors, the actual value used is only updated at restarts (NOT every timestep /
substep)
 Further on, trying to find, what value has actually been used ( debugging), yields different
results, depending on where you look.
 „Edit circuit“ shows the name of the function
 „List circuit“ shows a value (in henry), but this is updated according to the function
 Consulting the “CIRCUIT DATA” section of the .res file seems most reliable.
 The saturation characteristic to be used for the reactor needs to take into account the way the
inductance value will be computed (e.g using peak current data or using rms current data);
Nevertheless, it will be a +/- severe (depending on the application) simplification.
 A more accurate possibility would be the inclusion via functional drives, although
at the price of a higher complexity ( debugging)

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$para #u +/-L(#some_current) * some_didt
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check the sign;
equation to use has to follow the circuit topology
Results
 (Simple) Thermal model in the control routine
 Functional conductivity of the damper bars

Taking the temperature calculated at the end of the previous run
 Changing skin effect with changing conductivity considered
 Especially interesting for materials with (comparatively) high TC
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Any Questions?
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