Transcript cern.ch\dfs\Users\e\eravaiol\Public\Planning of the

Main dipole circuit simulations
Behavior and performance analysis
PSpice models
Open issues
Test planning
Emmanuele Ravaioli
TE-MPE
December 14th 2010
LHC main dipole circuit
Power converter
Crowbar
Switch2
Filter
Magnets
Switch1
Magnets
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
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Comparison between newQPS data and simulation
RB.A12 31/05/2010 22.08 I_max = 2 kA; dI/dt = -10 A/s; Delay_s1 = 350 ms; Delay_s2 = 600 ms
Power converter
shut down
First
switch opening
Second
switch opening
Power converter
shut down
First
switch opening
Second
switch opening
When the power converter is shut down, voltage waves start running through the circuit due to the filter
installed at the output of the power converter.
In case of a fast power abort, two switches are opened in order to quickly discharge the circuit; this
produces another set of voltage waves.
The complex transients have been successfully simulated by means of a complete model of the circuit,
developed with the Cadence suite (PSpice-based).
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
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Comparison between oldQPS data and simulation
RB.A12 31/05/2010 22.08 I_max = 2 kA; dI/dt = -10 A/s; Delay_s1 = 350 ms; Delay_s2 = 600 ms
Power converter
shut down
First
switch opening
Second
switch opening
Power converter
shut down
First
switch opening
Second
switch opening
The QSO signal shows the difference between the voltage across the two apertures of each magnet.
The model correctly simulates the behavior of the magnets which do not exhibit a singular behavior; as it
will be shortly presented, unfortunately a large number of dipoles behave in an unexpected way during the
transient following the shut down of the power converter.
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
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Comparison between measurement in the PHall and simulation
PHall 02/11/2010 19.31
I_max = 5.9 kA; dI/dt = 0 A/s; Delay_s1 = 340 ms; Snubbers installed
A simplified system (PC + 4 mH load + 1 extraction-system) has been installed in the PowerHall for studying
the behavior of the switches and of the snubber capacitors.
The simulations give good results with respect to the current flowing through the load, and to the voltage
across the PC and the extraction resistor.
The data about the switch opening will be useful for the improvement of the switch model.
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
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Open issues
1.
QSO signals: In each sector, about 60% of the dipoles present an unexpected
behavior: during the PC shut-down, U_QSO reaches values ~5 times larger than
the other magnets and than the values calculated by PSpice simulations.
Analyses showed that there is no correlation between the bad behavior of the
magnets and the electrical or physical position, the magnet manufacturer, the
date of installation.
Additional info: \\cern.ch\dfs\Users\e\eravaiol\Public\Past presentations\Analysis of the QSO signals after PC shut down at different current levels - ver2.ppt
2.
Model of the switch: The new measurements in the PowerHall showed the
necessity of an improved model of the switch.
3.
nQPS signals: The measured frequency of the voltage oscillations across the PC
filter is 28.5Hz, while the measured nominal value is 31.8Hz.
nQPS signals: The dumping of the oscillations in the PC filter is slower than in
the real system.
4.
5.
LHC main quadrupole circuit: Validation of the model by comparison with
measurement data.
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
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Inexplicable behavior of some dipoles
The following plots refer to the same experiment.
They show the QSO signal during the transient after the PC shut-down (no switch
opened so far). On the left image, only the magnets that behave as expected are
plotted; on the right one, the remaining ones are plotted.
From the measurements it is clear that there are two typologies of dipoles – or of
acquisition systems – which exhibit a different behavior.
A set of tests has been foreseen in order to assess this issue.
Magnet 001  Blue
Magnet 154  Red
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
Magnet 001  Blue
Magnet 154  Red
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Planning of the Measurements of Voltage Oscillations after a FPA
Mid-February: Planned tests – FPA triggered by QPS
Ramp at 10 A/s to 1 kA, 2 kA, 3 kA, 4 kA, 5 kA, 6 kA
Flat-top at 1 kA, 2 kA, 4 kA, 6 kA
Planned measurements in Sector 67
Signals
Frequency of acquisition
Voltage range
V_OUT of PC
U1 and U2 of magnet MB.A9R6
U1 and U2 of magnet MB.B9R6
U1 and U2 of magnet MB.A10R6
U1 and U2 of magnet MB.A11R6
U_RES switch pt6
U_RES switch pt7
500 kS/s
125 kS/s
125 kS/s
125 kS/s
125 kS/s
500 kS/s
1.25 MS/s
-160 V – +160 V
-10 V – +5 V
-10 V – +5 V
-10 V – +5 V
-10 V – +5 V
+0 V – +900 V
+0 V – +900 V
Safety issues
• The full commissioning of the circuit up to 6 kA and an ElQA test are required before the
tests. It is therefore important to install the equipment before the ElQA test already
planned for the circuit.
• No ElQA test is required after the measurements (Nuria Catalan confirms).
• All the equipment will be fully tested for 1.9 kV before the installation in the tunnel
because it will have to sustain the ElQA test.
Additional info: \\cern.ch\dfs\Users\e\eravaiol\Public\Planning of the measurements in the tunnel during Christmas stop 2010-2011\Measurements of Voltage
Oscillations after Fast Power Abort in Sector 67 during the Christmas stop 2010-11.ppt
Emmanuele Ravaioli - MPE Workshop - December 14th 2010
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