1. Measurements of Voltage Oscillations after a Fast Power Abort in Sector 67 during the Christmas stop
Emmanuele Ravaioli – TE/MPE
Thanks to A. Verweij, F. Formenti
24 November 2010

2. Main goals of the measurements
Understanding the behavior of the circuit during the power-converter shut down, with particular attention to the oscillations of the aperture voltages, and their difference.
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.
Assessing the voltage across the switches (after the installation of the snubber capacitor).
The proposed measurements are required because the oldQPS and newQPS have a sampling frequency that is too low (200 Hz and ~1 kHz) to properly analyse the transitory.
It is important to understand the unexpected behavior of U_QSO, since this issue concerns about 60% of the magnets and the analysis of the present data shows that it is not related with the electrical or physical position of the magnets, nor with the magnet and cable manufacturers, nor with the chronology of installation.
Emmanuele Ravaioli

3. Scheme of the measurement system
Point 6
Arc 67
Point 7
25 m
40 m
0.3 km
2.7 km
SW8 PC A A A A A A
SW1
3 Crates hosting
2x3 Isolation amplifiers
AD210
Differential Probes
Differential Probe
:100
:100
:100
Card
NI USB-6251-BNC
Card
NI USB-6251-BNC
Card
NI USB-6251-BNC
1 MS/s
1 MS/s
1 MS/s
USB
USB
USB PC PC PC
Wi-Fi
Wi-Fi
Wi-Fi
Isolation
Transformer
Isolation
Transformer
Isolation
Transformer
VDSL
VDSL
VDSL
Wi-Fi
Wi-Fi
Wi-Fi

4. Safety issues
No magnet will be touched; the measurements will be performed accessing to the QPS cabling (only QPS & ElQA experts will touch the cabling).
The NI card measuring the magnets will be isolated from the magnets themselves by means of insulator amplifiers.
Fuses have been installed in the magnet patches, to protect the IFX cable in case of a short circuit inside the patch.
The three measurement systems will be fully floating; this will be assured by insulator transformers.
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 (after January 20th ?).
No ElQA test is required after the measurements (Nuria Catalan confirms), provided the items are uninstalled with the proper carefulness.
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.
Emmanuele Ravaioli

5. Status Persons involved
All the required material is already available.
In the past weeks, the material has been tested:
Patches for connection to the QPS cables of the magnets (fuses added to improve safety)
NI Cards
Insulator amplifiers & Crates
Wi-Fi modules (tested in the tunnel)
Yesterday (17 November 2010) the first test of acquisition with the software-based triggering have been successfully performed.
A full test of the acquisition system is foreseen in the PowerHall after the campaign for the snubber qualification.
Persons involved
System architecture: E. Ravaioli; G. J. Coelingh; A. Rijllart
Hardware preparation & testing: E. Ravaioli; F. Formenti; Fabienne Boisier; Gaelle Dib
Installation in the tunnel: E. Ravaioli; Mathieu Favre
Software: Odd Oyvind Andreassen
Other contributions: F. Formenti; K. Dahlerup-Petersen; N. Catalan Lasheras; B. Panev; R. Denz;
G. D’Angelo; H. Thiesen; M. Solfaroli; A. Verweij
Emmanuele Ravaioli

6. Frequency of acquisition
Planned measurements
Signal:
Triggering
Time frame
( t=0 at triggering)
Frequency of acquisition
Voltage range
Vout of PC
Software
0 s – 5 s
500 kS/s
-160 V – V
U1 and U2 of magnet MB.B9R6
150 kS/s
-10 V – +5 V
U1 and U2 of magnet MB.A10R6
U1 and U2 of magnet MB.A11R6
U_RES switch pt6
+0 V – V
U_RES switch pt7
1.25 MS/s
Assembly name
Top assembly name
Electrical numbering
Distance from IP6
Relative distance
MB.B9R6
LBBRS.9R6
# 153
331.97
~ 25 m from MB.B10R6
MB.A10R6
LBARL.10R6
# 3
MB.A11R6
LBARA.11R6
# 4
395.84
~ 39 m from MB.B10R6
Emmanuele Ravaioli

7. Planned tests
A set of tests are planned in Sector 67 in order to clarify the odd behavior observed in some of the main dipoles.
(Additional info: Analysis of the QSO signals after PC shut down at different current levels - ver2 )
At least four tests will be launched; in each test, the current of the RB circuit will be raised with a dI/dt = 10 A/s. When I_max is reached (while the current is still raising), the power converter will be shut down (triggered by the QPS); after 350 ms, the first switch (pt7, middle of the chain) will be opened; after another 250 ms, the second switch (pt6, close to the power converter) will be opened as well.
The values of I_max in the four tests are: 1 kA, 2 kA, 4 kA, 6 kA (actually a bit below 6 kA, because the PC slows down at the end of the ramp).
If there is sufficient time possibly also tests with I_max = 3 kA and 5 kA can be performed. Another set of tests with dI/dt = 0 A/s (no ramping up) would also be interesting, at the same current levels. NB: Every test above 2 kA requires a sensible time due to the cooling down of the switches.
(Additional info: \\cern.ch\dfs\Users\e\eravaiol\Public\Planning of the measurements in the tunnel during Christmas stop \ )
Emmanuele Ravaioli

8. Emmanuele Ravaioli - TE-MPE
Schedule of the tests
Activities
Time
Comment
Test of the equipment items
Oct-Nov 2010
NI cards, isolation amplifiers, Wi-Fi modules, …
Test of the acquisition software
Nov 2010
Installation and testing of the equipment in the PowerHall
Dec 2010
After snubber campaign is finished
Installation of the equipment in Sector 67
after 7 Jan 2011
Before commissioning and ElQA!
Testing of the equipment in Sector 67
Acquisition of the signals from a power supply
Commissioning up to 6 kA and ElQA test of the circuit
after 20 Jan 2011
Tests from the Control Room
During the night
Tests to be performed (FPA via QPS)
Duration
First check test (Ramp to 1kA, 10 A/s)
15 min
Test + PM buffer receiving
Preliminary data analysis (to check every signal is fine)
30 min
(NI cards, oldQPS, newQPS)
Ramp to 2 kA, 10 A/s
Ramp to 4 kA, 10 A/s
1 h
Test + PM buffer receiving + Switch cooling
Ramp to 6 kA, 10 A/s
1.5 h
Ramp to 3 kA, 10 A/s
45 min
Ramp to 5 kA, 10 A/s
1.25 h
Ramp to 1 kA, 0 A/s
Ramp to 2 kA, 0 A/s
 Test + PM buffer receiving
Ramp to 4 kA, 0 A/s
Ramp to 6 kA, 0 A/s
Total time
9 h
Emmanuele Ravaioli - TE-MPE

9. Annex
Emmanuele Ravaioli

10. Magnet choice
The three magnets have been selected based on the behavior they showed during past tests:
Magnets 3 and 153 showed a U_QSO signal during the PC shut-down transitory at 2 kA bigger than that at 6 kA.
Magnet 4 showed a regular behavior, but has been selected to highlight the difference as compared to the other two magnets.
Besides, the three magnets are physically close each other, and this will simplify the operations and reduce the number of the required insulator transformers.
Emmanuele Ravaioli

11. Presentation of the issue (1)
Since the oscillations in the QSO signals (difference between voltage across the apertures of each magnet) are caused by a voltage wave travelling throughout the magnet string, one would expect that larger voltage waves cause larger QSO signals.
On the contrary, during the PC shut down (before switch openings), some magnets present bigger values of the QSO signal at lower current (2 kA), when the voltage wave is slightly smaller.
Magnet 001  Blue
Magnet 154  Red
Magnet 001  Blue
Magnet 154  Red
Emmanuele Ravaioli

12. Presentation of the issue (2)
Looking closer to the results, one can notice that not every magnet of the string exhibits the same behavior: about half of the magnets show a smaller QSO signal at 2 kA, as one would expect, while the other half presents values 5-6 times larger.
In the plots below one can observe the measurements of the same experiment shown in the previous slide: on the left only the normally-behaving magnets have been plotted; no the right only the oddly-behaving ones.
Magnet 001  Blue
Magnet 154  Red
Magnet 001  Blue
Magnet 154  Red
Emmanuele Ravaioli

13. Max QSO before switch opening – 2 kA
The PSpice model simulates well only the behavior of the ‘normal magnets’
Emmanuele Ravaioli

14. Max QSO before switch opening – 6 kA
The PSpice model simulates well only the behavior of the ‘normal magnets’
Emmanuele Ravaioli