Download EEreviewSector45-Knud

Essential lessons from commissioning of the 28 EE systems of
LHC sector 45
600 A corrector circuits
Magnet
type
Number of L per
magnets in magnet / L per
Circuit names circuit aperture circuit
[mH]
[mH]
I
Energy in
Number Energy in the circuit
Theoretically
of the circuit
at
Energy at I to Energy to
circuits at I I_ultimate Rextraction
Rextraction
[A]
[kJ]
[kJ]
[kJ]
Max. ramp Quench R parallel
rate
Back
(Rp)
Req circuit
t
t
[kJ]
[s]
[s]
10
10
[A/s]
Yes/no
[mOhm]
[mOhm]
80
1E+13
662
700
MCS
MCD
RCS
RCD
154
77
0.8
0.4
123.2
30.8
550
550
16
16
18.6
4.7
22.2
5.5
17.6
4.7
21.0
5.5
corrected
0.18 0.186
0.04 0.044
MO
MO
ROD, ROF
ROD, ROF
8
13
1.5
1.5
12
19.5
550
200
16
16
1.8
0.4
2.2
3.5
1.8
0.4
2.2
3.5
0.02
0.03
0.017
0.028
0.5
0.5
yes
yes
1E+13
1E+13
700
700
MQT (MQS) RQS
MQT
RQTF, RQTD
4
8
31
31
124
248
550
550
8
32
18.8
37.5
22.3
44.6
11.0
27.8
13.1
33.0
0.18
0.35
0.301
0.478
0.5
0.5
yes
yes
250
250
412
519
MQTL
MQTL
RQTL9
RQ6
2
6
120
120
240
720
550
450
8
8
36.3
72.9
43.2
86.4
13.2
46.0
15.7
54.6
0.34
1.03
0.943
1.629
0.5
0.5
yes
yes
200
200
255
442
MS (MSS)
MS
MS
MU*
RSS
RSF1, RSF2
RSD1, RSD2
RU.R4 - L4
4
10
12
1
36
36
36
1200
144
360
432
1200
550
550
550
450
16
32
32
2
21.8
54.5
65.3
121.5
25.9
64.8
77.8
150.0
10.1
37.1
47.0
32.0
12.0
44.2
56.0
39.5
0.21
0.51
0.62
1.71
0.446
0.754
0.857
6.514
0.5
0.5
0.5
0.5
yes
yes
yes
150
150
150
250
323
477
504
184
600 A EE –sector 45
• No non-conformities were detected on any system. The performance of
all facilities met the specifications.
Only a minor problem was discovered at the level of the acquisition of
certain voltage signals. Reason: Inadequate filter parameters (not fast
enough (5 ms), will be reduced to 0.5 ms for the next sector test).
• Tunnel measurements (routine tests for verifying the correct
performance of the switches) were performed
-at PLI3.b1 (200A) for all circuits, with a few exceptions
-at PNO.b1 (550A) on three RCD circuits.
• The measurements on the equipment are vital for the evaluation of the
long term stability of the switch-gear as they will confirm the correct
operation of the commutation assistance and the arc suppression. This
information is not obtained through the P.M.
• The system can only be released for operation after approval of this
step.
600 A EE –sector 45
•
However, the measurements can be simplified and rationalized:
•
•
•
•
•
Only performed at a single current level (Inom, better signal-to-noise ratio,
not required for approval of the commissioning steps)
Grouped so to cover all concerned circuits of a powering sub-sector
Presence in tunnel only required to change instrumentation between
circuits. Remote controlled oscilloscopes are used.
Expected rate: 10 circuits/hour (3 hours total for a sector).
Grouped closing of switches for commissioning of next sectors:
•
•
The requirement has been defined by MEI/pe and a Macro-routine is
presently being prepared for sector 5/6 by AB/CO.
A sequential procedure is required in order to avoid simultaneous current
rush from UPS (closing of extraction breakers is by motor-drive, typically
40 A / system for 300 ms. Time between two circuit closings: 5 seconds.
13 kA EE –sector 45
•
Three incidents occurred during the commissioning, fortunately
without compromising the protection of the circuits:
1.
Routine measurements of switch opening times allowed the detection at
low current of the absence of the fast release on one of the 32 extraction
switches (RB, UA47).
Reason: A solder was forgotten in the pulsed power line inside the
breaker! Repaired in-situ.
2.
The DQRQF extraction resistor showed too low resistance (2.4 mΩ
instead of 6.6 mΩ). The unit was replaced (7 hours of hard work,
acknowledgment of highly appreciated assistance by TS/HE and TS/CV).
Reason: Short-circuit between two resistor packages, caused during road
transport (vibration), but clearly having its origin in poor manufacturing
quality and/or insufficient quality assurance at the manufacturer (wrong
type (or missing ?) insulating spacers between packages and supports cut
too short, allowing displacement during transport).
Repair is ongoing (not complicated).
All other DQR’s have been checked and found correct.
So, it looks like a single event.
13 kA EE –sector 45 (contd)
3.
-A spurious trigger occurred in the back-up system, which is
implemented for the case that an opening command to the extraction
switches is not being executed. This scheme consists of the firing of a
pre-selected set of quench heaters (61 dipoles per EE and 13 quads per
QF/QD circuit) so to get the same time constants as for normal extraction.
-The incident occurred during preparations for the replacement of the
DQRQF resistor unit, at the moment where the UPS power line
(‘Normabar’ distribution panel) was moved, probably causing a short
supply interruption.
-Although the event happened under unusual circumstances, an
interruption of the UPS line cannot be excluded and the back-up system
must be insensitive to such a (rare) event.
-The heater firing had no real consequences as there was no circuit
current. However one single quench detector triggered – sign that
quenching of persistent currents was sufficiently asymmetric to be
detected?
-A spurious firing of the pre-selected quench heaters during a fast
discharge may lead to a FULL SECTOR QUENCH as the local quench
detectors of the non-quenching magnets are likely to trigger due to large
dI/dt. This may even lead to dangerous reverse voltages across the
diodes.
13 kA EE –sector 45 (contd)
-It was decided to continue commissioning without the back-up
system, based on the arguments, that
-the introduction of the back-up scheme was decided in 2003, when no real
experience with the extraction switches was available. Reliability calculations
showed a probability to suffer an SOF failure of between 0.03 and 3.7 % during
20 years of operation. It was based on poor statistics from the Russian
manufacturer.
-Since then 20 switches of the series have individually been subjected to
endurance tests (exceeding 88 kc total). Not a single failure has been
observed.
-The complete DQS switch array has a 4-fold redundancy of the release
system (two breakers in series, two independent opening features).
-It has been possible to reproduce the false trigger. It occurs when
the UPS power is re-established to the Interface Module after the
end of the autonomy (15 sec) of the local energy reserves of the
controls crate.
Although equipped with the necessary pull-ups one (or more) of the
signals to the FlashEPROMS has a wrong state.
13 kA EE –sector 45 (contd)
• Solutions:
– In addition to preventing the false state of the incriminated signal(s) we
shall consider a reduction of the number of heaters to be fired during an
SOF.
The present situation is very conservative (see next slide).
As an example, an increase in the discharge time constant from 104 s
to 170 s would allow a reduction from 61 to typically 32 magnets to be
quenched, while the diode busbar temperature would still remain
acceptable.
However, before proposing this solution, detailed calculations must be
made taking into account contributions from the bb contact resistance
and the quench margin must be carefully evaluated.
Until then, we suggest to continue without the back-up system activated
(very easily disconnected).
Maximum component temperatures as function of discharge
time constant