SNS Modulator Fires; Causes, Mitigation, and Long-Term Plans David E. Anderson.
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Transcript of SNS Modulator Fires; Causes, Mitigation, and Long-Term Plans David E. Anderson.
SNS Modulator Fires; Causes, Mitigation, and Long-Term Plans
David E. Anderson
2 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Simplified Block Diagram
IGBT SWITCH PLATE ASS'Y. (3X)
SAFETY ENCLOSURE
B PHASE SHOWN
CRes
CRes
CRes
A
B
C
5th Harmonic Trap 7th Harmonic Trap
13.8 kV : 2100 Vdelta wye
50 mH
OUTSIDE FILTERS AND TRANSFORMER
1.5 MVA
FUSEDDISCONNECT
BUILDINGINTERFACE
Fuse / Contactor
4 mH450 A
4 mH450 A
SCR CONTROLLER
+/-1300 V, 450 A
DC+
DC-
DC+
DC-
0.112 F
0.112 F
40X RG-8
40X RG-8
RdeQ
2X 0.03 uF500 pF
HV divider
CT
OIL-FILLED MODULATOR TANK
CONTROLRACK &
CONTROLLER
CAP RACK
3 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Major Subsystems
4 Managed by UT-Battellefor the U.S. Department of Energy
Cavity/Klystron/Modulator Layout
• Multiple HVCM/Klystron Configurations
• Peak Power 11 MW, Average Power 1 MW design
115 kV125 kV
≤135 kV ≤75 kV 75 kV
5 Managed by UT-Battellefor the U.S. Department of Energy
HVCM “Smoke Generating” EventsHVCM Events by Year
9
41
20
2007
2008
2009
HVCM Events by Unit
0123456789
10111213
CC
L-1
CC
L-2
CC
L-3
CC
L-4
RFQ
-DTL
-1
DTL
-3
DTL
-5
SC
L-1
SC
L-5
SC
L-9
SC
L-12
SC
L-14
SC
L-15
SC
L-18
SC
L-21
RF-
Test
Unit
Num
ber o
f Eve
nts
70 Total Events1 during last production run
Most do not result in fires but response is consistent until incident evaluated
6 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Fire Causes – Bus Arcing• 1st fire, none since, in RF Test Facility• Workmanship or residual dirt believed responsible• Repeated arcing acted as ignition source for combustibles• Corrected with improved training of assemblers, no faults w/ same root
cause since (Jan 07)
7 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Fire Causes – Insulation Degradation• Cause of 2 fires and likely many of the IGBT failures• Original design relies on single layer of DMD to insulate cooling tubes from
different polarity bus• Interference fit between tube and bus compresses DMD and can cut material
if sharp edges present• Corona degrades insulation over time, resulting in arc event• Insulation double, short-term sol’n., cutout long-term
8 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Fire Causes – Capacitors• Mfgr.’s cap lifetime ratings 100,000 hours @ 3000 V, Expanded the lifetime on the
spec. to 1 million hours
• Experience indicates 10-15 khours @ ≤ 2300 V
• Replaced all warm linac caps w/ higher lifetime spec caps
• Replacing all other caps with new caps, starting to see failures of RSO units
9 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Capacitor ComparisonDielectric Fluid Dissipation Factor
0
0.001
0.002
0.003
0.004
0.005
0.006
10 100 1000 10000 100000
frequency, Hz
Diss
ipat
ion
Fact
or
DF IPB1DF IPB2DF RSODF SODF BTDP
Capacitor Type
Oper. Temp. Range
IPB 100-120°FBTDP small 140-150°FBTDP large 135-160°FRSO 100-120°FSolid Potted <100°F
• IPB no longer available, original batch of capacitors as delivered• Others tried
– Reconstituted mica, failed in tens of minutes– Another manufacturer’s RSO, failed in 18 hours
IPB Isopropyl BiphenylBTDP Benzyltoluene DiphenylethaneRSO Rapeseed Oil
10 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Fire Causes – IGBTs
• Usually less severe, lower collateral damage
• At transition to 60 Hz operation, incidents increased significantly
• Improved thermal bonding procedures implemented
• Overvoltage problem solved, minimal problems since
11 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Fire Mitigation – CO2 Suppression• Dedicated CO2 system installed• Smoke detector installed• EPICS screens updated• Manual discharge from CCR if smoke
detector trips• Prevent or minimize system damage
12 Managed by UT-Battellefor the U.S. Department of Energy
HVCM Fire Mitigation – Additional
• Over Current detection on energy storage capacitor bank to limit fault energy
• Retraining workers / rewriting procedures for operators• Implement Alarm Handler for smoke detector events• Installing shrapnel shields around capacitors to minimize collateral
damage• Emergency Off modified to remove 2100 V primary energy source
automatically• Replace combustible materials inside Enclosure with UL-94 V0 rated
plastics (G9 Phenolic)• Replace cables with plenum-rated cables• Design new IGBT drive circuitry to shut IGBTs off if over current detected
13 Managed by UT-Battellefor the U.S. Department of Energy
Future Capacitor Replacement
IC
VCE
VC
RSO Plastic Case Self-Clearing Metallized Polypropylene
• Ran capacitors until July shutdown• Assess self-clearing capacitor degradation• Simulate 10 years of faults on preferred capacitor• Choose and order capacitor selected• Install when delivered during 1st FY10 Extended Shutdown Period
14 Managed by UT-Battellefor the U.S. Department of Energy
Future “Series Switch”
IC
VCE
VC
• Decouples primary energy storage when fault detected• Minimizes energy delivered to fault, prevents collateral damage• Can be used to add a future redundant H-bridge
15 Managed by UT-Battellefor the U.S. Department of Energy
Capacitor / IGBT Preventative Maintenance
IC
VCE
VC
• Liquid dielectric– Monitor case temperature– Inspect periodically for leakage– Inspect for case dimensions out of tolerance– Return suspect units to manufacturer for analysis and design improvements
• Solid potted self-clearing– All of above– Periodically measure capacitance value and replace when 5% degradation occurs
• IGBTs– Monitor for changes in
• Turn on time• Turn on delay• Turn off time• Turn off delay• Gate characteristics• Monitor substrate temperature with thermal interlocks
All monitored via transformer flux monitoring system
Periodically monitored during shutdowns
16 Managed by UT-Battellefor the U.S. Department of Energy
ORPS Reporting• ORPS reporting threshold is the activation of an automatic fire suppression
system but NOT a manually-actuated or detection system– No automatic suppression employed
– Building central detection system (VESDA) rarely detects HVCM events
– ORPS considers burn times > 5 minutes significant
– No HVCM event has passed the reporting threshold
– All events have been contained inside the aluminum / stainless steel Safety Enclosure
• UT/Battelle and DOE ORO periodically review the HVCM smoke event history through self-assessment and oversight activities
17 Managed by UT-Battellefor the U.S. Department of Energy
Conclusion• Many “smoke generating” events to date, none severe
• Engineering and procedural controls and protection systems put in place
• Nature of component failures believed to be well understood, PM and component replacement underway to address
• Additional protection systems in design to further enhance system availability
• Hopeful that these event can be significantly reduced in the future
QUESTIONS?