# Presentation: 299345

## LARG LV Power Supplies (1)

- DC-DC converters close to the calorimeter
- 58 PS to be installed on detector
- 280V DC input / 4.5 kW per box
- Radiation tolerant. N+1 Redundancy scheme
- Several problems during the production in early 2006
- Weak components
- Thermal problems
- Poor contact in current return
- Problems assumed to be solved at the end of spring 2006
- Reliability was still a concern and one LVPS was put on long-term burn-in early March
- ... and it failed early July 2006

## LARG LV Power Supplies (2)

- Production continued but:
- Delivery from the manufacturer never reached the rate was planned (lots of rework on PS modules at the factory)
- Failure rate during production tests in BNL has always been critically  high
- Of the 50 produced and delivered (end of Dec. 06) ~40% passed acceptance tests @BNL and have been shipped to CERN
- Only 14 currently installed on the barrel EM calorimeter are being commissioned
- Some of the 14 have accumulated >60 days @ full load
- ... started failing one after the others...
- As of today it has been clear that the reliability of these LVPS would have not allowed operation of the detector’s readout for an extended period of time
- A new strategy has been defined and implemented (Oct 06)
- Setup of a task-force for a complete circuit and failure analysis with the goal to define changes to be retrofitted on the LVPS modules and ultimately guarantee mid-term (~next 2 years) needs of LArg before a possible replacement may become available
- Develop a concurrent backup plan for the long term

## LARG LV Power Supplies (3)

- Large-scale investigative effort (based at BNL):
- Task-force : 6 EE, 3 Phy, 1 PE, 1 ME Designer, 4 Techs
- Essential contribution from Atlas LARG collaboration (LAL)
- Good support by BNL and US-Atlas management
- Full Reverse Engineering of the LVPS through an external company
- External consultants (top level PS eng.) “hired” to complement task-force activities: math modeling, SPICE simulation, failure analysis, WCA, FMECA and reliability prediction. Also redesign of parts to address some of the issues
- Lots of findings in the last several months. Analysis completed end of Feb (longer than anticipated!!!).
- Bottom line: *Architecture of the converters is relatively simple (forward topology and passive sharing by current drooping). However many deficiencies have been discovered (and still are being investigated) in the implementation of the circuit mainly due to a superficial analysis of the design, of the layout and of the assembly...*
- Findings and issues can be categorized as (in several cases issues are inter-related):
- Mechanical
- Workmanship
- Thermal
- Component Stress
- Tolerances and Design flaws

## LARG LV Power Supplies (4)

- Converter design undergoing through  deep changes:
- Magnetic redesigned at large extent (output filter inductors, transformers for the 11V)
- Switching frequency
- Both current and voltage feedback loops
- Current limiting circuit
- Over-voltage protection and inhibit circuitry
- Mechanical assembly and integration in the unit
- Thermal management corrections
- The Task-force has evaluated each of the issues detected by the analysis and simulation
- Troubleshooting of failed units confirmed most of the issues found
- About 30 components/module are being changed
- 27 modules/unit ---> ~900 components to be changed in each unit
- Huge rework campaign started in March.
- Demanding a High Profile Assembly House
- Significant manpower and resources (both professionals and engineers)
- Tech certification (IPC-A-610D class III, J-STD-001C)
- In-house testing infrastructures and test-design capability
- Excellent QA/QC (ISO-9001 certification)
- To meet Atlas installation schedule high throughput required (>5/week) with provisions of at least 10/week processing capability

## LARG LV Power Supplies (5)

- A Source Selection Committee was set-up end of December to identify such a possible Assembly House
- The bidding phase has been completed early January
- The selection process has been completed end of Jan. The Selection process rated  the  technical proposals submitted by the vendors, references from recent past projects and field-visits
- Meanwhile all the units still at the manufacturer’s facility have been returned (as of Jan 19th) as from our request. Most of those units are not functional as determined by screening tests in BNL. Several of them have been delivered not completely assembled.
- Contract has been awarded early Feb..
- Algen Design Services Inc. *(*_[http://www.algendesign.com/](http://www.algendesign.com/)_*)*
- Company known for the high quality of the LARG FEB assemblies, BNL QCD super-computer
- LVPS experience: 3000 (400-600W) DCDC converters assembled last year
- First steps (Feb-early Mar)
- Preparation of the infrastructure (in particular for what concerns testing),
- Cable assemblies (several to be replaced)
- LVPS disassembled: each module has been uninstalled, cleaned and stored
- Full Retrofitting Operations (end of Mar - mid July)

## LARG LV Power Supplies (6)

- Develop a concurrent backup plan
- LVPS reliability improved but not expected to be sufficient for the lifetime of the experiment
- A new revision of the LAr LV Power Supply Specification has been drafted
- Request for Proposal (end of Mar)
- Source-Selection Committee to evaluate proposals and to give technical recommendations to Procurement (under completion)
- Considering 2 backup options at different time scales
- Plan to award first manufacturer by end of April 07.