Maximizing Magnet Electrical Performance: NSLS-II Project Insights

1. Abstract Electrical Issues John Escallier, NSLS-II Project To achieve high quality electrical characteristics for storage ring magnets, it is important to clearly detail the electrical and magnetic performance specifications prior to quoting and purchase of the magnets.  Historically, the biggest problems arise as a result of under specifying qualities such as insulation resistance and magnetic field polarity. Some specifications are over-constrained, such as coil matching and klixon string resistance. Also of concern is the need to specify parameters which are to be used for acceptance testing as well as database entry for machine operating.  Our experience with the NSLS2 project clearly indicates where we excelled in specifying as well as providing us opportunities to learn for the future. *Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886 Magnet Production Lessons Learned

2. Magnet Production Electrical Issues National Synchrotron Light Source II (NSLS-II) Project John Escallier April 11/12/13 2012 Magnet Production Workshop

3. Contents • Magnetic field convention • Coil electrical limits • Klixon specifications • Magnet insulation requirements Magnet Production Workshop

4. Magnetic field convention • Specify without ambiguity how the magnetic field presents with specific current drive • For magnets which have a well defined orientation, include the beam direction in the print • Magnets with two possible orientations, do NOT include a beam direction • Include in the print the pole magnetic polarities • Clearly specify the sectional view perspective for the magnetic polarity • Use terminal designations which are non ambiguous • Establish field maps for steering and multipole elements • Establish a convention for current drive and magnetic function • Work with physics and design engineering to establish definitions • For steering magnets, current into terminal A (supply positive connected to A) produces a right bend • For multipoles, current into terminal A produces a focus element. Magnet Production Workshop

5. Magnetic field convention This plumbing is overly difficult to split and re-assemble Magnet Production Workshop

6. Coil electrical limits • Magnet Specifications • Full power voltage drop • Operational current maximum • Water inlet temperature • Flow rate • Coil specifications • Inductance • Establish overall coil to coil tolerance allowed • 4% is the historically useable number • Resistance • Coil to coil tolerance allowed • 2% is the historically useable number • Impulse testing • 500/1000/2000 volt impulse at the coil level (post impregnation) • No assembled magnet impulse for DC magnets. • Eddy currents in the yoke and weld bead lamination shorts bother the test. Magnet Production Workshop

7. Klixon specifications • Klixon string resistance specification • Supplier specific • Recommend future purchases have required supplier for switches • Klixon form factor • Present machine has several mechanically incompatable switch designs • Complicates stockroom requirements • Recommend one switch vendor and/or form factor where possible • Switch contact requirements • Gold plated for low current operation • Always place them on the outflow side of the coil Magnet Production Workshop

8. Klixon switch variations Magnet Production Workshop

9. Magnet Insulation requirements • Coil Dielectric withstanding tests • 24 hour salt water immersion • Required to find small impregnation defects • Alternate tests • Foil covering • Short dwell immersion • Testing within impregnation structure • Magnet wire or litz wire immersion • Limited to wire insulation capabilities • Generally 1200 volts or less • Bare conductor insulation • Epoxy wrapped • Heatshrink • Epoxy paint after bending conductors • Shielding structures • Lexan the material of choice • Establish physical guidelines for protection of energized conductors Magnet Production Workshop

10. Summary • Establish magnetic convention early • Eliminate the possibility of miswiring in the machine • The establishing of the electrical specifications prior to prototype and production builds prevents later headaches during incoming inspection • “To be determined” and “or equivalent” are to be avoided unless they are absolutely necessary • Sometimes unavoidable, such as coil inductances or coil resistance • Matching tolerances produces surprises with inductance and resistance of coils • Mechanical tightness of wound coils caused the variations • 1% tolerances were opened to 2% and in some cases, 4% • Specify common components where possible to reduce stock requirements • Specify production tests good enough for verification, not overkill • Clearly identify pass/fail metrics as well as trending metrics • Specify production tests which require database archival Magnet Production Workshop