Workshop on appraisal of disassembled magnets Lesson learnt March 17 th , 2005

1. Workshop on appraisal of disassembled magnetsLesson learntMarch 17th, 2005 Inter-turn shorts The few cases observed G. Molinari

2. Outline • Static inter-turn shorts • Dynamic inter-turn shorts • Conclusions - Actions Inter-turn shorts - The few cases observed - GM

3. Static inter-turn shorts • These are detected by electrical tests (by resistance measurements) with the collared coils under pressure in the collaring-press • Then, the localization is done via analysis of the warm magnetic measurements (see Boris’ talk) • The following collared coils were concerned: • 1046a, 1080a, 1103b, 1127, 1141, 1154c, 1165, 1178 and 1217 • 2087 and 2101 a) Trials were done to reproduce and so localize the short by pressing the affected pole, section by section (of about 20 cm length) in the E-modulus press. Because this did not work, it was proposed to use the w.m.m. system b) As from item 1103, localization using the w.m.m. in the collaring-press c) Special case, dynamic and static tests have been performed in the collaring-press Inter-turn shorts - The few cases observed - GM

4. In the collaring-press, the 4 poles are connected together like in a “Wheatstone Bridge” One generates an input voltage (VIN) at the entrance of the bridge … … And one measures an output voltage (UOUT), which should be “0”*. If the equivalent resistance exceeds that of one turn, then one measures the resistance of all the poles and so determine the pole, which has a short * On the condition all the cables belong to a unique batch Static inter-turn shorts, cont’d D1UP D2UP D1LOW D2LOW Inter-turn shorts - The few cases observed - GM

5. Static inter-turn shorts, cont’d • Finally, the warm magnetic measurements system, QIMM, is used to localize the longitudinal and azimutal positions of the short according to Boris’ analysis • an accuracy of ± 350 mm can be achieved if one uses the standard mole of 750 mm length • an accuracy of ± 62.5 mm can be achieved if one uses the short mole of 125 mm length Inter-turn shorts - The few cases observed - GM

6. Dynamic inter-turn shorts • These are detected with the electrical discharge test programme (“EDMA”), ITP9i • The localization is not that easy as for the static shorts (“court-circuit franc”) • The following collared coils were concerned: • 1105, 1111, 1124 and 154 Inter-turn shorts - The few cases observed - GM

7. Dynamic inter-turn shorts, cont’d • After collaring, on the occasion of the standard discharge tests at 4 kV (as per specification, i.e. @ 100 V/turn), one compares the discharge curve of the measured magnet with that of a reference magnet. The curves shall be crossing at U=0, otherwise there is a problem • To determine the critical voltage corresponding to the short appearance, one can repeat the discharge test at increasing voltage and compare the curves between them Inter-turn shorts - The few cases observed - GM

8. Dynamic inter-turn shorts, cont’d • Magnet 1111, D1 Lower • Response voltage [kV] as a function of time [s] • 4 steps with increasing voltage • Conforming pole Inter-turn shorts - The few cases observed - GM

9. Dynamic inter-turn shorts, cont’d • Magnet 1111, D2 Lower • Response voltage [kV] as a function of time [s] • 4 steps with increasing voltage • Pole with short Inter-turn shorts - The few cases observed - GM

10. Dynamic inter-turn shorts, cont’d • How to localize? • If short in outer layer or at the interface between the inner and outer layers, then localization is not possible (only the noise can be heard) • If short in inner layer at the interface with the c.b.t., then localization is possible but at the extremity only (say at less than 50 cm from the end). It gives the longitudinal and azimutal positions Extremity of last end spacer Inter-turn shorts - The few cases observed - GM

11. Dynamic inter-turn shorts, cont’d • In most cases of dynamic inter-turn short detected at ITP9i, the layer is damaged and rejected Inter-turn shorts - The few cases observed - GM

12. T Conclusions - Actions • Inter-turn shorts can be detected at the collared coils production stage • The measurements software, EDMA, has been up-dated for detecting the time variation as compared to a reference time period of the voltage oscillation (after the trigger) • In some cases, the tests can be destructive Inter-turn shorts - The few cases observed - GM