March 17th, 2005

Workshop on appraisal of disassembled magnets

Lesson learnt

March 17th, 2005

Inter-turn shortsThe few cases observed

G. Molinari

March 17th, 2005 Inter-turn shorts - The few cases observed - GM 2

Outline

Static inter-turn shorts Dynamic inter-turn shorts Conclusions - Actions

March 17th, 2005 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 2101a)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

March 17th, 2005 Inter-turn shorts - The few cases observed - GM 4

Static inter-turn shorts, cont’d

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

D2LOW

D2UPD1

UP

D1LOW

March 17th, 2005 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

March 17th, 2005 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

March 17th, 2005 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

March 17th, 2005 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

March 17th, 2005 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

March 17th, 2005 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

March 17th, 2005 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

March 17th, 2005 Inter-turn shorts - The few cases observed - GM 12

Conclusions - Actions

Inter-turn shorts can be detected at the collared coils production stage

T

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