TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

1

Non-conform MCBY circuits

IntroductionHypothesis

ModelTests plannedConclusions

2011 Planning

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

2

Introduction

We have found an unexpected behavior in some 120A circuits (individual powered correctors).

6 MCBY & 3 MCBC magnets are quenching when ramping up/down, usually when going to 0A.– List of circuits:

Several tests have been made in 2008, 2009 to discard power converters, cryo conditions…

• RCBCV8.L1B2

• RCBYHS4.L5B1

• RCBCH7.L8B1

• RCBYH4.L2B2

• RCBYHS5.R8B1

• RCBCV7.L2B2

• RCBYH4.R8B1

• RCBYV5.L4B2

• RCBYHS4.R2B1

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

3

Introduction

Symptoms:

– The magnets cannot stand the nominal di/dt

– We can observe a bump in themeasured current when the magnet quenches

– No appreciable degradation in the quenches

– Power converter instability problem, dueto different TF of the magnets.This was solved by EPC group addinga virtual resistance of 70 Ohm in parallelto the magnet in the PC model.

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

4

Hypothesis

The first idea, pointed by Glyn Kirby, was a kind of transformer effect.

That could happen when a loop is shorted in the middle of the coil.

We will have N1=29 and N2=1. The change in flux in the large inductance will produce a high current in the lower inductance, that will quench the loop in short.

This is a detail of the presumable place for the short.

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

5

Model

A model of the MCBY with the short is done in Matlab. It’s based on the work started by Bernhard Auchmann.

The circuit is analytically resolved and simulated in Matlab, adding the thermodynamic calculations.

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

6

MCBY vs Model (replica of a real quench)

Real quench. PM file: 091124-50723.820

70 80 90 100 110 120 130 140 150 160 17041

42

43

44

45

46

47

48

49

50

51

I coilI ref

Simulation in Matlab, with the same ramps and times.

Similar results.

Differences:• Magnitude of the bump• Current in the quench

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

7

MCBY vs Model (replica of a real quench)

Explanation of the quench, seeing what is happening in the loop in short.

0 20 40 60 80 100 120 140 160 180 200-100

-50

0

50

100

150

t (s)

I (A

)

I coilI loop in shortI ref

Imax

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

8

Temperatures & Voltages

The simulations are done assuming the adiabatic case, so we are in the worst case, to be sure that the magnet will besafe.

0 50 100 150 200 250 300-60

-40

-20

0

20

40

60

80

100

120

140Quench @ I=72A, Plat=30s, dI/dt=0.66A/s, Rs=0.002

I coilI loop in shortI ref

147.5 148 148.5 149 149.5 150

20

40

60

80

100

120

140

Temp 1Delta T1Temp 2Delta T2

147 148 149 150 151 152 153

-200

-100

0

100

200

300

400

500

Ind V coilRes V coilInd V loop in shortRes V loop in short

0 50 100 150 200 250 300 350 400-10

-8

-6

-4

-2

0

2

4

6

8

t (s)

V (V

olts

)

V PC

Currents Temperatures

Voltages(in the magnet)

Voltagein the PC

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

9

Tests planned

To validate the model and fix some parameters affecting the simulations, we need to fake a short and see what is happening in this turn.

Test proposals:– Magnet: Using a spare one (HCMCBYB001-TE000043). It’s ready and

stored in building 927.– Place for the tests: Block 4 (SM18)– Instrumentation: both apertures with

Vtaps in all turns– Faking a short in one aperture.

This is done with a stainless steel piece soldered between two turns, with an Rs=0.0015 Ohm.

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

10

Tests planned

Examples of the current cycles planned:

0 200 400 600 800 1000 1200 14000

1020304050607080

dI/dt= 0.66

0 200 400 600 800 1000 1200 1400 1600 1800 20000

1020304050607080

dI/dt= 0.3

0 200 400 600 800 1000 1200 1400 1600 1800 20000

10

20

30

40

50

60

Imax=50

0 200 400 600 800 1000 1200 1400 16000

5

10

15

20

25

30

35

Imax= 30

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

11

Conclusions

Main parameters affecting the results of the simulation are:

– modeling and value of the short resistance

– quench velocity propagation

– exact current that makes the loop in short quench

We will know them empirically, measured in the tests, to have better and more realistic simulations. Once these parameters are fixed, we should be able to reproduce the measured voltages and currents.

We will be able to know the maximum voltage developed inside an MCBY coil during a quench, in a healthy and in an sick magnet.

Voltage withstand could be re-defined for these magnets, as it was not fully measured.

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

12

2011 Planning

The maximum time length for the tests should be around one week, including installation of the magnet, cooling, tests and warming.

The date is not fixed, we are waiting for the confirmation.

Relative to LHC:– There’s a good margin with the sick MCBY’s and MCBC’s. They are

working well within their safety parameters. In fact, some of them are not being used, but the working parameters are changing depending on the optics.

– Just taking in account the safe maximum ramp rate (different for each magnet) there shouldn’t be any problems to go to 4 Tev or 4.5 Tev.

TE-M

PE W

orks

hop

14/1

2/20

10, M

anue

l Dom

ingu

ez, T

E/M

PE

-EI

13

Thank you for your attention.