Quench Protection

Quench Protection
Vicky Bayliss, Tom Bradshaw,
Elwyn Baynham
Contents
• Starting conditions
• Model simplifications
• Models used
- U (ϴ): heat balance in unit winding
- xquench model
- Opera QUENCH model
• Conclusion
Starting conditions
• Building 300mm formers – protect individually
• Imagine the circuit inside the cryostat will look
something like this:
Model Simplifications:
Cross-over wire heat calculation
1
1.E-05
1.E-04
1.E-03
1.E-02
Time (s)
5
• Conduction from quenched coil
• Resistive heating in the wire
500
450
400
350
300
250
200
150
100
50
0
1.E-01
1.E+00
1,200
Conducted Heat
1,000
Resistive Heat
800
600
400
200
1.E-05
1.E-04
1.E-03
1.E-02
Time (s)
1.E-01
Heating (W)
2
3
End Temp
4
End temperature (K)
3
4
2
5
1
Excel model to consider effect of the
energy dissipated in the cross-over wire
by:
0
1.E+00
-200
Model Simplifications:
Spacing at the back
- Lower the thermal conductance through the winding in this region
- Calculated quench propagation velocity is ~38m/s
Model Simplificatons:
Quench propagation velocity
- Calculated quench propagation velocity is ~38m/s
- Both the Opera and xquench models assume that the quench is contained to
one groove
- Quench will travel the length of the 90mm cross-over wire in 2.5ms
U(ϴ): heat balance of unit
volume winding
The maximum temperature reached in a winding following a quench is estimated by
considering the heat balance of unit volume of winding:
𝑥
2
𝐽 𝑇 𝑑𝑇 =
0
Where
J
T
ρ
γ
C
Td
ϴ
𝐽02 𝑇𝑑
=
𝜃𝑚
𝜃0
𝛾𝐶(𝜃)
𝑑𝜃 = 𝑈(𝜃𝑚 )
𝜌(𝜃)
current density (Am-2)
normalised time (s)
resistivity (Ωm)
density (kgm-3)
heat capacity (Jkg-1)
characteristic quench time
temperature (K)
‘Superconducting magnets’, Martin Wilson, Chapter 9 Quenching and Protection
U(ϴ): heat balance of unit
volume winding
xquench model
•
Fortran code written by Martin Wilson in 1969 , later developed by Elwyn
Baynham and Jim Rochford at RAL
•
Calculating the spread of the normal region through a coil of length L and
cross-sectional area A
– For applying to SCU it is assumed that the normal region will be confined to a single
coil
•
Circuit:
xquench circuit
[‘Computer simulation of the quenching of a
superconducting magnet’ by Martin Wilson (1969)]
SCU proposed circuit
xquench model
500
450
400
Results set using:
• SCU coil parameters
• inductance of 0.017H
• no breaker delay
• 1Ω protection resistor (RSW)
350
300
Current (A)
250
200
150
100
50
0
0
140
0.02
0.03
Time (s)
120
100
80
Tmax(K)
0.01
60
40
20
0
0
0.01
0.02
0.03
Time (s)
0.04
0.05
0.06
0.04
0.05
0.06
xquench model conclusions
500
400
External Voltage (V)
• R1 (RSW) must be less than 1Ω
300
200
100
0
0
• Switch must open within 3ms
0.01
0.02
0.03
0.04
Time (s)
0.05
0.06
xquench model conclusions
•
Required electrical breakdown voltages
Consider a simplified circuit…
R1
L
RQ
Voltage
Location
VQ
VR1
R1
L RQ L
Coil to ground
L
Electrical
Breakdown
Voltage
3kV
Turn-to-turn
120V
Coil-to-crossover
wire
430V
xquench model conclusions
Diodes should be used with a voltage limit of ≤1V
- for maximum ramp rate > 0.11V limit required
- in a quench scenario <1mJ additional energy would be dissipated in the magnet
8
Energy Difference (mJ)
•
7
6
5
4
3
2
1
0
0
1
2
Diode Voltage Limit (V)
3
4
Opera QUENCH Model
• Uses a transient thermal solver and a transient EM simulation (Elektra)
• Extreme non-linearity handled with adaptive time-stepping
• Quench is forced with a heat input on a defined plane
• Limitations:
- simplified geometry
- symmetry means top and bottom formers quench simultaneously
- inaccuracies in material properties
Opera QUENCH Model
Temperature (K)
160
140
Tmax_Coil1
120
Tmax_Coil2
100
80
60
40
20
0
0.15
0.2
0.25
0.3
0.25
0.3
Time (s)
Resistance (Ohms)
0.7
0.6
0.5
R_Coil1
R_Coil2
0.4
0.3
0.2
0.1
0
0.15
0.2
Time (s)
Summary design implications
• Quench protection heaters won’t be used
• 1Ω resistor and diodes with a 0.15V voltage limit should be used
• The circuit breaker between the magnet and the power supply must
open within 3ms.
• SCU windings should be electrically insulated to withstand the
voltages summarised in Table 1
• The use of copper spacers at the back of the winding should be
considered for improving the heat dissipation it the winding in that
region
Thank you
Questions?

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