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Q5R4 corrector shorted to ground. Ongoing investigation

Status at 18 June 2007

N. Catalan Lasheras

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History of Q5R4

No electrical NC during manufacturing

Electrical insulation tests done in SMI2 on 24/07/06 includes MCBY to MQY, Quench Heaters, ground, and each other.

– Results ok (EDMS 759062)

Installed in the tunnel on 2 August 2006

Major movements of the D4-Q5 magnets and supports in 4R (NC 833372)

– Q5 moved 9 mm under vacuum. Came back to 6 mm in atmospheric pressure

– Interconnection open to check PIM. Ok. Closed again.

– Re-test in vacuum foreseen. (?)

HV breakdown on circuit RCBYH5.R4B2 during ELQA at warm (NC 842369)

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MCB corrector short-circuited in Q5R4, EDMS 842369V. Chareyre

A discharge occurred during the electrical insulation test (voltage level at warm, 300 V)

Resistance to ground around 180 Ω (before pressure test in sector 45)After the pressure test, the problem has been deteriorated: around 2 Ω

A current of 70 mA is impressed in the circuit

Voltage drops across voltage-taps are measured, ground is used as a voltage pick-up

Short localized between the cold v-tap B and the coil BUT the v-tap is very close to the coil

The problem may be at the level of the connection of the coil

DFLES.5R4.1

DFLES.5R4.2

Current lead

Bus-bar, L~ 5.6 m

+ 3.758 mV

+ 3.753 mV

+ 35.8 V

+ 3.753 mV

+ 0.33 mV

I

V-tap Cold v-tap A

V-tapCold V-tap B

A

B

Voltage pick-upConnection bus-bar to coil

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Measure repeated after the pressure test. R. Mompo

A third test confirmed that the short is on the lead side and not inside the corrector.

Voltage measurement performed from the IFS box on connector P25:Polarity 1:

EE871 Voltage, resistive lead ext A warm V-tapEE811 Voltage, dipole orbit ext A V-tapEE812 Voltage, dipole orbit ext B V-tapEE872 Voltage, resistive lead ext B warm V-tap

Results of the continuity test: I= 0.03 A

Polarity 1:

EE871 15.36 VEE811 15.36 VEE812 2.00 mVEE872 0.39 mV

Polarity 2 Inversed polarity of DC PS and multimeter reference

EE871 0.299 VEE811 1.93 VEE812 15.57 mVEE872 15.53 mV

Polarity 1 vs Ground

EE871 15.63 V EE871 15.64 VEE811 15.63 V EE811 15.64 VEE812 0.03 mV EE812 0.025 mVEE872 -1.60 mV EE872 -1.61 mV

Polarity 2 vs GroundUsing another ground reference

EE871 -15.56 mV EE871 -15.57 mVEE811 -15.56 mV EE811 -15.57 mVEE812 -0.078 mV EE812 -0.070 mVEE872 1.55 mV EE872 1.57 mV

Investigation carried out on 24/05/2007 on circuit RCBYH5.R4B2 related to NC 842369: Sketch

Ground taken at the level of the cover flange

P25

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What could have gone wrong?

Bus-bar of D4 and corrector very close.

They may have been put in contact after stretching D4 bus bar during the vacuum test.

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What to do?

According to the optics database not used for optics. Only orbit correction.

Proposal:

Measure short after cool-down.

– Monitoring the movement of the cold mass and the short could be a possibility

Open the interconnect after warm-up. Use and endoscope to check/confirm the contact

In the worst case a repair in situ seems feasible.

– Insert extra insulation

– Open the cold mass cylinder and repair connections