qxfp01 heater hipotting and autopsy€¦ · •after physically removing the short, we repeated the...

QXFP01 Heater Hipotting and Autopsy

S. Krave, V Marinozzi, M. Parker, L. Elementi., M. Baldini

20 March 2019

• QXFP01 was the first long prototype coil

• Successfully tested in mirror configuration

• One of the OL midplane traces never failed, which is

consistent with what we found

• The other OL midplane trace failed at 2340 V (breakdown)

immediately after warmup, which is somewhat consistent

with what we measured: first failure measured by us was a

ramp-hi at 2.15 kV. However, after some testing, first

breakdown has been at 2.73 kV, so higher than the one

measure by Carlo.

• The two pole traces failed after warm up respectively at 1500

V and 2070 V (breakdown). All traces passed electrical test at

2500 V before testing

• The coil had 22 training quenches, and 30 QH induced

quenches

3/20/2019 S. Krave | QXFP01 Autopsy Continued2

Background

After Dissassembly and Hipot testing,

heater 2 (Pole, Transition) A short was

created at a location that was determined

by thermal imagery. This location was later

verified by poking it and watching the

resistance change

A plan was determined as follows:

• Peel glass off of heater and observe

location, check if short is still there

• Separate heater from trace and examine

area

• Check for other shorts

And after discussion

Work to develop and identify more shorts

Practice heater and glass removal was

completed on inconsequential areas of the

coil and practice traces.


Background

Just above the black mark pointed out

a couple weeks ago

Verified by closer observation of

thermal camera


Burned Spot

Heater removal


The Short


Continuity measured from short location to coil

• Hipot failure on heater 2 led to

resistive condition

• Current was applied

• Short was detected using thermal

camera

• There was a concern that foreign

material may have been involved,

but upon closer inspection that

does not appear to be the case.

• The burning was likely a result of

the power applied during thermal

imaging.(6 volts ,0.5A in <1mm^2

for a prolonged period of time)


Kapton Removed From Short

• The short was one of 5 similar looking bubble areas in the region of the short.

– It was the only one that showed continuity with a multimeter.

• There was another similar looking bubble area ~3” away from the short.

• This bubble area looks similar to the blisters that appear on the ID of coils at

superfluid helium.

• It was relatively easy to remove the heater.

Other Observations


• After physically removing the short, We repeated the hipot test to look for failure

areas

• Breakdown and arc resulted in audible snap at failure location

Looking for more shorts…


After removing the heater in the region of the first short, and therefore the short, hipot of the

remaining part of the quench heater has been performed.

The list of all the tests performed, with results, is the following:

1) Target: 3.7 kV, 10 V/s, max leak current 10 μA Breakdown @ 2.57 kV, Ileak > 10 mA

2) Target: 3.7 kV, 100 V/s, max leak current 10 μA Arc fail @ 1.61 kV, Ileak = 1.4 μA


4) Target: 3.7 kV, 10 V/s, max leak current 10 μA Breakdown @ 2.27 kV, Ileak > 10 mA

5) Target: 3.7 kV, 10 V/s, max leak current 10 μA Ramp-Hi @ 1.24 kV, Ileak = 10.1 μA

6) Target: 3.7 kV, 100 V/s, max leak current 100 μA Breakdown @ 1.75 kV, Ileak > 10

mA


8) Target: 3.7 kV, 10 V/s, max leak current 100 μA Ramp-Hi @ 0.4 kV, Ileak = 174 μA

9) Target: 3.7 kV, 10 V/s, max leak current 100 μA Arc fail @ 0.65 kV, Ileak = 707 μA

EXAMPLE DATA FROM

SINGLE HIPOT LOCATION

Location Verification by antenna technique


Second Hipot failure location


2nd Hipot failure location


Not failure


Epoxy cracking as a result of loading? Potential for future failure?

• Hi-pot heater region

• Record ultimate voltage and failure mode (or pass)

• Verify region of failure (usually by listening)

• Physically remove shorted area of heater

• Repeat until there is nothing left or all passes

• Areas with visible fracturing or blistering were

catalogued by size. If the region failed hipot this was

noted in a spreadsheet

• Assume elliptical region

• Some length along coil

• Some Length Radially

• Calculate area

• Some areas had visible holes through the Kapton after

heater removal. These regions failed 3680V hipot

• Some that didn’t have visible blistering also failed, but

at a lower rate


Categorization of Bubble Areas ~15mm

~10mm

A ≈ 118 mm^2

Bubble Map


Bubble size represents relative area

of region. This dot is ~120 mm^2

Bubble Color Key

Passes 3680V Hipot

1500V Hipot Failure

2590V Hipot Failure

3680V Hipot Failure

Note several failures

at 2160 mm

Locations and voltage


Area vs Hi-pot Failures


• Gap along coil midplane provides

low resistance to epoxy flow

• Epoxy Racetracking

• Epoxy passes coil during fill

process and covers coil end,

trapping gas inside of coil

• Epoxy flows from this channel

radially inward

• Remaining trapped gas

coalesces near pole and is

unable to be extracted.

• FNAL has placed filler in this

region in coils after QXFP01b

• These fillers led to substantial

reduction in resin sucked back

into coil after potting typically

<20ml


Explanation for regions near pole?

Related Information


Blistered regions show

beach marks originating

from location of voids in

coil

• These marks travel

outward from origin,

sometimes in opposite

directions of

progression of trace

peeling and are not

likely a result of the

peeling operation

• Thought he actual

separation may be

• These look similar to

progression of fatigue

failure in materials


Fatigue

Examples of blistering


Example: Mechanics of tungsten blistering: A finite element study

Fracking?


From: Recent Advances in Global Fracture Mechanics of Growth of Large Hydraulic Crack Systems in Gas or Oil Shale: A Review

QXP105


QXFP105


2160mm (add 6cm to ruler to

compensate for position in

tooling)Shell Weld Seam


QXFP103

Line at

~2180

qxfp01 heater hipotting and autopsy€¦ · •after physically removing the short, we repeated the...

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