Konstantinos Papastergiou

TE-EPC

25 May 2018

Electrolytic Capacitor Tests

Summary

Background work

Motivation of the test

Test objectives

Test protocol

Test Results

Conclusions

Capacitor banks for energy recovery

Electrolytic Capacitors for Energy Storage Purposes

• Applications: Energy recovery of power converters supplying magnets- SIRIUS power converter family (e.g. TT2 Consolidation Programme)- Future medium power converters with energy recovery capacitor banks

• Benefits:- Increased energy efficiency of power converters supplying magnets- Improved power quality from power network

LF-R/2

LF-R/2

+

-

Rectifier bridge

RCB

CCB

Capacitor bank

VD

C CF-DC

400 V50 Hz

Grid & Transformer

T1

T2

T3

T4

Chopper H-bridge

LF-H/2

LF-H/2

RST

Boost

D

Tb ICB

CF-H

CFd-H

RdRm

Lm

Magnet(load)

Vm

Im

RCr

TCr

Crowbar

Single brick SIRIUS power converter

Master Thesis work by Luca Sburlino

Single Capacitor Ratings: Worst Case Requirements

Capacitor bank

Min – max voltage 600 V – 900 V

Cycle duration (freq.) 1.2 s (0.833 Hz)

Configuration 3 series x 5 parallel

Single screw-terminal Al-ELCAP ratings

RMS voltage 400 V

RMS current 11 A

Peak current 50 A

Voltage swing 300 V – 206 V

Capacitance ≥ 29 mF

Ambient temperature 40 ºC

Minimum Lifetime 100’000 h operation

Worst case cycle acting on single capacitor

Master Thesis work by Luca Sburlino

Construction Technology• Enhanced heat dissipation by using:

- Extended cathode (axial direction)- Corrugation (radial direction)- Thermal conductive glue (may clog safety vent)

Screw-terminal aluminium electrolytic capacitor

Manufacturing Process• Increase capacitance density: Anode and cathode foils etching (1)

surface increase of 60x for 400 V capacitors

• Obtain capacitor rated voltage: Anode foil forming (2)Vformation ≈ 540 V for 400 V capacitors

• Increase capacitor quality, reduce early failures: Ageing (7)Vr < Vageing < Vformation

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Manufacturing process

Lifetime Influences: Charge-Discharge ApplicationsTab-heating in charge-discharge applications

Charge-discharge applications:Elevated heating on tabs.

Consequences: Local electrolyte vaporisation and damage on

tabs more likely

Transient Thermal, Electrical and Lifetime Analysis of Large-Can Al-ELCAPs,Cornell Dubilier – Sam G. Parler, Jr., P.E.

Lifetime Influences: Charge-Discharge ApplicationsAgeing and failure modes diagram

Motivation for the Tests by the manufacturer

Previous experience with capacitive energy storage shows the need to understand the failure mechanism of capacitors.

To have enough input in order to decide compensatory safety measures Visualisation of the cabinet (video) during the test

Visualisation of the vapour release from the cabinet (video) during the test

Visualisation of the test area (video), to assess the potential projection of debris

Measurement of the voltage/current during the test

Measurement of the sound pressure at 1 m from the cabinet

Photos of the cabinet (exterior+interior) after the test

Detailed photos of the capacitor bank after the test

Qualitative assesmnet of impact to the floor.

Objectives

Qualitative assessment of the impact of a capacitor failure

Verify Sirius metallic enclosure withstand to a destructive failure

Qualitative assessment of the impact on surrounding equipment From heat and fire

From debris and flying parts

From the electrolyte evaporation

Identify the audible magnitude of a failure

Test Protocol

Test 1: Continuous rated peak voltage across a capacitor Single point of failure will result in this condition Withstand over long time to be determined Repeat on three different samples

Test 2: Continuous over-voltage (x2) across a capacitor A double failure will result in this condition Worst case if energy source not disconnected Repeat on three different samples

Test 3: Reverse polarisation Reverse polarisation of a capacitor May occur as a result of manufacturing error Repeat on three different samples

EDMS 1919992

Test setup description

Test 1 & 2 Overvoltage on DUT

With and without external source

S1a b

CXDUT

E1

CB1

E2

CB7

CB6CB2

S1a b

CXDUT

E1

CB1CB2

Test 3 Reverse polarisation of DUT

Gradual increment of source voltage

Test 1 Results: continuous peak voltage

Shot 1: 450V on DUT -> no failure during 1h

Shot 2: 550V on DUT -> instant destructive failure

Shot 3: gradual increase 450V to 520V on DUT:• Failure at 520V after 1320sec

Test 2 Results: over-voltage (x2)

Test 2

Shot 1: 900V on DUT with external source -> failure after 73s

Shot 2: 900V on DUT, external source disconnected -> no failure, DUT operational after test

Shot 3: 900V on DUT, external source disconnected -> no failure, DUT operational after test

Shot 4: 900V on DUT with external source -> destructive failure

Test 3 Results: reverse polarisation

Shot 1: Reverse polarisation of DUT with external source -> failure, open vent

Summary of test results

• Test 1 & 2: single point of failure• Over-voltage <37%** : No failure after 1 hour of exposure• Over-voltage >37% with Sirius capacitor banks energy: Failure mode is

uncertain • Over-voltage >37% with Sirius capacitor bank energy and external

energy source: Destructive failure mode after some time

• Test 3: polarity reversal• Failure with open-vent after 900sec if source remains energised.

** Over-voltage with respect to the application operating voltage

Sirius Capacitor Failure Tests - Conclusions

• Electrolytic capacitors are prone to failure if exposed to over-voltage.• There is no evidence that energy stored in a Sirius brick can cause by itself

destructive failure or fire.• A failure may become destructive in case an energy source remains energised after

the event.

• Key findings:• Destructive failure of capacitors (fumes, debris) is contained by the enclosure • Destructive failure of capacitors has no structural impact on the Sirius metallic

enclosure• Destructive failure has limited impact on the equipment directly above• The peak observed sound level was 135.5db at 0.5 meter from the cabinet

*Destructive is a failure that results on visible damage to the capacitor can or its surroundings

*Reports and media in EDMS folder CERN-0000189820

A report is circulated internally for approval and will be placed under CERN-0000189820