An introduction to HV cables J Borburgh With

An introduction to HV cables J. Borburgh With valuable input from B. Balhan, L. Ducimetiere and T. Kramer. 22/6/2016 An introduction to HV cables, TE/ABT group meeting 2

Outline • • • High Voltage cable types Cable construction Cable testing Cable aging tests Procurement 22/6/2016 An introduction to HV cables, TE/ABT group meeting 3

Usage of HV cables Within TE/ABT group HV cables are commonly used for: • • Kicker PFN + Transmission; pulsed application, impedance very critical, low loss requirement Electrostatic septa; DC application, high voltage requirement, low leak current, resistance to radiation, low capacitance Voltage range in use: • Pulsed: 10 - 80 k. V • DC: 150 - 300 k. V 22/6/2016 An introduction to HV cables, TE/ABT group meeting 4

HV DC links proposed for Europe • Several projects have been studied to transport energy in Europe over large distances. • All rely on HV DC current cables. • The potential market for this type of grid, sparked interest of several cable companies and HVDC cables are being developed for higher voltage than ever before. • Norms for HV cables (AC as well as DC) are now An example of a proposal for a 800 k. V HVDC grid getting more and more overlaying the 400 k. V AC grid presently in place mature [2, 4] [1]. 22/6/2016 An introduction to HV cables, TE/ABT group meeting 5

Conventional Coaxial HV-cable Foam Dielectric • Good signal transmission properties • However voids in the foam will not allow for HV (used up to ~15 k. V) • 22/6/2016 An introduction to HV cables, TE/ABT group meeting 6

Conventional Coaxial HV-cable Commonly used for septa and kickers - Our “work horse”. • Solid PE dielectric, copper braid. • Used in ABT up to 300 k. V. • Exists in different variants • • • 22/6/2016 With/without semiconducting layer Several impedances An introduction to HV cables, TE/ABT group meeting 8

SF 6 gas filled HV-cable (kickers) • • Dielectric: thin PE foil wrapped around inner conductor, pressurized with SF 6 gas fills all voids Superior dielectric strength Lower velocity factor due to PE core No issues with surface discharge Low attenuation/losses (no semiconducting layers) ~14 km in operation at CERN since the seventies (no issues seen so far) Nominal voltages up to 80 k. V Disadvantage: • Vacuum and SF 6 gas systems needed • Special gas tight connectors ( in house production) • No quick disconnect • Cable relatively stiff and heavy (FAK: 1 PFL =2. 6 t ) 22/6/2016 An introduction to HV cables, TE/ABT group meeting 10

GIPFL – Gas Insulated Pulse Forming Line © TE-ABT-FPS Used for energy distribution (up to 500 k. V/5 k. A) e. g. installed below Palexpo, extensively used in the alps for caverned hydropower stations. Advantage: • Simple and robust. • Perfect for tunnel installation (fire safety). • Long life time (~50 yrs). • No maintenance (gas enclosed). • Largely self healing. Siemens GIL Disadvantage: • Spacers are critical for surface discharges. • Not (yet) designed for pulse transmission. • Not flexible. • Bigger diameter than SF 6 cables. • High velocity factor due to gas insulation (<er).

Also a “gas” insulated coax: Reusenleitung “cage lines” used for signal transmission to longwave radio transmitter e. g. in Poland (left) and Austria (right, 240 k. W). Low loss, high power.

Outline • • • High Voltage cable types Cable construction Cable testing Cable aging tests Procurement 22/6/2016 An introduction to HV cables, TE/ABT group meeting 16

HV Cable extruding facility Extruder heads Vulcanisation Cool down Outer conductor winding 22/6/2016 17

Conventional HV coaxial cable construction S: insulation breakdown voltage [V/m] D: outer insulation diameter [m] d: inner insulation diameter [m] 22/6/2016 An introduction to HV cables, TE/ABT group meeting 18

Impedance Reflection coeff. In case of inhomogeneity's the reflection coeff. will be ≠ 0 For cables with very small losses L and C dominate hence simplified: Material and diameters can be selected

Attenuation / losses • Resistive losses skin effect, proximity effect • Losses in the dielectric • Radiated losses for high frequencies only ( less important for our applications)

Outline • • • High Voltage cable types Cable construction Cable testing Cable aging tests Procurement template 22/6/2016 An introduction to HV cables, TE/ABT group meeting 23

AC cable acceptance tests Typically 3 types of tests [2, 3]: • Type tests Done on cable sample, or cable sample of comparable cable; Fire tests [5] Bending test Tan δ Heating cycle test Impulse voltage test Partial discharge test • • Routine tests • Done on each cable length produced; non destructive electrical tests • • Partial discharge test Voltage test Electrical test on non-metallic sheath Sample tests • Done on samples of cable from same production batch; • • • Measurement of material properties, thickness, resistance of conductor, … Destructive electrical tests to determine cable limits (CERN) Aging tests 22/6/2016 An introduction to HV cables, TE/ABT group meeting 24

DC cable acceptance tests For DC cables the 3 types of tests used for AC cables are complemented with a 4 th type [4]: • Pre-qualification tests • on cable and accessories (connectors) • • done at 1. 45 x rate voltage Done with using varying (predefined) daily load cycles Done in different thermal conditions (pre-defined) Minimum duration 360 day! 22/6/2016 An introduction to HV cables, TE/ABT group meeting 25

Partial discharge test aims at finding localised breakdowns of a small portion inside the insulation. Usually these indicate the presence of voids, cracks or inclusions in the insulation. Partial discharge test, done at 10% below rated voltage, sensitivity 10 p. C (routine test). 22/6/2016 An introduction to HV cables, TE/ABT group meeting 26

Tests of interest to kickers and septa • • • AC cable tested at ~1. 4 x rated voltage. DC cable tested at 1. 85 x rated voltage. Bending test: • • Bending of cable on a drum (1 turn at least), unwinding and repeat process in reverse direction, followed by partial discharge test. Lightning impulse test: 10 positive and 10 negative impulses (@ 250 k. V for 45 k. V cable, 750 k. V for a 160 k. V cable!) 22/6/2016 An introduction to HV cables, TE/ABT group meeting 28

Outline • • • High Voltage cable types Cable construction Cable testing Cable aging tests Procurement 22/6/2016 An introduction to HV cables, TE/ABT group meeting 29

Cable aging can be verified artificially according to IEC 60811. Sample is kept at 100°C for 42 days, equivalent to 10 yrs of normal (= non radioactive environment) operation. State of cable materials can be assessed using: • Traction Tests (TT), where elongation at break is measured, • Differential Scanning Tests (DSC), where the Oxygen Induction Time (OIT) is measured. Two contributions to aging: • exposure to air (mainly oxygen) and UV (storage conditions) • exposure to ionising radiation 22/6/2016 An introduction to HV cables, TE/ABT group meeting 30

DSC vs. TT results Cable lifetime strongly influenced by additives to base material (for ex. anti-oxidants, colour pigments etc. )! 22/6/2016 31

MKP RG-220 cable installed during LS 1 60 cables replaced in 2013 during the LS 1 [6]. Cable CLP 50 TT 118121 Position In operation Storage, installed during LS 1 From 2013 (LS 1) Behind shielding wall From 1994 to 2013 Manufacturing year 2004 Downstream TIDVG, installed From 1994 to 2013 1993/94 Behind shielding wall From 2000 to 2013 1997 Estimated integrated dose 0 2. 5 105 GY 2. 5 105 GY 1. 8 105 GY Traction Test: Elongation at break Sheath 293% ± 7% PE 478% ± 3% PE 208% ± 44% Sheath 127% ± 16% PE 509% ± 55% Sheath 140% ± 30% PE 417% ± 212% PE : 28 min PE : 1. 4 - 18 min PE : 0. 2 - 19 min PE : 0 – 4. 6 min Traction test: Elongation at break after artificial ageing (100°C 42 days) DSC test: Oxygen Induction Time after artificial ageing (100°C 42 days) Should foresee replacement in 2023. 22/6/2016 An introduction to HV cables, TE/ABT group meeting 32

Outline • • • High Voltage cable types Cable construction Cable testing Cable aging tests Procurement 22/6/2016 An introduction to HV cables, TE/ABT group meeting 33

Cable specification template In 2014 RIAC* WG developed a cable specification template [7], to make sure the requirements for cable aging testing to be included systematically. The template can be found at the procurement service templates webpage: https: //procurement. web. cern. ch/documents/procurement-templates *Replacement of Irradiated and Aging Cables Working Group 22/6/2016 An introduction to HV cables, TE/ABT group meeting 34

References [1]L. Barthold et al. , “ DC is where we started”, IEEE Power & Energy society e. News Update, April 2016 [2] “Power cables with extruded insulation and their accessories for rated voltages above 30 k. V (Um = 36 k. V) up to 150 k. V”, IEC 60840, 2011 [3] “Power cables with extruded insulation and their accessories for rated voltages above 150 k. V (Um = 170 k. V) up to 500 k. V (Um = 550 k. V)”, IEC 62067, 2006 [4] “Recommendations for testing DC extruded cable systems for power transmission at a rated voltage up to 500 k. V”, CIGRE WG B 1. 32, Technical Brochure 496, 2012 [5] IS 23, Criteria and Standard Test Methods for the Selection of Electric Cables and Wires with Respect to Fire Safety and Radiation Resistance, EDMS 335745, 2012 [6] L. Ducimetiere, “SPS-TS 1+ Kicker HV Cables (RG 220) - History and Tests Analysis”, EDMS 1385241 [7] D. Ricci et al. , “TEMPLATE FOR TECHNICAL SPECIFICATIONS SUPPLY OF CABLES”, EDMS 1137965 22/6/2016 An introduction to HV cables, TE/ABT group meeting 35