Progress in CIGRE Working Groups on Lightning and

Progress in CIGRE Working Groups on Lightning and Grounding (and IEEE Task Force on HVDC Line Design) Member Report: William A. Chisholm W. A. Chisholm@ieee. org 19 July 2016

Meetings Attended • Montreal, May 2016 – B 2. 56, Ground Potential Rise at Overhead AC Transmission Line Structures during Power Frequency Faults – B 2. AG 06. TF 007, Don’t Put your Arresters near our Dampers – Petrache paper on CEATI studies (CDEGS Hi. Freq vs NEC-4) – Lots of interest in German Hybrid AC/DC with positive pole exposed to lightning

Meetings Attended • GROUND 2016, Brazil June 2016 – C 4. 23, Guide to Procedures for Estimating the Lightning Performance of Transmission Lines – C 4. 33, Impact of Soil-Parameter Frequency Dependence on the Response of Grounding Electrodes and on the Lightning Performance of Electrical Systems • XIII SIPDA, Brazil, September, 2015 – C 4. 36, Winter Lightning: Parameters and Engineering Consequences for Wind Turbines – C 4. 410 TB 633, Lightning Striking Characteristics to Very High Structures – Published October 2015

Meetings Attended • PES Annual Meeting, July 2016 – HVDC Line Design Guide Task Force (July 18) – HVDC Line Design Subcommittee (July 20, 8 AM)

Meetings Attended • Montreal, May 2016 – B 2. 56, Ground Potential Rise at Overhead AC Transmission Line Structures during Power Frequency Faults – B 2. AG 06. TF 007, Don’t Put your Arresters near our Dampers – Petrache paper on CEATI studies (CDEGS Hi. Freq vs NEC-4) – Lots of interest in German Hybrid AC/DC with positive pole exposed to lightning

B 2. 56 Appendix 2: Step Potential Verification Method • Demonstration of the use of two different methods (modeling, testing) to cross-check. 7 m V 78

B 2. 56 Appendix 2: Step Potential Verification Method • Tower base current injected with electric fence pulse generator. 7 m V 78

B 2. 56 Appendix 2: Step Potential Verification Method • Voltage between two probes measured with oscilloscope. Shown: V 6 -7 6 m V 67

B 2. 56 Appendix 2: Step Potential Verification Method • Demonstration of the use of two different methods (modeling, testing) to cross-check. • Measured and modeled: Peak from 7 to 8 m

B 2. 56 Appendix 2: Step Potential Verification Method • Conclusions: – Cross check of field test to calculation is mandatory. – Uniform soil assumption worked here in spite of complex infrastructure (sewer, pipelines) nearby. • Recommendations: – Coordinate with C 4. 33 to confirm the validity of the impulse test method, considering frequency dependence of the soil. – Evaluate range of two-layer soil contrast (reflection coefficient) for which inverse distance / quasiuniform soil model is valid.

B 2. 56 Appendix 2: Step Potential Verification Method Inverse Distance Good Poor

Meetings Attended • Montreal, May 2016 – B 2. 56, Ground Potential Rise at Overhead AC Transmission Line Structures during Power Frequency Faults – B 2. AG 06. TF 007, Don’t Put your Arresters near our Dampers – Petrache paper on CEATI studies (CDEGS Hi. Freq vs NEC-4) – Lots of interest in German Hybrid AC/DC with positive pole exposed to lightning

B 2 -AG 06 -TF 007 INTERACTION OF VIBRATION DAMPERS WITH SURGE ARRESTERS SUMMARY OF MEETING IN MONTREAL May 12, 2016 by David Havard

v SCOPE OF TF 007: v Most transmission line surge arrester (TLSA) installations are fitted after construction to improve lightning performance. v Surge arresters are large, heavy and often placed on conductors outside vibration damper locations. v The objective is to produce a paper for CIGRE Journal of Science and Engineering guideline. Havard, B 2 AG 06 TF. 007 14

v SCOPE OF TF 007 (CONT’D): v Scheduled completion 2016. v Originally on application of dampers to retain aeolian vibration control for surge arresters applications. v Based on inputs from WG members, now includes other vibration modes and other forms of failure. Havard, B 2 AG 06 TF. 007 15

v Meeting of May 12 2016 v 23 Members and guests in attendance: v Agenda included: v. Outlining points added to the paper since the last meeting v. Review of new material contributed by email in the last week v. Furtado re failure of support for TLSA v. Vingradov re explosive failure of TLSA and need for Standard Havard, B 2 AG 06 TF. 00 v 16

v. A review of the 6 th draft of the paper v. Highlighting key points in the paper v new experiences offered by members present v. Van Dyke re use of AGS clamp support v. Halsan re loosened corona ring on TLSA v. Chisholm re damage to supporting chain Havard, B 2 AG 06 TF. 007 17

v Future activities: v Update paper with recently acquired and other new material v Target date within one month v Next (final? ) meeting in Paris (Boulogne) in August 2016 Havard, B 2 AG 06 TF. 007 18

AUTHOR: DR. DAVID G. HAVARD CONVENOR CIGRE B 2 -AG 06 TF 007 PRESIDENT, HAVARD ENGINEERING INC. TEL: 1 -905 -273 -3076, E-MAIL: dhavard@rogers. com WEB PAGE: www. havardengineering. com ADDRESS: 3142 LINDENLEA DRIVE, MISSISSAUGA, ONTARIO, CANADA, L 5 C 2 C 2 Havard, B 2 AG 06 TF. 007 19

Meetings Attended • GROUND 2016, near Recife, Brazil June 2016

Meetings Attended • GROUND 2016, Brazil June 2016 – C 4. 23, Guide to Procedures for Estimating the Lightning Performance of Transmission Lines – C 4. 33, Impact of Soil-Parameter Frequency Dependence on the Response of Grounding Electrodes and on the Lightning Performance of Electrical Systems • XIII SIPDA, Brazil, September, 2015 – C 4. 36, Winter Lightning: Parameters and Engineering Consequences for Wind Turbines – C 4. 410 TB 633, Lightning Striking Characteristics to Very High Structures – Published October 2015

C 4. 23 Meeting, Brazil, June 2016 • Responsible: – Chris Engelbrecht (convenor) – Imre Tannemaat (secretary) • Present draft: 99 pages

C 4. 23 Meeting, Brazil, June 2016 • Overview of methodology

Meetings Attended • GROUND 2016, Brazil June 2016 – C 4. 23, Guide to Procedures for Estimating the Lightning Performance of Transmission Lines – C 4. 33, Impact of Soil-Parameter Frequency Dependence on the Response of Grounding Electrodes and on the Lightning Performance of Electrical Systems • XIII SIPDA, Brazil, September, 2015 – C 4. 36, Winter Lightning: Parameters and Engineering Consequences for Wind Turbines – C 4. 410 TB 633, Lightning Striking Characteristics to Very High Structures – Published October 2015

Frequency-Dependent Resistivity • Resistivity at 100 k. Hz or 1 MHz is significantly lower than resistivity measured at 100 Hz – Effect is strongest for high soil resistivity – Effect is well supported by test data

Liaison Report: C 4. 33 Introduction Basic Physical Aspects Cites the Cole-Cole approach: “The permittivity of a material can be described [51] as a complex number given by: The real part of permittivity ( ’) The imaginary part ( ’’) … Such losses represent the fraction of energy …

Frequency-Dependent Resistivity • Draft is 74 pages. • Contributions in chronological order.

Frequency-Dependent Resistivity

Frequency-Dependent Resistivity Typical models, 1000 m soil

Organization of Technical Brochure Contributions on the frequency dependence of soil parameters in a chronological order: – – – – Smith-Rose (1930 s) Scott et al. (1964 -1966) Eberle et al. (1969 -1983) Longmire and Smith (1975) Messier (1980 -1985) Visacro and Portella (1987) Portella (1997 -2000) – CIGRE WG C 4. 2. 02 (1995 -2005) – – Chisholm et al. (2003 -2016) He et al. (. . ) Visacro and Alipio (2011 -2016) Montaña et al. (2012)

CIGRE TB 275 Inclusion • CIGRE WG C 4. 2. 02 (1995 -2005) • In 1995, CIGRE Working Group 02 of Study Committee 36 noted that seven countries (France, Germany, Belgium, Spain, Great Britain, Italy and South Africa) were making use of an ABB HW 2 A instrument to test the earthing resistance of individual pylons. – Fixed frequency of 26 k. Hz. – Electrically “isolates” the tower under test from neighbours, using the high inductive reactance of any overhead groundwire connections. – Analysis in TB 275 suggested that 150 k. Hz would be more appropriate for this purpose.

CIGRE TB 275 Inclusion • REN (Portugal) compared ABB HW 2 A instrument with measurements of soil resistivity at 4 m depth. • Weak power-law relation, with structure impedance at 26 k. Hz varying roughly to the 1/3 power of low frequency resistivity.

CIGRE TB 275 Inclusion • Anticipated relation between Z 26 k. Hz and o from substitution of f = 26 k. Hz into a Alipio/Visacro model for (f), and normalization to an effective tower perimeter of 30 m (giving 10 at 0 = 300 m). • Additional influence of r (f) (21) at 26 k. Hz is modest, even at 0 = 3000 m.

Time-Dependent Effects

Resistivity vs time, 500 to 1000 ns

(f) Versus Ionization • Effect on peak tower base voltage – (f) effect is strong initially, weaker by about 2 s – Ionization models introduce onset time constants on the order of 2 s • Effect on large-dimension footings – (f) effect is the same, large or small dimension – Ionization is not so important for footings of transmission lines, compared to single rods • Testability in full scale – (f) effect is easy to verify with 1 -10 A test current – Ionization calls for impulse currents of 30 to 200 k. A

Meetings Attended • PES Annual Meeting, July 2016 – HVDC Line Design Guide Task Force (July 18) – HVDC Line Design Subcommittee (July 20, 8 AM)

Administrative Influence • Encouraged HVDC group to prepare a PES Technical Report rather than a Standard or Guide – Faster – More tolerant of a range of opinions and options – Easier to modify and add new experiences

Technical Influence – Chapter 3. 4 • Grounding – considered as “return electrode” – HVDC should always be designed with Overhead Groundwires (OHGW), never unshielded. – Role of end-to-end optical fiber cable. – Expected dc resistance of OHGW as line return electrode • 0. 25 for length > 60 km with 9/16” aluminum clad steel • 0. 03 for length > 300 km with 336 kcmil Linnet ACSR – Introduces Insulated Earth Return Wire (below phases) – Foundation grounding issues – expected relation to soil resistivity; corrosion aspects; two-layer soil case. – Worst case: Separate return electrode (Appendix C) in domain of Substation Committee (Guide 80, Guide 81).

Technical Influence – Chapter 3. 5 • Lightning – role of dc voltage bias • Positive pole adds to stress from negative lightning to tower, so it has lower “critical current” and thus higher backflashover rate. • Use critical current of negative-pole backflashover to estimate the two-pole to ground fault rate.

Technical Influence – Chapter 3. 5 • Lightning – role of insulated earth return in improved lightning performance • Covered in IEEE Standard 1243/1997 Figure 9, without the supporting matrix math. • Technical Report includes 3 x 3 and 4 x 4 matrices for surge impedance coupling coefficients without corona.

Technical Influence – Chapter 3. 5 • Lightning – role of guy wires on HVDC towers – Steel monopole: 250 to 300 – Typical lattice tower: 160 to 200 – Slender lattice tower with 4 guy wires: < 100

Technical Influence – Chapter 3. 5 • Lightning – role of guy wires on HVDC towers – Steel monopole: 250 to 300 – Typical lattice tower: 160 to 200 – Slender lattice tower with 4 guy wires: < 100 Desirable Lightning Protection Aspects: • Two OHGW, widely separated • Relatively large-diameter tower body • Four guy wires attached to tower with individual soil anchors

Technical Influence – Chapter 3. 5 • Lightning – role of guy wires on HVDC towers – Typical lattice tower: 160 to 200 – Slender lattice tower with 4 guy wires: < 100 – Steel monopole: 250 to 300 Desirable: Twin Earth Return Undesirable Lightning Protection Aspects: • All groundwires above phases • Earth wires too high, too close • Thin tower body and arms • Single pier foundation rather than 4, 5 or 8 paths to ground

TR Conclusion / Recommendations • Technical Report gives an overview of the specific issues related to HVDC overhead line design and some perspective on the production variations in existing HVDC line designs. • Some weakness and internal consistency can be improved, but it is ready for next-level approval and publication. • Try to avoid the long delay in TR-17 on aeolian vibration, in getting from 99 to 99. 9%.