Earthing and Lightning Protection of Utility Scale PV Plant - What - - PowerPoint PPT Presentation

Earthing and Lightning Protection of Utility Scale PV Plant

• What is Missing? -

by Dr Pieter H Pretorius, TERRATECH, South Africa

 INTRODUCTION  IMPLICATIONS - DESIGN  IMPLICATIONS – INSTALLATION  MITIGATION OPTIONS  CONCLUDING REMARKS

OVERVIEW

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 Context – Large, Free Field Photovoltaic Plant;  Experience has shown that earthing and lightning protection deserves special attention;  With more responsibility / accountability now on the EPC contractor for lightning protection, in particular, and with a new round of projects developing in South Africa as well as Sub- Saharan Africa, it is imperative that awareness be created of what can go wrong in the context of earthing and lightning protection;

INTRODUCTION

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 AIR TERMINATIONS Components of an external lighting protection system:

IMPLICATIONS - DESIGN

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Air termination rod Down conductor Earth electrode Air termination rod

 AIR TERMINATIONS – No air terminations

IMPLICATIONS - DESIGN

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 AIR TERMINATIONS - Reason

IMPLICATIONS - DESIGN

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Thermogram of polycrystalline cells shaded by lightning rod and the view of shaded part of PV module .

Ref: E Bozek, G Basista, Thermographic Research of Photovoltaic System Operating in Shaded Conditions Measurement Automation Monitoring, Jun. 2015, vol. 61, no. 06

 AIR TERMINATIONS - Analogy

IMPLICATIONS - DESIGN

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 LIGHTNING GROUND POTENTIAL RISE (GPR)

IMPLICATIONS - DESIGN

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Potential (V) Distance from Strike Point (m) Potential function of soil resisity and electrode geometry / mesh density

IMPLICATIONS - DESIGN

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• Higher soil resistivity

presents higher GPR, as expected;

• Higher frequencies in the

lightning current have a localized effect on the GPR;

• The localized effect of the

GPR eradicates the “equipotential” across the electrode;

• Equipotential (Quasi-

equipotential) is only relevant at lower frequencies; Main point: Loss of Equipotential

Ref: P H Pretorius, Loss of Equipotential During Lightning Ground Potential Rise on Large Earthing Systems, Joint IEEE International Symposium on Electromagnetic Compatibility & Asia‐Pacific Symposium on Electromagnetic Compatibility (2018 Joint IEEE EMC & APEMC), Suntec Convention and Exhibition Centre, Singapore, 14 to 17 May 2018.

IMPLICATIONS - DESIGN

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Ref: P H Pretorius, Loss of Equipotential During Lightning Ground Potential Rise on Large Earthing Systems, Joint IEEE International Symposium on Electromagnetic Compatibility & Asia‐Pacific Symposium on Electromagnetic Compatibility (2018 Joint IEEE EMC & APEMC), Suntec Convention and Exhibition Centre, Singapore, 14 to 17 May 2018.

Part of PV plant electrode with panel support structures. Calculated GPD across part of an electrode shown

Finding: Over relatively short distances (23 m to 50 m), significant differences in potential (up to 66.1 kV) can be presented.

8,3 m 4,5 m

 LIGHTNING GROUND POTENTIAL RISE (GPR)  Standards – limited application - lightning risk assessment – not so obvious:

IMPLICATIONS - DESIGN

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IEC 62305-2, supported by Parts 1, 3 and 4 forms, together, perhaps the most elaborate set of lightning protection standards referenced in many countries, including South Africa. However, it is specifically noted from IEC 62305-4: “The scope of this part of IEC 62305 deals with the protection of equipment within structures and not protection of interconnected structures to which isolation transformers may provide some benefit”.

Finding: This is seen as a limitation of the standard (in the context of the discussion

• n lightning GPR) that requires further attention in future versions of the standard.

Ref: IEC 62305-4, “Protection Against Lightning - Part 4: Electrical and Electronic Systems Within Structures”, 2010

 UNIQUE CONDITIONS (SOUTH AFRICA)

* High soil resistivity (> 1000 Ω.m) * Lightning activity ( 3 – 6 Flashes / km2 / year) * Wire-line technology

IMPLICATIONS - DESIGN

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Ref: P H Pretorius, On Ground Potential Rise Presented by Small and Large Earth Electrodes Under Lightning Conditions, IEEE AFRICON 2017, Victoria and Alfred (V&A) Waterfront Cape Town, South Africa, 18 to 20 September 2017. P H Pretorius, C R Evert, Elevated Lightning Flash Density at Large PV Plant Environments – A Hypothesis and Preliminary Findings, CIGRE, 8th Southern Africa Regional Conference, Lord Charles Hotel, Somerset West, Cape Town, 14 – 17 Nov 2017.

 UNIQUE CONDITIONS (SOUTH AFRICA)

* High soil resistivity (> 1000 Ω.m) * Lightning activity ( 3 – 6 Flashes / km2 / year) * Wire-line technology

IMPLICATIONS - DESIGN

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 SMALL MISTAKES CAN CONTRIBUTE TO DAMAGE

IMPLICATIONS - INSTALLATION

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 SMALL MISTAKES CAN CONTRIBUTE TO DAMAGE

IMPLICATIONS - INSTALLATION

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 HOW MUCH PAIN  One thunderstorm – 3 direct strikes (-30 kA; -11kA; -17 kA): R 1,5 m ($ 104,000)

IMPLICATIONS - INSTALLATION

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 Philosophy: “Give and take and use knowledge available” (Protect the Boxer and use your arms)

MITIGATION OPTIONS

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 Lightning GPR not a new phenomenon – existing techniques to mitigate;  No Air Terminations

• Harden Equipment;
• Improve Zoning (LPS, EM);
• Better shielding;

 Air Terminations - Supplement (German only)

MITIGATION OPTIONS

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 Lightning GPR

• Consider in Risk Assessment
• Single Point Earthing
• Apply isolation devices;
• Technology selected(eg Fibre vs Wire Line)

 Installation

• Inform Site Supervisor
• Quality Management Procedures

MITIGATION OPTIONS

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 To answer the question: What is missing? * Awareness of damage mechanisms and how to design for these in specific conditions. * Awareness of unique conditions that contribute to damage; * Awareness of implication of small installation errors. * Awareness of mitigation options.  Possible role to create awareness by Participating Universities / SAIEE Lightning Chapter.

CONCLUDING REMARKS

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THANK YOU

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Pieter H Pretorius, PhD TERRATECH, South Africa www.terratechnology.co.za

• ffice@terratechnology.co.za

Thank you for your kind attention. Questions are welcome.