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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o Higher soil resistivity

presents higher GPR, as

expected;

o Higher frequencies in the

lightning current have a

localized effect on the GPR;

o The localized effect of the

GPR eradicates the

“equipotential” across the

electrode;

o 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

on 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

office@terratechnology.co.za

Thank you for your kind attention.

Questions are welcome.