Lightning protection, earthing and electricity production of Photovoltaic Power Plants (PVPP)

Design regulatory framework


ORDINANCE No3 of 9.06.2004 on the design of electrical systems and power lines promulgated, SG, volume 90 of 13.10.2004 and volume 91 of 14.10.2004, effective from 15.01.2005, amended and supplemented, volume 108 of 19.12.2007

ORDINANCE No6 of 9.06.2004 on the connection of producers and consumers of electricity to the transmission and distribution electricity networks (promulgated, SG, volume 74 of 24.08.2004; amended by Decision No2535 of 21.03.2005 of the Supreme Court of the Republic of Bulgaria – volume 27 of 29.03.2005, effective from 29.03.2005; amended and supplemented, volume 25 of 5.03.2008 )

ORDINANCE No9 of 9.06.2004 on the technical operation of power plants and networks (promulgated, SG, volume 72 of 17.08.2004, effective from 18.12.2004, amended and supplemented, volume 26 of 7.03.2008)

ORDINANCE No16 of 9.06.2004 on easements for energy sites, issued by the Minister of Energy and Energy Resources, the Minister of Agriculture and Forestry and the Minister of Regional Development and Public Works, (promulgated, SG, volume 88 of 8.10.2004)

ORDINANCE No14 of 15.06.2005 on technical rules and regulations for the design, construction and use of facilities and equipment for the production, conversion, transmission and distribution of electrical energy (promulgated, SG, volume 53 of 28.06.2005, effective from 29.09.2005, amended and supplemented, volume 73 of 5.09.2006)

ORDINANCE No4 of 22.12.2010 for lightning protection of buildings, outdoor facilities and open spaces (SG, volume 6 of 2011)

ORDINANCE on the formation and application of electricity prices and tariffs
Annex No1 to Article 1 of Ministerial Council Decree No 53 of 6.03.2002, promulgated, SG, volume 27 of 15.03.2002, effective from 6.03.2002; amended by Decision No 7278 of 18.07.2002 of the Supreme Court of the Republic of Bulgaria – volume 74 of 30.07.2002, effective from 30.07.2002; amended and supplemented, volume 74 of 30.07.2002, effective from 22.07.2002, repealed, volume 17 от 2.03.2004

Lightning strike. Impact.

Direct lightning strike – the lightning charge passes through elements of the PV plant structure. The damage is noticeable and with lesions indicating the passage of a large amount of energy – disruption of the integrity of elements or physical deformation.

Indirect lightning strike – impacts caused by lightning flowing to the ground or into the atmosphere, as well as by the accumulation of static electricity.

Impacts:

  • through closely located lightning protection system points to earthing conductors or electrical installation routes,
  • through closely located lightning rods to elements – structural or plant electrical elements,
  • through accumulation of static electricity on the input cables of communication systems.

PVPP lightning protection design. Earthing

Two approaches to building lightning protection:

  1. Common grounding loop for lightning protection and electrical installations – all metal parts of the photovoltaic panel structure, the elements of the power transmission network (Concrete Complete Transformer Stations , inverters, distribution boards), as well as the lightning conductors of the lightning protection installation are connected to a common network (grounding loop), which occupies the area of ​​the entire power plant and divides it into cells of such sizes as to guarantee equal potential in the protected area.
  2. Separation between the grounding loops of the electrical and lightning protection installations – the metal structure, as well as the grounding of all elements of the power transmission network, are connected in a common loop, which is separate from the grounding of the lightning protection installation.

Important:

  • The two circuits should not have a galvanic connection between them, and it is necessary that their grounding points are located at a safe distance from each other (usually 5 – 6 m).
  • It is also necessary for the lightning rods to be at a safe isolating distance from the metal structural elements of the power plant.

PVPP design plans

Risk elements in construction of lightning protection

  • The lightning protection provides 80% to 95% efficiency depending on the site protection degree. Objects located along the perimeter of the protection zone are more likely to be struck by lightning.
  • Presence of unprotected by lightning rods areas of the PV power plant.
  • Presence of power lines (medium voltage – 20 kV) on the territory of ​​the power plant and photovoltaic panels located in the power line easement areas.
  • Proximity of lightning rods to photovoltaic panels.
  • Proximity of lightning rods to elements of the electrical installation – power lines, transformer stations, inverters.
  • Proximity of photovoltaic panels to the edge of the protected area.
  • Installation of photovoltaic panels above electrical lines.
  • High structures or trees located near the power plant increase the risk of inducing overvoltage in the PVPP system.
Presence of an unprotected by lightning rods area near the PVPP.

Lightning protection system and surge protection basic elements

АC – alternative current;
DC – direct current;

Early streamer emission

Early Streamer Emission – head

Main mast – basement, earthing

Damage caused by lightning strikes

Direct lightning strike

Indirect lightning strike

Overvoltage in the electric transmission grid

Frequent power outages – connecting transformers to a medium voltage network (20 kV) create the possibility of steep and large power peaks.

Induction of dangerously high voltages:

  • in parallel and close routing of cables with high currents and low-current installations (communication cables),
  • in parallel routing of cables from the power grid near the lightning rod grounding loop,
  • creating of parasitic capacitances between the electrical cables and the structure in the DC part of the PV power plant.

Emergency outages in the electricity transmission grid

Overvoltage in the medium voltage (20 kV) power transmission grid caused by emergency power shutdowns and starts on transformers primary side.

Photos show a breakdown of one of the transformer windings to its core.

PVPP earthing

Common earthing problems :

  1. Poor connection between the earthing loop elements and the ground wire of the inverters due to poor workmanship, wear or corrosion.
  2. Poor connections between circuit elements – connection failures in earthing cells due to corrosion and insufficient maintenance.
  3. High transition resistance between the earthing rods and the ground – may occur in rocky or sandy soil. When the soil characteristics are not taken into account during design.

Transition resistances in grounding of PVPP. Constructive elements.

Assembly elements of grounding in PVPP

Earthing loop assembly element – according to design documentation (left) and in actual implementation (right).

Partial shading – the hot spot effect

Partial shading of one element of the photovoltaic panel turns the shaded area from a generator into a load. This leads to the flow of the entire current of the panel through it and the release of a large amount of heat in the element. Its temperature rises and this leads to its destruction.

To prevent this effect, so-called reverse diodes are installed (connected with reverse polarity) to divert the generated current away from the shaded element.

Typically, panels consist of 36, 48 or more elements. The most suitable option is to install diodes in parallel on each element, but for economic reasons, several diodes are installed distributed in volumes of elements of 12 or 18 elements.

Their location on installation is in the PV Junction Box, where the terminals of the photovoltaic panel are located.

Partial shading – the hot spot effect

Conditions for the occurrence of the hot spot effect

  • Due to unmaintained row spacing.
  • Upon closely spaced tall objects.
  • From fallen leaves or objects on the panels.
  • Uneven dusting of the panels.

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