Solar Earthing Kit in India

Earthing kits in solar power plants are designed to protect personnel and equipment by providing a safe path for fault currents to flow into the earth. They also play a crucial role in lightning protection and ensuring the efficient operation of the solar power system.

• Soil Model: Effective earthing design requires an understanding of the soil characteristics. A common approach is to use a three-layer soil model with specific resistivity and thickness for each layer. For example, a model might use 50 Ohm.m for the top layer (2m thick), 120 Ohm.m for the middle layer (33m thick), and 65 Ohm.m for the bottom layer. This highlights the importance of conducting soil resistivity tests to determine the appropriate earthing design for a specific location.
• Fault Current: The earthing system must be designed to handle the expected fault current levels. A typical design might consider a fault current of 1000 A at 50 Hz.
• Earth Resistance: The required earth resistance varies depending on the system voltage and application. For installations with more than 1000 V, a resistance of 0.5 Ohm is required. For installations with a power of less than 100 kVA, the resistance should be no more than 10 ohms.

Earthing kits consist of various components that work together to provide a safe and reliable grounding system. These components include:

• Earthing Electrodes: These are the primary components that establish a connection with the earth. They can be rods, pipes, plates, or mats made of conductive materials like copper or galvanized steel.
  • Driven Rods or Pipes: These are commonly used and involve driving rods or pipes vertically into the ground.
  • Buried Electrode Grids or Meshes: These consist of a network of conductors buried in the soil.
  • Concrete-Encased Electrodes: These use steel reinforcing bars or bare copper conductors encased in concrete.
  • Ground Rings: These involve burying a ring of bare copper conductor in the earth.
  • Plate Electrodes: These use plates made of iron, steel, or copper buried in the ground.
  • Metal Underground Water Pipes and In-ground Support Structures: These can also serve as grounding electrodes if they meet specific requirements (e.g., direct contact with the earth for a certain length).
• Grounding Conductors: These are wires or strips that connect the earthing electrodes to the various components of the solar power plant. Copper or aluminum wires are commonly used due to their high conductivity.
• Installation Accessories: These include bolts, clamps, and other accessories used to fix the earthing materials and ensure secure connections.
  • Grounding Lugs/Clamps: These are used to attach the grounding conductors to the frames of solar panels, inverters, and other equipment.
  • Grounding Bus Bar: This centralizes the connection of all grounding wires, providing a common point for grounding.
• Lightning Arrester: This protects the solar power plant from lightning strikes by diverting the surge current to the ground.
• Chemical Compounds: These are used in the earthing pit to improve soil conductivity and reduce earth resistance. They typically include a mixture of charcoal and bentonite clay.
• Insulators: These are used to isolate the earthing material from the surface area or wall to prevent the spread of high voltage impulses during a lightning strike.
• Conductors: Earthing systems typically use bare copper conductors with a cross-section of 70mm² or larger. Galvanized iron (GI) conductors are also used, with sizes varying based on the application (e.g., 75 x 10 mm for AC side and 25 x 6 mm for DC side).
• Module Frames: Solar PV modules must have anodized aluminum frames with provisions for earthing. This ensures electrical safety and compatibility with the mounting structures.

Specific earthing requirements exist for the AC and DC sides of solar power plants:

• AC Side: The main earthing grid for the AC side is typically formed with GI conductors of a size not less than 75 x 10 mm.
• DC Side: The main earthing grid for the DC side is typically formed with GI conductors of a size not less than 25 x 6 mm.

The sizes of other equipment and components should comply with relevant Indian standards and statutory regulations.

Earthing requirements can vary based on the capacity of the solar inverter:

• 1kW to 3kW: Two earthing points are typically required, one for the inverter and one for the lightning arrester.
• Above 3kW: Three earthing points are generally needed, with an additional one for the solar PV modules.

Solar power plants often incorporate lightning protection systems to safeguard equipment from voltage surges. These systems include:

• Lightning Arresters: These devices divert lightning strikes to the ground.
• Surge Protection Devices (SPDs): These protect sensitive electronic equipment from voltage fluctuations.

It's important to emphasize that a comprehensive approach to lightning protection involves both external lightning protection (e.g., lightning rods) and surge protection devices.

Different types of earthing kits are used in solar power plants based on the specific requirements of the installation. Common types include:

• Pipe Earthing: This common method uses galvanized steel pipes buried deep in the ground to connect to the electrical conductors.
• Mat Earthing: A mat of bare metallic conductors is buried in the soil, connecting horizontal and vertical electrodes.
• Plate Earthing: This method uses copper or GI plates buried deep in the ground to prevent static charges and stray current issues.
• Marconite Earthing: This method uses a mixture of marconite (a grey substance), cement, and water to create earthing. It is considered safe and efficient, using low-resistance copper earth electrodes.
• Electronic Earthing: This type is used for inverters and control rooms, employing copper flats with lead coating and epoxy insulators.

The choice of earthing kit depends on factors such as soil composition, moisture levels, and the overall design of the solar power plant.

Earthing design and installation in India must comply with relevant standards and regulations to ensure safety and efficiency. Key standards include:

• IS 3043: Indian Standard Code of Practice for Earthing. This standard provides comprehensive guidelines for various aspects of earthing systems, including:
  • Selection of earthing materials and electrodes.
  • Design and installation procedures.
  • Testing and verification of earthing systems.
  • Safety precautions and maintenance requirements.
• IEC 60364 & IEC 62561: International Electrotechnical Commission standards for electrical installations and lightning protection systems. These standards provide internationally recognized guidelines for earthing design and implementation.

In addition to these general standards, specific regulations apply to solar power plants in India:

• Earthing of Combiner Boxes: Combiner boxes, which combine the output of multiple solar panels, must have proper earthing to ensure safety and prevent electrical hazards.
• Interconnection of Earth Strips: Earth strips used in the earthing system must be interconnected through proper welding to ensure a continuous and reliable earthing path. Bolted connections are not permitted.
• Use of Indigenously Manufactured PV Modules: Solar power plants in India are required to use indigenously manufactured PV modules that conform to specific standards and certifications (e.g., IEC 61215 Edition II / BIS 14286).

Some specific requirements for earthing kit components include:

• Lightning Arresters: Copper rod with a height of 1.2 - 1.5 meters and a resistance of 3 - 5 Ohms.
• Wires: 16 sq.mm thickness for both DC and AC applications.
• Earthing Pit: Dimensions vary based on the terrain (e.g., 4.5 ft. to 10 ft. in plain areas).
• Earthing Rods: 8 feet in length, with the quantity depending on the system size and design.