GROUNDING AND LIGHTNING PROTECTION SYSTEMS IN WIND TURBINES Mustafa Kemal AVŞAROĞLU, Tuğcan TEKİN, Sevim SERİNDAĞ RADSAN A.Ş. mavsaroglu@radsan.com.tr, tt@radsan.com.tr, sserindag@radsan.com.tr ABSTRACT It is quite difficult to imagine air as a fluid. Because air is invisible. Unlike liquids, air moves faster and occupies every part of its environment. With the rapid displacement of air, the movement of the particles within it is also rapid. The process of converting this property of air into kinetic energy is called Wind Energy. Similarly, obtaining energy by using the displacement property of liquid substances such as water is called hydroelectricity, and the center where it is produced is called a Hydroelectric Power Plant. Centers that produce electricity from wind energy are called Wind Power Plants. After Wind Power Plants are built, the propellers rotate the shaft to which they are connected with the movement of the wind (air). With a suitable generator, this kinetic energy is converted into electrical energy. Grounding is necessary in wind turbines to minimize the risk of electric shock to workers and animals in the surrounding area, to provide effective protection for the work by installing a low-impedance line for leakage currents to pass to the ground, to increase lightning protection, and to protect workers and equipment by preventing the formation of high electrical potential differences. GROUNDING IN WIND TURBINES In its simplest form, a wind turbine consists of three parts: 1. Propeller Blades: When the wind blows, it hits the blades of the propeller, causing them to rotate. 2. Shaft: As the blades rotate, the shaft connected to them also begins to rotate. The rotation of the shaft creates movement within the motor, providing energy output and powering the motor. 3. Generator (Induction): It has a fairly simple working method. Electrical energy is produced through electromagnetic processes. It is a system similar to the electric motor in small toy cars. It contains magnets. In the center of these magnets is a section wound with wires. When the propeller shaft rotates, this winding section inside the motor begins to rotate finely in the center of the surrounding magnets. As a result, alternating current (AC) is generated. Despite the risk of corrosion that wind can cause in wind turbines, the tower bodies must be grounded at all times. The tower base and the administration building groundings must be grounded to obtain a good grounding system. The electrodes, connected to each other, are laid in the tower base to provide effective personal protection. Grounding with a resistance below 10 Ohms is recommended in wind power plants. The ribbed steel of a gravitational foundation is a fundamental part of the grounding system and thus provides sufficient internal connection to the foundation to allow lightning and fault currents to pass through. [3] Galvanized steel strip rebar of suitable cross-section or copper cable is connected to the foundation. Connection is made from the external rebars to the copper rods in the ground with bare copper cables. As specified in Table 5 of the TS EN 62305 standard, bare copper with a cross-section of at least 50 mm² should be used as the grounding conductor. Wind power plants are often spread over an area extending for kilometers, and due to the height of modern turbine towers, they are more frequently exposed to lightning strikes. Furthermore, they are usually built on hills in areas with high resistance. Therefore, applying normal grounding procedures in these facilities is not easy and requires special applications. This wind power plant requires uninterrupted grounding. The grounding system must include all equipment, substations, transformers, towers, turbine generators, and electronic equipment. This application, generally involving the addition of a bare conductor along the power collection cable, ensures that all equipment in the wind power plant is interconnected and reduces the resistance of a long horizontal grounding electrode system. The grounding system in a wind farm must be able to function effectively both for 50/60 Hz grid current frequencies and against lightning strikes, which typically have a rise time of less than 10 µs. Figure-1: Grounding and Equipotentialization in a Wind Turbine[2] Figure-2: Wind Turbine Grounding and Spikes [5] While they used to produce turbines of high power, today they are moving towards 7 MW and larger power levels. For these turbines to operate efficiently, the wind needs to be stronger and more stable, and the turbine hub needs to be larger. The large turbine hub and the orientation of the turbines make the production and transmission of energy to the grid more reliable. Wind turbine components are protected in various ways: Blades The blades are protected by a dedicated protection system that has been laboratory tested to withstand currents up to 200 kA without showing any signs of damage other than surface welding marks from the lightning strike itself. Each blade has a lightning termination pad system. The pads protrude slightly above the blade surface on both sides. A flexible down conductor located within the blade provides a conduction path from the pads to the rotor hub, which is used as a conductor from the main body. The electrical and hydraulic equipment located within the hub is fully protected by the Faraday cage of the hub itself. [8] The nacelle rear canopy is manufactured in a 5 mm steel plate that acts as a Faraday cage for the nacelle. The canopy protects meteorological instruments, and a separate lightning rod projection system is installed over these instruments. All components are effectively grounded and surge protection devices within the controller provide temporary protection from the effects of nearby lightning strikes. [8] The controller is equipped with mechanical overload protection to prevent explosion in the event of a direct lightning strike. The devices protect the turbine controller. All lightning protection is required on DIN rails, cabinet doors and components. Figure 3: Wind Turbine Foundation Grounding [5] Figure 4: Equipotential Grounding Bar [6] All grounding is required on the basis of being installed in wind turbines. Grounding rods can be installed depending on the ground characteristics. The grounding network for lightning strike protection in wind turbines consists of protection modules that can be used to protect against lightning and surges, such as potential equalization and shielding. Maintenance, lightning and surge protection costs have decreased, and the increase in powerful turbines installed in wind fields and offshore areas has become acceptable. A few years ago, manufacturers effectively grounded small EMC metal parts. [8] (GL): Guidelines for the certification of wind turbines, Germanischer Lloyd, 2003, with electrical assembly appendix 2004:8.9 Lightning protection guidelines for the certification of offshore wind turbines, 2005: Electrical assembly of lightning protection Figure 5: Lightning strike on a wind turbine Figure 6: Lightning protection of a classic wind turbine[7] STANDARDS FOR PROTECTION AGAINST LIGHTNING AND SUDDEN OVERVOLTAGE SURGES IN WIND TURBINES The relevant standards form the basis of lightning and overvoltage protection. IEC61400: Wind • Generator Systems - Part 24: Lightning Protection Turbine • DIN EN 62305 ’Lightning Protection“ Figure 7: Wind Turbine Lightning Protection Zone Regions In these standards - LPZ 0 to LPZ 3 - Lightning Protection Zone - different protection zones are defined. LPZ 0A • Area where direct lightning discharge is possible • Area where the effect of lightning current and the resulting electromagnetic field will be highest. LPZ 0B • Zone protected from direct lightning discharge • Area where the effect of the electromagnetic field resulting from lightning will be highest • Partial lightning currents occur. LPZ 1 • Electrical surges are limited due to surge protection products and current sharing at zone transitions. • The magnetic field resulting from lightning is reduced by shielding. LPZ 2…n • Electrical surges are further limited due to surge protection products and current sharing in zone transitions. • Magnetic field resulting from lightning is further reduced by shielding. Figure 8: Wind Turbine Blades [4] LIGHTNING PROTECTION OF ELECTRICAL COMPONENTS IN WIND TURBINES equipment equipotential connection in zones Various and electrical devices must be resistant to possible hazards. Protection is provided by shielding and lightning and surge protection modules, which include lightning and surge protection factors. Lightning and surge protection modules reduce surges to a level that cannot cause damage. A three-stage protection concept is necessary for energy. These products are used in the transition from LPZ0A to LPZ1. PROTECTION OF COMMUNICATION TECHNOLOGIES IN WIND TURBINES Since energy plays a leading role in the operation of a wind turbine, communication technologies must also be protected. The comprehensive study will increase the continuity of the protection concept and reduce the risk of failure due to lightning or overvoltages. The availability of turbine installations makes them safer and more economical. This will facilitate the adoption of wind turbines and wind turbine areas by reducing costs. Figure 9: Wind Turbine Generator Area Lightning Protection[6] The lightning arresters, which will be mounted on the turbine body where the anemometer is installed, must be installed together with aircraft warning lights. MATERIALS USED IN GROUNDING AND LIGHTNING PROTECTION OF WIND TURBINES Figure 10: Equipotential Grounding Bar REFERENCES 1. Kadir TEKİN - Istanbul Technical University Master's Thesis. 2. Wind Turbine Lightning Protection Project - Brian McNiff, McNiff Light Industry, Harborside, Maine 3. TS EN 61400 24 - Lightning Protection in Wind Turbines 4. TS EN 62305 - Lightning Protection – Part 3: Physical Damage and Life Hazard in Structures. 5. www.copper.org 6. Gama Energy 7. Yasuda Yoh, IEEJ Trans 2006; 1: 314–319 8. www.elektrikhaber.net Mustafa FAZLIOĞLU Figure 11: Catch Rod Figure 12: Copper Cable Figure 13: Aircraft Warning Lamp A wind turbine with a basic grounding system, all metal components connected to an equipotential bonding system, surge suppressors, low-voltage panels, and information technology devices protected from lightning on the turbine body, is protected against overvoltages and lightning strikes. As stated in international standards, precautions against electric shocks and sudden shocks do not provide 100% protection. While the highest level of protection is achieved, a small risk always remains.
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