Custom Case Study
As the build-out of clean energy continues, the number of wind turbines deployed continues to increase. In fact, there are nearly 30 000 wind turbines installed in Germany alone (source: BWE Bundesverband WindEnergie e.V.).
Given their installation locations — including offshore and remote locations at high elevations — wind turbines are exposed to severe weather conditions, such as very high gusts and sustained winds. In addition, the very operation of wind turbines results in the entire system being subjected to extremely high and extended vibration forces. As a result, electrical connections of the high power components inside the system are potential “weak points.”
Adequate contact pressure over the long term and a low contact resistance for these component connection points is key. Power dissipation is converted into heat, which increases when current flows at the connection point. Because electrical connections are made of metal, the increase in resistance can generate temperatures of up to 600 °C at the defective connection point, depending on the magnitude of the contact resistance and of the current flowing (P = R x I²).
Power dissipation of 50 W or more is considered combustible, and processes that change the current load can further increase the already elevated contact resistance, because they subject the electrical connection to the expansion and contraction of pronounced thermal stress. This also results in a further degradation of the contact pressure, and the thermal stress usually causes further degradation in the conductivity of the conducting material, which leads to an even higher contact resistance. Maintaining a stable contact connection is therefore a very important requirement for these systems, in terms of safety and long term operating performance.
Given all of the above, catastrophic damage to wind turbines is quite possible. In fact, according to TÜV (German Technical Inspection Authority), it occurs around fifty times per year in Germany alone. One such potential failure mode is that the system catches fire. Once this happens, there is the possibility that a thirty meter long rotor blade will crash to the ground from a height of around one hundred meters. Fire departments are typically unable to extinguish flames due to the height of the wind turbine. Instead, they are forced to cordon off the area and attempt a controlled system burn until it exhausts the combustible material. In extreme cases, the towers can break and / or collapse, causing damage to other units or buildings in the immediate vicinity. The cost of a system fire, and replacing damaged equipment, can reach into the millions.
To solve this loose connection problem — especially in environments undergoing sustained vibration over the long term — Vishay developed the ESTAspring attachment system for the next generation of LVAC power capacitors. Instead of traditional screws, it utilizes lever-action spring contacts.
ESTAspring is a lever-lock spring connection for premade flexible conductors from 2.5 mm² to 25 mm² with bootlace ferrules. The maximum rectangular crimp geometry is 6.0 mm x 7.6 mm, and the spring is made of stainless steel that is corrosion-resistant. It uses a copper alloy conductor material that can handle currents of up to 90 A.
Vishay’s ESTAspring offers unprecedented ease-of-use. No tools or torque specifications are required for integrating these connections. The lever being closed assures a reliable contact with the necessary contact force and a simple visual check is all that is necessary for confirmation of a reliable connection.
Vishay’s PhMKP series capacitors — available with an oil filling or dry with a gas filling — are the first capacitors of this type available worldwide that offer the new ESTAspring safe connection technology. The devices feature rated voltages from 230 V to 1000 V, maximum reactive powers ranging from 2 kVAR to 37.1 kVAR, and maximum connection currents of up to 90 A.
The always-constant contact force of ESTAspring assures a reliable connection over the entire service life of the capacitor and makes fires caused by defective contacts almost impossible. In addition to the improved reliability and safety for this harsh environment application, they provide a maintenance-free connection system for low voltage power factor improvement or harmonic filters in wind turbines, and other applications that experience high vibration environments.
UL/ULC has approved the polypropylene foil capacitors, in combination with ESTAspring, as a complete system.
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