URT
URT
Ultra-Rapid Fuse Links for the Protection of Semiconductor Rectifiers 1.General The design of rectifier equipment requires specific provisions in the switchgear for the protection of power semiconductor components. Because of the semiconducor's low thermal capacity, the requirements for the planned protective device exceed those of standard devices. Both the rated current and voltage as the criteria for the fusing selection are no longer sufficient and the following has to be considered: • Hgh ispeed of response in the overload range. • Operating integrals adjusted to the limited load integrals of the semiconductor cell. • Low switching voltages during breaking process. • Low temperature rise and power loss of the protective device under operating conditions. Further important design aspects are the price of the protection device in relation to the total cost of the equipment, as well as down time after a fault. SIBA ultra-rapid fuse links meet these requirements and efficient protection is provided. Features include: • Extremely fast time/current behavior and low operating integral values. • Low temperature rise at the insulating body due to excellent thermal conductivity of the ceramic material. • Low power loss under rated conditions. The technical information presented here is intended to be used as a basis for design and includes all the basics necessary for the selection of devices offering the maximum protection for rectifiers. Firstly, the fuse specific data is explained in detail, rendering a basis for the following chapters which examine the breaking process. SIBA data sheets include characteristic curves, these are described in this documentation and examples given. The most commonly used rectifier circuits are shown in tabular form, properties of parallel and series connection of fuse links are given, and possible faults in circuits are treated. Thermal influences, alternating load operation and current shock loads are considered and compensated by conversion coefficients described in the following sections. Finally, the last section shows the criteria for calculating the optimum fuse link, and includes a flow diagram for an easy overview. 2. Characteristic Values of Fuse Links Rated Voltage - U N The rated voltage of a semiconductor fuse link is the RMS value of a sinusoidal AC voltage. All test conditions and the operating voltage limit are stipulated on that basis. The fuse link rated voltage has to be determined in order to be higher than the voltage causing the short circuit current. Rated Current - I N The rated current of a fuse link is the RMS value of a sinusoidal AC current at a frequency range of 45Hz to 62Hz. It is the current with which the fuse link can be loaded continuously under determined conditions without changing its characteristics. These conditions, provided by the standards, are: • Ambient temperature (20 5) °C. • No external cooling. • Connecting cross section specified. • Fuse links are mounted in open test rigs while testing. In practice, however, conditions are usually more diverse, and so additional calculations are necessary, which may result in decreasing the fuse links rated current. • Free of ageing, due to the use of pure silver elements. • Low switching arc voltage due to special element design.
portal: www.siballc.net e-mail: info@sibafuse.com
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