HH
Rated current I n
The current value, according to IEC 60282-1, that a HV fuse can carry continuously under speci fied conditions. Determined figures are both the free in air mounting, as well as a maximum ambient temperature of 40°C.
Rating I
In some fuses, a double designation is used to specify a current, e.g. 200RC140A. The first value designates the time- current characteristic, such as 200A in this example. The “RC”, which stands for “Rated Current“, is followed by the rated current, which considers the maximum permissible warming of the fuse under normative conditions. In the example this is 140A.
Minimum breaking current and class
Minimum value of a prospective current, which a fuse is able to interrupt at a stated voltage under prescribed conditions; • • • Maximum breaking current (breaking capacity) Maximum value of a prospective current, given in kA, which a fuse is able to interrupt at a stated voltage under prescribed conditions. Back-up: given by the manufacture Full-range: current which causes melting equal to the fuses rated current General-purpose: melting time 1 hour
Cut-off current
Maximum peak value which occurs during the switching process of the fuse.
Rated voltage U n
The range of application is given by two different voltages, a lower and upper value, e.g. 6/12kV. The first being the lower value represented here as 6kV reflects the minimum operating voltage and the higher value 12kV the maximum operating voltage that the fuse is allowed to operate with. The higher voltage is named "Rated Voltage" according to the definition of IEC 60282-1.
5 Application Guide Replacement of HV Fuses in 3-phase systems
The standards, IEC 60282-1 and VDE 0670 – part 4, recommends that in a 3-phase system, that if a fuse activates in any of the phases, that fuses in all three of the phases be replaced.
HV Fuses for transformer protection
To protect transformers in distribution networks, back-up fuses are mainly used. To ensure for a suitable protection, the values of selection according to VDE 0670 part 402, table 2 may be applied. The extended tables based on this are included in the technical annex. These tables give recommendations for transformer ratings of 50kVA - 2000kVA and are separated into three different applications, which consider the concept of protection on the secondary side of the transformer:
Protection with low voltage fuses of class gTr Protection with low voltage fuses of class gG Solid links only without any protection device
• • •
HV Fuses for the protection of motor circuits
Fuses for motor circuits are designed to protect motor switches against unacceptably high over currents, which may cause contact welding. Moreover, in case of short-circuits, they have to be able to provide interruption within milliseconds to protect the circuit against the dynamic effects of such currents. If determined correctly, all HV fuses from SIBA can be used in motor circuits. However, SIBA also offers special HV fuses for motor circuits that function as back-up fuses developed with the requirements of motor circuits in mind. To select the right fuse for a given motor, not only the operating current must be borne in mind, but also the motor startup current as well as the number and duration of startups. The resulting rated current can well be a multiple of the motor current. When taking into account cyclical loads and high ambient temperatures, high voltage motors with reduced startup current also should be protected by fuses whose rated current depending on the type is in the range of 1.3 to 2 times the operating current.
portal: www.siballc.net e-mail: info@sibafuse.com
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