The basics of device circuit breakers | Differences between the technologies
Tripping characteristics Thermomagnetic device circuit breakers are available with different characteristic curves . This allows them to meet the wide range of requirements that result from different application cases . The characteristic curve ( Fig . 11 ) indicates that the thermal trip [ a ] responds considerably later than the magnetic trip [ b ]. This can be explained by the required heating time of the temperature-dependent trip mechanism . However , even currents that are slightly higher than the nominal current are identified as overload currents and shut down . Magnetic tripping responds very quickly to rapidly rising currents that exceed the nominal current . This is particularly advantageous for detecting and switching off short-circuit currents . Alternating currents trip faster than DC currents at the same nominal value . This is depicted by the blue area in the curve . This behavior is generally applicable to all characteristic curves . Nevertheless , it is only used for circuit breakers with the M1 characteristic curve . Circuit breakers with the SFB or F1 characteristic curve also trip so fast with direct current that they would respond overly sensitively during operation with alternating current .
SFB characteristic curve Circuit breakers with the SFB tripping characteristic ( Fig . 12 ) offer maximum overcurrent protection , even in extensive systems with long cable paths . SFB stands for Selective Fuse Breaking , i . e ., selective shutdown . Protective devices with this characteristic curve prevent an unnecessarily early switch-off
Fig . 11 : Typical tripping characteristics for thermomagnetic circuit breakers a Operating range for thermal tripping b Operating range for magnetic tripping t Switching time ( in seconds ) xI Multiple of the nominal current / tripping factor 1 Current range for which the characteristic curve applies 2 DC tripping range ( gray ) 3 AC tripping range ( blue ) 4 Tripping maximum 5 Tripping minimum
in the event of brief current increases and starting currents during operation . They simultaneously prevent unnecessarily long , persistent overload currents , which may lead to the hazardous generation of heat in operating equipment .
M1 characteristic curve Circuit breakers with the M1 characteristic curve ( Fig . 13 ) trip later than those with SFB or F1 characteristic curves . They withstand starting currents for somewhat longer periods but consciously respond less swiftly to fault situations . In comparison to the direct current characteristic curve , the alternating current characteristic
SFB technology
QUINT power supplies from Phoenix Contact feature Selective Fuse Breaking Technology , also known as SFB . These power supplies can supply six times the nominal current for a few milliseconds . This enables them to provide the necessary current reserve for safe tripping of the protective devices .
curve is dragged forward on the axis of the nominal current multiple . Even at a lower multiple of the nominal current , alternating currents cause the circuit breaker to trip .
F1 characteristic curve Circuit breakers with the F1 characteristic curve ( Fig . 14 ) trip quickly . They react very quickly to overload situations . However , this can lead to unnecessary shutdowns during operation . This means they offer optimal protection for sensitive loads with very low starting current and thus provide protection over great distances . End devices , which can be damaged by temporary overloads and slightly increased operating current , are also protected by these circuit breakers .
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