Influence Of Ambient Temperature On Circuit Breaker Characteristics

Circuit breaker is one of the electrical appliances used widely in distribution system. Customers are generally concerned about how to reduce capacity of different types of circuit breakers in different places and conditions. For example, the circuit breaker is installed in the complete set of electrical appliances (switchgear, box), due to a variety of electrical appliances (knife switch (or load switch), contactor, circuit breaker, connecting copper bar, etc.). One of the problems to be considered is the influence of ambient temperature on circuit breaker characteristics.
1 Plastic case type circuit breaker
From the current large number of plastic shell circuit breakers sold in the domestic and foreign markets, there are full electromagnetic type (commonly known as oil cup type release), thermal-electromagnetic release type, electronic release and microprocessor release and so on.
1) The electromagnetic oil cup trip device is not only used for overload long delay, but also for transient protection of short circuit current (that is, overload and short circuit protection use the same oil cup trip device). The delay of overload long delay protection relies on the reaction spring in the oil cup and the methyl silicone oil to damp the upward movement of the floating core (when the floating core in the oil cup is under a large current, it can draw down the trip device armature without floating upward to make the circuit breaker trip).
2) The largest number used is the thermodynamic - electromagnetic type. Its overload long delay using hot bimetal components, short circuit current transient using electromagnet system. Different manufacturers, in the provided instructions or samples, take the relationship between the operating current and the ambient temperature of the circuit breaker capacity reduction table, or in the curve of temperature and current, called the temperature compensation curve.
3) Overcurrent protection circuit breaker for household or similar places. The circuit breaker conforms to the standard GB10963, it is different from the 1), 2) class (in line with GB14048.2) is the benchmark check temperature is 30 degrees, (of course, as the protection of household appliances, its overload long delay and short circuit transient protection characteristics are not the same).
2 Universal (frame) circuit breaker
1) Universal circuit breaker, such as DW15-630 has thermal-electromagnetic type (using thermal relay for overload long delay protection, electromagnetic trip for short circuit transient protection), its capacity reduction is basically the same as that of plastic-case thermal-electromagnetic type. Other universal circuit breakers, such as SRW45 universal circuit breakers are the same.
2) Electronic release (including microprocessor release)
Electronic and microprocessor trip breakers are more used in universal (frame type) circuit breakers. At present, plastic shell circuit breakers with large current specifications are used in industrial electronic components, which adapt to a wide ambient temperature range (-40-85), that is, in this temperature range, the performance of electronic components will not change. Analysis of the reason: the change of ambient temperature has no effect on the performance of electronic components. High current specifications to drop capacity because the wiring copper at high current heating caused by the rise of the overall temperature rise. For low-voltage appliances, the ambient temperature within 10-40 circuit breaker temperature rise basically has no effect, and more than 40 has an impact, the degree of impact is small.
To sum up, when the ambient temperature exceeds the reference temperature for circuit breaker characteristic check, the circuit breaker installed in the switch cabinet needs to appropriately reduce the current value, which is the rated current multiplied by the capacity reduction factor. The maximum allowable ambient temperature (box and cabinet environment) of the complete set of devices is different according to the type and quantity of the electrical components inside. Users should use this maximum allowable ambient temperature, such as 50, 55 or 60, and then reduce the capacity according to the current-temperature relationship table or temperature compensation factor provided by the circuit breaker manufacturer.