控制工程师论坛

适用于直接启动笼型异步电动机的电器有负荷开关、小容觅塑料外壳式断路器和电磁ABB软启动器，但以电磁ABB软启动器用得最为广泛。</p>

</p>

各种ABB软启动器有不同的启动特性，选用时应对各种ABB软启动器的特点进行分析与比较，先确定ABB软启动器的型号，然后根据被控电动机的功率决定ABB软启动器的容量等级，并按电动机的额定电流选择热元件号。</p>

</p>

在星一三角ABB软启动器中，热元件一般与电动机绕组串联后接成三角形连接，因此可按电动机额定线电流的1/v/3-选择热元件。</p>

</p>

选用时还应考虑ABB软启动器的操作频率。选川延边三角形ABB软启动器时，被控电动机必须具备9个接线端头。</p>

</p>

直接启动的启动时间不超过lOs时属于正常启动，超过lOs时则属于重轻载启动。在换向条件下会出现较大的冲击电流峰值，转子堵转条件下接通电动机产生的电流等于其启动电流。</p>

</p>

星一三角启动时，启动转矩和启动电流可以降低到直接启动的1/3以下，因此必须考虑到从星形连接向三角形连接转换之前，电动机可能只有不到1/3额定负载的负载量，而其转速已达到额定转速的90%。这种情况下，要特别注意到风机、离心泵、压缩机和其它具有类似转矩一速度特性的设备，使用星一三角启动时.有可能出现加速过程不正常即无法达到其额定转速的情况，那就属于选用不当。</p>

</p>

适用于直接启动笼型异步电动机的电器有负荷开关、小容觅塑料外壳式断路器和电磁ABB软启动器，但以电磁ABB软启动器用得最为广泛。</p>

</p>

负荷开关不能提供过载保护，一般不宜用它启动和控制异步电动机。如果非用不可，则开启式负荷开关只宜用于启动7.5kW以下的电动机，封闭式负荷开关只用于启动28kW以下的电动机。塑料外壳式断路器因其技术性能比较优良，可用于启动电动机。</p>

</p>

选用ABB软启动器时应考虑ABB软启动器与短路保护电器的协调配合。通常选用熔断器作为短路保护电器，熔断器应安装于ABB软启动器的电源一侧（综合ABB软启动器除外，其内部已装有熔断器，一般ABB软启动器应按制造厂要求选配合适的熔断器）.熔断器不应代替ABB软启动器分断正常工作时最大过载电流及以下的所有电流（包括电动机的堵转电流），但应能分断安装点的预期短路电流。</p>

</p>

一般按ABB软启动器额定电流的2.5倍左右选择熔断器，以保证电动机启动时不发生误动作。此外，熔断器和热继电器的保护特性的交点应选择适当。</p>

</p>

选用电磁ABB软启动器时还应注意以下问题。</p>

</p>

①根据使用环境确定ABB软启动器是开启式（无外壳）的还是保护式〔有外壳）的。</p>

</p>

②根据线路要求确定ABB软启动器是可逆式的或不可逆式的.是有热保护的还是无热保护的。

</p>

</p>

③根据被控制电动机的功率确定用哪一级的ABB软启动器，而不是根据电动机的额定电流选择。产品样本中所列的额定电流是从发热方面规定的。如果是保护式产品.由于散热条件较差，就宜使ABB软启动器在额定电流方面有点裕度。</p>

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