ABB NU8976A99 HIER466665R0099模块
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ABB NU8976A99 HIER466665R0099在24 V直流配电系统中使用保险丝不是故障安全措施。如果一组发生短路，那么在保险丝熔断之前，电压很可能会下降；因此所有组将经历电压下降。电缆保护24 V直流配电系统电缆必须采用保险丝保护。为了考虑过载/短路情况，电源输出电流受到限制。允许电源具有至少为最大连接保险丝额定电流值3-4倍的额外容量，并记住在计算中包括长电缆电阻。连接备选方案现场设备电源的连接方式可与AC 800M装置的连接和供电方式相同（参见第177页图61和第178页图62）。ABB NU8976A99 HIER466665R0099但是，应注意，同一电源断路器单元可用于控制和隔离两个电源。或者，可以在每个支线上使用独立的电源断路器（参见第178页图62）。从外部电源供电AC 800M控制器可以从外部+24 V DC电源供电。该电源通常用于许多不同类型的电厂设备，导致AC 800M控制器的电力电缆过长ABB NU8976A99 HIER466665R0099
ABB NU8976A99 HIER466665R0099模块The use of fuses in the 24 V DC distribution system is not a fail-safe measure. If a short circuit occurs in one group, then voltage will most likely drop before a fuse blows; consequently all groups will experience a drop in voltage. Cable Protection 24 V DC distribution system cables must be fuse-protected.ABB NU8976A99 HIER466665R0099 In order to allow for overload/short circuit situations, the power supply output current is limited. Allow the power supply an extra capacity of at least 3-4 times the rated current value of the largest connected fuse and remember to include long cable resistance in the calculation. Connection Alternatives The field equipment power supply can be connected in the same manner as that used for connecting and powering the AC 800M units (see Figure 61 on page 177 and Figure 62 on page 178).ABB NU8976A99 HIER466665R0099 However, it should be noted that the same Mains Breaker Unit can be used to control and isolate both power supplies. Alternatively, independent Mains Breakers can be used on each spur (see Figure 62 on page 178).Powering from an External Source The AC 800M Controller can be powered from an external +24 V DC source. This source is often common for many different types of plant equipment, resulting in long power cables to the AC 800M ControllerABB NU8976A99 HIER466665R0099
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