Branch fuses in a capacitor bank.

Hello everyone,

I'm trying to figure out why you would need to place two branch fuses in every branch of a delta connected capacitor bank (see picture below, ignore the left diagram [inline fusing]). If one of the fuses in a branch trips, that capacitor is disconnected from the circuit...end of story, right? Not according to here http://www.gilbertelectricalsystems...apers/technical_discussions/TD-004/TD-004.php

 

It needs two fuses because it has two polarities.

 

Could you elaborate on that? It does have two polarities, but that doesn't mean we need to connect a fuse to each, does it? If we place only one fuse then that fuse will be enough to cut the current flowing through that capacitor (and it will be effectively disconnected).

 

there's a couple of reasons for branch, one being that fusing can be targeted to the current fault. In line fusing, your fuse would be much larger, and may not protect a specific overcurrent condition, such as a cap failure with impedance. Because the branch fuses target the specific cap, they will reduce the likelyhood of rupture, compared to the line fusing.

if one of the fuses trips, only one supply is disconnected. Don't assume that the current is adhering to the intended path, especially in overcurrent conditions.

 

I think the OP is asking why two fuses appear in each delta branch -one solid & one hatched. The diagram is not indicating two fuses are required - rather it is simply showing that the sole required fuse placement can be either side of the individual branch capacitor without loss of protection integrity.