Switch over breaker vs fused switch with Main secondary
Switch over breaker vs fused switch with Main secondary
(OP)
OK here's the thing. I normally research my topic thoroughly prior to coming into the eng-tips forums, but I am on a tight deadline to have answers on this topic very soon. So I am apologizing up front for now making attempts at due diligence.
Now that I got that out of the way...
My question is I have always, always, always seen a Fused isolation switch on the primary of the Substation XFMR with a main secondary breaker (My industrial sector that I have have exposure to is Pulp and Paper some chemical and some semiconductor). I am being asked to investigate the switch over breaker option where the primary switch has a breaker that has relaying to protect the primary and secondary of the transformer, and the secondary is forgoing the main breaker. I did have briefly seen the advertisement by Eaton concerning their switch over breaker product line. I thought that a fuse reacts faster then a breaker so I am afraid that the switch over breaker design would be not as effective as what my experience is with the proposed scheme. My guess is that they are putting the breaker in maintenance mode when maintenance personnel have to deal with the arc flash occurrences. Does breakers with fast acting instantaneous settings protect for arc flash more effectively than a fuse?
General question is this becoming a new design that industry is moving towards? Thanks in advance for your comments!
Now that I got that out of the way...
My question is I have always, always, always seen a Fused isolation switch on the primary of the Substation XFMR with a main secondary breaker (My industrial sector that I have have exposure to is Pulp and Paper some chemical and some semiconductor). I am being asked to investigate the switch over breaker option where the primary switch has a breaker that has relaying to protect the primary and secondary of the transformer, and the secondary is forgoing the main breaker. I did have briefly seen the advertisement by Eaton concerning their switch over breaker product line. I thought that a fuse reacts faster then a breaker so I am afraid that the switch over breaker design would be not as effective as what my experience is with the proposed scheme. My guess is that they are putting the breaker in maintenance mode when maintenance personnel have to deal with the arc flash occurrences. Does breakers with fast acting instantaneous settings protect for arc flash more effectively than a fuse?
General question is this becoming a new design that industry is moving towards? Thanks in advance for your comments!






RE: Switch over breaker vs fused switch with Main secondary
RE: Switch over breaker vs fused switch with Main secondary
87 protection is considered a luxury on smaller transformers. Having said that; I recently installed several 1500KVA transformers at a Site c/w;
My original thinking here was to use the cost savings (of not having a secondary CB) to upgrade the transformer protection to include 87 and 50/51 on the secondary. This in turn would reduce the AF levels on the LV side of the transformer, including the incoming section of the MCC. While this did help to reduce the LV AF levels, they were not as low as I had originally envisioned. At the end of the day, the Client ended up with 87 protection, and reduced AF protection, for less cost.
From my experience a primary CB, should provide lower secondary AF levels, when compared to a fused LISw. Even more so if the primary CB is equipped with transformer LV 50/51 protection.
Don't forget to spec a 3-cycle CB, and not a 5-cycle CB, if you plan to go down this (reduced AF) path.