MCCB vs Fuse-switches 10

[STONE85]

Good morning,
With regards to the use of fuse switches and MCCBs what is the process in selecting one over the other. I know they each have their advantages and disadvantages but does it come down to the load they are protecting?

Thank you

 

[edison123]

Hey, people can have pipe dreams, can't they?

Muthu

http://www.edison.co.in

 

[FacEngrPE]

When all you have is a fused disconnect, and all you needed was a switch
This is a real part.

 

[LionelHutz]

We've done lots of fault testing with CLB and fuses. In a bunch of cases, the CLB achieved the same fault rating as class J fuses so they can work just as well at limiting the fault current. The only time the fuses did better was getting above 100kA where the breakers reached their limit. But, how many 480V or 600V systems with > 100kA fault current actually exist?

 

[Mbrooke]

Ask Con Edison- they've got services above 200ka

 

[che12345]

Dear Mr. Mbrooke (Electrical)
[highlight #204A87]"...Ask Con Edison- they've got services above 200ka"[/highlight]
Che. 1. In general, there are exceptions; for a LV (<1kV)installation planning the switchboard should aim to limit SC (<150kArms) and continuous current rating (<6300A). This can usually achieved by breaking them down into sections; with N.O. couplers inserted in between sections. Using smaller transformers with %Z (=>6%), limit the number of generators feeding into per section etc.
2. The reason for suggesting the data in 1 above is based on less switchboards and switchgears (breakers) are designed/tested to above these criterial. They are usually of special (improvise) design with long delivery time and higher cost.
3. Withdrawable ACB rated Iu=6300A, Icu at 400V=(150kArms), Icw for 1s=(100kArms) are readily available on the market. Note: fuses (>1600A) are not easily available on the market, not to mention (>2kA).
Che Kuan Yau (Singapore)

 

[Mbrooke]

Fuses up to 6000 amps with a 300,000 amp interrupting are relatively available:

https://www.grainger.com/product/BUSSMANN-Fuse-49ZU92

My understanding is that at 200-300ka amps these low peak fuses will let less energy through than a current limiting CB.

The disadvantage with normally open couplers being that it reduces service continuity, poorer voltage regulation, increase protection complexity, requires divided loading/more feeders, and does not maximize the available kva of each transformer post contingency (unless all couplers close afterwards). Feeding 4-7 transformers into a single collector bus or meshing the secondaries at the street level is cheaper, while typically up to two primary feeder cables can be lost without needing to shed any load let alone an outage while couplers wait to close in.

 

[Coco_HueHueHue]

Based on my little experience, for example an MCC, when buckets have breakers, it is more expensive than when they have fuses.
That can also be taken into consideration in the design.

 

[che12345]

Dear Mr. Coco_HueHueHue (Electrical)
" Based on my little experience, for example an MCC, when buckets have breakers, it is more expensive than when they have fuses...."
Che. 1. In general, it is true because Breaker is say 30% more than fuse-switch or fuse+mounting base. However, breaker or fuse is only say 15% total cost of the bucket assembly. The bucket frame is the same with the exception of different mechanism for switching the breaker instead of fuse-switch. The bucket size and the other components comprising of contactors +thermal over-load and control transformer etc., the switchboard mechanical structure, busbar assembly remained the same. Therefore, the total additional cost for the whole MCC should not be more than 5%.
2. Breaker besides other advantages also prevents "single-phasing" which is sure to happen which damage motors. A single motor damaged by single-phasing would pay for the additional cost. Not to mention the cost for the production down-time to replace the motor +rewinding cost.
3. It is almost impossible to carry out a thermal scan on the components inside a servicing/fully loaded starter bucket.
Che Kuan Yau (Singapore)