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hino
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Join Date: Sep 2014
Posts: 4

Transformer Maximum Load & Breaker Setting

01/26/2015 3:01 AM

Hi.. I have a 1600kVA (6/0.4kV) Transformer, this transformer already loaded with 2 bridge crane (cap 220/55/5Ton) in 1 feeder and another load (motor) in other feeder included another spare feeder. as the picture below

This crane is loaded by 1 feeder with 2000A breaker setting and every crane has main breaker with capacity 1400A. I already calculated 1 bridge crane has total 603,63kW and 1264,75A (Full Load Rating from Motor), using NEC code for calculating the breaker capacity and it turn out to be 1400A (same as the existing) But the problem is if I have 2 crane I would have apprx. 1207kW and 2529A total. But until now we don't have any problem with 2000A setting.

And also we have a plan to add another bridge crane with the same rating, how to know that my transformer is still able/not to power the load?

Please help me thank you.
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Pathfinder Tags: breaker bride crane setting transformer
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Tornado
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Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

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#1

Re: Transformer maximum load & breaker setting

01/26/2015 3:27 AM

Your crane ratings are not believable. Please state the HP of all motors.

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hino
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Join Date: Sep 2014
Posts: 4
#2
In reply to #1

Re: Transformer maximum load & breaker setting

01/26/2015 4:22 AM

This is my motor rating in 1 bridge crane :

  1. 160 kW - 330 A (HOIST 220T)
  2. 160 kW - 330 A
  3. 125 kW - 250 A (HOIST 55T)
  4. 7,4 kW - 20 A (HOIST 5T)
  5. 0,85 kW - 2,8 A
  6. 30 kW - 66 A (TROLLEY TRAVEL)
  7. 0,48 kW - 1,95 A (TROLLEY TRAVEL 5T)
  8. 30 kW - 66 A (CRANE TRAVEL)
  9. 30 kW - 66 A
  10. 30 kW - 66 A
  11. 30 kW - 66 A
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Tornado
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#3
In reply to #2

Re: Transformer maximum load & breaker setting

01/26/2015 4:58 AM

Probably not all of these items are running at the same time. The hoisting stuff (1-4) adds up to 930 A, and maybe even that is not all alive at once. Your numbers seem reasonably consistent, including the 1400 A service to each crane. Most of the time, though, the load will be less than that. You should do some sort of time study to determine what your loads really are. You may then find that you have enough capacity for the existing needs, plus more.

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PWSlack
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#4

Re: Transformer Maximum Load & Breaker Setting

01/26/2015 7:58 AM

Consider diversity and cabling before selecting the breaker. Get a qualified Electrical Engineer onto this project.

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cristle
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Join Date: Jun 2011
Location: New Zealand
Posts: 75
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#5

Re: Transformer Maximum Load & Breaker Setting

01/26/2015 10:57 PM

Hi,

Looking at the schematic leaves the impression that it was designed with diversity in mind, and the original engineers may be your first port of call. A question I would have is about the proposal to have CB BC1 and CB BC2 both under CB Q05. It appears that CB Q05 is there to protect the conductor. Can the conductor carry the additional load? If not then consider installing CBQ06 and have CB BC2 subordinate to it alone.

The usual answer of "use local standards and local skilled engineer" comes to mind.

Q? Why do not people go there first?

A. Many are seeking to have an idea of what to ask them to do and appear as a easy mark that can be ripped off by a consultant; or,

B. Or develop a scope of works; or,

C. Still others are seeking to justify asking for budget to spend on one of the aforementioned consulting engineers and need some background information to support their concerns; or,

D. The small remainder are freeloaders.

What are your thoughts.
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pnaban
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#6

Re: Transformer Maximum Load & Breaker Setting

01/27/2015 12:16 AM

Apply correct diversity factors.

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raghun
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#7

Re: Transformer Maximum Load & Breaker Setting

01/27/2015 4:23 AM

There are in fact two different diversity factors that need to be applied here - one is for the loads within each crane and the other is for the three cranes (whether all the three cranes could be working simultaneously??).

As always, a good understanding/study of the type of loads and their working is important to optimise sizing of the transformer / supply power system.

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