Using 300kva Xfrmr as source of temp power

[mstrlucky74]

Engineer is asking for the following.

So regarding phasing notes 1 & 3( see attached).
I also only attached a portion of the EM riser but enoughthat you can see the new switch that feeds the 300kva( that that they areasking to be used a source of temp power) and from there the xfrmr feeds a busdetail and switches which feed other equipment.

So according to phasing note # 1 they want this EM schemeinstalled and up and running. Then in phasing note #3 they want us to temp out(5) 600A distribution panels( notnecessarily at once).
My question is how could the 300kva xfrmr be used as a temppower source if it’s already being used for it’s intended uses as shown on theone line and spelled out in phasing note #1? Is this possible even if youshutdown power to make temp connections could the xfrmr handle all that?

I’m thinking once everything is up and runningper phasing note # 1 then you would have to disconnect the 120/208v side (3)sets and safe it off then run your temp from the xfrmr to the distributionpanels then when temp is no longer needed connect back the (3) sets.

Thanks a lot for any input/advice.

 

[mstrlucky74]

Anyone able to help with this? Thanks

 

[infinity]

I'm having trouble reading your attachment.

 

[iwire]

I could not figure out the question but yes a shut down must be planed to add secondaries to a transformer.

 

[mstrlucky74]

Here is the dropbox link with the images. Hopefully better.

Iwire. per phasing note #1 the EM distribution( shown on my one line) is to be up and running..this includes the 300kva xfrmr. After that per phasing note #3 we are to use the 300kva as a temp power source to feed a few distribution panels. Can you run temp feeders from the 300kva when it's up and connected with permanent feeders as shown on the one line? I doubt that. So what would you have to do? Disconnect secondary side feeder and connect temp feeders then when done with temp disconnect and reconnect permanent?



https://www.dropbox.com/sh/yjq6mcmfs7rw19q/AACzq8WXTGx095Wwspr5ElwWa?dl=0

 

[jim dungar]

Can you run temp feeders from the 300kva when it's up and connected with permanent feeders as shown on the one line?

The physical act of installing the conductors must be done be applicable safety codes. However, there is no prohibition against temporary and permanent feeders sharing the same transformer secondary.

 

[mstrlucky74]

The physical act of installing the conductors must be done be applicable safety codes. However, there is no prohibition against temporary and permanent feeders sharing the same transformer secondary.

Which is also my question. So if those permanent secondary feeders are connected is it physically/technically possible to also connect say temp MC feeder cable at the same time? I have to temp out (3) 600A panels. So again:

1. Can the temp feeders be connected to the transformer at the same time it has the permanent secondary side feeders connected?
2. If so how many 600A temp feeds would be able to be connected at once?

Unusual temp scenario huh

 

[iwire]

Which is also my question. So if those permanent secondary feeders are connected is it physically/technically possible to also connect say temp MC feeder cable at the same time? I have to temp out (3) 600A panels. So again:

1. Can the temp feeders be connected to the transformer at the same time it has the permanent secondary side feeders connected?
2. If so how many 600A temp feeds would be able to be connected at once?

Unusual temp scenario huh

You are allowed up to six sets of transformer secondary conductors

Each has to end in an over current protective device.

The fact some are temp and some are permanent makes no difference.

 

[augie47]

You are allowed up to six sets of transformer secondary conductors

Each has to end in an over current protective device.

The fact some are temp and some are permanent makes no difference.

The total rating of your secondary overcurrent devices could be limited unless you transformer primary protection is properly rated (125%)so you
might check that also.

 

[mstrlucky74]

You are allowed up to six sets of transformer secondary conductors

Each has to end in an over current protective device.

The fact some are temp and some are permanent makes no difference.

Thanks Iwire. Where does the limit of 6 sets come from? Code? How much 3Phase 208v amperage/load total can be connected to the secondary side of 300kva? About 800a?

 

[mstrlucky74]

The total rating of your secondary overcurrent devices could be limited unless you transformer primary protection is properly rated (125%)so you
might check that also.

Can you explain a little further. Thank you!

 

[iwire]

Can you explain a little further. Thank you!

If the transformer requires secondary protection, the total of the overcurrent protection can not exceed the rating of the transformer.

So for example if the transformer secondary was rated 600 amps you could have one 600 amp breaker, or two 300 amp breakers or six 100 amp breakers.

To be clear it could be breakers, fuses or a combination of them.

How do you know if the transformer requires secondary protection? That depends on the transformer type and the primary overcurrent protection selection.

 

[mstrlucky74]

So according to previous comments:

My secondary OCP's can be limited of the xfrmr primary is not properly rated(125%). How do I determine if it is?

How do I determine the rating of the secondary of the xfrmr?

Which transformers required secondary protection?

 

[mstrlucky74]

Another question. According to my calc for secondary current va/1.73*voltage I get about 835 amps. So this xfrmr is feeding a 1200a bus detail with several 400a switches. I assume the load Can't exceed 835 amps?

 

[augie47]

Your 300kva transformer's primary current would be 361 amps so the 400 amp over-current would be withing the 125% range to protect the transformer. You can, therefore, apply the 6 secondary rule I-wire referenced in Post #8 and not exceed 1,080 amp +/- (865 x 1.25)

 

[mstrlucky74]

Your 300kva transformer's primary current would be 361 amps so the 400 amp over-current would be withing the 125% range to protect the transformer. You can, therefore, apply the 6 secondary rule I-wire referenced in Post #8 and not exceed 1,080 amp +/- (865 x 1.25)

Thanks Augie, I'm going to google/ research more about this so I can be knowledgeable.