Medium Voltage to Substation

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Lady Engineer

Lady Engineer

Senior Member
Location
New Jersey
Ok, I have a new job where the client wants to bring in 13.2KV to a 480V 1500KVA oil-filled transformer. Or shall I propose a substation?

I'm clueless other than knowing the secondary side for cable sizing. The transformer is oil-filled. It will be outdoors (of course), but I'm not sure how to size the wires properly.

Can I please have pointers?
 
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skeshesh

Senior Member
Location
Los Angeles, Ca
You will likely want to trench to the HV side, 15kV class medium voltage cables, %133 insulation, size the conductors according to load, but I think at that voltage class you have to special order the cable smaller than 1/0 or so, so keep that in mind. I think a substation is a good idea. I've specified the eaton substations before, they got all the accessories you may need, I think they use cooper transformers (but so does everyone other than sqd). Is this a primary unit from the utility or is the 13.2kV some sort of campus loop distribution?
 
B

BJ Conner

Senior Member
Location
97006
Contact the Utility for details.

Contact the Utility for details.

:)
Lady Engineer said:
Ok, I have a new job where the client wants to bring in 13.2KV to a 480V 1500KVA oil-filled transformer. Or shall I propose a substation?

I'm clueless other than knowing the secondary side for cable sizing. The transformer is oil-filled. It will be outdoors (of course), but I'm not sure how to size the wires properly.

Can I please have pointers?
Click to expand...

High side is the same as the low side I=1,500/13. * 1.732)
Thnen to TAble 310.78. Aluminum cable works good at 15KV.
The primary cable can be direct burried or run in conduit.
I would run PVC encased in flowable fill.

I would recommend you contact the local utility and get a copy of their distribution standards. They should have standards and service guidelines that show you everything from the H1,2,3,0 leads of the transfromer back to their connection point.
 
bob

bob

Senior Member
Location
Alabama
This is not an unusual installation but it is usually installed by the utility. I am not sure what you mean buy substation. I usually think of something like 22.4 mva as a substation. Does you customer have a 13.2 overhead system in place? As SK said you will eventually have to install an underground cable to the transformer. You may choose cable something like this

http://www.okonite.com/Product_Catalog/section2/section2-pdfs/2-9.pdf. Utilities will use something similar in aluminum.
 
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skeshesh

Senior Member
Location
Los Angeles, Ca
bob said:
I am not sure what you mean buy substation. I usually think of something like 22.4 mva as a substation. Does you customer have a 13.2 overhead system in place?
Click to expand...

I think she's talking about a unit substation, a packaged unit of primary switch and fusing, transformer, and secondary side distribution board. I'm also guessing that this is some sort of military or educational campus with a distribution loop with a much larger main substation connected to the utility feed.
 
steve66

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Is the 13.2 KV utility power, or does the customer have their own HV distribution?

If its the customers own HV distribution, then the HV cable should be sized per the upstream fuses. You don't want 600A fuses protecting 1/0 wire.

Is it a loop feed or a radial feed?

As far as a substation goes, I usually think of a substation as having a HV disconnect section, a transformer section, and a low voltage (either 208 or 480V) switchboard section all in one unit. Most of the time you would want the low voltage switchboard inside the building. Or do you mean something else by a switchboard?
 
B

BJ Conner

Senior Member
Location
97006
skeshesh said:
As a side note: BJ do you often specify the grout? I'd be really interested in hearing about if it's a good common practice and why.
Click to expand...

IF you specify the right mix it has a Rho of about 65 or so.
It's not really grout it's one sack concrete with flyash back fill. Your local batchplant should have a spec on it.

It goes in fast, and sets up fast. There is no backfill, compact, fill some more, compact and back fill again.
When you going through pave areas you can put the last asphalt patch on right away and it won't settle.
You can put red powder on the fill, that along with marker tape makes it less likely to dig up.
PVC will float in it so you have to anchor it down.
 
T

Thedroid

Member
The IEEE Red Book chapter 12 gives pointers on selecting the proper cables for industrial distribution systems. I also copied this little tidbit from another IEEE recommended practice book I have.

"3.2.3 Cable sizes
Use cable sizes larger than the size that may be thermally damaged by maximum fault current on the distribution system for the time required to isolate the fault. Short-time ratings of copper cables are shown in figure 8 in clause 7.. Consider the time to isolate the fault as the sum of the time it takes the protective breaker relay to operate plus the operating time of the circuit breaker. The commonly used circuit breakers isolate faults within 57. cycles at 60 Hz above 2 kV. Low-voltage breakers are faster and may only require 1.5 to 2 cycles to clear a fault."

You should know exactly what size and type and why before you go any further.
 
Lady Engineer

Lady Engineer

Senior Member
Location
New Jersey
Thanks!

Thanks!

I just surveyed an existing application like this today.

BJ Conner gave me the information needed, which out over analyzing it.

It's not running a loop, because I have done that before, and I obtained the standards from the utility. It's just a MV line, to a substation with transformer, fuses, in a indoor enclosure.

I'll discard the rest. Thanks BJ Conner!
 
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