Electrical capacity of plant

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Ainsley Whyte

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Jamaica
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Senior Electrical Engineer
Transformer -32500 KVA 2.5MVA13.8k/2400
Transformer -41000 KVA 1MVA13.8k/480
Transformer -5750 KVA 0.75MVA13.8k/480
Transformer -11500 KVA 1.5MVA13.8k/2400
Transformer -21000 KVA 1MVA13.8k/460
Transformer -61500 KVA 1.5MVA13.8k/480

I have the following transformers as listed above all of them are fed from the same 13.8kv feeder . is it correct to say the plant capacity is 9.25 MVA .SUM OF ALL THE MVA
 
Not at all. And what is "plant capacity"? The amount of power that can be supplied? The PoCo regularly overloads (on paper) their transformers since they know the cost/life of them- they might put out a 1000KVA transformer knowing that it'll usually only see 500KVA but occasionally get 1200KVA (and might call that a 1600amp 480v service).

The NEC doesn't let us do that. It's almost never a matter of just summing the transformers or breakers.
 
zbang said:
Not at all. And what is "plant capacity"? The amount of power that can be supplied? The PoCo regularly overloads (on paper) their transformers since they know the cost/life of them- they might put out a 1000KVA transformer knowing that it'll usually only see 500KVA but occasionally get 1200KVA (and might call that a 1600amp 480v service).

The NEC doesn't let us do that. It's almost never a matter of just summing the transformers or breakers.
Click to expand...
And what is "plant capacity"? The amount of power that can be supplied? Yes that is what I mean My friend
 
All six substations are fed from the same 13.8KV cable? Are you sure?
Ussually, that 13.8KV switchgear will have a separate breaker for each substation each having it's own 13.8KV cable.
Then an emergency cable fed from another 13.8KV breaker will be looped to all the substations.
And then they like to tie the same voltage secondary's together via tie breakers for even more redundancy.
Although, your case could certainly be different.

As far as plant capacitiy, you plant can handle a load up to 9.25 MVA and probably beyond.
As far as how much power it is actually pulling today, you could randomly guess that as half as much power as the 9.25 MVA.
You can't say for sure unless you read it on a meter. What does you meter say at the 13.8KV gear? They also call this demand load.
 
powerpete69 said:
All six substations are fed from the same 13.8KV cable? Are you sure?
Ussually, that 13.8KV switchgear will have a separate breaker for each substation each having it's own 13.8KV cable.
Then an emergency cable fed from another 13.8KV breaker will be looped to all the substations.
And then they like to tie the same voltage secondary's together via tie breakers for even more redundancy.
Although, your case could certainly be different.

As far as plant capacitiy, you plant can handle a load up to 9.25 MVA and probably beyond.
As far as how much power it is actually pulling today, you could randomly guess that as half as much power as the 9.25 MVA.
You can't say for sure unless you read it on a meter. What does you meter say at the 13.8KV gear? They also call this demand load.
Click to expand...

Please see drawing one feeder feeds two substations which comprises of a total of 6 transformers.

Can you used the drawing to decide on the maximum load in MVA for the plant ?
 

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Ainsley Whyte said:
Can you used the drawing to decide on the maximum load in MVA for the plant ?
Click to expand...

According to the drawing the primary feeder is limited to 10MW, so that is your absolute maximum load capacity. However you may never be able to obtain, that depending on the fuse protection of each individual transformer as well as your breakers feeding multiple transformers..
 
zbang said:
Capacity is a tricky word- a loading dock might have the capacity of 4 trucks (4 bays), but since one of the bays has a dumpster can only hold 3 right now.
Click to expand...

Yes,
Definitions are important, in your example the capacity (meaning potential amount) is 4 trucks, however it present capacity (amount it can contain) is only 3 trucks.

In my answer the capacity (maximum amount that can be deployed) was based on the limitation of the cable feeding the plant.

Thanks Merriam-Webster.;)
 
Ainsley Whyte said:
Transformer -32500 KVA 2.5MVA13.8k/2400
Transformer -41000 KVA 1MVA13.8k/480
Transformer -5750 KVA 0.75MVA13.8k/480
Transformer -11500 KVA 1.5MVA13.8k/2400
Transformer -21000 KVA 1MVA13.8k/460
Transformer -61500 KVA 1.5MVA13.8k/480

I have the following transformers as listed above all of them are fed from the same 13.8kv feeder . is it correct to say the plant capacity is 9.25 MVA .SUM OF ALL THE MVA
Click to expand...
Opps! There is something wrong with the addition there!
The total is just 8.25 MVA, not 9.25!
 
Ainsley Whyte said:
Transformer -32500 KVA 2.5MVA13.8k/2400
Transformer -41000 KVA 1MVA13.8k/480
Transformer -5750 KVA 0.75MVA13.8k/480
Transformer -11500 KVA 1.5MVA13.8k/2400
Transformer -21000 KVA 1MVA13.8k/460
Transformer -61500 KVA 1.5MVA13.8k/480

I have the following transformers as listed above all of them are fed from the same 13.8kv feeder . is it correct to say the plant capacity is 9.25 MVA .SUM OF ALL THE MVA
Click to expand...
What is maximum you can draw without opening any of either yours or POCO's overcurrent devices? Might be more, might be less than total VA of the transformer ratings.
 
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