Electrical capacity of plant

[Ainsley Whyte]

Transformer -3	2500 KVA 2.5MVA	13.8k/2400
Transformer -4	1000 KVA 1MVA	13.8k/480
Transformer -5	750 KVA 0.75MVA	13.8k/480
Transformer -1	1500 KVA 1.5MVA	13.8k/2400
Transformer -2	1000 KVA 1MVA	13.8k/460
Transformer -6	1500 KVA 1.5MVA	13.8k/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

 

[zbang]

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.

 

[Ainsley Whyte]

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.

And what is "plant capacity"? The amount of power that can be supplied? Yes that is what I mean My friend

 

[powerpete69]

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.

 

[Ainsley Whyte]

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.

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 ?

 

[jim dungar]

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

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]

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..

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.

 

[Ainsley Whyte]

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.

so true my friend

 

[jim dungar]

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.

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.

 

[topgone]

Transformer -3	2500 KVA 2.5MVA	13.8k/2400
Transformer -4	1000 KVA 1MVA	13.8k/480
Transformer -5	750 KVA 0.75MVA	13.8k/480
Transformer -1	1500 KVA 1.5MVA	13.8k/2400
Transformer -2	1000 KVA 1MVA	13.8k/460
Transformer -6	1500 KVA 1.5MVA	13.8k/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

Opps! There is something wrong with the addition there!
The total is just 8.25 MVA, not 9.25!

 

[kwired]

Transformer -3	2500 KVA 2.5MVA	13.8k/2400
Transformer -4	1000 KVA 1MVA	13.8k/480
Transformer -5	750 KVA 0.75MVA	13.8k/480
Transformer -1	1500 KVA 1.5MVA	13.8k/2400
Transformer -2	1000 KVA 1MVA	13.8k/460
Transformer -6	1500 KVA 1.5MVA	13.8k/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

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.

 

[Ainsley Whyte]

Opps! There is something wrong with the addition there!
The total is just 8.25 MVA, not 9.25!

you are correct thanks