Opinion on current design of a 13.2kV outdoor substation

[JuanBC]

Hello,

I would like your opinion regarding the following situation:

In a facility we are building (almost finished) someone designed a 13.2kV outdoor substation with (1) incoming overhead line entering through a recloser, and (7) outgoing feeders also equipped with reclosers.

All the reclosers are identical (ABB OVR-15 rated 600Amps with a RER-615 controller).

(4) of the reclosers are feeding "small" transformers (primary current = 8.7A @13.2kV)

Previous to the startup we discovered that the minimum setting for the recloser primary current is 24A, and therefore there is no way to protect this (4) transformers (protection functions are based on this sitting)

I will appreciate your ideas to find a nice solution. Find attached a simplified one-line diagram

Best regards,

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[JuanBC]

PS. The substation is already built. Find photo attached.

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[dpc]

I would first check with ABB to see if they might be able to come up with a more sensitive current sensor for the OVR or perhaps wrap additional turns around the toroid on the recloser control current inputs.

Alternatively - add external CTs and separate protective relays that trip the recloser. Or add fuses for each transformer.

 

[waross]

Aren't the recloser trips instantaneous?
24 Amps / 8.7 Amps x 100 = 275%. That may be a little low to energize the transformers.
That will give you short circuit protection. Consider adding fused disconnects for overload protection.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JuanBC]

Hi,

Thank you both dpc & Bill!

We'll check with ABB on monday but I wanted to have an external opinion beforehand

add external CTs

Yep external CTs may work, thanks!

Aren't the recloser trips instantaneous?

The relay has a 3 step overcurrent protection. 1st step is supposed to be set with an inverse time characteristic, the 2nd may be set with a delay definite time and the 3rd step is instantaneous

Yeah, fuses should work, but their presence makes the existence of the recloser meaningless LOL




JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[RRaghunath]

The overload protection, in case of transformers, is catered by the OTI (Oil Temperature trip / alarm).
So, the recloser is providing only short circuit protection, for faults on secondary as well as on primary.
Thus, high pickup with reference to transformer rated current is not a problem.
If the recloser protection coordinates with the LV incomer protection and the upstream incomer recloser protection is coordinated in turn with that in individual outgoing feeder recloser controllers, the arrangement should work fine.

Rompicherla Raghunath

 

[JuanBC]

Hello RRaghunath,

Thank you for your input.

Three out of four of this transformers do not have OTI.
Anyway, it is true that transformers are protected from overload in the LV side, but in general I like to have backup overload protection on MV.

Do you think this backup protection is not necessary? The 3 transformers that do not have OTI are feeding a VFD each.






JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[donalax]

Some Utilities require backup protection on the incoming line.

If you haven't already, I recommend checking with the Utility Company just to avoid future problems.

 

[Hoxton]

Assuming that this 'Substation' is not the 'DNO' in UK terminology, and is say 'private' then there will be a 'Connection Agreeement' with the utility.

Oh yes there will!!!

Find it!

I have been three times to a site in the north of the U.K. in the last 30 years, at each meeting. The site manager has said "We do not have this connection agreement""

At each I have handed him a copy of said agreement, they express surprise!
Problem is "Fred"

Fred is the guy who collects all this and reminds management when they are going astray.

Management do not like this because, well because, so when Fred retires, they throw out Fred's filing cabinet "We do not need that crap any more "


Wish I had an MBA


Typical budget £50,000 to replace Fred's crap. One site I know £500,000"

So remember tHe Alamo, remember Fred!!"

 

[JuanBC]

Donalax, Hoxton,

Thank you for the advice!! Luckily both the incoming line and the generation is private (own by our customer).
So.. there is not a 'Connection Agreement' haha

Nice story tho!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[RRaghunath]

JuanBC,
The three Transformers without OTI have fixed loads and unlikely to be subjected to overload. Isn't it.
So what is the problem!!

Rompicherla Raghunath