Utility metering of 34.5kV station service power on BESS site

[rockman7892]

I'm working on a project for a 150+ MW BESS which is connected to utility transmission via a 34.5kV to 138kV step-up transformer (120MVA).

On the 138kV primary of the transformer the utility has a meter for revenue metering purposes but it is also now being requested to install a meter on the secondary of the station service transformer (150kVA) connected to 34.5kV bus.

With main 138kV meter on primary handling revenue metering for any PPA agreements etc.. the metering for station service would strictly be for performance guarantees etc... from battery site?

Was curious to hear from others what experience's they've had with BESS connected to HV transmission and need to monitor station service power.

 

[cranky108]

I like to attend those meetings, as I love to watch a fight.
150 MW when producing. How much when needing power from the system? Calculate the CT ratio needed to be in the accuracy rango for each direction, and see if they overlap.
Extended range CT's have been used, also optical CT's have been used, but really what is the most cost effective method of measuring station load, and power produced.

 

[bacon4life]

Station service metering has become much more complicated in my region as more utilities join CAISO. CAISO's station service metering guide is at

https://www.caiso.com/Documents/StationPowerProgramOverview.pdf.

BPA is a large transmission providing in my area. Section 5.9.9 of BPA's metering-application-guide explains their accuracy practices for station service loads.

 

[scottf]

As Cranky mentioned, it is common to use Extended-Range CTs (ERCTs) on the primary side that have an accuracy range low enough to accurate capture station service loading from the high side.

As an example, my company (Ritz) makes ERCTs for HV application where 0.15B1.8 accuracy is maintained from 0.05% to 200% Inom and ratios of 500:5A, 1000:5A, or 2000:5A and are available in primary reconnection (500x1000x2000:5A) where the ratio is selectable in the field.

For 150MW metering point, the 500:5A ratio would give 0.15% accuracy from 0.25A to 1000A primary current at 138kV.

Of course we love to sell CTs and VTs for primary AND secondary side metering too

Bacon4life-

The BPA guide is a good...and spec's the Ritz ERCT range

 

[thermionic1]

We have many joint use sub stations that were previously owned by a single entity. When it's time to upgrade the AC service, new AC panels are installed that separate the transmission from the distribution equipment loads. Revenue meter(s) are installed so the transmission AC load can be separately accounted for. These are basic form 2S meters that communicate back to the distribution utility. Most station AC is 240V single phase, but there are stations with 3 phase, so that's another meter, if required. The distribution company also owns the generation while also being a majority shareholder in the transmission company, so I have no real idea why all the fuss, but it is done, nonetheless.

 

[Overvoltage]

I'm guessing that parts are regulated and other parts aren't, so to ensure the maximum rate of return for each, they're making sure to break everything down into individual sections. Or, it could have to do with said regulation and requirements due to that.

 

[cranky108]

Likely all of it is regulated, but, the transmission losses are spread across all the transmission customers (entities), and not just the one customer (entity).
Just how people look at things.