Current and Voltage Transformer ratios


This page details information and processes for Current Transformer (CT) and Voltage Transformer (VT) ratios as well as guidance on how to amend the CT and VT valid set. You can also access the valid list of transformer ratios from the Elexon Portal. This list is to be used by Licenced Distribution System Operators (LDSOs) and Meter Operator Agents (MOAs) . 

How this relates to you

The BSC is placing an obligation on LDSOs and MOAs to only enter CT and VT ratios from an agreed list.

Metering Systems can be comprised of measurement transformers such as CTs and VTs. The ratios for these transformers are communicated between Parties via Meter Technical Detail (MTD) data flows. These ratios are instrumental in allowing a meter to record the correct primary energy flow to or from a site.

Under the Master Registration Agreement (MRA), ratios are detailed via two data items, J0454 and J0455, which represents the CT and VT ratios respectively.

Why is this important?

Accurate measurement of transformer ratios is essential for the commissioning process, which is a series of site tests and checks on Metering Equipment. This ensures that the energy flowing across a Defined Metering Point (DMP) is accurately recorded by the associated Metering System.

CT and VT ratios

The list of valid CT and VT ratios spreadsheet is updated when a new CT or VT ratio is required or an old one is removed.

The valid set can be found on the Elexon Portal.

Amending the transformer ratios 

Requests to amend the ratios list must be sent to the Metering team.

LSDO process 

BSCP515 – Licensed Distribution, will define the process LDSOs would need to follow to amend the list of valid transformer ratios.

MOA process

BSCP514 – SVA Meter Operations for Metering Systems Registered in Supplier Meter Registration Service (SMRS), will define the process MOAs need to follow to amend the list of valid transformer ratios.

Next steps

On receipt of a request to amend the list of valid transformer ratios, Elexon will check that the submitted ratios meet the valid format before adding the CT/VT ratio to the valid transformer list, which will be published on the Elexon Portal.

Where there is a request to add or remove a ratio from the valid transformer ratio list, Market Participants will be notified 10 Working Days (WDs) before the valid set is amended and published.


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