Metering Dispensation consultation on remaining Class 2 Meters and Class 0.5 CT

We are seeking views from BSC Parties on whether they support the proposed Metering Dispensation (D/544). This Metering Dispensation is giving the affected parties’ time to use up old existing stocks of Class 2 Meters and Class 0.5 CT’s.

Summary

Category 2 non-compliances (following a TAA visit) against Metering Systems potentially being outside of the overall accuracy limits have been noted as a significant issue for a number of years. Tightening the requirements to ensure that all Meters registered against CoP5 are class 1/class B Meters will remove the need to present Calibration Certificates for LV CoP5 Metering Systems.

By mandating that class 0.5S CTs are installed for Metering Systems registered against CoPs 3, 5 and 10, it is more likely that the errors of the CT at the operating load will be known. Whilst it is feasible that, for low capacity sites, a CT may not measure currents greater than 5% of the rated current, it is far less likely that the energy associated with a Metering System will be consistently less than 1% of the rated current of the CTs. This will assist the MOA with assuring the Overall Accuracy of the Metering System.

Metering Dispensation D/544 has been raised on the back of CP1553 which is tightening the requirements for the minimum accuracy classes for Meters in Code of Practice (CoP) 3, 5 & 10 and Current Transformers (CT) in CoPs 3, 5 and 10.

Currently, the minimum accuracy class required for a Meter in CoP5 ‘the metering of energy transfers with a Maximum Demand of up to (and including) 1MW for Settlement Purposes’ is class 2 (or class A), which means that the Meter must have an accuracy within ±2% over most of its current range. However, the overall accuracy limit for a CoP5 Metering System is ±1.5%. This makes it difficult for Meter Operator Agents (MOAs) to assure overall accuracy of a Metering System is met, if they do not, or cannot, provide Calibration Certificates, for certain items of Metering Equipment. Calibration Certificates detail the actual errors obtained through testing. This can result in the Technical Assurance Agent (TAA) assigning a category 2 non-compliance for overall accuracy not being maintained.

Additionally, the minimum accuracy class for a CT in CoPs 3 ‘the metering of circuits not exceeding 10 MVA for Settlement purposes’, 5 and 10 ‘the metering of energy via low voltage circuits for Settlements Purposes’ is class 0.5. This standard requires class 0.5 CTs to be tested to a minimum of 5% of rated measuring current. This means that when a CT measures current below 5% of rated measuring current, its errors, and therefore its contribution to the overall accuracy of the Metering System, will not be known. Knowing the CT errors at currents below 5% provides assurance that overall accuracy is more likely to be maintained when CTs operate at low such loads.

The Metering Dispensation is needed to allow for old stock to be used creating a transition period and mention the supply chain issues.

Consultation questions

Q. Do you agree that the proposed Metering Dispensation D/544 should be granted on a temporary basis for a period of 18 months.

Q. Please provide your reasoning for the answer given in question 1 of this consultationHow to respond

How to respond

Please complete the proforma shown below and send your response to [email protected] by 17:00 on Friday 13 May 2022.

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