Ismael Esteban
Ossa
 
By Ismael Esteban Ossa

The current codes for the metering of energy are being updated with the aim of being able to cover the majority of the uncertainties that arise from electrical, regulatory and environmental factors. In Colombia, the metering code, which constitutes part of the network code, came into force in 1995, and subsequently has undergone a few slight but necessary modifications to refine it.

With the best intentions of carrying out appropriate reform, there have been attempts since 2007 to reach an agreement by involving all the relevant parties in the electricity sector, including users, generators, transporters, distributors and traders. The differences found in the proposal from the regulator, CREG, suggest that the changes would affect economically a fragment of the sector, as well as introduce changes in the way of operating and auditing the metering systems.

Meanwhile, the end user continues to be affected by the current tariff structure and supports economically the uncertainties that are not covered or audited in the current metering code.

The metering code relates the constitutive elements of a metering system and its conformity at the different voltage levels. A metering system is composed of voltage and current transformers, connection cables, equipment for auxiliary recording, a meter, communication equipment, and IT equipment and software for management and analysis. Each element has its own uncertainties that are included in metering codes internationally. Therefore, uncertainty inherent to the metering system must be evaluated and this has a cost.

The figure below evaluates the behavior of a Class 0.2S metering system, required for a level 4 voltage.

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The system above does not consider the uncertainties in the same manner as other factors, such as the connection, type of installation, compensations at the point of measurement, burden applied to the core of measurement, etc. The following figure shows the influence of a lower burden than is required to guarantee the exactness of the measurement, which is a problem present in the current transmission and distribution networks, due to their modernization with electronic devices that are of insufficiently high accuracy.

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Finally, if one considers the errors of each transformer and meter, which add up to +/- 0.6, the total error is:
Total error (including measurement uncertainty) = Error Meter + Error CT + Error VT + MU Meter error + MU CT error + MU VT Error

This can displace the actual measurement further and can be observed in the following graph showing a positive increase, which is the worst case scenario that may present itself.

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The result is that due to the inaccuracy of the metering system the energy metered is greater than the energy supplied, and this impacts on the user who pays under the assumption that the system is of the required accuracy.

Taking the calculated value of the total error and converting it into pesos, one can see that with a difference from 0.22% and 1%, which on the commercial level with supplies of 100 MWh can amount to an additional 1 MWh, this translates into an additional billing of $60,000 per hour (at a rate of $60 per kWh).

The billing to the end user includes a service charge identified as “PR” (for recognized losses), which is made up of two components – the technical losses and non-technical losses. The loss considered in the case above is a technical loss, but it also could be considered a measurement error in the metering system due by shortcomings in auditing the system.

The determination of the tariff is:
Cost to serve = (G + T + D + PR + R + Cv) * Consumption + Cf

G, T, D = Generation, transmission and distribution costs
PR = Recognized losses
R = Restrictions
Cv, Cf = Commercialization costs

According to Dr Arnie Reimer, “Technical losses are losses of energy due to aspects related to the design, planning, construction and operation of the electrical system being generated in conductors, transformers and electrical equipment. Non-technical losses, on the other hand, are mainly due to inefficiencies in administrative and commercial practices: errors in measurement, theft and fraud.”

The main conclusion is: “Don’t transfer to the user all the costs associated with the inefficiencies of companies,” which requires an enhancement to the current metering code with emphasis on the definition and follow-up of auditing.