HIGH VOLTAGE METERING Overcome multiple i w th direct high voltage metering H igh voltage (HV) metering is not new in the metering industry; however, the concept of direct HV meters is still a fairly recent development. As a brief introduction, let us consider the categories for distribution transformers, as any transformer in the distribution system will fall into one of two categories. Public transformers is the most common category where transformers are installed at one end of feeders supplying electricity to multiple customers. In the case of private transformers this category is installed at the border of the distribution grid and feeds directly to one customer, with the output directly connected to the electric circuit of that customer. Private transformers are almost certainly equipped with C&I (commercial and industrial) meters. Whereas installing meters on public transformers is not as common as on private transformers, a reasonable number are equipped with meters thus assisting utilities to: • Calculate the losses from a particular feeder • Detect unauthorised energy consumption (tampering) • Foresee transformer overloading and take remedial action Regardless of whether the transformer is public or private there are several ways to meter the energy passing through it. The classic solution is to install an ordinary CT-connected meter on the secondary side of the transformer and periodically read it manually through LCD or a hand-held unit (HHU). However, this approach is outdated and not recommended due to the following reasons: 1. The shortest period between manual meter readings is from one to two weeks. As a result the data analysis is conducted off-line with 56 2. 3. 4. 5. significant delay and processing vital alarms become meaningless and of no value. Since there is no suitable way to quickly adjust the (real time) clock of these meters, they do not run synchronously with the clock of other meters: for example, the meters of customers under the transformer. As the timestamp of data for these meters is not synchronous with other meters, the majority of the analysis, such as loss analysis, cannot be run effectively and the load data of these meters lose their value. Reading of these meters manually is a costly exercise over the lifetime of the meter, which can be decades long. Ordinary meter readings are prone to errors that may happen on purpose or by mistake. Meter reading may not be possible due to the meter location being in an unreachable area or inside a locked switchboard. Through the use of automated meter reading (AMR) and later smart meters these challenges have been solved. Since smart meters have non-disputable added value for transformer monitoring, using them in this domain is much more common than other domains, such as residential customers. By replacing ordinary transformer meters with the equivalent smart meters or installing new sets of smart meters on the primary and/or secondary side of the transformers, most of the listed problems above are solved, but not all of them. Prior to installing any type of transformer meter regardless of whether it is ordinary, AMR or smart, additional installations should be done such as installing a set of CT and PT on primary, secondary and possibly tertiary sides of the transformer. Also after the physical meter installation, wire connections should be established and all connections should be secured against unauthorised manipulation. Disadvantages of this type of transformer metering are: 1. Several devices including CTs, PTs, meter, wire pipes and connectors should be obtained with each device being compatible with the other. For example, nominal current, maximum current, burden and accuracy class of CT should be compatible with the related meter specification. 2. Field installation of these devices are usually difficult, time consuming and prone to some errors, such as wrong connection of CT polarity, or lost connection. 3. Due to the connection between devices, this kind of installation is easier for unauthorised people to manipulate, so preventing tampering may be more difficult and costly, and cannot be guaranteed. 4. The existence of several devices and multiple connections in the system decreases reliability and lifetime of the system. To overcome the above challenges, Hexing Group introduce a utility friendly solution called ‘Direct High Voltage Meters’ or simply ‘HV meters’. HV meters are meters that include all the necessary equipment and are directly installed on MV lines, including the 6kV, 11kV, 20kV and 33kV sides of the transformer (or any point of the grid) in only one step. ESI AFRICA ISSUE 1 2015