In 1991 the vertically integrated company EGS, that comprised the electrical energy production, transmission and distribution sectors in Slovenia, was split up into several companies. One of those companies was ELES, which became responsible for transmission system operation, maintenance and construction. In addition ELES assumed the role of a single electrical energy wholesaler in Slovenia, buying or importing the bulk of its electrical energy from the production companies and selling it to those distribution companies and big consumers directly connected to the transmission network.

This role required that the existing energy metering system, which up to then had been used for internal accounting of yearly plan-based energy flows, be expanded and improved to facilitate accounting of energy flows on a monthly basis at different tariff times to and from different partners with whom ELES had contracts for the purchase or supply of electrical energy.

All high precision meters from Siemens, Landis+Gyr and Iskra installed in substations, power plants and factories were connected to registering devices from GEC Measurement and Landys+Gyr, which recorded multiple measuring channels in the form of meter pulses or direct readings of meter counter values via serial communication. The registering devices were connected to the central meter data collection system via telephone lines or dedicated communication lines.

This system was at first simply a collection of custom-written computer programs and applications that operated on a set of files with meter data. Soon it became apparent that an integrated system based on a relational database was needed. Consequently the DGC2000 meter data acquisition system from Landis+Gyr was purchased in 1997. The meter data collected was routinely checked for completeness and consistency, and reconciled on a monthly basis with our corresponding partners (distribution companies, power plants and consumers). Some of them also had their own meter data acquisition systems, and even redundant measurements installed on the accounting points. There was usually enough time and redundant data available to substitute missing or erroneous meter readings.

DEREGULATION AND THE CHANGED ROLE OF METERING

At the end of 1999, in accordance with the EU requirements and regulations, the government of Slovenia passed new legislation which started the deregulation process of the electrical energy sector. Electrical energy was proclaimed a commodity, and time limits were set for opening and liberalising the electrical energy market.

The new legislation had a big impact on the operations of ELES, which now became solely a transmission system operator. The company was no longer allowed to trade with electrical energy except in special cases stated by law. New organisations and associations emerged that assumed their roles in the liberalised market, such as market operator, market regulator, distribution network operators, traders and balancing groups.

This in turn resulted in a change of the required functionality of our meter data collection system. There was no more revenue metering of electrical energy received or delivered. Instead, meter data was used for the calculation of:

  • Use of the network fees for consumers connected directly to the transmission grid.
  • Imbalances between scheduled and actual energy exchange of balancing groups.
  • Imbalances between scheduled and actual energy import and export.
  • System losses.

We also identified the need to have the on-line meter data available in the national control centre, in order to be able to supervise the situation of energy exchanges of cross-border and inter-balancing group flows more timeously and accurately, and with better correlation with the official meter data. For this purpose a separate system was established that enables an on-line delivery of one-minute energy readings from registering equipment in substations to the national control centre.

In addition there was a growing demand for meter data exchange between different market players. Data had to be made available to the market operator, distribution grid operators and also individual large consumers.

To facilitate all these new demands, ELES decided to purchase a new system for energy data acquisition and management – Converge from Landis+Gyr. In addition to meter acquisition, Converge also incorporates the Internet information system www100 that can be used by consumers to view and manipulate their energy profile information via the Internet.

As a consequence of all these new circumstances, the time available to the measurement department to validate and possibly substitute the acquired raw meter data was shortened considerably, from the previous one month down to several hours. This was because data had to be forwarded to our market partners in the course of the next working day for the previous day. To cope with this tight schedule, additional programming tools were specified and commissioned that enabled quick and flexible data verification and correction by means of graphically oriented tools with drag-and-drop functionality, structured lists and ad-hoc reports.

OPERATING IN THE UCTE INTERCONNECTION

Since the construction of the 400kV grid in the 1970s, the Slovenian transmission system has been connected to the UCTE (at that time called UCPTE) interconnection. The parallel operation of the JUGEL control block with the UCPTE continued until 1991, when war in the former Yugoslavia caused the disconnection of the power systems of Yugoslavia, FYR Macedonia, Greece, small parts of Bosnia and Hercegovina and Albania from the main part of UCTE.

At that time ELES was forced to quickly establish a system for automatic generation control (AGC), a function previously performed by Belgrade, to be able to continue operating in the interconnection with the power systems of Croatia and Bosnia and Herzegovina. Since then, ELES has acted as a control block operator of the SHB block and performs the corresponding duties.

An important aspect of these duties is the acquisition of the cross-border tie-line measurements, their on-line transmission to the control block control centre and to UCTE co-ordination centre south in Laufenburg, and also the collection of meter data for the calculation of the inadvertent exchange and compensation schedule. These measurements also include those at measuring points outside the Slovenian power system.

At the moment these measurements are acquired over direct links to the RTUs in the corresponding substations in Croatia and Hungary. With the resynchronisation of the first and second UCTE synchronous zones scheduled for the end of 2004, however, the set of measurements that need to be acquired and transmitted to the control block operator will be increased considerably, as five 220 and 400 kV tie-lines will be reconnected.

The solution adopted to communicate these values was to extend an existing ETSO Electronic Highway data network from Zagreb to Sarajevo, and to establish an ICCP (TASE.2) link between the control centres of ZEKC (the joint TSO of Bosnia and Herzegovina) and ELES. A similar link is already in operation between ELES and ETRANS, Laufenburg, for the purpose of forwarding the on-line measurements to the control block co-ordinator. Meter data will be collected in the form of daily reports of verified values with the agreed structure sent via e-mail by each control area operator.

FUTURE WORK

The changes that have taken place in the past few years, and those yet to come, are forcing continuous adaptation of our measurement system. This leaves very little time to consolidate and integrate it for effective and reliable long-term operation. One of the important future tasks is therefore tighter integration of our meter data acquisition and management system with the existing control centre for use in the despatching department and its linkage to the company’s existing business information systems. We also plan to extend the system with a comprehensive self-supervision system, which would ensure that possible errors or malfunctions are promptly identified and reported to maintenance personnel.