- Increased load and arising imbalance between electricity consumption and generation, as well as the efforts to optimise operation of sources, force the transmission systems to look for possibilities of mutual co-operation with neighbouring systems.
- The first parallel co-operation of the Slovak transmission system (as a part of the former Czechoslovak transmission system) was accomplished with the Hungarian transmission system in 1952 at the 110 kV Nove Zamky - Kisigmand line. In 1954 the operation of 2x100 kV Bystricany - Vac line was commenced. Based on increasing demands on the international co-operation and electricity transits, the Bystricany - Vac line was extended to a 220 kV switching station Zuglo and connected to the 220 kV system in 1954.
- As a part of co-operation development between neighbouring countries, transmission systems of Poland, former Czechoslovakia, and former German Democratic Republic were interconnected via 220 kV lines. The interconnection of the transmission systems via 220 kV lines was extended to the former USSR (Lemesany – Mukacevo) in 1963.
- At that time the mutual relations in electricity supplies and operation of the interconnected transmission systems were controlled by national dispatching centres on the bilateral agreement basis. Operation modes required a common control body of the interconnected system (ICS) due to the ICS extending and increased exchanges. Having agreed in the Board of COMECON (Council for Mutual Economic Co-operation), the participated countries established the Central dispatching organisation (CDO) on February 25, 1962 based in Prague.
- The rapid increase of electricity consumption in the ICS countries required building up a 400 kV transmission system. The first 400 kV connection was operated from Mukacevo (former USSR) to Lemesany in 1965.
- Increasing demand of the former East-European COMECON countries on electricity imports from USSR brought about the need of building up a large-capacity between USSR and ICS. Therefore in addition to erection of 400 kV lines there was also a 750 kV line Vinica - Zapadoukrajinskaya – Albertirsa (Hungary) constructed in 1979. Linked to the 750 kV line, there was the second 400 kV interconnection transmission line between Slovakia and Hungary (Levice - Göd – Albertirsa) erected. Another 750 kV connection from Chmelnitska NPP to Poland (Rzeszow) was built and commissioned in 1985.
- CDO was an ad-hoc organisation of the member countries. CDO activities included monitoring of the electricity supplies bilateral agreements, keeping the final balance in the member countries, monitoring of electricity transits, and dealt with system emergency and disintegration situations, as well as played important role in the mode operation preparation. Rising loads, power transits, delayed capital construction and resulting insufficient margins of the regulation capacity had an adverse impact on the quality of ICS basic operational parameters. A negative role was also played by a high failure-rate of generation facilities in comparison with other systems in the world. As a result of economic and political changes in the Central European region the CDO CCP was step-by-step divided and stopped functioning.
- A co-operation with West European countries (joined in the UCTPE system) in the transmission system of the former Czechoslovakia had taken place since 1956. There were minor seasonal electricity exchanges in form of special supplies to the Austrian transmission system through on-way connections (Dürnrohr ; Etzenricht). The important turn in co-operation with the UCPTE system came only after 1990. On October 11, 1992 the CENTREL system was established, which associated the transmission systems of Poland, Czech Republic, Hungary, and Slovakia with the aim of joint efforts to connect the systems to the Western system UCPTE. A set of recommendations and measures "Massnamenkatalog" was developed by representatives of Western companies for each national system to be connected to UCPTE.
- On April 1, 1994 the common control of the Czech and Slovak transmission systems was split, and the Slovak Power Dispatching at Zilina took over the function of the national power dispatching of the Slovak Republic. In a very short time the Slovak Power Dispatching staff had to get familiarised not only with their specific tasks in the complex control of the Slovak transmission system, but also in terms of the international co-operation so that the transmission system of the Slovak Republic became a reliable partner of the interconnected systems.
- Implementation of the “catalogue of measures” was urgent. The catalogue included technical, economic, and organisational measures in the Slovak transmission system, which were necessary for connection to UCPTE system (primary and secondary control of generator power, keeping the power margin, keeping U and Q at the required level, measures against major failures, etc.). All the measures were successfully met and accomplished. Based on this, the Slovak transmission system as a part of the whole CENTREL block was synchronously connected to UCPTE system on October 18, 1995 for a trial operation.
- On October 1, 1996 the control and clearing centre of CENTREL EACC was commenced in Warsaw as an independent control and clearing unit of UCPTE.
- On September 30, 1997 the 2-year trial parallel operation of CENTREL and UCPTE was completed and assessed. The final report says that all measures within CENTREL are fulfilled. Based on this the CENTREL members applied for a full membership in UCPTE on October 1, 1997.