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Sustainable economic development is also determined by the availability of primary energy supply. Geographical incoherence of energy production and consumption areas leads to new challenges in providing consumers with energy. The purpose of this work is to analyze and assess trends and problems related to the provision of energy resources, mainly of the natural gas for Republic of Moldova in the context of new challenges in the natural gas market and rhe changes in their transport infrastructure. The investigative methodology is based on the analysis of time series of production, consumption and import of energy resources at global and regional level in 1990-2017. It is proposed to using the linear approximation functions. The coefficients and the its signs of these functions ("plus" or "minus") and the value of and the determination coefficient are used for the quantitative analysis of the production, consumption and import trends of primary energy and natural gas. Europe and Asia ensure their energy balance by massive energy imports. The Southeast European region, including the Republic of Moldova, imports large sums of primary energy resources. The need to import natural gas in the Romania-Moldova-Ukraine sub-zone is currently estimated at about 12 million tons of oil equivalent. The new energy corridors for the transportation of natural gas will lead to new challenges regarding the natural gas supply of the Republic of Moldova. Information on possible scenarios of natural gas supply to the Republic of Moldova is presented and the estimated costs for natural gas transport for these scenarios are presented.

The purpose of this paper is to estimate the possibility of technical use of the 110 kV voltage lines (OPL) for the interconnection of the power systems of the Republic of Moldova and Romania, taking into account in the unified power system regime, which includes the power system of the CIS countries, of Moldova, Romania, Ukraine and other countries in the region.In the calculation scheme of the permanent synchronous regime of the integrated system, the interconnection zone of the Moldovan and Romanian systems was highlighted for the lines of 110 kV: Stanca-Costeşti, Ţuţora (Fai) -Ungheni and Hushi-Cioara.Transformer phase difference angle adjustment devices have been introduced in the 110 kV OPLto provide the bidirectional power shift regime. In the existing topology of electricity networks, power flows at the power system interface are directed from the Republic of Moldova to Romania.Changing the direction of the power flows is possible through the 110 kV OPLA when equipped with phase shift devices. The results of the calculations of the permanent regime have demonstrated the possibility of achieving the reciprocal power exchange regime between the interconnected power systems by adjusting the phase difference angle. It was shown the possibility of stable operation when using 110 kV overheadpowerlines as interconnection lines of the Moldovan and Romanian power systems.The issue of interconnection through the 110 kV lines is complex and requires an individual approach to how to achieve it.

Types of intersystem controlled tie-lines, that may allow the joint work of power systems of Moldova, Ukraine and Romania, are proposed in this paper. The use of intersystem controlled ac transmission lines based on compact one-circuit overhead transmission lines (OHTL) and two-circuit controlled self-compensated OHTL (CSCTL) with phase-shifting transformers on the other hand is also stated. Two types of phase-shifting transformers are considered: the first one – with bounded range of phase angle control between the voltage vectors’ system at the output with respect to the other at the input; the second one – with circular rotation of one voltage vectors’ system with respect to the other. The first type of devices is aimed to control the power flows within the system or through the intersystem tie-lines of synchronously operating systems. The second type of phase-shifting transformers is aimed to interconnect power systems that operate non-synchronously and to control the power flows between them through connecting OHTL. The first type of devices was introduced in calculation model in 330 kV Moldavskaya GRES – Chisinau OHTL and the second one – in the OHTL that are connecting the power systems of Moldova and Romania. The dependences of power flows through power system’s and intersystems’ OHTL are established on base of performed calculations, research and analysis.

The results of analysis of the operating mode of power system of the Republic Moldova when accomplishing the interconnection with the power system of Romania using the Back-to-Back (BtB) power unit at the transformer station Vulcanesti have been presented in the paper. Installation of BtB leads to the loading of overhead power line (OPL) 330kV Vulcanesti-Chisinau up to 571 MW with the change of the value and the direction of power flux in OPL from Chisinau toward Kuchurgan power station, the decrease of power flux entering the north of the country (OPL 330kV HPP Dnestrovsk - Balti) and in the OPL 330kV (Kotovsk- Kuchurgan power station). Essential changes of the active power flux occur at the buses of Kuchurgan power station toward Ukraine in comparison with the actual topology of power network (base regime). The change of the direction and of values of power flux through the unified power system has as a consequence the increase by 171MW (from 2961MW to 3132MW), as well as the increase by 7,1% of the losses of power in high voltage Moldovan network comparing with the base regime. It is pointed that the accomplishment of asynchronous interconnection with Romania has the impact at regional scale causing the change of power fluxes both in the power system of the Republic of Moldova and of Ukraine with Romania including the Kuchurgan power station. Assessment of financial aspects indicates to the trend of increasing of the project’s cost of the interconnection with Romania, but in the case of investment return considering the increase of the cost for the service of transmission of power is expected the necessity to increase the tariff with nearly 154% in comparison with the value of 2015 year, considering zero value of bank and inflation rates during the 10 years of investment return, as well as the constant exchange rate of MDL to EURO during the 10 years investment return period.

The basic theoretical principles to create compact controlled transmission lines are analyzed in the paper. The results of technical and project elaboration of some variants of such type of power transmission lines are presented and the comparison between their technical and economic indicators with those of traditional power transmission lines and foreign analogues is made in the paper. The efficiency of compact controlled transmission lines application to form power systems and to create intersystem ties as well as distribution electric network is also stated in the paper.

The basic theoretical principles to create co mpact controlled transmission lines are analyzed in the paper. The results of technical and project el aboration of some variants of such type of power transmission lines are presented and the comparison between their technical and economic indicators with those of traditional power transmission lines a nd foreign analogues is made in the paper. The efficiency of compact controlled transmission lines application to form power systems and to create intersystem ties as well as distribution electric network is also stated in the paper.

The article presents an assessment of problems of extra-consumption of fuel resources in Moldova, as a result of underloading of CPH of national energy system, as well as, increasing share of electricity produced by condensing power plants for ensuring supply of established energy demand. It is shown that, every year, over-consumption of about 100 thou t.c.e. is observed at CHP, due to inefficient loading factor of regimes in which are forced to be operated power plants as a result of un-bounding or disconnections of some consumers of heating energy and un-coordinated policy in the field of heat supply.

The Transmission Power Lines of new generation are described in the article (single- compact, double-circuit compact, double-circuit Controlled Self-compensating High Voltage Transmission Power Lines (CSHVL). Basic principles of creation, design elements and comparative characteristics of the transmission lines of the new generation are described, the advantages of its are showed. Methodical approaches to the choosing of a new generation of transmission lines and facilities management FACTS are formulated. Methodical approaches to the choice of options for transmission lines 220 kV and facilities management are shown.

Investigation of power regimes of Southern Eectrical Networks of 110 kV in case of disconnecting of the high voltage electric transmission line of 400 kV of Moldavian condenced power plant ( MCPP ) – Vulcaneshty