The Hydro Ltd. specialists created in the last years a method for completely automated technological process of MHPP on the ground of especially elaborated software and the industrial controllers of ABB from Procontic series, which guarantee exclusive security and reliability in the exploitation of small hydroelectric stations without the presence of a constant operative staff.

The method for upper water level control mode of operation for MHPP (keeping the water level in a small upper compensating basin and in separate cases, when there is none such practically, even in the pressure pipeline) without level sensors for the water level in the upper compensating basin is of a special interest nowadays.

The practice of MHPP exploitation especially in the high-mountainous areas shows, that the construction of long cable lines from the power house to the upper compensator where sensors for the water level should be installed, is highly ineffective, due to the necessity present electric feeding at the sensor fixing point, difficult protection of the equipment, hampered maintenance most of all due to damages made by atmospheric super tensions, as these elements are very sensitive to the latter.

The application of this specific Hydro Ltd. design completely solves the above problems and ensures maximal effective usage of the water resource with minimal expenses. The principal sites, where this system of MHPP control has been applied in the last years are:

• Sevlievo MHPP - built on the drinking water pipeline to Sevlievo completely by Hydro Ltd. and its property. /2001/
• Peev MHPP - built in the Yantra river valley near Gabrovo, a rehabilitated old power plant from 1925 with brand-new electrical parts and automatics, property of private investor. /2002/
• Chepelare MHPP - built in the outskirts of the city zone of Chepelare, on Chaya river, property of private investor. /2003/
• Kresna MHPP - built on the drinking water pipeline to Kresna village, property of private investor, etc. /2004/

Currently are running building projects of Hydro Ltd. for electrical equipment, controls and automation also for the power plants Etropole, Siroko, Stankova Reka, the rehabilitation of Ledenika, etc with release term expiring in 2006.

On the basis of detailed designs of Hydro Ltd. in the beginning of 2006 has started the rehabilitation of Rakita HPP, where new digital turbine governor and microprocessor control system designed by Hydro Ltd. are to be installed in the future.