Determination of conditions for the successful start-up of Combined Cycle Power Plant (CCPP) from Black Start Diesel Generators (BSDG)

Abstract

Failures in energy systems can cause disconnection of power plant from power system for an extended period of time and subsequent autonomous start-up of power plant. The main difficulty of power plant start-up is associated with the launch of auxiliary motors from an independent power source, for instance, Black Start Diesel Generators (BSDG). Rated power of BSDG is selected in accordance to estimated loads determined by the sum of the capacities of all auxiliary loads of CCPP taking into account load factor and simultaneity factor. However, as the experience of operating of CCPP shows, the power of BSDG selected in this way does not always ensure a successful start-up of CCPP. Thus, selected power of BSDG for CCPP-450T unit of Kaliningradskaya Thermal Power Plant 2 didn’t bring CCPP-450T unit into operation during black out in 2011. In this regard, there is a need to conduct a research to determine the conditions for successful start-up of a CCPP unit. The essence of the problem lies in the determination of BSDG power capacity sufficient to provide an allowable voltage drop on the BSDG buses at the start of supplying auxiliary loads (with different auxiliary motors) of CCPP, as well as the determination of minimum cost of BSDG. A technique for determining BSDG power capacity sufficient to supply power to auxiliary loads at the start-up of CCPP has been developed. This technique takes into account transient processes in diesel engine and synchronous generator with excitation system when those trigger asynchronous motors and a thyristor starting devices. Moreover, the technique takes into account criteria for maintaining the minimum voltage level at BSDG buses for successful supplying of auxiliary loads. Performed research of CCPP-450T start-up process made it possible to determine the optimum power of BSDG and under various conditions for the start-up of auxiliary motors showed a direct simultaneous start-up of all auxiliary motors of CCPP unit with gas pressure in the pipeline above 2.3 MPa to be successful. However, start-up of auxiliary motors with gas pressure below 2.3 MPa (taking into account gas booster compressor) is possible only with sequentially developing start-up of auxiliary motors.

Keywords

• combined cycle power plant (ccpp)
• black start diesel generators (bsdg)
• start-up of a ccgt
• auxiliary load