Research On Optimal Power Flow In Operating Network Of Black Start Service Combination

A severe snow disaster hit China Southern area in early 2008 while blackout happened in several power systems. The purpose of black start is to restore power system quickly and reliably after blackout. When serious disasters happen in power grid, power supply must be provided by black start for the emergent power demand of social security and emergency rescue.When black start plan of regional power grid is making, local generators which are able to start up by themselves are selected to become black start units. Many enterprises own large backup diesel generators in Yangtze River delta and Pearl River delta developed areas. Based on actual situation of these city power grids which are lack of hydroelectric units, a plan called"black start service combination"(BSSC), i.e. self-provided diesel generators of enterprises are used as the black start units, is proposed in this paper. The effect of black start units is restoring the power supply for important customers, so BSSC operating network is needed to form. BSSC operating network is composed of distributed backup diesel generators, awaiting start-up unit and transmission lines connecting them. The main task of operating network is providing auxiliary power for local plant, starting up thermal power unit. After thermal units start on by one, important load of local power grid can be restored and emergency power supply demand can be satisfied.When start-up power of diesel generators is transferred by operating network, the power is much smaller than normal transmission capacity of lines. Therefore, the network is under lightly loaded condition, and the transmission lines occur capacitive. The capacity of diesel generators is small, the ability of absorbing reactive power is weak, and so the problem of generator self-excitation is worth considering in operating network. When BSSC operating network is constructed, the self-excitation of single generator energizing single transmission line can be analyzed by engineering criterion, and a solution is proposed to avoid self-excitation in this period. When thermal unit is supplied by operating network, an analysis of operating network is made to obtain the operating characters of such network, and then an optimal power flow modal of BSSC operating network is built. Considered that self-excitation may happen when generators generating capacitive reactive power, so it can be avoided by optimal power flow when network is operating, primal-dual interior point algorithm is adopted to solve optimal load flow in this paper.According to"power grid lifeline"project proposed by Jiangsu electrical power company, a certain power grid of Jiangsu is used as a testing system for researching on the plan of black start units. Power grid is divided into several zones, BSSC operating network is built in every zone, and then the problem of self-excitation is analyzed. The results demonstrate that the working point given by interior point optimal load flow is feasible, and BSSC operating network can solve the self-excitation problem.