| The load featured with periodic or non-periodic sharp change is named as surge load, while the large capacity surge load has features such as high grade voltage, large power variation amplitude and high frequent power variationn in its interconnect system, which shows load properties of power impact, nonlinearity and three phase asymmetry. With the development of industry modernization and wide application of power electronic energy conversion technology, all kinds of generalized surge loads have been put into operation in a great amount, which can effectively save energy and increase efficiency, whereas may cause the power quality problem on public power grid and further yield serious influence on the security and stability of power system. Such load influences mainly include the frequency deviation and low power grid asset utilization arisen by active power unbalance, the deviaton, fluctuation and flicker of voltage and increased line lose arisen by reactive power unbalance, the power equipment nonlinear breakdown and power lose arisen by harmonic, and the motor heating and operation instability arisen by negative sequence current,etc.The AC arc furnace steelmaking and electrical railway are now the most serious surge loads in our country, and the dissertation focuses on the key influence technologies of AC arc furnace and electrical railway surge loads, which are the load characteristics, infuence on public power grid, interconnecting system design and comprehensive governance. Herein, the 150t AC arc furnace in Baogang is employed as an example to study the technologies of power modeling, surge property on power grid and test assessment for the AC arc furnace surge load, and the AC arc furnaces in Zhangjiagang are employed to study the influence and interconnecting technologies of cluster surge loads on the public power grid. Moreover, the traction station of Ling-hang high speed railway in Hushu is further taken as an example to investigate the key technologies of load characteristic modeling and simulation, test assessment and comprehensive governance for the electrical railway surge load. The detailed contents are as follows:1. The classification method of surge loads is firstly proposed by employing the FCM fuzzy cluster algorithm. In order to explore the generalied rule of surge loads, a classification method is proposed to divide surge loads into the large surge load and medium surge load, on basis of the FCM fuzzy clustering algorithm and really measured PCC capacity, active power and reactive power, because the surge load has different catgeories, the load property, interconnecting voltage, PCC capacity, active power and reactive power are different, and their power quality assessment method, system design optimization and comprehensive governance measure are different, too. As a result, the AC arc furnace and the electrifical railway are obtained as typical large capacity surge loads, which establishes a theoretical basis for following studies of the surge load modeling, interconnect system calculation and simulation, power quality assessment and comprehensive governance.2. The load modeling is focused on both AC arc furnace and electrical railway surge loads. Because the AC arc furnace steelmaking concerns complicated product scheme and technological process, and the electrical railway also concerns complicated transport program and procedures of traction power supply, train operation control and running dispatch, the influence mechanism of both AC arc furnace and electrical railway on the power grid is thus acquired to deeply investigate. According to the system composition of AC arc furnace, power supply condition and really measured data, a new resistor model of AC arc furnace is proposed upon the operation power calculation, which has high precision and is easy to realize optimum control on the electric pole and improve the power supply efficiency, and reduce the lose of durable material and electric pole. Furthermore, a generalized surge load characteristic model of electrical railway is established upon the traction power supply system and its power use property, which involves the sub-system models of traction tranformer, traction rectifier, traction inverter and traction motor. The above-established models will provide a theoretical foundation for studying the preliminary assessment and test assessment about the AC arc furnace and electrical railway surge loads.3. The preliminary and test assessments for both AC arc furnace and electrical railway surge loads are investigated in the dissertation. As a category of load, the AC arc furnace and electrifical railway have the common impacting, nonlinear and unbalanced characteristics, and acquire quite higher power supply quality and meantime may cause heavy influence and pollution on the power supply quality, which relates to multi-directional and multi-level interaction and cross impact for the power supply and distribution. As a result, the preliminary assessment method for the AC arc furnace and electrical railway should be deeply investigated. Herein, the system variation is theoretically analyzed upon three periods of small disturbace transient state stability and materials about the power grid and surge load characteristics, and a preliminary assessment method is further built up for assessing indexes of the voltage fluctuation, voltage flicker, harmonic, three-phase unbalance and active power in a systematic manner, by applying PSASP comprehensive analysis program for power system and MATLAB simulation software; and the power quality indexes and really measured curve data, offered by Jiangsu power quality monitoring platform, are employed to verify effectiveness of the proposed preliminary assessment method for AC arc furnace and electrical railway surge load models, which establishes a solid foundation for further studying the comprehensive governance of AC arc furnace and electrical railway surge loads.4. The key technologies of comprehensive governance and control for the surge load is conducted. According to the cluster analysis result of surge loads, an optimized voltage level selection scheme is poroposed for the surge load innterconnection, upon the strategy of hierarchical partition and collaborative governance, and can thus offer an ideal condition for the comprehensive governance of surge load. In order to investigate the power supply governance scheme of decoupling isolation for the cluster surge and sensitive loads, the cluster surge loads in Zhangjiagang are taken as an example innerconnecting to the power grid, in which the power supply voltage grade is 500kV for the cluster arc furnace loads. Consequently, because the cluster group has superposition effect, the total disturbance decreases greatly and the governance cost is also decreased, as well as the decoupling and isolating with sensitive power consumers is effectively realized. The proposed scheme by innerconnecting the cluster arc furnaces into 500kV power grid is initally proposed in the world, and has yielded better social benefit. Furthermore, aiming at the high frequency harmonic problem caused by large impact excited emerging current and switching of on-off components when the electrical railway locmotive switches on, a new scheme is proposed to add penecontemporaneous control device in front of the automatic equipment and increase the voltage angle judgement, such that the excited emerging current decreases more than 50% and the investment cost is only 0.2% of the dynamic compensation equipment. Moreover, so as to effectively overcome the power impact and high frequency harmonic of traction power supply system, it is proposed to add RPC and high-pass filter in the traction substation, and thus establishes the key comprehensive governance technology for AC arc furnace and electrical railway surge loads. |
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