| As the development of economy, the demand of electricity is increasing.So large province 1000MW coal-fired units that coal consumption is relatively small, effort is great , the rate of plant consumption is low and investment of per kilowatt is relatively small will be more and more applied in the power market,these large-capacity generating units will become the main power system unit. However, there are some problems such as short-circuit current is high, start-up is difficult and especially the reliabity of power system in the large-capacity unit.This thesis for the features of 1000MW thermal power generating units, compares several power programs in the technology and economy ,and then choose the the most reasonable power connection program. This paper will be expounded on the following:(A) Reliability. The reliability of power distribution system related to the reliability of electricity delivered to the user as well as the power quality problem,but the reliability of power plant related to the safe operation of power distribution system, only guarantee a reliable auxiliary power system, the safe operation of the entire power net may be guaranteed. < Factory Technical Regulation >provides that,in two units, if there are more than one alternate transformers are stared, the wiring system is reliable.The reliability means reliable start and safe shutdown of plant.This article bases on the Markov algorithm to attempt to calculate the thermal power capacity of 1000MW power plant unit wiring system ,finally assess the advantages and disadvantages of reliability of auxiliary power system through data.(B) Power flow (Voltage fluctuation). Power flow means electricity network power flow, bus voltage level is a direct reflection of the flow, so the the scope of bus voltage fluctuations is the standard to evaluate the flow merits. Power system flow calculation is a basic calculation, it is the basis of analysis for power system, its task is based on the given operating conditions to determine the power distribution network, power loss, as well as the bus voltage. Power flow calculation divides into on-line power flow calculation and off-line power flow calculation, the former mainly used for the trend-line power system control center, through the dynamics of power-line trend reflected the real-time scheduling. Power system uses the off-line power flow calculation, by simulates the design programs estimating the power flow situation. Newton-Raphson calculation is effective to solute nonlinear equations and has better astringency. N-R calculation for power flow calculation is bases on admittance matrix, because of the symmetry, sparsity and order to optimize the node ID of the admittance matrix, it has the obvious advantages on convergence, EMS, computing speed, so we choose the N-R calculation on plant-power system flow calculate.(C) Short-circuit current. It means when a certain bus short-circuit current the level in the flow of it, short-circuit level is to choose the size of power system equipment breaking the decisive factor. There are three-phase on the power distribution system, line- ground, line-line, line-line- ground, three-phase short-circuit current calculation is very important of the electrical engineering design. The current method of calculating short-circuit current, there are two main methods: < Power plant Technology Prescript>standard and GB/T 15544 standard. The latter equivalent using IEC 909(1988)standard (short form:IEC 909). This method is equivalent with a equivalent source to replace all of the voltage source. Short-circuit point is instead by equivalent voltage source cU 3, it is the only voltage source of the network, other power, such as synchronous generators, synchronous motor, asynchronous motor and the feed network is treated as a zero-electric potential, instead of internal impedance. Check motor start. When the motor start-up, it is a small impedance connecting in the bus load for the system, it absorptions a lot of current from the system, equivalents to six times of the motor rated current, allowing the system to have a voltage drop, interferes the other systems with normal movements. At present, the latest motor up-to-date algorithm including: dynamic motor to accelerate and static electric start. During the later one start and accelerate, make it start in locked rotor form, simulates the worst impact of the normal operation. We use static starting model, induct the conception of block running current finally the simulation data verify its correctness.(D) Plant power consumption rate and economy. The rationality of voltage selection is not only reflected in the reliability and safety on power supply ,but also reflected in the applicability and economy of the programs.We should consider availability of equipment, investment and so on.In this paper, we compare the two units` number of equipment and materials(transformer, common-closed bus, motor, cable and other main primary equipments). Finally simulates several cable programs, argument the merits of the programs according to data. It has a practical guide for the future power plant design and planning of the project.(E) Plant power consumption rate and economic calculation. In this paper, the scope of the economic comparison of the two units by the number of equipment and materials (transformer, busbar closed a total of boxes, motors, cables and other major one equipment) to carry out. Come to the conclusion, program one of the best economic. Three options in the same factory with the load, generating a total capacity of the same power plant, therefore the rate of three options are 4.99%. If the system did not use suction fan, booster fan and denitrification combined load, the system works for the 5.44% margin. This shows that the merger will be the motor is related to a point of order and system to meet the load requirements of the request of a small, lower power consumption rate of the plant, to that end, the motor is a combination of economic significance.Raised by several cable simulation program and the results of the data further argued the merits of the program, the paper recommended the program three wiring. |
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