电气工程专业英语CHAPTER 4 The Load-flow Problem电气工程专业英语CHAPTER 4 The Load-flow Problem.pdfVIP

CHAPTER 4 THE LOAD-FLOW PROBLEM 4-1 The Nature of the Load-Flow Problem The general power-system components to be encountered in the load-flow problem are generators, loads, transmission lines, transformers, synchronous condensers, static capacitors, voltage regulators, phase shifters, and so on. The load-flow problem has its origin in the way loads are specified. It is a common industry practice to specify loads in kilowatts. In addition, power factor or the amount of reactive is also specified. Unfortunately, the power engineer usually needs to know the voltages and currents that exist on the power system so that he can check performance in terms of ampere loading and voltage regulation. The conversion of the specified loads from power and reactive to voltage and current is the load-flow problem. The best way to understand the complexities introduced by the load-flow problem is by example. The dc problem is the simplest example. Suppose that a 10 V dc source feeds an 8-W load through a 2- Ω resistor. The desired answers are the load or receiver end voltage and the load current. Even in this simple example the desired answers are not obvious without algebraic manipulation. Figure 4.1 shows the circuit and the steps that may be used in solving the problem. The current must be established as a function of the sending end voltage, the resistance of the line, and the watts of the load. In setting up the algebra for this problem, the current occurs in the form of a quadratic. In the figure it is determined by the use of the quadratic formula. It is important to note that the quadratic formula yields two values of current that will fulfill the specified condition. Now from a mathematical point of view, either current will be satisf