This chapter introduces the characteristics of traditional and distributed power systems
Whether it is traditional or distributed, the power system is composed of interconnected and coordinated equipment to transport power from the place of production to the place of consumption. Strictly speaking, this simple definition can be described as a flashlight, including the power source (battery), the conduction “transmission” path (usually the main body of the flashlight) that transfers power to the electrical load, which in this example refers to the light bulb that consumes electricity , And the control system (switch) that controls the operation. However, in normal use, the power system is composed of more powerful and expensive equipment, which generally does not include end-use equipment (light bulbs in the flashlight example), but only requires production, transmission, control, and switching. Except for exceptions such as rarity and specialization, all power systems around the world, traditional and distributed power systems have these characteristics:
⑴Constant power supply voltage
For whatever reason, humans have chosen to build a constant voltage power system. A perfect constant voltage power system will provide a constant voltage at each power consumption point, regardless of time, system operating conditions or usage, the voltage will not change slightly. In practice, the allowable voltage varies a little due to different practices and conditions. “How to reach 3% in a short period of time, but in actual use, the power is changed by the coup current. For example, a 12W device is a small light bulb. One is designed to extract 0.1A from 120V. In contrast, a device that requires 120W, such as a small motor, is designed to extract 1A from the same 120V, while a hair dryer that requires 1200W should It is designed to extract 10A from 120V. In the above example, the electrical impedance of 10Ω, 1Ω and 0.1Ω can be used to achieve the corresponding power. All power systems in the world operate on this principle. All user equipment is Designed based on this constant voltage/variable current environment. Power system design, operation, protection and safety rules are also based on this basic concept. It is worth noting that a power infrastructure is established on the basis of a constant current system It will be possible. In this system, the current of the line is relatively constant, and the corresponding use demand can be achieved by changing the voltage at the point of use. It can be said that such a system can run and work well. But although it is interesting, it has not been adopted. The discussion of methods is not a fruitful discussion, and I will not go into further details here.
For AC power systems, voltage and current flow forward or backward in the entire system cycle, 50 or 60 times per second. This is the opposite of a DC power system, where the voltage in a DC system does not change direction. AC power systems have an overwhelming advantage in traditional power system design: transformers are allowed. Electrical engineers regard a transformer as a device that changes the voltage and current combination at the same power: a transformer with a turns ratio of 10:1 can convert 1kW power of 100V, 10A into 1kW power of 1000V, 0.1A. Except that the transformer consumes a very small amount of power during operation, the power basically does not change significantly. However, as the voltage level changes, the economies of scale of power transmission will change highly. In the same electricity system, the transformer allows the use of high-voltage transmission lines to economically transmit large amounts of electricity, and the ground line black uses the low-voltage receiver to enable the local province to send a small amount of electricity to the residents in the shop community. Transformers are used for alternating current, so all power systems are alternating current.
⑶ Natural stability
If all equipment in the system runs and operates as expected, even if it is disturbed by unexpected equipment failures or reasonable load changes, the traditional power system will continue to operate because it can provide power with good voltage, power quality, and continuity. The system is naturally stable-even if it is disturbed, it will return to the current operating mode, as long as the device control or system operation settings are not changed. Although this may seem like an unimportant feature, it is actually a feature that is difficult to implement and requires a lot of engineering work. Many types of systems are naturally unstable. Not only small disturbances can disrupt their operating behavior, but the natural characteristics of their normal operation will even try to switch to an impermissible operating mode for no reason. Therefore, this type of system requires continuous modification and change. Control input, etc. However, in traditional public facilities or industrial power systems, the design should be designed to maintain reasonable natural stability at all times, so that the system is stable enough, even if interference occurs, human-computer interaction is not required to maintain short-term stable operation. Large modern systems rely on automatic control to ensure this: the system is not inherently unstable, but its operation is complicated, and humans may inadvertently switch it to a dangerous state, at least partially. Automation guarantees control actions, so as to maintain fast operation without human-computer interaction. Additional fluctuations in renewable energy and other changes in the disturbed power system are one of the reasons for the need to improve the “smart” control system in the future, even if the economic and performance advantages of smart devices are abandoned. The above are the characteristics of traditional and distributed power systems.