Nowadays, many people like to talk about “power quality”. There are many products of power quality, such as SVG, APF and three-phase unbalanced regulator, which have become “hot-selling products”. But what are the benefits of improving power quality for people?
Improving power quality is of great significance to the safe and economic operation of power grid, ensuring the quality of industrial products and the normal conduct of scientific experiments, and reducing energy consumption. Power quality is directly related to the overall benefits of the national economy.
Good power quality is undoubtedly beneficial to the operation of electrical equipment, but the adverse impact of poor power quality on the operation of power system has not attracted enough attention. From the point of view of harm degree, the harm of some power quality problems is destructive. For example, the overvoltage caused by harmonic resonance in lightning impulse, capacitor and cable switching often causes insulation and mechanical damage of electrical equipment, thus affecting the normal operation of power system. The misoperation of relay protection device caused by harmonic and negative sequence interference will cause huge economic losses in large-scale blackout of power grid. Short-term power supply interruption or voltage drop may lead to production chaos or a large number of industrial smelting products scrapped or even endanger personal safety. On the other hand, some power quality problems mainly affect the performance indicators of electrical equipment. For example, abnormal voltage and frequency deviation will cause the change of speed and power of asynchronous motor load, which will reduce the efficiency of transmission machinery and affect the quality of textiles, papermaking and other products. Harmonic currents circulate in transmission and distribution equipment such as rotating motors, transmission lines and transformers, which overheat these equipment due to additional losses, thus reducing the life or capacity of these equipment. However, it can not be explained that the former power quality problem is more important than the latter. The actual situation is that the latter power quality problem, due to the wide range of electrical equipment involved, has the same impact as the former power quality problem.
There have been a lot of achievements on the study of the harm of deterioration of power quality indicators to electrical equipment. However, different indicators of power quality have different effects on different equipment. Especially when there are multiple indicators of power quality, the impact of different combinations on equipment is a very complex problem. At present, there is no accurate quantitative formula, only some rough formulas and conclusions. The results can be used for engineering estimation.
Therefore, in general, the closer the power quality index is to the rated value, while ensuring continuous and reliable power supply is the symbol of high quality of power. However, from production to consumption of electric energy is an integral whole. The generation, supply and use of electric power system are always in a dynamic balance, and any link of it will have an impact on the quality of electric power. The control of power index needs considerable investment (including the improvement of power grid structure, the balance of active power and reactive power, the use of various frequency modulation, voltage regulation, filtering and reactive power compensation devices, as well as the technical management of dispatching and operation), and the control technology of various index is constantly developing and improving. In fact, the deviation between the power quality index and the rated value is inevitable. The task of formulating power quality standards is to determine the appropriate allowable deviation of power quality indicators from the current (or recent) technical level.
The criteria for judging whether the criteria are reasonable or not should be:
1.Basically, it can ensure the security, continuous power supply and economic operation of the power system.
2.On the whole, it can ensure the normal use of electricity for users’electrical equipment.
3.On the basis of the current technological level, the power sector (including interfering users) should be able to meet the standards after making certain efforts.
Meeting users’ requirements:
-Capacitive and inductive reactive power compensation
-Three-phase unbalance compensation
Meeting users’ requirements:
– PF=0.99 and THDi < 5%
– Compensation for 2- to 50-order harmonics
– Capacitive and inductive reactive power compensation
– Three-phase unbalance co