Power production requirements for power systems

1 . Guarantee the reliability of power supply to users

    The destruction of system operation reliability will cause system equipment damage or power supply interruption, resulting in the suspension of production and operation of various sectors of the national economy and the destruction of people's living order, and even equipment and personal accidents.

    Power users have different requirements for power supply reliability. Even in various departments or workshops in an enterprise, the requirements for power supply continuity are different. According to the requirements of power supply continuity, users can be divided into three levels.

    Primary load. Refers to users who cause personal injury or death due to interruption of power supply, such as coal mines, large hospitals; or users who interrupt power supply and cause great losses to the country politically and economically, such as large smelters, military bases, etc.; or interruption of power supply will affect the country. The users of the department's normal work, such as important state organs, railway hubs, communication hubs, etc., as well as public places where a large number of people are concentrated, and urban public lighting. For a type of load user, two or more independent power supplies should be set up, so one type of user requires high power supply reliability.

    Secondary load. Refers to users who cause political and economic losses due to power interruption, such as damage to major equipment, scrapping of large quantities of products, and large-scale production reduction of key enterprises; or interruption of power supply, users who will affect the normal work of important units, large theaters, large Shopping malls, etc. For the second class of users, special power supply lines should be set up, and dual-loop power supply can also be used when conditions permit.

    Three-level load. Generally speaking, users who have short-term power outages will not cause serious consequences, such as small towns, small processing plants and rural electricity.

    When an accident occurs in the system and there is insufficient power supply, the power load of the three types of users should be removed first to ensure the power supply of the first and second users.

2 . Guarantee the good quality of electrical energy

    The power system must not only meet the user's need for electrical energy, but also ensure the good quality of the electrical energy. Frequency, voltage and waveform are the three basic indicators of power quality, and their ratings are the best operating conditions for electrical equipment design. When the frequency, voltage and waveform of the system do not meet the rated value of electrical equipment, it will affect the normal operation of the equipment, resulting in increased vibration and loss, accelerated aging or even damage to the insulation of the equipment, endangering equipment and personal safety, and affecting users. Product quality, etc. Therefore, the frequency, voltage and waveform of the power supplied by the system must be in accordance with the ratings.

    The system frequency is mainly determined by the balance of active power in the system. Insufficient active power from the generator will cause the system frequency to be low. The node voltage is primarily dependent on the balance of reactive power in the system. If the reactive power is insufficient, the voltage is low. Waveform quality problems are caused by harmonic pollution. The waveform quality is represented by the total distortion rate of the waveform. The distortion rate of the sine wave is the percentage of the square root of the sum of the squares of the effective values ​​of the harmonics to the effective value of the fundamental wave. Guaranteed waveform quality is to limit the harmonic components in the voltage and current in the system.

    The rated frequency of the power system specified in China is 50 Hz, the frequency deviation of the large-capacity system is ±0.2 Hz, and the frequency deviation of the medium- and small-capacity system is ±0.5 Hz. 35kV and above rated voltage allowable deviation ± 5%; 10kV line rated voltage allowable deviation ± 7%, voltage waveform is sinusoidal, its waveform total distortion rate is not more than 4%; 380V/220V line rated voltage allowable deviation ± 7% The total distortion rate of the voltage waveform is not more than 5%.

    The load on the power system is constantly changing, and the voltage and frequency of the system are bound to change. This requires that the dispatcher must always pay attention to the voltage, frequency change and the balance of active and reactive load of the system, and give instructions to the power plant and the substation at any time to quickly and timely adjust the excitation current or motive force of the generator through the automatic device. Stop or start the backup power supply and cut off part of the load, so that the reactive power and active power generated in the power system are balanced with the reactive and active power of the load to maintain the stability of the rated voltage and rated frequency of the system and ensure the power quality of the system.

3 . Guarantee the stability of power system operation

    A short circuit accident will inevitably occur during the operation of the power system, and the load on the system will suddenly change. When the stability of the power system is poor, or the accident is not handled properly, the interference of the local accident may lead to the complete collapse of the entire system (that is, most generators and systems are unpacked), and it takes a long time to recover. This causes large-scale, long-term blackouts, so stability is an important factor affecting the operational reliability of large-scale power systems. In order to maintain stable operation of the power system, in addition to requiring proper configuration of system parameters, the automatic device is sensitive, reliable, and accurate. It should also be reasonably dispatched to deal with accidents and correctness.

4 . Ensure the safety of operators and electrical equipment

    Ensuring the safety of the operation personnel and electrical equipment is the basic principle of the operation of the power system. Therefore, it is required to continuously improve the technical level of the operating personnel and keep the electrical equipment in good condition. In this aspect, it is required that the equipment should be reasonably selected so as not to be damaged under the action of certain overvoltage and short-circuit current; on the other hand, preventive tests on electrical equipment should be arranged in time according to the requirements of the regulations, and hidden dangers should be discovered early. Carry out repairs. Strictly follow the relevant rules and regulations in operation and operation.

5 . Ensure the economics of power system operation

    In order to make electric energy in the process of production, transportation and distribution high efficiency and low loss, in order to minimize the cost of electric energy and realize the economic operation of power plants and power grids, it is necessary to minimize the fuel consumption rate (or water consumption) of power plants. Rate), power consumption and line loss. It should be noted that the reduction of the cost of electric energy will not only reduce the cost of each power sector, but more importantly, it will save energy resources, which will bring huge economic benefits and long-term social benefits. In order to realize the economic operation of the power system, in addition to reasonable planning and design, it is necessary to implement the best economic dispatching of the whole system, realize the reasonable distribution of the load of thermal power plants, hydropower plants and nuclear power plants, and at the same time improve the management technology of the whole system. Level.

    In summary, ensuring the stability of the operation of the power system, providing sufficient, high-quality and economical power to the user safely and reliably is a basic requirement of the power system.