Electric Power System

an aggregate of electric power plants interconnected for parallel operation, power transmission lines, transformer substations, and consumers of electric power. An electric power system has standby equipment for common use and a centralized supervisory office for day-to-day coordination of the operations of the power plants, substations, and distribution systems.

Electric power systems are often associated with heat and power systems that include district heat and power plants and district heat supply systems. A heat and power system in conjunction with centralized power transmission and distribution provides centralized heat supply for cities and industrial centers. With respect to science and technology, a transition to the broader concept of a heat and power system implies not only consideration of the electrical part of the system and the electrical and electromechanical processes occurring in it, but also consideration of the associated mechanical and thermomechanical processes in turbines, boilers, and pipelines.

Heat and power systems may be classified according to installed capacity, the presence of interconnections with other systems, the system’s structure, the power generated, the territory covered, the load distribution, and the physical configuration. Systems are divided (in a first approximation) into three groups by installed capacity: systems with a capacity of more than 5 giga-watts (GW), those between 1 and 5 GW, and those with less than 1 GW (the last group also includes independent power supply systems, such as those in mobile units, for example, ships and aircraft). The structure of a heat and power plant and the installed capacity depend on the type and capacity of the system’s power plants (fossil-fuel-fired steam power plants, hydroelectric power plants, atomic power plants, and other types). The physical configuration of a heat and power system and its switching can be diverse (the physical configuration of a system refers to the relative locations of the system’s power plants, the principal transmission and distribution systems, or, in the case of an interconnected system, the individual subsystems; switching refers to the connections between power plants and the centers of power consumption). The electrical sections of individual heat and power systems are interconnected by main line connections that transmit power in one direction from one system to another by inter-system lines designed for the exchange of electric power.

The operation of an electric power system or a heat and power system is characterized by an operating mode—a group of processes that determine at any moment of time the values of the power, voltage, current, and frequency as well as other quantities that vary during operation of the system. A distinction is made between the steady-state and transient operating modes of a heat and power system. In the steady-state mode the power, voltage, current, and so on are practically constant; in the transient mode they vary either as a result of a control action, that is, a directed action by personnel or by automatic equipment (normal transient processes), or as a result of random disturbances that disrupt the operating mode of the system (emergency transient processes). A corresponding distinction is made between the normal operating mode, in which a heat and power system functions according to prescribed conditions with normal quality indicators for the electric power, and the emergency mode, in which the operation of the system differs from the normal mode when emergencies occur and the quality indicators are abnormal. The postemergency mode is defined as the state of the system after the emergency has been eliminated.

The quality of operation of an electric power system depends primarily on the reliability of the power supply and the quality indicators of the electric power. The reliability of a heat and power system as a whole is determined mainly by the stability of the electric power system and its ability to counteract the development of emergencies (system viability). To a considerable extent the reliable operation of a heat and power system is assured by counteremergency automation, which includes automatic regulation of excitation and a protective relay system as well as preventive protection, by which reports are made on the condition of the system’s elements and on the possible danger of a failure. Counteremergency automation includes automatic isolation for frequency variation and, in a number of cases, for voltage variation (that is, the disconnection of some consumers when there is a dangerous change in the operating parameters), automatic switch-in of standby facilities, automatic reconnection of system elements, automatic elimination of asynchronous operation for a portion of the system, and other measures.

The primary task of a heat and power system is to provide a centralized power supply with integrated day-to-day supervision of the generating, transmitting, and distribution processes for electric power. In the USSR control of a system’s operation is handled by the supervisory services of the regional power administrations, which are subordinate to the Integrated Supervisory Offices of the heat and power system. Day-to-day supervision of the functioning of integrated heat and power systems is accomplished by the Central Supervisory Office of the Integrated Electric Power System of the USSR.

Achievement of the optimum level of electrification in a country with the most economical and reliable electric power supply requires the solution of many scientific problems, including the optimization of development and the day-to-day supervision of the operation of heat and power systems. The solution of such problems requires the extensive use of the systems approach, systems analysis, and the methods of cybernetics.

The creation of a heat and power system provides an economically advantageous increase in the capacity of electric power plants and power units, improves the reliability of electric power supply by means of more flexible manipulation of system reserves, and reduces the total (combined) maximum load as a result of the noncoincidence of the daily load peaks in different regions, thereby reducing the required capacity for an integrated power system. It makes it possible to establish the most efficient operating modes for different types of electric power plants and units, reduces the amount of fuel that must be transported, and facilitates the extensive use of hydroelectric resources that are often far removed from the principal consumers of electric power.

In the countries of Western Europe and in the USA, interconnections between electric power systems are also being intensified. However, the formation of an integrated electric power grid on a national scale does not conform to the capitalist method of production. Electric power supply, which is provided by individual electric power systems that are interconnected only for the reciprocal sale of electric power, often does not provide the quality of electricity required. This is reflected in the nonconformity of technological development with current technological, economic, and social conditions. In the USA, for example, efforts are being made to overcome this disparity by creating associations of private companies to pursue the joint development and operation of electric power systems.

In the USSR the development of electric power systems is inseparably tied to the concentration of electric power generation and the centralization of power distribution. By 1970 construction of the Integrated Electric Power Grid of the European part of the USSR was practically completed. It includes 61 regional heat and power systems and seven interconnected power systems. Interconnected heat and power systems have been created for Siberia and Middle Asia. The Mir international power system, which connects the systems in the member countries of the Council for Mutual Economic Assistance, has undergone extensive development.