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August 3, 2020
Types and functional characteristics of generators
A generator is a device that generates electricity when subjected to mechanical power. In this conversion process, mechanical power comes from various other forms of energy, such as wind energy, water energy, thermal energy, and solar energy. According to the different types of electricity generated, generators are mainly divided into two categories: DC generators and AC generators.
1. Features of DC generator
The DC generator has the characteristics of convenient use and reliable operation, and can directly provide electrical energy for various electrical equipment requiring DC power. However, there is a commutator inside the DC generator, which is easy to produce electric sparks and the power generation efficiency is low. DC generators can generally be used as DC power supplies for DC motors, electrolysis, electroplating, charging, and AC generator excitation.
2. Functional characteristics of alternator
Alternator refers to a generator that generates alternating current by external mechanical force. This type of generator can be divided into synchronous alternating current generation
Synchronous generators are the most common in AC generators. This type of generator is excited by DC current and can provide both active power and reactive power, and can be used to supply power to various load devices that require AC power. In addition, synchronous generators can be divided into four types: steam turbine generators, hydroelectric generators, diesel generators, and wind generators according to the different prime movers used.
The application of AC generators is very wide. For example, various power stations, enterprises, shops and home backup power sources, automobiles, etc. all use generators for power supply.
The model and technical parameters of the generator
In order to facilitate the production management and use of generators, the country has unified the compilation method of the generator model, and the nameplate of the generator is affixed in a more obvious position of its shell. The parameters contained mainly include the model, Rated voltage, rated power, rated power, insulation class, frequency, power factor and speed, etc.
The meaning of the generator model
The model of the generator is usually a description of the model of the unit, which contains information such as the type of voltage output by the generator, the type of the generator unit, control characteristics, design serial number, and environmental characteristics.
In addition, some generator models are more intuitive and simple, and easier to identify, as shown in Figure 6, which includes the product number, rated voltage, and rated current.
(1) Rated voltage
Rated voltage refers to the rated voltage output by the generator during normal operation, in kV.
(2) Rated current
Rated current refers to the maximum working current when the generator is working normally and continuously, and the unit is kA. When the other parameters of the generator are all rated, the generator runs at this current and the temperature rise of the stator winding will not exceed the allowable range.
The rotation speed of the generator refers to the maximum rotation speed of the generator shaft within 1 min. This parameter is one of the important parameters for judging the performance of the generator.
Frequency refers to the reciprocal of the alternating current sine wave period in the generator, and its unit is Hertz (Hz). For example, if the frequency of a generator is 50Hz, it means that the parameters such as the direction of the alternating current change 50 times in 1s.
(5) Power factor
Generators generate electricity by electromagnetic conversion, and the output power can be divided into two types, namely reactive power and active power. Reactive power is mainly used to generate a magnetic field and convert electricity to magnetism; while active power is provided for users. In the total power output by the generator, the proportion of active power is the power factor.
(6) Stator connection
The stator connection of the generator can be divided into two main types, namely the triangular (△-shaped) connection and the star-shaped (Y-shaped) connection, as shown in Figure 9. In generators, usually the three windings of the generator stator are generally connected in a star shape.
(7) Insulation class
The insulation grade of a generator mainly refers to the high temperature resistance of its insulating material. Insulating materials are the weakest link in generators, which are easy to accelerate aging or even damage at excessively high temperatures, so different insulating materials have different heat resistance levels. This parameter is usually represented by letters, where Y means heat-resistant temperature is 90℃, A means heat-resistant temperature is 105℃, E means heat-resistant temperature is 120℃, B means heat-resistant temperature is 130℃, F means heat-resistant temperature The temperature is 155°C, H indicates that the heat-resistant temperature is 180°C, and C indicates that the heat-resistant temperature is 180°C or higher.
In the generator, in addition to the above technical parameters, there are also parameters such as the number of phases of the generator, the total weight of the unit and the date of manufacture. These parameters are relatively intuitive and easy to understand when reading, and are mainly for users to refer to when using or purchasing.
Three, the symbol identification of the generator in the line
The generator is one of the indispensable parts in the control circuit of electric drive and machine tool. When drawing the corresponding schematic diagrams of each control circuit, the generator is not represented by its actual appearance, but is marked by symbols such as drawings or diagrams, letters and other symbols representing its functions.