When water with potential energy or kinetic energy is thrown against the turbine, the turbine begins to rotate. If we connect a generator to the turbine, the generator can start producing electricity. If we raise the water level to flush the turbine, we can see that the speed of the turbine increases. Therefore, it can be seen that the greater the water level difference, the greater the kinetic energy obtained by the turbine and the greater the electrical energy that can be converted. This is the basic principle of hydroelectric power. The energy conversion process is as follows: the gravitational potential energy of the upstream water is converted into the kinetic energy of the water flow. When the water flow passes through the hydraulic turbine, the kinetic energy is transferred to the steam turbine. generator to rotate and convert kinetic energy into electrical energy. This is therefore the processprocess of converting mechanical energy into electrical energy.
Due to the different natural conditions of hydropower plants, the capacity and speed of hydroelectric generator set vary greatly. Generally, small hydrogenerators and high-speed hydrogenerators driven by impact turbines mainly adopt horizontal structures, while large and medium-speed generators mainly adopt vertical structures. Since most hydroelectric plants are located far from cities, they usually have to power the load via long transmission lines. Therefore, the power system imposes higher requirements on the operational stability of the hydroelectric generator: the engine parameters must be carefully selected. ; The required moment of inertia is large. The appearance of a hydrogenerator is therefore different fromthat of a steam turbine generator. Its rotor has a large diameter and a short length.
The hydropower unit takes a short time to start and connect to the grid, and the operation schedule is flexible. In addition to general electricity generation, it is particularly suitable as a peak shaving unit and as a peak shaving unit. emergency rescue unit. The maximum capacity of the hydrogenerator unit reached 700,000 kilowatts. As for the principle of a generator, it is very clear in high school physics. Its operating principles are based on the law of electromagnetic induction and the law of electromagnetic force. Therefore, the general principle of its construction is: using suitable magnetic and conductive materials to form magnetic circuits and circuits that conduct electromagnetic induction among themselves to generate electromagnetic energy and achieve the purpose ofenergy conversion.
How many categories of power plants are there? What are the functions of each?
Direct current and alternating current
(1) Direct current and alternating current
Current can be divided into direct current and alternating current. The carbon rod in the middle of the dry battery is the positive electrode, and the zinc skin on the case is the negative electrode. The potential of the carbon rod is always greater than the potential of the zinc skin. If the positive and negative poles of the power supply are connected to the small electric beads with wires, then the current in the circuit will always flow out of the positive electrode of the dry battery, pass through the small electric bead, and then flow into the dry battery of the negative electrode. The magnitude and direction of the current will remain unchanged. This current of constant amplitude and direction is called “direct current” or “DC” en abbreviated. Batteries and DC generators are both DC power sources.
The potential of the two poles of the mains supply is different from that of the dry battery. It does not have a fixed polarity. For a certain time, the upper end is the positive electrode and the lower end is the negative electrode; for a certain time, the upper end is the negative electrode and the lower end is the positive electrode, that is, the polarity of its electrode changes with it. time, and the voltage between the two electrodes also changes with time. If both poles of the power supply are connected to the bulb with wires. Then, the magnitude and direction of the current in the circuit also changes with time. AC current starts from zero, gradually increases, then gradually increases after reaching a maximum positive value. Decrease until it reaches zero, then gradually increase.t in the opposite direction, then gradually decrease to zero after reaching the negative maximum value, thus completing a complete change. This current whose magnitude and direction changes with time is called "alternating current" or "alternating current" for short.
The number of complete changes of alternating current per second is called the “frequency” (symbol: F) of the alternating current. The unit is Hertz, called Hertz (symbol: Hz). The electrical industry uniformly stipulates that all alternating currents use a frequency of 50 Hz.
The time it takes for the alternating current to make a complete change is called a "cycle." For example: an alternating current with a frequency of 50 Hz has 50 complete changes every second, so its period is equal to 1/50 = 0.02 seconds.
For various reasons, two alternating currents (or voltages) of the same frequency may not reach the maximum possible value.tive at the same time, but have a time difference. This time difference is called two alternating currents (or voltages). In a bipolar synchronous generator, when the rotor rotates once, the alternating voltage of the stator makes a complete change. For 50 Hz alternating current, the time required to complete a complete change is 0.02 seconds, and each rotation is equivalent to a 360 degree rotation. Therefore, the phase difference can also be expressed by the angle difference. For example: when the time difference is 0.01 seconds, the corresponding angle difference is 180 degrees; when the time difference is 0.005 seconds, the corresponding angle difference is 90 degrees. If two alternating currents of the same frequency reach the maximum positive value at the same time, they are said to be "in phase" (i.e. the phase is the same or the phase difference is equal to zero if their differencephase rate is 180); degrees, they are called "anti-phase", which means that the phase is opposite. In the case of reverse phase, when one alternating current reaches a maximum positive value, the other alternating current reaches a maximum negative value.
The amplitude of the alternating current (or voltage) is generally expressed by the “rms value”. For example: the scales of AC ammeters and voltmeters, the rated current and rated voltage of electrical motors and appliances are all expressed in rms values. The effective value of alternating current (or voltage) is 0.707 times its maximum value.
The current generated by the generators of hydroelectric plants and the electricity used for lighting and electricity in rural areas are both alternating currents. Alternating current has many advantages over direct current. For example, it is easy to use a transformur to change voltage and it can transmit energy to remote locations. It uses alternating current to generate, transmit and consume electricity, with small investment, simple operation and reliable operation.
(2) Single-phase alternating current and three-phase alternating current
Alternating current is divided into single-phase alternating current and three-phase alternating current. For example: electric lamps, radios, etc. use single-phase alternating current. Single-phase alternating current is derived from and connected to the power supply through two wires.
Almost all alternating current generated by this power source. Hydroelectric power plants are three-phase alternating current, generated by a three-phase synchronous generator. For example, a three-phase bipolar synchronous generator has three identical windings that are spatially different from each other (AXBYCZ). The frequencyThe maximum e and voltage of the alternating current emitted by these three windings are equal, but there is a phase difference of 120 degrees between these three voltages. It is called "three-phase symmetrical voltage". Generally speaking, three-phase voltage refers to symmetrical unless otherwise noted. In fact, the three-phase voltages we usually encounter are basically symmetrical.
The three windings of the three-phase power supply can be connected in star or delta 1. The star connection method in rural areas often connects the three ends of the three windings together to form the "point". neutral", a line drawn from the neutral point is called a "neutral line" (also called a "neutral line" or "earth line"). The conductive wires at the first ends of the three windings are three "live wires". three windings The connection method is called “star connection” (egalso called Y connection) of the three-phase generator.
What is connected to the three-phase motor is a three-phase AC line, which is connected by a live wire, while what is connected to the lighting circuit is a single-phase line, which is connected by n any live wire and ground wire sticking out.
In three-phase alternating current, the three live wires are often represented by ABC (or yellow, green and red), and ground is represented by "N" or "O". The voltage between the live wire and the live wire is called "line voltage", and the voltage between each live wire and the ground wire is called "phase voltage". The line voltage is 1.73 times the phase voltage. For example, when we connect a live wire and a ground wire to a lamp, the voltage between them is the phase voltage, which is specified as 220 V while there are three live wires connected to the motor, and the tension between eachone of the two live wires; The wires are line voltage, specified as 380 V, which is 1.73 times that of 220 V.
Sometimes the number 400/230 volts or 380/220 volts is written in the voltage column rating of the generator nameplate or motor enclosure, meaning: The number above the slash is the line voltage rating, and the slash numbers below are the phase voltage ratings.
The current through each phase winding of the generator is called "phase current", and the current through each live wire is called "phase current". In star connection, the line current is equal to the phase current.
2. The three-phase delta connection generator windings can also be connected in “delta connection”. At this point, the rear end of each group of windings should be connected to the first end of. the other group in successionnce. Connect so that the three sets of windings form a closed loop and run three live wires from the three ABC connection points.
In the triangle connection method, since any two live wires extend from the rear end and the first end of a phase winding of the power supply, the line voltage is equal to the phase voltage, for example: UAB=UAX, where UAB is the line voltage and UAX is the phase voltage. However, in delta connection, line current and phase current are different. If the three-phase voltages are symmetrical and the loads on all three phases are exactly the same, then the line current is 1.73 times the phase current.
Classification of power plants:
Thermal power plants, hydroelectric power plants, nuclear power plants, wind power plants
Thermal power plants: thermal energy production It uses thermal energy from the combustion of fuels (coal, oil and derived products, natural gas, etc.) to produce electricity. There are two main forms of thermal power generation units: boiler is used to generate high temperature and high pressure steam to drive the turbine to rotate and drive the generator to produce electricity, called unit steam turbine generator.The fuel enters the gas turbine and converts the thermal energy directly into mechanical energy to drive the generator to produce electricity, called a gas turbine generator set. Thermal power plants generally refer to power plants dominated by steam turbine generators.
Hydroelectric power plant: Hydroelectricity involves diverting water from a high altitude river (or lake water, river water) downstream through the through a detournement to form a space which drives the rotation of the turbine and drives the generator to produce electricity. . A power plant that uses a hydroelectric generator to produce electricity is called a hydroelectric power plant.
Nuclear power plant: Nuclear power generation uses thermal energy released by the slow fission of nuclear fuel (such as uranium) in an atomic reactor to produce steam (replacing the boiler in a thermal power station) to power the steam turbine then drive the generator to turn and produce electricity. Power plants that primarily produce nuclear energy are called nuclear power plants.
Wind farm: Using the wind to blow the large blades built at the top of the tower to rotate and drive the generator to produce electricity is called wind power generation. She iscomposed of several, dozens, even dozens. wind turbines.
The function of a power plant:
The conversion of various energy sources into electrical energy by chemical and physical means is the function of a power plant. For example, coal, oil and natural gas are converted into electrical energy by chemical means; and solar energy, wind energy, etc. are converted into electrical energy by physical means. Electrical energy is carried to households via lines and can be converted into thermal energy, light energy, kinetic energy, etc.