Structure and working principle of generator

I. Main structure of generator

Main mechanism of generator

The generator is usually composed of stator, rotor, end cap and bearing. The stator consists of a stator core, a wire wrap winding, a frame, and other structural parts fixing these parts. The rotor is composed of rotor core (or magnetic pole, magnetic choke) winding, guard ring, center ring, slip ring, fan and rotating shaft and other components.

The stator and rotor of the generator are connected and assembled by the bearing and the end cap, so that the rotor can rotate in the stator, do the motion of cutting the magnetic force line, thus generating the induced potential, which is led out by the terminal and connected in the loop, and the current is generated.

Two. Generator working principle

How a generator works

Generators are based on Faraday's law of electromagnetic induction, which states that a piece of metal, such as a copper wire, moves in a magnetic field and generates an electric field inside the metal.

The charge inside the metal flows along the electric field. If the piece of metal were not a ring, the charge would accumulate at both ends, in the form of a voltage, and by connecting the piece of metal in a loop (the rest of the loop is not in a magnetic field), an electric current would be generated, and electricity would be generated by the generator.

Therefore, the basic principle of the generator is to fix the permanent magnet or metal, let the metal or permanent magnet keep moving, the movement is relative, so that the piece of metal that keeps moving in the magnetic field will continue to generate electricity.

From this point can distinguish different generators, hydraulic generators is to use the energy of water falling from the height to maintain the movement of metals, thermal power is to use the power of the steam produced by fire boiling water to maintain the movement of metals

Iii. Generator classification

There are many types of generator sets, and there are different types of units according to different standards, such as:

1. Divide according to power source

There are diesel generator set, gas generator set, gasoline generator set, wind generator set, solar generator set, hydropower generator set, coal-fired generator set and so on.

2. Electric energy mode

According to the conversion of electrical energy can be divided into alternator and DC generator two categories.

Alternator is divided into synchronous generator and asynchronous generator two kinds. Synchronous generators are divided into hidden pole synchronous generators and salient pole synchronous generators. Synchronous generators are most commonly used in modern power stations, and asynchronous generators are rarely used.

One of the most commonly used is the diesel generator set.

Iv. Common generators

The following is the working principle of various common generators.

4.1Three phase AC synchronous generator

Synchronous generator is one of the most commonly used alternator. In the modern power industry, it is widely used in hydroelectric power generation, thermal power generation, nuclear power generation and diesel power generation.

Because the synchronous generator generally uses DC excitation, when it runs independently, it can easily adjust the voltage of the generator by adjusting the excitation current. If it is incorporated into the power grid operation, because the voltage is determined by the power grid, it cannot be changed, and the result of adjusting the excitation current is to adjust the power factor and reactive power of the motor.

The stator and rotor structure of synchronous generator is the same as that of synchronous motor, generally adopts three-phase form, and only single-phase armature winding is used in some small synchronous generator.

The performance of synchronous generator is characterized mainly by no-load characteristics and load operation characteristics. These characteristics are an important basis for users to choose generators.

Working principle of synchronous generator

How it works:

The basic working principle of synchronous generator includes the following aspects.

1. Establishment of magnetic field. When the generator is running, the excitation winding through the DC excitation current, the same polarity of the excitation field is established, that is, the main magnetic field is established.

2. Cutting motion. The process in which the prime mover, diesel generator set or gasoline generator set drag the rotor to rotate, and the exciting magnetic field of the same type rotates with the shaft and cuts the stator phase winding in sequence.

3. After the operation of the current-carrying conductor generator, the three-phase symmetrical current group acts as a power winding, which is called the induced electromotive force or the carrier of induced current.

4. Generation of alternating electromotive force

The working principle of the synchronous generator is actually the principle of electromagnetic induction. The mechanical energy is converted into electrical energy by the relative motion of the rotor magnetic field and the stator windings. When the rotor is driven by the prime mover, the rotor magnetic field and the stator conductor do relative motion, that is, the conductor cuts the magnetic route, so the induced electromotive force is generated in the conductor, and its direction can be judged according to the right hand rule of u. Because the position of the rotor pole is that the conductor cuts the magnetic field line in a vertical direction. Therefore, the induced electromotive force in the stator winding is maximum at this time, when the magnetic pole is rotated 90 degrees, the magnetic pole is horizontal, the conductor does not cut the magnetic field line, and the induced electromotive force is zero. When the rotor is rotated 90 degrees, the induced electromotive force of the stator winding cuts the magnetic force line in the vertical direction, so that the induced electromotive force reaches the maximum value, but the direction is opposite to the previous. When the rotor turns another 90 degrees. And the induced electromotive force is zero. In this way, the rotor rotates one week, and the induced electromotive force of the stator winding also changes positively and negatively. If the rotor is continuously and evenly rotated, a periodically changing AC electromotive force will be induced in the stator winding, and the AC current can be output through the lead line.

4.2Hydraulic generator

Hydropower generator set is also known as "water turbine generator set", the role is to rivers, lakes and other high water with potential energy to the low, by the turbine into the mechanical energy of the turbine, the turbine and then promote the generator to generate electricity, the mechanical energy into electrical energy. (e.g. Three Gorges in China).

How it works:

The energy conversion process of hydroelectric generating units is divided into two stages:

Firstly, the potential energy lost by water is converted into mechanical energy by water turbine, and then the mechanical energy of water turbine is converted into electrical energy by generator.

The specific process is as follows: under the impact of water flow, the turbine begins to rotate, converting the potential energy of water into mechanical energy; The turbine also drives the coaxially connected generator to rotate, under the action of the exciting current, the rotating rotor drives the exciting magnetic field to rotate, and the stator winding of the generator cuts the exciting magnetic force line in which the induced electromotive force is generated, and at the same time the output of electrical energy will produce an electromagnetic braking torque on the rotor in the opposite direction of its rotation. Since the water flow acts on the turbine continuously, the rotating torque obtained by the turbine from the water flow is used to overcome the electromagnetic braking torque generated on the motor rotor, when the two torques reach balance, the hydroelectric generator set will run at a constant speed, stably emit electricity, and achieve energy conversion. Therefore, the water turbine and the generator are the two most critical components of the hydroelectric generator set.

4.3Wind turbine

Wind turbines convert wind energy into mechanical work and drive the generator to generate electricity, which is a new type of power generation system with low price, reliable operation and no greenhouse gas emissions.

How it works:

The wind drives the windmill blades to rotate, and then the speed of rotation is increased through the speed reducer to promote the generator to generate electricity. According to current wind turbine technology, a breeze speed (the degree of breeze) of about three meters per second can start generating electricity.

4.4Automobile alternator

How it works:

The principle of current generation of alternator and DC generator is the same, both are "moving magnetic field magnetic field line" in "cutting" fixed wire, or "moving wire" in cutting fixed magnetic field magnetic field line, as long as the output current of the wire and the generator magnetic field relative motion, the generator can generate electricity. The relative motion here is achieved by dragging the rotating part of the generator (rotor) to rotate it, but the DC generator is rectified into direct current output by a device called the commutator (also called the commutator), and the alternator has no commutator and directly outputs alternating current.

4.5Three phase asynchronous generator structure diagram

Induction generator is also called "induction generator".

How it works:

An alternator in which a rotating magnetic field in the air gap between the stator and the rotor interacts with the induced current in the rotor winding. The steering of the rotor is the same as that of the rotating magnetic field, but the speed is slightly higher than the synchronous speed of the rotating magnetic field. Commonly used as a small power hydrogenerator.

4.6Diesel generator

Diesel generator set is an independent power generation equipment, refers to diesel fuel, diesel engine as the prime mover to drive the generator power machinery.

How it works:

In short, the diesel generator drives the generator.

In the cylinder, the clean air filtered by the air filter is fully mixed with the high-pressure atomized diesel oil sprayed out of the fuel nozzle. Under the upward extrusion of the piston, the volume shrinks and the temperature rises rapidly to reach the burning point of the diesel oil. Diesel is ignited, the mixture of gases burns violently, the volume expands rapidly, and the piston is pushed down, which is called "work". Each cylinder does work in a certain order, and the thrust acting on the piston becomes the force driving the crankshaft through the connecting rod, thus driving the crankshaft to rotate. The brushless synchronous alternator and diesel generator crankshaft are installed coaxial, you can use the rotation of the diesel generator to drive the rotor of the generator, using the principle of "electromagnetic induction", the generator will output induced electromotive force, and the closed load loop can produce current.

4.7Permanent magnet DC tachometer generator

Tachometer generator is a micro generator measuring speed, he converts the input mechanical speed into a voltage signal output, and requires the output voltage signal to be proportional to the speed. The principle will not be repeated.

V. Proportion of power generation energy

National installed power structure from 2011 to 2020 (unit: 10,000 kW)

By the end of 2020, China will have a total installed capacity of 1.25 billion kilowatts of full-caliber thermal power, 370 million kilowatts of hydropower, 49.89 million kilowatts of nuclear power, 280 million kilowatts of grid-connected wind power, 250 million kilowatts of grid-connected solar power and 29.52 million kilowatts of biomass power.

The proportion of installed electric power in China from 2011 to 2020

From the perspective of power supply structure, the proportion of installed traditional fossil energy power generation in China has continued to decline in the past decade, and the proportion of installed new energy has increased significantly. In 2020, the proportion of thermal power installed capacity decreased by 15.7 percentage points compared with 2011, the proportion of wind power and solar power installed capacity increased by nearly 20 percentage points, and the installed structure of power generation was further optimized.