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Generator overview, structure, operating principle and classification

1. An overview of the
Electric energy is one of the most important energy sources in modern society. Generator is to convert to other forms of energy into electrical energy machinery and equipment, it consists of turbine, steam turbine, diesel engine or other power mechanical drive, water, air, fuel burning or nuclear fission energy into mechanical energy to generator, is converted to electricity by a generator. Generators are widely used in industrial and agricultural production, national defense, science and technology and daily life.
Generators come in many forms, but their working principles are based on the laws of electromagnetic induction and electromagnetic force. Therefore, the general principle of its construction is that suitable magnetic conduction and conductive materials are used to form magnetic circuits and circuits for electromagnetic induction to generate electromagnetic power and achieve the purpose of energy conversion.
The classification of generators can be summarized as follows:
Dc generator, ac generator; Synchronous and asynchronous generators (rarely used)
Ac generators can also be divided into single-phase and three-phase generators.

2. Structure and working principle
A generator is usually composed of stator, rotor, end cover, stand and bearing.
The stator consists of a pedestal, a stator core, a wire-wrap winding, and other structural elements that hold these parts together.
The rotor is composed of a rotor core (magnetic choke, magnetic pole winding) slip ring, (also known as copper ring, collector ring), fan and shaft.
By bearing and end cover of generator stator and rotor connected together, can make the rotor spinning in the stator, do the exercise cutting lines, thus induced potential, through terminal lead, in the circuit, the electric current is produced.
Steam turbine generator and steam turbine supporting generators. In order to achieve high efficiency, steam turbines are usually made at high speed, usually 3000 RPM (frequency: 50 hz) or 3600 RPM (frequency: 60 hz). In the nuclear power plant, the turbine speed is low, but also above 1500 RPM. In order to reduce the mechanical stress caused by centrifugal force and reduce the wind friction, the rotor diameter is generally smaller and the length is larger, that is, the slender rotor is adopted. In particular, the rotor diameter of high capacity high-speed units above 3000 RPM is strictly limited due to the material strength. Generally, the rotor diameter cannot exceed 1.2 meters. The length of the rotor body is limited by the critical speed. When the body length is more than 6 times of the diameter, the second critical speed of the rotor will be close to the running speed of the motor, and large vibration may occur during operation. Therefore, the size of rotor of large high speed turbogenerator is strictly limited. The rotor size of an air-cooled motor of about 100,000kw has reached the above limit size. To increase the motor capacity, it can only be realized by increasing the electromagnetic load of the motor. Therefore, the cooling of the motor must be strengthened. Therefore, the steam turbine generator with a cooling effect of hydrogen cooling or water cooling is adopted for over 50 to 100 thousand kilowatts. Since the 1970s, the maximum capacity of turbogenerators has reached 1.3 to 1.5 million kilowatts. Since 1986, great breakthroughs have been made in the study of high-critical temperature superconducting electrical materials. Superconducting technology is expected to be applied in turbogenerators, which will bring a new leap in the development of turbogenerators.
Water wheel generator
A generator driven by a water turbine. Due to the different natural conditions of hydropower station, the variation range of capacity and speed of water wheel generator set is very large. In general, the high speed hydro-turbine generators driven by small hydro-turbines and impact turbines are mostly horizontal, while the large and medium speed generators are mostly vertical (see figure). Because most of hydropower stations in places far from the city, usually need to go through a long load power transmission line approach, as a result, the running stability of the power system for hydro-generator put forward higher requirements: motor parameters need careful selection; The rotational inertia of the rotor is required. Therefore, the appearance of water wheel generator is different from that of steam turbine generator, its rotor diameter is large and its length is short. In addition to general power generation, it is especially suitable for peak regulating unit and emergency standby unit. The maximum capacity of the water wheel generating unit has reached 700,000 kilowatts.
A generator driven by an internal combustion engine. It starts quickly and operates easily. But internal combustion is expensive, so diesel generators are used mainly as emergency backup power or in areas where mobile power stations and large power grids have not yet arrived. Diesel generators typically rotate at or below 1000 revolutions per minute and have a capacity of several to several thousand kilowatts, especially for units under 200 kilowatts. It's easy to make. The torque output on the diesel shaft fluctuates periodically, so the generator works under the condition of severe vibration. Therefore, the structural components of diesel generators, especially the rotating shaft, should be strong and rigid enough to prevent them from breaking due to vibration. In addition, in order to prevent the rotating angular velocity caused by the torque ripple generator uneven, cause the voltage fluctuation, cause the lights flashing, diesel generator rotor also requires larger moment of inertia, and should make natural torsional vibration frequencies of the shafting and diesel engine torque ripple in either the frequency of the alternating component differs by more than 20%, lest produce resonance, broken shaft caused by accident.
Diesel generating set is mainly composed of diesel engine, generator and control system, diesel engine and generator has two kinds of connection mode, a flexible connection, which even the axis machine the two parts of docking, secondly, rigid connection, the generator with high strength bolt connection rigidity and diesel engines can be connected with the fly wheel, currently use some more rigid connection, diesel engine and generator connected and installed on the chassis, deserve to go up and then all kinds of sensors, such as water temperature sensor, through the sensors, to display the running condition of diesel engine to the operator, and with these sensors, you can set an upper limit, When reach or exceed the limit control system will alarm in advance, this time if the operator did not take measures to control system will automatically stop unit, diesel generating sets is to take the way of self protection. Sensors are used to receive and feedback various kinds of information. It is the control system of the unit itself that truly displays the data and performs the protection function.
4. Principle of wind generator
It is a power machine that converts wind energy into mechanical work, also called windmill. Broadly speaking, it is a kind of heat energy utilization engine with the sun as the heat source and the atmosphere as the working medium. Wind power USES natural energy. It's much better than diesel. But if emergency use, or diesel generators. Wind power cannot be considered a backup power source, but it can be used for a long time.
The principle of wind power generation is to use the wind to drive the blades of windmills to rotate, and then increase the speed of rotation through the speed-increasing machine, so as to promote the power generation of generators. According to current windmill technology, about three meters per second of wind speed (the degree of wind) can start generating electricity.
Wind power is becoming a global craze, with no fuel problems and no radiation or air pollution.
Wind power is popular in countries such as Finland and Denmark. China also vigorously advocated in the western region. Small wind power system efficiency is very high, but it is not only composed of a power head, but a small system: have a certain scientific and technological content of wind generator + charger + digital inverter. The wind generator consists of a head, a rotating body, a tail, and a blade. Each part is important. The function of each part is: the blade is used to receive the wind and convert it into electricity through the head. The tail fin keeps the blades facing the incoming wind in order to get the maximum wind energy. The rotating body enables the head to rotate flexibly to realize the function of the tail fin to adjust the direction. The rotor of the machine head is permanent magnet, and the stator winding cuts the magnetic force line to generate electric energy.
Wind turbines for air volume is not stable, so its output is 13 ~ 25 v alternating current change, must obtain the charger rectifier, recharging the battery again, make the wind generator produces electrical energy into chemical energy. Then, the inverter power with protective circuit is used to convert the chemical energy in the battery into 220V ac power supply, so as to ensure stable use.
It is generally believed that the power of wind power is entirely determined by the power of wind turbines, and it is not correct to buy larger ones. Current wind turbines only charge batteries, which store electricity, and the size of the power used is ultimately more closely related to the size of the batteries. The size of power depends more on the amount of wind, not just the power of the head. On the mainland, smaller wind power opportunities are better than bigger ones. Because it is more likely to be driven by a small amount of wind to generate electricity, a small constant wind can provide more energy than a sudden gust. People when there is no wind also can be normal use of wind power, that is to say, a 200 w wind turbines can also be used through the big battery and inverter, 500 w and 1000 w and more power.
Use of wind turbines, is continuously turn wind energy into our family to use standard mains, the degree of saving is obvious, a family of electricity a year the price of only 20 yuan battery fluid. Now than a few years ago the performance of the wind power generator is a great improvement, just in a few outlying areas before use, the wind turbine after another 15 w bulb directly electricity, one bright one dark and often damage the light bulb. Now, due to technological progress, wind power has become a small system with a certain amount of technology and can replace normal municipal power under certain conditions with advanced charger and inverter. The mountain area can use the system to make a street lamp for years without spending money. The highway can be used as a night beacon. Children in mountainous areas can study at night under the sun light. Wind turbines can also be used on the roofs of small high-rise buildings in cities. The family USES the wind generator, not only can prevent power failure, but also can increase the life interest. Wind turbines are becoming a hot spot for people to buy in tourist areas, border areas, schools, troops and even backward mountainous areas. Radio enthusiasts can also enrich themselves by using their own technology to generate wind power for mountain people, keeping people watching TV and lighting in sync with cities.
5. Principle of diesel generator
A diesel engine drives a generator that converts diesel energy into electricity.
In diesel engine cylinder, after air filter to filter the clean air and nozzle jet of high pressure atomized diesel hybrid, under the extrusion of the piston upward, shrinkage, temperature rise rapidly, to achieve the diesel ignition point. Diesel fuel is ignited, the mixed gas burns violently, the volume expands rapidly, pushes the piston down, known as' work '. Each cylinder works in a certain order, and the thrust acting on the piston becomes the force pushing the crankshaft to rotate through the connecting rod, thus driving the crankshaft to rotate.
The brushless synchronous ac generator and diesel engine crankshaft coaxial installation, can use the rotation of the diesel engine to drive the generator rotor, using the 'electromagnetic induction principle, the generator will output induction electromotive force, the closed load circuit will generate an electric current.
The basic operating principle of a generator set is described here. A series of diesel and generator controls, protective devices and circuits are also needed to achieve a usable and stable power output.
Diesel generator set is a kind of independent power generation equipment, which refers to the power machinery that drives the generator to generate electricity with diesel engine as the fuel. The whole set consists of diesel engine, generator, control box, fuel tank, storage battery for starting and control, protective device and emergency cabinet. The whole can be fixed on the foundation, used for positioning, or mounted on the trailer for mobile use. Diesel generator set is a non-continuous power generation equipment. If it runs continuously for more than 12h, its output power will be about 90% lower than the rated power. Despite the power of diesel generator set is low, but because of its small size, flexible, lightweight, supporting complete, convenient for operation and maintenance, so widely used in mining, railway, field construction, road maintenance, as well as factories, companies, hospitals and other departments, as the standby power supply or temporary power supply. At the same time, this kind of small generating set can also be used as a small mobile power station, and become the backup power of many enterprises.
6. Type of generator
Different generators can be made because of different primary energy forms.
Water wheel generator can be made by using water resources and water turbine. Because the reservoir capacity and head drop difference are different, the water wheel generator with different capacity and speed can be made.
Steam turbines can be made from coal, petroleum and other resources in cooperation with boilers and steam turbines. Most of these generators are high-speed motors (3000rpm).
In addition, there are wind, atomic energy, geothermal, tidal energy and other types of generators.
In addition, because the working principle of the generator is different, it is divided into dc generator, asynchronous generator and synchronous generator. The large generators in wide use are synchronous generators.
7. Precautions for use of roller dc generator
1. The purchase and use of generators shall meet the technical requirements on the nameplate, such as voltage, power and rated output current. For example, it is used for harvest-27 tractor, dongfanghong-40 tractor and so on. It is commonly used for 150-watt generator and its rated output current is 13 amps. Used in 220-watt generator for tienu - 55 tractor, rated output current is 18 amps.
2, generator is usually used for tractor is shunt type, that is to say, the generator excitation winding is parallel, so the total want to have one end through the chassis is parallel with the armature coil, so always have one end through the casing and the armature coil. If the excitation coil is connected to the armature coil through the casing of the generator, it is called the internal lapping iron generator (fig.5-1). If the excitation coil passes through the regulator lapping outside the generator (FIG. 5-2), it is called the "outer lapping generator". The dc generators used by domestic tractors are all built - in lattes. When wiring, it is necessary to connect the lead wire of the exciting coil to the carbon brush frame of the lapping iron. The exciting coil will not pass through the current, and the generator will not generate electricity. In addition, some imported tractors use the external latting-iron generator. If it is changed to the internal latting-iron generator, it only needs to replace the spool connection of the exciting-coil of the generator.
3. The two terminals on the generator case are generally marked with the words "armature" and "magnetic field". If the text is not clearly marked, it can be identified by the following methods.
1) armature junction: thicker diameter; It's attached to an insulated brush holder.
2) magnetic field terminal: smaller diameter; The magnetic field coil has one end on it.
4, the generator is driven by the engine on the tractor, so the direction of rotation is certain, if at the time of repair will generator reverse rotation is not power, this is because the positive transfer under the action of the armature coil in the magnetic field induction of electricity flows through the regulator and excitation coil are interlinked. The magnetic field direction of the excited coil is the same as that of the iron core after it is energized. When the current direction is opposite to that of the forward one, the magnetic field of the excited coil is opposite to that of the iron core after it is energized. The magnetic field becomes weaker and weaker, which makes the generator unable to generate electricity.
5. When the generator armature is not short-circuited by load, the generator box will not burn out. This is because the dc generators used on the tractor are parallel - excited. When the generator operates at rated power, the current generated by armature winding is mostly transmitted to the external circuit, while a small part of the input excitation winding generates magnetic field. When the armature terminal and chassis short circuit, the generator current increases rapidly, at this time to produce a lot of pressure drop in the motor armature reaction and strong, make the output voltage has fallen sharply, exciting current is rapidly disappearing, the generator voltage is close to zero. Therefore, the generator will not be damaged when the armature junction post and the casing are short-circuited.
6. During use, sudden changes in the polarity of the generator are sometimes found (i.e., changes in the direction of the current emitted). This is because the strong armature reaction inside the motor changes the direction of iron core residual magnetism when the output current increases suddenly. In this case, it must be changed to make the charging circuit work normally. The method of change is: connect the positive electrode of the battery to the machine case, and contact the negative electrode with the magnetic field terminal for 2-3 seconds, which can change the residual magnetic direction of the magnetic pole iron core. (in a positive lap system). Sometimes, in the maintenance battery is used for power supply, jump spark method to check the failure in the excitation coil, if you don't pay attention to the polarity connection, the battery cathode as iron pole, changed the direction of current excitation coil, so that the core remanence direction changes. As the remanent magnetic direction changes, the generator voltage polarity also changes. This should be noted.
7. In general, the mica plates between the copper plates of rectifier of dc generator are lower than those of copper plates. This is because the copper pieces wear faster than mica pieces, and when used for a period of time mica pieces will be higher than the rectifier copper pieces, causing the carbon brush to be suspended. This creates a strong spark between the commutator and the brush. In order to avoid this phenomenon, the mica was cut by saw blade after the fairing machine was finished. But some dc generators such as ZF - 28 and ZF - 33, commutator copper using artificial mica, it similar to copper wear speed, so the factory does not cut mica sheet is low, maintenance the generator does not cut low.
8. Synchronous generator
Synchronous motor for generator operation. It is one of the most commonly used ac generators. In the modern power industry, it is widely used for hydroelectric, thermal, nuclear and diesel power generation. Because synchronous generators generally use dc excitation, when the single machine is running independently, the voltage of the generator can be conveniently adjusted by adjusting the excitation current. If it is connected to the power grid, because the voltage is determined by the power grid and cannot be changed, the power factor and reactive power of the motor are adjusted as a result of adjusting the excitation current.
The stator and rotor structure of synchronous generators are the same as that of synchronous machines, generally in the form of three phases, and only in some small synchronous generators the armature winding is single phase.
The working characteristics of synchronous generators are mainly no-load and load operating characteristics. These characteristics are an important basis for users to choose generators.
When no-load characteristic generator is not connected with load, armature current is zero, which is called no-load operation. At this point, the three-phase winding of the motor stator only has the no-load electromotive force E0 (three-phase symmetry) induced by the excitation current If, and its size increases with the increase of If. However, due to the saturation of the magnetic core of the motor, the two are not proportional. The curve that reflects the relationship between no-load electromotive force E0 and excitation current If is called the no-load characteristic of synchronous generator.
When the armature is connected with a symmetrical load, the three-phase current in the armature winding will generate another rotating magnetic field, which is called armature reaction magnetic field. The speed is exactly the same as that of the rotor, and both rotate synchronously.
The armature reaction magnetic field and rotor excitation magnetic field of synchronous generator can be approximately assumed to be distributed according to sinusoidal rule. The spatial phase difference between them depends on the time phase difference between the no-load emf E0 and armature current I. Armature reaction magnetic field is also related to load conditions. When the load of the generator is inductive, the armature reaction magnetic field plays the role of demagnetization, which will lead to the voltage reduction of the generator. When the load is capacitive, the armature reaction magnetic field ACTS as a magnet to increase the output voltage of the generator.
Load operating characteristics mainly refer to external characteristics and adjustment characteristics. The external characteristic is the relationship between the generator terminal voltage U and the load current I when the speed is rated, the excitation current and the load power factor are constant, as shown in figure 2. The adjustment characteristic is the relationship between the excitation current If and the load current I when the speed and terminal voltage are rated and the load power factor is constant, as shown in figure 3. Resistance, capacitance, and inductive loads are also shown in figure 2. Because armature reaction magnetic field influence is different, the curve of all three is different also. In the external characteristics, the degree of variation of voltage from no-load to rated load is called voltage change rate one-time, and the common percentage is denoted as follows
The voltage change rate of synchronous generator is about 20 ~ 40%. General industrial and household loads require that the voltage remain essentially constant. Therefore, with the increase of load current, the excitation current must be adjusted accordingly. Figure 3 shows the adjustment characteristics under three different nature loads. Although the change trend of adjustment characteristics is exactly opposite to that of external characteristics, for inductive and pure resistive loads, it goes up, while for capacitive loads, it generally goes down.
The structure and classification synchronous generators are divided into high speed and low (medium) speed according to their speed. The former is mainly used in thermal power plants and nuclear power plants. The latter is usually associated with low - speed turbines or diesel engines. In structure, high - speed synchronous generators are multi-purpose crypto-pole rotors and low (medium) speed synchronous generators are multi-purpose salient pole rotors.
Because most of the generator and high-speed synchronous generator prime mover gang, coal-fired power plants are using high speed turbine as prime mover, so the steam turbine generator usually use high speed 2 pole machine, turn it ran 3000 revolutions per minute (in the grid frequency is 60 hz, 3600 revolutions per minute). Nuclear power plants use four-pole motors with a speed of 1500 RPM (1800 RPM when the power grid frequency is 60 hz). In order to meet the requirements of high speed and high power, the high speed synchronous generator adopts the stepless rotor and the special cooling system.
Horizontal and concealed pole type rotor: it is cylindrical in appearance, and the dc excitation winding is placed in the grooves on the cylinder surface. Because of the great centrifugal force when rotating at high speed, high mechanical strength of rotor is required. The crypto-type rotor is usually forged from high strength alloy steel, and the groove is usually open for installing the excitation winding. About 1/3 of the slots are not grooved in each polar distance, forming large teeth. The rest of the teeth are narrow and are called small teeth. The center of the big tooth is the center of the rotor magnetic pole. Sometimes the big teeth also have some smaller air vents, but no windings embedded; Sometimes a narrow and shallow slot is also milling at the bottom of the slot as a vent. There are metal guard rings and center rings on the axial ends of the rotor body. The ring-guard is a thick-walled cylinder made of high strength alloy to protect the end of the field winding from being thrown out by great centrifugal force. The central ring is used to prevent axial movement of the end of the winding and to support the guard ring. In addition, a collector ring and a brush are installed on the motor shaft in order to circulate the excitation electricity into the excitation winding.
(2) the cooling system that the energy losses in the motor and the motor is proportional to the size of its scale and the scale of the motor which affects three proportional to, and motor cooling level just below the scale of which affects a quadratic. Thus, when the motor size (restricted by material, increase the motor capacity will have to increase its size), the motor need to send out quantity of heat per unit surface increases, the rise of temperature of the motor will be increased. In high speed turbogenerator, centrifugal force will cause great tangential stress on rotor surface and rotor center hole surface. Therefore, within the allowable stress limit of the forging material, the rotor body diameter of the 2-pole turbogenerator should not exceed 1,250 mm. Large turbogenerators can only increase the capacity of a single engine by increasing the length of the rotor body (i.e., slender rotor) and increasing the electromagnetic load. Currently, the length of the rotor can reach 8 meters, which is close to the limit. To continue to increase the capacity of a single machine, can only increase the electromagnetic load of the motor. This makes the heat and cooling problems of large turbogenerators particularly acute. Therefore, a variety of cooling systems have been developed. For turbine generators under 50000 kw, the closed air cooling system is adopted, and the fan in the motor is used to blow the heating parts to cool down. Hydrogen cooling is widely used for generators with a capacity of 50 to 600 megawatts. Hydrogen purity (99%) of the cooling performance is better than air, use it to replace the air is not only the cooling effect is good, and can make the ventilation greatly reduce friction loss of motor, which can significantly improve the efficiency of the generator. However, the use of hydrogen cooling must have anti-explosion and leak-proof measures, which makes the motor structure more complex and increases the consumption and cost of electrode materials. In addition, liquid media can be used for cooling. For example, water has a relative cooling capacity of 50 times that of air, which takes away the same heat and requires much less water flow than air. Therefore, a part of hollow wire is used in the coil, and the wire is cooled by water, which can greatly reduce the temperature rise of the motor, delay the aging of insulation and increase the life of the motor. In 1956, the first 12,000 - kilowatt stator coil water - cooled turbine generator was created in Britain. By zhejiang university, China in 1958, Shanghai electric first developed into the first set, rotor winding are used in cold water in cold 12000 kw dual water turbine generator, which laid a foundation for the cooling way. Water cooling technology is also widely used in large capacity electric machines in some countries in the world, and several hundred thousand to one million kilowatts of giant generators have been produced. In addition to water, liquid cooling medium can also use transformer oil, the relative thermal capacity about 40% of the water, insulation performance is good, the generator can be rated voltage up to tens of thousands of volts, thus saving the investment of step-up transformer. In recent years, the evaporative cooling technology using freon as cooling medium has been studied. Freon is well insulated and easily vaporized, and its latent heat of vaporization is used to cool the motor.
Low-speed synchronous generators are mostly driven by low-speed turbines or diesel engines. The number of magnetic poles varies from 4 to 60 or more. The corresponding speed is 1500 ~ 100 RPM and below. Because of the low rotating speed, the salient pole rotor with low material and manufacturing technology requirements is generally adopted.
Each magnetic pole of a salient pole rotor is usually made of steel plate 1 ~ 2 mm thick, riveted into a whole, and the magnetic pole is covered with an excitation winding (FIG. 4). The excitation winding is usually made of flat copper wire. The magnetic pole boots are often equipped with damping winding. It is a short circuit formed by bare copper strips in the pole shoe damping groove and copper rings welded at both ends. The magnetic poles are fixed to the rotor yoke, which is cast from cast steel. Salient pole rotors can be divided into horizontal and vertical rotors. Most synchronous motors, cameras and generators driven by internal combustion engines or impact turbines are horizontal. Low - speed and high - capacity water - wheel generators are vertical structures.
The rotor of horizontal synchronous motor is mainly composed of main magnetic pole, magnetic yoke, excitation winding, collector ring and rotating shaft. The stator structure is similar to the asynchronous motor. The vertical structure must bear the gravity and water downward pressure of the rotating part of the unit with thrust bearing. Large hydro-generator, this force can be up to four, fifty million cattle (or the equivalent of about 4, five thousand tons of gravity of the object), so this kind of complex structure of thrust bearing, the processing technology and installation requirements are high. According to the position of thrust bearing, vertical hydro-generator can be divided into two types: suspension type and umbrella type. The suspended thrust bearing is placed on the upper or middle part of the upper frame, and runs stably on the machine with high speed, small ratio of rotor diameter to iron core length. The thrust bearing of the umbrella is placed on the lower frame of the rotor or the top cover of the turbine. The load-bearing frame is a small-sized lower frame, which can save a lot of steel and reduce the height of generators and factories calculated from the base of the frame.
Most synchronous generators operate in parallel and are connected to the grid. The frequency, voltage and phase of the synchronous generators operating in parallel must be consistent. Otherwise, at the moment of parallel closing, the internal circulation will be generated between the generators, causing disturbance and even damaging the generators in serious cases. However, before the two generators are put into operation in parallel, their frequency and voltage are generally not the same as the magnitude and phase. In order for synchronous generators to operate in parallel, there must be a synchronous parallel process. Synchronous juxtaposition can be divided into quasi-synchronous and self-synchronous methods. After the synchronous generator is put into parallel operation, the load distribution of each machine depends on the speed characteristic of the generator. By adjusting the governor of the prime motor and changing the speed characteristic of the generator set, the load distribution of each generator can be changed and the power of each generator can be controlled. By adjusting the excitation current of each generator, the reactive power distribution of each generator can be changed and the voltage of the power grid can be adjusted.
Quasi-synchronizing parallel will have to add generator excitation of the stay was put into operation by adjusting the rotational speed of the prime mover and change the generator excitation, make its and operation of the generator frequency difference is not more than 0.1 ~ 0.5%. In both mechanical and electrical voltage phase difference is not more than 10 ° switching moment of parallel, both can automatically pull in synchronous operation. Quasi-synchronous parallel operation can be done manually or by automatic device.
Self synchronous parallel put stay in parallel of the generator speed to close to the power grid of the synchronous speed, under the condition of without excitation is closing in parallel, and then join the excitation, relying on generators and power grid of circulation and corresponding created between the electromagnetic torque of the generator quickly pull in sync. Using the synchronous coordinate, due to reduced regulated voltage and generator speed, select the time needed for the closing moments, so in the process of fast, particularly suitable for power system accident cases of emergency. However, the current impact of this method is relatively large at the moment of side-by-side closing, which will cause the power grid voltage to decrease in a short time, and the end of the motor winding will bear large electromagnetic force.

The development prospect of generators
The country created serious shortage of water and electricity supply for many reasons, the electricity is limited by a certain degree, and in recent years, it is China's industrial economy period of rapid development, many enterprises have foot horsepower into mass production. Followed by the previous two years many manufacturers to buy generator for emergency, when buy, not the long term and changed the purchased small generators already can not adapt to the new requirements, in this case, update the generator also accounted for a large part of; Moreover, the annual export of electromechanical products is increasing, and the market space of pumps and generators will be very large in recent years. It is under the promotion of three factors that the market of pumps and generators in wujincheng ushered in a new development opportunity.