alternator

[f ā diàn j ī]

Mechanical equipment that converts other forms of energy into electrical energy

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Generators mechanical energy convert to electric energy Of mechanical equipment , which is Water turbine 、 Steam turbine 、 Diesel engine Or other power machinery drive , the energy generated by water flow, air flow, fuel combustion or nuclear fission is converted into mechanical energy and transmitted to the generator, and then converted into electrical energy by the generator.

Generators are widely used in industrial and agricultural production, national defense, science and technology and daily life. There are many forms of generators, but their working principles are based on electromagnetic induction Law and the law of electromagnetic force. Therefore, the general principle of its structure is to use appropriate magnetic conductivity and conductive materials to form a magnetic circuit and circuit for mutual electromagnetic induction to generate electromagnetic power and achieve the purpose of energy conversion.

Chinese name: alternator
Foreign name: Generators
Category: equipment

component: Stator, rotor, end cover and Bearing
Discipline: alternator
Classification: DC generator and alternator

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Main structure

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alternator^[9]

The generator is usually composed of stator, rotor, end cover and Bearing And other components.

The stator is composed of stator core, wire wrapped winding, frame and other structural parts that fix these parts.

The rotor is composed of rotor core (or magnetic pole, magnetic choke) winding, retaining ring, center ring, slip ring, fan, shaft and other parts.

The stator and rotor of the generator are connected and assembled by the bearing and end cover, so that the rotor can rotate in the stator and do the movement of cutting magnetic lines of force, thus generating induced potential, which is led out through the terminal and connected to the circuit, and then generating current.^[1]

Main categories

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alternator (8 sheets)

The classification of generators includes:

Generator: DC generator and AC generator;

alternator Score: Synchronous generator and Asynchronous generator (rarely used);

Alternators can also be divided into single-phase generators and three-phase generators.

There are many kinds of generators. In principle, it can be divided into synchronous generator, asynchronous generator, single-phase generator and three-phase generator. It can be divided into turbogenerator 、 Hydro generator 、 Diesel generator 、 Gasoline generator Etc. In terms of energy, it can be divided into thermal power generator, hydraulic generator, etc.

Main characteristics

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Operating characteristics:

The main characteristics of synchronous generator performance are no-load characteristics and load operation characteristics. These characteristics are important basis for users to select generators.

No load characteristics:

When the generator is not connected to the load, Armature current Zero is called no-load operation. At this time, the three-phase winding of the motor stator has only excitation current I The no-load electromotive force E0 (three-phase symmetry) induced by f varies with I F increases. However, the motor magnetic circuit iron core is saturated, so the two are not proportional. Reflect no-load electromotive force E 0 and excitation current I The curve of f relation is called the no-load characteristic of synchronous generator.

Armature reaction:

When the generator is connected to a symmetrical load three-phase current Another Rotating magnetic field , called armature reaction magnetic field. Its speed is just equal to the speed of the rotor, and both rotate synchronously.

The armature reaction magnetic field and the rotor excitation magnetic field of synchronous generators can be approximately considered to be distributed in a sinusoidal manner. The space between them phase difference Depends on no-load electromotive force E 0 and armature current I Time phase difference between. The armature reaction magnetic field is also related to the load. 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 plays a role in assisting magnetism, which will increase the output voltage of the generator.

Load operation characteristics:

It mainly refers to external characteristics and adjustment characteristics. The external characteristic is the voltage at the generator terminal when the speed is rated, the excitation current and the load power factor are constant U Relation with load current I. The regulating 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.

The voltage change rate of synchronous generator is about 20-40%. General industrial and household loads require the voltage to remain basically unchanged. Therefore, with the increase of load current, the excitation current must be adjusted accordingly. Although the change trend of adjustment characteristics is opposite to that of external characteristics Pure resistance nature load It is rising, while under capacitive load, it is generally falling.^[4]

History of invention

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In 1831, French scientist Faraday invented the disc generator, which was the first generator in human history;^[10]^{[11 ]}

In 1832, the French Bixie invented the hand-operated type DC generator The principle is to rotate the permanent magnet flux Change occurs in the coil Induced electromotive force And output the electromotive force in the form of DC voltage;

In 1866, Siemens of Germany invented the self-excited DC generator;

In 1870, Belgium Gram made the ring armature and invented the ring armature generator. This kind of generator uses water power to turn Generator rotor After repeated improvement, 3.2KW output power was obtained in 1875;

In 1882, Gordon of the United States produced a two-phase giant generator with output power of 447KW, height of 3m and weight of 22t;

In 1896, Tesla's two-phase alternator was located in Nyala power plant Start labor operation, 3750KW, 5000V AC power is delivered to Buffalo City.^[2]

working principle

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Diesel generator

The diesel engine drives the generator and converts the energy of diesel into electric energy.

In the cylinder of the diesel engine, the clean air filtered by the air filter is fully mixed with the high-pressure atomized diesel fuel injected from the fuel injection nozzle. Under the upward extrusion of the piston, the volume shrinks and the temperature rises rapidly, reaching the ignition point of the diesel fuel. When the diesel is ignited, the mixed gas burns violently, and the volume expands rapidly, pushing the piston downward, which is called "work".

Gasoline generator

The gasoline engine drives the generator to run and converts the energy of gasoline into electric energy.

In the cylinder of the gasoline engine, the mixed gas burns violently, and the volume expands rapidly, pushing the piston downward to do work.

Whether it is a diesel generator or a gasoline generator, each cylinder works in a certain order. The thrust acting on the piston becomes the force that drives the crankshaft to rotate through the connecting rod, thus driving the crankshaft to rotate. When the brushless synchronous alternator is installed coaxially with the crankshaft of the power machine, the rotation of the power machine can be used to drive the rotor of the generator. Using the "electromagnetic induction" principle, the generator will output the induced electromotive force, and the current can be generated through the closed load circuit.^[3]

Relevant regulations

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Installation procedures

Preparation before unit startup:

1. Check the lubricating oil level, coolant level and fuel quantity;

2. Check the oil supply, lubrication cooling Whether all pipelines and joints of the system have oil and water leakage;

3. Check whether the electrical circuit has potential leakage hazards such as skin breaking, whether the electrical circuit of the grounding wire is loose, and whether the connection between the unit and the foundation is firm;

4. If the ambient temperature is lower than zero, a certain proportion of antifreeze must be added to the radiator;

five Diesel generator set For the first start or restart after shutdown for a long time, exhaust the air in the fuel system with a hand pump first.

Start:

1. After closing the fuse in the control box, press the start button, and press the button for 3~5s. If the start is unsuccessful, wait for about 20s to start again. If the startup is unsuccessful for many times, the startup operation shall be stopped, and the battery voltage or oil circuit and other fault factors shall be eliminated before starting again;

2. Observe the oil pressure when starting. If the oil pressure does not show or is very low, stop immediately for inspection.

function:

1. After the unit starts, check the parameters of the control box module; Oil pressure, water temperature, voltage, frequency, etc;

2. In general, the speed of the unit directly reaches the rated speed after starting; For units with idle requirements, the idle time is generally 3~5min, and the idle time is not easy to be too long, otherwise the generator related components may be burned out;

3. Check the leakage of oil, water and electrical equipment of the unit;

4. Check the fastening of each connection of the unit for looseness and severe vibration;

5. Observe whether various protection and monitoring devices of the unit are normal;

6. When the speed reaches the rated speed, start No load operation Switch on power supply after all parameters of are stable;

7. Check whether the parameters of the control panel are within the allowable range, and check the vibration of the unit again for three leakage and other faults;

8. Overload is strictly prohibited during unit operation.

Normal shutdown:

The switch must be opened before shutdown. Generally, it needs to run for 3~5min after unloading.

Emergency stop:

1. In case of abnormal operation of the generator set, it must be stopped immediately;

2. In case of emergency shutdown, press the emergency stop button or quickly push the fuel injection pump shutdown control handle to the parking position.

Maintenance items:

1. The replacement time of diesel engine filter element is 300H; Air filter element The replacement time is every 400H; Oil filter The first replacement time is 50H, and then 250H.

2. The first oil change time is 50H, and the normal oil change time thereafter is every 250H.

Operating Procedures

1. Before starting, check whether the fuel tank is full of oil, and there is no oil leakage at each oil pipe and joint; Whether the cooling system water is sufficient, clean and free of leakage, Fan belt Whether the tightness is proper. Check that the transmission part of the internal combustion engine and the generator should be reliably connected, the wire of the output line should be well insulated, and all instruments should be complete and effective.

2. After starting, it shall run at low speed for 3~5 minutes, and the operation can be started only after the temperature and oil pressure wheel are normal. The generator shall be free of abnormal noise during speed increase, and the brush on the slip ring and commutator shall be in good contact, without jumping and sparking. When the operation is stable and the frequency and voltage reach the rated value, the power can be supplied externally.

3. In case of abnormal noise, odor, sharp rise of water temperature and sharp drop of oil pressure during operation, stop the machine immediately for inspection and troubleshooting.

4. The power factor of generator shall not exceed 0.95 of late phase (lagging). The variation range of frequency value shall not exceed 0.5HZ.

5. Before shutdown, cut off the main switches of each power supply shunt to gradually reduce the load, then cut off the main switch of the generator power supply, return the excitation rheostat to the position of the maximum resistance, reduce the voltage to the minimum, cut off the excitation switch and neutral point grounding switch, and finally stop the operation of the internal gas turbine.^[3]

matters needing attention

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Proper use and maintenance of the generator set can extend the service life of the generator set:

Preparations before starting:

1. The operator of the machine room shall observe Safe Operation Procedures , wear work clothes and insulating shoes, and the crew should have a clear division of labor;

2. Check whether the guardrail covers of flywheel and generator are intact;

3. Check all gearboxes, clutches, governors, oil levels, fasteners, etc., and confirm that they are in good condition. Only when the oil and water temperature is not lower than 20 degrees can they be started;

4. Set the pipeline gates of each system at the "working" position;

5. Check and fasten the connecting bolts of the transmission mechanism;

6. Check whether the clutch handle pressure is normal and whether the overspeed safety device is positioned;

7. Check whether the pressure of the gas cylinder is normal and whether the overspeed safety device is positioned;

8. Open the blow down valve of the air pump;

9. Check whether the circulating water pump, oil pump and fuel pump are normal;

10. Place the excitation resistance at the maximum resistance position and disconnect the power transmission switch.

Startup and operation:

1. For units that have been shut down for more than 24h, the test valve must be opened first and the engine oil pump must be started. For units that have been shut down for more than 7 days, the insulation resistance of exciter and operating circuit shall be measured, which must meet the requirements;

2. Start the fuel pump, discharge the air in the pipeline, and observe whether the voltage is within the specified range. If it is normal, it can be started formally;

3. Check whether the voltage of starting power supply meets the requirements. If the voltage is normal, press the start button, etc Diesel engine Release after normal operation;

4. When the diesel engine is running, observe the indicated value of the oil pressure gauge. When it rises above the specified value, stop the oil pump, close the scavenging pump drain valve, and thread the front clutch screws;

5. When the generator is started, the generator and all electrical The equipment has been charged, and the human body shall not touch the charged parts;

6. After the generator is started, the speed of the diesel engine shall be gradually increased, and the inspection before power transmission shall be carried out;

7. Gradually adjust the speed of the diesel engine, but pay attention to observe whether the generator operates normally during the adjustment. Under normal conditions, the electric brush on the collector ring and commutator shall be free of bounce, spark and abnormal sound;

8. Adjust the output voltage and frequency of the generator. The voltage value should be stable and reach 380v+- 10v, and the frequency should reach 50Hz+-0.5Hz.^[2]

Common types

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Wind power generator

As a new type of power generation system with low price, reliable operation and no greenhouse gas emissions, the installed capacity of wind power generation system is increasingly applied worldwide with an annual growth rate of more than 30%, and has formed a global industry with an annual output value of more than 5 billion dollars. However, small wind power generation systems for independent power supply in remote areas still need to overcome many technical difficulties to be widely used. With China's increasing investment in "agriculture, rural areas and farmers", and the sustained and rapid economic development, farmers, herdsmen and fishermen are eager to improve their living environment, improve their quality of life, and solve the urgent requirements of living electricity. Using small wind power generation systems to provide power for local loads can not only reduce one-time huge investment, but also eliminate greenhouse gas emissions from thermal power generation systems, Improving the environment and energy structure in rural areas is beneficial to sustainable development.

Wind power generator It converts wind energy into mechanical work and drives generators to generate electricity. In a broad sense, it is a heat energy utilization engine with the sun as the heat source and the atmosphere as the working medium. Wind power uses natural energy. It is much better than diesel power generation. But if it is used for emergency, it is not as good as diesel generator. Wind power generation can not be regarded as standby power supply, but it can be used for a long time.

Operation management:

Wind turbine The control system of is controlled by an industrial microprocessor, which is generally run by multiple CPUs in parallel. Its own anti-interference ability is strong, and it can be connected to the computer through communication lines for remote control, which greatly reduces the workload of operation. Therefore, the operation of the fan is to conduct remote troubleshooting, statistical analysis of operation data and analysis of fault causes.

Remote troubleshooting:

Remote reset control and automatic reset control can be performed for most faults of the fan. The operation of the fan is closely related to the quality of the power grid. In order to carry out two-way protection, the fan is equipped with multiple protection faults, such as high and low grid voltage, high and low grid frequency, etc. These faults can be reset automatically. Due to the uncontrollability of wind energy, the limit value of wind speed can also be reset automatically. There are also temperature limits that can be automatically reset, such as high generator temperature, high and low gearbox temperature, and low ambient temperature. The overload fault of the fan can also be reset automatically.

In addition to the failure of automatic reset, other remote reset control failures are caused by the following reasons:

1. Fan controller gives false alarm;

2. Misoperation of each detection sensor;

3. The controller believes that the fan operation is unreliable.

Statistical analysis of operation data:

It is an important part of wind farm management to carry out detailed statistical analysis on the situation of wind farm equipment in operation. Through statistical analysis of operation data, the assessment and quantification of operation and maintenance work can be carried out, as well as the design of wind farms and the assessment of wind resources, Equipment Selection Provide effective theoretical basis.

The monthly power generation statistical report is one of the important contents of the operation work, and its authenticity and reliability are directly linked to the economic benefits. Its main contents include: monthly power generation of wind turbine, field power consumption, normal working time of wind turbine equipment, failure time, standard utilization hours, power grid outage, failure time, etc.

The statistics and analysis of the power curve data of the wind turbine can provide practical basis for improving the output of the wind turbine and improving the utilization rate of wind energy. Through the statistics and analysis of the wind condition data, the output law of each type of fan changes with the seasons can be mastered, and a reasonable regular maintenance schedule can be formulated to reduce the waste of wind resources.

Small wind turbine ：

Wind turbine is a machine that converts wind energy into electric energy. From the perspective of energy conversion, wind turbine is composed of two parts: one is wind turbine, whose function is to convert wind energy into mechanical energy; The second is the generator, whose function is to convert mechanical energy into electrical energy.

The structure of small wind power generation system is generally composed of wind turbine, generator, tail rudder and electrical control part. Conventional small wind turbine is mostly composed of induction generator or permanent magnet synchronous generator plus AC/DC converter, battery and inverter. Driven by the wind, the wind wheel rotates, transforming the aerodynamic energy into mechanical energy (speed+torque). The hub of the wind wheel is fixed on the generator shaft, and the rotation of the wind wheel drives the rotation of the generator shaft, which drives the permanent magnet three-phase generator to send out Three phase alternating current 。 The current and voltage generated by the generator change with the constant change of wind speed. The generated electricity is rectified by the controller and changed from AC to DC with a certain voltage, which charges the battery. The DC output from the storage battery is converted into 220V AC through the inverter to supply household appliances for users.

According to different applications, wind turbines can be divided into grid connected and off grid wind turbines. Off grid wind turbine, also called independent operation wind turbine, is a wind turbine applied in areas without power grid, and its power is generally small. Independent operation wind turbine generally needs to form an independent operation wind turbine power generation system together with batteries and other control devices. This independent operation system can be several kilowatts or even dozens of kilowatts to solve the power supply system of a village, or dozens to hundreds of watts of small wind turbines to solve the power supply of a household.

Due to the randomness of wind energy, the frequency and voltage of the electric energy generated by the generator are unstable, and the battery can only store DC electric energy, which cannot directly supply power to AC loads. Therefore, in order to provide stable and high-quality electric energy for the load and meet the demand of AC load, it is necessary to add a power conversion device between the generator and the load. This power conversion device is mainly composed of rectifier, inverter, controller, battery, etc.

As a part of rural energy, the promotion and application of small wind power generation system will play a positive role in improving the power consumption structure, especially in the production and living energy consumption in remote mountainous areas, and promoting the development of ecological environment construction, so it has broad market prospects. Wind energy has randomness and uncertainty, and wind power generation system is a complex system. Simplifying the structure of small wind power generation system, reducing costs, improving reliability and realizing optimal operation of the system are of great significance for the promotion of small wind power generation system.

WTG maintenance:

Wind turbine is a comprehensive product integrating electrical, mechanical, aerodynamics and other disciplines, and all parts are closely linked. The quality of wind turbine maintenance directly affects the amount of power generation and economic benefits; The performance of the wind turbine itself should also be maintained through maintenance. Timely and effective maintenance can find hidden trouble, reduce the occurrence of faults and improve the efficiency of the wind turbine.

Fan maintenance can be divided into regular maintenance and routine troubleshooting maintenance.

1. Regular maintenance of fan

Regular maintenance can keep the equipment in the best condition and extend the service life of the fan. The main contents of regular overhaul and maintenance include: bolt torque inspection between fan connectors (including electrical connection), lubrication between transmission parts and various function tests.

When the fan is in normal operation, the bolts of all connecting parts are operated in the resultant force of various vibrations for a long time, which is very easy to loosen. In order not to cause uneven shearing of local bolts after loosening, the bolt torque must be checked regularly. When the ambient temperature is lower than - 5 ℃, the torque shall be reduced to 80% of the rated torque for fastening, and recheck shall be conducted after the temperature is higher than - 5 ℃. Generally, the bolt fastening inspection is arranged in the windless or low wind summer to avoid the high output season of the fan.

The lubrication system of fan mainly includes thin oil lubrication (or mineral oil lubrication) and dry oil lubrication (or grease lubrication). The gear box of fan and yaw reduction gear box are lubricated by thin oil, and the maintenance method is supplement and sampling test. If the test results show that the lubricating oil can no longer be used, replace it. Dry oil lubrication parts include generator bearing, yaw bearing, yaw gear, etc. These components are easy to deteriorate due to high operating temperature, resulting in bearing wear. During regular maintenance, they must be supplemented every time. In addition, the additional amount of generator bearing must be added according to the required quantity, not too much, to prevent too much from squeezing into the motor winding, which will burn the motor.

The function test of regular maintenance mainly includes over speed test, emergency stop test, fixed value test of various components of hydraulic system, vibration switch test and torsion cable switch test. Some routine tests can also be carried out on the limit setting of the controller.

In addition to the above three items, regular maintenance should also check the hydraulic oil level, whether each sensor is damaged, whether the sensor power supply works reliably, and the wear of the brake pad and disc.

2. Daily troubleshooting and maintenance

During the operation of the fan, some faults may occur and must be handled on site.

First, carefully observe whether the safety platform and ladder in the fan are firm, whether the connecting bolts are loose, whether there is paste smell in the control cabinet, whether the cable is displaced, whether the clamping plate is loose, whether the pull ring of the torsion cable sensor is worn and broken, whether the lubrication of the yaw gear is dry and deteriorated, whether the yaw gear box, hydraulic oil and gear box oil level are normal, and whether the gauge pressure of the hydraulic station is normal, Whether there is wear between rotating parts, whether there is leakage at each oil pipe joint, whether the indication of gear oil and hydraulic oil filter is in normal position, etc.

The second is to listen to whether there is a discharge sound in the control cabinet. If there is a sound, it may be that there is a loose terminal or poor contact. You must carefully check whether the sound is normal when listening to yaw, whether there is a sound of dry grinding, whether there is an abnormal sound in the generator bearing, whether there is an abnormal sound in the gearbox, whether there is an abnormal sound between the brake disc and the brake pad, and whether the wind cutting sound of the blade is normal.

Third, clean up your own work site and wipe all components and pipe joints of the hydraulic station to facilitate future observation of whether there is leakage.^[5]

Hydro generator

Hydro generators are power machines that convert the kinetic energy and gravitational potential energy of water into mechanical work (such as the Three Gorges in China). Nuclear power generation is the best in power generation, but it is relatively polluting. Therefore, coal is widely used for power generation in China. China is short of coal resources, and coal prices have been rising, which is the main reason why there is a power shortage.

Synchronous generator

Generator operated Synchronous motor 。 It is one of the most commonly used alternators. It is widely used in modern power industry Hydropower 、 thermal power 、 Nuclear power generation And diesel power generation. Since the synchronous generator generally adopts DC excitation, when it operates independently, the voltage of the generator can be easily adjusted by adjusting the excitation current. If it is connected to the power grid for operation, the voltage is determined by the power grid and cannot be changed. At this time, the result of adjusting the excitation current is to adjust the power factor and Reactive power 。

The structure of stator and rotor of synchronous generator is the same as that of synchronous generator, which generally adopts three-phase form, only in some small synchronous generators Armature winding Single phase is adopted.

High speed synchronous generator:

Since most generators are coaxial linked with prime movers, thermal power plants use high-speed steam turbines as prime movers, so steam turbine generators usually use high speed 2-pole motors with a speed of 3000 rpm (3600 rpm when the grid frequency is 60 Hz). Four pole motors are commonly used in nuclear power plants, with a speed of 1500 rpm (1800 rpm when the grid frequency is 60 Hz). In order to meet the requirements of high speed and high power, the structure of high-speed synchronous generator is to adopt implicit pole rotor and set special cooling system.

Implicit pole rotor: cylindrical in appearance, grooved on the cylindrical surface to place DC Excitation winding And fastened with metal slot wedges, so that the motor has a uniform air gap. Due to the huge centrifugal force during high-speed rotation, the rotor is required to have high mechanical strength. The non salient pole rotor is generally forged into a whole piece of high-strength alloy steel, and the slot shape is generally open for the installation of excitation winding. About 1/3 of each pole distance is not grooved, forming big teeth; The rest of the teeth are narrower, called small teeth. The center of the big tooth is the center of the rotor pole. Sometimes the big tooth also opens some smaller ventilation slots, but the windings are not embedded; Sometimes, narrow and shallow small grooves are milled at the bottom of the wire slot as ventilation grooves. A metal retaining ring and a central ring are also installed at the axial ends of the rotor body of the non salient pole rotor. The retaining ring is composed of High strength alloy The thick walled cylinder is made to protect the end of the excitation winding from being thrown out by the huge centrifugal force; The central ring is used to prevent the axial movement of the winding end and support the retaining ring. In addition, in order to connect the excitation current to the excitation winding, the motor shaft is also equipped with a collecting ring and brush 。

Cooling system: since the energy loss in the motor is proportional to the motor volume, its magnitude is proportional to the third power of the motor linearity, while the magnitude of the motor cooling surface is only the second power of the motor linearity. Therefore, when the size of the motor increases (due to material limitations, the size of the motor must be increased if the motor capacity is increased), the heat required to be emitted per unit of surface of the motor will increase temperature rise Will improve. In high-speed turbo generators, centrifugal force It will generate huge tangential stress on the rotor surface and the rotor center hole surface. The larger the rotor diameter, the greater the stress. Therefore, the diameter of the rotor body of the 2-pole turbo generator shall not exceed 1250mm within the allowable stress limit of the forging material. To increase the single unit capacity of large steam turbine generator, only by increasing the length of rotor body (i.e. using slender rotor) and improving Electromagnetic load To solve the problem. The rotor length can reach 8 meters, which is close to the limit. The only way to continue to increase the capacity of a single machine is to increase the electromagnetic load of the motor. This makes the heating and cooling problems of large turbo generators become particularly prominent. For steam turbine generators below 50000 kW, closed circuit is usually adopted Air cooling system Use the fan in the motor to blow the heating parts to cool down. Hydrogen cooling is widely used for generators with a capacity of 500000-600MW. The heat dissipation performance of hydrogen (purity 99%) is better than that of air. Using it to replace air not only has a good heat dissipation effect, but also can greatly reduce the ventilation friction loss of the motor, thus significantly improving the efficiency of the generator. However, hydrogen cooling must be provided with explosion-proof and leak proof measures, which makes the motor structure more complex and increases the consumption and cost of electrode materials. In addition, liquid medium can also be used for cooling. For example, the relative cooling capacity of water is 50 times that of air, which takes away the same heat. The flow of water is much smaller than that of air. Therefore, a part of the coil is hollow wireway Water cooling in the conductor can greatly reduce the temperature rise of the motor, delay the insulation aging and increase the service life of the motor.^[3]

Low speed synchronous generator:

Most of them are driven by hydraulic turbines or diesel engines with lower speed. The number of motor poles ranges from 4 to 60 or more. The corresponding speed is 1500~100 rpm and below. Due to the low speed, salient pole rotors with low requirements on materials and manufacturing process are generally used.

Each magnetic pole of salient pole rotor is usually stacked by 1~2mm thick steel plate and assembled into a whole with rivets. The magnetic pole is sheathed with excitation winding. The excitation winding is usually made of flat copper wire. The pole shoe of the magnetic pole is often equipped with Damping winding 。 It is a short circuit circuit formed by the bare copper bar in the damping groove of the pole shoe and the copper ring welded on both ends. The magnetic pole is fixed on the rotor yoke, which is made of cast steel. Salient pole rotor can be divided into horizontal type and vertical type. majority synchronous motor 、 Synchronous condenser And internal combustion engines or Pelton turbine The driven generators are of horizontal structure; Low speed and large capacity hydro generators are of vertical structure.

The rotor of horizontal synchronous motor is mainly composed of main pole, yoke, excitation winding, collector ring and shaft. Its stator structure and Asynchronous motor be similar. Vertical structure must use thrust bearing It bears the gravity of the rotating part of the unit and the downward pressure of water. In large capacity hydro generators, this force can be as high as four or fifty meganewtons (about equivalent to the gravity of four or five thousand tons of objects), so the structure of this thrust bearing is complex, and the processing technology and installation requirements are very high. According to the position of thrust bearing, Vertical hydro generator It can be divided into suspension type and umbrella type. The suspended thrust bearing is placed on the upper or middle part of the upper frame. When the rotating speed is high and the ratio of rotor diameter to iron core length is small, the mechanical operation is stable. The umbrella type thrust bearing is placed on the lower frame under the rotor or on the top cover of the turbine. The load bearing frame is a lower frame with smaller size, which can save a lot of steel and reduce the height of the generator and plant from the base foundation.

Synchronous generator parallel operation Most synchronous generators operate in parallel and are connected to the grid for power generation. All synchronous generators operating in parallel must have the same frequency, voltage and phase. Otherwise, at the moment of combined switching, internal circulation will be generated between generators, causing disturbance, and even damaging the generator in serious cases. However, before the two generators are put into parallel operation, generally speaking, their frequency and voltage size and phase are not identical. In order to enable synchronous generators to be put into parallel operation, there must be a process of synchronous paralleling. The methods of synchronous parallel can be divided into quasi synchronous and self synchronous. After the synchronous generator is put into parallel operation, the load distribution of each generator is determined by the speed characteristics of the generator. By adjusting the governor of the prime mover and changing the speed characteristics of the generator set, the load distribution of each generator can be changed and the generating power of each generator can be controlled. By adjusting the excitation current of each generator, the generator can be changed Reactive power Distribute and regulate the voltage of the power grid.^[1]

Permanent magnet synchronous wind turbine:

Permanent magnet synchronous wind turbine (PMSG) has become another important wind turbine after doubly fed induction wind turbine (DFIG) due to its advantages of low mechanical loss, high operating efficiency, low maintenance cost, etc., and has been widely concerned and gradually put into use. The basic structure of permanent magnet synchronous wind power generation system is mainly composed of wind turbine, permanent magnet synchronous engine, frequency converter and transformer.

The basic principle of permanent magnet synchronous wind power generation is to use the wind to drive the wind turbine blades to rotate, and drag the rotor of the permanent magnet synchronous generator to rotate to generate electricity. The permanent magnet synchronous wind power generation system is similar to the cage type variable speed constant frequency wind power generation system, except that the generator used is a permanent magnet generator, and the rotor is a permanent magnet structure, which does not need to be provided externally Excitation power supply , improving efficiency. Its variable frequency and constant speed control is realized in the stator circuit, which converts the variable frequency AC power of the permanent magnet synchronous generator into the AC power with the same frequency of the power grid through the inverter to realize the grid connection of wind power generation, so the capacity of the inverter is the same as the rated capacity of the system.

In the past decades, permanent magnet synchronous generators have become more and more attractive due to the improvement of the properties of permanent magnet materials and power electronic devices. The wind power generation system with permanent magnet synchronous generator has the following characteristics:

1. The permanent magnet synchronous generator system does not need excitation devices, and has the advantages of light weight, high efficiency, high power factor, good reliability, etc;

2. Wide range of variable speed operation, namely, super synchronous operation and sub synchronous operation;

3. The rotor has no excitation winding, the magnetic pole structure is simple, the inverter capacity is small, and it can be made into a multipolar motor;

4. The synchronous speed decreases, making the turbine and Permanent magnet generator It can be directly coupled, eliminating the gearbox in the wind power generation system, reducing the maintenance work and noise of the generator, and making the direct drive permanent magnet wind power generator system.

Applicable occasions:

1. In areas where power facilities are scarce, transportation is inconvenient, and conventional fuel is scarce, but wind resources are abundant, some power problems can be solved, such as providing power for highway lighting equipment;

2. In wind farms with small unit capacity, the permanent magnet synchronous power generation system can be efficiently connected to the grid for power generation;

3. Provide AC or DC power supply for remote and light load users in rural areas, pastoral areas, border posts, meteorological stations, etc.

alternator

In daily life, when an alternator is used to supply electric equipment, it often happens that the electric equipment cannot work normally. The reason is that the alternator outputs alternating current It is not stable enough. It is necessary at this time Power regulator To stabilize the voltage, which is commonly used in daily life AC regulated power supply AC regulated power supply can stabilize the output voltage accuracy of the generator to the allowable range for normal operation of electrical equipment.

Alternator construction

The structure of the alternator is slightly complicated. However, whether it is single-phase or three-phase, it is composed of the following main parts:

(1) Excitation part: including exciter and magnetic field part.

(2) Armature part.

⑶ Casing part: including the iron frame and base of the device spare part.

Asynchronous generator

Asynchronous generator is also called“ Induction generator ”。 utilize stator Air gap rotating magnetic field between rotor and Rotor winding An alternator in which induced currents interact. The rotation direction 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. It is commonly used as a small power hydro generator.

Since the rotor of AC excited generator adopts AC voltage Excitation, so that it has a flexible operation mode Power frequency overvoltage Variable speed constant frequency power generation Pumped storage power station The speed regulation of motor generator sets has advantages that traditional synchronous generators cannot compare with. AC excited generator The main operation modes are as follows:

1) Operating in variable speed constant frequency mode;

2) Operating in the way of reactive power regulation in a large range;

3) It operates in the power generation electric mode.

With the power system Transmission voltage When the transmission power of the line is lower than Natural power In order to improve the operating characteristics of the system, many technologically advanced countries began to study the application of asynchronous generators in large power systems in the early 1960s. They believed that the stability, reliability and operating economy of large systems can be improved by using asynchronous generators

The asynchronous generator is commonly used as a small power hydro generator for grid connected operation due to its convenient maintenance and good stability. When the prime mover is used to drag the rotor of the asynchronous motor along the direction of magnetic field rotation and make its speed exceed the synchronous speed, the motor will enter the generator operation and input mechanical energy It is converted into electric energy and sent to the power grid. At this time, the excitation current of the motor is taken from the power grid.

The asynchronous generator can also be connected in parallel with the capacitor, self excited by its own remanence, and generate electricity independently. At this time, the voltage and frequency of the generator are determined by factors such as the capacitance value, the speed of the prime mover, and the size of the load. When the load changes, the parallel capacitance value should be adjusted accordingly to maintain Voltage stability 。 When the asynchronous motor is connected in parallel with the capacitor, it can generate power independently without additional excitation power supply, so the load It is a relatively stable occasion and has its merits. For example, it can be used as a simple rural power station Lighting power supply Or as standby power supply.^[2]

Tachometer generator

Tachometer generator It is a micro generator that measures the speed. It converts the input mechanical speed into a voltage signal and outputs it. The output voltage signal is required to be proportional to the speed.

Classification of tachogenerators: tachogenerators are divided into DC tachogenerator And AC tachogenerators.

DC tachogenerator: The DC tachogenerator is essentially a micro DC generator, which can be divided into electromagnetic type and permanent magnet type according to the excitation mode of stator pole. The working principle of DC tachometer generator is the same as that of ordinary DC generator.

AC tachogenerator: the rotor structure of AC asynchronous tachogenerator has cage type and cup type, and hollow cup rotor asynchronous tachogenerator is often used in the control system. There are two windings on the stator of the asynchronous tachogenerator with hollow cup rotor, one is the excitation winding, the other is the output winding, which differ from each other by 90 ° in space.

The errors of AC asynchronous tachogenerator mainly include:

Nonlinear error : The nonlinear error of tachometer generator is caused by the change of direct axis magnetic flux;

Residual voltage: in actual operation, when the rotor is stationary, the tachometer generator outputs a small voltage;

Phase error: due to the leakage reactance of the excitation winding and the leakage reactance of the hollow cup rotor, the phase of the output voltage and the excitation voltage is different.

AC synchronous tachogenerators are divided into permanent magnet type, induction type and pulse type.

Diesel generator

Diesel generator set is an independent power generation equipment, which refers to the power machinery that uses diesel as fuel and diesel engine as prime mover to drive the generator to generate electricity. The whole unit is generally composed of diesel engine, generator, control box, fuel tank, storage battery for starting and control, protection device, emergency cabinet and other components. The whole can be fixed on the foundation, positioned for use, or mounted on a trailer for mobile use. The diesel generator set is a non continuous operation generating equipment. If the continuous operation exceeds 12h, its output power will be about 90% lower than the rated power.^[6]

Related terms

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Generator: can handle mechanical energy The general term for equipment converted into electric energy. The generated electric energy can be either DC or AC.

Grounding: refers to the connection between the circuit and the earth or with some conductive objects connected with the earth.

Idle speed control: a system that can directly control the idle speed of the engine according to the electrical load.

Ignition coil : for spark plug A device that provides DC voltage.

Permanent magnet generator: an alternator with permanent magnet, which is used to generate the current required for ignition of internal combustion engine.

Ohm: Unit of resistance.

Phase: The amplitude or magnitude of alternating current changes evenly and periodically. Three phase alternating current consists of three different sine wave currents, and the phase difference between them is 120 degrees.

Power conversion system: the system can safely connect the generator to the household power system.

Rated speed: the design working speed of the unit (revolutions per minute).

Rated voltage: one set of engine Generator Set Of Rated voltage Is the designed working voltage.

Rear bearing bracket: one casting , used as rotor bearing housing. The rotor bearing supports the rotor shaft.

Rectifier: A device that converts alternating current into direct current.

Inverter: It is used to convert DC electric energy (battery, battery) into current (generally 220v50HZ sine or square wave).

Relay: An electric switch, usually used in a control circuit. And current Contactor In contrast, its contacts can only pass a small current.

Resistance: to current resistance 。

Rotor: rotating element of generator.

Single phase: one AC load Or power supply. Generally, if it is a load, there are only two input terminals. If it is a power supply, there are only two output terminals.

Stator: the stationary part of the motor.

Vibration support: a rubber device located between the engine or generator and the frame, which can minimize vibration.

Volt: Unit of electromotive force. A constant unit electromotive force applied to a conductor with a resistance of 1 ohm will produce a current of 1 ampere.

Voltage: potential difference, expressed in volts.

Voltage regulator: the equipment can automatically keep the generator voltage at a correct value by controlling the DC power of the excitation rotor.

Watt: Unit of power supply. For direct current, it is equal to volts times amperes. For alternating current, it is equal to Voltage effective value (Volts) multiplied by Current effective value (Ampere) times the power factor times a constant (its value depends on the number of phases).

Winding: all coils of generator. stator winding It is composed of several stator coils and their interconnection lines. rotor The winding consists of all windings and wiring on the rotor pole.^[7]

testing procedure

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Step 1: Check whether the connection parts of each external conductor of the generator are broken, wrongly connected or short circuited, and use a voltmeter to measure whether there is battery voltage at point B+.

Step 2: Turn the key door to the "open" position, but do not start the engine. At this time, use a voltmeter to measure whether there is voltage at D+point, and observe whether the charging indicator is bright.

Step 3: Start the engine and measure the voltage at B+point of the engine with a voltmeter, which should reach the following values

Step 4: Turn on some loads, such as lights

Step 5: Turn on the air conditioner, lights and other major electrical appliances

At the third step, the generator has no voltage output, so the following methods can be used to check. For the generator with excitation D+point, a 2.5mm2 lead wire can be led from the battery positive pole. After starting the engine, click the D+point with the other end (within 1s), and then use a voltmeter to measure whether there is voltage output at B+point. If there is, check from the third step to the fifth step, At the same time, it is judged that there is an open circuit in the circuit of the vehicle charging indicator light (generally the indicator light is damaged, the instrument panel rod connector is loose, and the circuit is open). If there is no voltage output, the generator has no power generation fault.

Naming rules

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According to《 2013-2017 China's generator and generator set industry market outlook and investment opportunity analysis report 》。 In order to standardize and manage the diesel generator set, the country has made unified regulations on the name and model preparation method of the diesel generator set. According to the provisions of JB/T1403-99, the model naming rules of the unit

one

two

three

four

five

six

seven

The meanings of the seven boxes from left to right are as follows:

1 -- The rated output power of the generator set is expressed in figures, in KW;

2 -- Use letters to indicate the type of generator output current, where G represents power frequency, P represents AC intermediate frequency, S represents AC dual frequency, and Z represents DC;

3 -- Use letters to indicate the type of generator set, F for land use, FC for marine use, Q for automobile power station, and T for trailer;

4 -- Use letters to indicate the control characteristics, and in case of absence, it indicates manual operation, Z indicates automatic model, S indicates low-noise model, and SZ indicates low-noise automatic model;

5 - Indicate the design serial number with numbers;

6 -- Number for deformation code;

7 - Use letters to indicate environmental characteristics, if absent, it indicates ordinary type, and TH indicates temperate type.

For example, 75GFS3 represents a diesel generator set with rated power of 75KW, AC power frequency, land use, low noise and design No. 3.^[8]

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