Part 2 – Introduction of diesel generator

300kva generator weichai

☆2 Introduction of diesel generator

☆2.1 The composition of the generator

A modern diesel generator is a rigid whole composed of a three-phase AC brushless synchronous diesel engine, a generator control box, a radiating water tank, an electrical appliance control box, a fuel tank, a silencer, a common base, and other components. The control safe mailbox of the generator with larger output power is installed separately, and the other main components are installed in the public bottom welded by the section steel, which is more or less convenient for movement and installation. The axial direction of the diesel engine’s flywheel and the AC generator is directly connected to the bump positioning into one, and the SAE standard’s just-wheel connecting disk is used, and the electric drive is driven directly, the generator rotates. This connection mode is fixed together by screws, so that the two are connected into one, ensuring that the concentricity of the crankshaft of the diesel engine and the rotor of the AC generator is within the allowable range. In order to reduce the vibration of the generator, the main components such as diesel engine alternator water tank and electrical control box are usually equipped with shock absorbers or rubber shock absorbers at the connection with the public under-frame.

☆2.2 Characteristics and uses of diesel generator

① Diesel generator is a type of AC power supply equipment for self-contained power station, which is a small and medium-sized independent power generation equipment. Compared with other power generation equipment, diesel generator has the advantages of compact structure, small footprint, high thermal efficiency, rapid start, flexible control, and convenient fuel storage.

② The diesel generator is suitable for the city power grid, which can not be transmitted to the communication Bureau station, mining area, forest area, fieldwork, national defense engineering, and other occasions requiring independent power supply as the main power supply for power and lighting. For areas with mains supply and units with high requirements for power supply reliability, which do not allow power failure or require a rapid power supply in a few seconds, it can be used as an emergency standby power supply to provide a stable AC power supply quickly once the mains supply fails.

③ The diesel generator is an important part of the communication power supply equipment. Its main requirements are to be able to start at any time, supply power in time, operate safely and reliably, ensure the voltage and frequency of power supply to meet the requirements of communication equipment.

☆2.3 Classification of diesel generator

There are many kinds of diesel generators, which are classified according to different standards.

① According to its nature and use, it can be divided into a common generator and a standby generator. Generators in common use run all year round and are generally located in areas far away from events or near industrial and mining enterprises to meet the construction, production, and domestic power consumption of these places. The standby generator is in general, and electricity is supplied by the main supply of the city. When the city’s electric power pull or other reason is interrupted, to ensure that the user basically produces life or for some important equipment emergency power supply generator.

② According to the structure form, control mode, and protection function, it can be divided into:

  1. Basic type generator ——This type of generator is the most common, by the diesel engine, closed radiator, fuel tank, silencer, synchronous AC, generator control box, coupling, and chassis components. The generator has the function of automatic regulation of voltage and speed, and can usually be used as the main power supply or standby power supply.
  2. Self-starting generator ——This type of generator is based on the basic type of generator to increase the automatic control system so that it has the function of automation. When the power supply is cut off suddenly, the generator can automatically start the function of automatic switching switch, automatic operation, automatic power transmission, and automatic shutdown. When the oil pressure is too low, oil temperature, or cooling water temperature is too high, it can automatically send out sound and light alarm signals. When the generator is over-speed, it can automatically shut down for emergency protection.
  3. Microcomputer controlled automatic generator ——The generator is composed of a diesel engine with perfect performance, a three-phase brushless synchronous generator, automatic fuel supply device, and automatic control panel. The automatic control panel is controlled by a programmable automatic controller or special micro-processing controller for a diesel engine. It not only has the functions of self-starting, self-switching, self-running, and self-stopping but also is equipped with various fault alarms and automatic protection devices. In addition, he connects with the host computer through RS232 or RS485 communication interface for centralized monitoring, realizes remote control, remote signal, and remote measurement, and achieves unattended.


☆2.4 Basic structure and working principle of diesel generator

☆2.4.1 Diesel engine overall structure

The diesel engine is a type of internal combustion engine, which is an energy conversion device that converts the heat energy released by fuel combustion into mechanical energy. The diesel engine is a powerful part of a generator, generally compensated by the crankshaft link mechanism and the body assembly grasping mechanism and the intake exhaust system, a diesel supply system lubrication system, a cooling system, and an electrical system. The overall structure of diesel engines generally includes the above several systems, but due to the number of cylinders, cylinder arrangement, and cooling methods, there are slight differences in the structure of various models.

① Heat energy this must provide a certain amount of fuel into the combustion chamber, and the air is fully mixed and burned to produce heat, so there must be a fuel system. It includes a diesel fuel tank, oil filter, fuel injection pump and nozzle, and other parts.

② In order to convert the heat energy into mechanical energy, it needs to be completed by a crankshaft connecting rod mechanism. This mechanism is mainly composed of the cylinder block, crankcase, cylinder head, piston, piston pin, connecting rod, crankshaft, and flywheel. When the fuel is ignited and combusted in the combustion chamber, pressure is generated at the top of the piston due to the expansion of the gas, which pushes the piston to do linear reciprocating motion. With the help of connecting rod conversion, the crankshaft rotates to drive the crankshaft to work and do work mechanically.

③ For a device to continuously realize the transformation of heat energy into mechanical energy, it must also be equipped with a set of gas distribution agencies to ensure regular intake of fresh air, exhaust after combustion. This mechanism is composed of an intake valve, exhaust valve, camshaft, and drive parts.

④ In order to reduce the friction loss of diesel engines and ensure the normal temperature of various parts, diesel engines must have a lubrication system and cooling system. The lubricating system consists of an oil pump, oil filter, and lubricating oil duct. The cooling system consists of a water pump, radiator, thermostat, fan, and water jacket.

⑤ In order to make the diesel engine start quickly, it is necessary to configure the starting device to control the diesel engine starting. According to different starting methods, the components of the starting device are usually started by an electric motor or pneumatic motor, and compressed air is used for a high-power generator.

☆2.4.2 Common terms for internal combustion engine

Work CycleThe conversion of heat energy and mechanical energy in the internal combustion engine is completed by the four processes of the piston working in the cylinder, continuous intake compression, work, and exhaust. The machine does not carry out such a process, which is called a work cycle.

Top Stop Point and Bottom Stop Point:

Figure 2.1 shows the position diagram of a single-cylinder four-stroke internal combustion engine

When the piston moves in the cylinder, the piston crown is at the highest position in the cylinder, which is called the top stop point. The lowest position of the piston crown in the cylinder is called the bottom stop point.

Location map of a single cylinder 4-stroke internal combustion engine
Figure 2.1. Position Diagram of single-cylinder 4 strokes internal combustion engine

Piston StrokeThe minimum straight-line distance between the upper and lower stop point is called the piston stroke, is also called the stroke, usually represented by S. The minimum linear distance between the center of the connection between the crankshaft and the big end of the connecting rod and the center of rotation of the crankshaft is called the radius of rotation of the crank.

Working VolumePiston from top dead center to bottom dead center, the cylinder swept by the volume known as the working volume of the cylinder or piston displacement.

Compression RatioAfter fresh gas is inhaled into the cylinder, it fills the total volume of the whole cylinder system, while the total volume of the cylinder includes the volume of the combustion chamber and the working volume of the cylinder. The size of the compression ratio shows that the air or mixture in the cylinder is compressed, and the multiple volume reduction also shows the degree of compression of the gas. The larger the compression ratio, the more compressed the gas is when the piston moves, the higher the temperature and pressure of the gas, and the higher the efficiency of the internal combustion engine.

☆2.4.3 The working principle of four-stroke diesel engine

In the thermodynamic process, only in the process of expansion can the working medium have the ability to do work, and we require the engine to continuously produce mechanical work, we must make the working medium repeatedly guarantee. Therefore, we must try to restore the metric system to its original state, and then expand it. Therefore, the diesel engine must return to the starting state after electrical compression expansion exhaust, so that the diesel engine continuously produces mechanical work, so the above four thermal processes are called a working cycle. If the diesel engine piston goes through, four strokes complete a cycle of work, the machine is called a four-stroke diesel engine. If the piston goes through two strokes to complete a working cycle of the diesel engine, it is called a two-stroke diesel engine. At present, diesel generators are equipped with four-stroke diesel engines. The working process of the four regenerative diesel engines is illustrated in Figure 2.2.

Working process of 4-stroke diesel engine

Intake StrokeThe purpose of the intake stroke is to draw in fresh air to prepare the fuel for combustion.In order to realize the pressure difference between the intake cylinder and the outside of the cylinder. Therefore, this stroke exhaust door is closed, the opening of the piston is down-stop, the volume of the cylinder above the moving piston is gradually expanded, and the gas pressure in the cylinder is lower than the atmospheric pressure, about 68 ~ 93 kPa. Under the action of atmospheric pressure, fresh air is sucked into the cylinder through the intake valve when the piston reaches the bottom stop point. The intake valve closes and the intake stroke ends. Fig 2. 2. Working process of 4-stroke diesel engine

Compression Stroke.The purpose of the compression stroke is to increase the pressure and temperature of the air in the cylinder to create conditions for fuel combustion. Because the keys and exhaust valves are closed, the air in the cylinder is compressed, and the pressure and temperature are easy to rise, and the degree of rising depends on the degree of compression. When the piston is close to the top stop point, the air pressure in the anus reaches 3000-500 kPa and the temperature reaches 500-700 C, which far exceeds the natural temperature of diesel fuel.

Expansion Work Stroke.At the end of the piston lift, the injector begins to inject diesel fuel into the cylinder and mix it with air to form a combustible mixture that immediately ignites. At this time, the pressure in the cylinder rises rapidly to about 6000 ~ 9000 kPa, and the temperature is as high as 1800 ~ 2200 ℃. Under the thrust of high temperature and high-pressure gas, the piston moves downward and drives the crankshaft to rotate to do work. As the gas expands and the piston descends, its pressure gradually decreases until the exhaust valve is opened.

Exhaust Stroke.The purpose of the exhaust stroke is to remove the exhaust gas from the cylinder. At the end of the power stroke, the gas in the cylinder has become exhaust gas and the temperature drops to 800 ~ 900 ℃ and the pressure drops to 249 ~ 392 kPa. At this time, the exhaust valve opens, the valve closes the piston, moves from the bottom stop point up to the stop point, and the exhaust gas is discharged out of the cylinder under the road of residual pressure and piston push in the cylinder. The exhaust process ends when the piston reaches the top stop point again. At the end of the exhaust process, the exhaust valve closes the key, the valve opens again, and repeats the next cycle, starting again and again, constantly doing work for the outside.

☆2.4.4 Classification of governors

The function of the governor is to automatically adjust the amount of fuel supply with the change of external load within the range of diesel engine speed, so as to maintain the basic stability of diesel engine speed. For a diesel engine, the fuel supply can be changed simply by turning the plunger of the fuel injection pump. With the increase of supply, the power and torque of the diesel engine increase accordingly, and vice versa.

The load of the diesel generator is often changed, which requires the power of the diesel output to change frequently, and the frequency of power supply is stable, which requires the speed of the diesel engine to maintain stability. Therefore, the diesel engine of the generator must be equipped with a commissioning mechanism. A governor generally consists of two parts: an inductor and an actuator. According to the different working principles of the governor, it can be divided into the mechanical governor, electronic governor, and EFI speed control governor.

Mechanical Governor

The mechanical speed control system operates with a flying hammer rotating with the rotation speed corresponding to the diesel engine, the exit force generated when the hammer is rotated, can automatically adjust the amount of oil in the oil pump when the generator speed is changed, thereby reaching automatic Adjust the purpose of the generator speed. Fig. 2.3 is a schematic diagram of the principle of the centrifugal full speed governor. The position of the moving handle can change the tension of the spring so that the tension acts on the whiteboard is in the forefront position while changing the position of the oil pump teeth, so that the diesel engine is adjusted to the required speed, and automatically stabilizes work under the speed.

Centrifugal type the schematic diagram of the working principle of the full speed governor

Figure 2.3 Centrifugal type the schematic diagram of the working principle of the full speed governor

Usually, the speed of a diesel generator with a mechanical speed control system will decrease slightly with the increase of load, and the automatic change range of speed is ±5%. When the generator is under rated load, the speed of the generator is about 1500 rpm.

 Electronic governor

An electronic governor is a controller that controls the speed of the engine. Its main function is to make the engine idle speed can be set to maintain the speed so that the working speed of the engine can be set to maintain the speed, not affected by load changes. The electronic governor is mainly composed of a controller, speed sensor, and actuator. The engine speed sensor is a variable reluctance electromagnet, which is installed in the flywheel housing, above the flywheel ring gear. When the teeth on the ring gear pass under the electromagnet, they will induce an alternating current. The electronic controller compares the input signal with a preset value and sends a correction signal or a sustain signal to the actuator. The controller can be adjusted in many ways, such as idle speed, running speed, sensitivity, and stability of the controller, starting fuel quantity, engine speed, and acceleration. The controller is an electromagnet, which converts the control signal from the controller into the control force. Control signals from the controller to the actuator are transmitted to the fuel control rack of the fuel injection pump through a system of connecting rods.

 EFI speed regulation

The electron-joining engine is an electronic control module (ECU) on a diesel engine that controls the injector, the detected diesel engine, various information detected by a series of sensors, and adjusts the fuel injection timing and injector. In the best working condition. The main advantages of EFI speed regulation.:The mechanical performance of diesel engines can be optimized by electronically controlling the fuel injection timing and injection pressure. By accurately controlling the amount of fuel injected by echo, the fuel consumption of diesel engines is reduced more economically in normal operation. It has lower emissions and meets the European off-road internal combustion engine emission standards. The data communication line can be connected and installed with the special diagnostic tool of the external instrument panel, which is easier to increase the detection of the fault point and is more convenient for troubleshooting. The composition of the electronic injection diesel engine management system is shown in Figure 2.4.

Management system of electric diesel engine

Fig. 2.4 Management system of electric diesel engine

Explanation: CIU refers to the control interface device, such as the control panel; ECU means electronic control module, ECU is mounted on the diesel engine.

☆2.5 Alternator

☆2.5.1 The working principle of alternator

The alternator and the three-phase AC synchronous generator are mainly composed of the main electronic main rotor duration electronic reverse time segment rotating rectifier and automatic voltage regulator. It is a device that converts mechanical energy into alternating current electrical energy. Fig. 2.5 Schematic diagram of a synchronous generator.

Schematic diagram of a synchronous alternator
Fig. 2.5 Schematic diagram of a synchronous alternator

① Usually the stator of a three-phase synchronous alternator is the armature and the rotor is the. The whole process begins with the diesel engine landing to drive the internal components of the alternator. The principle of the brushless self-excited alternator is to use the testimony of the master and slave to produce a small AC voltage signal on the master stator. This small AC signal is sent to the automatic voltage regulator (AVR), AVR rectification into a DC signal, and it will be added to the excitation electronics.

② When this direct current is passed through the exciting stator, a magnetic field is generated, and an alternating voltage is induced on the excitation rotor and is delivered to a rectifier that is rotatable with its synchronous rotation, and the AC voltage is converted to DC.

③ When this DC voltage appears in the main rotor, it produces a stronger magnetic field than the original instantaneous, so a higher AC voltage is induced on the main electron.

④ This higher AC voltage circulates through the entire system and induces a higher DC voltage back to the rotor. This is repeated until an approximate rated alternator output voltage is produced. At this point, the automatic regulator begins to limit the voltage to the force, magnetic, and electronic, which in turn limits the total output voltage of the alternator. The whole accumulation process of voltage from no to the set value generally does not exceed one second, which is very short, so that users can be satisfied with the requirement of putting it into use as soon as possible. Figure 2.6 is a schematic diagram of a self-contained AVR-controlled alternator. The stator of the main machine provides magnetic power for the exciter magnetic field through AVR. AVR makes feedback according to the voltage induction line number from the electronic winding of the main machine and regulates the rectified output power of the exciter armature by controlling the low-power exciter magnetic field, so as to meet the requirements of controlling the main machine magnetic field current.

 Intelligent AVR Controlled Alternator Schematic

Figure 2.6  Intelligent AVR Controlled Alternator Schematic

Brushless provide a stable magnetic field through a separate exciter and use the magnetic field to generate electrical signals. In a similar way, the voltage establishment time is shorter and the anti-interference ability is stronger. Figure 2.7 is a schematic diagram of an alternator with permanent magnet-controlled excitation.

schematic diagram of a permanent magnet controlled magnetic force alternator
Fig. 2.7 schematic diagram of a permanent magnet controlled magnetic force alternator


☆2.5.2 Automatic voltage stabilizer

① Automatic voltage regulator (AVR) enables the main alternator to maintain a relatively stable voltage from no-load operation to full load operation. The host stator provides power for excitation and low magnetic field through AVR, and can automatically adjust the current of the exciter magnetic field. The AVR item comes from the voltage sensing signal of the host stator winding makes feedback, and the rectified output power of the particle machine is adjusted by controlling the low power excitation machine magnetic field, thereby achieving the purpose of controlling the host magnetic field. The output voltage of the three-phase four-wire AC system of the main stator is proportional to the current of the main rotor winding.

② The AVR has a voltage-frequency proportional characteristic that correctly adjusts to reduce the output voltage of the main alternator when the speed of the generator is reduced. This proportional characteristic helps protect the diesel generator during sudden load increases.

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