1、 Basic type of generator set
The generator set is a device that converts the heat energy of fuel (usually gasoline or diesel) into mechanical energy and drives the generator to convert it into electrical energy. The generator set using gasoline as fuel is called gasoline generator set, and the generator set using diesel as fuel is called diesel generator set.
Diesel generator sets are mainly used in communication bureaus (stations).
2、 Types and uses of diesel generator sets
The output voltage of the diesel generator set configured in the communication bureau (station) is generally 230V/400V, which can be divided into mobile and fixed types according to the installation mode.
1. Fixed generator set
The fixed generator set is divided into indoor installation and outdoor container installation.
The indoor installation requires a separate oil engine room. The diesel generator set and its auxiliary equipment are installed in the oil engine room. The engine room is required to have sufficient area, unobstructed air inlet and outlet, convenient for noise reduction and maintenance. This installation mode is applicable to all communication bureaus (stations).
The outdoor container installation mode can be used without fixed equipment room installation. The capacity of the unit is generally small, and the heat dissipation and noise elimination of the unit are inconvenient, and the cost is high. Due to the requirements of the operating environment of the unit, it is not suitable for use in cold areas.
2. Mobile generator set
Mobile generator sets are mainly applicable to communication bureaus (stations) such as communication base stations, microwave stations and optical cable relay stations. With small capacity and flexible use, replacing fixed oil engines can reduce the investment of the whole project. Mobile generator sets are mainly divided into trailers
There are three types of vehicle, portable and vehicle bench. Among them, the portable capacity is small, and most of them use gasoline generator sets.
3、 Working principle of diesel engine
The diesel engine converts the heat energy of the fuel into mechanical energy, and completes the energy conversion through four processes of continuous intake, compression, operation and exhaust in the cylinder. The up and down movement of the piston is realized by connecting the connecting rod with the crankshaft, which transforms the linear movement of the piston into the circular movement of the crankshaft. There are two valves on the top of the cylinder, one is the intake valve, the other is the exhaust valve.
The piston has two extreme positions in the cylinder movement: top dead center and bottom dead center. The distance between top dead center and bottom dead center is called the piston stroke. The volume that the piston moves from top dead center to bottom dead center is called cylinder working volume, also called piston displacement. The sum of working volume and combustion chamber volume is called total cylinder volume. The ratio of the total volume of the cylinder to the volume of the combustion chamber is called the compression ratio. The compression ratio indicates the degree of compression of the gas in the cylinder. The greater the compression ratio, the more intense the compression of the gas. The greater the temperature and pressure of the gas in the compression process, the greater the pressure after combustion, and the higher the efficiency of the diesel engine.
The working cycle of the four stroke diesel engine is shown in Figure 1. The crankshaft rotates for two cycles (720 °), that is, in the four strokes of reciprocating piston movement, the four processes of intake, compression, operation and exhaust are completed.
1. Intake stroke
The piston moves from top dead center to bottom dead center. At this time, the inlet valve opens, the exhaust valve closes, and the piston moves downward. The pressure in the cylinder is lower than atmospheric pressure. The air outside the cylinder is sucked into the cylinder through the inlet valve. When the piston reaches bottom dead center, the top of the piston is full of air.
2. Compression stroke
The piston moves from BDC to TDC, the inlet valve and exhaust valve are closed, and the air in the cylinder is compressed. After the compression stroke is completed, the air pressure in the cylinder can reach 30~50kg/cm2 and the temperature can reach 600~700 ℃.
3. Working stroke
After the compression stroke, the piston reaches TDC, and the inlet and exhaust valves are still closed. The fuel injection nozzle at the top of the cylinder starts to inject diesel into the cylinder, which is ignited by high temperature gas. The temperature and pressure in the cylinder rise rapidly. The high temperature and high pressure gas expands in the cylinder, pushes the piston to move to TDC, and rotates the crankshaft through the connecting rod to generate kinetic energy.
4. Exhaust stroke
At the end of the working stroke, the piston moves from the bottom dead center to the top dead center, the intake valve closes, and the exhaust valve opens to exhaust the exhaust gas generated after working from the cylinder.
After the above four strokes, a working cycle of the diesel engine is completed.
The above is a cycle process of a single cylinder four stroke diesel engine. The crankshaft rotates for two cycles, the piston moves up and down twice, and works in the third stroke, while the other three strokes are driven by the crankshaft to move the piston. Therefore, the diesel engine needs to install a heavy flywheel on the crankshaft, and use the inertia of the flywheel to drive the piston to complete the other three strokes. The crankshaft speed is uneven. Therefore, diesel engines with large power use the structure of multiple cylinders to achieve stable operation.
4、 Structure of diesel generator set
The diesel generator set is a rigid whole composed of diesel engine, three-phase alternator, control panel (box), radiator tank, coupling, daily oil tank, muffler and common base. For high-power diesel generator set, the oil engine control panel and fuel tank shall be installed separately, and other main components shall be installed on the common base. In order to reduce vibration, the connection between the main components of the diesel generator set and the base is usually equipped with a damping device.
The axial direction of the flywheel housing of the diesel engine and the front cover of the generator is directly connected by the shoulder positioning, and the flywheel drives the generator to rotate by the coupling.
The diesel engine is mainly composed of cylinder, crankshaft connecting rod mechanism, valve distribution mechanism, oil supply system, lubrication pump system and cooling system.
1. Cylinder
The cylinder is the main body of the diesel engine, and its structure is shown in Figure 2. The cylinder is mainly composed of cylinder head, cylinder block, crankcase, etc. It is the skeleton of the diesel engine and the basis for the work of various mechanisms. The cylinder bears various loads of the engine, and the engine body should have sufficient rigidity and strength.
The cylinder block is the main body of the cylinder. The crankcase is divided into upper and lower parts. The lower crankcase is used to support the crankshaft. The cylinder cover is installed on the upper part of the cylinder to seal the upper part of the cylinder and form the combustion chamber. In order to ensure the tightness of the cylinder head, a cylinder gasket is installed between the cylinder head and the cylinder block. The cylinder gasket plays an important role in preventing air leakage, oil leakage and water leakage.
2. Crankshaft connecting rod mechanism
Crankshaft and connecting rod mechanism is an important part of oil engine, which is composed of piston, connecting rod, crankshaft, flywheel and other parts. Its structure is shown in Figure 3. Its function is to convert the heat energy generated during fuel combustion into mechanical energy, and convert the up and down linear movement of the piston in the cylinder into the circular movement of the crankshaft, so as to drive other machinery to do work.
(1) Piston
The piston and cylinder form a working chamber, which transmits mechanical energy to the crankshaft through the piston pin and connecting rod. When the oil engine is working, the piston bears very high temperature and pressure, and it moves very fast with great inertia. Therefore, the piston must have good mechanical strength and thermal conductivity. In order to make a close contact between the piston and the cylinder, the upper part of the piston is also equipped with a piston ring. There are two kinds of piston rings: gas ring and oil ring. The role of the gas ring is to prevent the cylinder from leaking air, and the role of the oil ring is to prevent oil from entering the combustion chamber.
(2) Connecting rod
The connecting rod connects the piston with the crankshaft, thus transmitting the pressure borne by the piston to the crankshaft, and transforming the reciprocating linear movement of the piston into circular movement through the crankshaft. When working, the small end of the connecting rod reciprocates with the piston, the big end of the connecting rod rotates with the connecting rod journal of the crankshaft, and the whole connecting rod swings around the piston pin. The gas pressure borne by the connecting rod and the inertia of the piston are dramatically changed, with impact loads, so the connecting rod must have sufficient strength and stiffness.
(3) Crankshaft flywheel
Crankshaft is one of the main parts of diesel generator set, and its assembly diagram is shown in Figure 4. Generally, the diesel engine is multi cylinder, which needs to continuously bear the force transmitted from the piston through the connecting rod during the power stroke. At the same time, the connecting rod also needs to push the pistons of each cylinder for suction, compression and exhaust, and drive other valve mechanisms and auxiliary devices.
The crankshaft of a multi cylinder diesel engine is a long shaft that rotates at a high speed. A flywheel is installed at one end of the crankshaft. The function of the flywheel is to ensure that the speed of the crankshaft is uniform.
3. Valve mechanism
The function of the valve distribution mechanism is to timely open and close the inlet valve and exhaust valve, send combustible gas into the cylinder, and discharge the burned exhaust gas. The valve distribution mechanism shall ensure sufficient intake and clean exhaust, accurate intake and exhaust time, and good sealing performance. The valve train is composed of intake valve, exhaust valve, camshaft, push rod, tappet, rocker arm and other components.
4. Oil supply system
The fuel supply system of diesel engine consists of fuel tank, diesel filter, low-pressure fuel pump, high-pressure fuel pump, fuel injection nozzle, etc. When the diesel engine is working, the diesel oil flows out of the oil tank, is filtered by the coarse filter, boosted by the low-pressure oil pump, further filtered by the fine filter, boosted by the high-pressure oil pump, and then sent to the fuel injection nozzle through the high-pressure oil pipe. At the appropriate time, the diesel oil is sprayed into the cylinder in the form of mist for compression ignition.
5. Lubrication system
When the oil engine is working, friction resistance will be generated in the movement of various parts of the engine. In order to reduce the wear of parts and prolong the service life, lubricating oil must be used for lubrication.
Lubricating oil includes engine oil and grease. Butter is generally only used in bearings of starting motors, generators, etc., while most moving parts are lubricated with engine oil. The lubrication system is usually composed of oil pump, oil pipeline, oil pan, oil filter, oil cooler and safety protection device.
The oil in the oil pan is sucked into the oil pump through the coarse screen and the oil suction pipe. The role of the oil pump is to increase the oil pressure. The oil pump presses the oil into the oil filter, which can filter out the impurities in the oil to reduce the wear of parts. After entering the filter, the engine oil is divided into two parts. One part is filtered by the fine filter and then returns to the oil pan. The other part is filtered by the coarse filter and sent to the engine oil cooler for cooling. The cooled engine oil is continuously sent to the parts to be lubricated.
6. Cooling system
When the oil engine is working, the temperature is very high, which will make the parts expand and deform, and the friction will increase. In addition, the oil may also become thinner due to high temperature, thus reducing the lubrication effect. In order to avoid excessive temperature, the oil engine is usually equipped with a cooling system to ensure that the oil engine operates at a suitable temperature. There are two cooling methods for diesel engines, water cooling and air cooling. Most diesel engines use water cooling.
The air cooling mode uses air as the cooling medium and consists of fan and air guide cover. It has the characteristics of simple structure and convenient maintenance, but the cooling effect is poor and the noise is large.
The water cooling mode uses water as the cooling medium. The cooling system includes water jacket, radiator, water pipe and water pump. The cooling water circulates in the cooling system after being pressurized by the water pump. The circulation path is: water tank - sewer pipe - water pump - cylinder water jacket - cylinder head water jacket - thermostat - water supply pipe - water tank. The thermostat can automatically adjust the amount of water entering the radiator so that the oil engine can always operate at a suitable temperature.
5、 Installation requirements of diesel generator set
The diesel generator set is usually connected to the diesel engine and generator by coupling and installed on the steel chassis. Whether the diesel generator set can operate normally depends largely on good installation conditions.
(1) When selecting the oil engine room, pay attention to the unobstructed air inlet and outlet of the engine room, reserve enough floor height and area of the engine room, and leave enough space for the working walkway and maintenance.
(2) The operation of diesel generator set has certain requirements for temperature. If the conditions are not met, corresponding insulation or cooling measures shall be taken.
(3) The machine room should be located near the power distribution room, as far away from the communication machine room as possible.
(4) Noise measures shall be taken according to environmental requirements to meet the requirements of GB3096-2008 Environmental Quality Standard for Noise.
(5) The foundation has a very important impact on the life and operation of the diesel generator set. Therefore, the installation of the oil engine has certain requirements on the foundation. Concrete should be used to pour the corresponding foundation according to the size and bearing requirements of the oil engine chassis, and a damping groove should be left around the foundation.
(6) Capacity: in combination with the development of communication system load, the capacity of diesel generator set shall be selected according to the project demand.
(7) The multi cylinder diesel generator set with 1500r/min speed and electric starting mode is selected.
(8) Rated voltage: 230/400V three-phase AC;
Rated frequency: 50Hz;
Power factor: 0.8 (lagging).
(9) The sinusoidal distortion rate of line voltage waveform of the unit at no-load rated voltage shall not be greater than 5%.
(10) The voltage and frequency performance of the unit at 95%~100% rated voltage shall meet the provisions in Table 1.
(11) The fuel consumption rate of the unit under rated conditions is shown in Table 2.
(12) The unit with rectifier and battery load shall not generate low-frequency vibration.
(13) The success rate of unit startup shall be greater than 99%.
Table 1 Steady State and Transient Indexes of Unit
performance parameter | Operating limit value |
Voltage ④ | Steady state voltage deviation (%) | ≤±1 |
Transient voltage deviation | 100% sudden power reduction (%) | ≤+20 |
Sudden power ④ (%) | ≤−15① |
Voltage recovery time ② (s) | ≤4 |
Voltage unbalance (%) | 1③ |
Frequency ④ | Frequency drop (%) | ≤3 |
Steady state frequency band (%) | ≤0.5 |
Transient frequency deviation (for rated frequency) | 100% sudden power reduction (%) | ≤+10 |
Sudden power ① (%) | ≤−7① |
Frequency recovery time (s) | ≤3 |
Relative frequency tolerance band (%) | two |
① For the generator set of turbocharged engine, follow the manufacturer's technical regulations. ② Unless otherwise specified, the tolerance band used to calculate the voltage recovery time is: 2 × steady-state voltage deviation × rated voltage/100. ③ When the units operate in parallel, the value should be reduced to 0.5. ④ Refer to GB/T2820.6-1997 for test method. |
Table 2 Fuel consumption rate of the unit
Rated power of unit (kW) | 12<P≤40 | 40<P≤75 | 75<P≤120 | 120<P≤250 | 250<P≤600 | 600<P≤1500 | 1500<P≤3150 |
Fuel consumption rate (g/kWh) | three hundred and ten | two hundred and ninety | two hundred and eighty | two hundred and seventy | two hundred and sixty | two hundred and fifty | two hundred and forty |
6、 Maintenance requirements of diesel generator set
For the diesel generator set used by the communication bureau (station), its maintenance requirements shall meet the communication industry standard YD/T1970.6-2009 Technical Requirements for Maintenance of Communication Bureau (Station) Power System Part 6 Generator Set System.
1. Basic requirements
(1) The unit after installation and before delivery shall be subject to full load test on site according to the requirements of YD/T502-2007.
(2) The unit and generator room shall be kept clean and regularly cleaned, and the phenomenon of oil leakage, water leakage, air leakage and electric leakage (referred to as "four leakage" for short) shall be frequently checked. The components on the unit shall be intact, the wiring terminals shall be firm, the instruments shall be complete, the indication shall be accurate, and the screws shall not be loose. Check whether the wall and ceiling sound absorbers are deformed and loose; Whether the thermal insulation cladding of smoke exhaust pipe is damaged or loose.
(3) According to the climate and seasonal changes in various regions, fuel and engine oil with appropriate grades shall be selected.
(4) Keep the oil, fuel and their containers clean, and clean and replace (oil, fuel and air) filters regularly. The lubricating oil shall be replenished regularly for the external running parts of the oil engine.
(5) The starting battery of the fixed unit shall be in floating charge state, and the starting battery state shall be checked regularly.
(6) In winter, when the room temperature is lower than 0 ℃, antifreeze should be added in the water tank of the oil engine, and the jacket water heater should be connected to the listed power supply.
(7) The generator set in fixed use shall be able to start and supply power normally within 15min after the mains power outage. If the power supply needs to be delayed, it shall be reported to the superior competent department for approval. The delayed start time of the automation unit used in the unmanned station shall meet the requirements for safe power supply of the communication system.
(8) Regular no-load test run and loading test run shall be conducted. The filter screen at the air inlet and outlet of the oil machine room shall be cleaned regularly.
(9) The air inlet and exhaust louvers shall be regularly checked for deformation and rain; The electric air inlet and exhaust louvers shall be tested regularly to see whether the automatic actuator and manual mechanism are in good condition; The air inlet and exhaust silencing room shall be cleaned regularly.
(10) In areas with high humidity in the south, the generator should be used to drive tide.
(11) The overhauled unit shall be tested, and can be put into use only after the performance index meets the requirements of YD/T502-2007. The maintenance period of units that continue to be used beyond the effective service life shall be shortened.
2. Conditions to be met before startup
(1) The oil and cooling water levels meet the specified requirements.
(2) The air inlet and exhaust ducts of the air cooling unit are unblocked.
(3) There is enough fuel in the daily fuel tank.
(4) The voltage and liquid level of startup battery are normal.
(5) There are no tools, parts or other items placed in the unit or nearby.
(6) Whether the main switch of the unit is in the off state.
3. Inspection during startup and operation
(1) Whether the oil pressure, oil temperature and water temperature meet the specified requirements.
(2) Whether the indicators of various instruments and signal lights are normal.
(3) Check whether the air inlet and smoke exhaust are normal.
(4) Whether there is severe vibration and abnormal sound when the oil engine is running.
(5) The power can be supplied only after the voltage and frequency (speed) meet the specified requirements and operate stably.
(6) Whether the system has low-frequency oscillation after power supply.
(7) Check the temperature of output terminals and busbar at all levels.
(8) Monitor the level change of the daily fuel tank.
4. Shutdown, fault shutdown inspection and record
(1) Normal shutdown: when the mains power supply is restored or the commissioning is completed, the machine shall be shut down after cutting off the load and no-load operation for 3~5min.
(2) Fault shutdown: in case of low oil pressure, high water temperature, high rotating speed, abnormal voltage and other faults, it shall be able to shut down automatically or manually.
(3) Emergency stop: When the speed is too high (runaway) or other personal accidents or equipment hazards occur, immediately cut off the oil and gas routes (air intake) for emergency stop, and press the emergency stop button.
(4) After failure or emergency shutdown, check and record shall be made, and the unit shall not be restarted until the failure is eliminated and the unit returns to normal.
7、 Maintenance of diesel generator set
In order to maintain the normal operation of the diesel generator set and extend the service time, in addition to the normal operation according to the operating procedures, it is necessary to regularly carry out systematic inspection, adjustment and cleaning of all components of the unit, and maintain them according to the operating instructions and technical specifications of the unit, so as to provide good guarantee and maintenance for the normal operation of the unit. See Table 3 for maintenance items and maintenance cycle of diesel generator set.
Table 3 Maintenance Items and Periods of Diesel Generator Set
S/N | project | cycle |
Someone is standing | Unmanned station | Mobile unit |
one | Equipment patrol | day | season | half a month |
two | No load test for 5~10min | month | season | month |
three | Check whether various instruments and signal indications are normal (during operation) | month | season | month |
four | Check the starting battery and charge it if necessary | month | season | month |
five | Check whether the coolant, lubricating oil and diesel oil are sufficient (before starting) | month | season | month |
six | Check whether the air inlet and exhaust ducts of the air cooling unit are unblocked (before starting) | month | season | month |
seven | Check for odor, abnormal noise and four leakage phenomena (during operation) | month | season | month |
eight | Clean the air filter | season | season | season |
nine | Check the drive belt tension | season | season | season |
ten | Check whether fire-fighting equipment and lighting are normal | season | season | season |
eleven | Cleaning equipment | month | season | month |
twelve | Check whether the starting, cooling, lubrication and fuel systems are normal | month | season | month |
thirteen | On board unit running test | | | month |
fourteen | Loading test for 15~30min | half a year | half a year | half a year |
fifteen | Calibration instrument | year | year | year |
sixteen | Check the enclosure grounding and insulation | year | year | Before on-site startup |
seventeen | Replace engine oil and three filters | to specification | to specification | to specification |
eighteen | Cleaning of diesel daily fuel tank and oil storage tank | 3 years | 3 years | 3 years |
