In the power supply design of high-rise buildings, it must be clear under what circumstances diesel generator sets should be set. Let's start with the load level of high-rise buildings: the first level load should be shared by two power sources. When conditions permit, the secondary load should also be powered by two circuits, especially for the secondary load that belongs to fire power, it should be powered by two circuits of the secondary load. It can be seen that high-rise buildings require high reliability of power supply and require two power supplies.
Selection of unit type.
1. Starting mode.
When the diesel engine starts, it must rely on external force to drive the crankshaft to rotate. When it reaches a certain speed, the air in the cylinder is compressed to a certain pressure and temperature, so that the fuel injected into the cylinder starts to burn, and then the diesel engine starts to run normally.
There are three starting modes of diesel engine:
① Start the diesel engine by hand.
② Electric starting: use the motor as the power and drive the crankshaft to rotate through the transmission mechanism to start the diesel engine. The power supply for electric starting is the battery, and the voltage is generally 24V.
③ The compressed air is introduced into the cylinder of the diesel engine, and its pressure is used to push the piston to rotate the crankshaft of the diesel engine.
When the engine reaches a certain speed, the compressed air is stopped, and fuel is injected into the combustion chamber to start the diesel engine.
When the automatic signal is used to control the starting motor or control the compressed air valve, and measures are taken for the lubrication system and cooling system, the automatic starting of the unit can be realized.
Electric starting mode should be adopted in high-rise buildings, and compressed air starting mode should be avoided. The diesel generator set with self-starting device must be selected in a class of high-rise buildings. Once the power supply of the city network is interrupted, it must be powered within 15 seconds (30 seconds is required for the high regulation). In Class II high-rise buildings, the unit with self-starting device should also be used when conditions permit, and the manual starting device can also be used when there are difficulties.
Diesel generator sets are divided into high, medium and low speed. High-speed speed ≥ 1000 rpm, medium-speed speed is 300~1000 rpm, and low-speed speed speed ≤ 300 rpm.
High-speed units with rotating speed of 1000~1500 rpm should be selected in high-rise buildings. This unit has the advantages of small size, light weight and reliable operation.
3. Cooling mode.
The diesel engine generates high temperature due to the combustion of diesel during operation. In order to ensure that the heated parts of the diesel engine and the supercharger shell are not affected by the high temperature, and to ensure the lubrication of all working surfaces, it is necessary to cool the heated parts. When the cooling of diesel engine is poor and the temperature of engine parts is too high, some faults will be caused. Diesel engine parts should not be overcooled. Too low temperature of the parts will also cause adverse consequences. It can be seen that the function of the cooling system is to transfer part of the heat from the heated parts to maintain the normal working temperature of the parts.
There are two cooling modes of diesel engine: water cooling and air cooling. Water cooling means water cooling the cylinder, and air cooling means air cooling the cylinder. One of the water cooling units is the closed self-circulating water cooling unit, which is the water cooling chamber of the diesel engine body pumped by the radiator tank and then returned to the radiator tank. The radiator tank is cooled by the fan on the unit, and the other is the open circulating cooling unit. In high-rise buildings, generally, the closed water circulation cooling unit should be selected as a whole, which occupies a small area and space.
4. Excitation system.
The excitation system is the main component of the generator. The main tasks of excitation system regulation are to maintain the voltage at a certain level, increase the transmission power and transmission distance, and improve the dynamic stability of the system. There are many kinds of excitation devices. Brushless automatic excitation devices are generally selected in high-rise buildings. The characteristics of the generator set adopting this excitation mode are that when it is used together with the automatic voltage regulation device, its static voltage regulation rate can be guaranteed to be within ± 2.5%. This type of generator set can adapt to various operation modes and is easy to realize unit automation or remote control of the generator set.
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