High-rise buildings have high requirements on the reliability of power supply, many parts of the first level load should be powered by two power sources, and conditions allow it should also be powered by two circuits, especially the firepower of the second level load also requires two circuit power supply. When should diesel generator set be installed in the power supply design of high-rise buildings? Let’s start with the load class of high-rise buildings and the principle of configuring diesel generator sets:
For high-rise buildings that can provide two independent power sources from the grid, diesel generator sets can not be installed in principle on the premise that the requirements of the first-class and second-class loads have been met. However, for special high-rise buildings (such as super high-rise buildings), potential serious risks should be considered in the internal load. For example, when one power supply system is overhauled or fails, another power supply system also fails. In this case, diesel generator sets should be set as emergency power supply. For high-rise buildings where the local grid can only provide one power supply, or it is difficult to obtain a second power supply, a diesel generator set should be set up to provide a second power supply. At this point, the diesel generator sets are used as backup power and not just for emergency use. In some high-rise buildings, even though the power supply is quite reliable, they have set up their own emergency generator set so that in case of interruption of the power supply grid, on the one hand, they can ensure the need for fire fighting power during the power outage and maintain the order of the building.
Diesel-generating unit capacity
Generally, 12kW-2000kW can meet the requirements.
- Starting mode
When the diesel engine starts, it must rely on external forces to drive the crankshaft to rotate. When it reaches a certain speed, the air in the cylinder is compressed to enough pressure and temperature to make the fuel injected into the cylinder start to burn, and the diesel engine starts to operate normally. There are three starting modes of diesel engines:
- Manual start: that is, start the diesel engine by hand;
- Electric starting: that is, the motor as power, through the transmission mechanism to drive the crankshaft rotation so as to start up the diesel engine, the power supply used for the electric starting battery, the voltage is generally 24V;
- Compressed air starting. That is, the compressed air is imported into the cylinder of the diesel engine and the pressure is used to push the piston, so that the crankshaft of the diesel engine rotates. When the air is stopped at a certain speed, the fuel is injected into the combustion chamber, and the diesel engine can be started up. When the starting motor or the compressed air valve is controlled by an automatic signal, and the lubrication system and cooling system are taken measures, the unit can be realized self-starting.
In high-rise buildings, it is advisable to use electric starting mode and avoid using a compressed air starting mode. A diesel generator set with a self-starting device must be selected in a Class A high-rise building. Once the power supply from the grid is interrupted, it must be powered within 15 seconds (30 seconds for high standards). In second-class high-rise buildings, units with self-starting devices should also be used when conditions permit, and manual starting devices can also be used when difficulties arise.
2. Rotational speed
Diesel generator sets can be divided into high, medium and low speeds. High speed ≥1000 RPM; Medium speed in 300 ~ 1000 RPM; Low speed ≤300 RPM. In high-rise buildings should choose the speed of 1000 ~ 1500 RPM high-speed unit. The unit has the advantages of small size, light weight and reliable operation.
3. Cooling mode
Diesel engine produces the temperature in the operation of diesel combustion, in order to ensure that the diesel engine parts and supercharger shell parts are not affected by high temperature and ensure the lubrication of the working surface, it is necessary to cool the heated part, because the temperature is too high will cause failure. Of course, excessive cooling can also cause problems because the parts are too cold. The function of the cooling system is to transfer part of the heat from the heated parts to maintain the normal working temperature. The cooling methods of the diesel engine are water cooling and air cooling. Water cooling means water cooling cylinder, air cooling means air cooling cylinder. One of the water cooling units is a closed self-circulating water cooling unit, which is composed of the cooling water tank, the water pump, the water cooling chamber of the diesel body, and then returned to the cooling water tank, and the cooling water tank is cooled by the fan of the unit, and the other is the open circulation cooling unit. In high-rise buildings, the integral unit with closed water circulation cooling should be selected in general because it takes up less space.
4. Excitation system
The excitation system is the main component of the generator. The main task of the excitation system is 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, high-rise buildings generally choose brushless automatic excitation devices. The characteristics of this type of generator set include: when used with automatic voltage adjustment device, the static voltage adjustment rate can be guaranteed within ±2.5%, it is suitable for various operating modes and easy to realize the automation of the unit.