发电机组如何选购 How to choose a generator set

发电机组是指能将机械能或其它可再生能源转变成电能的发电设备。一般我们常见的发电机组通常由汽轮机、水轮机或内燃机(汽油机、柴油机等发动机)驱动，可再生新能源包括核能、风能、太阳能、生物质能、海洋能等。由于柴油发电机组的容量较大，可并机运行且持续供电时间长，还可独立运行，不与地区电网并列运行，不受电网故障的影响，可靠性较高。尤其对某些地区常用市电不是很可靠的情况下，把柴油发电机组作为备用电源，既能起到应急电源的作用，又能通过低压系统的合理优化，将一些平时比较重要的负荷在停电时使用，因此在工程中得到广泛的使用。

1、合理的选用发电机组。

市场上有燃气机发电机组、柴油发电机组、水力发电机组及风力发电机组等。不同类型的发电机组其性能、使用范围、市场情况等也有所不同，应合理的选用发电机组。燃气发电机组一般都是用来做常载，它所使用的燃料为天然气，具有输出功率范围广，启动和运行可靠性高、发电质量好、体积小重量轻、维护简单、低频噪声小、成本低、有利于环境保护等优点，但天然气需就地取得，而在我国没有大面积分布天然气能源，供应范围受到影响。另外对不太专业的使用者也存在安全隐患。柴油机组通常作为紧急或备用电源，所使用的燃料为柴油，属不可再生资源，成本较贵，但柴油的购买及保存较天燃气方便，单机容量大，使用范围广、热效率高、燃油消耗低、起动迅速，维修技术成熟，因此一般市场上选用柴油发电机组的最多。水力发电机组一般用于各种水电站，具有成本低、体积小、重量轻、结构简单、运行可靠、安装使用方便等特点，适合于水力资源的山区农户解决照明、电视机等用电的发电设备，但需要具备丰富的水资源条件。风力发电机组利用的是自然能源，无污染，属可再生能源，相对柴油发电要好的多，但作为应急来用不如柴油发电机。风力发电机不可视为备用电源，但是却可以长期利用。一般适宜远离电网的地区，风力资源丰富的牧区、山区、海岛等地区使用。另外无论是成本还是技术同传统的火电、水电相比还有较大的差距，也需要国家政策的扶持。所以在工程上一般宜选用柴油发电机组作为发电设备。

2、机组选择时应考虑几个因素。

主要包括机械与电气性能、机组的用途、负荷的容量与变化范围、机组的使用环境条件(包括海拔高度、气候条件、噪声)、自动化功能等。由于柴油发电机组可用于常用、备用和应急等3种情况，因此不同用途对柴油发电机组的要求就有所区别。

3、常用发电机组的选择。

常用发电机组持续工作时间长，负荷曲线变化较大，机组容量、台数、型式的选择及机组的进行控制方式与应急机组不同。(1)容量的确定:按机组长期持续运行输出功率能满足全工程最大计算负荷选择，并应根据负荷的重要性确定发电机组备用机组容量。柴油机持续进行的输出功率，一般为标定功率的0.9倍。(2)台数的确定:一般设置通常为2台以上，以保证供电的连续性及适应用电负荷曲线的变化。机组台数多，才可以根据用电负荷的变化确定投入发电机组的进行台数，使柴油机经常是在经济负荷下运行，以减少燃油消耗率，降低发电成本。柴油机的最佳经济运行状态是在标定功率的75%-90%之间。为保证供电的连续性，常用机组本身应考虑设置备用机组。(3)转速的确定:一般民用上宜选用转速为1000~1500转/分的高速机组，而转速为300~350转/分的低速机组适用作船用主机。(4)电压的确定:发电机输出电压的确定与应急发电机组相同，一般为400V，个别用电量大，输电距离远的工程可选用高压发电机组。

4、备用发电机组的选择。

负荷容量之和，乘以需要系数之后的计算负荷小于应急柴油发电机组的容量时，备用系数按1.2考虑，即1.2倍计算容量小于应急柴油发电机组的容量，在市电停电后，由应急发电机组向负荷供电。负荷容量之和，乘以需要系数之后的计算负荷大于单台应急柴油发电机组的容量时，可选择2台型号、容量相同、调压、调速特性相近的自动化发电机组。在市电停电后，由其中一台或二台机组向生活和商业用电供电;当市电停电，又发生火灾时，由2台机组向消防负荷供电，以利消防。

5、应急发电机的选择。

应急发电机一般宜选用高速、增压、油耗低、同容量的发电机组。高速增压柴油机单机容量较大，占据空间小;柴油机选用配电子或液压调速装置，调速性能较好;发电机宜选用配无刷励磁或相复励装置的同步电机，进行较可靠，故障率低，维护检修较方便;当一级负荷中单台空调器容量或电动机容量较大时，宜选用三次谐波励磁的发电机组;机组装在附有减震器的共用底盘上;排烟管出口宜装设消声器，以减小噪声对周围环境的影响。(1)容量的确定:应急发电机组作应急用，经常处于待机应急起动状态，连续运行的时间不长，一般不超过8h，因此可按"备用功率"来确定容量。按一级负荷的容量之和(不计备用容量)，考虑经修正后的机组容量，并能满足一级负荷中最大一台电动机的起动要求，据此以确定应急柴油发电机组的容量。应急发电机一般选用三相交流同步发电机，其标定输出电压为400V。(2)台数的确定:一般选用1台自动化、转速1000~1500转/分、无刷励磁、400/230V、三相四线带控制屏、充放电设备及共用底盘的发电机组。可要求共用底盘带日用油箱，以减少管路和占用面积。另外从可靠性考虑也可以选用2台机组并联进行供电。供应急用的发电机组台数一般不宜超过3台。当选用多台机组时，机组应尽量选用型号、容量相同，调压、调速特性相近的成套设备，所用燃油性质应一致，以便进行维修保养及共用备件。

6、机组起动方式的选择。

柴油机的起动方式有三种：①手摇起动;②电动起动;③压缩空气起动。在高层建筑中宜采用电起动方式，避免采用压缩空气起动方式。一类高层建筑中一定要选择带自起动装置的柴油发电机组，一旦市网供电中断，必须在15秒内供电(高规要求30秒)。二类高层建筑中有条件时，也宜采用带自起动装置的机组，有困难时也可采用手动起动装置。

7、性能和质量必须符合有关标准要求。

作为通信用柴油发电机组，必须达到GB2820-1997中G3级或G4级规定的要求和《通信用柴油发电机组的进网质量认证检测实施细则》规定的24项性能指标要求，同时要通过通信电源设备质量监督检验中心的严格检验。作为军事通信用柴油发电机组，必须达到有关GB2820-1997、GJB相关标准和部队有关部门制定的《通信电源设备的质量检测标准》的规定，并要通过有关组织部门对设备质量的严格检验。

8、与三相电动机匹配需注意的问题。

发电机组与三相电机容量选配时，建议考虑安全系数1.5，即1.5倍的电机容量(必需是软启动方式)。

9、注意额定功率和后备功率的关系，KVA和KW的关系。

市场上有些厂家仅说一个"功率"，把后备功率当作额定功率来介绍和销售机组。实际上后备功率=1.1x额定功率。而且后备功率只能在12小时连续运行中使用1小时。在国内普遍都是用额定功率来标识柴油发电机组的，而在国际上是采用备用功率来标识。KVA是视在功率，KW是有效功率，他们之间的关系为IKVA=0.8KW。进口机组一般用KVA表示功率单位，而国内用电设备一般都用KW表示。

10、认清机组的品牌。

一般进口的发电机组均为组装机，但对国产机组来说，有一体化的机组(即发电机和发动机是同一品牌)，虽体积比进口的大，但在性能上也同有些进口机组不分上下，而且价格便宜，故在选购时应全面了解机组的柴油机、发电机、控制柜的制造厂家及品牌(因有些厂家只报柴油机或发电机品牌，不报产地，不报机组品牌等)，才能综合评估出机组的档次。

A generator set refers to a power generation equipment that can convert mechanical energy or other renewable energy into electrical energy. The commonly used generator sets are usually driven by steam turbines, water turbines, or internal combustion engines (gasoline engines, diesel engines, etc.). Renewable new energy sources include nuclear energy, wind energy, solar energy, biomass energy, ocean energy, etc. Due to the large capacity of diesel generator sets, they can operate in parallel and provide continuous power supply for a long time. They can also operate independently without parallel operation with the regional power grid and are not affected by power grid failures, resulting in high reliability. Especially for some areas where the commonly used mains power is not very reliable, using diesel generator sets as backup power sources can not only serve as emergency power sources, but also optimize the low-voltage system to use some important loads during power outages. Therefore, it is widely used in engineering.

1. Reasonably select generator sets.

There are gas turbine generators, diesel generators, hydroelectric generators, and wind turbines on the market. The performance, scope of use, and market conditions of different types of generator sets also vary, and generator sets should be selected reasonably. Gas generator sets are generally used for constant load, and the fuel used is natural gas, which has the advantages of wide output power range, high starting and operating reliability, good power generation quality, small size and light weight, simple maintenance, low low-frequency noise, low cost, and environmental protection. However, natural gas needs to be obtained locally, and there is no large-scale distribution of natural gas energy in China, which affects the supply range. In addition, there are safety hazards for less professional users. Diesel generators are usually used as emergency or backup power sources, and the fuel used is diesel, which is a non renewable resource and relatively expensive. However, diesel is more convenient to purchase and store than natural gas, with a large single unit capacity, a wide range of uses, high thermal efficiency, low fuel consumption, fast start-up, and mature maintenance technology. Therefore, diesel generators are generally the most commonly used in the market. Hydroelectric power generation units are generally used in various hydropower stations, with the characteristics of low cost, small size, light weight, simple structure, reliable operation, and easy installation and use. They are suitable for rural households in mountainous areas with hydropower resources to solve power generation equipment such as lighting and television, but they need to have abundant water resources. Wind turbines utilize natural energy, are pollution-free, and belong to renewable energy. They are much better than diesel power generation, but they are not as effective as diesel generators for emergency use. Wind turbines cannot be considered as backup power sources, but they can be used for a long time. It is generally suitable for use in areas far from the power grid, pastoral areas with abundant wind resources, mountainous areas, islands, and other regions. In addition, there is still a big gap between the cost and technology and the traditional thermal power and hydropower, which also needs the support of national policies. Therefore, diesel generator sets are generally preferred as power generation equipment in engineering.

2. Several factors should be considered when selecting a crew.

It mainly includes mechanical and electrical performance, the purpose of the unit, the capacity and variation range of the load, the environmental conditions of the unit's use (including altitude, climate conditions, noise), automation functions, etc. Due to the fact that diesel generator sets can be used in three situations: common, backup, and emergency, the requirements for diesel generator sets vary depending on their usage.

3. Selection of commonly used generator sets.

The commonly used generator sets have a long continuous working time and a large variation in load curve. The selection of unit capacity, number, and type, as well as the control method of the unit, are different from those of emergency units. (1) Capacity determination: The selection should be based on the long-term continuous operation output power of the unit that can meet the maximum calculated load of the entire project, and the standby capacity of the generator set should be determined according to the importance of the load. The continuous output power of a diesel engine is generally 0.9 times the calibrated power. (2) Determination of quantity: Generally, it is set to 2 or more units to ensure the continuity of power supply and adapt to changes in the electricity load curve. Only with a large number of units can the number of generators to be put into operation be determined based on changes in electricity load, so that diesel engines often operate under economic loads to reduce fuel consumption and lower power generation costs. The optimal economic operating state of a diesel engine is between 75% and 90% of its rated power. To ensure the continuity of power supply, the commonly used units themselves should consider setting up backup units. (3) Determination of rotational speed: Generally, high-speed units with a rotational speed of 1000~1500 rpm are recommended for civilian use, while low-speed units with a rotational speed of 300~350 rpm are suitable for use as marine engines. (4) Voltage determination: The determination of the output voltage of the generator is the same as that of the emergency generator set, generally 400V. For some projects with high electricity consumption and long transmission distances, high-voltage generator sets can be used.

4. Selection of backup generator sets.

When the calculated load after multiplying the sum of load capacity by the demand factor is less than the capacity of the emergency diesel generator set, the reserve factor is considered to be 1.2, that is, 1.2 times the calculated capacity is less than the capacity of the emergency diesel generator set. After a power outage, the emergency generator set will supply power to the load. When the calculated load after multiplying the sum of load capacity by the required coefficient is greater than the capacity of a single emergency diesel generator set, two automated generator sets with the same model, capacity, and similar voltage and speed regulation characteristics can be selected. After a power outage in the city, one or two units will supply power to residential and commercial use; When there is a power outage and a fire occurs, two units will supply power to the firefighting load to facilitate firefighting.

5. Selection of emergency generators.

Emergency generators are generally recommended to use high-speed, turbocharged, low fuel consumption, and same capacity generator sets. High speed turbocharged diesel engines have a larger single unit capacity and occupy less space; Diesel engines are equipped with electronic or hydraulic speed control devices, which have good speed control performance; The generator should be selected with a synchronous motor equipped with brushless excitation or phase compound excitation device, which is more reliable, has a low failure rate, and is easier to maintain and repair; When the capacity of a single air conditioner or motor is large in the first level load, it is advisable to use a generator set with third harmonic excitation; The machine is assembled on a shared chassis with shock absorbers attached; Silencers should be installed at the exhaust pipe outlet to reduce the impact of noise on the surrounding environment. (1) Capacity determination: The emergency generator set is used for emergency needs and is often in standby emergency starting state. The continuous operation time is not long, generally not exceeding 8 hours. Therefore, the capacity can be determined according to the "standby power". The capacity of the emergency diesel generator set is determined based on the sum of the capacities of the first level load (excluding reserve capacity), taking into account the modified unit capacity and meeting the starting requirements of the largest electric motor in the first level load. Emergency generators are generally selected as three-phase AC synchronous generators, with a calibrated output voltage of 400V. (2) Determination of quantity: Generally, one automatic generator set with a speed of 1000-1500 revolutions per minute, brushless excitation, 400/230V, three-phase four wire with control screen, charging and discharging equipment, and shared chassis is selected. It is possible to request a shared chassis with a daily fuel tank to reduce piping and footprint. In addition, considering reliability, two units can also be connected in parallel for power supply. The number of emergency generator sets should generally not exceed 3. When selecting multiple units, it is advisable to choose complete sets of equipment with the same model and capacity, similar pressure and speed regulation characteristics, and consistent fuel properties for maintenance and shared spare parts.

6. Selection of starting method for the unit.

There are three ways to start a diesel engine: ① manual starting; ② Electric starting; ③ Compressed air start. It is advisable to use electric starting method in high-rise buildings and avoid using compressed air starting method. In a type of high-rise building, it is necessary to choose a diesel generator set with a self starting device. Once the power supply to the city grid is interrupted, the power must be supplied within 15 seconds (30 seconds is required by high standards). When conditions permit, units with self starting devices should also be used in Class II high-rise buildings, and manual starting devices can also be used when difficulties arise.

7. Performance and quality must comply with relevant standard requirements.

As a communication diesel generator set, it must meet the requirements of G3 or G4 level specified in GB2820-1997 and the 24 performance indicators specified in the Implementation Rules for Network Quality Certification and Testing of Communication Diesel Generator Sets. At the same time, it must pass the strict inspection of the Communication Power Equipment Quality Supervision and Inspection Center. As a military communication diesel generator set, it must meet the relevant GB2820-1997, GJB standards, and the "Quality Inspection Standards for Communication Power Equipment" formulated by relevant departments of the military, and must pass strict inspections of equipment quality by relevant organizational departments.

8. Issues to be noted when matching with three-phase motors.

When selecting the capacity of the generator set and three-phase motor, it is recommended to consider a safety factor of 1.5, which is 1.5 times the motor capacity (must be in soft start mode).

9. Pay attention to the relationship between rated power and backup power, as well as the relationship between KVA and KW.

Some manufacturers in the market only mention one "power" and introduce and sell units with backup power as the rated power. Actually, the backup power is 1.1x of the rated power. And the backup power can only be used for 1 hour in 12 hours of continuous operation. In China, diesel generator sets are generally identified by rated power, while internationally, standby power is used for identification. KVA is apparent power, KW is effective power, and their relationship is IKVA=0.8KW. Imported power units are generally expressed in KVA, while domestic electrical equipment is generally expressed in KW.

10. Recognize the brand of the unit.

Generally, imported generator sets are assembled machines, but for domestic units, there are integrated units (i.e. the generator and engine are of the same brand). Although they are larger in size than imported units, their performance is also comparable to some imported units, and they are cheaper. Therefore, when purchasing, it is necessary to comprehensively understand the manufacturers and brands of the diesel engine, generator, and control cabinet of the unit (as some manufacturers only report the diesel engine or generator brand, without reporting the place of origin, unit brand, etc.), in order to comprehensively evaluate the level of the unit.