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What Should Be Considered When Purchasing Diesel Generator Set

Dec. 04, 2018

As an emergency backup power source, diesel generator sets are increasingly accepted and used by many industries due to its reliability, timeliness and safety. However, purchasing a suitable diesel generator set is not an easy task.


If you decide to buy a diesel generator set, you are advised to read the below instructions before placing an order.

Elements we should consider when purchasing diesel generator set.jpg


1. Common Enquiry

A. Power supply parameters: output voltage 230V/400V, frequency 50HZ, genset speed 1500r/min.


B. Automatic display and recording of operating data: including water temperature, oil pressure, speed and running hours.


C. Protection device: diesel engine overspeed, start or stop failure, low oil pressure, high oil temperature, excessive cooling water temperature, generator overload, short circuit, loss of pressure and failure of the vehicle, etc, the genset will give alarm according to different conditions (including lighting, audible alarm), open and even stop automatically.


D. It should be equipped with 24V DC starter motor and battery as electric starting system battery power is monitored by computer control.


2. Capacity


A. The rated operating power of the generator set is not less than the rated power of the stable load.

B. The standby operation power of the generator set is not less than the peak power of the load.

C. When the maximum motor starts, the instantaneous voltage drop of the generator is no more than 15%-20%.


3. Selections of Starting Method

There are three ways to start a diesel engine: manual start, electric start and compressed air start. Among them, the electric starting is to use the electric motor as the power to drive the crankshaft to rotate through the transmission mechanism, so that the diesel engine is started, the power supply battery used by the electric motor, and the starting mode should be adopted in the high rise building. At the same time, the selected genset should be equipped with fast automatic start and automatic power switch device to ensure power supply within 15s after the power supply of the city network is interrupted.


4. Speed

The diesel engine used for power generation has an adjustment diesel engine with a speed of not less than 1000r/min, the medium speed diesel engine has two speeds of 750r/min and 600r/min. In the high rise building, an adjustment unit with a rotational speed of 1500r/min should be used. This unit has a large volume per unit volume, so the volume is small and the weight is light, which can save floor space. The disadvantages of large running parts and short life spans are not considered for emergency genset with short running times.


5. Does The Generator Set Have a Supercharger?


When the generator set is equipped with a supercharger, the air required for combustion is supercharged by the supercharger and sent to the diesel engine, so that the density of the intake air is greatly increased. The same cylinder volume can burn more fuel, and the same type of non-supercharging. After the diesel engine is boosted, its output power can be increased by 50%. the turbocharger of the general diesel engine is an exhaust gas turbocharger, and the exhaust gas discharged from the diesel engine drives its work. The main disadvantage of the supercharged diesel engine is that the supercharger has a high rotational speed, short life span, and is prone to failure. But currently, the new machine has solved these problem and make it better.


6. Excitation Mode Selection

There are many kinds of excitation devices, such as a generator with a DC exciter, a self-excited constant voltage generator without a DC exciter, and a brushless excitation generator. The brushless excitation generator is a new type of generator developed in recent years. This kind of generator completely eliminates various carbon brushes and it reliable in operation. When used with the automatic voltage regulating device, the static voltage adjustment rate error can be guaranteed within 2.5%. This type of machine can adapt to various operating modes, and it is easy to realize automatic or remote control of the genset.


7. Selection of Cooling Method

There are two types of cooling methods for diesel engines: water cooling and air cooling. The complete unit of closed water circulation cooling is widely used in high-rise buildings due to its small footprint.


8. Selection of Genset Automatic Power


As an emergency generator set, the genset can quickly supply power to the emergency load when the external power supply fails. Therefore, the generator set should have the single-machine automation functions such as emergency self-start, automatic shutdown, automatic fault protection and recording mentioned above. For the specific situation, the following automation functions are selected.


A. Automatic grading loading: Some units are not allowed to suddenly increase the full load, and also prevent the inductive load from starting at the same time. Automatic grading loading can be set.

B. Automatic parallel: When the unit is automatically connected, the automatic parallel system can be set to automatically parallel the vehicle in the same way.

C. Automatic frequency modulation and load regulation: When the machine is running in parallel, the unit throttle is automatically adjusted to keep the power supply frequency and the load of each unit within the allowable deviation range.

D. Remote control of the unit: The genset needs to have RS232 standard interface and communication protocol, in line with the world-wide Lonworks technical standards.

E. Automatically maintain the starting state: The auxiliary system of the generator's starting, lubrication, fuel and cooling should be automatically kept ready to start, including automatic charging, automatic heating of lubricating oil and cooling water.


Traps We Should Beware of When Purchasing Diesel Generator Set


1. Only report the diesel engine or generator brand, do not report to the place of production, do not report the genset brand, such as Cummins in the United States, Volvo in Sweden, and Stamford in the United Kingdom. In fact, it is impossible for any diesel generator set to be completed independently by a single company. Customers should fully understand the diesel engine, generator, control cabinet manufacturer and brand of the unit in order to comprehensively evaluate the grade of the generator set.


2. The second mobile phone refurbished machine was sold to the customer as a brand new machine, and the refurbished diesel engine was equipped with a new generator and control cabinet, so that the general non-professional users could not tell whether it was a new machine or an old machine.


3. Regardless of the relationship between long-line (rated) power and backup power, only one "power" is used, and the backup power is sold to the customer as long-term power. In fact, backup power = 1.1x long line power. Moreover, the backup power can only be used for 1 hour in 12 hours of continuous operation.


4. Confuse the relationship between KVA and KW. Think of KVA as KW and sell it to customers. In fact, KVA is the apparent power, KW is the effective power, and the relationship between them is IKVA=0.8KW. Imported genny generally use KVA to represent power units, while domestic power equipment is generally indicated by KW. Therefore, when calculating power, KVA should be converted into KW by 8 fold.


5. The power of the diesel engine is as large as the power of the generator to reduce costs. In fact, the industry generally stipulates that diesel engine power ≥ generator power is 10% because of mechanical losses. Even worse, some diesel engine horsepower is misreported to the user as kilowatts, and the diesel engine is used to configure the unit. It is commonly known as: small horse-drawn cart, and the unit life is reduced, maintenance is frequent, and the use fee is No high.


6. The genset without protection function (commonly known as four protections) is sold to the customer as a fully functional unit. What's more, the generator set with incomplete meters and no air switch is sold to the customer. In fact, the industry generally requires more than 10KW units must be equipped with full instrument (commonly known as five meters) and air switches; large units and automation units must have self-protection.


7. Do not talk about random accessories, such as with no silencer, fuel tank, oil pipeline, what grade battery, large capacity battery, several batteries and so on. In fact, these attachments are important and must be stated in the contract. What's more, even the water tank fan is not included, allowing customers to open the pool.


8. Regardless of the brand grade of diesel engines and generators, the configuration of control systems, not to mention after-sales service, we only talk about price and delivery time. Some will also use non-power station special oil engines, such as: marine diesel engines, and vehicle diesel engines for generator sets. The quality (voltage and frequency) of the end product of the unit cannot be guaranteed. Units with too low a price are generally problematic


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