Professional Generator Supplier
Correction method for Cummins generator set power on-site conditions


02 2024

Under non-rated on-site conditions and special loads, the rated power of Cummins generator sets needs to be corrected. Dongfeng Cummins generator set price,  Xiamen ZTA Power tells what the correction methods are:


1 Power correction of ambient temperature


When the ambient temperature is too high, the air density decreases, the amount of oxygen during diesel engine combustion decreases, and the combustion efficiency decreases, thereby reducing the mechanical output power of the diesel engine; at the same time, the generator needs cold air to cool the winding when it is working. When the ambient temperature is too high, the cooling effect is reduced, and the internal temperature of the generator winding increases. In order to ensure that the winding temperature of the generator is within the allowable range, the output power of the generator must also be reduced.


The output power of diesel engines and generators of various brands is affected by the ambient temperature. Due to different designs, the correction parameters are also inconsistent; the same brand, different models, and different speed control systems have different correction parameters. Generally, the correction parameters of the original diesel engine manufacturer should be used as the standard. Usually, the power loss can be calculated according to the output power decrease of 3%~4% for every 5increase in ambient temperature above 40. However, it should be noted that the nominal power of some manufacturers' units is based on the output power at an ambient temperature of 25.


2 Power correction at altitude


When the altitude increases, the air density will also decrease, which also affects the output power of the diesel engine and generator. Different brands of diesel generator sets should refer to the manufacturer's power correction curve to calculate the actual power after capacity reduction. Usually, the power loss of generator set  can be calculated according to the output power decrease of 4%~5% for every 500m increase in altitude when the altitude exceeds 1000m. However, it should be noted that the nominal power of some manufacturers' units is based on the output power at an altitude of 300m. Electronic injection diesel engines use electronic injection control technology, which controls the injection timing and injection amount of each injector through various data of the diesel engine detected by a series of sensors installed on the diesel engine. Since the electronic control unit precisely measures the intake pressure and fuel temperature of the intake manifold and controls the injection timing and injection amount, the electronic injection diesel engine has a lower power drop in high altitude and high temperature environments. Therefore, the use of electronic injection generator set in high altitude and high temperature environments can obtain greater output power and economy.

3 Power correction of nonlinear loads


Nonlinear loads Loads containing inductive and capacitive components are all nonlinear loads, such as computer room air conditioners, uninterruptible power supplies UPS, lighting dimming systems and rectifier filter equipment. This type of load is usually widely used in key departments such as communications, network data, data exchange, financial settlement, airport runway lighting dimming and important system scheduling.


Non-linear loads will reflect a large number of high-order harmonics to diesel generator sets, among which the 5th and 7th harmonics are the most serious, especially when the non-linear load is large and the generator capacity is small. The harm is more obvious. The consequences will be the resonance of the unit, prolonged stabilization time and malfunction of the load equipment. In severe cases, the AVR and load equipment will be damaged. This problem is often not given enough attention during the selection of the unit (because it has little effect when powered by the mains), and it is not until it is operated that it is found that it cannot work normally, causing irreparable losses.


The starting current of the direct-started room air conditioner is 6 to 7 times the normal current when the induction motor is directly started, and the power factor is very low. At the moment of motor starting, the terminal voltage of the generator will drop to below 80% of the normal value, thereby affecting the power supply of other loads.

4 Power correction of added load


For naturally aspirated units, the maximum allowable one-time load is equal to the used power. After adopting turbocharging technology, the power of the engine has been significantly improved, but the ability to suddenly add load has decreased. When the boost ratio is higher, the drop in sudden load capacity is more obvious. The impact of turbocharging on sudden load is mainly because a considerable part of the power of a turbocharged diesel engine is achieved through turbocharging, and the turbocharging value mainly depends on the power and speed of the engine. When the engine is idling, the boost pressure is very low (or close to the non-boosted state). At this time, loading the rated power of the turbocharger (or adding a larger load) is equivalent to a transient sudden load exceeding the rated power of the non-supercharger. The result is either a failure to add load suddenly, or a speed drop exceeding the limit, or a long recovery time, which will affect the power supply performance of the unit.

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