# Influence Of Different Types Of Loads On The Capacity Of Diesel Generator Set

Nov. 25, 2022

Jiangsu Starlight Electricity Equipments Co.,Ltd. Guide: Different types of loads have different requirements on the capacity of generator sets. The load types are generally divided into linear loads such as resistive and inductive loads and nonlinear loads containing rectifier circuits (also called rectifier loads). What impact do they have on diesel generator set capacity?

(1) Influence of inductive load on capacity.

The characteristic of inductive load (such as three-phase cage asynchronous motor) is that there is a large current when starting, and the power factor is much lower than the normal operating value. If it is started directly, the starting current value is 5-7 times of the normal operation value, which requires that the unit capacity is large enough to meet its starting requirements. However, the following problem is that the power of the unit is larger, and the power is far less than the rated value of the unit during normal operation, which is obviously uneconomical.

If the unit is selected according to the current value, it can be determined that when the rated voltage is 380V, the maximum output current is 126A, and the power is 70kW.

Due to starting current I ON=5 ▪ I=510A, in order to meet the starting requirements, the unit with maximum output current value of 532A and power of 300kW has to be selected. Obviously, the unit power becomes larger, and the power is far less than the rated power during normal operation, which is very uneconomical. In order to reduce the impact of motor startup, the method of step-down startup is often used, that is, reduce the voltage applied to the motor stator winding during startup, and restore the voltage to the normal value when the motor speed is close to stability.

(2) The influence of nonlinear load on capacity.

Nonlinear load (such as electronic computer) equipment has starting impulse current, harmonic feedback, current mutation and other disturbances, and often has high requirements for unit voltage drop. As the power supply sent by the diesel generator set not only has a large voltage distortion, but also with the reduction of the rated output power capacity of the unit, the contradiction of increasing its internal resistance will become more prominent. When the load is resistive, the effect is relatively small. However, the normal operation and even service life of the load will be affected when the computer and communication equipment, such as rectifier filter load or UPS, are equipped.

In terms of voltage drop requirements, large capacity units with smaller loads produce smaller voltage drop, and PMG is much smaller than SHUNT. When SHUNT brushless self-excited units are equipped with UPS without input filter, the capacity is usually required to be 2~2.5 times of UPS capacity. If UPS with high efficiency input filter or PMG permanent magnet unit is selected, the capacity matching can be very close.

In a word, the performance of each load shall be defined when calculating the capacity of the generator set to make correct choices. See Table 1-7 for the reference characteristic parameters of several loads.

(3) Other considerations.

After carrying out the computer group capacity according to the existing load, other considerations should be added, such as whether some loads may be overloaded, and whether there is a need to expand the load in the future. It is recommended to increase the unit capacity appropriately according to your actual needs.

In addition, if economic conditions permit, it is recommended to use two or more generator sets, some of which are used for sensitive loads (such as electronic computer systems and other electronic equipment), and others are used for insensitive loads (such as resistive loads and motors). Prevent the influence of voltage waveform distortion of unit on sensitive load caused by motor startup.

Jiangsu Starlight Electricity Equipments Co.,Ltd., as an OEM supporting manufacturer authorized by Cummins to provide Chinese diesel generator sets, has professional manufacturing technology, perfect quality management system and strong R&D technical strength. It can provide users with generator sets of various specifications from 15KW to 2500KW. It can also provide users with one-stop service of design, supply, debugging and maintenance at any time. welcome contact us by email sales@dieselgeneratortech.com.

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