Noise and vibration of diesel generators

The main noise sources of diesel generator sets all originate from the diesel engine, including exhaust noise, mechanical noise and combustion noise, cooling fan and exhaust air noise, intake air noise, generator noise, and noise generated by the transmission of foundation vibrations. The most fundamental way to reduce noise from generators is to address the source of the sound, by employing conventional noise-reduction techniques ； Things such as silencers, sound insulation, sound absorption, and vibration isolation are the most effective solutions. 1. Exhaust noise is the main source of noise for the unit; it is characterized by extremely high levels of noise, a fast exhaust speed, and great difficulty in controlling it. The use of a specially designed impedance-type composite silencer can generally reduce exhaust noise by 40–60 dB(A). 2. When reducing the noise of the cooling fans in generator sets, two issues must be taken into account: one is the pressure loss permitted in the exhaust duct ； Second is the required sound attenuation level; for these two points, a resistive panel silencer can be used. 3. Sound insulation, sound absorption, and vibration isolation: The doors and windows of the machine room are fire-resistant and sound-insulating; the five walls in the machine room, excluding the floor, can be treated for sound absorption. Based on the spectral characteristics of the generator set, a perforated plate resonance sound absorption structure is used ； Good sound insulation in the machine room prevents air convection inside it when the closed-water-cooled generator set is shut down, which also prevents the high temperature in the room from dropping quickly. This issue can be resolved by using low-noise axial flow fans together with resistive panel-type silencers ； Before installing the generator set, vibration isolation measures must be carried out strictly in accordance with the information provided by the manufacturer, in order to prevent the propagation of structural noise over long distances and the emission of airborne sound during that propagation, which could otherwise result in noise levels exceeding the permitted limits at the factory boundary. Diesel generator sets consist of electrical and mechanical components; therefore, the causes of vibration problems in such generators can also be divided into two categories. Generally speaking, oscillations in silent diesel generator sets are caused by imbalances in the rotating parts, electromagnetic issues, or mechanical defects. 1. The rotating part is unbalanced; the solution is to first balance the rotor. If there are large drive wheels, brake wheels, couplers, or shaft couplings, they should be separated from the rotor and balanced separately. Another cause is mechanical loosening in the rolling part ； 2. Problems in the electrical part are caused by electromagnetic factors; for example, broken bars in the rotor of a cage-type asynchronous motor, or deformation of the rotor core, which leads to uneven air gaps between the stator and rotor. This results in an unbalanced magnetic flux in the air gaps, thereby causing vibration.