Procedure to Test Sound Level of Diesel Generators

Most of the business establishments, industrial units and also some housing complexes install diesel generators (DG) as a back-up to the erratic electrical supply. Such establishments should also know applicable regulations is the noise limit specified by regulatory body Central Pollution Control Board (CPCB, Ministry of Environment, Forest and Climate Change. One most important regulatory requirement is that all such DG sets must be provided with acoustic treatment. Another regulatory requirement is that the allowable limit of sound power levels (SPL) in case of DG sets up to 1000 KVA is 75 decibel in A-scale. While in case of DG sets up to 1000 KVA there is a requirement of minimum insertion loss of 25 dB(A) before and after acoustic treatment. The CPCB has also a specified procedure for the determination of SPL as to be carried out according to ISO: 8528 (Part 10), meeting the requirement of grade 2 accuracy. Any DG set without acoustic enclosure as per GSR 371(E) dated 17th May 2002 is not allowed to operate with effect from 1st June 2015. In case the material used in the enclosure is foam or any inflammable material, a test report on flammability as per IS: 7888 "Methods of Test for Flexible Polyurethane Foam" should be produced by the supplier from an accredited laboratory.

The generator set to be tested for type approval or conformity of production shall be a complete system and shall include the engine, the alternator, the air inlet system, exhaust system and the cooling system in the acoustic enclosure. The silencer should be provided without extension of exhaust piping. The exhaust pipe tail end shall be within the hypothetical parallelepiped surface at 1 m distance from the enclosure.

In order to test the sound pressure level, the DG set should be run and adjusted to the load for half an hour at the rated load. Next is to measure the difference between the air temperatures inside the enclosure at 50 mm from the combustion air intake, away from the hot spot, and outside the enclosure. This difference should not be more than 7°C. The ambient air temperature, while this test is carried out, shall not be less than 25°C. And also it is required to carry out the exhaust back-pressure measurement at rated load at the location as mentioned in IS 10000. The back-pressure measured should not exceed the maximum pressure requirement specified by the engine manufacturer in its application for Type Approval for compliance with the emission limit for the engine. If the specified temperature and backpressure requirements are not met, the test should be discontinued.

Once the above conditions are attained then noise measurements could be carried out as per ISO: 8528 (Part 10). The test result should be calculated in A-weighted Sound Pressure Level from Sound Power Level, assuming free field over the ground, at 1 m. All these conditions of monitoring with date and time, as well as load at which the measurement was carried out, should be mentioned in the test reports. The test reports should also contain the reference of the applicable limits as specified by CPCB or any regulatory agencies.

Any generator set having engines not engraved with the manufacturer’s name and date of manufacturing is not allowed to operate from 01.06.2015. Generator sets manufactured on or after17-05-2002 need to be scrapped and dismantled after 15 years from the date of manufacturing or 50000hours of operation, whichever is earlier. However, it is counted to 16 years in case of agricultural uses.

Sunita Mishra
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  1. Nice information and updates. Really i like it and everyday am visiting your site..
    generator dealers in hyderabad

  2. Really fantastic and useful stuff. Life cycle is either 15 years or 50000 is new information for me. thanks

    1. Hai sir, for an industry power cat may be 500hrs to 750 Hrs / annum. 15 years it self replace the DG set is possible. now a days power cut is less.


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