Friday, 14 June 2019

Generator sizing

One of the most important decisions that needs to be made in a factory or unit is the determination of the diesel generator size. Will it be used for continuous power supply or will it serve as a standby source? While you will be consulting an expert, who will recommend a size, this article aims to give you a basic understanding about the factors you need to consider for generator sizing.

1)    Generator Ratings

Diesel generator ratings are either continuous, prime or standby.

Ø  Continuous Rating is when a dg set is expected to work 24 hours a day, 365 days a year.
Ø  Prime rating allows some fluctuation in the load, and
Ø  Standby means the backup running time is up to 200 hours per year.

2)    Performance Classes

Generators are divided into the below classes as per their performance: 

a)    Class G1 is for general purpose loads, example lighting.

b)    Class G2 is meant for public electricity supply, pumps and fans. 

c)    Class G3 is used for telecommunications and thyristor-controlled loads.

d)    Class G4 is used in data processing or computer systems where the demands are stringent. 

3)    Start-up times

You can also choose your diesel genset on start-up times. 

A.    Manual starting for generators without a specified start-up time.

B.    Automatic start-up – Long Break: - A generator started from stationary on grid failure.

C.   Automatic start-up – Short Break: - When power is disrupted for only a few milliseconds while the electrical transfer takes place. 

D.   Automatic start-up – No Break: - A continuously running electrical machine providing an uninterrupted supply in the event of power failure. 

4)    How much power do you need

It is a myth that smaller dg sets can be used for standby requirements since they will not be used all the time. This thinking can lead to generator damage and other assets connected to it and create unsafe situations. 

5)    Assess your needs 

While it may be tempting to visit your nearest dealer and pick up the cheapest generator available, it won’t make good business sense. You should study and understand your power requirements before you go shopping for a generator. 

6)    Make a list

ü  Start with listing all units that will need to be powered by the diesel generator.
ü  The next step is to list the starting and running wattage of items.
ü  Finally, you should calculate the total power requirements. 

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