Monday, 30 October 2017

Low power factor in dg sets – Part 1

The state of power supply has been erratic for a long time and many areas in the country are still struggling for a reliable source of electricity. Especially the industries that need uninterrupted power supply for economic sustainability have shown a tremendous rise in moving to diesel generators as an important source of electricity and not just a temporary arrangement. With the increase in usage and desirability of diesel generators the need to find ways to improve their efficiency and power factor (PF) is also on the rise.

What are the causes of low power factor?

Different load sizes that come with different power factor effects is the primary cause for the overall reduction in the power factor of an electrical layout. But various other reasons contribute to power factor output being low and in a significant way. The reasons are primarily connected to the fundamental limitations of a power generator.
A diesel power generator is a source of power that doesn’t have a network of sources and loads to load it. Thus, it has a limited capacity to fulfill sudden and large demands of reactive power. To build more on this limitation, the below can be associated as reasons why there is lower power factor in dg sets:

1.      Over sized dg sets

Designers of a plant usually tend to oversize a dg set or limit its loading owing to a largely existent myth that 0.8 is the ‘designed’ PF for dg sets. This essentially leads to liberally sized diesel guzzlers that do not deliver the full version of their economic capability. The alternator of a dg set is same as its larger variants connected to utility power turbines with scaled down proportions. Which means that it by design has the capability to deliver the exact amount rated as its KVA (kilovolt-ampere). So, 0.8 is not a design variable but it’s more like a thumb rule inferred from the average power factor in any industrial electrical layout with a general set of inductive - PF values .8 to .85, non-linear – Power Factor values .5 to .65 and linear (unity PF) - 0.80.

2.      Phase loading that’s unbalanced

Most of the industrial electrical layouts have loads that are liberally connected on various power phase lines because physical limitations of the process layouts are simpler to visualize when compared to the electrical balancing on every line. This doesn’t seem to be a problem when it comes to the grid connected situation where the primary connection of a phase maintains the sync in the remaining from the utility side owing to a grid’s macro effect. But in the case of a dg set that’s’ captive, syncing the phases is not even a function built into its power electronics.

3.      The load of compensation

From various reports on the effect of different power factors on dg sets and detecting safe zones it has become evident that close to unity Power Factor is achievable and safer but low Power Factor for greater periods has more negative impact.

This is part one of a two-part series. In the second part, learn how to correct dg sets with low Power Factor.

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