Smart Consumer - Understanding Power Factor

Understand the ‘Power Factor’ of your AC Load

Are you facing problems like a generator tripping due to Over Current Alarm or excessive black smoke?

Have you been advised to reduce the electrical load to suit the capacity of your generator?

If you are using a generator in a Factory, at a construction site or for any other commercial purpose, you may have faced such a situation. Most likely, you did not hire any electrical consultant to evaluate your electrical load before buying the generator.

A poor Power Factor (PF) might be the reason for these kind of problems. Keep reading for a fundamental understanding of what is a power factor.

The Beer analogy is the most popular and easy way to understand the Power Factor.

In a glass of beer there will be beer and also few inches of foam. You are paying for per glass of beer, therefore more beer and less foam is better value for money.

Let us compare this glass of beer with electrical power.

Glass of Beer                      = Beer + Foam

Apparent Power               = True Power + Reactive Power

True Power (Beer) is the power which we actually use, but Apparent Power (Beer + Foam) is the power we pay for.

Power Factor (PF)                            = True Power (kW) / Apparent Power (kVA)

Apparent Power (kVA) x PF          = True Power (kW)

The value of Power Factor will be between 0 - 1.

A Power Factor of 1 is best, but practically very difficult to achieve. A higher Power Factor value is always better.

There are various types of electrical loads. Broadly electrical loads can be divided into following three types.

1.       Resistive Load

2.       Inductive Load

3.       Capacitive Load

Pure Resistive, Inductive or Capacitive loads are never present in practical application, it is always a combination of different types of loads. Each type of load has different impact on the PF. 

Bad Power Factor

Bad Power Factor means more Reactive Power (foam of Beer) which is useless. Bad Power Factor reduces the capacity of Electricity Board supply lines. There is a provision of Penalty fees by the Electricity Board for having bad (very low) PF in your Loads. For domestic use there is no such penalty.

Commonly there will be more Inductive Loads which negatively affects the Power Factor.

Inductive Load causes Lagging Power Factor

Inductive Loads tend to hold back the current and results in a Phase shift between the Voltage and the Current. 

Capacitive Loads causes Leading Power Factor

This is opposite to the Inductive Load. Capacitive load tends to hold back the voltage, causing a phase shift.

Rectifying Leading Power Factor :- 

If you have a leading power factor caused by high capacitive loads ,

- Add Inductive Load to the circuit.

Pure Resistive Load causes Unity Power Factor – THE BEST

Pure resistive loads have a PF value of 1. There will be no phase shift between the Voltage and Current.

It means the Voltage and Current (in AC circuits) will cross the 0 value together at the same time.

Benefits after improving Power Factor

1.       Increase in efficiency of system and devices

2.       Low Voltage Drop

3.       Can use optimized size of Power Cable which will give a cost benefit.

4.       An Increase in available power

5.       Appropriate Size of Generators.

6.       Eliminate the penalty of low power factor from the Electric Supply Company

7.       Saving in the power bill

8.       Better usage of power system, lines and generators etc.

For further guidance or information on diesel/gas gensets visit our website at www.mahindrapowerol.com/ or call us at 1-800-419-1999

How to deal with low power factor (PF) in DG sets? - Part 2

Robust Power Factor correction systems have been designed by expert power electronics developers as per the given limitations and system boundaries (in Part 1). The newly designed systems deploy the principles of the conventional Automatic Power Factor Corrector (APFC) but they differ significantly on aspects like the control logics and subsequently the controller hardware that are cutting-edge and sophisticated. In common language, this corrective mechanism is known as reactive power consumption whereby a mirror image of the tracked power factor is formed to correct it in real time.

To put this into effect you would need the below things:

1.      Thyristors with solid state relays - As the name itself suggests and unlike the conventional magnetic induction relays, these are made up of solid state electronics (semiconductors) that are helpful in eliminating transient currents and reducing the time lag between the consecutive switchovers of capacitors.

2.      Multiple current sensors-A current transformer should be available for every electrical phase of the layout. It will virtually balance the load and correct the power factor on every phase line.

3.      Microprocessor-based controllers - The additional phase-wise data parameters and the calculation of power for correction determination have rendered micro controller based controllers slow and sluggish. That is why hardcoded PLCs or faster microprocessors work better than them.

Advantages of correcting the Power Factor with the above advanced methods:

1.      More alternator efficiency- The copper losses that are associated with an alternator are directly proportional to the square of the current that it delivers. Thus, the correction of power factorwill lead to lesser current per unit power and reduce the associated copper loss.

2.      Reduced overheating and voltage fluctuations - There’ll be reduction in the currents in the total system. Due to this, overheating and voltage fluctuations in the windings and the transmission network due to the shuttling of loads is greatly reduced. This further saves T&D losses.

Please visit our website for enquiries: www.mahindrapowerol.com

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.

Please visit our website to inquire further: www.mahindrapowerol.com