Showing posts with label Power Factor. Show all posts
Showing posts with label Power Factor. Show all posts

Thursday, March 8, 2012

Understanding Power Factor and why it's important
March 08, 2012

Understanding Power Factor and why it's important

In a typical industrial plant, AC induction motors constitute a large portion of the equipment. Since induction motors are mainly inductive loads, they are likely to lead to a low power factor. Some of the benefits of improving your power factor include:

Lower Utility Fees

Inductive loads, which require reactive power, are the main cause of a low power factor. This increase in required reactive power (KVAR) causes an increase in required apparent power (KVA), which is what the utility company supplies to your facility
So, a facility's low power factor causes the electricity company to have to increase its generation and transmission capacity in order to handle this extra demand. By lowering your power factor, you use less KVAR. This results in less KW, which equates to a dollar savings from the utility company. Also note that a utility company will charge any consumer whose power factor is less than 0.95 an additional fee. If you reduce power factor you can avoid this additional fee.

Increased System Capacity

By improving power factor, the KW capacity of the system is increased. This implies that for a given KVA, as we improve power factor, the reactive power component, KWAR, decreases and the KW component increases.

Reduced System Losses

As current flows through conductors, the conductors produce heat. This heating is power loss. Power loss is proportional to current squared (PLoss =I2R) and current is proportional to the power factor. In any given electrical distribution system, Conductor loss can account for as much as 2-5% of total load.
By improving your power factor, these losses can be reduced. With the current rise in the cost of energy due to ever increasing fluctuations in the price of crude oil, increased facility efficiency is very desirable. And with lower system losses, you are also able to add additional load to your system.

Increased Voltage Level and Cooler and More Efficient Motors

Uncorrected power factor causes power system losses in the distribution system. As power losses increase, voltage drops. Excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment.
By improving the power factor of your plant, you will minimize these voltage
drops along feeder cables and avoid related problems. Your motors will run cooler and be more efficient, with a slight increase in capacity and starting torque. Also note that Severe over-correction (P.F. greater than 1) will cause a voltage rise that can damage insulation & equipment; or result in utility surcharges!
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Wednesday, March 7, 2012

March 07, 2012

Basics of Power Factor in Electrical Distribution Systems


In AC circuits, power is utilized in two basic forms: 

  • Active or Useful power measured in KW 
  • Reactive power measured in KVAR. 

Before we get to understanding the concept of power factor, let us define the terms measured above:

Active Power

This is the useful working Power (also called Actual Power or Real Power). It is the power that actually powers the equipment and performs useful work. This power is measured in KW.

Reactive Power

It is the power that magnetic equipment (transformer, motor and relay) needs to produce the magnetizing flux.

Apparent Power

It is the vectorial summation of KVAR and KW. It is measured in KVA. So vectorially,
KVA = KW + KVAR

In summary, Reactive power is required to set up the magnetic field while the Active power produces the useful work (shaft horsepower in the case of electric motors). Total Power is the vector sum of the two and typically represents what we pay for in electricity bills. Having understood the basic concepts above, we now define power factor.

 Power Factor (P.F.) is the ratio of working power to apparent power. This is defined mathematically as:


Thus, for a given KVA:
  • The lower the ratio of KW to KVA, the lower the power factor 
  • The higher the ratio of KW to KVA, the larger the power factor.
Power factor has a maximum value of 1.
The Power Triangle illustrates this relationship between KW, KVA, KVAR, and Power Factor:


 
From this power triangle, we can deduce that a system with good power factor will possess the following characteristics:
  • KVAR would be very small (approaching zero)
  • KW and KVA would be almost equal
  • The angle (formed between KW and KVA) would approach zero 
  •  Cosine would then approach one
  • Power Factor would approach one  
In order to have an efficient system, we want power factor to be as close to 1.0 as possible. In practice however, our electrical distribution sometimes has a power factor much less than 1.0.  What then causes low power factor in the electrical distribution system?

Causes of Low Power Factor
The cause of low power factor in the electrical distribution system especially in an industrial complex is mainly Inductive Loads. Most plant loads are Inductiveand require a magnetic field to operate. The magnetic field is necessary, but produces no useful work. Typical inductive loads found in a plant are:
  • Transformers
  •  Induction motors
  • Induction generators (wind mill generators)
  • High intensity discharge (HID) lighting

These inductive loads constitute a major portion of the power consumed in industrial complexes. Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in the electrical distribution system. This increase in reactive and apparent power results in a low power factor.
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