Power Factor Correction

DOE Article
Brief Intro
Definition
Main Causes of Low Power Factor
Typical Power Factor Ratios
Solution
Harmonics
Oncor Penalty


Average Power Factor Correction Savings by RPM in Downtown Dallas

Brief Intro

Power factor penalties are a way in which utility companies simultaneously enhance grid efficiency while generating revenue. Most utilities add a significant charge to electricity bills if the power factor is below a certain percentage. Facilities with corrected power factor benefit from a smaller electricity bill and increased electrical efficiency. RPM has been one of the leaders in power factor correction since the start of our company in 2002. Understanding the financial and technical dynamics of power factor can be difficult for plant personnel to fully grasp, so RPM uses a consultative approach to work with our clients on a tailored strategy. RPM focuses on safety first in our solutions due to the technical dynamics of a power factor installation.


Here is an example:

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Definition

Power Factor Correction requires a general understanding of the components of electricity and their interaction. The information below is intended for a conversational perspective of power factor and does not include many of the more technical issues that would affect each project.

Basic Electricity

There are 3 primary components and alternating current 3 phase electricity:

    Watts – W
    Volt Amperes – VA
    Volt Amperes Reactive – kVAr

In commercial terms these components of electricity are usually referred to as

    Kilo-volt amperes (kVA) – Apparent power – As produced by generator
    Kilo-watts (kW) – Real power – As utilized by load
    Kilo-volt Amperes Reactive (kVAr) – Reactive power – Unused power

Below is a diagram of the relationship of these components in a typical load situation.  In the triangle, the kVAr component on the right is that which affects the power factor. 

 

 

Power Factor

Power factor is a technical measurements which is the calculation of kw/kVA, or ratio of real (working)/ apparent power.

In a perfect world power factor would be 100%.  However, in the real world electrical equipment is loaded and unloaded.  When that equipment unloads and operates at less than it's rated capacity, power factor goes down.  The amount of apparent power (kVA) the device is using goes up and amount of reactive power (kVAr) goes up.  The triangle below shows a low power factor situation.

To correct power factor, capacitors, or capacitive (kVAr) is added to the circuit to offset the amount of inductive kVAr being produced by the load.  The corrected triangle below shows how capacitance offsets inductance by reducing the angle between kW and kVA.

The result of correcting power factor will be a reduction in amp load, increased kVA, and reduce power factor penalties.


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Main Causes of Low Power Factor

  • Over-sized induction motors
  • Induction heating equipment
  • Arc-Flash welders
  • HID lighting

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Typical Power Factor Ratios

 

Facility Type Power Factor Ratio
Chemical Plant 70%
Commercial Building 88%
Foundry 80%
Furnace or Oven Operation 75%
General Light Manufacturer 80%
Job Shop/Metal Fabricator 70%
Plastic Injection Plant 70%
Printing Plant 70%
School Building 85%

 

Below are some examples of power factor correction installations.

    

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Solution

The most common and economical solution to correcting poor power factor is to install capacitors. Capacitors have been used to correct poor power factor since 1917.   Capacitors act as a temporary storage bank for kVAR, thus consumers no longer receive their reactive power from the utility but from the capacitor bank that is located within their facility. This has no effect on the kW or real power but reduces kVA or apparent power as the kVAR have been reduced from the utility.

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Harmonics

Harmonic distortion is becoming a constant cause for concern in modern electric systems. Harmonics are not easy to describe, but an oscilloscope can display the effect harmonic distortion has on a sine wave. An un-distorted sine wave looks like the “voltage” wave on top.  The bottom line displays the “current” waveform which has been affected by an electronic device causing harmonic distortion.

The distortion is caused by the device drawing electricity at a specific point of the sine wave.  The draw of electricity causes a distortion of the wave. Dependent on the device, distortion can cause varying effects on the sine wave.

In the United States, the standard voltage frequency is 60 hertz (HZ).  The specific harmonic level at which the electricity is affected is determined by a multiple of the fundamental frequency.  An example of this would be a device which affects at the 5th harmonic on a 60 HZ system is 300 HZ.   The second wave-form within the system creates an electrical current within the system.  This harmonic current can cause additional problems on other devices in the system.


In power factor correction scenario, transformers and capacitor banks can create a resonant condition which leads to amplified harmonics, thus causing heat and damage to the capacitor bank. RPM always educates the consumer on the risk of potential resonant conditions as to put forth the safest and most reliable solution.

Note-We advise shoppers to be wary of products that promise reduced power factor correction along with energy savings as these products are misleading. They use small legalese language and prey on consumers that just focus on the myth of great savings to push their over-priced product as a solution to poor power factor correction.

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Educational Articles

Oncor Penalty

Please click on the below link to read about the Oncor Electric Delivery definition of Power Factor and how it is calculated. Oncor Penalty Definition

DOE Article

An article from the U.S Department of Energy on reducing power factor cost. Open PDF FIle