Power Factor (PF), also known as Demand Factor (DF), is a unit of measure (dimensionless) of how efficiently a commercial or industrial client of a utility company is consuming the electrical energy in their own installations. This is mainly a Utility company concern since it affects their system and they will bill you for this (and this makes it a concern to you as well). This is the Demand Charge part of your electrical bill, please read the explanation:
The unit is usually expressed either in decimals of 1.0 (e.g., 0.87) or in a percent (e.g. 87%). The optimum efficiency of this unit is 1.00 or 100%. This is only a small but very important aspect of Energy Savings Engineering (it is by no means an indicative of the efficiency of how the total energy consumed at such installation, these are totally separate concepts). This is one of the most easily implemented Energy Savings Equipment. In addition, they have a very rapid payback period.
To understand the concept, and trying to minimize the mathematics involved, let me explain it in a very simple but realistic way. By definition, the Power Factor is equal to the total KW divided by the total KVA used in a defined time frame. If the maximum KW used in the billing period was 480 KW and the maximum KVA on the same time interval was 640 KVA, then:
PF= KW = 480 KW = .75 or 75% Power Factor
KVA 640 KVA
Most Utilities use a default value of .85PF until they have a chance to install a “recorder” which will measure the actual PF. Usually most utilities define this (i.e. PF) as the maximum value observed by the meter in time frame of 15 minutes intervals. You need to understand that if, as an exaggeration but nevertheless a fact, if your facilities are “OFF” for an entire billing cycle (i.e. usually a month) but you did turn ‘ON’ all of you electrical loads for more than 15 minutes, the electrical meter will record this reading and your company will be billed for the same. This is so because it is not the same, from the utility company point of view, if the end user chooses to power up all of his electrical loads at full consumption for such a short period vs., powering up different loads alternatively or selectively ( this is also known as Demand Control). This is irrespectively of the total KWHR consumed for that billing period.
A simple analogy to this would be that; it is not the same as having a “man” load 100 sacks of 50 lbs into a truck sack by sack (i.e., one at a time) vs. having the same “man” trying to perform the same task carrying 2, 3 or more sacks at a time. Clearly, the result would be the same (i.e., to have all of the sacks loaded into the truck, analogy to KWHR) but it is totally different on the way such task was performed, one sack or more at a time (analogy to KVA).
Obviously performing the task quicker required more energy (i.e. KVA) to be used in a shorter time span while it was being performed. This is known as the Demand and, when expressed in dollars and cents, it is known as the Demand Charge. Again, this charge does not pay for a single KWHR consumed. Thus if you use more energy in a shorter time period, you will be penalized by a higher Demand Charge by the Utility.
Back to Power Factor. This is the best analogy I can make to explain this concept; if you want to cross a river by rowing a boat from one shore to the other shore, the minimum effort expected would be just the energy required to row in a straight line across the same. Let’s call the effort KW or the distance A-B in the illustration bellow.
However, this is hardly the case. The river is moving and thus has a flow of water which is perpendicular to your intended route to cross the river. Let’s call this force Reactive KVA or KVAR. This would be represented by the distance B-C in the illustration below.
Then in reality if you would try to row across this river you would have to expend energy first to get from one shore to the other (KW, or distance A-B) plus the energy required to overcome the river flow (KVAR, or the distance B-C). As a result, in reality the total energy required would be the algebraic sum (e.g. the hypotenuse of a square triangle) of getting from point “A” to point “B” plus the effort required to overcome the river force illustrated as equivalent as the distance from point “B: to point “C” as shown in this illustration:
As indicated above, the total energy that would actually be needed in reality would be the equivalent of the distance from point “A” to point ‘C”, If we call the angle between A-B and A-C, angle “Ø”, then also by definition the Cosine of Ø = PF. Also the KW = PF x KVA or KW= Cos Ø x KVA.
Now if we were to counteract the force of the river by some means like say, a guyed wire that would avoid the boat from being carried by the river (analogy to adding Capacitors which add negative KVAR to the system), then our effort now would be limited only by just the effort of getting from point “A” to point “B”. This would the mean that the energy component represented by the distance from point “B” to point “C” would be cancelled (KVAR=0) and that the distances in the referenced triangle A-B and A-C would be the same. At this condition the angle Ø = 0 and we know the Cosine of 0° = 1 (i.e. PF =1 or 100 %.). When a system reaches a PF of 1.00, then by definition the KW = KVA. Enough of math!
Why is the reason for this analogy? The reason is that the reactive component KVAR illustrated in here by the river flow is in reality created in any electrical installations by any equipment with electrical windings in them. These include: electric induction motors (by far the most typically used motors), transformers, electromagnetic fluorescent lighting ballasts (the type we have been using for the past 50 or more years) and other similar equipment. We call this electrical effect Inductance (see definition).
The easiest way to counter or cancel this “effect” (KVAR) is by adding the opposite electrical effect called Capacitance or better known as Capacitors or Condensers. These provide negative KVAR to the electrical distribution system. Properly sized and engineered they can entirely cancel this effect thus lowering to total demand KVA. This will lower the system KVA and will have the desired effect of lowering the “Demand Charge” and thus save money. Big money, especially in installations with many large or many “lightly loaded” induction type motors.
However many engineers tend to locate the Capacitors on a centralized area, the typical installation consists of multiple capacitors (i.e., Capacitor Bank) controlled by a dedicated computer control which switches some of the capacitor On or OFF in order to maintain the desired Power Factor as the load profile varies. This solves part of the problem only, each installation should be carefully engineered and usually the best solutions includes a mixture of dedicated Capacitors next to large motors and supplementary, automatic adjustable Capacitor Banks, located in the main substation area just before the utility meter.
These parameters are typically measured very accurately with a proper meter that will store either in a graphical of numeric data the different parameters. These studies and date gathered are usually performed for at least a week. With this information known as a Power Survey (see Power Survey section) a qualified engineer will be able to determine the size, quantity, location and other parameters that are required to effectively implement these “Power Factor Correction Capacitors” in any electrical installation.
The installation of Capacitors in order to lower the Demand KVA is by far the most common and economical way to commence improving the Energy Savings of any installation. Also, their installation costs have a very short payback period.
Contact us in order to evaluate and improve your system Power Factor