The apparent or total electrical power (Kilo Volt Amperes or kVA) used in an electrical system by an industrial or commercial facility has two components:
- Productive Power (Kilowatts or kW) which produces work.
- Reactive Power (Kilo Volt Amperes Reactive or kVAR) which generates the magnetic fields required in inductive electrical equipment (AC motors, transformers, inductive furnaces, ovens, etc.)
While the inductive electrical equipment employing magnetic fields requires this Reactive Power, it produces no productive work. Therefore , the Total Power (kVA) provided by the generating source (your utility) must always be greater than the Productive Power (kW). The ratio of Productive Power (kW) to Total Power (kVA) is called the Power Factor (PF = kW / kVA). It is a measure of the systems electrical efficiency in an alternating current circuit and is represented as a % or a decimal.
Power Factor Triangle:
The relationship between kVA, kW and kVAR is non-linear and is expressed: as: kVA² = kW² + kVAR²
Some of the most important reasons for improving Power Factor are:
1. To Reduce Utility Power Billing
Electrical Utilities charge a penalty for poor power factor which can be quite substantial approximating 20-40% of the Demand Charges plus high I²R Losses. Therefore a key reason is to eliminate needless financial losses.
2. To Increase System Capacity
Improving Power Factor releases system capacity and permits additional loads (motor, lighting, etc.) to be added without overloading the system. In a typical system with a PF=0.80, only 800kW of productive power is able to be used out of a 1000kVA installed. By correcting the system to unity (PF=1.00) the kW will equal the kVA. Now the corrected system will support 1000kW. Resulting in an increase of 200 KW over the uncorrected condition.
3. Improved System Operating Characteristics
Power Factor can be improved by one or more o the following methods:
1. replacement of existing motors with more energy efficient ones
2. ensuring motors are properly sized for their application and duty cycle
3.use of high power factor lighting ballasts
4. installation of Power Capacitors.
In general, the installation of Power Capacitors the most cost-effective method of improving Power Factor.
1. Harmonics on the electrical system
2. future expansions to the facility.
To best explain how Demand Billing works lets start with some real world readings and examine them as they are used by a utility when billing. Then we will look at ways to possibly decrease the amount we have to pay for our power through the use of Power Factor Correction equipment.If you do not understand the components that make up your electrical systems Demand (kW, kVA, kVAR) , please read the short article "What is Power Factor?" for an overview before proceeding.
Example: At the end of the billing period the utility records the following Peak reading numbers at your
- kW = 100
- kVA = 150
- Power Factor = kW / kVA = 100 / 150 - 0.67 or 67%
- 100% of the kW reading
- Or 90% of the kVA reading
Do not be misled by the term "Billed kW" as may be listed on your utility bill. This term is generically used only to indicate the reading value that rates are being applied to, not whether its kW or kVA as they would have you believe. Although "Billed kW" seems to infer that the demand is based on kW, this number may in fact be either the kW reading or 90% of the kVA reading depending on which is the largest and being used for billing purposes.
Hydro One - Conditions of Service
188.8.131.52 Components of Distribution Rates
To determine what reading numbers the rates will be applied to in our example lets have a look:
- 100% of kW = 100
- 90% of kVA = 150 x 0.9 = 135
- As we can see, 135kVA is the greater number, thus rates will be applied to this reading.
- So, our Demand Billing (or Billed kW as it may be called) for this period would be 135 x $9.00 = $1,215.00.
Now that we know how much we are billed and on what readings we are billed lets look to see if we can reduce this cost.
By correcting the Power Factor in this example to above 90% ensures that no additional expenses are being incurred.